As Many Exceptions As Rules

Biology concepts – umami, taste, flavor, gustation, glutamate, chemoreception, CD36, fat taste, water receptor, calcium

Perhaps I was a little hasty when I said umami wasn’t the name

of a new band. Apparently “Umami” is the name of a band from

Minneapolis. They are described as an electro/psych band,

whatever that is. I like it when obscure science words are used

in culture – makes me think I’m in on some secret. Umami isn’t

that obscure a word, but I used to know a band made up of

statisticians called The Outliers.

Ever heard of umami? It’s not the name of a new band, or even a bad Robin Williams movie. It’s a taste; the fifth taste that humans can sense. Umami is the taste of savory; meats and other high protein foods. And what do we have to thank for umami? Seaweed.

Until 1908, science believed that most flavors were just combinations of the four traditional tastes - sweet, salty, sour, and bitter. But don’t get the idea that taste and flavor are the same - oh no. Taste is our gustatory sense, but that isn’t the same as flavor– flavor is something bigger than taste.

You know how having a head cold makes food bland? Well, that’s because smell is a big part of flavor; you don’t smell your food when you have a cold. Food stimulates all your senses - temperature, touch, smell, what it looks like and even how it sounds as you chew it. All these things add up to flavor.

This is why chefs say you eat with your eyes first, and why they try to incorporate different textures into a single dish. They’re trying to appeal to all your senses. Therefore, eat slowly to enjoy your food more. Give all your senses time to participate. And you might just eat less, since your satisfaction will come from the total experience, not just the craving for a particular taste.

But back to the origins of umami. The Japanese had an idea that there was another taste, mostly since their traditional cuisine used so much seaweed, and this flavor couldn’t be accounted for by the other four tastes. Chemist Kikunae Ikeda wanted to identify the active molecule in seaweed, the one that gave it taste. He called it umami, from the Japanese words for delicious (umai), and taste (mi).

Ikeda’s biochemical studies led to the identification of glutamates as the molecules to which people reacted. And they aren’t just in seaweed, most living organisms contain truckloads of glutamates. When cooked, all glutamates convert to L-glutamate, the amino acid. Ikeda determined that this is what some of our gustatory (taste) receptors sense. Gustation is from Latin gustare = taste, and this is where the word gustocomes from; to taste life.

It turns out that umami taste is not produced by just L-glutamate.

Glutamate comes mostly from meat, as they are high in proteins,

but the nucleotides inosinate and guanylate also perceived as

savory tastes. Inosinates are also found in meats, but also in

seafood. Vegetables are a major source of guanylates, but so are

mushrooms – and we all know that mushrooms are fungi – right?

When you taste something, a chemical signal in the taste cells on

the tongue is converted to an electrical impulse. This is carried by

either the facial nerve or the glossophayrngeal nerve to the brain.

The most palatable form of glutamate that Ikeda could identify was monosodium glutamate (MSG), so he immediately set out to produce and sell it, starting in 1909. Made a pretty penny, he did. Now MSG is a common flavor enhancer in Japanese cooking, including soy sauce. World-class chefs are designing “U-bombs” (umami-filled dishes) to take advantage of the new official taste.

This is why identifying an umami taste receptor for L-glutamate makes sense. This is nature telling you that you need to eat protein, and by giving it a favorable neural response (it tastes good), it increases the chances that you will seek out protein sources for nutrition.

Glutamate has several functions, even beyond its role as one of twenty protein building blocks. Glutamate is the most common neurotransmitter in the central nervous system, and plays a crucial role in long-term potentiation (LTP) and learning. Glutamate is also an intermediate in synthesizing many of the molecules in glycolysis, gluconeogenesis, and the citric acid cycle. I’ve said it before and I hope it jumped into your mind just now – nature hates a unitasker.

So you sense L-glutamate through a gustatory receptor that is specific for that molecule, and the electrical impulse is converted to a specific taste – we call it savory. The cloning of the taste receptors in the late 1990’s (actually umami was the first) started people thinking about other possible tastes. Could there be a sixth taste sense – how about fats? Do we taste fats?

When in the insula of the brain, the input is sorted with other

input and interpreted as a taste. It is the perception that is

important. For the fatty acid receptors, they are receptors, they

are located in the taste cells, and they do carry information via

the same two nerves to the same part of the brain. But are they

then interpreted as a taste?

Much research has been performed in this area in the past few years and a couple of fatty acid receptors on the tongues of rodents and primates have been identified, specifically, CD36 and GPR120. But does this mean we “taste” fat? We said taste doesn't equal flavor – we should now add that sensation may not be the same as taste. Just because there are specific chemoreceptors on taste cells for different fatty acids doesn’t mean that we perceivethe sensation as taste.

It has been shown that fatty acids in the oral cavity do have a threshold level for sensation, and that the fatty acid taste receptors do lead to specific changes in physiology. When subjects were given fatty acids on their tongues, they very quickly showed increased serum triglyceride levels, increased pancreatic hormone release, increased release of GI lipases (enzymes to breakdown fat) and a slowly of the GI tract (it takes more time to digest fats).

What is lacking here is a conscious perception of the discernable nature of the fatty acid (like how sugars are sweet or glutamates are savory). The 2009 studies by Mattes and colleagues controlled for the mouth feel, smell, and so forth of fats, so it was definitely the fatty acid receptor that was stimulating the responses, but no where did it say the subjects tastedsomething. However, his 2011 paper says that fat may very well be a basic taste.

This gives us a new way thinking about taste receptors. Taste is a type of chemoreception, but perhaps it’s only one subset of oral chemoreception. Gustatory chemoreception is a lot more than just tasting something. However, some researchers challenge this division, saying that participants do have a measurable psychophysical response when fatty acids on the tongue reach a threshold level – they dotaste something.

Again I say, “nature hates a unitasker.” CD36 is the fatty receptor in

taste cells, but it also works in macrophage recognition of oxidized

fatty acids and the onset of atherosclerosis, and in the activation of

platelets by fatty acids. You can see in the cartoon that CD36 sticks

into the membrane at two places and loops out of the cell. If you

change the order of its amino acids, it’s shape will change. How well

it binds to fatty acids, or activates all those downstream signals will

also be affected. This is why people with different versions of CD36

may eat different amounts of fat. I wonder if people with poor CD36

versions also have more trouble with CD36 functions in other cells?

The CD36 glutamate receptor has been especially well studied in the past couple of years. It comes in several slightly different forms (polymorphisms– slight differences accounted for by single or few amino acid differences in the sequence of the protein), but these differences have a big effect.

When divided into groups based on which variant of CD36 they possessed, a couple of studies from 2012 (here and here) show that responses to fat and how much the subjects craved fats were different. Those who sensed fats most readily (at lowest concentrations) tended to eat less than those who needed more fat in order to trigger the responses.

The hypothesis of a 2013 review of fat taste and obesity says that those who sense less fat are more likely be tipped toward a hunger stimulating hormonal profile, while those who more readily sense the fatty acids in their food tip toward satiety (fullness). There are many hormones involved here and we could get bogged down very fast, so let’s leave it at that for now; undoubtedly someone is trying to make a diet pill based on it.

So, could there be more oral chemoreception events going on – a seventh taste? An eighth? Let’s talk very briefly about two possibilities. Maybe we can taste calcium. Yes, you could taste your Tums. A 2008 study indicated that mice can perceive calcium as a specific taste. A single 2012 study extends this to humans as well. Calcium is sensed via a certain receptor (Tas1R3), which works with other proteins to sense sweet and umami. But here, it apparently works on its own (we will talk more about the receptors in the posts to come). I need to see more research before I buy calcium taste completely.

Taste number eight - do you think you can taste water? The common argument is that you can taste what is in the water, not the water itself. How or why would you taste water; you’re 65-70% water all the time! What good is it to taste the main ingredient of life? How about this – do you sense the water by taste receptor, not just by temperature, sound, smell, or mouth feel?

There are voluntary swallows an involuntary swallows. But even

in voluntary swallows there are involuntary parts. You don’t think

about closing off your trachea with your epiglottis, it just happens.

This closing is how you keep food and liquid from ending up in

your lungs. Water in your laryngeal pharynx is one stimulus to get

you to swallow and close off the wind pipe until the possible

problem is gone.

Yep, mammals have receptors in the oral cavity that specifically sense the presence of water. In some mammals, like dogs and rabbits, using salt water inhibits the firing of the laryngeal nerve fibers connected to the water receptors; not so in cats and rats. We’ll get to why in a second.

What is the purpose for water receptors in the oral cavity (really, they are in the entrance to the throat, the laryngeal pharynx)? It may be that this is an evolutionary protection from aspirating(breathing in) liquid to the lungs. Liquid in the lung is a bad idea, since it stops gas transfer and promotes bacterial growth. If acids or other liquids that could damage the lungs or throat get in their somehow, it would definitely be better to swallow them than to breathe them in.

When you were a fetus and a very young infant, stimulation of the water receptors in your throat caused you to swallow immediately. As you aged and gained more muscular control, the reflex was replaced by coughing – this is the hypothesis of a 2001 study on the reflex. But the water receptors are still there and still aid you as a stimulus for voluntary swallowing. Whether we taste water or not, I’m glad I have the chemoreceptors.

So, the dampening of the reflex by Cl- in salt might be helpful keeping you from constantly having the urge to swallow. This leads to another point – the power of suggestion. Can you do anything right now other than think about the saliva in your mouth and whether you should be swallowing? Creepy, isn’t it.

Don’t count out the idea of water as a basic tastant (something you can taste). A 2010 study showed by monitoring brain waves that people respond to water using the same pathways as taste, and the responses look the same. And a 2012 studyindicates that rats have distinct portions of the gustatory cortex of the brain for identifying both salt and water. If we can taste umami to make sure we eat enough protein, and sweet to make sure we eat enough carbohydrate, why not water to make sure we keep hydrated?

The idea here is that everything seems better if you are in love.

With love, this is a fantastic summer day in a beautiful place.

Without love, it’s just sand in a whole lot of uncomfortable places.

Same with taste, water is water – unless you're in love.

One final point that reflects just how complex taste is – did you know that being in love makes water taste sweeter? Participants in a December 2013 experiment were asked to think or write about love, hate, or jealousy. Then they were asked to describe the taste of a new product (really just distilled water). Those who wrote or thought about love rated the water to be sweeter than those who contemplated hate or jealousy.

It seems that the brain pathways for rewarding feelings in love and in consuming sweet are the same. You can’t discern between the two, and one can stimulate the other. So when you say you love eating sweets, maybe you really do!

Next week, we can go further into taste. Do people who are supertasters taste good or taste well?

Newman L, Haryono R, & Keast R (2013). Functionality of fatty acid chemoreception: a potential factor in the development of obesity? Nutrients, 5 (4), 1287-300 PMID: 23595136

Pepino MY, Love-Gregory L, Klein S, & Abumrad NA (2012). The fatty acid translocase gene CD36 and lingual lipase influence oral sensitivity to fat in obese subjects. Journal of lipid research, 53 (3), 561-6 PMID: 22210925

Keller KL, Liang LC, Sakimura J, May D, van Belle C, Breen C, Driggin E, Tepper BJ, Lanzano PC, Deng L, & Chung WK (2012). Common variants in the CD36 gene are associated with oral fat perception, fat preferences, and obesity in African Americans. Obesity (Silver Spring, Md.), 20 (5), 1066-73 PMID: 22240721

Chan KQ, Tong EM, Tan DH, & Koh AH (2013). What do love and jealousy taste like? Emotion (Washington, D.C.), 13 (6), 1142-9 PMID: 24040883

MacDonald CJ, Meck WH, & Simon SA (2012). Distinct neural ensembles in the rat gustatory cortex encode salt and water tastes. The Journal of physiology, 590 (Pt 13), 3169-84 PMID: 22570382

For more information or classroom activities, see:

Umami –

http://www.macheesmo.com/2012/01/what-is-umami/

http://www.foodrepublic.com/2013/07/11/food-scientist-explains-umami-molecular-level-now

http://bitesizedbiology.tumblr.com/post/55028228406/understanding-umami-imagine-taking-a-bite-of-your

http://www.buedelmeatup.com/2012/12/11/umami-the-fifth-primary-taste/

http://www.cf.ac.uk/biosi/staffinfo/jacob/teaching/sensory/taste.html

http://www.youtube.com/watch?v=W2xPOZPlxo4

http://www.nature.com/nature/journal/v457/n7226/full/457160a.html

http://chemse.oxfordjournals.org/content/27/9/843.full

Fat taste –

http://www.washingtonpost.com/national/health-science/fat-might-be-the-sixth-basic-taste/2012/06/04/gJQAt218DV_story.html

http://recipes.howstuffworks.com/why-does-fat-taste-so-good.htm

http://www.foodnavigator-usa.com/R-D/Fatty-taste-receptor-may-explain-fatty-food-preference-Study

http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=0CCkQFjAA&url=http%3A%2F%2Fwww.9healthfair.org%2FContent%2Ffile%2FSugar%2520Salt%2520and%2520Fat.pdf&ei=GdnWUq2eMILQyAH_9IHAAQ&usg=AFQjCNFS5vk34it-6dSFErpK7tiwZMnFYA&sig2=cMULFKdRRH8UkovtgD4aYg

http://www.sciencedaily.com/releases/2001/12/011204073223.htm

Water receptor –

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2967336/

http://link.springer.com/article/10.1007/s00221-013-3641-y

http://ajpgi.physiology.org/content/301/2/G197

http://ajpgi.physiology.org/content/270/2/G347

Biology concepts – gustatory sense, taste receptors, supertasters

We have discussed recently the reasons organisms taste their food are related to nutritional needs (sweet, umami, salt, fat) and protection from toxins (sour, bitter). Sweet is the exceptional case here because it's the only taste that works across a great range of concentrations. You can sense low levels of sugar, and it just gets sweeter as more sugar is added. For sour, too much is not a great thing – think sour patch kids. And bitter? India pale ales have way too much hops for me.

The idea that sugar is sweet across all concentrations is

challenged anecdotally by Glucola. This is a drink with 50

grams of glucose. It is used to test for diabetes, especially

gestational diabetes. Many people claim it is too sweet,

nectar of the devil they call it. My wife, on the other

hand, asks for more.

This is an amazing preventative measure in organisms – remember that Paracelsus said that only the dose makes the poison– too much of a good thing can be bad – too much protein leads to hyperaminoacidemia and hyperammonemia (too much amino acid and ammonia in blood). Too much salt can throw ionic balance out of whack, and very bitter tastes suggest a toxin. But too much sweet, no way! Evolution decided there is no such thing as too much sugar – the body wants as much energy (carbohydrate) as it can get.

If this is the case, then why can’t cats taste sweet things? It has been known for a while (2005) that allcat species lack a functional Tas1R2 protein, one part of the sweet receptor (other part is Tas1R3). Cats happen to be obligate carnivores – they only eat meat – so they don’t need to crave carbohydrates – they get enough from metabolizing the compounds in the meat.

Now, a 2012 study has expanded the results to other obligate carnivores. Jiang and his group tested many other species for nonfunctional Tas1R2 protein. Included in the list of animals that can’t taste sweet are the asian short-clawed otter, the spotted hyena, seal lions, dolphins, the fossa, and harbour seals.

Other animals, like dogs, giant pandas, termite-eating hyenas (aardwoles), Canadian otters, and raccoons were found to still have functional Tas1R2 proteins, probably because these animals sometimes eat things other than meat.

On the left is the spotted hyena, also known as the laughing hyena.

It is the largest of the hyenas and is an obligate meat eater. The

right picture is of an aardwolf, another species of hyena. Of the

four extant species of hyenas, the aardwolf is the only

insectivore; the aardwolf diverged from the other common

ancestors about 15 million years ago. It has an amazing

digestive system, being one of the few animals that can stand

the terpene compounds held inside soldier termites. The

aardwolf has a sweet sense, but the spotted hyena doesn’t; this

divergence occurred within the last 10 million years or so.

It isn’t just one change that makes Tas1R2 non-functional, the different animals had different changes, so they must have had a common, sweet-tasting ancestor. Some mutations were probably recent; notice that spotted hyenas can’t taste sweet, but termite eating hyenas can. Canadian otters have functional sweet receptors, but asian otters do not.

The 2012 study of Jiang, and another 2012 study indicate that many seal and sea lion species are double losers – they have lost the use of the Tas1R1 protein as well. To taste umami, the receptor is Tas1R1 + Tas1R3. Yet another 2012 study indicated that 31 different species of bat (fruit, insect, and blood feeding) have lost sweet perception), and vampire bats have lost both sweet and umami (non-functional Tas1R1 and Tas1R2 proteins). Apparently, 2012 was a big year for studying taste loss in animals.

But the kings of poor taste may be the bottlenose dolphins. They have non-functional Tas1R1 and Tas1R2, so no sweet or umami for them, but they have also lost about half of the genes for functional bitter receptors. Why? They swallow their food whole – so taste isn’t a big priority for them.

So cats have no sweet perception, but dogs still have it. But dogs are exceptional in another way. They have a reduced ability to taste salt. Dogs seem to have additional receptors for meat contain chemicals, so they really crave meat. But meat is full of salt, so they don’t have to crave it. It gets weirder though.

We said above that too much of something can be bad, and if dogs eat too much meat, they get too much salt. This can throw all ionic mechanisms into chaos, which includes about every function of every cell. Dogs need to balance their salt intake with their water intake – more salt, then more water to flush it out.

Dogs have water receptors on the tip of their tongue.

There increased sensitivity makes them crave water

after eating salt. But lapping doesn’t occur on the top of

their tongue. The pictures show that they actually scoop

water with the back of their tongue, sort of like how the

elephant uses their trunk. They lapit up, they

don’t lick it up.

To do this, dogs and other carnivores have taste receptors for water. We said last week that humans have receptors for water, mostly for the swallowing reflex, but in the cases of dogs and cats, they are hooked up to taste perception. Here’s the amazing part. Dogs may not perceive salt very well, but taking in salt makes their water receptors much more sensitive. This means water will be tastier to them after having eaten meat. This mechanism triggers dogs to drink more water after eating meat so that salt concentrations don’t get too high!

So now we know that taste perception varies across species. How about within a species - do all people taste things similarly? No way, just ask a supertaster.

It was recognized in the 1930’s that some people react to bitter tastes more strongly than other people. A chemical called phenylthiocarbamide (PTC) accidently got loose in a lab, and only some lab members tasted the powder in the air. Now we use a similar chemical called propylthiouracil (PROP, it's safer than PTC) to test if people have a strong bitter taste sense.

About 25% of the population reacts strongly to PROP, these are the supertasters (coined by Dr. Linda Bartoshuk in 1991). Another 15% of people don’t taste it at all. These are the non-tasters. But many people lie somewhere in between – medium tasters.

However, as Dr. Bartoshuk continued researching, it became apparent that there was more going on. Here is where genetics enters the picture. The bitter receptor (Tas2R38, one of 25 or so bitter recptors) for PROP or PTC comes as several different alleles; one which reacts strongly (T), one that reacts weakly (t), and five that are in between and much more rare.

There is basic mendelian dominance here. If you inherited 2 T alleles, you were considered a supertaster. Two t alleles made you a non-taster, and a Tt genotype landed you in the middle. But there was too much variation. Some people with Tt reacted strongly, while others with tt reacted strongly to other tastes (sweet or sour or even umami).

The cartoon on the left shows how The Tas2R38 bitter receptor

alleles can be inherited. If you are TT, then you taste the bitter

chemical PROP very strongly. If you inherit two t alleles, you won’t

taste PROP at all. The majority of us are Tt, we taste it PROP but it

doesn’t gag us. The right cartoon depicts a generic sweet or umami

receptor. They are heterodimer, made up of two different proteins.

Tas1R1 + Tas1R3 = umami perception; Tas1R2 + Tas1R3 = sweet

perception. The bottom part shows that the dimer fits in the membrane

with each protein having seven transmembrane domains

(the grey rectangles).

More must be at work. Dr. Bartoshuk (2013) has been part of research that has now shown that Tas1R1 (part of umami receptor) also comes in different forms, and demonstrates different intensities of reaction. There is also a paper that suggests that because people with sensitive bitter receptors also react strongly to other tastes, there must be a central pathway for taste perception in the brain that is turned up in supertasters.

Because some people react strongly to more than just PROP, scientists changed the definition of supertaster to those that had both increased sensitivity to PROP/PTC and increased sensitivity to other tastes or food qualities. So you have to define now how your supertaster - pST is a supertaster for PROP alone, while gST is for increased sensitivity to several tastes.

This still can’t account for all the variations in taste intensity seen in different people. Dr. Bartoshuk also discovered that people can have different numbers of taste buds. Taste buds house the taste cells that have the taste receptors; more buds means more receptors means more intense taste.

You can easily test if you have a sensitivity to PROP using small pieces of paper soaked in PROP, but you can also see if you have an above average number of taste buds. Take some blue food dye and a ring reinforcer (those little circles you put on papers so the three ring binder won’t tear through the hole punch hole). Put a drop of dye on your tongue and rinse. The darker blue areas are the filliform papillae; they don’t have taste buds.

The classroom is a great place to count fungiform papillae. The close

up on the right shows that the fungiform papillae take up less stain;

they are the roundish bump, not the dark blue areas. Remember, you

are counting papillae, not taste buds – taste buds are housed at and

beneath the surface of the papillae. Each fungiform papillae may

have many taste buds (1-20) with those on the tip of your tongue

having more buds. Each bud has 50-150 taste cells, and each cell

has hundreds of receptors.

The lighter staining, round areas are the fungiform papillae; this is where the taste buds are located. Put the ring reinforcer on your tongue and count the number of fungiform papillae in the open circle. If you count more than 30, you're probably a supertaster.

The number of fungiform papillae is genetically controlled, as is the expression of different receptor alleles, but the mechanism hasn't been worked out yet for taste bud number. The take home message – both the number of receptors and the alleles of the receptors determine if you are a supertaster or not.

On the other end are the non-tasters. If you count fewer than 10 fungiform papillae in the circle on your tongue, you are most likely a non-taster. On average, humans have about 10,000 taste buds. This is many more than dogs (avg. 1700) or cats (avg. 470). Supertasters may have more than 25,000, while non-tasters may have fewer than 5,000. I have no idea how many taste buds a supertasting dog has.

Non-tasters are said to be taste blind, either generally (ageusia, from Latin a = without and geusia = taste), or just to specific tastants (specific ageusia), like PROP for example. But don’t feel bad for the non-tasters; this doesn’t condemn them to tasting nothing. It just takes more for them to get their craving satisfied.

Guess which cartoon character is more likely to depict a

supertaster. The one on the left – it looks like his food is

super tasty. But really, supertasters – on average – have a

harder time finding foods that don’t overpower their taste

buds. Non-tasters are much more likely to find foods that

are not too salty, too sweet, too bitter, too sour, or too savory.

On the other hand, supertasting isn’t always super. Bitter things may be too bitter to enjoy. In general, supertasters survive better in new environments because they are less likely to eat something toxic. But non-tasters are safer in known environments, because they can find more foods that they can enjoy enough to eat. But always remember, this is a complex system that can be overcome by learning. Some people consider some things too sweet, just as supertasters can learn to enjoy very bitter foods.

One last tidbit – for some unknown reason, the myth that the tongue has specific areas for certain tastes is still being propagated. This just isn’t so. There are places where certain receptors may be more or less numerous, but you can sense all tastes on all parts of your tongue. I hope that settles that.

But even this is an incomplete picture of taste. Next week we will discover that you don’t taste with just your tongue. Heck, an insect tastes things, and it doesn’t even have a tongue!

Rawal S, Hayes JE, Wallace MR, Bartoshuk LM, & Duffy VB (2013). Do polymorphisms in the TAS1R1 gene contribute to broader differences in human taste intensity? Chemical senses, 38 (8), 719-28 PMID: 24000232

Zhao H, Xu D, Zhang S, & Zhang J (2012). Genomic and genetic evidence for the loss of umami taste in bats. Genome biology and evolution, 4 (1), 73-9 PMID: 22117084

Sato JJ, & Wolsan M (2012). Loss or major reduction of umami taste sensation in pinnipeds. Die Naturwissenschaften, 99 (8), 655-9 PMID: 22777285

Jiang P, Josue J, Li X, Glaser D, Li W, Brand JG, Margolskee RF, Reed DR, & Beauchamp GK (2012). Major taste loss in carnivorous mammals. Proceedings of the National Academy of Sciences of the United States of America, 109 (13), 4956-61 PMID: 22411809

For more information or classroom activities, see:

Supertasters –

http://www.pbs.org/wgbh/nova/education/activities/0404_01_nsn.html

http://www.scoop.it/t/taste-and-smell

http://sciencenetlinks.com/lessons/a-taste-of-exploratopia/

http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=3&ved=0CDsQFjAC&url=http%3A%2F%2Fwww.ifr.ac.uk%2Finfo%2Fsociety%2FTasteandFlavour%2FForTeachers.pdf&ei=FoLZUvL2HqPSyAG8pIDYBA&usg=AFQjCNGU7Rg66soR1GBfyu9G0e5lnlg3LA&sig2=Co1NmKEOchWN06A9G83hqQ&bvm=bv.59568121,d.aWc

https://www.google.com/#q=supertaster+classroom+activity

http://www.bbc.co.uk/science/0/22941835

http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=10&ved=0CHIQFjAJ&url=http%3A%2F%2Ffacstaff.gpc.edu%2F~ddonald%2Fbiolab%2FSupertasters.pdf&ei=FoLZUvL2HqPSyAG8pIDYBA&usg=AFQjCNG9tGypJR2RlQxERYA6v2wuJzmOxg&sig2=FzHnZy1mDagmq6WCXrTsRA&bvm=bv.59568121,d.aWc

http://www.abc.net.au/catalyst/stories/3308031.htm

http://www.scientificamerican.com/article.cfm?id=super-tasting-science-find-out-if-youre-a-supertaster

http://science.howstuffworks.com/life/human-biology/taste4.htm

http://online.wsj.com/news/articles/SB10001424127887324392804578362833147151480

http://www.bbc.co.uk/science/humanbody/body/articles/senses/supertaster.shtml

http://www.livescience.com/17190-supertaster-nontaster-tongue-evolution.html

http://www.pbslearningmedia.org/resource/nvsn6.sci.bio.taster/what-is-a-supertaster/

http://www.npr.org/templates/story/story.php?storyId=127914467

http://www.the-scientist.com/?articles.list/tagNo/1290/tags/supertaster/

Biology concepts – taste sensation, non-lingual taste receptors, solitary chemoreceptor cells

Bitter melon (Momordica charantia) goes by many names,

like goya, kalera, etc. It is native to the subcontinent and Asia,

and is used in many cuisines. I have not tried it, but I have

heard it described as tasting like evil, or a cross between

uncooked collard greens and chewing on aspirin. Despite this,

there is a bittermelon soda sold in Japan. My point – even

though bitter is supposed to warn of poison, people can learn

to love it. Are they more likely to be poisoned?

In our recent discussions of the gustatory sense (here, here, and here), we have highlighted the idea that taste is basically a nutrient/poison detection system. You can avoid toxins (sour, bitter) or find nutrients (salty, sweet, umami, fat) of based just on taste. In terms of avoiding toxins; you taste it, and hopefully don’t swallow enough to be harmful to you.

A question occurs to me in this scenario – why not taste things somewhere other than the opening of your gastrointestinal (GI) system? You would be much less likely to ingest a toxin if you never put it in your mouth. Tasting something with the ends of your fingers, for example, would identify sour and bitter – things to toss toward your enemy, and could identify cupcakes and filet mignon as well. Everything would be finger food.

Yet there they are, all those taste buds sitting on our tongue, the inviting front porch swing to our GI tract. Frogs, civet cats, owls – vertebrates of all types have oral taste buds. But it gets weird if you want to start counting all of them, because they aren’t all on your tongue. There are taste buds on your palate (roof of your mouth) and in your throat, and these are just the taste buds. It gets weirder - animals have taste cells and taste receptors in some really weird places.

We have discussed, and will discuss again, how closely related are smell and taste, how they work on a molecular level and how the senses work together to form a flavor. We know now that mammals have taste receptors in their noses!

Bitter taste receptor cells are scattered throughout the nasal cavity, not grouped together in taste buds, so they are called solitary chemoreceptor cells. Maybe this is a way to detect bitter and possibly toxic stimuli before you put them in your mouth - our idea of evolving protective taste sense outside the GI tract may not be some dumb after all. However, the original paper saw that they were linked to increasing respiration rate (to get toxic substances out of the lungs faster).

Here is most of your gastrointestinal tract. The elements

underlined in red have been shown to express taste

receptors. They may acts as nutrient sensors, as hunger

modulators, or even protection against poisoning. To

understand what those mean – read the post! Those not

underlined most likely express the receptors too, they

just haven’t been studied for that yet.

The GI system happens to have many taste receptors; the stomach, small bowel, and large bowel (colon) of mammals have receptors for sweet, fat, bitter, and umami. Interesting that these are the receptors for nutrients and toxins. If you happen to swallow a bitter toxin, the gut receptors stimulate an ion release into the gut.

Water follows the ions due to osmotic pressure, and this would help to flush the toxin through the system faster (ie. diarrhea). This makes sense, but I don’t know if it plays out that way in real life. Not everybody gets to spend hours in the bathroom after eating something bitter - there are probably other issues in play.

On a sweeter note, it has been shown that many intestinal cells express functional sweet heterodimer receptors (T1R2 + T1R3). Cells call enteroendocrine cells (entero = gut, endo = within, and crine= distinguish) produce many of these receptors, and act as sensors for sugar in the gut.

When the enteroendocrine cells detect sugar or artificial sweeteners, they produce hormones that stimulate other gut cells to make more glucose transporters. This is another way that your body works hard to make sure you get all the carbohydrate you can for energy production – it never wants a carbohydrate to get through the gut without being snatched up for use.

Umami receptors are also found in the gut, including the enteroendocrine cells. It was shown in 2013 (here and here) that amino acids are sensed by these receptors, and stimulate release of a hormone called cholecystokinin (CCK), which works in part to tell your brain you that are full.

Cholecystokinin (CCK) is a multifunctional hormone

released from the small intestine after consuming proteins

or fats. It is a hunger suppressant; appetite is controlled by

the hypothalamus of the brain. It can’t cross the blood brain

barrier (BBB), but the hypothalamus isn’t protected by the

BBB. Interesting, no? It just happens that CCK is inhibited

by capsaicin, so maybe it isn’t a good idea to eat spicy and

fatty foods in the same sitting.

CCK also stimulates the release of bile from the gall bladder to aid in the digestion of fats. Fats and amino acids go hand in hand, since meat contains much of both. This may account for the presence of fat taste receptors (CD36 and GPR120) in the gut as well. Fat is harder to digest that other nutrients, so CCK stimulates a slowing of the bowel and a longer retention time in the stomach and gut.

Outside the gut, your GI system also expresses taste receptors in the pancreas. You are constantly sensing how much sugar is your blood, and how much is coming in via your gut absorption. Your pancreas has beta cells that produce insulin to increase the amount of sugar taken up by your cells; this reduces your blood sugar levels.

There are multiple mechanisms by which your pancreas knows to make or release more insulin. Chewing, blood glucose levels, stress levels, exercise, and other signals control the balance between hormone signals that reduce (insulin) or increase (glucagon) blood glucose levels. Now these mechanisms must include sweet receptors on the beta cells.

A 2009 paper showed that functional sweet taste receptors were located on the beta cells in mouse pancreas, they have also been found now in humans. Activation of these receptors by sugars or artificial sweeteners stimulate the beta cells to release insulin and lower blood sugar levels. A more recent study indicates that fructose is also sensed by sweet receptors on beta cells and can amplify insulin signals triggered by binding glucose. This is just more evidence that postprandial (after a meal) nutrient sensing in the pancreas is mediated, at least in part, through taste receptors.

The hypothalamus works in several systems, including

appetite. Interestingly, different parts of the hypothalamus

are in charge of satiety (being full) and the want of feeding.

Water is a whole other matter. All together, the different

nuclei manage the basic control systems of the body, food

water, temperature, blood pressure, etc.

There are even taste receptors for sugars in your brain. The hypothalamus is a part of your brain – an important part - O.K. so all the parts are important. But it seems that blood glucose sensing is particularly acute in the hypothalamus. This is a little harder than it would seem at first thought. You have to sense the glucose levels without being thrown off by sensing the levels of glucose being metabolized in the cell itself. Since cells manage their internal glucose levels, any monitoring system based on this would always report the same result.

But the hypothalamus expresses sweet receptors on the outside of its neurons. Even more, the numbers of receptors is influenced by the nutrient state of the animal. More glucose sensed in other parts of the body (like the taste receptors of the gut), will result in reduced expression in the hypothalamus. This relates to the function of the hypothalamus in appetite as well. More receptor activity relative to the number of receptors, the more signals will be sent out that you are full.

There are more even brain areas that express taste receptors. A 2012 study shows that the rat brainstem has bitter receptors to sample the extracellular fluids for bitter compounds. This may be to try and act as a late protector of the brain against toxins. We have talked before about how the blood brain barrier is designed to protect the brain from toxins better than the blood vessels of the rest of the body.

