title: Inhibition of the response to pain by the action of serotonin and carbachol topically applied to the area postrema of conscious guinea pigs.
abstract: The amplitude of vocalization and the motor defense response evoked by painful electrical stimulation were recorded in unanesthetized guinea pigs submitted to topical application of 1.0 microgram/microliter carbachol to the area postrema. Carbachol was found to have an analgesic effect. A similar application of 3.0 micrograms/microliter 5-hydroxytryptamine (5-HT) also had an analgesic effect, whose duration, however, was only half that of carbachol and whose intensity was lower, although the latency of the response was 2 seconds for both drugs. When 100 micrograms/microliter lysergic acid was applied to the area postrema the results did not differ significantly from control values, with only a small tendency toward hyperalgesia being observed. The present results, taken together with those obtained with noradrenalin in a previous study, suggest that the rich endowment of neurotransmitters in the area postrema may indicate a polyvalent analgesic mechanism able to provide a finer regulation of analgesia.
mesh_terms: D000698:Analgesia; D000818:Animals; D002217:Carbachol / Q000494:pharmacology*; D002552:Cerebral Ventricles / Q000187:drug effects* / Q000502:physiology; D004558:Electric Stimulation; D006168:Guinea Pigs; D008237:Lysergic Acid / Q000494:pharmacology; D008297:Male; D009619:Nociceptors / Q000187:drug effects*; D010146:Pain; D012701:Serotonin / Q000494:pharmacology*
chemical_list: D012701:Serotonin; D002217:Carbachol; D008237:Lysergic Acid