Inhibition of the response to pain by the action of serotonin and carbachol topically applied to the area postrema of conscious guinea pigs.
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.
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*
D012701:Serotonin; D002217:Carbachol; D008237:Lysergic Acid