February 25, 2009

Study: Capsaicin can cause, relive pain

U.S. scientists have discovered the mechanism that allows capsaicin to be both an irritant causing a burning sensation as well as acting as an analgesic.

University of Buffalo researchers said capsaicin creams are natural pain-relieving folk medicines, effective for a variety of pain syndromes. Now the scientists have linked those analgesic effects of capsaicin to a lipid called PIP2 in the cell membranes.

The researchers led by Associate Professor Feng Qin said capsaicin works by stimulating a receptor on nerve endings in the skin, generating the sensation of pain.

The receptor acts like a gate to the neurons, said Qin. When stimulated it opens, letting outside calcium enter the cells until the receptor shuts down, a process called desensitization. The analgesic action of capsaicin is believed to involve this desensitization process. However, how the entry of calcium leads to the loss of sensitivity of the neurons was not clear.

The authors found the receptor remains fully functional after desensitization. What changed was the responsiveness threshold, said Qin. This property, called adaptation, would allow the receptor to continuously respond to varying stimuli over a large capsaicin concentration range.

The researchers, including post doctoral student Jin Yao, said their findings -- published in the journal PLoS Biology -- have implications for pain-sensation mechanisms as well as clinical applications.