Alterations in brain 5HT and tryptamine content during indoleamine-induced myoclonus in guinea pigs

L-5-Hydroxytryptophan (5HTP) (with or without carbidopa pretreatment), L-tryptophan (plus pargyline pretreatment), or tryptamine (plus pargyline pretreatment) all induced dose-dependent myoclonus in guinea pigs. At the time of maximal behavioural response animals were killed for determination of brain indoleamine content. Administration of 5HTP (50-200 mg/kg) to naive guinea pigs, or of 5HTP (20-80 mg/kg) to carbidopa- (25 mg/kg 1 hr previously) pretreated animals, markedly elevated brain 5-hydroxytryptamine (5HT) concentrations but depressed whole brain tryptamine content. L-Tryptophan (50-200 mg/kg) administration to pargyline- (75 mg/kg 30 min previously) pretreated animals also increased cerebral 5HT levels. L-Tryptophan (200 mg/kg plus pargyline), elevated whole brain tryptamine content. Administration of tryptamine (40 mg/kg) to pargyline-pretreated guinea pigs caused a small increase in brain 5HT levels, but markedly elevated cerebral tryptamine content. 5HT appears to be the indoleamine mainly responsible for 5HTP-induced myoclonus but tryptamine predominates in tryptamine-induced myoclonus. Both 5HT and tryptamine may contribute to myoclonus induced by L-tryptophan.