Transient receptor potential (TRP) receptor expressed by primary sensory neurons mediate thermo sensitivity and may play a role in sensory pathophysiology. Nociceptors with peripheral and central projections express temperature sensitive transient receptor potential (TRP) ion channels, also called thermo TRP’s. Chemo sensitivity of thermo TRP’s to certain natural compounds eliciting pain or expediting thermal properties has proven to be good tool in characterising these receptors. Capsaicin, a pungent chemical in hot peppers, has assisted in the cloning of the first thermo TRP, TRPV1. The transient receptor potential vanilloid-1(TRPV1) cation channel is a receptor that is activated by heat (>42°C), acidosis (pH<6) and a variety of chemicals among which capsaicin is the best known. The activity of TRPV1 is controlled by multitude of regulatory mechanism that either causes sensitization or desensitization of the channel. As many proalgesic pathways converge on TRPV1 and the nocisensor is up regulated and sensitized by inflammation and injury, TRPV1 is thought to be a central transducer of hyperalgesia and prime target for the pharmacological control of pain. In addition to endogenous agonists, a wide variety of chemical agonists and antagonists have been discovered to activate and inhibit TRPV1. Efforts are underway to determine conditions under which agonist mediated desensitization of TRPV1 or inhibition by antagonist can produce analgesia. The search for a role of TRPV2 in pain remains dormant due to lack of suitable experimental models. However TRPV3 and TRPV4 encoding for detection of warm temperature and expressed in nociceptors can’t be excluded. This review will discuss current knowledge on the role of capsaicin receptor in nociception.
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