Taste receptors in the brain (brainstem, hypothalamus, etc)

are attached to neurons, not epithelial cells. It’s the brain, for

gosh sakes, there’s nothing but neurons. This makes the system

more like smell than taste. No taste cells; the signal is directly

transduced to an action potential.

Perhaps sensing bitter compounds in the brain fluid results in a further clamping down on what molecules can get into the brain by manipulating the BBB. The 2012 paper only speculated that the receptors might have other, non-gustatory functions. We have seen above how taste receptors help sense nutrient levels, so it is plausible that bitter receptors in the brain could be sampling for toxins, and then induce some protective response. I bet that's being studied as we speak.

Lastly, recent evidence may show that monitoring taste receptor expression in different tissues may be moot. It may be that every cell in your body has taste receptors! It may be that the T1R1+T1R3 amino acid taste receptor is in/on every cell sensing whether it has enough free amino acids available.

Amino acid availability is crucial for cellular function. Your cells are producing new proteins all the time, to replace old proteins and to make different proteins that would respond to changes in cell condition and environment. Without a constant source of amino acid building blocks, each cell has to seek out an amino acid supplier. Autophagy(auto = self, phagy = eat) is the answer in most cases.

In times of low amino acid stores, a 2012 study indicates that decreased signaling through the umami taste receptors on your cells will trigger a cascade of responses and the cells start to digest themselves (autophagy). They will break down organelles and proteins so that the amino acids can be recycled for proteins of immediate need. As you can guess, this isn’t the best way to run a business, robbing Peter to pay Paul, so autophagy beyond the normal (getting rid of unneeded or old structures) will have consequences. Muscle wasting in starved individuals is often a result of autophagy.

Every cell has to have a source of free amino acids. There is a

balance that must be maintained. On the bottom right, “intake”

represents the eating of protein. If that doesn’t occur, then

amino acids must be made from building blocks (bottom left).

If there is intake, then new proteins can be made (synthesis).

But if there is no intake, and little de novo synthesis, then

proteolysis (a form of autophagy) will result in free amino

acids for protein synthesis.

A 2005 paperhypothesized (now proven) that all these extraoral taste receptors on solitary chemosensory cells form a diffuse chemosensory system. The taste buds are just the most visible part of a much larger, more complex system of taste. The big picture – organisms taste themselves to monitor their nutrition and health. This isn’t really an exception, just a huge misconception.

So nature evolved extraoral taste receptors for mammals. Why didn’t it take the next step and get rid of oral taste buds? Come back in a million years and maybe we’ll be tasting with our elbows. Sounds ridiculous, doesn’t it. Well, not so fast. Next week we will see that some organisms taste things with some very peculiar body parts.

Sundaresan S, Shahid R, Riehl TE, Chandra R, Nassir F, Stenson WF, Liddle RA, & Abumrad NA (2013). CD36-dependent signaling mediates fatty acid-induced gut release of secretin and cholecystokinin. FASEB journal : official publication of the Federation of American Societies for Experimental Biology, 27 (3), 1191-202 PMID: 23233532

Kyriazis GA, Soundarapandian MM, & Tyrberg B (2012). Sweet taste receptor signaling in beta cells mediates fructose-induced potentiation of glucose-stimulated insulin secretion. Proceedings of the National Academy of Sciences of the United States of America, 109 (8) PMID: 22315413

Wauson EM, Zaganjor E, Lee AY, Guerra ML, Ghosh AB, Bookout AL, Chambers CP, Jivan A, McGlynn K, Hutchison MR, Deberardinis RJ, Cobb MH. (2012). The G protein-coupled taste receptor T1R1/T1R3 regulates mTORC1 and autophagy. Mol Cell., 47 (6), 851-862 DOI: 10.1016/j.molcel.2012.08.001

Dehkordi O, Rose JE, Fatemi M, Allard JS, Balan KV, Young JK, Fatima S, Millis RM, & Jayam-Trouth A (2012). Neuronal expression of bitter taste receptors and downstream signaling molecules in the rat brainstem. Brain research, 1475, 1-10 PMID: 22836012

For more information, see:

Extra-oral taste perception – Most of this information is recent enough that scientific journal articles are the only source of information. Follow the links in the post and those below.

http://www.sciencedirect.com/science/article/pii/S1084952112001462

http://www.sciencedaily.com/releases/2007/08/070820175426.htm

http://www.adelaide.edu.au/news/news64082.html

http://consumer.healthday.com/diabetes-information-10/diet-diabetes-news-178/pancreas-may-taste-fructose-hinting-at-links-to-diabetes-661517.html

http://www.physoc.org/proceedings/abstract/Proc%20Physiol%20Soc%2016PC35

http://www.sciencedirect.com/science/article/pii/S0006291X11001999

Biology concepts – taste/gustation, aposematism, carnivore, herbivore, omnivore, Jacobson’s organ, palatal organ, parasite

What animal do you think has the most taste buds? There are bunches of animals out there, so let’s make it a bit easier. What sorts of animals do you think would need more taste buds? Omnivores might be a good choice, since they eat more different kinds of foods.

Cows are big, so they have big tongues. It isn’t too surprising

that they have many taste buds. However, the density (number

per unit area) is higher than most animals too, since they eat

plants, and they have to pick the non-poisonous plants from the

poisonous. Some people eat beef tongue – Bill Cosby said he

didn’t want to taste anything that might taste him back. I would

add that I don’t want to eat anything that could have been

in a cow’s nose.

Carnivores could be a choice, since they have to worry (most of them, vultures excepted) about rotted or diseased meat. But then again, herbivores might be the answer; they eat plants, and plants are the source of most poisons. The same could be said about insectivores, the insects they eat are often toxic – formic acid in ants or stored plant toxins.

Let’s take a survey of animals and see if a pattern develops. Humans have about 10,000 taste buds on average. Young people have more than the elderly; you lose about half your taste buds by age 65. Women generally have more than men. And supertasters can have double the number of non-tasters. But 10,000 is a good number to go by.

Pigs have about 15,000 taste buds while cows have 25,000 and rabbits average 17,000. Lions and other cats come in at about 450 taste buds, but dogs fair better, averaging about 1200. Birds have very few and some fish have alot, but we will talk about them below.

Sort the numbers out and it appears that herbivores have the highest number of taste buds, carnivores and insectivores the fewest, and omnivores lie somewhere in the middle. It looks like keeping an eye (or tongue) out for poisonous plants is the most important mechanism for taste. Carnivores’ strict diet means they need fewer, as we saw when we discussed the loss of sweet taste receptors in cats.

But the winner in the taste bud count? Believe it or not – catfish! Even small catfish (6 in/15 cm) have about 250,000 taste buds. They are literally covered in taste buds. Mind you, we’re talking about taste buds, not just taste receptor cells like we discussed last week. These are full-fledged taste buds, with at least five different tastes represented (sweet, salt, bitter, sour, umami).

On this light colored fish skin, you can see the dots that

are the microscopic taste buds. I eat fish skin, but I don’t

equate it to eating cow tongue.

Most fish have the majority of their taste buds in their mouths - that makes sense. Some fish, especially bottom feeders like carp, are designed so that food coming into contact with the back of the roof the mouth will stimulate an area called the palatal organ which has thousands of taste buds. When the muscular palatal organ tastes food, it automatically clamps down on the food particle. Everything else - water, stones, inedible things - are then flushed from the mouth by blowing them out. Only the food is left and they swallow it.

That’s pretty much it for fish with scales, but catfish, sharks, and some other fish don’t have scales, they are covered with tissue that is more like skin. In these kinds of fishes, it’s like their tongues have migrated all over their bodies. They taste with everything – mouth, lips, gills, fins, body, tail, whiskers.

The catfish, as ironic as it may be, doesn’t have taste buds on its tongue! Why would it be important for catfish to have so many taste buds but none on their tongues? It’s because they live in muddy water. Their sight is impaired, so the taste buds on their body allow them to find food. In truth, most fish have very few taste buds on their tongue (called a basihyal amongst ichthyologists).

This is fortuitous for a fish parasite called Cymothoa exigua. It may sound disgusting, but this isopod (iso = identical, and pod = foot) parasite makes its living by getting into a fish’s mouth through its gills, eating its tongue and then replacing the missing tongue with its own body. Now, everything that comes into the fish’s mouth can be nibbled on by the parasite.

C. exigua doesn’t so much eat its host’s tongue as it causes it to disappear. It grabs on to the tongue, and sucks the blood out of it. The longer this goes on, the more the tongue atrophies (a = no, and trophic = feeding) and shrinks away to nothing. Then the parasite grabs hold of the stump with its back legs and takes its place.

An amazing picture of the isopod parasite C. exigua acting

as the tongue of a captured fish. It lives in the gulf of

California and usually selects the rose snapper as a host.

Every once in a while, a fish lands in the grocery store

with a parasite still hanging on, looking for the next meal.

I’m guessing that fish gets returned and a lot of store

credit is issued. Photo credit to Dr. Nico Smit.

Talk about exceptional; this is the only known instance where a parasite functionally replaces a host’s own organ. The isopod is willing to act like a tongue, holding food up against the small teeth on the roof of the fish’s mouth, because this is how it ensures food for itself.

We know that taste is important for animals to separate toxins from those foods that are good for them, so it is probably fortunate that fish don’t use their tongue for tasting. If losing their tongue caused fish to die more often from ingested poisons or from starvation, then the parasite would be sealing its own fate – it wants its host to survive.

Moving on to something a little less disgusting. We talkedlast week about solitary chemosensory cells and their work in non-gustatory organs. An interesting 2013 paper studied the SCC and taste buds of fish and compared them to those of mammals. Their results indicate that taste buds did not evolve from SCCs or vice versa, the two developed independently. This means that taste, smell and nutrient sensing all developed on their own, yet they have similar and overlapping structures and functions. A good smell idea is a good taste idea.

Snakes show again the similarities between taste and smell. Most snakes (some sea snakes excepted) have taste buds, often lined up near their teeth. What is different is the vomeronasal organ (Jacobson’s organ) for sensing volatile chemicals. Present in amphibians, most reptiles (not crocodiles or chameleons), and some mammals, the VNO is for sensing pheromones and other scents.

On the left is a cartoon showing the snake veromonasal organ

(VNO). It sits in the roof of the mouth and neurons from it go

to the olfactory bulb. As the tongue pulls in molecules, it

presses the tongue up into the VNO. On the top right, you see

how the snake spreads its tongue out to pick up as many signals

as possible. Now you know why snakes have forked tongues.

On the bottom right, you see that the VNO doesn’t even

communicate directly with the nostrils, the moth is more

important for this smelling.

In snakes, however, the scents are not brought to the organ by breathing in. In fact, the VNO in snakes isn’t even open to the nasal compartment. Instead, snakes bring the scent molecules in with their tongue, and press them into the VNO for sensing. This makes it a quasi-direct chemosensory organ, like taste. And thus, we run up against the crossover of smell and taste again.

Humans can taste some volatile compounds as well. One nasty example is gasoline. If confronted with gasoline fumes in sufficient density, some will enter your mouth and mix with saliva. If enough molecules come into contact with your taste buds, you will taste the gas – not an especially pleasant taste.

Even more exceptional, you can also taste a gas you didn’t breathe in. There is a chemical called dimethyl sulfoxide (DMSO) that is used in many laboratories. It’s famous for being a great solvent. A solvent is a liquid in which other chemicals will dissolve. Water is a very good solvent, but there are many things that are not water-soluble.

Once inside the body, DMSO starts to be metabolized by your cells. One of the products of its breakdown is dimethyl sulfide (DMS). This travels around in your blood, but wants to a gas, so it passes from your blood to your lungs. From here you breathe it out. When you exhale DMS, you taste it. It tastes and smells like garlic, so if you taste this and haven’t had Italian for lunch, then you might have contaminated yourself with DMSO - oops.

DMSO is a by product of the wood industry and is a great

solvent. It is polar solvent, meaning that it has a partial

positive charge and a partial negative charge within its

structure. Scientists first thought that the sulfur (S) oxygen

(O) bond was a double bond, but it turns out to be a single

bond with the excess charge being shared as a huge dipole.

Being so much more polar makes it a great solvent, it can get

in between nonpolar, positive or negative structures to

help things dissolve.

The oops is because the structure of DMSO allows almost anything to go into solution – it would put your car into solution if you have enough of it. Its structure also makes it so DMSO can be absorbed directly through your skin to your bloodstream. Any molecule dissolved in DMSO will also be carried straight into your tissues.

This works out well for medicine and chemistry, as certain tests or drugs require that the chemical be dissolved. But, if you happen to be using a toxic chemical in DMSO and get some of it on your skin or mucous membranes - you’ve now been poisoned and you just hope it wasn’t enough to kill you.

Back to taste buds. At the low end of the taste bud spectrum are the birds. They have merely dozens (Japanese quail) to a couple hundred taste buds; chickens and songbirds are especially taste-poor. But that doesn’t mean they can’t be interesting. In the 1970’s, it was discovered that ducks had taste buds in a weird place – on their beaks.

Mallard ducks therefore have about 400 taste buds on their jaws, since beak parts are extensions of the maxilla (upper jaw) and mandible(lower jaw) bones. The taste buds are located in five concentrations, four on the maxilla and one on the mandible.

These positions just happen to correspond to where the duck grasps and holds food as it decides whether it is safe to swallow. Once again, life is protected by taste sense.

The leopard lacewing caterpillar on the left warns predators

with its bright colors that it is poisonous. This is

aposematism, although some animals aren’t above

faking that they are poisonous by just adopting the colors.

On the right is the crimson speckled moth, it is bright and

patterned, but it does it for a different reason. This is a

secondary sex characteristic for attracting mates.

So birds can taste their food, but they don’t rely just on that. It was back in Darwin’s day that the question was raised as to why birds would eat green and brown caterpillars but leave bright colored caterpillars alone. This led Alfred Russel Wallace (the other guy who came up with natural selection) to demonstrate the concept of aposematism (apo = away, and semantic = sign), coloration to warn of toxicity in order to ward off predation.

The bright color says, “Don’t eat me, I’m poisonous.” This is important because even a single peck with a beak could be lethal to a caterpillar. Birds learned quickly to avoid the bright caterpillars, suggesting that birds could taste. This tale is well recounted in the 2012 book of Tim Birkhead, called Bird Sense.

In a strange twist, there are a few birds that are toxic because of their diet, the pithoui and the ifrita. We have discussed these birds in terms of toxins. These birds are brightly colored, so they are using the concept of aposematism to keep themselves safe, just like many potential bird snacks do.

Speaking of caterpillars, we’ll get to arthropod gustatory sense next week. It turns out that some insects taste with their wings, while others taste different things based on their jobs.

Kirino M, Parnes J, Hansen A, Kiyohara S, & Finger TE (2013). Evolutionary origins of taste buds: phylogenetic analysis of purinergic neurotransmission in epithelial chemosensors. Open biology, 3 (3) PMID: 23466675

Tim Birkhead (2012). Bird Sense: What It Is Like To Be Bird Walker Publishing, New York

For more information, see:

Cymothoa exigua–

http://www.wired.com/wiredscience/2013/11/absurd-creature-of-the-week-the-parasite-that-eats-and-replaces-a-fishs-tongue/

http://phenomena.nationalgeographic.com/2013/02/28/tongue-eating-fish-parasites-never-cease-to-amaze/

http://www.talksciencetome.com/treasures-the-tongue-eating-sea-louse/

Biology concepts – sensilla, uniporous sensilla, gustatory receptor, RNA world hypothesis

Chalcanthite (copper containing) is used in traditional

medicines, even though it is toxic. Recent study shows

it is anti-inflammatory when mixed with egg white. A

2013 study shows that after burning off the water from

chalcanthite and mixing it with egg white to eliminate

toxicity, the concoction inhibits several signaling

pathways that would otherwise stimulate

inflammation. I’m not sure you would have to taste

this mineral to know what it was.

Yukon Cornelius, you know- the prospector of Rudolph the rode-nosed reindeer fame, used to taste the end of his pick after ho tossed it into the air and it stuck in the ground. He was looking for gold, and the action implied that he could know if there was gold in the ground by how it tasted.

Don’t laugh, I’ve seen many a geologist taste a rock to get some information about it and the area from which it came. Halite is an easy one (Greek hals = salt), but other minerals have tastes as well.

Borax is sweet and alkaline. Ulexite tastes alkaline while chalcanthite is sweet and metallic (see picture). There are others as well, just be careful that you have a clean area to taste, not one that has been exposed to overflying birds.

Believe it or not, this does have application in biology. Geologists are looking for older and older borates, like borax and ulexite, because there are hypotheses that these might have been important in stabilizing the ribose of RNA in the prebiotic RNA World. They field test samples by tasting to find borates to test for age.

But I don’t know about Mr. Cornelius using taste to find gold. Gold is famously inert, it shouldn’t have any taste at all. In fact, professional ice cream testers use gold spoons just so they won’t be influenced by anything but the product.

It’s not probable, but perhaps geologists and ice cream tasters learned from insects about taste. Arthropods are famous for finding interesting uses for taste. They taste their way to food, to find mates, and even to find appropriate places to lay eggs. But what is most exceptional is how and where they do it. Insects are our big exceptions for the day.

Insects (just one class of arthropods) are invertebrates, so they don’t have the traditional taste buds associated with mammals, fish, and birds. Instead they have taste receptors house inside gustatorysensilla. There are several types of sensilla on insect bodies, and different types can house different senses. Gustatory sensilla are usually of the trichome (or trichoid, meaning three faces) type, meaning that they look like hairs and most people call them hairs. They are not hairs because they are not made of keratin protein. They are made from chitin, the same material as the crunchy insect exoskeleton, and they are hollow.

This is a photomicrograph of an insect antenna, with

several different types of sensilla. Look closely to see

the differences. The sharper ones come in two lengths,

shorter (b) and longer (a), but they are both considered

trichome type. Others are blunter and thicker, these are

the basiconic type (c). Trichoid house touch and taste

receptors. Basiconic hold olfactory (smell) receptors.

The end of the sensilla has a single opening, a verysmall opening (10 nm/4 x10^-7 in). Because of the single opening, it is also called a uniporous sensilla. The pore is so small that water molecules trapped within it can’t evaporate. If the sensilla then rubs up against a surface and some surface molecules get trapped in the water. These molecules can stimulate the gustatory receptors and the insect can taste what they have touched.

These sensilla are common among the arthropods. The arthropod phylum includes the chelicerae(scorpions, spiders, etc), myriapoda(millipedes and centipedes), hexapods(insects, beetles, ants, butterflies, etc.), and crustaceans (crabs, lobsters, shrimp, etc.). I was surprised to find that crayfish and lobsters have sensilla on their legs – antennae, O.K., but on those hard legs? Spiders, even the ones that aren’t hairy, have gustatory and olfactory sensilla, as do millipedes and similar. Since there are more than 500 arthropod species for every mammalian species on Earth, it would seem that uniporous sensilla are the common way to taste. Taste buds like ours are the exception.

The gustatory receptors of arthropods are located on neurons housed within the sensilla. The neuron depolarizes based on the strength of sense signal and transmits that information to the central nervous system. We’re talking about insects here, so “brain” isn’t really the right word to use. In arthropods, both gustatory and olfactory inputs go to an olfactory center, so one could argue if it is really a taste they are sensing. It’s perceived in the smell center, but comes from direct contact, not a gaseous molecule from a distance – let the discussions begin.

However they perceive it, gustatory receptors in uniporous sensilla of insects are used for a variety of purposes. That’s not exceptional – we do too. But insects tend to do it better and for more varied reasons. The obvious function is for finding food, but here insects take shortcuts that other animals do not. Take, for instance, one of the most important research animals ever, the fruit fly (Drosophila melanogaster).

Top left: the proboscis of the fruit fly can be seen projecting

forward, like an insect elephant trunk. Top right: the

proboscis monkey, while at the bottom is the Darwin’s hawk

moth. The term “proboscis” can be used with invertebrates

or vertebrates, but it means different things in each case.

When speaking invertebrate, proboscis means tubular

mouth parts. In the vertebrate tongue, it doesn’t mean

tongue at all, it means nose or snout.

The fruit fly shortcut is seen when it tastes something sweet or tastes water, the neural circuitry automatically causes muscular movements that extend the fly’s proboscis (pro = forward, and boskein = to feed) for feeding. Similarly, if the fly tastes something bitter, the reflex is for the proboscis to retract and feeding to either stop or not start. Muscle movements are connected directly to taste sensation. We can’t do that, unless you count the face kids make when they eat broccoli.

Also in feeding, it seems that insects are the exception to the rule of a limited number of taste receptors. Insects that feed on only one type of plant (feeding specificity) tend to evolve taste receptors for chemicals made only by that particular plant. This leads to many receptors with novel and new specificities.

Depending on the diet or other uses for receptors, insect species also vary greatly in the number of different receptor genes they have. Fruit flies have more than 70 different receptor genes, while honeybees may have as few as ten. However, they probably all have a receptor for tasting water.

The water receptor was recently identified in Drosophila. A 2010 paper in Nature describes a gene and protein called pickpocket 28 (ppk28). The scientists tracked the brain responses to water in flies when the gene was stimulated or when they removed the gene. There was more activity when plain water was given than when it was mixed with salt or sugar (more water if no solute). When mutated to become nonfunctional, flies drank water for much less time (3 seconds versus 10 seconds) and showed much less brain activity in response to water.

Studies like this are hard, but the amount of brain space devoted to sensing things like this makes it easier. Undoubtedly, the ants (still in the arthropod phylum) are king when it comes to sensing taste and smell. For example, worker ants can distinguish between different single and double sugars, meaning that they differentiate many subtle differences in taste.

Here we witness a heartwarming act from the animal world.

C. japonicus ants have adopted the fusca caterpillar out of the

goodness of their hearts. Don’t even consider that the

caterpillar has tricked the others into think he is an ant, or

that the ants feed him just so he will secrete sugars that the

ants can snack on. No way - it’s a Hallmark special, not a

reality TV episode.

But they can also select different sugars based on immediate needs; whether they would be good for stored energy or immediate energy. This suggests nutrient sensing as well as taste differentiation. For example, Camponotus japonicus ants have a symbiotic relationship with Niphanda fusca butterfly larvae (caterpillar).

The ants protect the caterpillars because the caterpillars provide the ants with sugars, specifically, a disaccharide called trehalose + an amino acid, glycine. The ants actually adopt the caterpillars and raise them with their colony because the caterpillars secrete a pheromone that mimics that of the ants. The ants accept them because they taste like one of their own. The gift of sugar reinforces the relationship.

Other ant species will select different sugars equally, but the C. japonicus ants prefer trehalose. What is more, those ants prefer trehalose + glycine even though no ant species prefers glycine alone. So in this species, symbiosis drove evolution of a taste receptor for trehalose, and is modified by glycine.

One last example on ants, leaf cutter ants (Atta vollenweideri) produce different taste receptors based on the caste they belong to (large workers, small worker, soldiers, queens). A 2013 paper shows that the different castes and subcastes also have different numbers of taste receptors on their legs and antennae, so they respond to stimuli differently. One stimulus might be cohorts (members of the same colony) or, in other insect cases, for finding mates.

Drosophila fruit flies have been studied for this as well. A 2012 paper showed that different gustatory receptors and different pheromones are found on male and female flies. Fruit flies perform many different courtship rituals, and these take energy and time. It wouldn't pay to be courting another male – so sensing whether another fly is male or female is important.

Courtship in fruit flies is more complex than teenage dating.

The motions shown above are just a few of the actions that

take place, but the others aren’t G rated, so I decided not to

show them. The male doesn’t pick the female based on looks,

smarts, or ability to stick to a budget. New research shows

that he picks her based on the fact that she doesn’t

taste like a male.

This study mutated certain taste receptors. When male receptors are stimulated by male pheromones, courtship rituals stop. But if a female is tasted, the courtship continues. In the mutant flies, males would court males. When only mutant males were placed together in a container, they would line up in a long line, one fly courting the male ahead of it and being courted by the male behind it.

In butterflies, these different receptors give clues about evolution. In the postman butterfly (Heliconius melpomene), researchers found 73 putative gustatory receptor genes, but the number of copies of gene and the variations of some genes varied between males and females. Fully one third of the genes shows a female bias in expression level, many being found on female legs, but not male legs. The results also showed that many of these were also the result of many recent gene duplications.

Gene duplications allow for more genetic drift, and this would result in a greater number of possible receptors. Varied expression suggests that females are using the receptors for things that the males are not. So female behaviors seem to driving the expression and evolution of the gustatory receptors in butterflies. Once again, the women are in charge.

Next week, we should look at the weird places insects have taste receptors and how taste plays a role in egg laying. Even weirder, insects may taste plants, but it turns out that the plants are tasting them right back.

Choi EA, Park HY, Yoo HS, & Choi YH (2013). Anti-inflammatory effects of egg white combined with chalcanthite in lipopolysaccharide-stimulated BV2 microglia through the inhibition of NF-κB, MAPK and PI3K/Akt signaling pathways. International journal of molecular medicine, 31 (1), 154-62 PMID: 23128312

Briscoe AD, Macias-Muñoz A, Kozak KM, Walters JR, Yuan F, Jamie GA, Martin SH, Dasmahapatra KK, Ferguson LC, Mallet J, Jacquin-Joly E, & Jiggins CD (2013). Female behaviour drives expression and evolution of gustatory receptors in butterflies. PLoS genetics, 9 (7) PMID: 23950722

Koch SI, Groh K, Vogel H, Hansson BS, Kleineidam CJ, & Grosse-Wilde E (2013). Caste-specific expression patterns of immune response and chemosensory related genes in the leaf-cutting ant, Atta vollenweideri. PloS one, 8 (11) PMID: 24260580

Thistle R, Cameron P, Ghorayshi A, Dennison L, & Scott K (2012). Contact chemoreceptors mediate male-male repulsion and male-female attraction during Drosophila courtship. Cell, 149 (5), 1140-51 PMID: 22632976

For more information or classroom activities, see:

Mineral taste –

http://www.galleries.com/minerals/property/taste.htm

http://geology.about.com/od/mineral_ident/ss/beginminident_9.htm

https://www.google.com/search?noj=1&biw=1645&bih=926&q=taste+of+minerals&oq=taste+of+minerals&gs_l=serp.3..0j0i22i30.30242.32674.0.32848.17.16.0.1.1.1.188.1768.3j13.16.0....0...1c.1.32.serp..4.13.1201.Lyq6KNFdWjA

Uniporous sensilla –

http://www.ncbi.nlm.nih.gov/pubmed/10607382

http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=12&ved=0CG4QFjAL&url=http%3A%2F%2Fweb.neurobio.arizona.edu%2Fgronenberg%2Fnrsc581%2Fpowerpoint%2520pdfs%2Fmechanoreception.pdf&ei=z7vlUou8JqmysASr54DADQ&usg=AFQjCNE8KfKTUBEeiGQmHoSf4JBinK5KSg&sig2=VEdmTBHsB75K5fORnIZE0w&bvm=bv.59930103,d.cWc

http://connection.ebscohost.com/c/articles/34467365/mouthparts-associated-sensilla-south-american-moth-synempora-andesae-lepidoptera-neopseustidae

Proboscis –

http://scienceprojectideasforkids.com/2010/fly-proboscis/

http://www.butterflyfunfacts.com/butterfly-proboscis.php

http://www.microscopy-uk.org.uk/mag/indexmag.html?http://www.microscopy-uk.org.uk/mag/artmay98/probob.html

http://www.jove.com/video/193/proboscis-extension-response-per-assay-in-drosophila

http://www.amentsoc.org/insects/glossary/terms/proboscis

http://biologicalmarginalia.wordpress.com/tag/proboscis/

Niphanda fusca–

http://bio390parasitology.blogspot.com/2012/02/niphanda-fusca-raised-by-ants.html

http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=36&ved=0CEIQFjAFOB4&url=http%3A%2F%2Fchemse.oxfordjournals.org%2Fcontent%2F26%2F8%2F983.full.pdf&ei=Rs7lUvKwBJW_sQSa1oG4Ag&usg=AFQjCNE4uh05t8QXRttG21wGQ6w4W-I6dw&sig2=FNBNnUbz8TzjeUKnadcLNg

http://books.google.com/books?id=Rl0ER01ZI8cC&pg=PA101&lpg=PA101&dq=niphanda+fusca&source=bl&ots=ReHPKi1a27&sig=634TgCSUeNGX4CLiX9hJ7_qTtrc&hl=en&sa=X&ei=dM7lUrKFLum0sQSW44DYCw&ved=0CC0Q6AEwAjgo#v=onepage&q=niphanda%20fusca&f=false

Leaf cutter ants -

http://video.nationalgeographic.com/video/kids/animals-pets-kids/bugs-kids/leafcutter-ant-kids/

http://www.arkive.org/leaf-cutter-ant/atta-cephalotes/

http://www.pbs.org/wgbh/evolution/library/01/3/l_013_01.html

http://www.rainforestanimals.net/rainforestanimal/leafcutterant.html

http://www.alexanderwild.com/Ants/Making-a-Living/The-Farming-Ants-Leafcutters

http://www.blueboard.com/leafcutters/what.htm

Biology concepts – metamerism, tagmentizaton, taste, arthropods, receptor, parasitism

Carbonated sodas come in all flavors, but across all cultures, it is

the carbonation that is the same. Mauby is a tree bark flavored

soda sold in the West Indies islands of Bermuda, Trinidad and the

like. On the left is a bird’s nest/white fungus soda sold in Vietnam.

I don’t think it includes the bird.

There is no doubt that humans love the taste of carbonated sodas. There are as many flavors as you can imagine, but the common element among them is the infusion of carbon dioxide (CO₂). Do you taste the carbon dioxide or is it important for some other reason?

Many insects will tell you that it’s the CO₂ that makes the difference. Fruit flies, mosquitoes, ticks and other insects can taste CO₂ on surfaces and in the air. For mosquitoes and ticks, tasting CO₂ helps them find food. These are hematophagous(blood-eating) organisms, and they find their victims by flying upstream along their exhaled CO₂ and the CO₂ that is exuded from their skin.

Even more amazing, fruit flies and other insects taste the increased CO₂ that stressed (injured, diseased) flies emit. They may avoid other insects that are dying so they won’t be near disease or danger. In other insects, they may follow it to animal carcasses - their buffets. In either case, the insects can actually taste death.

But are they tasting CO₂? It’s a gas, and we have said that gases are detected and perceived by smell, not taste (except for us and DMS). It turns out that CO₂ sensation is really an exception. A 2007 paper from John Carlson’s group showed that the receptor heterodimer (hetero = different, and dimer = two different proteins) is made of GR21a and GR63a, two gustatory proteins (hence the GR in the name).

However, the two taste receptors are located on olfactory neurons. The signal is detected by taste signaling on a smell neuron, and the signals are then sent to the smell portion of the brain! This may be one of the biggest exceptions in all of taste science, and it’s the insects that have it and use it.

For insects to accomplish many different tasks with taste, it helps to have the taste receptors in specific places. Catfish had them all over their body, but that’s not very specific. In insects they are found in distinct places, and may have distinct functions.

The shrimp is a good example to show metamerism in arthropods.

All the parts are just reiterations of the same subunit. Some kept

their appendages, and some changed them into something else.

Tagmentization is the result of modifications so that some of the

somites act together as the cephalothorax, and others

from the abdomen.

Many arthropods have taste receptor sensilla on exterior mouthparts, on their legs, on their antennae, and even on their wings. These may seem like a lot of work to develop them on so many different structures, but maybe not. Metamerism is at work.

Metamerism (meta = subsequent, and mer = unit) is a biology concept for efficient addition of complexity in an animal. Over time and evolution, certain specific structures and functions may develop in response to pressures. It is much more efficient to just create another unit using the same blue prints instead of creating a new part from scratch. The repeat is metamerism; the specialization over time of the different mers is called tagmatization.

You can see metamerism and tagmentization at work in arthropods and annelids (worms) by looking for repeating units. Millipedes and centipedes are great examples. Their bodies are made from many copies of the same basic unit. In many animals, repetition of units allows for drift over time and slow changes in structure and function, even grouping of different mers together for special function (tagmatization).

Mers (or somites) in insects include appendages like legs. But over time, many of the appendages evolved into other structures, like mouthparts, antennae, and egg-laying apparatus. Some characteristics are retained, others are dropped or altered, and some new characteristics appear.

Feel like your being stared at? The left picture is good for showing

the mouthparts of a grasshopper. Every one is a remnant of an

appendage. The mostly come in pairs, one from each modified

appendage. On the right, the cartoon shows the different

mouthparts, the labrum (lr) and hypopharynx/labium (hp/lb)

have fused to form just one piece. md = mandible, mx = maxilla

In terms of taste, the appendages seem to have been a seat of gustatory receptor sensilla. When several appendages evolved into mouthparts, the taste receptors were there. When some appendages developed in antennae, the taste receptors were there. But there is still the chicken and the egg question - did taste receptors on mouthparts result from them being derived from appendages, or did taste receptors on legs and other appendages come from early appendages being used as mouthparts?

