Peripheral and central actions of capsaicin and VR1 receptor

Vanilloid receptor subtype 1 (VR1), a capsaicin receptor, is expressed in p rimary sensory neurons and vagal nerves. Heat and protons as well as capsai cin activate VR1 to induce the influx of cations, particularly Ca2+ and Nai ions. Characteristic effects of capsaicin are the induction of a burning s ensation after acute administration and the desensitization of sensory neur ons after large doses and prolonged administration. The latter feature made capsaicin cream applicable for the treatment of chronic pain and pruritus. Capsaicin alters several visceral functions, which may be mediated by acti on on vagal nerves and central neurons. Capsaicin affects thermoregulation after intra-hypothalamic injection and releases glutamate from the hypothal amus and cerebral cortex slices, while VR1-like immunoreactivity is not app arent in these regions. These findings taken together suggest the existence of other subtypes of vanilloid receptors in the brain.