Scientists Connect Taste and Temperature

Mint feels cool and soothing. The heat of chili peppers or wasabi can make you cry. Now, scientists at the University of California, San Francisco have figured out the connection between taste and temperature. Debbie Elliott talks to lead researcher David Julius about his findings.

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DEBBIE ELLIOTT, host:

Another bit of science news caught our eye this week. A team of researchers has analyzed something we all experienced when we suck on a cough drop or nibble a peppermint patty. Mint and menthol feel and taste cool and soothing. Scientists at three universities can now tell us why after mapping out the connection between taste and temperature.

One of the researchers is Dr. David Julius, professor of physiology at UC San Francisco. Welcome.

Dr. DAVID JULIUS (Professor of Physiology, University of California, San Francisco): Hello.

ELLIOTT: Let's start with the very basics. Do the same nerve receptors in our bodies detect pain, heat and cold?

Dr. JULIUS: Well, there are probably some separate receptors: some detect heat, some detect cold, and some of those also detect painful stimuli.

ELLIOTT: You've isolated the cool receptor in our bodies. How does it work?

Dr. JULIUS: It's a protein that sits on the surface of nerve endings, say a nerve ending that would innervate your skin or lips or eyes. And when temperature drops below a certain point, this protein opens up, sort of like a little donut in the membrane and allows ions from outside the cell to flow across the membrane of the nerve terminal. And this generates an electrical current, which, of course, is the currency of information transmission of the nervous system. And then this information is eventually sent to the spinal cord in your brain, where you perceive this event as a cold stimulus.

ELLIOTT: Now, you have called this the menthol receptor?

Dr. JULIUS: That's right. So some years ago, we identified a receptor that is activated by menthol, which, of course, is the cooling, main cooling ingredient in mint plants. And this same receptor or ion channel that sits on the nerve terminal, we found this also activated by cold.

ELLIOTT: Why is it that mint gives you the same reaction as cold?

Dr. JULIUS: Once you activate these receptors once you activate these neurons, they send signals to the same place in the spinal cord and ultimately the brain, irrespective of the stimulus. So really, what menthol is doing is mimicking a sensation of cold because in the end, or really upfront, they're doing the same thing. They're acting on the same detector, and thereby stimulating the same set of nerve cells that encode this response.

ELLIOTT: Tell us how you and your fellow researchers discovered this menthol receptor?

Dr. JULIUS: Well, for several years before that, we had been trying to understand how sensory nerve endings detect stimuli that cause pain. We began our studies by asking how hot chili peppers work to evoke a sensation of burning and tingling pain. And we've sort of followed this path along in our research where we're trying to look at natural products and how they elicit painful sensations.

And - so chilly pepper is sort of one of the great questions in the field of time because it contains a pungent ingredient called capsaicin. And so we ask how capsaicin evokes the sensation of burning pain and that lead us to identify another receptor or ion channel that's not only activated by chili pepper extracts and capsaicin but also by heat.

And so we believe that we had found some part of the process whereby our nervous system detects pain-producing heat.

And then we wanted to see how general this phenomenon was and so we ask, can we learn something about how our nervous system detects cold? And so we turn to the same strategy, which is to say are there plants or natural products out there that elicit a sensation of cooling rather than heating and, of course, the well-known example is the mint leaf.

ELLIOTT: Dr. David Julius is chair of the Department of Physiology at the University of California San Francisco. He conducted his minty fresh research with colleagues at Yale and at the Medical College Of Wisconsin. Thanks for talking with us.

Dr. JULIUS: Thank you very much.

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