A run down of tasting anatomy is hard for insects as a whole, because different arthropods taste with different parts, but some structures are more common. Mouthparts seem to be a favorite, and that makes sense. Flies taste with their probsocises (am I making up the plural?), but they also taste with the ends of their legs. Arthropod legs come in segments, and the last segments are called the tarsi.

Flies can taste food with their tarsi just by landing on it, but the also have taste receptors higher on their legs as well. Honeybees taste primarily with their antennae, but other flying insects can actually taste things with their wings! Wing tasters include fruit flies and mosquitoes, and they are more of an exception than you might think. We talked above about how tasting with different parts isn’t so crazy, since metamerism is just the modification of similar starting parts. But wings are not modified appendages.

Wings actually evolved from abdominal gills, and most insects have either given up these early structures and those that have them don’t taste with them. It may be that taste receptors on wings developed on their own, or that taste is older than metamerism. We don’t know their function yet – you work on that one.

Drosophila is the quintessential research model. The left

cartoon shows the olfactory and gustatory receptors. Notice

how many taste receptors are around the proboscis. On the

right, the red dots show all the different places gustatory

receptors are found. Wing margins, legs, tarsi, and mouthparts

all have taste receptors.

We have introduced mosquitoes and taste when we talked about CO₂ above, but they come into play again here, according to a 2010 study. They taste with wings, and this may have something to do with how we can keep mosquitoes away from us. The two main chemical deterrents to mosquitoes are DEET and citronella candles. And they work differently.

Citronellal is only smelled by mosquitoes; the active molecule triggers only olfactory receptors. But DEET triggers both olfactory and gustatory receptors, it is smelled and tasted. Both senses stimulate avoidance responses in insects, so even if a mosquito lands on you, the DEET you put on will be tasted and may keep it from biting.

So some insects taste with wings - is that as weird as it gets? Nope, some females taste with their ovipositors(ovi = egg, and posit = laying). Ovipositors are a result of metamerism, they are modified appendages. The females of many species can taste the plants or places they land to determine if they are a suitable place to lay eggs.

The ovipositors most likely have rare taste receptors, applied to only to this one specific task. For example, there are two subspecies of a particular fruit fly called a goldenrod gall fly (Eurosta solidaginis). The females look for specific plants, and then for buds of the right age in which to insert their eggs. The growing larvae then feed on the bud, and cause a tumor (gall) to form.

The ovipositor of a female wasp or fruit fly is also a modified

appendage. In the wasp on top has a rigid ovipositor that may

be used to inject eggs into a caterpillar larva. On the fruit fly

ovipositor below, you can almost see the sensillae that

contain the taste receptors.

The interesting point is that there are two different kinds of goldenrod and two different kinds of flies. One type of fly will never pick the other type of goldenrod to lay it eggs on. The slightly different plants must have slightly different tastes, and the two subspecies of flies have evolved to react favorably to only one of the two tastes.

Obviously, some insects pick their plants very carefully. Let me give you an example that really knocks this point home. Tiger moth (Grammia incorrupta) caterpillars are sometimes parasitized by flies or wasps that lay their eggs inside the wooly bear (tiger moth caterpillar). A 2009 paper shows that when this occurs, the caterpillars switch the kind of plant food they eat, opting for poisonous plants that contain pyrrolizidine alkaloids (PA).

The PA-rich food is much less nutritious than the caterpillar’s regular food, so it definitely costs the caterpillar in terms of grown and health, but the PA is toxic to the parasites. The food choice sometimes depends on the number of parasitic eggs laid in one individual caterpillar. Just one egg – a caterpillar may eat some PA-rich plant material and let its immune system do the rest of the work. But with more eggs, the woolly bear will consume PA-rich plants exclusively – hoping to kill off all the eggs. The caterpillars are self-medicating, tasting their way back to health.

Turnabout is fair play – we haven’t discussed the plants that are being eaten by all these insects. In some cases, it turns out that the plants are tasting them right back, and even tasting each others' messages.

You can see the parasitic wasp injecting eggs into the

caterpillar. When the eggs hatch, they will feed on the

caterpillar through their larval stage. Two things may

happen. The caterpillar may switch plants (based on taste)

to try and poison the parasites. Second, the plant they are on

now may have called in the wasps to kill the caterpillar using

volatile chemicals, and the toxic plant that the caterpillar

switches to may do it again.

Corn plants (maize) get munched on by caterpillars. In response, they produce chemicals to attract predators of the caterpillars. This has been known for a while. But a 2000 study showed that the plants respond to the caterpillars saliva; the maize tastes it (contact chemosensation) and starts to send out the volatile chemicals that will attract parasitic wasps looking to lay eggs in the caterpillars. A more recent study shows that the caterpillars play an even bigger role in their own demise.

The volatile chemical that maize uses comes in two forms; it’s the switch from primarily one form to the other that attracts the wasps. But even before the plant starts to produce the attractive form, the caterpillar’s saliva converts the inactive form to the attractive form. The attractive message starts about a day beforethe plant starts to make the attractive form. The maize molecule has evolved to make the caterpillar call the cops on itself.

What is more, plants can send taste messages to nearby plants through the dirt. In a 2011 study, researchers induced drought like conditions on one row of plants. In less than an hour, plants five rows away started to close their stomata (pores in leaves) to conserve water for an impending drought. Plants that were just as close, but planted in a different container did not prepare for drought, so the message had to be traveling through the soil. I leave it to you to decide if this is really a taste sense.

So - if you’re a raw food enthusiast, you might be being tasted back. And maybe your food is spreading the word about you to his neighbors. Next week – why do we call spicy food "hot?"

Falik O, Mordoch Y, Quansah L, Fait A, Novoplansky A (2011). Rumor Has It…: Relay Communication of Stress Cues in Plants. PLoS ONE, 6 (11)

Lee Y, Kim SH, & Montell C (2010). Avoiding DEET through insect gustatory receptors. Neuron, 67 (4), 555-61 PMID: 20797533

Singer, M., Mace, K., & Bernays, E. (2009). Self-Medication as Adaptive Plasticity: Increased Ingestion of Plant Toxins by Parasitized Caterpillars PLoS ONE, 4 (3) DOI: 10.1371/journal.pone.0004796

Allmann S, & Baldwin IT (2010). Insects betray themselves in nature to predators by rapid isomerization of green leaf volatiles. Science (New York, N.Y.), 329 (5995), 1075-8 PMID: 20798319

Kwon JY, Dahanukar A, Weiss LA, & Carlson JR (2007). The molecular basis of CO2 reception in Drosophila. Proceedings of the National Academy of Sciences of the United States of America, 104 (9), 3574-8 PMID: 17360684

For more information or classroom activities, see:

Carbon dioxide taste in insects –

http://www.webmd.com/allergies/features/are-you-mosquito-magnet

http://science.howstuffworks.com/zoology/insects-arachnids/mosquito.htm

http://labs.russell.wisc.edu/mosquitosite/carbon-dioxide-baited-mosquito-traps/

http://pestcontrol.about.com/od/bitinginsectprofiles/a/Why-Are-Mosquitoes-Attracted-To-Some-People.htm

http://www.universityherald.com/articles/6037/20131206/mosquitoes-are-attracted-to-the-smell-of-carbon-dioxide-exhaled.htm

http://www.nytimes.com/2010/06/15/health/15real.html

http://www.utsandiego.com/news/2013/Dec/05/ray-riverside-mosquito-neuron-skin-carbon-dioxide/

http://jeb.biologists.org/content/216/12/vi.short

http://www.nature.com/nature/journal/v461/n7261/edsumm/e090910-12.html

http://ndri.com/news/fruit_fly_has_opened_new_era_of_taste_behavior-367.html

http://www.livescience.com/32255-does-carbonation-have-flavor.html

Parasitic wasps –

https://insects.tamu.edu/fieldguide/cimg329.html

http://www.sciencedaily.com/releases/1999/06/990622055654.htm

http://www.youtube.com/watch?v=vMG-LWyNcAs

http://www.organicgardening.com/learn-and-grow/parasitic-wasps

http://www.environmentalgraffiti.com/animals/news-parasitic-wasp-larvae-emerging-caterpillar

http://www.drmcbug.com/parasitic.htm

http://www.livescience.com/14706-ladybug-wasp-parasite-protection.html

http://10e.devbio.com/article.php?id=92

http://www.natureworldnews.com/articles/5221/20131207/fruit-flies-hide-eggs-oranges-protect-parasitic-wasps.htm

http://scienceblogs.com/notrocketscience/2008/06/03/parasitic-wasp-turns-caterpillars-into-headbanging-bodyguard/

http://www.ncbi.nlm.nih.gov/pubmed/10549546

DEET/citronella –

http://www.thenakedscientists.com/HTML/news/news/1000334/

http://news.vanderbilt.edu/2011/05/biologists-discover-new-insect-repellant/

http://npic.orst.edu/factsheets/DEETtech.html

http://www.theglobeandmail.com/life/travel/activities-and-interests/heat-beats-deet-in-bug-battle/article12785109/

http://naturalcommunitiesmag.com/2009/10/16/insect-repellent-deet-is-toxic-to-brain-cells/

http://www.independent.co.uk/news/science/secrets-of-insect-repellent-deet-could-prove-decisive-in-the-war-on-malaria-dengue-and-west-nile-fever-8854228.html

http://www.pnas.org/content/105/36/13195.extract

http://chemistry.about.com/od/factsstructures/ig/Chemical-Structures---C/Citronellal.htm

http://www.sciencedirect.com/science/article/pii/S0040402007006138

http://www.cell.com/current-biology/abstract/S0960-9822%2810%2901006-7

http://ento.psu.edu/extension/factsheets/citronella-ants

http://bonnieplants.com/products/herbs/mosquito-plant-citronella

Plant volatile defense chemicals -

http://www.plantphysiol.org/content/121/2/325.full

http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0062299

http://link.springer.com/article/10.1007%2Fs00442-012-2539-x

http://www.researchgate.net/publication/233930866_Induced_plant_defense_via_volatile_production_is_dependent_on_rhizobial_symbiosis

http://www.universityofcalifornia.edu/news/article/29065

http://umbs.lsa.umich.edu/research/projects/do-plants-make-scents-in-theories-of-plant-defense.htm

http://books.google.com/books?id=Cg8crn8EOy8C&pg=PT102&lpg=PT102&dq=plant+volatile+defense&source=bl&ots=kHb_1vAtUp&sig=5RcJNvG9dV586B39ITAs-46j5fs&hl=en&sa=X&ei=9lroUt6eN6O_sQTNz4C4AQ&ved=0CFQQ6AEwBTgU#v=onepage&q=plant%20volatile%20defense&f=false

http://www.frontiersin.org/plant-microbe_interaction/10.3389/fpls.2013.00262/full

http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0000852;jsessionid=4B7B9F5601D810829BE98381AD8293BC

Biology concepts – fruit, spice, capsaicin, Scoville heat units, TRPV1 heat sensor, taste, true berry

Preface: I had intended on finishing our series on taste sense with a single post on how spicy foods are a taste exception. But the information and exceptions kept pouring out of the literature; every turn gave me a new feature to look at in more depth. So, instead of a single post, here is the first in a series on spicy foods and how our sensation of spiciness or coolness is related to many biological concepts and functions. We experience these daily without ever thinking about them, but the exceptions will show just how inventive life can be.

Here is the fruit of the jalapeno pepper. It is formed from

a single ovary, where the pericarp (ovary wall) is made up

of the exocarp, mesocarp, and endocarp. The placenta is

also called the septum, and on the sides of it are the

capsaicin glands.

Quick, name the spiciest fruit you've ever tasted. Spicy fruit? Is this some bizarre candy commercial? Nope. I bet we've all had a spicy fruit – how about jalapeno fruits, or habanero fruits?

Chili peppers are indeed considered fruits. They are true berries, but they are the exception in berries, as they don’t have a fleshy middle; they're mostly hollow. They form from a single ovary, and the chili is the entire ovary wall ripened into an edible form called a pericarp.

The capsaicin (the dominant spicy molecule in chili peppers) is present in all the fruit structures, but there are higher concentrations in the seeds and the ribs (septa) that hold the seeds to the inner face of the fruit wall. Even the hottest peppers have tastes other than spice, but it's really a matter of how much capsaicin is packed into the flesh that determines the overall sting of the pepper.

Chili peppers got the name "pepper" because they were spicy, like the black pepper plant, but there's no botanical relationship between these two kinds of plants. Chili peppers are from the genus Capsicum. There are about 27 species in the genus, but each species comes in several varieties – bell peppers and jalapenos come from the same species. The Capsicum genus is just one of the 90 or so genera in the family Solanacae, the nightshades. This is a diverse family of plants, including potatoes, tomatoes, tobacco, petunias, and even some trees.

Fusarium fungi preferentially grow on fruits. They are

the primary cause of pre-dispersal seed mortality. Humans

are susceptible to infections with the fungus, and eating

bread made from contaminated grain is lethal. In the

2000’s the US proposed using fusarium mycotoxins as

a way of killing drug crops in South America.

Why would plants make their fruits, leaves, and stems spicy? As a defense, I would guess. It seems that this discourages many an herbivorous predator. A 2008 report shows that Fusarium fungus has a hard time growing on plants that produce capsaicin, but easily infects those that do not. The development and increase in capsaicin levels is a result of evolutionary pressures applied by fungal chili plant pathogens.

But on the other hand, why put the hot stuff in the fruits? Don’t you want animals to eat the fruits and then spread the seeds around in their feces? Isn’t that the point of making a fruit – to entice some animal to disperse your seeds? It makes one wonder.

For what ever reason they do it, there's a new king of the spicy fruits: the Carolina Reaper. Bred in South Carolina specifically to be the world’s spiciest pepper, the Reaper weighs in at a whopping 1.6 million Scoville heat units. Here is a video of some nut downing one, but be careful – there's vomiting involved. That should give you some idea of this pepper’s powerful potency.

What’s a Scoville heat unit (SHU), you ask? In the test originally designed by pharmacist Wilbur Scoville in 1912, this number referred to the number of squirts of sugar water needed to extinguish the flames in your mouth after you bite a pepper. Later, SHU became more scientifically defined as the number of dilutions needed to make a given mass of chili flesh lose its sting. But this was still a subjective measure, with different people reporting different dilutions as necessary.

Born in January 1865, Wilbur Scoville’s middle name was Lincoln,

after the President who would be assassinated later that same year.

He was a pharmacist at Parke Davis when he devised the Scoville

Organoleptic Test for hot food spice, but he was famous for other

reasons in pharmacy. He wrote several textbooks that were used up

until the 1960’s. On the right is the madness Scoville wrought. This is

the Carolina Reaper, bred only to be hot. It is grown only in one plot

in South Carolina, appropriately named Pucker Butt Farms. Notice

that the person is not wearing gloves. I really hope he didn’t rub

his eyes or pick his nose after this.

Nowadays, scientists use a laboratory test called high performance liquid chromatography (HPLC) to measure the amount of capsaicin in each sample. One part capsaicin per million parts pepper is equal to 15 Scoville units (or approximately 18 µM capsaicin/SHU). Pepper eaters agree that the HPLC method gives SHU values about 20-40% below those of the old methods.

The 1.6 million SHU for the Carolina Reaper is about 100,000 units more than the previous record holder, the Trinidad Morgua Scorpion pepper, which is still the spiciest pepper that grows in the wild. Take note that the value is the average for a batch of the peppers grown at the same time at the same place, but the SHU will vary from pepper to pepper.

For the Reaper, at least one individual pepper has been measured at more than 2.2 million SHU, and a Morgua Scorpion individual has come close to this at 2.01 million SHU. The individual differences can come from slight variations in environmental and soil conditions between plants.

A 2013 study found that temperature will affect capsaicin levels. For several pepper cultivars, as the growing temperature increased, so did the capsaicin levels. But the effect was the opposite in jalapenos; higher growing temperatures led to lower capsaicin levels.

The cause of all this spiciness – capsaicin. It's not a protein, but is more aptly described as a nitrogen containing fatty acid – yet another amazing fat. It is one of many compounds called vanilloids, named after one member, the vanillin molecule that gives us vanilla taste and aroma.

Capsaicin is an alkaloid fatty acid. The long hydrocarbon

tail makes the molecule fat soluble but water insoluble.

It also adds to the molecular weight and reduces its

volatility. This is lucky, nobody wants a snoot full of

capsaicin. Some people live for the hot food, enough to

wear it as a permanent marker on their body.

The fact that capsaicin is a fat is pertinent to eating hot peppers. Chemists say, “Like dissolves like,” meaning that a fat will be soluble in fat, but not in water. So when eating spicy foods, remember that drinking water isn’t going to douse the fire no matter how much you drink. Alcohol will work, but beer doesn’t have enough alcohol to make a difference.

The best bet to take the sting out of your curry is whole milk. Why? Because whole milk has sufficient fat to draw the capsaicin off your tongue, and milk also contains a protein called casein. Casein is lipophilic (lipo = fat, and philic = loving), so it will take the capsaicin off your tongue too. You won’t look very manly, but at least you’ll survive.

Many “professional” chili eaters don’t worry about the manly thing at all. After proving how strong they are by eating a ghost pepper or a Carolina Reaper, they will often fill their mouth with Cheez Whiz, or even shove cheesecake up their nose to try and placate their burning nasal membranes!

Pure capsaicin is rated at 16 million SHU, so even the hottest Carolina Reaper is only 1/8 as spicy as theoretically possible. Of course there is no way you could make a pepper that contains only capsaicin. The chili with the best public relations firm is the Ghost Pepper (Bhut Jolokia) of India. The Ghost is all the rage in culinary spice these days, but it only carries a 1 million SHU warning. I wonder if your mouth can actually feel (not taste) the difference between a Carolina Reaper, a Morgua Scorpion and a Ghost Pepper. I’m not planning to investigate my question.

Habaneros range from 350,000 to 500,000 SHU, depending on the cultivar (Red Savina habaneros were developed to be hotter). Jalapenos manage only a 3500-8000 on Scoville’s scale, and I have a hard time with these!

The Mayans and Incas used chili peppers in war, especially

against the Spanish. The Incas burned chili plants to create a

burning smoke screen, while the Mayans filled gourds with

chili extract and threw them as grenades. In the 2000’s, the

Indian Defense Council considered using Ghost Peppers in

hand grenades as a riot weapon. Everything old is new again.

As little as 10 parts per million (ppm) of capsaicin brings pain to the skin, eyes, mouth or nose. This may be why capsaicin is used as pepper spray weaponry. Pepper spray come in at about 2 million SHU, so some individual Carolina Reapers have more capsaicin than pepper spray. No wonder people vomit when they eat one.

Now for a question with a seemingly easy answer, but one that opens many doors for investigation. Why do we say that spicy foods are “hot?”In culinary terms, “hotness” is made distinct from other spice characteristics by being called piquancy. Chili peppers are piquant (from Middle French for irritating or pricking), not hot. This is where we get the name of picante sauce.

The capsaicin in chili peppers causes pain in the mouth, like a burning sensation. It burns on the skin as well. And eating peppers make you sweat, just like when it is very hot. I'm guessing that this is where the term "hot food" came from. With very spicy peppers, like the reaper or the Morgua Scorpion, the amount of capsaicin brings blistering of the oral mucosa. Basically, your body is sensing a burn, and creates blisters to try and keep the burning compound away from the deeper tissue.

It's true that the closer to the equator people live, the more chili peppers they tend to eat. Believe it or not, eating peppers helps to cool you off. On a very hot day, the heat builds up in your body and you need to get rid of it. Sweating is one way we dissipate heat; the evaporation of water from the skin requires an input of energy, and this comes from the heat of the skin. The loss of heat makes you feel cooler.

We have talked about endorphins in a previous post on exercise and

mood. Pain stimulates the release of endorphins that then block the

transmission of pain signals. It would be nice if you could get the

effect without the pain. Endorphins also impart a sense of elation,

which is one reason chili eaters indulge so often and so heavily.

This is one reason people eat chili peppers. Another reason could be that people like the taste. Chilies do have taste, they aren’t just heat. But I think this a cover for eating them as an endorphinrush. Pain sensation in the body is met with an internal pain-killing cascade that includes the production of endorphins that make a person feel elated and numbs the pain. It’s like the old joke where the guy hits himself in the head with a ball peen hammer because it feels so good when he stops.

So how does eating a pepper turn into a sensation of burning and pain? You definitely transmit neural signals of pain when you are burned by heat, and this is the key. The protein on pain neurons that sense burning heat and conduct the signal to the brain to be perceived as pain – well that same protein is activated by capsaicin! The signal is the same; your brain doesn’t know the difference between activation by capsaicin and activation by scalding heat – it interprets them both as pain!

The protein responsible for this is called TRPV1, and we will have much more to say about this ion channel in the weeks to come. It's a heat sensor, a pain sensor, an acid sensor. It can create pain and inhibit pain. It can cause itch and cough, and maybe prevent cancer. Oh, and it creates vampire bats too.

González-Zamora A, Sierra-Campos E, Luna-Ortega JG, Pérez-Morales R, Rodríguez Ortiz JC, & García-Hernández JL (2013). Characterization of different Capsicum varieties by evaluation of their capsaicinoids content by high performance liquid chromatography, determination of pungency and effect of high temperature. Molecules (Basel, Switzerland), 18 (11), 13471-86 PMID: 24184818

Tewksbury JJ, Reagan KM, Machnicki NJ, Carlo TA, Haak DC, Peñaloza AL, & Levey DJ (2008). Evolutionary ecology of pungency in wild chilies. Proceedings of the National Academy of Sciences of the United States of America, 105 (33), 11808-11 PMID: 18695236

For more information or classroom activities, see:

Scoville heat scale –

http://www.thechileman.org/guide_heat.php

http://visual.ly/scoville-scale-hotness

http://www.all-food-considered.com/2012/09/culinary-lesson-9-whats-difference.html

http://scovilleheatscale.com/

http://ushotstuff.com/Heat.Scale.htm

http://culinarycompost.wordpress.com/required-reading/the-scoville-heat-index/

http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=16&ved=0CIwBEBYwDw&url=http%3A%2F%2Fwww.umaine.edu%2Fmaineplants%2Fscovilleheatunit.pdf&ei=aIACU6euJMnR2QWd7oCoCQ&usg=AFQjCNGIr0djWkWk08RIM5jNGvhc1t9UgQ&sig2=DnZY7Ql9_e-CiRW-LZw1fQ&bvm=bv.61535280,d.b2I

http://culinaryarts.about.com/od/culinaryreference/a/Scoville-Scale.htm

http://aces.nmsu.edu/pubs/_h/H237/

http://www.eatmorechiles.com/Scoville_Heat.html

Chili fruits –

http://chilipeppers.nithincoca.com/are-chilies-fruits-or-vegetables/

http://waynesword.palomar.edu/fruitid1.htm

http://www.resnet.wm.edu/~mcmath/bio205/fruits.html

http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=14&ved=0CIYBEBYwDQ&url=http%3A%2F%2Fwww.horticulturebc.info%2Flabreviews%2Fpdfs%2FFruit%2520Types.pdf&ei=NIMCU7WzM6Wg2AXn8IG4Dg&usg=AFQjCNF8gRx-N0VZuBGQkGojOvpgfNkE2w&sig2=vFTlO5gxqH3VbzWDlx6X2w

Fusarium fungus –

http://www.doctorfungus.org/thefungi/fusarium.php

http://www.ipm.ucdavis.edu/PMG/GARDEN/PLANTS/DISEASES/fusariumwlt.html

http://aggie-horticulture.tamu.edu/archives/parsons/turf/publications/fusarium.html

http://www.agriculturesolutions.ca/topics-and-ideas/preventing-fusarium-head-blight

http://www.apsnet.org/publications/apsnetfeatures/Pages/FusariumRot.aspx

http://www.omafra.gov.on.ca/english/crops/facts/01-083.htm

Endorphins –

http://www.medicinenet.com/script/main/art.asp?articlekey=55001

http://science.howstuffworks.com/life/endorphins.htm

http://www.ivillage.com/endorphins-101-your-guide-natural-euphoria/4-a-108211

http://kidshealth.org/teen/your_body/take_care/exercise_wise.html

http://www.pbs.org/wgbh/pages/frontline/shows/heroin/brain/

Biology concepts – capsaicin, TRPV1, heat sensing, thermoregulation, taste, ligand

Eating spicy food can seem like having fire in your mouth.

Interestingly enough, some people do that. Fire eaters do

not use “cold flames” or anything in their mouths other

than spit. One fire eater famously said that the key to being

a good fire eater is the ability to endure pain.

Early in our dating experience, my wife and I visited a Thai restaurant in our old college town. As part of the ordering process, you were allowed to tell them just how hot you would like your food. Eager to impress, I asked for the hottest they had. Big mistake.

Not long after my first bites, the burn started in my mouth. I began to sweat and my eyes watered. My nose ran and the area around my mouth and nose turned red. I looked like I was attending my best friend’s funeral on a sunny 110˚F afternoon. This was not the impression I was hoping for.

Little did I know that I was demonstrating one of the body's most amazing receptors, TRPV1, the capsaicin ion channel. To this day, even though I now appreciate the biology of the experience, I have nightmares where little Thai chilies grow large: towering over the child-like me on a dream playground, the peppers twist my arm, take my lunch money, and give me a wedgie.

TRPV1 stands for the transient receptor cation channel subfamily V (vanilloid) member 1. That’s a mouthful; let's see if we can make it easier. Transient means that it is not activated all the time, something has to come along to activate it. Cationchannel means that when activated, the receptor allows for the flow of positive ions (cations) from the outside of the cell to the inside.

There are many cations in the body, but TRPV1 is especially good at letting calcium (Ca⁺⁺) ions flow into the cell. Calcium movement is at the heart of many of the functions we will talk about in the coming posts.

Here all the known members of the human TRP family,

including all the subfamilies. There six members of the

TRPV subfamily; our discussion will be about TRPV1.

The lone member of the ankyrin subfamily, TRPA1 will be

a big player in the weeks to come. Likewise, TRPM8 is a

cold receptor and we will talk about it extensively. I don’t

know much about the P, C, and ML subfamily members.

The fact that TRPV1 is a channel means that it is not a one to one ratio. Activation of the channel is like opening a gate, where many ions will flow through. Finally the fact that it is a subfamily means that there are many channels that are similar to it and this one is activated by molecules that look like vanillin, an alkaloid fatty acid - capsaicin is a vanilloid compound.

TRPV1 is expressed on many cell types, but is most often found on nociceptive (pain sensing) neurons of the class-C type (these are small and respond to only some types of noxious stimuli). The class-C nociceptive neurons are found in the peripheral nervous system, like in your skin and mucosa, but also in the central nervous system, especially those parts that interpret pain signals. Those TRPV1 receptors located in tissue cells and neurons can lead to some bizarre functions, and we will talk about those in later posts.

TRPV1 is a primarily a heat sensor, but there are other heat-sensing members of the TRPV subfamily. TRPV3 is activated by temperatures around 33˚C to 39˚C, while TRPV4 senses temperatures in the 27-34˚C range.

Since TRPV1 is also a pain transducer, it senses heat that would cause pain, specifically, temperatures above 43˚C (110˚F). Because TRPV1 transduces (changes) the heat into a signal for pain, you pull your hand back when you stick it in hot water because it is painful. If you didn’t, the water could do damage to your tissues; the pain from TRPV1 activation is an effort to prevent tissue damage.

Both Adelta and C neurons carry pain signals to the

brain. Adelta nerves are large than C fibers, and they

transmit information much faster. A delta fibers

signals travel about 5-35 meters/second, while

C fibers depolarize at only0.5 to 2 mm/s. However,

the signal is also shorter lasting. C fibers give a longer

sense of pain, called second pain. C fibers also carry

signals of chemical pain, while Adelta fibers do not.

The signals from TRPV1 travel up several nerves to the brain, but seem to involve the trigeminal nerve centers most often. Noxious (noxa is Latin for harm, same root as for nociceptive) neural signals don’t travel to the gustatory centers of the brain. This is why it’s said that you don’t taste capsaicin, you merely perceive it as burning heat and pain. But this may be a misconception.

Capsaicin is a vanilloid type molecule. So is vanilla. You taste vanilla, so why not capsaicin too? Supertasters seem to have more neurons with TRPV1 channels, so they taste more andthey sense more capsaicin. Some drugs that interfere or kill taste buds also make hot foods not so spicy. So who’s to say we aren’t tasting capsaicin?

During my thai chili/dating incident, I noticed that I was only getting the pain and the burn, I wasn’t tasting my food much. It might have been due to the excruciating pain ruining my dining experience, or it might be that capsaicin can suppress some tastes.

A 2009 paper showed that mice that were fed capsaicin seemed to crave sugar more strongly. The idea we talked about during our taste posts was that if you taste it less, you need more to satisfy a craving. So perhaps the mice tasted less sugar after having been fed capsaicin.

This is supported by a 2010 study that showed that TRPV1 receptors are expressed in taste receptor cells of the circumvallate papillae, and are often co-localized (are on the same cell) with sweet or bitter taste receptors. The authors hypothesized that activation of TRPV1 by capsaicin modulates taste receptors to suppress (not eliminate) sweet and bitter tastes.

Some high mineral foods can give a metallic taste in

the mouth, but more often this is the result of metals

on their own or disease. Gum disease is common cause,

but drugs are a more common cause. Some uncommon

antibiotics give a metallic taste as do many cancer drugs.

Lithium, used to treat bipolar disorder, tastes like

metal because it is a metal.

In addition, a 2009 study talked about how some compounds are sensed as metallic tastes, and these are mediated, in part, by TRPV1 signaling. This is part of the reason why humans and other animals avoid heavy metal tastes and why they can be uncomfortable as well. High concentrations of artificial sweeteners can give an uncomfortable metallic taste, again linking TRPV1 with sweet taste receptors.

It seems that even if we don’t taste capsaicin itself, it can change what it is we do taste. So capsaicin is involved in our sense of taste. But perhaps we can go further. TRPV1 knockout mice (genetically engineered mice with no TRPV1 receptors) still have changes in taste for sweet, bitter and metal. So at least some of the capsaicin signaling is occurring via the taste receptors themselves – and we could call that tasting capsaicin.

Let the tasting arguments begin, and you might want to include the following in the discussion. If TRPV1 activation by heat results in the same signaling as with capsaicin, does it follow then that we taste heat?

Let’s talk more about TRPV1 as a noxious heat sensor. When activated by high heat, TRPV1 signals your brain (particularly the hypothalamus) that your body is too hot. Your brain then activates mechanisms to increase the release of heat from your body to the environment. This might include sweating, breathing faster… things like that.

When you eat spicy foods, the message to the brain via TRPV1 is exactly the same. The capsaicin tricks your brain into believing your body is overheated, and kicks in the cooling mechanisms. This is why people in hot regions of the world eat spicy food - it helps cool them off. The truth of this comes from those same TRPV1 knockout mice. They never get the signal to cool the body because they never sense that they are too hot. Therefore, these mice tend to suffer from hyperthermia (hyper= excess, and thermia = heat). People with TRPV1 problems are hyperthermic too.

On top is a cartoon demonstrating the key in lock model for

protein/ligand interactions. On the bottom is a cartoon

showing the difference between protein denaturation by heat,

and protein conformation change by heat. TRPV1 can undergo

the first and third scenarios.

This is today's exception - that TRPV1 is activated by such different mechanisms (heat and capsaicin), but that the activation results in exactly the same signaling. The receptor is a protein, and we have seen many times that receptors are activated by other molecules through the lock and key mechanism. The shape of the ligand (the molecule that binds or ligates to the receptor) matches exactly a pocket in the receptor, so they fit together like a key in a lock - and the receptor function is unlocked.

But how can heat fit into a ligand binding site on the TRPV1 ion channel? It’s just a physical state, not a solid object. New research is showing that the heat changes the shape of TRPV1, and this conformation (con = together, and form = shape) change activates the ion channel. In isolated receptors with no extra proteins around, heat alone was enough to activate the receptor, so the conformation change is all that is needed to have the ion channel open.

Heat changing the shape of a protein is common; that’s what happens when you cook food. Roasting, pan frying, poaching, toasting - in every kind of cooking the protein becomes denatured (de = without, and nature= form). Proteins lose all shape and function when cooked. In the case of TRPV1 and noxious heat, the protein changes conformation, but is not denatured; therefore, it can be activated by the heat.

On the left is a myotonic arm and hand. This is a state of hyper-

excitation. One contraction leads to repeated action potentials

and waves of contraction. The action potentials occur in the

muscle fibers, not in the neurons that lead to the muscle. On the

right is paramyotonia. You see the hand/arm is in a pan of cold

water – well, take my word for it, it’s called. This is the opposite

of myotonia, in this case the relaxation is extended and the

muscle won’t contract. It can be brought on by cold.

A protein that is thermosensitive is amazing, but apparently it has happened more than once in history. There is a condition in some humans (maybe other animals, but we haven’t asked them) where heat can induce myotonia (prolonged contraction) and cold can induce paramyotonia (prolonged relaxation, nearing paralysis). In 2000, a group in Japan described a family in which this condition is a dominantly-inherited, genetic disease.

