Role of peripheral mechanisms in the behavioral effects of 5-hydroxytryptophan.
The effects of 5-hydroxytryptophan (5-HTP) were studied in rats trained to press a lever under a fixed-ratio (Fr-32) schedule of water presentation. d-, l-and d,l-5-HTP all decreased responding in a dose-related manner. The levo isomer (12.5-25 mg/kg) was twice as potent as the racemic form (25-50 mg/kg) in this respect. Moderate doses of d-5-HTP (less than 100 mg/kg) did not affect responding, whereas 200 mg/kg produced almost complete suppression. The response decrement produced by 25 mg/kg l-5-HTP was completely antagonized by pretreatment with either 50 mg/kg or 400 mg/kg of the decarboxylase inhibitor, benserazide (Ro4-4602). The specific peripheral decarboxylase inhibitor, carbidopa (MK-486) (50 mg/kg) and the peripheral serotonergic antagonist, xylamidine tosylate (1 mg/kg) also antagonized the effects of 25 mg/kg l-5-HTP. These results suggest that at least some of the behavioral effects of 5-HTP are due to increases in levels or turnover of 5-HTP in peripheral serotonergic neuronal systems.
D006916:5-Hydroxytryptophan / Q000494:pharmacology*; D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects*; D001545:Benserazide / Q000494:pharmacology; D002230:Carbidopa / Q000494:pharmacology; D008297:Male; D011377:Proglumide / Q000494:pharmacology; D051381:Rats; D012055:Reinforcement Schedule
D001545:Benserazide; D006916:5-Hydroxytryptophan; D011377:Proglumide; D002230:Carbidopa