Receptors & Stimuli

An important recent event was the isolation of vanilloid receptor-1 (VR1). Vanillins are a group of compounds, including capsaicin, that cause pain. This necessitated revision of the concept that a single pathway carries pain and only pain to the cerebral cortex. The VR1 receptors respond not only to the pain-causing agents such as capsaicin but also to protons and to potentially harmful temperatures above 43 °C. Another receptor, VRL-1, which responds to temperatures above 50 °C but not to capsaicin, has been isolated from C fibers. There may be many types of receptors on single peripheral C fiber endings, so single fibers can respond to many different noxious stimuli. However, the different properties of the VR1 and the VRL-1 receptors make it likely that there are many different nociceptor C fibers systems as well.