A certain sodium channel (SCN4A) is mutated and the mutation makes the sodium channel thermosensitive. At higher temperatures, the protein changes shape and makes it harder for the muscles to relax. For example, a person with myotonia might take a longer than normal time to release their grip on an object. In cold temperatures, SCN4A changes to a different shape and is almost non-functional, so relaxation is hard to overcome and contraction of a muscle is slow and weak.

In this case the mutation has an unwanted result, but one can see how TRP channels probably evolved from similar mutations. Once again, evolution shows itself to be non-directed; mutations can be good, bad, or indifferent - they only survive through generations if they confer an advantage. At some point, being able to sense heat via TRPV channels became advantageous. It must have been early in evolution, because yeast, insect, higher animals, and even plants have mechanisms to sense heat.

Next week, let’s meet a couple of animals that just won’t play by the rules. Heat and capsaicin don’t act on their TRPV1 the way it does for everyone else.

Cao E, Cordero-Morales JF, Liu B, Qin F, & Julius D (2013). TRPV1 channels are intrinsically heat sensitive and negatively regulated by phosphoinositide lipids. Neuron, 77 (4), 667-79 PMID: 23439120

Costa RM, Liu L, Nicolelis MA, & Simon SA (2005). Gustatory effects of capsaicin that are independent of TRPV1 receptors. Chemical senses, 30 Suppl 1 PMID: 15738113

Sugiura Y, Aoki T, Sugiyama Y, Hida C, Ogata M, & Yamamoto T (2000). Temperature-sensitive sodium channelopathy with heat-induced myotonia and cold-induced paralysis. Neurology, 54 (11), 2179-81 PMID: 10851391

Riera CE, Vogel H, Simon SA, Damak S, & le Coutre J (2009). Sensory attributes of complex tasting divalent salts are mediated by TRPM5 and TRPV1 channels. The Journal of neuroscience : the official journal of the Society for Neuroscience, 29 (8), 2654-62 PMID: 19244541

For more information or classroom activities, see:

Capsaicin –

http://abcnews.go.com/Health/capsaicin-ingredient-hot-peppers-offers-medical-benefits/story?id=15727011

http://npic.orst.edu/ingred/capsaicin.html

http://student.biology.arizona.edu/honors98/group12/pepper.html

http://www.mskcc.org/cancer-care/herb/capsaicin

http://antoine.frostburg.edu/chem/senese/101/features/capsaicin.shtml

http://www.scienceofcooking.com/capsaicin.htm

http://www.rsc.org/chemistryworld/podcast/CIIEcompounds/transcripts/capsaicin.asp

http://www.youtube.com/watch?v=qVoaHDsByJI

https://www.fiery-foods.com/article-archives/86-capsaicin/1823-the-nature-of-capsaicin

http://examine.com/supplements/Capsaicin/

TRPV1 –

https://www.caymanchem.com/app/template/Article.vm/article/2116

https://www.ucsf.edu/news/2013/12/110571/structure-key-pain-related-protein-unveiled

http://www.uni-leipzig.de/~pharma/main/research/schaefer/TRPV1_protons.html

http://www.guidetopharmacology.org/GRAC/ObjectDisplayForward?objectId=507

http://circres.ahajournals.org/content/100/7/934.full

http://www.youtube.com/watch?v=kQuVsw8LPhQ

Thermoregulation –

http://www.unm.edu/~lkravitz/Article%20folder/thermoregulation.html

http://www.healthline.com/health/thermoregulation#Overview

http://dwb.unl.edu/teacher/nsf/c01/c01links/www.science.mcmaster.ca/biology/4s03/thermoregulation.html

http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=6&ved=0CFgQFjAF&url=http%3A%2F%2Fwww.biologymad.com%2Fresources%2FA2%2520Homeostasis.pdf&ei=b7UCU7aFL-qSyAGJrYGoDw&usg=AFQjCNH2ruAI7USkyJDE_CVDxMfgLNyUgQ&sig2=UdkGCGfPUkhcQZv0iZEiWg

http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/heatreg.html

http://www.youtube.com/watch?v=TSUCdLkI474

http://people.seas.harvard.edu/~jones/cscie129/pages/health/thermreg.htm

Myotonia/paramyotonia -

http://www.springerreference.com/docs/html/chapterdbid/110140.html

http://hkpp.org/physicians/pmc

http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=5&ved=0CFAQFjAE&url=http%3A%2F%2Fwww.cnmd.ac.uk%2Fdocuments%2FNeuromuscular_Disorders_Muscle_Channelopathies.pdf&ei=e7YCU-a8EOXt2QW-_oGQDA&usg=AFQjCNGv-xpEsL2VdDgTDlzyc5vNFK4F8Q&sig2=KM0Qp9_UBIHZQCms-sz7sA&bvm=bv.61535280,d.b2I

http://ghr.nlm.nih.gov/condition/paramyotonia-congenita

http://jama.jamanetwork.com/article.aspx?articleid=302328

http://ghr.nlm.nih.gov/condition/myotonia-congenita

http://www.ninds.nih.gov/disorders/myotonia/myotonia.htm

http://www.genome.gov/25521207

http://www.myotonic.org/node/71

Biology concepts – thermoregulation, heat sensing, TRPV1, evolution, neurotransmitters, birds, ectothermy, diet-induced thermogenesis

BBC television has a very nice Sherlock Holmes show

running nowadays, but it has ticked off some mental

health professionals. Sherlock describes himself as a

high functioning sociopath. I have read several angry

letters from those in the profession saying that he

should stop doing so, he is using a mental disorder as

an excuse for just plain rude behavior.

Diseases of the mind are often more bizarre and more tragic than diseases of the body. Medicine and psychiatry use different terminology; terms of the mind are often less specific than terms of anatomy and physiology. For instance, what’s the difference between a psychopath and a sociopath?

There is an argument currently raging as to whether there is any difference between these two labels for anti-social personality disorder. The major similarity is in self-centered actions without remorse for doing wrong to others. The differences may lay in organization. Psychopaths are impulsive while sociopaths may plan things out and use charm to conceal themselves. Others say psychopathy is genetic and sociopathy is learned. But both groups are fine with breaking rules.

This blog has used rule breakers as models for explaining biology concepts, just as medicine uses them as ways to find corrections for when things go wrong. If one animal could be the poster child for rule breaking in biology, it would have to be the naked mole rat (Heterocephalus glaber). There are so many rules that this animal breaks or ignores, it makes one wonder if it's a sociopath or a psychopath.

In truth, the naked mole rat has no motivation for breaking rules. It’s merely a reflection of the evolutionary forces that its ancestors felt, adaptations to pressures over a long period of time. If rules had to be broken, so be it. It’s evolution that’s the psychopath.

The broken rules we are concerned with in this post relate to TRPV1. The capsaicin of chili peppers does not inflict pain on naked mole rats! H. glaber TRPV1 binds capsaicin just fine, it just doesn’t result in pain. The difference comes in the spinal cord. A 2008 paper shows that the connections from the TRPV1 expressing nociceptive neurons to those neurons that would convey the signal to the brain are different in naked mole rats, and the additional pathways result in a loss of the pain signal.

This isn’t just a pile of naked mole rats that someone

dumped out of a bucket. This is how they sleep. They

use each other to keep warm because they are cold

blooded. A cold-blooded mammal? Well, I never

imagined. But they break more rules – they live much

longer than other mammals, they don’t get cancer,

and they have a queen like in bee hives. Drum roll

please – the naked mole rat was named the vertebrate

of the year for 2013 by Sciencemagazine.

There’s no inherent advantage in altered TRPV1 signaling via capsaicin for H. glaber; they don’t eat chili peppers. But remember that TRPV1 is activated by more than just capsaicin, so perhaps the advantage lies in stopping some other activation of TRPV1 and it just so happens that it also stops capsaicin–induced pain.

One of those other TRPV1 activators is acid. We said that a pH below 5.5 activates TRPV1 and a pH between 5.5 and 6.5 makes TRPV1 more sensitive. This is pertinent for naked mole rats because they live entirely below ground. Their tunnels are high in CO₂ from all their exhalations. Excess CO₂ in the tissues causes an acidosis, a low pH situation. If the H. glaber TRPV1 acted as it does in every other mammal, then naked mole rats would be in constant pain.

New research (2011) shows that the acid does indeed make naked mole rat TRPV1 channels open just as capsaicin does, but the neurons don’t fire. Acid suppresses a certain sodium channel downstream of TRPV1. Normally, the calcium influx mediated by TRPV1 activates the Na_v1.7 sodium channel, and the neuron is depolarized and fires. But acid destabilizes the Na_v1.7 channel and there is reduced firing.

This suppression occurs in all mammals, but it is a much stronger suppression in naked mole rats, because two amino acids are changed in their version of Na_v1.7. Now we have two TRPV1 activators (capsaicin and acid) that no longer result in pain, but for two different reasons. Is there more?

Substance P is a neurotransmitter and modulator

that is important for pain signaling, but it also works

in vomit regulation. In the medulla of the brain lies

the vomit center, and it uses substance P to induce a

reversal of the motion of the GI muscles that usually

moves food through the GI tract. A spike of substance

P in the wrong place, and here comes supper for a

return engagement.

A neurotransmitter called Substance P is also important in TRPV1 pain signaling. Are you getting the idea that this is a complicated system - I sure am. It turns out that naked mole rats don’t make substance P (2010). Now we have three different reasons that naked mole rats don’t transmit pain signals via TRPV1. This is an evolutionary overkill, but it makes the mole rats able to live where they live without fear of unnecessary pain.

But the question remains, did the mutations in TRPV1 signaling permit H. glaber to move permanently underground, or did living underground put pressure on the naked mole rat to adapt through TRPV1 mutations? It’s hard to tell which was the cart and which was the horse.

The naked mole rat’s lack of pain signaling via TRPV1 may help us humans. The more we know about the mechanisms of H. glaber TRPV1 action, the better we can design pain killers for ourselves. Exceptions can often be our savior.

Another rule that naked mole rats break is that they are cold-blooded (ectothermic) mammals. We know that TRPV1 is important in heat sensing, so does having altered TRPV1 pathways mean that the naked mole rat can’t thermoregulate and that’s why it’s ectothermic?

The rats can still probably sense heat. Remember that there are other TRPV proteins that are important in heat sensing; nothing says these aren’t functioning just fine. For that matter, there is no evidence that the TRPV1 of H. glaber is defective in heat sensing. It just doesn’t result in a pain sensation.

And it would be wrong to believe that ectotherms don’t need to sense heat. It may be even more crucial for ectotherms. Cold-blooded animals must find the heat in their environment and soak it in – but not too much. This means they must be experts at knowing how much heat they have and where they can find more.

Ectotherms also need to know where the shade is, so they can cool off if they get too hot. To prove this, we know that reptiles with mutated thermosensors don’t shuttle between warmer and cooler areas and can’t maintain a satisfactory physiologic temperature.

As weird as the naked mole rat is, birds also seem to break the rules when it comes to TRPV1; they can order their food spicy as well. Why is it significant that birds don’t sense capsaicin as burning pain? Remember that chilies are a group of plants with fruits. Those plants have evolved capsaicin to inhibit herbivorous predators and fungal infections, as we talked about last week. Now we have the fact that birds don’t react to capsaicin. How are these linked?

Squirrels are the bane of every backyard birder’s

existence. They eat ten times as much feed as the

birds, and they can find some creative ways to

reach the bird food. Try adding pepper flakes to

the bird feed, squirrels feel the burn, but your

song bird visitors won’t.

The answer is seed dispersal. It is important that chili peppers are consumed and the seeds are spread. This is crucial for the survival of the plant species. But if the fruits are spicy and there is avoidance of same by most animals, how will the seeds be spread? Well, there better be some animals that don’t react to capsaicin – birds.

The TRPV1 of most birds doesn’t have a vanilloid binding site. The channels work for heat sensing and do react to acids, but there is no activation by capsaicin. Since there is no capsaicin binding site, birds only taste the peppers, they don’t get the burn. It's possible that they taste the many different vanilloid compounds, so peppers may taste a little like vanilla to birds.

I still have one question – there's certainly a reproductive advantage for peppers when birds don’t sense capsaicin (for seed dispersal), but where is the advantage for birds? And how could pepper plants force the evolution of a different TRPV1 in birds? One possibility - maybe birds evolved a different TRPV1 to take advantage of a food source that other animals avoid. No competition for food would definitely be a reproductive advantage for birds.

But this explanation has exceptions as well. The TRPV1 of chickens is activated by capsaicin. It is weak, taking 3-4 times more capsaicin to get a reaction, but it does work. So if you own chickens, don’t give them very spicy feed. Ducks on the other hand, have a TRPV1 that doesn’t sense capsaicin or heat.

Some foods are considered negative calorie items. They

supposedly cost more to digest than the energy they

provide in calories. I’m not sure if I believe that all these

foods are negative calorie foods. If they were, there would

be a lot of starving vegetarians. If not dead, they would be

awfully weak and tired.

You can inject huge amounts of capsaicin extract into the veins of ducks without them having any kind of a thermal response. Since TRPV1 senses heat and then initiates a cooling process, capsaicin in the blood will result in too much cooling – a hypothermia. In chickens this hypothermia occurs, but not in ducks.

So thermosensing must be important. Even in most animals that don’t respond to capsaicin, their TRPV1 still works in thermoregulation. I can give you an idea of how intricate and detailed this thermoregulatory system is by talking about digesting spicy food. Your body uses energy and metabolism to digest the food you eat. This energy use produces heat as a byproduct, and warms you up a bit. This is called diet-induced thermogenesis. Celery is an excellent diet food because the energy you use to digest it is the same or more than the calories in the celery itself.

For some reason, spicy foods increase diet-induced thermogenesis; you expend more energy and heat up more when eating spicy foods than when eating the same foods without the capsaicin. Recent evidence indicates that including capsaicin and medium chain triglycerides in a meal will increase diet-induced thermogenesis by over 50%. This combination also makes you feel full sooner and therefore decreases overall caloric intake.

The spice also makes you use more energy for digestion, but it also makes your body think it is warmer than it is, so it tries to cool down. Cooling down also takes energy, so eating spicy food really does burn more calories - maybe because fat takes more energy to digest and capsaicin is a lipid-like molecule.

Some weird products include capsaicin for the supposed health

benefits. Here are capsaicin drinks. Including capsaicin in a diet

will help you eat less, but I am thinking it may be because you

just get tired of sweating and feeling like your mouth is on fire.

Another recent study shows that the decrease in energy your body expends when you diet (an evolutionary adaptation to try and maximize fat reserves) is prevented by consuming capsaicin. So you burn more calories with spicy food and your body doesn’t even realize your dieting. Somebody should try breeding a capsaicin-packed celery stalk.

Next week we'll see that TRPV1 is even more amazing. Not every spicy food contains capsaicin, there’s mustard, black pepper, horseradish, ginger, cinnamon, etc. Some of these even make your capsaicin seem spicier.

Smeets AJ, Janssens PL, & Westerterp-Plantenga MS (2013). Addition of capsaicin and exchange of carbohydrate with protein counteract energy intake restriction effects on fullness and energy expenditure. The Journal of nutrition, 143 (4), 442-7 PMID: 23406619

Clegg ME, Golsorkhi M, & Henry CJ (2013). Combined medium-chain triglyceride and chilli feeding increases diet-induced thermogenesis in normal-weight humans. European journal of nutrition, 52 (6), 1579-85 PMID: 23179202

Smith ES, Omerbašić D, Lechner SG, Anirudhan G, Lapatsina L, & Lewin GR (2011). The molecular basis of acid insensitivity in the African naked mole-rat. Science (New York, N.Y.), 334 (6062), 1557-60 PMID: 22174253

Park TJ, Lu Y, Jüttner R, Smith ES, Hu J, Brand A, Wetzel C, Milenkovic N, Erdmann B, Heppenstall PA, Laurito CE, Wilson SP, & Lewin GR (2008). Selective inflammatory pain insensitivity in the African naked mole-rat (Heterocephalus glaber). PLoS biology, 6 (1) PMID: 18232734

Smith ES, Blass GR, Lewin GR, & Park TJ (2010). Absence of histamine-induced itch in the African naked mole-rat and "rescue" by Substance P. Molecular pain, 6 PMID: 20497578

For more information or classroom activities, see:

Naked mole rat –

http://animals.nationalgeographic.com/animals/mammals/naked-mole-rat/

http://www.youtube.com/watch?v=eHi9FvUPSdQ

http://www.bbc.co.uk/nature/life/Naked_mole_rat

http://www.latimes.com/science/sciencenow/la-sci-sn-mole-rat-longevity-20131001,0,6184646.story

http://www.sciencefriday.com/video/10/24/2013/the-inner-beauty-of-naked-mole-rats.html

http://www.huffingtonpost.com/2012/07/03/naked-mole-rat_n_1646441.html

http://www.sciencedaily.com/releases/2013/07/130731093255.htm

http://www.scientificamerican.com/article/naked-mole-rat-named-vertebrate/

Substance P –

http://arthritis.about.com/od/arthqa/f/substanceP.htm

http://www.medscape.com/viewarticle/409781

http://www.wisegeek.com/what-is-substance-p.htm

http://aqua4balance.com/health-conditions/fibromyalgia-syndrome/serotonin-and-substance-p.html

http://www.rndsystems.com/cb_detail_objectname_SP98_SubstanceP.aspx

http://www.wellnessresources.com/health_topics/cardiovascular-health/substancep.php

Seed dispersal –

http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=0CCoQFjAA&url=http%3A%2F%2Fwww.greeningaustralia.org.au%2Fuploads%2FOur%2520Services%2520-%2520Toolkit%2520pdfs%2FVIC_Landlearn_Activity_7_The_Peter_Pan_theory_of_seed_dispersal.pdf&ei=jFpwUpLgNPCWyAHugoGQAQ&usg=AFQjCNE0XiOySiVyQlyugDs8Uoag-lA4Vw&sig2=gPxSpKjD-07SIlS-ALf1WQ&bvm=bv.55123115,d.aWc

http://www.rspca.org.uk/education/teachers/lessonplandetails/-/education/LifeCyclesPollinationAndDispersal/section/aimsObjectives

http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=3&ved=0CDoQFjAC&url=http%3A%2F%2Fwww.mbgnet.net%2Fbioplants%2Fdownloads%2Fseeds.pdf&ei=jFpwUpLgNPCWyAHugoGQAQ&usg=AFQjCNFYW8CmWV8hX39O_IrPpMc6mAXVqg&sig2=G6IQ4g3clVYTbhkTaxPGrA&bvm=bv.55123115,d.aWc

http://seeddispersallessonplan.blogspot.com/2011/02/seed-dispersal-lesson-plan.html

http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=15&ved=0CHUQFjAO&url=http%3A%2F%2Fwww.aginclassroom.org%2FSchool%2520Gardens%2FSchool_Gardening_Lesson_Plans%2FSeeds%2520Lesson%2520-%2520Grade%25203%2520-%2520%2520Seed%2520Dispersal.pdf&ei=jFpwUpLgNPCWyAHugoGQAQ&usg=AFQjCNHhNc7leehidMxsA-DqJgO7qikffA&sig2=osk7QWnimRxTJIdrfoFIfQ&bvm=bv.55123115,d.aWc

http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=25&ved=0CEQQFjAEOBQ&url=http%3A%2F%2Fwww.teacherlink.org%2Fcontent%2Fscience%2Finstructional%2Factivities%2Fseeds%2Fseeds-print.pdf&ei=iVtwUq6hOaOiyAHnjIDwAQ&usg=AFQjCNGnvydovXHPh_kBQ3e9evwxMl8CJg&sig2=IqVVbE49hWD21vAIcrRyIg&bvm=bv.55123115,d.aWc

http://gardenatschool.wordpress.com/2012/05/17/seed-dispersal-ideas/

http://www2.bgfl.org/bgfl2/custom/resources_ftp/client_ftp/ks2/science/plants_pt2/dispersal.htm

http://waynesword.palomar.edu/plfeb99.htm

http://www.cas.vanderbilt.edu/bioimages/pages/fruit-seed-dispersal.htm

http://www.mbgnet.net/bioplants/seed.html

http://andromeda.cavehill.uwi.edu/Dispersal.htm

http://www.jstor.org/discover/10.2307/20046315?uid=3739664&uid=2129&uid=2&uid=70&uid=4&uid=3739256&sid=21102836267737

http://www.vtaide.com/png/seed-dispersion.htm

http://theseedsite.co.uk/dispersal.html

Diet-induced thermogenesis -

http://www.ncbi.nlm.nih.gov/pubmed/15507147

http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=5&ved=0CF0QFjAE&url=http%3A%2F%2Fwww.ncsf.org%2Fpdf%2Fceu%2Fdiet_induced_thermogenesis.pdf&ei=KqkCU6aGPKrA2QW2o4HADA&usg=AFQjCNE0youH2pxOSQmkDOHSNj6RvE01lA&sig2=OHM0UsrlJssg4stkIJ3DTA&bvm=bv.61535280,d.b2I

http://www.livestrong.com/article/461015-definition-of-dietary-thermogenesis/

http://eurekamag.com/research/005/188/does-diet-stimulated-thermogenesis-change-preferred-ambient-temperature-humans.php

http://www.30bananasaday.com/profiles/blogs/something-i-just-wrote-about-dietary-thermogenesis

http://books.google.com/books?id=aW0WAAAAQBAJ&pg=PT110&lpg=PT110&dq=%22dietary+thermogenesis%22&source=bl&ots=OUGWErvwFf&sig=IIhlQGpuorpeCpyH1VC1c1fKvH4&hl=en&sa=X&ei=1KwCU8qRLcGG2wWproDICg&ved=0CC0Q6AEwATgK#v=onepage&q=%22dietary%20thermogenesis%22&f=false

Biology concepts – cinnamaldehyde, nasal hyperreactivity, piperine, allyl isothiocyanate, eugenol, gingerol, tinyatoxin, osmotic stress, agonist/antagonist

The last few years have seen the rise and fall of The Cinnamon Challenge. I can’t tell you why it came, but I can explain why it went. And the reason relates to the capsaicin receptors we have been talking about.

Don’t think cinnamon candy can be hot. Your unbearably hot

cinnamon bears from Jelly Belly and your Atomic Fireballs are

both flavored with cinnamon oil. Fireballs have been around

since the 1950’s which explains the atomic reference. It takes

over two weeks to make one. Cinnamon is not ranked on the

Scoville scale because the main spicy compound is

cinnamaldehyde, not capsaicin. But there is some capsaicin in

cinnamon oil, so I think it could be ranked without breaking

some long standing policy.

The challenge goes like this: you take one tablespoon of cinnamon and try to swallow it all in 60 seconds without any water. If any one tells you they did it and came out O.K., they’re lying. If you see video of someone doing it easily, it's been faked.

Here’s how the challenge works for everyone. The compounds in cinnamon stimulate a coughing reflex (explained below). When you cough, you expel air and you have a compulsion to inhale. Here’s where the trouble starts. The inhalation carries a good portion of the cinnamon powder down your trachea and into your lungs.

Now you’ve done it. The ensuing coughing fit can be powerful enough to break ribs. The compounds in the cinnamon immediately begin to burn your lungs, make your eyes water, make your nose run, and increase your breathing rate. More inhalations carry more cinnamon into your lungs and the burn intensifies. YOU WILL blow it out, spit it out, vomit it out. The pain in your lungs will likely last for three weeks or more. Sounds like fun, doesn’t it?

Here’s the biology of the why it ends well for no one. Cinnamon contains compounds called cinnamaldehydeand eugenol, as well as capsaicin (much lower amount). The capsaicin and eugenol activate TRPV1 ion channels. Cinnamaldehyde is a different class of molecule from the capsainoids, so it does not activate TRPV1, but it does activate a powerful member of another subfamily, TRPA1. We will talk more about this receptor in later posts.

TRPV1 is involved in cough reflex, runny nose, and in the burn that the follows the challenge. The TRPA1 activation causes powerful pain in the lungs and trachea. Together, these compounds result in the involuntary cough, reflexive inhalation of cinnamon into the lungs, and all the pain that follows from activating the TRPV1 pain receptors in your lungs. Now you know WHY you should avoid the challenge.

Asthma is a trigger for airway or nasal hyper-reactivity.

It is easy to see how this could get out of hand, especially

when it can lead to chronic inflammation and damage of

the airway tissues. And to think, it is mediated in part by

the same receptor that makes your Sunday afternoon

chili stew spicy.

Don’t laugh at the portion of the response that takes place in your nose. My mother-in-law got some chili pepper oil up her nose once, and she still refuses to be in the same room as a chili. Her runny nose, sneezing, and watery eyes were directly due to the capsaicin. But for some people it happens for no reason. This is called nasal hyper-reactivity.

In some cases the exaggerated nasal response is due to an allergen, but in other people the trigger is unknown. The TRPV1 ion channels in the nasal mucosa may be over-expressed (too many of them). Their activation brings mucous, bronchoconstriction, cough, and sneeze.

The evolutionary strategy here is like with the cinnamon. Your body is trying to keep toxic or harmful substances out of your lungs. A new study has linked nasal hyper-reactivity to TRPV1 action alone, without need of other receptors. What is more, the paper identifies a new TRPV1 antagonist. An antagonist is a molecule that binds to the receptor but does not activate it, and it can prevent the receptor’s stimulation by molecules that wouldnormally activate it (agonists).

This new antagonist of TRPV1 can suppress the nasal hyper-reactivity and give some relief those afflicted. You may think nasal hyper-responsiveness is trivial, but it’s snot – get it? It’s snot.

Nasal hyper-reactivity is often diagnosed by assessing an exaggerated response to capsaicin in the nose. I can’t imagine how any response to nasal capsaicin could be considered exaggerated. It’s just lucky for us that capsaicin isn’t volatile. Less of it gets into the air because it has a long hydrocarbon tail.

Because it isn’t volatile, capsaicin doesn’t have an odor, not until you chew it and volatilize it yourself into your nose do you know you’re in trouble. The runny nose is your body recognizing there is something there that you really don’t want in your lungs. It’s bad enough with cinnamon, can you imagine getting capsaicin in your lungs?

The capsinoids are a group of compounds within the

vanilloids. You can see the resemblance to vanillin, so

there are all vanilloids. The different capsinoids are all

found in chili peppers, but capsaicin is the most

abundant and potent, but the structures of the different

capsinoids are very similar.

Pure capsaicin ranks at 16 million Scoville heat units (SHU). But it isn’t the only capsinoid in chili peppers. There is also dihydrocapsaicin (15 million SHU), nordihydrocapsaicin (9.1 million SHU), homocapsaicin (8.6 million SHU), and homodihydrocapsaicin (8.6 million SHU). Each of these can activate TRPV1 to bring the burn. But it doesn’t stop there; many other compounds can bind to TRPV1 as well. Here's some of them:

Piperine (100,000 SHU) is the spicy compound in black and white peppercorns. You already know black pepper is spicy, and it activates TRPV1 just like capsaicin. Remarkably, it's even more efficient than capsaicin at opening the TRPV1 ion channel. However, it's found in lower amounts that capsaicin in most chilies and has a greater ability to desensitize TRPV1, so it burns less. We will talk about desensitization of TRPV1 in the coming weeks.

Allicin is found in garlic and onions; they can burn too. Raw garlic is especially pungent; try it some time. Garlic is used in many folk medicines – it has been show to prevent or treat fungal infections, lowers blood pressure, is neuroprotective, and can slow the growth of some cancer cells. Some of these effects are mediated by TRPV1. Oh, and it wards off vampires too.

Eugenol is found in many foods, including cinnamon, bay leaf, clove, and allspice. It activates TRPV1, but like piperine, it can be desensitizing too. For this reason, eugenol has a numbing effect and is often used in dental preparations. If you have ever had a cavity filled with the silver amalgam, you probably smelled cloves in the process - that was the eugenol. Just recently it has been shown that eugenol also activates TRPA1 pain receptor, so maybe the dentists should be rethinking their strategy.

Radishes, horseradish, wasabi, and mustard contain allyl isothiocyanate (AITC). This compound binds to both TRPV1 and TRPA1, so they can generate a lot of pain, and the heat sensation as well. In mustard seeds, the AITC isn’t produced until the seeds are broken and an enzyme is released that converts one compound into AITC. This is why stone ground mustards with larger chunks of seeds are less spicy.

In the horse trade, a raised tail means a younger, livelier

horse. When someone wanted to sell an old, worn out

horse, but get more money, they might put a piece of

ginger in the anus of the horse. The burn from the

gingerol would make it raise it’s tail. It has also been

used in horse shows, but is now illegal. Oh yes,

sometimes “gingering a horse” also involved live eels.

The spicy compound is not stored in the plant as AITC because it's harmful to the plant as well. Only when an herbivorous predator comes along and starts munching on the plant is the toxic chemical produced. A new study (2013) shows that AITC actually makes TRPV1 more sensitive to heat, so using wasabi with hot food will really crank up the pain.

Ginger contains gingerol(60,000 SHU), but when you cook it gingerol is converted to the sweeter and more aromatic form called zingerone. Both can activate TRPV1. There is also gingerol in mustard oil, so both mustard and ginger have been used in folk medicine, like plasters they use to slather on wounds. For a less appropriate use of ginger, see the photograph at the right.

Camphor is used in things like Vicks VapoRub. It activates TRPV1, so you feel warm, but it can also activate a cool receptor, so it seems to open up your nose. We will have much more to say about this in a couple of weeks. Found in certain trees, camphor is slightly analgesic (pain killing), and is antimicrobial, so it does serve a purpose in Vicks.

In addition to these plant-based agonists, TRPV1 is activated by other things as well. We already talked about how the channel is opened by acid (excess protons), but it can be activated by inflammation in tissues and some endogenous pain killers as well, like the endocannabinoids we talked about at New Year’s.

Tinyatoxin (and resiniferatoxin for that matter) are

produce by the Euhorpbia poissonii plant. Native to Nigeria,

its extract is used by natives as a pesticide. The tinyatoxin

and resiniferatoxin are neurotoxic and can kill TRPV1-

expressing neurons, so they are being looked at as a

way to treat chronic pain.

There are artificially produced agonists as well. Resinferitoxin activates the heat receptor TRPV1. It rates 108.8 billion on the Scoville scale! Scientists are trying to find a use for it in chronic pain and other diseases (more in two weeks). There is also tinyatoxin from the Euphorbia plant. It is slightly less spicy, about 5.3 billion SHU. It is a neurotoxin and can kill you in large amounts.

One last agonist for TRPV1 – osmotic stress. This refers to the movement of water out of cells (so they shrink) or into cells (so they swell) when there is an imbalance of salts inside and outside of the cell. Too much salt in the extracellular fluid is called hypertonic, and water will flow out of cells and toward the more concentrated salts. Too little salt in the extracellular fluid is called hypotonic and water will move into the cells where the salt concentration is higher. We want an isotonic environment, where the slat is the same in and out of the cell.

TRPV1 sense osmotic changes, specifically hypertonicity. A 2010 paper shows that there is a TRPV1 in the brain that does not react to heat or capsaicin, but does respond to osmotic stress. TRPV1 sense cell shrinkage and signals the hypothalamus of the brain to release a hormone called vasopressin (also called ADH). This hormone causes more water to be retained and more salt to be excreted, This lowers the salt concentration outside the cells and the cell shrinkage can be corrected.

Osmotic pressure is related to the amount of water versus the

amount of salts in the water. In the cartoon, the salts are

represented by the blue spheres. Water will travel to wherever

salts are highest, because that means water concentration is

lower. Hypertonic means water will flow out of cells, while

hypotonic means water will swell the cells, even to the point of

lysing them. The representative cell is a red blood cell, since

they are very susceptible to osmotic changes.

Another receptor of the same subfamily, TRPV4, senses swelling during hypotonic crises. This then triggers the hypothalamus to release less vasopressin and the salt concentration will increase outside the cell; excess fluid in the cell will flow out of the swollen cells. A 2011 papershows that TRPV1 works only on shrunken cells and TRPV4 only on swollen cells.

Using TRPV1 in osmoregulation makes sense. It is closely related to thermoregulation, considering how you use sweating to get rid of excess heat. Sweating messes with osmotic pressures. Nature is smart that way.

Next week, more functions of TRPV1 – it can make pain worse and stop pain. How can that be?

