Effects of capsaicin on central monoaminergic mechanisms in the rat.
The acute and chronic effects of capsaicin (s.c.) on the monoamines in the preoptic region + hypothalamus (RPO-H), spinal cord, substantia nigra and striatum were studied. Levels of DOPA, DA, DOPAC, HVA, 3-MT, NA, Trp, 5-HTP, 5-HT and 5-HIAA were determined by means of liquid chromatography (HPLC-EC). In response to acute capsaicin treatment, the levels of DA, DOPAC and DA synthesis rate (DOPA formation) were increased in a dose-dependent manner in the RPO-H and spinal cord. The disappearance rate of NA was accelerated in both regions. In substantia nigra, increased DOPAC levels were found whereas the levels of 3-MT were decreased in striatum after acute capsaicin treatment. Only minor changes on the levels of 5-HT and 5-HIAA in the regions studied were noted. Neonatal or adult capsaicin treatment failed to affect the levels of NA, DA and 5-HT (measured two months or five weeks after injection, respectively) in the regions studied. A capsaicin injection to rats pretreated with the drug as adults did not affect either the monoamines in the RPO-H and spinal cord or the body temperature. In contrast, in rats pretreated with capsaicin as neonates, a second injection of the drug to adult animals elicited hypothermia and changes in monoamines similar to those observed in naive animals.
D000818:Animals; D000831:Animals, Newborn; D001831:Body Temperature / Q000187:drug effects; D002211:Capsaicin / Q000494:pharmacology*; D002395:Catecholamines / Q000502:physiology*; D002490:Central Nervous System / Q000187:drug effects*; D008297:Male; D010146:Pain / Q000503:physiopathology; D051381:Rats; D011919:Rats, Inbred Strains; D012701:Serotonin / Q000502:physiology*; D009435:Synaptic Transmission / Q000187:drug effects*
D002395:Catecholamines; D012701:Serotonin; D002211:Capsaicin