Capsaicin Receptors in Sleep Regulation

Capsaicin receptors are found not only in the skin, but also in many neural and non-neural tissues. Though their involvement in many functions is now known, their role in sleep regulation has not gained proper attention. As capsaicin receptors can alter body temperature, it has led to the belief that sleep changes result from an alteration in body temperature. There is now convincing evidence to show that the capsaicin receptors are an integral part of sleep regulation. The role of capsaicin receptors in sleep in rats was reported as early as the1980s. Most of the sleep-related studies were carried out on capsaicin-desensitized animal model. Sleep, especially slow wave sleep (SWS), was increased, while Rapid Eye Movement (REM) sleep reduced after the destruction of peripheral and central capsaicin receptors in rats. When peripheral capsaicin receptors were selectively destroyed, the sleep was increased, particularly due to an increase in REM sleep. Reduction in SWS and REM sleep after lesion of the preoptic area (POA) showed that the capsaicin receptors, in this sleep regulating area, play a major role in facilitating SWS and REM sleep. It is important to understand the sleep-related functions of the ion channels activated by capsaicin, to develop drugs for sleep-related disorders.