Holland C, van Drunen C, Denyer J, Smart K, Segboer C, Terreehorst I, Newlands A, Beerahee M, Fokkens W, & Tsitoura DC (2013). Inhibition of capsaicin-driven nasal hyper-reactivity by SB-705498, a TRPV1 antagonist. British journal of clinical pharmacology PMID: 23909699

Chung G, Im ST, Kim YH, Jung SJ, Rhyu MR, & Oh SB (2014). Activation of transient receptor potential ankyrin 1 by eugenol. Neuroscience, 261, 153-60 PMID: 24384226

Alpizar YA, Boonen B, Gees M, Sanchez A, Nilius B, Voets T, & Talavera K (2014). Allyl isothiocyanate sensitizes TRPV1 to heat stimulation. Pflugers Archiv : European journal of physiology, 466 (3), 507-15 PMID: 23955021

Ciura S, Liedtke W, & Bourque CW (2011). Hypertonicity sensing in organum vasculosum lamina terminalis neurons: a mechanical process involving TRPV1 but not TRPV4. The Journal of neuroscience : the official journal of the Society for Neuroscience, 31 (41), 14669-76 PMID: 21994383

Sudbury JR, Ciura S, Sharif-Naeini R, & Bourque CW (2010). Osmotic and thermal control of magnocellular neurosecretory neurons--role of an N-terminal variant of trpv1. The European journal of neuroscience, 32 (12), 2022-30 PMID: 21143657

For more information or classroom activities, see:

Agonist/antagonist –

http://www.biopsychology.com/6e/activity0403.html

http://biowiki.ucdavis.edu/Biochemistry/Transport_and_Kinetics/Enzyme_Inhibition/Agonist_and_Antagonist_of_Ligand_Binding

http://forums.studentdoctor.net/threads/understanding-antagonist-agonist-drugs.1005095/

http://employees.csbsju.edu/hjakubowski/classes/ch331/transkinetics/olinhibition.html

Eugenol –

http://pubchem.ncbi.nlm.nih.gov/summary/summary.cgi?cid=3314

http://www.nlm.nih.gov/medlineplus/ency/article/002647.htm

http://mentalfloss.com/article/12297/why-do-all-dental-offices-smell-same

http://www.ewg.org/skindeep/ingredient/702373/EUGENOL/

http://chemistry.about.com/od/factsstructures/ig/Chemical-Structures---E/Eugenol.htm

http://www.motherearthliving.com/plant-profile/eugenol.aspx

Gingerol –

http://www.whfoods.com/genpage.php?tname=foodspice&dbid=72

http://books.google.com/books?id=5WY08iuJyawC&pg=PA86&lpg=PA86&dq=gingerol&source=bl&ots=1LwF_y9UUy&sig=-phjWzpMtWo8-QbJ-RDayDgxZUg&hl=en&sa=X&ei=BhUEU67SBafuyQHFhYDYAw&ved=0CDYQ6AEwBTgK#v=onepage&q=gingerol&f=false

https://www.acs.org/content/acs/en/molecule-of-the-week/archive/molecule-of-the-week-gingerol.html

http://rucore.libraries.rutgers.edu/rutgers-lib/21328/

camphor -

http://www.webmd.com/vitamins-supplements/ingredientmono-709-CAMPHOR.aspx?activeIngredientId=709&activeIngredientName=CAMPHOR

http://www.botanical.com/botanical/mgmh/c/campho13.html

http://plants.ifas.ufl.edu/node/101

http://www.chemie.fu-berlin.de/chemistry/oc/terpene/campher_en.html

http://www.drugs.com/cdi/camphor-ointment.html

http://www.ipm.ucdavis.edu/PMG/GARDEN/PLANTS/camphor.html

tonicity –

http://www.phschool.com/science/biology_place/biocoach/biomembrane1/solutions.html

http://www.youtube.com/watch?v=_slUL3kMZlU

http://chemistry.about.com/b/2013/11/17/osmotic-pressure-and-tonicity.htm

http://differentmedicalcareers.com/hypertonic-hypotonic-isotonic-solutions/

http://www2.nl.edu/jste/osmosis.htm

http://www.slideshare.net/dewisivasamy/the-effects-of-hypotonic-hypertonic-and-isotonic

http://www.glencoe.com/sites/common_assets/science/virtual_labs/LS03/LS03.html

http://biology.unm.edu/ccouncil/Biology_124/Summaries/Membranes.html

http://www.biologycorner.com/bio1/notes_diffusion.html

http://mcatdaily.blogspot.com/2010/05/difference-between-hypertonic-hypotonic.html

Biology concepts – hyperalgesia, allodynia, analgesia, sensitization, potentiation, desensitization, habituation, burning mouth syndrome

Apparently this is how people shovel snow in the

cold climates. I agree with the form; always bend

with your knees not your back. But the bikini?

Really? I feel like kind of a wimp for talking about

my fingers hurting when I stay out too long.

You know that intense pain you get in your fingers when you've been out in the cold for a while? Why does that happen, and why does it get worse when your hands start to warm up or when you run them under lukewarm or warm water? Believe it or not, the pathways are the same as if you coated them in pepper spray.

Across the USA this winter it was snowy and cold. Where I live we had a record snow fall for December-February, and at least two cold snaps (the Polar Express) that drove wind chills to -25 ˚F or lower.

These conditions gave me ample time to contemplate the issue of hand and finger pain during and after my many shoveling campaigns. I figured it had something to do with exceptions called hyperalgesia (hyper = excess, and gesia = Latin for pain) and allodynia allo = other, and dynia = Greek for pain). It was the burning pain that helped me put it together with chili peppers.

We have talked about how the capsaicin in hot peppers can activate a receptor called TRPV1 that routinely is used by animals to sense noxious (painful) heat and generate a burning pain. Well, there also happen to be some receptors that work the same way for cold. They're called TRPM8 and TRPA1, and we will talk about them in more detail in the posts to come.

The cold sensors may also relay excess cold as pain, but that doesn’t explain why warming up your hands makes them hurt even more. This is requires the explanations of hyperalgesia and allodynia. Hyperalgesia is a perceived pain that is exaggerated beyond what can be accounted for by the stimulus. This does not include your sibling screaming in horror when you flick the lobe of their ear and they go running to mom claiming that you’re trying to kill them. Hyperalgesia is simply too much pain perceived.

Fibromyalgia is a disease that affects women 80-90%

of the time. It is caused by – well, we don’t know. It

may be secondary to hormone changes, due to CNS

dysregulation, or maybe even stress. Most believe that

it is brought on by a combination of physical and

emotional stressors. This cartoon shows SOME of the

symptoms that can be manifested. Some people have all,

some have only a few, and some have different

symptoms. My complaint is that under skin it says

“various complaints.” Since when does having your

clothes make you feel enormous pain qualify as a

various complaint?

Allodynia is different; this is when your sibling cries out in pain whenyou're nice to enough to let them have the last donut. In slightly more scientific terms, allodynia is when the body reacts to non-noxious stimuli as if there were noxious. There are basically two types of allodynia, pain brought on by light touch (static mechanical allodynia) and pain brought on by near ambient temperatures (dynamic allodynia).

Tactile (touch) allodynia is rare, it can occur with different kinds of neuropathies, like migraine headaches or a disease called fibromyalgia. Sometimes, even the touch of your clothes on your body can feel very painful, like having a sunburn all over - all the time. In migraines, the pain signals for the headache get mixed up in the central nervous system. This can make even the slightest touch on the face excruciating. And the more often you get migraines, the more likely you are to develop tactile allodynia. Pain is bad, pain when there shouldn’t be any would make me impossible to live with.

In order to explain our cold finger burn when we come inside from the cold out of doors, we need to talk about things like sensitization and potentiation. When one stimulus of a receptor strengthens it response to another stimulus, or when a stimulus to one type of receptor strengthens a stimulus to a second type of receptor – these are examples of sensitization.

On the other hand, if repeated activation of a receptor strengthens each subsequent firing, then this is demonstration of potentiation. Both of these can occur with the heat-sensing receptor TRPV1.

Sometimes capsaicin + TRPV1 makes the TRPV1 react more strongly to heat or more capsaicin. At other times, activation of another TRP, say TRPM8 by cold or TRPA1 by extreme cold or other noxious stimulus, can make TRPV1 activate more strongly to one of its ligands. These are examples of sensitization.

Since the major sensation perceived after TRPV1 activation is pain, sensitization of the TRPV1 by capsaicin or the activation of other TRPs can result in a larger amount of pain when TRPV1 is activated by acid, heat, or even more capsaicin. More pain from these somewhat painful inputs = hyperalgesia.

This cartoon shows the capsaicin/heat ion channel TRPV1

and the noxious cold and chemical pain receptor TRPA1.

Let’s say that you trigger TRPA1 with noxious cold. This lets

in calcium, which activates PKC, This leads to

phosphorylation of TRPA1 (P) which then keeps it open. But

this may phosphorylate TRPV1 too. Now TRPV1 is ripe to be

opened, easier then it normally would be. This is sensitization.

For a real world example, let’s go back to shoveling snow during our cold snap. My fingers got very cold, cold enough to activate the TRPA1 and TRPM8 ion channels. Then when I came inside, anything warm – air, water, a surface, caused much more pain than it should have. This was a result of sensitization of the heat responding TRPV1 channels.

The TRPV1 response was strengthened due to the synergistic response to a different stimulus. The TRPA1 pain receptors are very often expressed on the same neurons as the TRPV1 receptors, so the common pathways can get mixed up as to stimuli. Activation of the cold channels sensitized the heat channels so that warm was now interpreted as very hot – burning hot. It took a 5-10 minutes for pain to subside, but it sure seemed like longer.

In a similar way, but through a slightly different mechanism, TRPV1 signals can get amplified by other TRPV1 agonists. If you get punched in the eye really hard, it hurts. Then it swells up and turns colors. This is inflammation. Inflammatory mediators also activate TRPV1 pain channels. If someone touches your eye now – it hurts a lot more than just touching it before you got punched. This is an example of potentiation. The inflammation signals that activate TRPV1 make it much more excitable and it sends pain signals much more easily.

Another example of this was shown in a 2013 paper. Allyl isothiocyanate (AITC) from wasabi or onions binds can make hot food seem hotter. This applies to both hot meaning spicy, and hot meaning the opposite of cold. Scientists knew that AITC could activate TRPA1 pain sensors, so they thought AITC was sensitizing the TRPV1 through action on TRPA1, but this study showed that AITC can activate TRPV1 directly. Therefore, AITC may make TRPV1 active based on both sensitization and potentiation.

This cartoon tries to illustrate potentiation as different from

sensitization. Potentiation is important learning, you see there

is a higher level of neurotransmitters (dots) in the cleft (space)

after potentiation. Repeated firing strengthens the signal and

makes it easier to fire the neuron because there is more

neurotransmitter and more receptors.

The difference between sensitization and potentiation is in the number of receptors involved. Sensitization means that signaling through one receptor lowers the threshold for a second receptor, while potentiation means repeated signaling through the same receptors will lower its threshold. In both cases, the end result for TRPV1, TRPM8, and TRPA1 is that pains seem exaggerated – hyperalgesia.

What about allodynia – feeling pain when the stimulus shouldn’t be painful at all? TRPV1 and capsaicin can do that as well. This is also seen in my cold finger story. Sometimes, just coming inside and sitting down can make my fingers start hurting more and more. Room temperature shouldn’t cause pain at all; we have said before that TRPV1 is activated by heat only above 43˚C. This would mean that room temperature must be TRPV1-mediated allodynia.

Another 2013 study showed this in another model. Rats with inflammation in one masseter muscle (the big muscles in your cheeks that help you chew) could bring pain on chewing – in the opposite masseter muscle. This was blocked by TRPV1 antagonist, so it was definitely mediated through TRPV1, though they are the TRPV1 receptors in the central nervous system, not those in the muscles. The pain on chewing should have been only on the inflamed side, but it was on the other side too – that’s a form of allodynia.

I was looking for a picture to illustrate burning mouth

syndrome. This is what I found. People pierce their

uvulas?! The gag reflex would be unbearable, and it would

hang down at night and reduce your airway. If burning

mouth syndrome has no known cause, what causes this?

– true central nervous system dysreguation. I think I’d

rather have burning mouth syndrome.

Now for a more unfortunate example of allodynia that seems to involve TRPV1. There is a condition called burning mouth syndrome (BMS). Also known as idiopathic stomatodynia (idio = unknown, pathic = cause disease, stomato= mouth, and dynia = pain). Like the name says, it is a burning, itching, painful mouth disease for which no medical or dental explanation can be found and in which the oral mucosa appears normal. BMS feels like you are chomping on a Carolina Reaper or a Ghost pepper all the time.

BMS can be secondary to some diseases, but not caused by those diseases. It can last for months on end and then just go away, only to return later. There are different types, depending on whether you feel OK in the morning and then it gets worse as the day goes on, or whether it can come and go on a day to day basis.

So why talk about BMS in a story of TRPV1? Well, a 2013 paper shows that people with BMS tend to have more TRPV1 bearing neurons in their mouths. These same patients tended to have more of one type of cannabinoid receptor and less of another in their mouths as well. We know that some endocannabinoids can interact with TRPV1 capsaicin receptors, so it looks like the systems overlap here. And we also said before that supertasters have more TRPV1 neurons, so they would be more likely to get BMS.

The higher the number of TRPV1 ion channels, the more pain the patients reported, so it really sounds like these pain receptors are involved in BMS. But they might be the salvation as well.

Here is an example of a capsaicin spray for reducing

mouth pain. There is also one for nasal congestion. I,

personally, would stay away from that one. These are

based on the idea that some capsaicin can reduce pain in

the mouth – desensitization. And it has been studied in

burning mouth syndrome with some success. We'll

talk a lot more about it next week.

People with BMS often report that the pain is reduced when they eat, so perhaps gustatory sensing can overwhelm the pain sensing. And maybe chili peppers will lead the way. A 2012 study indicated that a capsaicin rinse (0.02% capsaicin) reduced the pain of BMS. It decreased the pain for most patients, but didn’t get rid of it for any of them. Ironically, they complained that it burned their mouths – as if they don’t feel that all the time.

An earlier review also showed that some studies showed a decrease in BMS symptoms via a topical capsaicin preparation. They just didn’t like the taste. This opens up a whole new bunch of questions. How can you use capsaicin to relieve burning pain? It causesburning pain!!

You use pain to stop pain – huh? You ponder that for a week.

Borsani E, Majorana A, Cocchi MA, Conti G, Bonadeo S, Padovani A, Lauria G, Bardellini E, Rezzani R, & Rodella LF (2013). Epithelial expression of vanilloid and cannabinoid receptors: a potential role in burning mouth syndrome pathogenesis. Histology and histopathology PMID: 24190005

Silvestre FJ, Silvestre-Rangil J, Tamarit-Santafé C, & Bautista D (2012). Application of a capsaicin rinse in the treatment of burning mouth syndrome. Medicina oral, patologia oral y cirugia bucal, 17 (1) PMID: 21743415

Simonic-Kocijan S, Zhao X, Liu W, Wu Y, Uhac I, & Wang K (2013). TRPV1 channel-mediated bilateral allodynia induced by unilateral masseter muscle inflammation in rats. Molecular pain, 9 PMID: 24377488

For more information or classroom activities, see:

I looked for good websites on sensitization and potentiation, but none are very good at explaining them in this situation, most are for learning pathways.

Pain from warm after cold –

http://www.thenakedscientists.com/HTML/questions/question/1467/

http://www.wildsnow.com/661/cold-hands-the-torture-cure/

Fibromyalgia –

http://www.mayoclinic.org/diseases-conditions/fibromyalgia/basics/definition/con-20019243

http://www.fmnetnews.com/fibro-basics/symptoms

http://www.huffingtonpost.com/stanford-center-for-sleep-sciences-and-medicine/sleep-tips_b_4770369.html

http://www.niams.nih.gov/health_Info/Fibromyalgia/default.asp

http://fmaware.org/PageServerded3.html?pagename=fibromyalgia

Burning mouth syndrome -

http://www.nidcr.nih.gov/OralHealth/Topics/Burning/BurningMouthSyndrome.htm

http://www.aafp.org/afp/2002/0215/p615.html

http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=6&sqi=2&ved=0CFkQFjAF&url=http%3A%2F%2Fwww.ada.org%2Fsections%2Fscienceandresearch%2Fpdfs%2Fpatient_53.pdf&ei=2MIHU-CgEcngrQHakoGIAQ&usg=AFQjCNFZAo5Dr5TEIt4Ns45D8zIk7Xb8AA&sig2=xjQsxltnlrig-FowGrUtcQ

http://abcnews.go.com/Health/PainManagement/story?id=4274230

http://www.webmd.com/oral-health/burning-mouth-syndrome

Biology concepts – desensitization, habituation, counter irritation, cautery, heat sensing, pain, chronic, acute, analgesia

Gout usually attacks middle-aged men and the big toe

joint is a favorite spot. But it can occur anywhere and

in anyone. The accretions or urates build up and clog

the joint, causng poor function and intense pain,

painful enough that even the weight of a sheet on it at

night is too much. Usually the acute attacks are far

worse, and become less painful gouty arthritis

as they become chronic.

Sometimes people use pain to combat pain, as silly as it may sound. Gout is an arthritis-like disease where uric acid crystals (a waste product from many different pathways, especially purine nucleotide metabolism) buildup in the joints and can cause life-altering pain.

Before adequate drugs and diet suggestions came along to help to rid the body of excess urates, people were sometimes left to to their own devices in trying to relieve the pain of gout. One home remedy was described in a history text from the 500’s CE called Historium Libri Decem.

In the book, the Bishop of Cahors had gout so bad that he would stick a fireplace poker in the embers and then apply it to his foot and shin. Man oh man, it must be some major discomfort if cauterizing your toes and foot becomes a good idea.

The practice of cautery(from Greek for branding iron) for gout lasted for hundreds of years, with a 17^th century century surgeon from France pronouncing that he didn’t really believe in external remedies for gout, except of course, for cautery with a red hot poker.

The above example falls under the heading of analgesia (an = not, and gesia = pain) by counter irritation. Counter irritants basically substitute one pain for another. You have two competing stimuli, both of which create pain. One is probably chronic (long-term, comes from chronus = time); this is pain from which the person wants relief.

The second pain is acute(from Greek for sharp). The second pain is geared toward relieving the first pain. Who hasn’t bitten a knuckle or lip while getting an injection or experiencing some other pain? Is it just a distraction, a placebo, or is there biology at work?

The concept of counter-irritation is old. Before we had any idea how it worked or even if it worked, counter irritant uses approached the bizarre. Heart attack and angina pectoris (pain from partially blocked cardiac vessels) often shoot a pain down the left arm. So early physicians decided that if counter irritants were placed on the left arm, they could short circuit the pain as it was sent out but before it could come back to the heart.

Cupping is one example of a counter irritant to relieve pain. The

little pins on the tops of the cups are for drawing a vacuum. Dry

cupping is shown on the left, no blood is drawn. Wet cuppin is

on the right, where more vacuum is used and blood is suck out

of the skin through the pores. Believe it or not,

wet cupping is more common.

Counter irritants these days are sometimes just as odd. For example, blistering horse legs to help their knees goes against common sense. There is also something called cupping, which is Chinese in origin. Suction is created in cups that then are placed on the skin. The skin is drawn up into the cup, and blood is drawn to the surface.

Originally used to promote healing, cups are used to quell pain too. As far as truly scientific studies, the only thing we know about cupping and pain relief is that the studies have been poorly conducted – better studies are needed. But never underestimate the power of the placebo. If a patient thinks it works, then it works.

Other types of counter irritants include scarification– scratching until the epidermis is removed. Many people with chronic itch practice this everyday of their lives. Chemical irritants that act on the skin are called rubefacients because they turn the skin red (through dilation of blood vessels underneath). Capsaicin, menthol, camphor, methylsalicylate (more on this below), eucalyptus oil, all have been tried as rubefacient counter-irritants.

This youngster suffers from Alagille syndrome.

It causes bile to stockpile in his liver which

makes him itch all over, all the time. He wears a

special suit to prevent him from scratching until he

bleeds. The scratching is a type of counter irritant

and will will talk more about itch and capsaicin in a

couple of weeks. The young boy is on the

liver transplant list.

Often, the counter-irritant is applied at the same place where the deep pain is, because the users believe it must act on the set of nerves that sense the pain in both areas. Capsaicin rubs, or things like BenGay (methyl salicylate) are rubbed on the skin where the muscles or joints ache. But this may not be the way that they act.

A study from 2009 showed you could counter a long-standing pain in the right leg by immersing your leftfoot in cold water. Painfully cold water activates TRPM8 and TRPA1. Doing this only to the left foot reduced shock pain in the right leg by 50%. Apparently it acts to confuse pain signals at the level of the spinal column.

So just how does counter irritation relieve pain? There are competing ideas. Perhaps the acute pain of the irritant sparks a release of endorphins (opiate pain killer made by our own body). This seems plausible, but chronic pain patients have very high levels of endorphins in their blood; they just seem to not respond to them.

The hypothesis of a nerve overload is less precise, and may actually reflect other mechanisms at work. Overload in general would mean that a huge amount of neural input at the same time overloads the spinal nerves at that point and results in no signals getting through. This may be how the left foot right leg example works.

Even if some of these mechanisms contribute to counterirritant action, additional processes are probably at work as well, namely desensitization and habituation. You’ll be surprised how much TRPV1 heat/capsaicin sensors are involved. Capsaicin causes pain because your body interprets it as noxious heat (TRPV1), but somehow, you can also use capsaicin to take away pain.

I have used the joke before, but it keeps working. Hitting

yourself with a hammer over and over could desensitize

pain receptors, induce endorphin release, distract from

other pain, confuse spinal signaling – all of which are

plausible mechanisms for counter irritation.

The truth is what makes it funny.

In simple terms, desensitization of the TRPV1 channels means that while some activation causes pain, continued activation depletes the neuron of the molecules need to create or transmit the signal, and the pain neuron can’t fire any longer. If it can’t fire, there’s no pain – analgesia.

There are two kinds of desensitization, homologous means that continued use of one agonist on a receptor makes that receptor less able to respond to that agonist. Heterologous desensitization is when other agonists work on receptors in another part of the tissue.

The heterologoustype of desensitization sounds an awful lot like the example above where really cold water on one foot reduces pain in the other foot. So this could be one of the mechanisms of counter irritants.

On the other hand, consider the old example of placing a frog in hot water (video here) – it jumps out due to TRPV1 heat/pain signaling. But if you place a frog in warm water and then heat it slowly, the frog won’t jump out. It will sit there until it’s a frog leg dinner. This is habituation (tolerance) and perhaps homologous desensitization as well. Perhaps capsaicin pain creams act by habituation and counter irritation, nothing says they can’t do both.

Another desensitization/habituation model uses resiniferatoxin injected into the covering of the brain (epidura) to stop neuropathic pain. Remember that resinferitoxin is a strong capsaicin-like molecule, with a score of 108.8 billion Scoville units. It is such a strong agonist that it alone can desensitize TRPV1 in short order - so much that it is termed an anti-nociceptive agonist.

Even more amazing, a Sept. 2012 study used two agonists of TRPV1, capsaicin and MRS1477. Use one or the other and you get hyperalgesia. But administer both at the same time and you get analgesia. In this case, they are hoping that this will be an alternative to opiates in cancer-mediated pain.

This all sounds great – TRPV1 is on small (C type) and some larger (Adelta) pain fibers, and wearing them out can reduce pain. But wouldn’t it just be easier to block them with an antagonist (something that binds but doesn’t activate)? Well, there’s a problem with that – TRPV1 does more than just signal pain.

If you block TRPV1 activity to produce analgesia, you also block its heat-sensing role. Now your body won’t know when it is getting hotter and won’t cool itself down. You end up with hyperthermia and that can kill you. This has been a consistent problem with TRPV1 agonists as analgesics, including if resinferitoxin is given orally – but who would want 108.8 billion SHU in their mouth?

It is the oral TRPV1 antagonists that seem to bring the hyperthermia when trying to treat osteoarthritis. The hyperthermia has been attributed to the action of TRPV1 antagonists in the GI tract. New work shows that activity of TRPV1 is increased (and the expression) in the joint during osteoarthritis, but no increase in expression or activity in the spinal column. Injection of a TRPV1 antagonist into the joint to stop the pain signals from the joint without the hyperthermia.

Wint-O-Green Life Savers are famous for emiting light

when chewed. This is called triboluminescenceand also

occurs when you rub quartz together or pull tape from

a roll. The mechanism is through energy release by

mechanical breaking of crystals or bonds. In the case

of life savers, sugar dried to crystal will undergo

triboluminescence, but the light is often in the UV

range. But the oil of wintergreen chemistry converts

the UV to visible light. And now you know.

But there's hope for oral TRPV1 antagonists. New polypeptides called APHC1 and APHC3 show analgesic activity in vivo at reasonable doses (0.01-0.1 mg/kg) by blocking capsaicin, heat, and acid activation and did not cause hyperthermia.They can be used IV or perhaps orally, they don’t need to be injected into a specific joint or into the spinal column.

Some chemicals may be both agonistic and antagonistic for TRPV1. A new paper states that methyl salicylate (oil of wintergreen) activates TRPV1, so it induces a warm feeling, but it also blocks TRPV1 activation by capsaicin, acid, anandamide, and perhaps inflammatory mediators. This means that it can be analgesic, which is why it's the main ingredient in BenGay.

However, the same paper indicates that analgesic activity of methyl salicylate might be due to its TRPV1-independent activity on a different system, the same pain generating system blocked by aspirin (cyclooxygenase). Arguing against this - BenGay is amazingly painful when loaded into a teammate’s underwear or jock. Take my word for it.

Acupuncture is a source of constant argument in science.

Does it really do something or is it all placebo. Recent

(2012-2014) papers are starting to show that it does have

specific physiologic actions. Here is shown the

electroacupuncture. In medical terms, this is equivalent to

TENS(transcutaneous electrical nerve stimulation). In TENS,

the current is passed through the area that is being

affected, but in acupuncture, a remote area may be used,

according to acupuncture charts.

On a completely different front, a 2012 study of electroacupuncture showed that it could reduce the size and frequency of the action potentials from TRPV1 nociceptive neurons. To determine how this might work, the same acupuncture point (st36) was shown in a 2014 paper to block pain by stimulating a pain pathway. If you block the anti-nociceptive TRPV1 channels with 1% capsaicin, then the acupuncture won’t stop the pain. Once again, TRPV1 works in both pain and anti-pain. That’s a confusing exception.

Next week, capsaicin receptors are also used in some other systems, not just heat and pain. Who would have guessed that eating chili peppers could stop but also cause cancer?

Andreev YA, Kozlov SA, Korolkova YV, Dyachenko IA, Bondarenko DA, Skobtsov DI, Murashev AN, Kotova PD, Rogachevskaja OA, Kabanova NV, Kolesnikov SS, & Grishin EV (2013). Polypeptide modulators of TRPV1 produce analgesia without hyperthermia. Marine drugs, 11 (12), 5100-15 PMID: 24351908

Tobaldini G, de Siqueira BA, Lima MM, Tambeli CH, & Fischer L (2014). Ascending nociceptive control contributes to the anti-nociceptive effect of acupuncture in a rat model of acute pain. The journal of pain : official journal of the American Pain Society PMID: 24412800

Lee MG, Huh BK, Choi SS, Lee DK, Lim BG, & Lee M (2012). The effect of epidural resiniferatoxin in the neuropathic pain rat model. Pain physician, 15 (4), 287-96 PMID: 22828682

Kelly S, Chapman RJ, Woodhams S, Sagar DR, Turner J, Burston JJ, Bullock C, Paton K, Huang J, Wong A, McWilliams DF, Okine BN, Barrett DA, Hathway GJ, Walsh DA, & Chapman V (2013). Increased function of pronociceptive TRPV1 at the level of the joint in a rat model of osteoarthritis pain. Annals of the rheumatic diseases PMID: 24152419

Because pain is involved, I am including demonstration links only for triboluminescence.

For more information, see:

Counter irritants –

http://www.racehorseherbal.com/Herbal_Therapies/Liniments/Counterirritation/counterirritation.html

http://www.medicine.ox.ac.uk/bandolier/booth/painpag/topical/topintro.html

http://relieffrompain.net/counterirritants/

http://arthritis.about.com/od/topicalcounterirritants/

http://www.pharmacytimes.com/publications/issue/2010/September2010/TopicalAnalgesics-0910

http://abcnews.go.com/Health/PainArthritis/story?id=5185473

Gout –

http://www.webmd.com/arthritis/tc/gout-topic-overview

http://www.niams.nih.gov/Health_Info/Gout/

http://www.rheumatology.org/practice/clinical/patients/diseases_and_conditions/gout.asp

https://www.arthritis.org/conditions-treatments/disease-center/gout/

http://emedicine.medscape.com/article/329958-overview

Acupuncture –

** http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3658605/

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3914330/

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3832370/

http://journals.lww.com/anesthesiology/Abstract/2014/02000/Mechanisms_of_Acupuncture_Electroacupuncture_on.35.aspx

http://www.medscape.com/viewarticle/501973_2

http://www.sciencedaily.com/releases/2013/03/130314085528.htm

http://www.hindawi.com/journals/ecam/2013/187182/

http://chinese-school.netfirms.com/acupuncture-mechanisms-of-action.html

Methyl salicylate triboluminescence –

http://www.instructables.com/id/Be-a-Scientist%3A-Learn-about-Triboluminescence-or,/

http://www.puttyworld.com/tr.html

http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=0CCUQFjAA&url=http%3A%2F%2Fwww.usc.edu%2FCSSF%2FHistory%2F2009%2FProjects%2FJ1524.pdf&ei=ovwMU-_mGYqIygGr8YCYDw&usg=AFQjCNGFkXamrW5_YSOqCNnZWJ6juxgwUQ&sig2=HJTnO8O2EXSSe1MRidX1dQ&bvm=bv.61725948,d.aWc

http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&ved=0CC4QFjAB&url=http%3A%2F%2Fwww.chem.ufl.edu%2F~kschanze%2Foutreach%2Fh4.pdf&ei=ovwMU-_mGYqIygGr8YCYDw&usg=AFQjCNE3Yfdz9ibHdHXA--60yJbgSz7sgQ&sig2=Q85iq4hQTULKZnpE1QkBXg&bvm=bv.61725948,d.aWc

http://chemistry.about.com/cs/howthingswork/a/aa060601a.htm

http://www.princeton.edu/~achaney/tmve/wiki100k/docs/Triboluminescence.html

http://scienceworld.wolfram.com/physics/Triboluminescence.html

http://pages.towson.edu/ladon/wg/candywww.htm

http://www.webexhibits.org/causesofcolor/4AB.html

http://www.bbc.co.uk/bang/handson/sugar_glow.shtml

Biology concepts – obesity, brown adipose tissue, agonist/antagonist, protective hypothermia, hyperthermia, reactive oxygen species, ischemia, hypoxia

When The Wizard of Oz was released in 1939, it just barely turned a profit. The '39 version was the third attempt at filming the children’s classic, and the first two efforts had not fared much better.

I don’t see how people didn’t take to the Wizard of Oz right away.

It had new technology for the movies, a good villain, and all those

little people. The tin man on the left was played by Jack Haley, but

originally it was supposed to Buddy Ebsen (Jed from the Beverly

Hillbillies). Unfortunately, the lead metal in the makeup almost

killed him during the makeup/costume tests. Glenda the good witch

(Billie Burke) had that squeaky voice. She only began acting

after her husband, Flo Ziegfeld, Jr. (son of the Ziegfeld Follies

creator), went belly up on Black Monday in 1929.

Over time, what was first considered bad has become a classic. In what many people consider the best year ever in film, The Wizard of Oz is now a favorite among favorites, more than Goodbye Mr. Chips, Mr. Smith Goes to Washington, Stagecoach, or even Gone With the Wind– all produced in 1939.

It’s smart to hang on to useless things and knowledge, something might change. For Oz – it was television. For some reason, this film translated better to TV than it did the big screen. The Library of Congress now rates it as the most viewed film ever. And it wasn’t even shown on TV until 1956. The weird part – very few people in 1956 owned a color television, so Dorothy’s entrance into the land of Oz was no big deal for most folks until the late 1960’s.

Why am I telling you this story? Because the same thing happens in biology and medicine. Problems can become assets if the right environment is created or the proper setting is found. We've been discussing the capsaicin receptor, TRPV1, for some weeks, and this is where I find a negative being turned into a positive.

As you know, the TRPV1 capsaicin receptor is primarily a heat sensing receptor for thermoregulation of the body. If activated by noxious (painful) high temperatures, it generates a pain signal and initiates a cooling program for the body, including sweating.

In an effort to block TRPV1 to create analgesia (no pain), the problem has been that blockers also stop thermoregulation and the patient overheats. This prevents most TRPV1 antagonists (substances that bind the receptor but don’t allow function) from being used as analgesics. But what about in other situations?

I was wondering if TRPV1 antagonists might be helpful in obesity, by helping burn off some fat through increased cooling activity. If they are indeed helpful, nobody knows about it yet. I couldn’t find even one paper that studied TRPV1 antagonists as a way to induce increased energy expenditure and weight loss. In fact, I learned just the opposite. Capsaicin and other TRPV1 agonists might help with weight loss.

On the left is brown fat and white fat. You can see that brown fat

actually looks browner because of all the mitochondria that it

contains. White fat contains a lot more lipid. The right cartoon

shows that a cold challenge initiates uncoupled fat metabolism in

brown fat, creating heat. But the cold also releases more fatty acids

from white fat, which can then be burned by the brown fat. The

involvement of bone comes from bone breakdown. Breakdown

releases a protein that stimulate white fat to release fatty acids,

this would provide energy for the brown fat.

We have discussed how TRPV1 activation by noxious heat helps to cool the body, but it turns out that noxious cold leads to TRPV1 activation as well, but in these cases, it brings an increase in heat production. So TRPV1 can cool you down or warm you up as needed. Pretty cool. You'll have to wait a few weeks to find out how a heat receptor senses noxious cold.

