5-Hydroxytryptamine (5-HT; serotonin) plays an important role in the descending control of nociception. 5-HT and its receptors have been extensively studied in the modulation of nociceptive transmission at the spinal level using behavioral tests that may be affected by the effects of 5-HT on motor performance and skin temperature. Using electrophysiological methods, the present study aimed to systematically investigate the roles of 5-HT receptor subtypes on the inhibitory effects of 5-HT on responses of the spinal wide dynamic range (WDR) neurons to C-fiber inputs in rats. Under basal conditions, topical application of 5-HT to the spinal cord inhibited the C-fiber responses of WDR neurons dose-dependently, whereas antagonists of 5-HT 1A [WAY 100635 [N-[2-[4-(2- The dorsal horn of the spinal cord is critical for nociceptive transmission. Nociceptive information impinging upon the dorsal horn from the skin, viscera, and other tissues is subjected to segmental, extrasegmental, and descending inhibitory controls (Melzack and Wall, 1965). It has been established that the descending control system from the brain exerts an inhibitory influence upon the spinal processing of nociceptive information. 5-Hydroxytryptamine (5-HT; serotonin) is a major neurotransmitter in the descending control system. In the spinal cord, at least four subtypes of 5-HT receptors (5-HT 1 -5-HT 4 ) have been identified, which are involved in spinal pain modulation. However, the roles of some of these receptor subtypes are not well defined, and previous
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