Feel the way: Nobel explores our sense of touch and temperature

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Paris (AFP)

What signals sparkle in our bodies when we feel the fiery heat of a chili pepper or the sudden pressure of a tap on the shoulder?

While scientists had long understood the mechanisms of sight and smell, how touch, heat, and cold trigger a response in the nervous system has remained a mystery until research by the winners of the this year’s Nobel Prize in Medicine.

Through their work, we understand how temperature and touch are converted into electrical impulses sent through the body – a crucial mechanism for perceiving and surviving the world around us.

It has also opened up the possibility of new treatments for a range of diseases.

– Too hot to handle –

Biochemist and molecular biologist David Julius has used a range of natural substances to examine how sensations of pain and temperature are transmitted to the brain.

Working in his lab at the University of California, San Francisco, Julius looked at tarantula toxins and the chemicals that produce the scorch in horseradish and wasabi.

Nobel Prize in Medicine 2021 Cléa PÉCULIER AFP

But it was his research in the 1990s to solve the “conundrum” of what exactly happens when the body is exposed to capsaicin, the molecule that produces the sensation of heat caused when we eat or touch chili peppers, which has been distinguished by the Nobel committee. .

His team has created a database of millions of DNA fragments from genes in sensory neurons, known to respond to pain, heat and touch.

They then located the gene that made cells specifically sensitive to capsaicin.

Further investigation revealed that a type of protein at the outer end of sensory nerves, which they called the TRPV1 ion channel, responds to both the “heat” of chili peppers and high temperatures.

When activated, this receiver “sends the electrical signal from the periphery – say, your lips or your eyes, wherever you smell the hot pepper – and it transmits the signal to the spinal cord,” Julius said in an interview. in 2019 with American Scientist.

The signal is then relayed by different neurons to the brain, “where you perceive it as something harmful and painful,” he said.

Julius and his colleagues have since identified another cold-responsive receptor, as well as the “wasabi receptor,” which responds to both the spiciness of the Japanese condiment and is also implicated in pain associated with inflammation.

– To push –

Working around the same time at Scripps Research in La Jolla, Calif., Ardem Patapoutian looked for specific receptors activated by mechanical stimuli such as pressure and touch.

He identified a type of cell that emitted a measurable electrical signal every time an individual cell was pricked with a micropipette.

“We literally pricked the cell while recording its electric current,” he told BrainFacts in an interview in 2020.

He then embarked on an arduous process of elimination, in search of a gene linked to the possible receptor.

To do this, the researchers inactivated dozens of candidate genes one by one to see which one was responsible for the cell’s sensitivity to touch.

The team named the hitherto unknown “mechanosensitive ion channel” Piezo1, after the Greek word for pressure, and they have since identified a second Piezo2 receptor.

Patapoutian said finding these receptors is like finding “a doorknob,” which could open the understanding of pain or touch.

“So the receiver is like the first point of entry – it allows you to open the door and start investigating what’s in that room,” he told BrainFacts.

While much remains to be learned about these protein receptors, the discovery “exploded this area of ​​research,” Bertrand Coste, who conducted the studies with Patapoutian, told AFP.

– Pain relievers? –

Coste said another crucial step is to find the receptors that detect the types of touch that cause pain, which would be “fantastic therapeutic targets” for chronic or inflammatory pain.

The pain itself plays an important role – from telling us when to pull away from something hot, to letting us know when we’ve been injured.

But he said he hoped that identifying the specific mechanisms behind these sensations would contribute to the development of painkillers that are not opioid dependent, which can have many effects on the body and lead to addiction.

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