The heat induced by cold comes from increased activity of brown adipse tissue (BAT) – brown fat. We have talked about BAT before, how it is especially important for infants because they lose heat so easily. Brown fat has lots of mitochondria, but they don’t make ATP. They convert all the energy they burn into heat.

New research is showing that BAT can be important to adults as well. Those people that have more BAT tend to have less white fat, the kind that makes you bigger. What is more, a 2013 paper shows that cold temperature exposure can help create more BAT, and this effect is mimicked by capsaicin and other TRPV1 agonists.

If you expose adults to mildly cold temperatures for six hours a day, they start to make more BAT and this means they burn more energy for heat; therefore less energy is left to be stored as white fat. But the study also showed that giving the people capsaicin for weeks in a row generated the same increase in BAT and stopped white fat accumulation.

One mechanism involved is that TRPV1 agonists stimulate an increase in uncoupling protein (UCP) expression in BAT. This is the protein that permits the BAT mitochondria to produce lots of heat instead of lots of ATP and a little heat. The uncoupling protein activity in BAT uses excess calories to produce heat, so those calories are not available to make fat.

Here is how a stem cell becomes a fat cell (adipocyte).

The mesenchymal cell can go two directions, one

toward fat and one toward muscle. But notice you can

get to a brown fat cell through the pathway meant for

muscle cells. PG stands for prostaglandins; different

profiles of prostaglandins lead to a decision to become

a brown fat cell or a white fat cell. We know this picture

is incomplete now, because we have evidence that

TRPV1 agonists can drive the decision between

brown fat and white fat.

But there may also be another mechanism at work. A 2014 study in laboratory petri dishes shows that cells destined to become white fat cells can be stopped from changing by capsaicin. In cells called preadipocytes, capsaicin stopped their proliferation (dividing to become more cells) and their differentiation (changing) to become full-fledged adipocytes (fat cells). Another study (2012) showed that in liver, capsaicin could prevent the accumulation of white fat build up (called fatty liver) and could actually induce UCP protein expression in some fat cells, turning them into liver BAT. Amazing.

This all sounds fine, but the proof is in the pudding, so to speak. Capsaicin and other TRPV1 agonists have been shown to reduce white fat and total body mass in rabbits fed a high-fat/1% capsaicin diet, in mice fed a high sucrose diet, and in human patients kept cold or fed hot. Tomorrow I’m going to start eating hot peppers in a cold house – I’ll shrink away before your eyes.

What about on the other end of the thermometer? People freeze to death when they get too cold, and TRPV1 agonists will cool you off when too warm. No TRPV1 activity causes a reactive hyperthermia, and too much TRPV1 activity will induce a reactive hypothermia. But is there a time when inducing cold in a body with capsaicin would be a good thing?

Would we be talking about it if there weren’t an exception? It's called protective hypothermia, and it has become a very important treatment adjunct during stroke and some over conditions.

Ischemia (left) is often associated with coronary (heart) arteries.

Ischemia means a reduction in blood flow to a tissue or the whole

body. With less blood flow comes less oxygen, so tissue cells suffer.

Several mechanisms can lead to a lessening of blood flow. On the

right is hypoxia, which is often used when referring to the brain or

specific organs. Hypoxia is a reduction in oxygen to the tissues,

whether it comes from a reduction in blood flow or some other

reason, like fewer red blood cells, lower oxygen in the air, etc.

Protective hypothermia is an induced cold that is used to protect tissues from post-ischemic injury. When there is a reduction in blood (ischemia) or oxygen (hypoxia) to a tissue or organ, the cells are starved for oxygen and then become starved for ATP (you need oxygen to make ATP). With lower oxygen over time, either from low oxygen or reduced blood flow, the tissues get used to having lower oxygen levels.

Getting used to it would include down-regulating the systems that would normally combat the damage that could be caused by reactive oxygen species(ROS). Whenever oxygen is being used in tissues, ROS are an unfortunate by-product. Their name tells you that they’re reactive, which means they can react with many molecules in the cell and they will do significant damage.

When normal blood flow or oxygen perfusion is re-established, the sudden increase in O₂ causes a spike in ROS (reperfusion injury) – until the cell can ramp up its antioxidant capabilities again. What medicine needs to do is find a way to increase the O₂ without increasing the ROS damage.

Cold seems to do the trick. Reducing the temperature of the body reduces cell death and ROS after cardiac arrest, stroke, neonatal encephalopathy, or traumatic spinal/brain injury. Why? There have been a few ideas why.

The old hypothesis was that the lower temperature would reduce cellular metabolism, so that there is less need for O₂. This would imply that the lower the temperature, the better. But very low temperatures might lead to injury or damage on their own. Also, extended cold could bring pneumonia or promote sepsis. Maybe colder isn’t always better.

There are many ways to get a perfusion injury when

oxygenation of the tissues is reestablished after hypoxia.

We talked about the free radicals (ROS) in the post. The

other injuries are a bit less obvious. We mentioned the

problems with membranes and the increase in apoptosis.

The other two are related to spasm of the muscle cells in

the vessels which would again reduce oxygen levels, and

a nonspecific activation of coagulation and cell killing that

would lead to damage as well.

Now scientists think protective hypothermia works in a couple of different ways. Colder temperatures bring a neuroprotective effect by preventing apoptosis (programmed cell death). Less O₂means less ATP being made, and a decrease in ATP usually means that the mechanisms for maintaining proper ion movements in and out of the cell are hampered. Increased ion flux triggers apoptosis. So lower temperature brings less ion flux, less damage, and less cellular suicide.

Even a small decrease in temperature can stabilize the cell membrane independent of ATP levels. This makes sense; membranes are mostly lipid, and lower temperatures make fats stiffer – like cold butter. This will decrease ion movement across the membrane and reduce cell damage.

Lastly, decreased body temperature brings less reperfusion injury. In this case, maybe the old hypothesis was correct. Colder tissues metabolize less, so less oxygen will be needed and less ROS will be produced.

So cold is helpful, but how do you do it? You can lower the body temperature by using cooled IV fluid, cold mist in the nose, or even wrapping specific body parts in cooled blankets. But perhaps TRPV1 agonists could help cool the body from the inside.

As of early 2014, the evidence for TRPV1 agonists is only in mouse models, but it’s looking good. A study in 2011 showed the an injection of capsaicin into the abdominal cavity three hours before inducing hypoxia reduced the volume of dead tissue and the amount of apoptosis in the brains of the mice.

This is the fruit of the Evodia rutaecarpa Bentham plant. It has been

used in Chinese herbal medicine for hundreds of years. We are

starting to learn why it does what it does. It has been shown to be

an anti-cancer, anti-obesity, anti-vomiting, anti-hypertension

anti-ulcer, anti-pain drug. Five thousand years of

culture leads to good drugs like this.

Two 2013 studies added strength to the 2012 study. One experiment used a Chinese herbal medicine that contained a chemical called evodiamine. It had been known that evodiamine helped in stroke victims, but we didn’t know why. Evodiamine was shown to be a TRPV1 agonist in 2012, and the 2013 study showed that after a stroke, the agonist increased cell survival mechanisms and reduced apoptosis.

The other study from 2013 showed that capsaicin also helps in reperfusion injury. Mice were given strokes by blocking an artery in the brain and then unblocking it to replenish the blood and oxygen. Injecting capsaicin within 90 minutes of the re-establishment of blood flow produced a mild hypothermia, reduced the volume of dead tissue in the brain, and increased neural function. This didn’t occur in mice without TRPV1, so we know the capsaicin receptor was responsible. Sounds like emergency rooms are going to start stocking hot peppers.

Today we discussed interesting uses for capsaicin and its receptor in temperature-related functions. Next week, some weird functions for TRPV1 that have little or nothing to do with temperature.

Yoneshiro T, Aita S, Matsushita M, Kayahara T, Kameya T, Kawai Y, Iwanaga T, & Saito M (2013). Recruited brown adipose tissue as an antiobesity agent in humans. The Journal of clinical investigation, 123 (8), 3404-8 PMID: 23867622

Feng Z, Hai-Ning Y, Xiao-Man C, Zun-Chen W, Sheng-Rong S, & Das UN (2014). Effect of yellow capsicum extract on proliferation and differentiation of 3T3-L1 preadipocytes. Nutrition (Burbank, Los Angeles County, Calif.), 30 (3), 319-25 PMID: 24296036

Yoneshiro T, & Saito M (2013). Transient receptor potential activated brown fat thermogenesis as a target of food ingredients for obesity management. Current opinion in clinical nutrition and metabolic care, 16 (6), 625-31 PMID: 24100669

Muzzi M, Felici R, Cavone L, Gerace E, Minassi A, Appendino G, Moroni F, & Chiarugi A (2012). Ischemic neuroprotection by TRPV1 receptor-induced hypothermia. Journal of cerebral blood flow and metabolism : official journal of the International Society of Cerebral Blood Flow and Metabolism, 32 (6), 978-82 PMID: 22434066

Cao Z, Balasubramanian A, & Marrelli SP (2014). Pharmacologically induced hypothermia via TRPV1 channel agonism provides neuroprotection following ischemic stroke when initiated 90 min after reperfusion. American journal of physiology. Regulatory, integrative and comparative physiology, 306 (2) PMID: 24305062

For more information or classroom activities, see:

Brown adipose tissue –

https://exploreb2b.com/articles/how-does-brown-fat-help-to-reduce-obesity

http://www.medicalnewstoday.com/articles/240989.php

http://www.webmd.com/diet/features/the-truth-about-fat

http://www.landesbioscience.com/curie/chapter/623/

http://diabetes.diabetesjournals.org/content/58/7/1482.full

http://arbl.cvmbs.colostate.edu/hbooks/pathphys/misc_topics/brownfat.html

http://www.marksdailyapple.com/a-primal-primer-brown-adipose-tissue/

http://wholehealthsource.blogspot.com/2013/07/brown-fat-its-big-deal.html

Protective hypothermia -

https://www.google.com/#q=protective+hypothermia

http://www.qscience.com/doi/full/10.5339/qmj.2012.2.19

http://ccforum.com/content/16/S2/A2

http://www.ctnow.com/health/ctn-woman-dead-revived-with-cpr-hypothermia-web,0,3890140.htmlstory

https://www.med.upenn.edu/resuscitation/hypothermia/

http://emedicine.medscape.com/article/812407-overview

Biology concepts – cochlear amplification, capsaicin, tinnitus, neural plasticity, long term depression, sperm capacitation, acrosome reaction, apoptosis, reactive oxygen species, cancer

On the left are the Red Hot Chili Peppers. I am most interested in the

member on the right – Flea. Acknowledged as the second best rock

bassist of all time (right behind John Entwhistle), he gathers as much

or more attention for his name choice and his seeming inability to

wear a shirt. On the right is Donnie Thornberry, of the Wild

Thornberrys. He was a feral child raised by animals in Africa. His

character is voiced by Flea – ahhh, it’s starting to make sense.

I have never been a fan of the Red Hot Chili Peppers (sometimes known as RHCP). The music is nails on a chalkboard to me, and their bassist is named for a plague-carrying arthropod. But in the interest of fair play, I looked deeper. In late 2013, lead singer Anthony Kiedis and “Flea” produced a film intended to honor the life of jazz pianist Joe Albany. Add to this that Kiedis acted in an ABC After School Special when he was a teenager, and I now see that the Chili Peppers are more than just bad music.

I use this story to introduce today’s topic - there is so much more to the capsaicin in chili peppers than just heat and pain. We learned last week how capsaicin and other TRPV1 agonists can combat obesity and damage from stroke, but these abilities were related to the TRPV1 function in thermoregulation. Today let’s look at some functions that are so far outside normal TRPV1/capsaicin function that they can be considered exceptional – like jazz piano from the RHCP.

Hearing

We have explained the mechanism of hair cell action in hearing before. The inner hair cells are bent by the sound wave in the cochlea and converted to a neural impulse to be detected as sound. The outer hair cellswork to amplify the wave so that the sound is louder and can register a signal in the inner hair cells.

Scientists know that TRPV1 is expressed on the inner and outer hair cells, and works in the cochlear amplification system particularly. However, we don’t know its exact function(s) there. On the down side, we know that TRPV1 must work in a narrow range, because drugs and agonists that excite TRPV1 can lead to hearing problems.

Acoustic injury (acute or chronic loud noise), gentimicin (an antibiotic), and cisplatin (a cancer drug) can all cause hearing damage. A 2009 study of gentimicin damage to the cochlea showed that it increased TRPV1 expression in the outer hair cells. A 2008 study of cisplatin showed that its damage to the hair cells could be suppressed if you decreased TRPV1 activity.

Most often people think of tinnitus as a ringing in the

ears, but it doesn’t have to be. It can be clicking, buzzing,

hissing, or roaring sounds as well. If you hear voices –

well, that’s something completely different. Also, tinnitus

is usually characterized as a neural transduction issue,

often from damage to the hair cells, so only you hear it.

But there are problems in blood vessels, muscles, or

bones (TMJ) near the ear that produce soucnds other

can hear. This is called objective tinnitus.

A 2013 study indicates that TRPV1 is important for the uptake of the drugs into the hair cells, and then they do their damage. An older study shows that even without drugs to be taken up, increased TRPV1 expression is the cause of acoustic injury tinnitus (ringing) and hearing loss. Another paper showed that capsaicin itself blocks the action potential in the outer hair cells and dampens the cochlear amplification system. Why anyone would stick a chili pepper in his ear is beyond me.

So we see that a little TRPV1 activity is good, but too much is bad. This is not to say that eating a lot of peppers will harm your hearing; dietary capsaicin never gets to your cochlea unless you’re a horribly messy eater. We will return to this idea with TRPV1 and capsaicin; it can be an angel or a devil.

Memory and learning

Neural plasticity (the ability to change neural connections, building some, losing others) is important in learning and memory. We have discussed long-term potentiation (LTP) in terms of memory, where a reinforcement of action potentials between two neurons or in a pathway lead to a strong connection and a new item learned or remembered.

The flip side is long-term depression (LTD). This mechanism is what allows you to weaken and lose connections between neurons that aren’t being reinforced. You can’t learn something as well unless you keep reinventing the connections, including losing some. However, don’t get the idea that you have to forget some thing in order to remember something new, it is much more complicated than that.

This is a good carton because it helps me point out a

dichotomy. Many people say that your brain is a muscle,

if you don’t exercise it, you will lose it. This is like the

atrophy of your muscles if you don’t use them. But we are

reading in this post that losing some neural connections

is important for learning. Long term depression is similar

to not using your brain. Those connections that are not

reinforced are lost – but here it is a good thing,

a necessary thing.

TRPV1 acts in LTD. Without TRPV1 activity, all connections could continue to be strengthened, and a ceiling level of excitability would be reached. Then you wouldhave trouble adding new information.

TRPV1 acts at the level of the hippocampus (important for memory) through an endocannabinoid called anandamide. We already know that anandamide is a TRPV1 agonist.A 2008 study indicated that there was no LTD activity in mice that had no TRPV1 channels. This study found that TRPV1 was “necessary and sufficient” for LTD, meaning that it was needed and only it was needed for the effect.

Another 2008 study points out how this is important for us. Stress brings too much LTD and not enough LTP. When you’re stressed it’s harder to learn new things and easier to lose established knowledge. Amazingly, TRPV1 agonists like capsaicin can regulate this in stress. Stress + TRPV1 agonists led to reduced LTD and improved LTP. It seems that capsaicin and other TRPV1 agonists regulate synaptic plasticity in both directions, keeping us on balance and always learning.

Reproduction

Put simply, without capsaicin channels none of us are here to read this great stuff. TRPV1 activity, through various agonists, is important for sperm motility and fertilization of the egg. The sperm meets the egg and here we go - is that the whole picture? Nope. It takes a lot to arrange their introduction, and some of it involves TRPV1 channels.

You ever wonder why the testicles are kept outside the trunk of the body? It’s to keep the sperm cool – heat kills sperm. TRPV1 receptors sense high heat and institutes local reactions to cool the sperm. A 2008 study showed that TRPV1 knockout mice had much higher levels of sperm death in the testicle when the temperature was raised. It didn’t make the mice sterile, but it was close.

On left is a cartoon of sperm capacitation, making it ready tofertilize travel to the egg. The loss of the cholesterol coat isimportant for increasing motility and for finishing the signals that point out whee the egg is. The acrosome is also prepared here, but there are more acrosome changes in the right image showing the

acrosome reaction. Here, the spem head becomes a weapon, dissolving the outer layers of the egg and stabbing it for entry.

So TRPV1 is important for sperm even before they start their journey. The first thing that happens after the sperm enters the female reproductive tract is that they undergo a process called capacitation. These changes make the sperm ready to bind to the egg. TRPV1 and its agonist anandamide (same as in LTD) are important late in capacitation. They prepare the sperm for transfer of the DNA to the egg.

TRPV1 and endocannabinoid receptors are also responsible for the increase in sperm motility after capacitation. The sperm swim toward the egg, but how do they know where she is? There are many signals, including osmolarity differences, hormones, temperature changes, pH changes, and liquid currents. We have seen that several of these (pH, temp., hormones, osmosis) are sensed by TRPV1 channels.

It’s been shown that TRPV1 on the sperm post-acrosomal and head regions are important for sperm motility. A 2013 study showed that inhibiting TRPV1 slowed down fish sperm. And in a 2013 study of infertile men, the motility of the sperm in men with low levels of anandamide was decreased.

Strangely, even though capacitated sperm are thermotactic (swim toward higher temperatures), this is one time where it DOESN’T involve TRPV1/capsaicin receptors. It still involves calcium, but the flux is through a different receptor system.

Once the sperm finds the egg, it undergoes the acrosome reaction. This makes it possible for the sperm - only one mind you - to enter the egg. A 2009 study indicated that anandamide and TRPV1 are crucial for the acrosome reaction as well.

From inside the male, to inside the female, to inside the egg, capsaicin receptors are crucial for making tiny humans. It doesn’t get more important than that. What I don’t know is if eating peppers affects any of this. Would a habanero make you more fertile or less?

The PSA test (prostate specific antigen) can be used

for monitoring treatment of prostate disease as well

as for diagnosis of prostate cancer in conjunction with

other tests. The tests measure s aprotein produced by

the prostate that is often elevated in those with prostate

cancer. PSA can be free or bound to a protein. You want

the free:bound ratio to be high, and low ratio is more

indicitive of cancer. However, there are noncancerous

reasons for an elevated PSA, so don’t go nuts if your

levels ar higher than normal (score of 4 ng/ml).

Cancer

In cancer we see the dual nature of TRPV1 again. In some cases it prevents or stops cancer, while in others, capsaicin might contribute to cancer.

Prostate cancer has been studied a lot with respect to TRPV1. Capsaicin, in particular, has an effect on prostatic cancer cells. It kills the cells and reduces tumor size in mice. However, in humans, little work as been done. One epidemiology study found that Nigerians that eat more peppers have a lower rate and later onset of prostate cancer.

In addition, a single study followed a man whose prostate cancer returned after several disease free years. His PSA value(prostate specific antigen, a sign of cancerous growth) started to double weekly, so he started taking 2 ml habanero sauce once or twice week. His PSA value increases slowed by half. He stopped and they sped up. He started daily habanero sauce and the PSA dropped. Sounds like a treatment to me.

The mechanisms of capsaicin action on prostate cancer cells has been determined in in vitro work. They are both TRPV1 dependent and TRPV1 independent. (studies) Capsaicin increases ROS, induces apoptosis, destabilizes membranes, throws off ion balances…basically everything capsaicin stopswhen used for protective hypothermia (from last week).

It isn’t just prostate cancer where capsaicin may help. In a mouse model of lung cancer, giving capsaicin prevent the lung tumors from forming by increasing apoptosis in the cancerous cells. Whether this is TRPV1 dependent or independent was not discussed.

But there is a darker side to capsaicin and TRPV1 in prostate cancer. The agonists have a small window of effectiveness. Low levels actually promote cancer growth, but higher levels cause cell cycle arrest and apoptosis. In one study, 10 µM capsaicin actually created prostate tumors in mice.

Where do you come down on the question of whether

peppers are good for you or not? Do they cause cancer

or prevent it? Do they cause pain or prevent it? I think

that as with most things, moderation is the key. Too

much of anything is bad for you, except maybe this blog.

One thing I do know; we have sharp canines for a reason -

we were meant to eat meat. This statement is why

she has that look on her face.

The bad news continues... maybe. Several studies have linked capsaicin to stomach, oral cavity, and gall bladder cancer. One epidemiologic study showed that US counties with higher Mexican American, Cajun, and Creole populations have higher rates of these cancers, and it just so happens that these are the folks that eat more chili peppers. Some skin cancers are also associated with capsaicin. This is a bit disconcerting considering the number of topical capsaicin pain creams on the market.

In squamous cell skin cancer, capsaicin can sometimes stunt the growth of tumors via apoptosis, but the mechanism seems to be TRPV1 independent, since a TRPV1 antagonist brings the same effect. The take home message is that TRPV1/capsaicin effects may be diet, individual, cancer specific. This will make it hard to develop therapeutics.

Next week - now its time to start talking about cool receptors. Like how the cigarette companies use "cool" to sell smokes.

Lee JH, Park C, Kim SJ, Kim HJ, Oh GS, Shen A, So HS, & Park R (2013). Different uptake of gentamicin through TRPV1 and TRPV4 channels determines cochlear hair cell vulnerability. Experimental & molecular medicine, 45 PMID: 23470714

Amoako AA, Marczylo TH, Marczylo EL, Elson J, Willets JM, Taylor AH, & Konje JC (2013). Anandamide modulates human sperm motility: implications for men with asthenozoospermia and oligoasthenoteratozoospermia. Human reproduction (Oxford, England), 28 (8), 2058-66 PMID: 23697839

Gonzales CB, Kirma NB, De La Chapa JJ, Chen R, Henry MA, Luo S, & Hargreaves KM (2014). Vanilloids induce oral cancer apoptosis independent of TRPV1. Oral oncology PMID: 24434067

Anandakumar P, Kamaraj S, Jagan S, Ramakrishnan G, & Devaki T (2013). Capsaicin provokes apoptosis and restricts benzo(a)pyrene induced lung tumorigenesis in Swiss albino mice. International immunopharmacology, 17 (2), 254-9 PMID: 23747734

For more information or classroom activities, see:

Cochlear amplification –

http://www.slideshare.net/lynnroyer/hair-cell-function-and-purpose

https://www.bcm.edu/healthcare/care-centers/otolaryngology/patient-information/how-ear-works/inner-outer-hair-cells

http://neuroscience.uth.tmc.edu/s2/chapter12.html

http://www.d.umn.edu/~jfitzake/Lectures/UndergradPharmacy/SensoryPhysiology/Audition/OHCFunction.html

http://147.162.36.50/cochlea/cochleapages/theory/hcells/hcells.htm

http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=5&ved=0CFQQFjAE&url=http%3A%2F%2Fwww.bcs.rochester.edu%2Fcourses%2Fcrsinf%2F221%2FARCHIVES%2FS11%2FCochlear_Amplifier.pdf&ei=YYoXU4X4NYS0ygHQ6oD4CA&usg=AFQjCNFHqR7wKBFlhBt1pSD9KRyFyt74Vg&sig2=G0wcwNIEzpSuSt5ZMkotlA&bvm=bv.62286460,d.aWc

http://medicalxpress.com/news/2012-12-cochlear-amplification-optical-technique.html

http://www.neurophys.wisc.edu/auditory/johc.html

http://science.howstuffworks.com/life/human-biology/hearing5.htm

Tinnitus –

http://www.dangerousdecibels.org/education/resources/dangerous-decibels-dvd/

http://www.ata.org/for-patients/student-zone

https://faculty.washington.edu/chudler/chhearing.html

http://faculty.washington.edu/chudler/hearing.html

http://www.ata.org/

http://www.webmd.com/a-to-z-guides/understanding-tinnitus-basics

http://www.mayoclinic.org/diseases-conditions/tinnitus/basics/definition/con-20021487

http://www.nlm.nih.gov/medlineplus/tinnitus.html

http://www.medicinenet.com/tinnitus_ringing_in_the_ears/article.htm

Sperm capacitation –

http://embryo.asu.edu/pages/sperm-capacitation

http://www.pbs.org/wgbh/nova/education/activities/2811_baby.html

http://www.keytoconceive.com/sperm-capacitation.php

http://www.glowm.com/section_view/heading/Sperm%20Transport%20and%20Capacitation/item/315

http://www.youtube.com/watch?v=rrFsTdfe2qw

http://www.wisegeek.org/what-is-sperm-capacitation.htm

http://www.youtube.com/watch?v=-J9deipbdSI

http://community.babycenter.com/post/a36676870/capacitation

Acrosome reaction –

http://education-portal.com/academy/lesson/acrosome-reaction-function-definition.html#lesson

http://www.youtube.com/watch?v=5-g8dLcERlM

http://www.youtube.com/watch?v=-jLyzWrSTOA

http://www.stanford.edu/group/Urchin/acrosome.htm

http://www.embryology.ch/anglais/dbefruchtung/akrosom02.html

http://worms.zoology.wisc.edu/urchins/SUfert_acrosome.html

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3181525/

http://arbl.cvmbs.colostate.edu/hbooks/pathphys/reprod/fert/fert.html

Biology concepts – TRPM8 cold sensor, menthol, evolution, cold pleasure

The old ads for menthol cigarettes are fascinating, from a biology
point of view. The “cool” and the “refreshing” aspects were reflected
by using spring and summer outdoor pictures, most often with lots of
cool water. At the end of today’s post, we see why this was so. We
also see an African American, since menthol cigarettes were targeted
much more strongly urban African Americans. They were newer
smokers and in typically hotter environments, so the coldness and
soothing abilities of the menthol were great selling points.

In 1924, Lloyd “Spud” Hughes patented the menthol cigarette. Not a big deal in the beginning, Hughes sold his patent to a cigarette manufacturer who marketed them as Spud cigarettes in 1927. They became the fifth largest seller, although there still wasn’t much in the way of profit. Kool cigarettes came along in 1933 and advertised the menthol casket nails as “soothing to the throat” and claimed they were actually medicinal.

The menthol cooled the feel of the smoke in the mouth and throat (much more next week on hos menthol feels cool). Menthol made it feel as though you weren’t sucking hot smoke into your lungs. And menthol deadened the discomfort that cigarettes could generate by irritating the lining of the throat and lungs.

These days, almost 90% of cigarettes contain some menthol, even if they don’t advertise themselves as menthol cigarettes. Why? The “cool” factor lends itself to novice smokers, while the throat analgesia appeals to the seasoned addict. But that may not be the main reason. A study from 2004 showed that menthol slows the metabolism of nicotine.

Slowing the metabolism of nicotine, menthol results in nicotine staying in the system longer and at greater concentrations - just perfect for developing a physical addiction. This, combined with the ability to comfortably smoke more cigarettes because of the slight throat numbing and apparent cooling of hot smoke would encourage more consumption, more addiction, and therefore more profit.

There is now (2013-2014) a push by the US Food and Drug Administration to ban or regulate menthol cigarettes. Did you know that menthol addition to shampoo is federally regulated but its addition to cigarettes is not? Let’s look at some of the reasons a change is being considered.

The tobacco plant has supplied cells that are used to show the
danger of menthol cigarettes. I just love that. But tobacco has been
involved in science in other ways as well. New efforts are
underway to have genetically modified tobacco produce medicines
or biodisel. And the tobacco mosaic disease actually led to the
discovery of viruses and the coining of the word “virus.” This same
virus was instrumental in establishing the fields of
virology, plant virology and all of molecular biology.

A 2013 series of experiments showed that menthol-containing cigarette smoke is more toxic to cells than non-mentholated cigarette smoke. Menthol alone had no toxic effect on the cells, so it is the combination of menthol and cigarette smoke that kills cells at a higher rate. In the most delicious irony imaginable, the two cell types that the researchers used to monitor cell death after smoke exposure were human lung cells and tobacco plant cells!!!

Additional recent evidence suggests that menthol interacts with the nicotine receptor in the brain. Brody and his co-workers showed that menthol cigarette smoke up regulates the number of nicotine receptors in the brain more than regular cigarette smoke. This might explain why it is harder for menthol cigarette smokers to quit smoking and why more of them fail in their efforts to quit.

Another 2013 study showed that menthol decreased the activity of the nicotine receptor, so that more nicotine was necessary to reach the same level of activation. Once again, this would contribute to a physical addiction. Just a bit of information if you are considering taking up the habit - the “cool” factor and refreshing cold of mentholated smoke just may contribute to your death.

So sensing cool or cold has its place in biology and in society. Chili peppers are sensed as burning hot because they just happen to bind to and activate the TRPV1 heat sensing ion channel– it’s the biological joke being played on us that we have talked about before. TRPV1 a receptor that reacts to both environmental (temperature, pH) conditions and food substances.

On the other end of the scale is the sense of cold. Do organisms sense cold like they sense heat? Isn’t cold just a lack of heat, so that a feeling of cold is just a lack of activation of TRPV receptors? Nope. There are receptors specifically designed to sense cool or cold. Are there exceptions in cold sensing like there were for heat? You should know that answer by now.

Melastatin was the first TRPM protein discovered. The name
comes from melanin (the pigment in skin and hair cells) and
statin, which means to stop. It was important because it could stop
the invasion of tumors of melanin producing cells. We call this
maliganant melanoma, one of the deadliest cancers. Tumors with
more melastatin were less aggressive and invasive, while those with
little melastatin killed patients much sooner.

We learned recently that there are six different TRPV cation channels, and at least four of them are important for sensing different ranges of temperatures. In some cases, like with TRPV1, noxious heat (or capsaicin) results in a sensation of pain and burning, and the body’s mechanisms for cooling are turned on.

Another TRP family member, TRPM8, turns out to be the receptor channel that senses cool temperatures, from about 28˚C (82 ˚F) down to about 10˚C (50 ˚F) or even lower. The M stands for melastatin, a name for the first TRPM, before they knew it was a family of proteins. Now there are eight known members of the TRPM subfamily of TRP ion channels.

TRPM5 is particularly interesting for our recent discussion of taste, since it works to change the mechanical energy of taste particles + taste receptors into an electrical signal that is sent to the brain. Once again, we see the close relationship between the ion channels, like TRPV1 for capsaicin, and the taste sense. Maybe cold and TRPM8 also influence taste. We shall see.

Less is known about TRPM8 as compared to TRPV1 although they were discovered about the same time (early 2000’s). The pain associated with capsaicin and noxious heat aspects of TRPV1 made it sexier to study. I think we will see that TRPM8 and TRPA1 can be quite interesting in their own right.

Here’s a quick overview of the thermosensing by TRPs.
We will talk about it more next week. The TRPVs are
generally for warm temperatures, while TRPM8 is for
cool temp.s. TRPA1 will be our focus in a few weeks; it
senses painful cold. But notice, the garlic and wasabi
pictured with TYRPA1 also activate TRPV1, and the camphor
shown for TRPV1 also activates TRPM8 (next week). These are
related and complex systems.

First of all, TRPM8 is involved in thermoregulation, just as is TRPV1. In humans and other mammals (the naked mole rat excepted), when TRPV1 is activated, the body automatically thinks it is too hot and initiates cooling mechanisms. With TRPM8, the effect is the opposite. Stimulation of this ion channel tells the body that it is too cold, and mechanisms are initiated to increase the core temperature. We will talk about how TRPM8 helps to regulate body temperature next week.

The big question is why it’s important to sense cold as well as heat. For some reason, we sense cool/cold with some distinct proteins and heat with different proteins. Remember, evolution doesn’t follow a plan to make things complex, functional and efficient. Sometimes the functions occur at separate times and come from different pathways; there is no evolutionary goal or roadmap to a destination. It’s all chance.

A 2013 review has an interesting hypothesis as to why sensing cold/cold is so important, aside from just alerting us to the chance we might freeze to death. Based on mouse study results from as early as the 1970’s, and on the answers that human subjects give, it seems that coolness is an evolutionary plus. No- I don’t mean that The Fonz from Happy Days was an evolutionary leap into the future, I mean that cool sensations somehow help us survive and propagate.

We typically heat food because it increases aroma, increases taste, and reduces the work in digestion. These are all important for getting us the nutrients and the calories we need. Taste, as we said several weeks ago, is nature’s way of getting us to eat those things we need and avoid those foods that might harm us.

So why would cool foods or sensations be helpful? Cooling would decrease aroma and taste, so it must be something other than taste. The obvious reason for drinking something cold would be that it cools off our body – but it doesn’t work that way. As soon as you drink a cold drink, your body reacts to the cold by constricting the blood vessels near the cold surface so that heat is not lost. TRPM8 also invokes heating mechanisms after it is activated by the cold water or soda. So in truth, cold drinks don’t cool you off.

On the left is a mint julep, famous in Kentucky and the Deep
South during the hot summers. It contains Kentucky bourbon,
which is why it is brownish. On the right is the mojito, also
good on hot days, but uses rum, so it is popular in the Caribbean
and Florida, where the rum is. The connection? They both use
mint (menthol) to increase the coolness and refreshing
characteristics of the drinks. TRPM8 hard at work to make
your Saturday evening a success.

