How Capsaicin Plays Tricks On Your Nerves

Capsaicin, the compound which gives chili peppers their burn, is also a popular pain-reliever found in over-the-counter and prescription medications. New research clarifies how capsaicin works to calm painful nerves, muscles, and joints.

Researchers from Rutgers New Jersey Medical School report new findings on how a nerve mechanism is activated by capsaicin to block pain signals. Tibor Rohacs, study leader, said:

“This study gives one potential piece in the puzzle of how capsaicin works as a local analgesic.”

Hot Illusions

Rohacs says his lab has been studying ion channels found in sensory nerve terminals that respond to heat and other stimuli.

In particular, his work has focused on an ion channel known as TRPV1, the capsaicin receptor, and Piezo2, a newly identified ion channel that mediates touch sensation. Rohacs explains:

“TRPV1 is a heat sensor, at least physiologically, and it has a chemical activator, capsaicin, which we all know is in chili peppers. They feel hot because they activate a heat-sensitive ion channel and they trick you into the sensation of heat. And it’s also pretty painful.

The idea is basically that this pain-causing, heat sensor ion channel does something to the nerve that in the long run sort of silences them or desensitizes them. The desensitizing effect, I believe, has a number of different components and different timescales.”

Surprises

Rohacs says capsaicin has been a popular research target and that multiple factors account for its calming effects on the nerves.

“We found that capsaicin completely silenced the Piezo2 channels that are activated by mechanical stimuli,” he says. “This may be an important part of how capsaicin inhibits mechanical pain.”

The research also produced results that Rohacs found surprising.

“It’s very fast, very robust, very long lasting,” he says. “The magnitude of the effect was to me the really surprising part.”

Rohacs says the jury is still out on the practical application of capsaicin as a pain medication, including the creams and patches already on the market.

A high concentration capsaicin remedy has to be injected along with a local analgesic that numbs the burning sensations until the remedy can begin desensitizing the nerves.

Rohacs says his research will continue in multiple directions to gain a better understanding of just how the mechanosensors work, as well as how large amounts of calcium are released to help shut down pain signals.

Istvan Borbiro, Doreen Badheka, and Tibor Rohacs
Activation of TRPV1 channels inhibits mechanosensitive Piezo channel activity by depleting membrane phosphoinositides
Sci. Signal., 10 February 2015, Vol. 8, Issue 363, p. ra15, DOI: 10.1126/scisignal.2005667

Photo: Austin Kirk/flickr