Enhancement of clonidine-induced analgesia by lesions induced with spinal and intracerebroventricular administration of 5,7-dihydroxytryptamine.
The role of serotonin (5-HT) in analgesia induced by clonidine was examined by determining the effect of intraspinal (i.s.) and intracerebroventricular (i.c.v.) injections of 5,7-dihydroxytryptamine (5,7-DHT) on analgesia produced by clonidine in the tail-flick and hot plate tests. Depletion of amines was verified by high performance liquid chromatography analysis. Intraspinal injections of 5,7-DHT potentiated the action of clonidine in both tests for analgesia and caused depletion of 5-HT in the spinal cord. Intracerebroventricularly injected 5,7-DHT also increased the action of clonidine and depleted 5-HT in brain as well as in the spinal cord. In the groups given intracerebroventricular injections, there appeared to be a biphasic increase in the action of the clonidine. Significant hyperalgesia from pretreatment with neurotoxin was observed only on a limited number of occasions. The present results indicate that 5-HT mechanisms in the CNS are important mediators of the analgesic action of clonidine. Interactions between clonidine and 5-HT systems at both spinal and supraspinal sites are considered.
D015116:5,7-Dihydroxytryptamine / Q000008:administration & dosage*; D000698:Analgesia; D000818:Animals; D002490:Central Nervous System / Q000187:drug effects* / Q000378:metabolism; D003000:Clonidine / Q000494:pharmacology*; D004102:Dihydroxytryptamines / Q000008:administration & dosage*; D007276:Injections, Intraventricular; D007278:Injections, Spinal; D008297:Male; D010146:Pain / Q000503:physiopathology*; D051381:Rats; D011919:Rats, Inbred Strains; D011930:Reaction Time / Q000187:drug effects; D012701:Serotonin / Q000378:metabolism / Q000502:physiology*
D004102:Dihydroxytryptamines; D015116:5,7-Dihydroxytryptamine; D012701:Serotonin; D003000:Clonidine