Yet they still feel refreshing on a hot day – what gives? Refreshing may be the key word here. People use many words that together make up “refreshing.” They say that cold drinks revive them, restore their energy, arouse them, reduce stress. All these feelings would promote survival behaviors in a hot environment. But we might also drink a cold drink on a cold day and deem it pleasant. In this case, pleasant can be equated to useful – and useful means promoting survival.

The 1970’s experiments showed that mice would lick a cold piece of metal when they were thirsty, showing that cold helps satisfy thirst. The more amazing thing was that the mice would lick the cold metal even if they could drink all they wanted. This meant that cold drinks were a reward; they activate a pleasure center in the brain. Many studies and experiments have shown these results to be true for humans as well.

So a cold drink on a cold day might be seen as unpleasant, while a cold drink on a hot day is very pleasant (useful). But more important, a cold drink on a cold day when you are thirsty is seen as pleasant and satisfying. It’s our brain helping us to garner the things we need; if cold water is all that’s available to a cold caveman, he better want to drink it. It works the same on skin, cold applied to the skin on a hot day – such as jumping into the pool on a warm day is seen as pleasant, even if it doesn’t cool the body all that much (see above). But the same cannonball on New Years day with the Polar Bear Club, is completely unpleasant.

Comedian and late night talk show host Jimmy Fallon took
the Polar Bear Plunge in Chicago this past New Years. Basically,
3000 people jump into a 34˚F (1˚C) Lake Michigan to support
Special Olympics. Some do it for the charity, some for the thrill,
some because they are unbalanced. For those with a heart
condition, it can kill you.

The brain is an amazing organ, it works with our body to get us what we need, and tricks us into doing it – that’s basically what pleasurable things are, evolutionary tricks. But remember – too much of a good thing can be bad in an environment where we can manipulate nature.

Unfortunately, evolution doesn’t look into the future, it only worries about what keeps us alive at this moment. This explains the danger of menthol in cigarettes – we find it pleasant even if it is bad for us in the long run.

We will talk more about the TRPM8 next week, about how menthol seems to cool you down, how TRPM8 is a lot like TRPV1, and how it may save your life.

Eccles R, Du-Plessis L, Dommels Y, & Wilkinson JE (2013). Cold pleasure. Why we like ice drinks, ice-lollies and ice cream. Appetite, 71, 357-60 PMID: 24060271

Noriyasu A, Konishi T, Mochizuki S, Sakurai K, Tanaike Y, Matsuyama K, Uezu K, & Kawano T (2013). Menthol-enhanced cytotoxicity of cigarette smoke demonstrated in two bioassay models. Tobacco induced diseases, 11 (1) PMID: 24001273

Brody AL, Mukhin AG, La Charite J, Ta K, Farahi J, Sugar CA, Mamoun MS, Vellios E, Archie M, Kozman M, Phuong J, Arlorio F, & Mandelkern MA (2013). Up-regulation of nicotinic acetylcholine receptors in menthol cigarette smokers. The international journal of neuropsychopharmacology / official scientific journal of the Collegium Internationale Neuropsychopharmacologicum (CINP), 16 (5), 957-66 PMID: 23171716

Ashoor A, Nordman JC, Veltri D, Yang KH, Al Kury L, Shuba Y, Mahgoub M, Howarth FC, Sadek B, Shehu A, Kabbani N, & Oz M (2013). Menthol binding and inhibition of α7-nicotinic acetylcholine receptors. PloS one, 8 (7) PMID: 23935840

For more information or classroom activities, see:
Menthol in cigarettes –
http://smokefree.gov/menthol-cigarettes
http://www.cancer.org/cancer/news/expertvoices/post/2013/08/28/menthol-cigarettes-whats-the-big-deal.aspx
http://www.npr.org/2014/01/01/258671720/fda-weighs-restrictions-possible-ban-on-menthol-cigarettes
http://www.huffingtonpost.com/2013/11/22/latino-smokers-menthol-cigarettes_n_4326094.html
http://www.forbes.com/sites/robwaters/2013/11/20/menthol-an-unequal-opportunity-killer-why-hasnt-the-fda-banned-it/
http://www.webmd.com/smoking-cessation/news/20110323/are-menthol-cigarettes-riskier-than-non-menthol http://www.theguardian.com/society/2013/oct/08/menthol-cigarettes-to-be-banned-eu
http://www.fool.com/investing/general/2013/12/14/judgement-day-for-menthol-cigarettes-is-getting-cl.aspx

http://www.dw.de/european-parliament-approves-stricter-tobacco-regulations/a-17458107

In lieu of additional web sources, I suggest investigating the National Center for Biotechnology Information site (http://www.ncbi.nlm.nih.gov/) from the National library of Medicine. This site has many resources, from looking at the amino acid or nucleotide sequences from any protein or gene you can imagine (GenBank, http://www.ncbi.nlm.nih.gov/genbank/) to scientific journal articles that may or may not be available to you. Look at PubMed Central (PMC, http://www.ncbi.nlm.nih.gov/pmc/) where all articles are available free to the public.

Biology concepts – thermoregulation, TRPM8, vasoconstriction, brown adipose tissue, agonists/antagonists

Pep-O Mint was the first Lifesaver flavor, invented

in 1912. This was followed quickly by the Lifesaver

car in 1918. Built on a Dodge truck chassis, the

important word was dodge, since the car didn’t have

a windshield and the driver had to stick his head out

the side window to see ahead.

Let’s do a demonstration. Borrow a peppermint lifesaver from a friend (well, not borrow really - you’re not going to give it back). Place it between your teeth, so you can close your lips around it and suck air in through the hole (this will be the control for our experiment).

Now put the candy in your mouth like normal and suck on it for a minute or two – don’t chew it up. Swallow to get the saliva out of your mouth and take out the candy. Now take in a long slow breath of air. How does it feel? Did the room get colder in the last two minutes?

If you are like most people, the air feels colder in your mouth now that you've eaten menthol (peppermint). Just like capsaicin can make hot things seem hotter via TRPV1, the cold sensing channel we talked about last week, TRPM8, can make room temperature air seem colder.

The TRPM8 cold sensing ion channel is important for keeping our body temperature in a normal range. Just like TRPV1 senses when we are too warm and initiates cooling mechanisms, TRPM8 tells us we are cold and institutes procedures to make us warmer. One way is to stimulate vasoconstriction, so less heat is lost from the blood through our skin. I’m sure you have noticed that your skin is paler when you are out in the cold. This is from vasoconstriction limiting the amount of blood moving into the surface vessels.

When your core temperature varies from your skin

temperature by too much, TRPM8 will institute

heat conserving and/or generating mechanisms.

For heat conservation, more of the blood (left

cartoon) that goes the skin can be shunted through

the capillaries before it gets to the surface. This

helps reduce the amount of heat loss via radiation

of the heat in the blood. On the right is the effect of

the arrector pili muscles. When cold, they contract

and raise the hairs, trap air, and therefore trap body

heat against the skin so less heat is loss. The

contraction also mounds up the skin – goosebumps.

TRPM8 can also stimulate shivering and the burning of fat to generate warmth. Through the sensations and reactions of TRPV1 and TRPM8, animals learn to maintain a more or less constant body temperature, seeking out temperatures that are good for physiology and avoiding temperatures that would change their core temperature by too much. This was shown in a series of studies described in a 2013 paper, where mice without temperature sensing receptors TRPV1 and/or TRPM8 would not avoid hot or cold temperatures and were prone to hyperthermia and or hypothermia.

So how does the TRPM8 channel sense cold? We saw that with TRPV1 the heat induced a conformation change that caused the channel to open and calcium to flow in and start a neural action potential. Could cold induce a conformation change as well? Maybe. What was seen in a 2011 study was that TRPM8 neurons started firing when the temperature dropped to 28.4˚C (83 ˚F). As the temperature dropped, the neurons would fire more and more strongly, so it could act as a thermostat.

When the temperature dropped severely (to 10˚C) the core temperature changed little, but skin temperature dropped considerably. The TRPM8 thermostat was targeted to keeping the organs and brain warm, not the skin. It accomplishes this by diverting heat via the blood away from the skin. A 2012 study showed that TRPM8 antagonists brought a systemic hypothermia, but repeated use of the antagonist reduced the magnitude of the temperature drop – so unlike most TRPV1antagonists (that bring bad hyperthermia), TRPM8 antagonists might be helpful in medicine.

We don’t yet know how cold activates TRPM8. In

warmth, the channel is closed. With cooler

temperature or menthol (M), the channel is open,

but we don’t know if cold achieves this by a

conformation change. If really cold, the regulatory

proteins break away and the channel can’t work.

So TRPM8 is active in a range of temperatures.

But this still doesn’t answer the questions as to how TRPM8 can detect cool temperatures. It may or may not be a conformation change, but what does occur is an alteration in the apparenttemperature threshold of the neuron. The cold temperature should inhibit firing (cold slows metabolism and chemical activity), but here it increases the metabolism and biochemical activities. TRPM8 makes the neuron seem warmer so that the firing is easier, and this transfers information that the area is in fact colder! That’s an exception.

However it manages the feat, TRPM8 is important for keeping mammals warm. It might even help you lose weight. Chronic cold stimulates TRPM8 all the time, and this ramps up your heat production. A 2012 study showed that for mice, chronic cold could actually prevent them from becoming obese.

Heat production takes energy, and burning more energy helps you lose weight. But there is an important balancing act at work here. Our fat also protects us against losing too much heat in the cold. Look at whales, they have a layer of blubber all over their body to insulate them from the cold water. It has been shown that people with an even layer of fat all over their body make good cold weather swimmers, like Lynne Cox, who swam from her perfectly good boat to the shores of Antarctica and across the Bering Strait in 4˚C (40˚F) water.

On the other hand, bactrian camels keep their fat limited to two humps (one for dromedaries) in order to prevent against having too much insulation in their desert environment. Camels need to be able to dissipate lots of heat. And no, the humps aren’t for storing water! Remember we said that one of the great things about fat is that you can store lots of energy in a small space precisely because can be stored without water.

In brown adipose tissue, there are ATP synthase

proteins (for making ATP) and uncoupling proteins

(for generating heat) in the inner mitochondrial

membrane. When cold, the number of UCP proteins is

increased, as is the number of mitochondria. About

65% of the energy of the proto gradient formed by the

respiratory chain can be converted to ATP by the ATP

synthase. But using the UCP to allow protons back in

means that 100% of the energy is changed to

heat, no ATP is made.

It seems that TRPM8 can stimulate the burning of fat to produce heat. We talked about this before with capsaicin as well. Brown adipose tissue has more mitochondria and more of a protein called UCP1 (uncoupling protein). UCP separates mitochondrial energy burning from ATP production; all the energy goes to making heat.

A 2014 study showed that chronic cold makes brown fat AND white fat upregulate UCP and generate more mitochondria. It makes white fat more like brown fat and this means that more fat is burned. In mice, this chronic cold is enough to keep them from becoming obese, even on a high glucose diet. So if you want to stay skinny, turn your thermostat way down all year round.

The study that showed that chronic cold kept mice from getting fat wasn’t as cruel as it may sound. They didn’t keep the mice at cold temperature all the time, they used a chemical that could mimic the cold and make the TRPM8 channels fire all the time. What did they use? Menthol.

This is a good place to point out the similar exception for TRPV1 and TRPM8. They are both proteins that can be activated by both environmental factors and by chemicals. We saw that TRPV1 is activated by capsaicin and other chemicals. The opening of the channel and firing of the neurons in response to these chemicals was interpreted exactly the same as if the neurons were exposed to damaging heat.

There are many agonists for TRPM8, similar to TRPV1.

In fact, some things that activate TRPM8 also activate

TRPV1. An interesting one is the synthetic agonist called

icilin. It is thousands of time more active on TRPM8 than

cool temperatures. However, it binds to TRPM8 in a

completely different way as compared to menthol and

cool temperatures.

With TRPM8, menthol (in mints) and some other chemicals open the ion channels just as cool/cold temperatures would, and our brains trick us into thinking the mouth or skin is colder than it really is. That’s what is behind our lifesaver trick at the beginning of the post. The air wasn’t any colder; your brain makes you think it was.

Menthol is a terpene alkaloid contained in plants of the genus Mentha (mint, from the Greek mintha). This genus includes 25 species of aromatic herbs, such as peppermint, spearmint, and pennyroyals. Most mints can be and are used in making foods and drinks, but the pennyroyals also contain toxic compounds that will induce liver failure and kill you.

At low concentrations in the mouth or on skin, menthol produces a pleasant cooling sensation, but higher concentrations produce burning, irritation and pain (this has to do with how it activates TRPV1, TRPV3, TRPM8, and TRPA1, depending on the concentration).

In the oral cavity, a small amount of menthol actually desensitizes TRPV1 activation by heat and capsaicin, so chili peppers might not seem so spicy. Biochemical evidence shows that menthol sparks a release of glutamate from neurons. But an increase in glutamate neurotransmitter can actually stop the type C nociceptive neurons from firing (an inhibitory neurotransmitter in this case).

Pennyroyal is a member of the mentha genus (left). It, like

many plants (right image is orange mint), has been used in

medicine. It can be ground and drunk with water to settle a

sick tummy or to induce perspiration. However, pennyroyal

has to be used carefully. In addition to menthol, it contains a

chemical called pulegone. Too much pulegone and here

come the seizures, organ failure and death. Don’t confuse

the two mints.

At this same time, menthol (or other TRPM8 agonists) will sensitize TRPM8 receptors, the combination of these two results means that sucking in air after a wintergreen or peppermint candy will make the air seem colder, but might also make a hot cup of coffee seem cold as well.

I think the only way to resolve these ideas is to start a controlled experiment. What do you predict would happen if you froze a chili pepper and then took a bite? How about eating peppermint laced with capsaicin, or a strong peppermint flavored tea that has been heated to near boiling? Who will win out, TRPM8 or TRPV1?

It may not be so easy to figure out. The agonists and antagonists of the TRPs can have effects on multiple receptors and the effects can be different at different concentrations. Menthol sensitizes TRPM8, but if the temperature is above 37˚ C (98˚ F) it actually makes TRPV3, a heat sensor, more active (2006).

Camphor comes from some species of laurel trees (left), as well as

from some herbs of the mint family, like camphor basil (right).

Dried rosemary leaves are up to 20% camphor. Camphor has

been used for many things, including as a flavoring in asian

sweets, an analgesic, an insect repellent, and a rust proofing

agent. I find it hard to rectify those uses with one another.

Take oil of wintergreen in BenGay for example. We showed that it was a TRPV1 agonist, so it could induce analgesia by counter irritation. But it is also a TRPM8 agonist. In the oral cavity at lower concentrations than used in BenGay, it activates TRPM8 and desensitizes TRPV1. The lifesaver trick will work with peppermint, spearmint, and wintergreen flavors; they all activate TRPM8.

And then there’s camphor. Like menthol, camphor is terpenoid chemical. Camphor can make things seem cool (by activating and sensitizing TRPM8), but it’s more complicated. It actually potentiates both heat and cold sensations. A 2013 study shows that it can sensitize or potentiate TRPV1 (painful hot) and TRPM8 (non-painful cool). Camphor can even activate the noxious cold sensor TRPA1 that we will talk about in a couple of posts. This means that it can be analgesic or painful, warming and cooling.

It becomes even more confusing when you realize that camphor activates TRPM8, just like menthol, but can inhibit the activation of TRPM8 by menthol. Weird, right? Well, consider this – Vick's VapoRub contains menthol and camphor as its active ingredients. Next week, we'll investigate how they can work together to open your nose and make you feel both warm and fuzzy while they cool and invigorate you at the same time.

Pogorzala LA, Mishra SK, & Hoon MA (2013). The cellular code for mammalian thermosensation. The Journal of neuroscience : the official journal of the Society for Neuroscience, 33 (13), 5533-41 PMID: 23536068

Rossato M, Granzotto M, Macchi V, Porzionato A, Petrelli L, Calcagno A, Vencato J, De Stefani D, Silvestrin V, Rizzuto R, Bassetto F, De Caro R, & Vettor R (2014). Human white adipocytes express the cold receptor TRPM8 which activation induces UCP1 expression, mitochondrial activation and heat production. Molecular and cellular endocrinology, 383 (1-2), 137-46 PMID: 24342393

Ma S, Yu H, Zhao Z, Luo Z, Chen J, Ni Y, Jin R, Ma L, Wang P, Zhu Z, Li L, Zhong J, Liu D, Nilius B, & Zhu Z (2012). Activation of the cold-sensing TRPM8 channel triggers UCP1-dependent thermogenesis and prevents obesity. Journal of molecular cell biology, 4 (2), 88-96 PMID: 22241835

Selescu T, Ciobanu AC, Dobre C, Reid G, & Babes A (2013). Camphor activates and sensitizes transient receptor potential melastatin 8 (TRPM8) to cooling and icilin. Chemical senses, 38 (7), 563-75 PMID: 23828908

For more information or classroom activities, see:

Thermoregulation –

http://beyondcoldwaterbootcamp.com/en/thermo-regulation

http://www.unm.edu/~lkravitz/Article%20folder/thermoregulation.html

http://dwb.unl.edu/teacher/nsf/c01/c01links/www.science.mcmaster.ca/biology/4s03/thermoregulation.html

https://worldofbiology.wikispaces.com/biol+2+classroom+presentations

http://www.pbslearningmedia.org/resource/lsps07.sci.life.reg.heatexchange/blood-flow-and-thermoregulation/

http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=5&ved=0CDwQFjAE&url=http%3A%2F%2Fbio.classes.ucsc.edu%2Fbio131%2FThometz%2520Website%2F9%2520-%2520Thermoregulation%2520Lab%25202012.pdf&ei=zSIzU6SuFqPEyQGZ4oD4CA&usg=AFQjCNERS9ye-sPF7qZM-dJHUsFPQ031Tw&sig2=xLwl_fcQ3rIxKcZiLictmw

http://www.life.umd.edu/classroom/bsci338m/Lectures/Temperature.html

https://www.khanacademy.org/science/mcat/organ-systems/muscular-system/v/thermoregulation-by-muscles

https://www.youtube.com/watch?v=kg7QdpOug2Y

http://www.nsta.org/publications/news/story.aspx?id=53687

http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=16&ved=0CEgQFjAFOAo&url=http%3A%2F%2Fwww.tarleton.edu%2F~jblevins%2Fexercise%2520physiology%2FSpring%252009%2Fpowers7_ppt_Chap12%2520%255BRead-Only%255D%2520%255BCompatibility%2520Mode%255D.pdf&ei=HSMzU-ToHaSHygGerwE&usg=AFQjCNHxnlMTdNoOKd1p9lJrSyv6yew6Jg&sig2=fsvfEpvq9j0LTxOVaSYQwQ

http://www.studyblue.com/notes/note/n/ch-40-hwpdf/file/9213703

http://vce-unit1and2biology.wikispaces.com/thermoregulation

http://en.wikioffuture.org/Dissertation_Research:_Olfactory_Modulation_of_Thermoregulation_and_Flight_in_Moths

http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/heatreg.html

https://www.youtube.com/watch?v=TSUCdLkI474

http://people.seas.harvard.edu/~jones/cscie129/pages/health/thermreg.htm

https://www.stanford.edu/group/stanfordbirds/text/essays/Temperature_Regulation.html

https://www.mdc-berlin.de/26954638/de/research/research_teams/temperature_detection_and_thermoregulation/Research?cntx=40550329

Biology concepts – thermoregulation, TRPM8, TRPV1, heat sensing, cool sensing, vasoconstriction, nasal resistance, viral cold

The common cold. The red nose is from irritation from

tissue and inflammation. The medicines are to treat the

symptoms. Colds are caused by viruses, and we don’t

really have treatments for viruses. What I don’t

understand is the thermometer; adults with colds very

rarely have fever. Kids usually run a fever, but not adults.

So either this is the oldest looking child or he is worried

about something other than a cold.

It sucks when you have a cold – or does it blow? Your nose is stuffed, it’s hard to breathe, you have a cough that won’t stop and seems to do you no good. You’re chilled, but don’t know if you want to feel warmer. Is there anything you can do? One popular treatment might just be a lie.

I have noticed two things that seem to help the stuffiness I feel with a cold. One is exercise – it always seems to open up my nasal passages and make it easier to breathe. The rush of endorphins doesn’t hurt either – I may not be getting better, but I don’t mind the cold as much with a good dose of endogenous opiates running through my veins.

For me, a second short-term nose opener is going outside into the cold weather to shovel snow or chop wood. Why would being cold help a stuffed nose? Ponder that question for a second while I vent on a common misconception. Why do we say we catch a cold? It’s a viral infection, does temperature have anything to do with it at all?

Sure, more people have colds in the winter – but you know from this blog that correlation does not imply causation. Having a cold in winter doesn’t mean that the winter weather had anything to do with catching cold.

Your mother always told you to wear your coat outside or you’d catch your death of cold. Your basketball coach did a hat check after practice to make sure you didn’t leave for home with wet hair on an uncovered head. Were there reasons for this?

Underneath all that winter gear is Randy Parker, Ralphie’s

little brother from A Christmas Story. His mother, in her

time-honored wisdom, didn’t want him to a catch cold by

being cold. The problem was that wrapping him up just

kept the cold from stimulating his metabolism and his

immune system over time. Plus, he found it hard to go

through doorways; he couldn’t put his arms down!

In a word, no. That isn’t to say that there is no effect from cold weather, but it's minimal. A cold is caused by a great many viruses. These viruses are transmitted from person to person via respiratory droplets and on surfaces. The closer people pack together, the more likely the virus will be transmitted from one person to another.

When are people most often closer to other people? The winter – people spend more time inside, heating systems recycle the air; it’s the season for sharing. The cold weather encourages people to stay inside, where they are more likely to receive a viral gift from someone else.

So the cold does play a role, including a slight decrease in immune function due to changes in blood flow, and the fact that cold air holds less moisture, so your mucosal membranes dry out and are a bit more susceptible to being invaded by a virus. But cold is by no means the main culprit, so I propose a letter writing campaign to rename the cold – maybe you could catch a crowd, or a doorknob, or maybe we could just call it Dennis.

O.K., now that thatissue is resolved, back to the question of how cool air and exercise can help you breathe better when you have a “cold.” The key is a concept called nasal resistance.

Nasal resistance is the main way to slow air entering the

lungs. Being slower and higher pressure keeps the lungs

from overinflating or collapsing. The nasal vestibule (1)

squeezes together as you inhale, the smaller space prevents

too much air from entering. Inside is the vestibule is the

valve (3), the narrowest region. The turbinates (5-8, superior,

middle, and inferior) can expand slightly to decrease the

nasal volume. There are small muscles (alae nasi) in the

vestibule which can contract to decrease resistance as well.

Paralysis of these muscles leads to collapse of the naostrils.

Basically, the more stuff in the way of the air, the higher

the resistance.

Nasal resistance is an important way to keep our lungs from popping or collapsing. If the resistance to air entering the lungs is too high, the lungs will collapse like a balloon with a hole in it. If the resistance is too low, you could overinflate and pop them – also like a balloon. The nose, believe it or not, is responsible for about 50% of the resistance to air entering the lungs (see picture).

Having a cold increases mucous production (trying to catch viral particles before they reach your cells). A cold virus infection also puffs up the nasal tissues due to immune inflammation reactions. These responses increase nasal resistance and decrease airflow. It is much harder to get the same volume of air into your lungs through your nose. This observation won’t win me the Nobel Prize; we’ve all experienced it.

Exercise reduces nasal resistance through stimulation of the sympathetic nervous system. Hard physical work is a lot like the fight or flight response. Your body vasoconstricts vessels in the periphery so that more blood can go to the big muscles. You also need more oxygen, so the alae nasi muscles in your nose relax and the airways get bigger. Both of these actions decrease nasal resistance and increase airflow to the lungs. During a cold this is helpful since your ventilatory spaces are clogged with snot.

On the other hand, my sojourns into the brutal winter are against the literature. Cold air is supposed to increase nasal resistance. Cold air is bad for the lungs – it saps heat from the rest of the body. Therefore, the nose anatomy functions to warm the air. When cold air enters and triggers the TRPM8 cool sensors (there’s our first reference to the topic we have been discussing), the alae nasi muscles contract and the blood vessels in the nasal mucosa dilate. This swells the internal nasal tissues, increasing the surface area and thereby transferring more heat to the air before it reaches the lungs.

Rebreathing is a good way to reduce nasal resistance. Just

hold your breath for a while or breathe into a paper bag.

Increased CO₂ in blood brings vasoconstriction, so tissues will

shrink and breathing will be easier. The same goes for changing

from a supine (lying) position to standing or sitting. The change

in filling of sinus vessels and nasal vessels will shrink tissues as

well and you will breathe easier for while.

This should increase the nasal resistance, which will be high anyway due to all the mucous production going on. The cold air should make it harder to breathe, but for me it clears my nose when I have a cold. Where’s the disconnect? In fact, what I have always attributed to the cold air is probably a result of what I was doing, not where I was doing it.

I go out in the cold to chop wood or shovel snow - I have a tendency to attack my work, so these activities become exercise. Upon reflection, I now realize that it was once again exercise that was reducing my nasal resistance and allowing me to breathe more normally, not the act of going out into the cold. I’m caught in my own correlation-causation trap; there were other factors that I had failed to take into account. I had too many variables in my experiment! I never considered going out into the snow and not working hard.

Now let’s consider another cold and cough treatment, Vicks VapoRub. The active ingredients in this concoction are menthol and camphor. We have talked recently about how menthol is a TRPM8 agonist (so mints make everything seem colder), and that camphor is an agonist for both TRPM8 and TRPV1, so it can induce feelings of warmth or cool, depending on the concentration and placement.

You rub the Vicks on your chest when you have a cold. The camphor stimulates TRPV1 and makes your trunk feel warm. The menthol vapors rise and your breathe some in, they make your nose less stuffy. Or so it seems.

Here is a late 1950’s ad for Vick’s VapoRub. Which child would

you rather have? A simple greasy rub on the chest and all the

problems are solved. If you can read the headline, it seems that

atom tracing shows that the vapors get into the lungs. One – is

there anything more 1950’s than talking about atoms? Two – we

now know that Vicks works in the nose, not the lungs.

The commercials for Vicks VapoRub show the menthol/camphor fumes entering the nose, and the cold sufferer then relaxing and breathing more easily - convincing stuff, visually. It does seem that it's easier to breathe. But it’s all a trick our brains are playing on us. Remember that TRPM8 senses cool/cold temperature differences.

When you breathe in quickly and deeply, the rushing air is colder than the air that was just hanging out in your nose. This triggers the TRPM8 sensor, and your brain interprets it as a lot of air rushing up your nose and to your lungs – decoding the signal means that you are breathing well and deeply.

Now switch to the situation where you have a cold and can’t bring in air through your nose. The menthol/camphor of the Vicks VapoRub penetrates your nose and stimulates the TRPM8 channels there. Your brain interprets this data just as if cool air was rushing over the TRPM8 channels. It concludes that you are breathing well. You think you are breathing easier, but no actual change has occurred in nasal resistance! A 2008 study showed this to be the case. Bad brain! We can’t fool Mother Nature, but apparently she fools us all the time.

One thing that is true about the VapoRub is that it can calm a cough. Menthol, in particular, is excellent in its anti-tussive capability. Tussiveis from the Latin tussis, meaning a cough, although I’ve never heard anyone say, “I have a very bad tussis today.” Likewise, does this mean that when you are coughing, you are really tussing? Do you need to “tuss up” that ten dollars you owe me? (Yes, I am aware of the snickering from those of you of the Cornish persuasion - look it up.)

Developed in 1865, Lofthouse was looking to help fisherman

with their seasonal colds. The lozenge contains menthol and

eucalyptus, just like Halls, but much earlier. The fisherman

liked them so much they called them their friend. Hence the

name; they’re still sold today. Menthol drops can calm a cough,

but menthol is also slightly analgesic, so some throat pain can

be reduced by them as well.

Nevertheless, recent studies have shown that menthol, through its activation of TRPM8, does have a calming effect on a cough. We knew this was so, Halls mentho-lyptus (for menthol and eucalyptus – another TRPM8 agonist) drops have been around since 1930’s, with other brands like Smith Brothers and Pines having predated Halls by some 80 years. But the 2012 study showed that menthol’s action on cough was through TRPM8 action.

A 2013 study went further. It assessed the anti-tussive action of menthol in guinea pigs and showed that the effect on TRPM8 was only effective when it was in vapor form and when it was applied to the nasal passages. Menthol on trachea or throat TRPM8 had no effect on cough. So – when you use Halls cough drops, it's the vapors from the dissolving drops that go up your nose and help stop the cough – don’t chew on them and swallow! You put them in your mouth, but they don’t act there. But don’t stuff them up your nose either – did I need to say that?

We have considered TRPM8 in thermoregulation, nasal resistance, and cough. Next week, let’s show some funky functions for cold receptors – like how they can stop cancer or how they screw up opiate addiction withdrawal.

Lindemann J, Tsakiropoulou E, Scheithauer MO, Konstantinidis I, & Wiesmiller KM (2008). Impact of menthol inhalation on nasal mucosal temperature and nasal patency. American journal of rhinology, 22 (4), 402-5 PMID: 18702906

Buday T, Brozmanova M, Biringerova Z, Gavliakova S, Poliacek I, Calkovsky V, Shetthalli MV, & Plevkova J (2012). Modulation of cough response by sensory inputs from the nose - role of trigeminal TRPA1 versus TRPM8 channels. Cough (London, England), 8 (1) PMID: 23199233

Plevkova J, Kollarik M, Poliacek I, Brozmanova M, Surdenikova L, Tatar M, Mori N, & Canning BJ (2013). The role of trigeminal nasal TRPM8-expressing afferent neurons in the antitussive effects of menthol. Journal of applied physiology (Bethesda, Md. : 1985), 115 (2), 268-74 PMID: 23640596

For more information or classroom activities, see:

Cold viruses –

http://www.brainpop.com/educators/community/bp-jr-topic/colds-and-flu/

http://www.discoveryeducation.com/teachers/free-lesson-plans/allergies-v-viruses.cfm

http://www.developingteachers.com/etgplans/etg1.htm

https://www.google.com/#q=cold+virus+classroom+activity

http://www.theguardian.com/teacher-network/teacher-blog/2012/dec/23/colds-viruses-resources-lessons

http://www.everydayhealth.com/cold-flu/exercise-for-common-cold.aspx

http://www.teachengineering.org/view_lesson.php?url=collection/duk_/lessons/duk_virus_mary_less/duk_virus_mary_less.xml

http://www.ncsta.org/reflector/archives/summer07/activity.html

http://www.eduplace.com/rdg/gen_act/survival/survive.html

http://www.scholastic.com/browse/article.jsp?id=3751431

http://health.howstuffworks.com/diseases-conditions/cold-flu/cold-causes.htm

http://www.mayoclinic.org/diseases-conditions/common-cold/basics/definition/con-20019062

http://www.cdc.gov/getsmart/antibiotic-use/uri/colds.html

http://kidshealth.org/parent/infections/common/cold.html

http://www.wired.com/2012/03/ff_antivirals/

http://www.webmd.com/cold-and-flu/cold-guide/understanding-common-cold-basics

http://www.commoncold.org/

nasal resistance –

http://emedicine.medscape.com/article/874822-overview

http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&sqi=2&ved=0CDEQFjAB&url=http%3A%2F%2Fotolaryngology.wdfiles.com%2Flocal--files%2Frhinology%2FNasal%2520resistance%2520%25E2%2580%2593%2520Ent%2520Scholar.pdf&ei=7FdBU_LlFoOZ2QXn1IHgCQ&usg=AFQjCNE0ZdBvXvkoPyXGZ23QL7vY809V6A&sig2=kR4-w2ncfzB8HKK3vWezfg

http://www.drtbalu.com/nasal_resis.html

http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=6&sqi=2&ved=0CFQQFjAF&url=http%3A%2F%2Fwww.researchgate.net%2Fpublication%2F7367287_Nasal_obstruction_and_its_impact_on_sleep-related_breathing_disorders%2Ffile%2Fd912f50b9db2c55ce8.pdf&ei=7FdBU_LlFoOZ2QXn1IHgCQ&usg=AFQjCNHZpXTK7gmaFTJCJD8D6feYbH_sNw&sig2=beqT9entOz6HfWYWcJKPow

http://www.specialistmedicalrandwick.com.au/the-chest-and-sleep-centre/nasal-resistance-testing/

http://oto.sagepub.com/content/143/2_suppl/P164.2.full.pdf+html

menthol and cough –

http://www.webmd.com/cold-and-flu/cold-guide/cough-syrup-cough-medicine

http://www.wisegeek.org/what-are-the-benefits-of-menthol-cough-drops.htm

https://www.zocdoc.com/answers/4547/do-cough-drops-work#.

http://askville.amazon.com/limit-cough-drops-period-time/AnswerViewer.do?requestId=16427900

http://www.aedrops.com/how-does-menthol-relieve-throat-irritation/

Biology concepts – thermosensing, cool sensing, allergy, cross-reactivity, cold allergy, sperm maturation, acrosome reaction, opiate withdrawal

You can be allergic to things that touch your skin – like poison ivy,

things injected, like bee venom, things eaten – like foods, or things

inhaled – like perfumes. But now we need to add something else

to this list – cold? On the right you see a common way to test for

allergy. Anything that produces a wheal and flare reaction

(blanched and raised surrounded by red) is considered positive.

