Evidence for involvement of 5-hydroxytryptamine in the actions of amphetamine.

1 Pargyline treatment, 1 h before (+)-amphetamine (1 mg/kg), reduced amphetamine-stimulated motor activity. This inhibition was reversed in animals pretreated with p-chlorophenylalanine (PCPA).2 Following treatment with PCPA or 5,6-dihydroxytryptamine (5,6-DHT), amphetamine-induced locomotor activity was significantly potentiated. The increased response to amphetamine in PCPA-treated rats was reversed in animals pretreated with 5-hydroxytryptophan.3 The inhibition of amphetamine-stimulated locomotor activity by treatment with 6-hydroxydopamine was not reversed by PCPA treatment.4 Stereotypies produced by amphetamine were not found to be altered by depletion of 5-hydroxytryptamine.5 Induction of adrenal tyrosine hydroxylase activity produced by chronic amphetamine administration was significantly potentiated by PCPA, emphasizing the involvement of a 5-hydroxytryptamine inhibitory system in more than one action of amphetamine.