But what if they’re just allergic to the metal needle?

Allergies can result when your immune system, specifically your mast cells, have an exaggerated response to something that should be innocuous. We have talked about the different kinds of immune hypersensitivity reactions before, but in general, allergy (or atopy, from Greek for out of place) occurs when your body produces a type of antibody (IgE) that recognizes foreign substances and causes your mast cells to release histamine.

Histamine release can lead to itching, watery eyes, runny nose, and even hives (urticaria, from Latin for nettle, see the post on nettle toxins). The IgE is good for helping you learn to avoid poisons and such, but what if your body makes and IgE to something that isn’t dangerous, like peanuts or latex?

Sometimes it isn’t even a case of building an antibody to something that is normally not deemed foreign. Sometimes a peanut molecule just looks enough like some other antigen that an IgE is tricked into binding to the peanut molecule or the banana molecule.

The fruit-latex syndrome is a good example of this. In many cases of people being allergic to latex (Hevea brasiliensis), they also have an allergy to avocados, kiwi fruit, bananas, or chestnuts. The IgE that recognizes the latex hevein protein cross reacts with a beta-glucanase enzyme protein from the fruits.

In the cases of cross-reacting antibodies, there are antibodies to innocuous antigens, your body reacts to them just like they were something dangerous. Histamine release results from IgEs grouping around an allergen and then attaching to a mast cell. If you have encountered this allergen before and have ramped up the number of IgEs that recognize this antigen, the mechanisms can lead to anaphylaxis. This life threatening condition is marked by inflammation that can cut off airways and a lowering of blood pressure that could kill the brain.

Spina bifida patients often develop latex and tropical fruit allergies.

Spina bifida is an incomplete closing of the spinal cord in the fetus

and can lead to severe difficulties in leg movement. It can range from

undetectable to very evident, like in the right image above. Lots of

treatment means lots of chances to develop latex hypersensitivity,

and almost 2/3 of spina bifida patients develop a latex allergy. A 2011

studysays that they first develop allergy to latex, and then this cross-

reacts with the fruit. So patients without latex allergy don’t have

to avoid the fruits.

People allergic to nuts or bee stings are forced to carry around injectors of epinephrine just in case their allergies are triggered. The epinephrine constricts blood vessels, increases the heart rate and the amount of blood moved, so your blood pressure won’t drop too far if you take it soon enough. It also dilates the airways and stops inflammation so you can keep breathing. These are all good things.

Like we said, this is how allergies can and sometimes dowork. But there are exceptions. Did you know that you can be allergic to cold weather? Yes, I hear you out there, chuckling that you’ve been allergic to shoveling snow for years. But what I’m talking about is a physical allergy – hives, breathing problems, itching, and cough – just because your skin and airways are exposed to cold air.

No – you can’t make an antibody to an environmental condition like cold – at least not as far as I know. But remember that TRPM8 is a cool sensor, stimulated by cold temperatures. What if your body skipped the antibody part and the cold temperature itself stimulated mast cell degranulation (release of histamine granules)? Maybe it does, but whether the cold acts via TRPM8 is another question.

Mast cells (in red) degranulate in response to allergens.

The allergen (1) is recognized and bound by the

appropriate IgE antibodies (2). The end of the antibody

opposite the allergen binding site has a receptor on the

mast cell surface (3). Crosslinking of more than one

surface recpeotr with Ab causes degranulation and

release of inflammatory mediators, like histamine (4)

from the granules usually stored in the cytoplasm (5).

There are only a couple of studies that have looked at TRPM8 and cold-induced urticaria. In 2010, a study using rat mast cells showed that they do express YRPM8 ion channels and that they do release histamine when exposed to cold or methanol (a TRPM8 agonist). The histamine release could be blocked, even at cold temperatures, by treating the cells with a TRPM8 antagonist. Pretty convincing, eh?

But the very next year, another study said it was unlikely that TRPM8 was responsible for cold-induced urticaria. This study used human mast cells and mice. Although they did find TRPM8 channels on the mouse mast cells, they didn’t release histamine in the presence of cold in their experimental model. And the researchers didn’t even find TRPM8 expressed on the human cells. This is a bit unusual, since mice are usually a great model for human physiology.

In mast cells from mice with no TRPM8 channels (TRPM8 knockout mice), the mast cell response to cold was normal, so this study concluded that TRPM8 is not involved in cold urticaria. Confusing, but a good opportunity to cheer the relentlessness of science. Study will continue until something is repeatable and can’t be proved wrong. Maybe it will be you – curing cold allergy might not make you rich, but cold-triggered asthma follows a similar stimulation – and solving that little problem will get you a Nobel Prize and a big fat check.

How about another exception? One important difference between TRPV1 warm/hot sensor and TRPM8 cool/cold sensor is that TRPV1 is often located on pain neurons, while TRPM8 is located on other types of neurons and other cell types. TRPM8 activation is not associated with pain sensation directly, since they don’t help depolarize pain neurons. But there is an exception – your teeth.

The left cartoon shows the dentinal pores and how they have

odontoblast processes in them. If the dentin is expose by

receding gums or by decay, the pores are then exposed. On

the right, different stimuli can cause the fluid in the pores to

move, which then puts strain or stretch on the processes, this

causes shifts in ions and that can cause the neurons to fire. These

neurons only carry one message – pain.

Inside the middle of each tooth is the pulp (in the pulp chamber), made up of a few layers of cells that can make more tooth material (odontoblasts), some blood vessels, and a set of nerves. Odontoblastsmake a product called dentin, which is hard, but not as hard as enamel. The enamel on your teeth is not very thick, most of the structure is dentin. As you age, insults to the tooth (like decay), can stimulate the laying down of additional layers of dentin inside the pulp chamber.

The dentin has minute pores that travel out from the middle to the base of the enamel layer. If decay or some other stimulus reaches the pore, processes (like fingers) of the odontoblasts in the pores can react to the stimuli. These then signal the neurons in the pulp. However, the pulp has onlypain sensing neurons. So every stimulus that reaches the pulp will be interpreted as pain.

The odontoblasts have TRPV1 channels, TRPM8 channels and TRPA1 channels (we will talk more about these next week). The hydrodynamic theory of tooth pain says that the changes in temperature that reach the odontoblast processes result in pressure changes and this puts mechanical stress (stretch or shear) on the membranes. These then trigger the channels and the signal is passed to the pain neuron.

A 2013 PLoS study says this is partially true. Their results seem to indicate that very cold and very hot stimuli do produce mechanical pressure on the membrane, so TRPV1 and TRPA1 are responsible for mechano-sensitive pain. But they suggest that in the case of TRPM8, cool/cold temperatures trigger the odontoblasts and neuron. The neuron only has one thing to say - pain – so when triggered by TRPM8 signals in the neighboring odontoblast, it responds the only way it knows how. Too bad, but it has spawned a million dollar industry in toothpastes for people with sensitive teeth.

This is a cartoon of the head of a sea urchin sperm, but many

of the concepts apply in humans as well. See all the red

arrows? Those represent the places where calcium flux is

important in maturation and function. And what do TRPV1

and TRPM8 move the best – calcium. The acrosome reaction

actually dissolved the membrane around the acrosome so that

it can more easily enter the ova. This has to be done at a proper

time; TRPM8 activation prevents it from happening too early.

Here’s another TRPM8 function that we will touch on only briefly. We talked about TRPV1 being important in sperm maturation and in entry into the egg. Well, it looks like TRPM8 is involved as well, only in the opposite direction. TRPM8 signaling, according to a 2011 study, TRPM8 activation preventssperm maturation. This is also important, you need the capacitation and the acrosome reaction to occur at the proper point because they shorten the sperm survival time.

TRPM8 signaling prevents the acrosome reaction, but when the egg is near, a chemical called CRISP4 is released from the egg or parts near there. CRISP4 is a TRPM8 inhibitor. When TRPM8 is inhibited, now TRPV1 can be stimulated to trigger the acrosome reaction.

The interesting part here is that up to the point of CRISP4 release, something is constantly stimulating TRPM8 activity in the sperm cell. I really doubt that there's a cold stimulus way up inside the uterus, so just what is activating TRPM8? We know about lots of endogenous activators of TRPV1, but there has only been one study saying that TRPM8 might have a body-produced agonist, a type of lipid called lysophopholipids. But I think we are missing a bunch of other agonists – maybe you could look for those someday.

OK, here’s the last weird function for TRPM8 today. Would you believe it works in morphine action and withdrawal (when addicted)? Opiates like morphine are analgesic andcold antinociceptive. You take morphine and you don’t sense cold – of course, you won’t sense much of anything else either. For cold, we know how it acts. Opiates cause the internalization of TRPM8 channels on neurons. If there are no exposed channels, they can’t be triggered to allow ions into the neuron.

It goes even further; this isn’t some byproduct or side effect. Menthol is known to create analgesia (one of the reasons they use it in cigarettes). But according to a 2013 paper, if you give naloxone (an opiate blocker) at the same time as menthol – no analgesia. TRPM8 internalization is required for morphine to work.

The term, “cold turkey” is fairly old, first appearing in print

around 1910. It means “without preparation,” but just where

it came from is a matter of question. It might refer to the fact

that cold turkey after Thanksgiving doesn’t need preparation.

It might also be related to “talk turkey, which means to get

down to business. But the way that drug addicts feel cold,

sweat, are pale and have goose bumps – the visual aspect is

not wasted. By the way – who would smoke a cold turkey?

This is important when you are trying to kick a morphine habit. As you stop taking the opiates, TRPM8 quickly relocates to the membrane of the cell and is very easily activated. This causes a cold hypersensitivity and hyperalgesia. People going through withdrawal feel cold because their TRPM8 channels are firing. This is one explanation for calling it, “going cold turkey.” It is uncomfortable and painful, and is one of the main reasons that patients fail detox.

The naloxone that is used to treat morphine addiction binds to the opioid receptor, but doesn’t produce the analgesia. It also allows the TRPM8 to remain externalized, so they don’t have the rebound feeling of cold and pain. Pretty impressive – and now you know how it works.

Next week – TRPM8 is for cold, then there’s the cold that hurts. That is a different receptor, called TRPA1. It makes cold hurt, abut it also saves you from the cold.

Gibbs GM, Orta G, Reddy T, Koppers AJ, Martínez-López P, de la Vega-Beltràn JL, Lo JC, Veldhuis N, Jamsai D, McIntyre P, Darszon A, & O'Bryan MK (2011). Cysteine-rich secretory protein 4 is an inhibitor of transient receptor potential M8 with a role in establishing sperm function. Proceedings of the National Academy of Sciences of the United States of America, 108 (17), 7034-9 PMID: 21482758

Shapovalov G, Gkika D, Devilliers M, Kondratskyi A, Gordienko D, Busserolles J, Bokhobza A, Eschalier A, Skryma R, & Prevarskaya N (2013). Opiates modulate thermosensation by internalizing cold receptor TRPM8. Cell reports, 4 (3), 504-15 PMID: 23911290

Medic N, Desai A, Komarow H, Burch LH, Bandara G, Beaven MA, Metcalfe DD, & Gilfillan AM (2011). Examination of the role of TRPM8 in human mast cell activation and its relevance to the etiology of cold-induced urticaria. Cell calcium, 50 (5), 473-80 PMID: 21906810

Cho Y, Jang Y, Yang YD, Lee CH, Lee Y, & Oh U (2010). TRPM8 mediates cold and menthol allergies associated with mast cell activation. Cell calcium, 48 (4), 202-8 PMID: 20934218

For more information or classroom activities, see:

Cold allergy –

http://www.accuweather.com/en/weather-news/allergic-to-cold-adapting-to-l/19934125

http://www.coldurticaria.info/

http://www.nbcnews.com/health/health-news/allergic-cold-gene-detectives-find-new-clues-f1C6435965

http://www.mayoclinic.org/diseases-conditions/cold-urticaria/basics/definition/con-20034524

http://usatoday30.usatoday.com/news/health/medical/health/medical/coldflu/story/2012-01-23/Allergic-to-cold-Its-a-real-condition-experts-say/52759906/1

http://www.drgreene.com/qa-articles/cold-allergies/

Hydrodynamic theory of tooth pain –

http://www.dentalcare.com/en-US/dental-education/continuing-education/ce200/ce200.aspx?ModuleName=coursecontent&PartID=1&SectionID=-1

http://www.wisegeek.com/in-dentistry-what-is-the-hydrodynamic-theory.htm

http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=14&sqi=2&ved=0CIwBEBYwDQ&url=http%3A%2F%2Fwww.mbfys.ru.nl%2Fstaff%2Fj.vangisbergen%2Fendnote%2Fendnotepdfs%2Fcolleges%2FTANDARTSEN%2FPLAATJES%2520EN%2520FILES%2Foral%2520neurophysiol%2520JUNGE%2Fhydrodynamic_theory_LECT06.doc&ei=W05IU7zCHaLCyQGTiYDQBQ&usg=AFQjCNEtK2R_BX3DAJj03Ep0_pPGB2ulwg&sig2=_F9lV6O4KCaixwoAnLugLw

http://www.drbui.com/artdentinhypersensitivity.html

http://www.juniordentist.com/theories-of-pain-transmission-through-dentin.html

Sperm maturation –

http://embryo.asu.edu/pages/sperm-capacitation

http://www.pbs.org/wgbh/nova/education/activities/2811_baby.html

http://www.keytoconceive.com/sperm-capacitation.php

http://www.glowm.com/section_view/heading/Sperm%20Transport%20and%20Capacitation/item/315

http://www.youtube.com/watch?v=rrFsTdfe2qw

http://www.wisegeek.org/what-is-sperm-capacitation.htm

http://www.youtube.com/watch?v=-J9deipbdSI

http://community.babycenter.com/post/a36676870/capacitation

http://education-portal.com/academy/lesson/acrosome-reaction-function-definition.html#lesson

http://www.youtube.com/watch?v=5-g8dLcERlM

http://www.youtube.com/watch?v=-jLyzWrSTOA

http://www.stanford.edu/group/Urchin/acrosome.htm

http://www.embryology.ch/anglais/dbefruchtung/akrosom02.html

http://worms.zoology.wisc.edu/urchins/SUfert_acrosome.html

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3181525/

http://arbl.cvmbs.colostate.edu/hbooks/pathphys/reprod/fert/fert.html

Drug withdrawal –

http://en.ria.ru/infographics/20100524/159134332.html

http://emedicine.medscape.com/article/819502-overview

http://www.addictionsandrecovery.org/withdrawal.htm

http://www.nlm.nih.gov/medlineplus/ency/article/000949.htm

http://www.hindawi.com/journals/tswj/2012/940613/

http://derekwmeyer.blogspot.com/2012/05/physical-component-of-opiate-withdrawal.html

http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=16&ved=0CH8QFjAFOAo&url=http%3A%2F%2Fwww.drneurosci.com%2Fcurrentissues%2Fthephysiologicalbasisofdrugaddiction.pdf&ei=81JIU8akN-reyAHNi4GgCA&usg=AFQjCNFpwBNfSjgwuPQ02N4fRj7wKeaQdA&sig2=gihQYdc3hBHJak9mxCBh2g&bvm=bv.64542518,d.aWc

http://www.eperc.mcw.edu/EPERC/FastFactsIndex/ff_095.htm

Biology concepts – cinnamaldehyde, nasal hyperreactivity, piperine, allyl isothiocyanate, eugenol, gingerol, tinyatoxin, osmotic stress, agonist/antagonist

Don’t think cinnamon candy can be hot. Your unbearably hot

cinnamon bears from Jelly Belly and your Atomic Fireballs are

both flavored with cinnamon oil. Fireballs have been around

since the 1950’s which explains the atomic reference. It takes

over two weeks to make one. Cinnamon is not ranked on the

Scoville scale because the main spicy compound is

cinnamaldehyde, not capsaicin. But there is some capsaicin in

cinnamon oil, so I think it could be ranked without breaking

some long standing policy.

Asthma is a trigger for airway or nasal hyper-reactivity.

It is easy to see how this could get out of hand, especially

when it can lead to chronic inflammation and damage of

the airway tissues. And to think, it is mediated in part by

the same receptor that makes your Sunday afternoon

chili stew spicy.

The capsinoids are a group of compounds within the

vanilloids. You can see the resemblance to vanillin, so

there are all vanilloids. The different capsinoids are all

found in chili peppers, but capsaicin is the most

abundant and potent, but the structures of the different

capsinoids are very similar.

In the horse trade, a raised tail means a younger, livelier

horse. When someone wanted to sell an old, worn out

horse, but get more money, they might put a piece of

ginger in the anus of the horse. The burn from the

gingerol would make it raise it’s tail. It has also been

used in horse shows, but is now illegal. Oh yes,

sometimes “gingering a horse” also involved live eels.

Tinyatoxin (and resiniferatoxin for that matter) are

produce by the Euhorpbia poissonii plant. Native to Nigeria,

its extract is used by natives as a pesticide. The tinyatoxin

and resiniferatoxin are neurotoxic and can kill TRPV1-

expressing neurons, so they are being looked at as a

way to treat chronic pain.

Osmotic pressure is related to the amount of water versus the

amount of salts in the water. In the cartoon, the salts are

represented by the blue spheres. Water will travel to wherever

salts are highest, because that means water concentration is

lower. Hypertonic means water will flow out of cells, while

hypotonic means water will swell the cells, even to the point of

lysing them. The representative cell is a red blood cell, since

they are very susceptible to osmotic changes.

Chung G, Im ST, Kim YH, Jung SJ, Rhyu MR, & Oh SB (2014). Activation of transient receptor potential ankyrin 1 by eugenol. Neuroscience, 261, 153-60 PMID: 24384226

For more information or classroom activities, see:

Agonist/antagonist –

http://www.biopsychology.com/6e/activity0403.html

http://biowiki.ucdavis.edu/Biochemistry/Transport_and_Kinetics/Enzyme_Inhibition/Agonist_and_Antagonist_of_Ligand_Binding

http://forums.studentdoctor.net/threads/understanding-antagonist-agonist-drugs.1005095/

http://employees.csbsju.edu/hjakubowski/classes/ch331/transkinetics/olinhibition.html

Eugenol –

http://pubchem.ncbi.nlm.nih.gov/summary/summary.cgi?cid=3314

http://www.nlm.nih.gov/medlineplus/ency/article/002647.htm

http://mentalfloss.com/article/12297/why-do-all-dental-offices-smell-same

http://www.ewg.org/skindeep/ingredient/702373/EUGENOL/

http://chemistry.about.com/od/factsstructures/ig/Chemical-Structures---E/Eugenol.htm

http://www.motherearthliving.com/plant-profile/eugenol.aspx

Gingerol –

http://www.whfoods.com/genpage.php?tname=foodspice&dbid=72

https://www.acs.org/content/acs/en/molecule-of-the-week/archive/molecule-of-the-week-gingerol.html

http://rucore.libraries.rutgers.edu/rutgers-lib/21328/

camphor -

http://www.webmd.com/vitamins-supplements/ingredientmono-709-CAMPHOR.aspx?activeIngredientId=709&activeIngredientName=CAMPHOR

http://www.botanical.com/botanical/mgmh/c/campho13.html

http://plants.ifas.ufl.edu/node/101

http://www.chemie.fu-berlin.de/chemistry/oc/terpene/campher_en.html

http://www.drugs.com/cdi/camphor-ointment.html

http://www.ipm.ucdavis.edu/PMG/GARDEN/PLANTS/camphor.html

tonicity –

http://www.phschool.com/science/biology_place/biocoach/biomembrane1/solutions.html

http://www.youtube.com/watch?v=_slUL3kMZlU

http://chemistry.about.com/b/2013/11/17/osmotic-pressure-and-tonicity.htm

http://differentmedicalcareers.com/hypertonic-hypotonic-isotonic-solutions/

http://www2.nl.edu/jste/osmosis.htm

http://www.slideshare.net/dewisivasamy/the-effects-of-hypotonic-hypertonic-and-isotonic

http://www.glencoe.com/sites/common_assets/science/virtual_labs/LS03/LS03.html

http://biology.unm.edu/ccouncil/Biology_124/Summaries/Membranes.html

http://www.biologycorner.com/bio1/notes_diffusion.html

http://mcatdaily.blogspot.com/2010/05/difference-between-hypertonic-hypotonic.html

Biology concepts – nature of science, TRPA1, thermoregulation, noxious sensor, chemical sensor, mutation, protein domains

"As we acquire more knowledge, things do not become more comprehensible, but more mysterious."

Albert Schweitser was an organist without compare. He toured

the world playing different organs for concerts. Some of these

organs were huge, this one has five keyboards and dozens of

different knobs and buttons. The money from his concerts

went directly to building his hospital complex in Africa

(bottom). At its height, there were over 70 different buildings.

All care was, and is, free.

These are the words of Albert Schweitzer, physician, theologian, philanthropist, and organist. Yep – he played a mean organ. Albert was born in the Alsace part of France in 1875, and was raised in a household of ministers and musicians. He turned out to be both - but so much more.

Schweitzer became a minister, but toured the world's great churches giving organ concerts for big bucks. He used the money to put himself through medical school and establish a hospital in French Equatorial Africa in the 1910’s. He expanded his hospital to over 70 buildings and treated up to 500 patients at a time, always funding his efforts with his organ concert money and the money he made from writing books.

He was awarded the Nobel Peace Prize in 1952. His quote above is true, whether he was speaking of the secrets of life in the spiritual or scientific sense. I personally phrase Schweitzer’s sentiment a little differently. The more we know, the less we know we know. Scientific knowledge is meant to do two opposite things – one, answer questions, and two, create questions. Every decent answer we think we find should bring to mind many more questions.

This naturally occurs when science works at its best, but the hardest part is knowing if we have an answer. If we aren’t sure about the answer, we have to keep looking. Of course we always keep looking, but some answers come to be so well supported that it is not the answer we question but the details of the answer – like evolution or fundamental forces.

But if the answers are tentative or not well supported, then how good are the questions that spring from them? Can our questions only be as good as our previous answers? This I where we're lucky, because bad questions can lead to good answers, if we keep our minds open to what we see and don’t find just we are expecting to find.

How does this apply to our discussion of thermoregulation and heat/cool sensing? Well, what happens when you find a thermosensor that you can’t get a good answer as to what it does? Makes it hard to design new questions doesn’t it?

The left image is of Thomas Hunt Morgan, an American researcher

who set out to disprove Darwin’s theory of evolution using fruit

flies. He chose them because they were cheap and bred quickly –

a new generation came along every 10 days. He started

inspecting them for mutations, and then bred the mutants to

normal flies. The proportion of mutant offspring was EXACTLY

as Darwin predicted. On the right are two images of different

mutants, often these are induced using radioactivity. On the

bottom, you can see a leg growing where an antenna ought to be.

The sensor ion channel that I speak of is the TRPA1. Studies assign it a role in pain sensation – just like TRPV1 for heat. But what stimulates it to generate a pain signal?

TRPA1 was first described in drosophila melongaster (fruit flies). Historically, fruit flies have made great models because they eat cheap and reproduce quickly. You can read about the history of their use in genetics in a great book called The Violinist’s Thumbby Same Keene.

The scientists would induce mutations in flies (and their subsequent offspring) by giving them radiation or chemicals. They wouldn’t have any idea which flies were mutated, or what the mutations were, it was just a shotgun method. They would then study the flies, looking for abnormal anatomy, abnormal behavior, or abnormal responses to stimuli. In some cases, the mutations were spontaneous, not caused by radiation or the chemicals, but finding them was done the same way, and the ionizing radiation or mutagenic chemicals just made the mutation rate much higher. When they found a fly with a change, then they would go to work and identify the mutation.

One mutation they noticed was that some flies wouldn’t avoid things that should have been painful. Before they knew what gene was involved, they decided to call it painless. Comparing it to known genes, they found it was the drosophila homolog to a mammalian TRP called TRPA1 or ANKTM1. TRPV’s and TRPM8 were already known, and they all have ankyrin repeats, so I don’t know why TRPA1 got the “A” for ankyrin.

Ankyrin is just one of thousands of known protein domains, meaning short sequences of amino acids that are known to have specific functions. Ankyrin is often found to mediate protein folding and protein-protein interactions, even though its own folding is a little out of the ordinary. Most proteins with ankyrin domains have about 4-6 repeats of the 33 amino acid sequence, but the parasite Giardia lamblia has a protein with 34 repeats.

This is a computer generated image based on ankyrin repeat

morphology. The different repeats are good for building a protein

interaction domain. The interesting thing is that although

most ankyrin repeats have this shape, they bind different

protein structures and induce different functions. Where's

the specificity? Good question - could win you a Nobel Prize.

As for the “1” in TRPA1, all I can say is that they must be anticipating the discovery of more TRPs of this type, although right now it stands alone. It’s kind of weird though, you don’t call a dad “Sr.” if there is no “Jr.” so why is there a TRPA1 if there are no other TRPA’s?

So, flies with broken painless(TRPA1) genes didn’t respond to pain; therefore, TRPA1 must be a gene that codes for a protein that confers a pain signal. This meshed well with the information from mammals showing that TRPA1 stimulated pain signals from some chemicals. But was this all?

This is where the controversy began and still continues. Some studies find that TRPA1 is a noxious chemical receptor, some say it's a noxious cold receptor. Some experiments show it to be both, a receptor for pain from cold and a receptor for pain from chemicals. And then there are those that show it to be a heat receptor! More on those studies in a couple of weeks – they’re cool… I mean hot!

Even within mammals, the results can sometimes be very different. Old studies suggested that TRPA1 was a noxious cold sensor (below 15˚C) in humans, but newer research (2013) shows that while TRPA1 does sense cold in rats and mice, it isn’t affected by cold in humans or monkeys. Many of the older reports suggesting that TRPA1 is a noxious cold sensor were based on studies in mice, so maybe they do act differently in humans.

The other possibility is that they don’t sense intense cold directly, but work with other TRPs to respond with pain when cold is sensed. A 2014 study showed that TRPA1 modulates TRPV1 activity. The two are often co-expressed on the same neurons, and they are also activated by many of the same chemicals. This study shows sensitization of TRPV1 by activation of TRPA1 – so maybe this is why your hands burn when you go out in to the cold for a long time.

Here is a cartoon comparison of TRPV1 and TRPA1. The parts

that go through the membrane (transmembrane domains)

look very similar, but you can see many differences

in the intracellular tails of each. Remember that TRPV1 and

TRPA1 bind many of the same chemical agonists, but look at

the difference in the ankyrin repeats and the other domains

of the tails, as well as the cytoplasmic sides of the TM

domains. These are where specificity occurs.

An earlier study (2012) also showed that activity from TRPV1-4 receptors could modulate the activity of TRPA1. Gentle warm temperatures could desensitize TRPA1 and therefore keep pain from being felt. Could this be one of the ways that warm compresses work against pain?

So, if TRPA1 modulates TRPV1 and vice versa for pain sensation, maybe TRPA1 works with TRPM8 to induce noxious cold pain. There have been papers that suggest TRPM8 does sense cold temperatures below 15˚C and when those cells are lost, mice have no aversion to painfully cold stimuli. It is probable that TRPA1 works with TRPM8 and TRPV1 to elicit pain to cold temperatures.

Maybe we could get some insights into the cold sensing of TRPA1 if we could find out if it participates in warming the body when it is cold. TRPV1 is a heat sensor and initiates cooling programs. TRPM8 sense cool and starts to warm the body – so what about TRPA1?

Well, it looks like we get no help there at all. Even in the species that are most likely to have noxious cold sensation via TRPA1 (rats and mice), the channel doesn’t look to be calling for warming responses. In fact, a 2014 study suggests that when TRPA1 ion channels are knocked out in mice, cold temperatures induced physiologic changes just as if the TRPA1 was there – TRPA1 was not a participant in inducing warming activities.

This cartoon gives you an idea of how TRPA1 can work with

other TRPs in order to increase pain or bring pain when other

signals alone might not. This example is with injury and

inflammation. Some things trigger TRPV1 but the activation

of TRPV1 can influence TRPA1 activity. This would sensitize

for more pain. Perhaps this is how pain is generated from

intense cold, even if TRPA1 doesn’t respond to cold on its

own. TRPM8 does respond to cold, so maybe it or TRPV1

are the triggers needed for TRPA1 to bring pain from cold.

In the same set up, blocking TRPM8 channels did result in a hypothermia (mouse bodies did not initiate a warming response to cold temperatures). So, the authors concluded that while TRPA1 does cause pain in response to cold, it doesn’t start or participate in a program to warm the mice.

Oh well, like we said at the beginning of the post, the more we know, the less we seem to know for sure. I think TRPA1 is probably involved in cold pain, even if it doesn’t sense it directly. But I can’t wait to see what they find out next.

What we do know is that TRPA1 is intimately involved with pain. Migraine headaches probably have a TRPA1 component. A 2013 paper summarized the evidence by saying that many migraine triggers are now known to be TRPA1 activators. Many of the endogenous stress activators of TRPA1, like oxidative damage, electrophilic stress, etc. also act to induce pain. Finally, many of the drugs and analgesics that work on migraines are being identified as TRPA1 antagonists.

Since it’s evident that TRPA1 doesn’t work in thermoregulation (see above), maybe we can use antagonists of TRPA1 as pain drugs without worrying about the hyperthermias and hypothermias associated with TRPV1 antagonists and TRPM8 antagonists. And wouldn’t you know it, a new antagonist for TRPA1 has just been discovered in a weird place.

Meet the Peruvian green velvet tarantula. It does have a

green hue on its legs and it is soft and velvety. But it isn’t

from Peru. It actually lives in northern Chile, south of the

Peruvian border. Its venom contains a TRPA1 antagonist,

but the problem is that even though it is not likely to bite

the hand that feeds it, it will fling urticating hairs at the

drop of a hat. This is important, as we discussed here.

The Peruvian green velvet tarantula (Thrixopelma puriens) has a peptide in its venom that is the first identified peptide (protein) TRPA1 antagonist. What’s it doing in venom? One of the purposes of venom is to cause pain – pain is a great teacher – enough pain and you won’t attack that spider again. But here is a potential pain killer in the venom, maybe the green velvet tarantula is trying to kill its prey, but doesn’t want to cause undue stress to its victim. Is that how evolution works?

One last tidbit about TRPA1 – it could save your life in the middle of the night. If you block mouse nasal activity of TRPA1, they won’t wake up in response to formalin, acrolein, or other noxious stimuli that should generate an avoidance response. Would a house fire be something you need to wake up from – you bet. Another recent study found that TRPA1 sensors in upper airway cells are important for sensing smoke from wood fires. Don’t hate the TRPA1 because it gives you pain – enjoy the pain – it’s keeping you safe.

Next week – prepare to throw TRPA1 a party; it’s saving your life in many more ways.

de Oliveira, C., Garami, A., Lehto, S., Pakai, E., Tekus, V., Pohoczky, K., Youngblood, B., Wang, W., Kort, M., Kym, P., Pinter, E., Gavva, N., & Romanovsky, A. (2014). Transient Receptor Potential Channel Ankyrin-1 Is Not a Cold Sensor for Autonomic Thermoregulation in Rodents Journal of Neuroscience, 34 (13), 4445-4452 DOI: 10.1523/JNEUROSCI.5387-13.2014

Spahn V, Stein C, & Zöllner C (2014). Modulation of transient receptor vanilloid 1 activity by transient receptor potential ankyrin 1. Molecular pharmacology, 85 (2), 335-44 PMID: 24275229

Benemei S, Fusi C, Trevisan G, & Geppetti P (2014). The TRPA1 channel in migraine mechanism and treatment. British journal of pharmacology, 171 (10), 2552-67 PMID: 24206166

Gui J, Liu B, Cao G, Lipchik AM, Perez M, Dekan Z, Mobli M, Daly NL, Alewood PF, Parker LL, King GF, Zhou Y, Jordt SE, & Nitabach MN (2014). A tarantula-venom peptide antagonizes the TRPA1 nociceptor ion channel by binding to the S1-S4 gating domain. Current biology : CB, 24 (5), 473-83 PMID: 24530065

For more information or classroom activities, see:

Albert Schweitzer –

http://www.nobelprize.org/nobel_prizes/peace/laureates/1952/schweitzer-bio.html

http://home.pcisys.net/~jnf/

http://www.lucidcafe.com/library/96jan/schweitzer.html

http://www.chapman.edu/research-and-institutions/schweitzer-institute/

http://life.time.com/history/albert-schweitzer-in-africa-behind-the-picture/

http://www.schweitzersymposium.com/en/home

http://people.bu.edu/wwildman/bce/schweitzer.htm

Protein domains/motifs –

http://www.fasebj.org/content/9/8/597.abstract

http://www.ebi.ac.uk/training/online/course/introduction-protein-classification-ebi/protein-classification/what-are-protein-domains