Time and dose influences on the behavioral effects of L-DOPA and 5-hydroxytryptophan after inhibition of extracerebral decarboxylase.
The influence of time and dose factors on the locomotor activity and gross behavioral effects of l-3,4-dihydroxyphenylalanine (L-DOPA) and 5-hydroxytryptophan (5-HTP) were assessed a albino mice pretreated with the peripheral decarboxylase inhibitor, MK-486, L-DOPA caused stereotyped behaviors and a decrease in orienting responses and locomotor activity, followed at the highest dose by increased locomotor activity. 5-HTP caused a dose-dependent increase in orienting responses and locomotor activity followed after 90 min by a dose-dependent decrease in locomotor activity. Administration of MK-486 and L-DOPA followed in the same animal by 5-HTP resulted in a diminution of the effects seen after either drug alone. This apparent antagonism may result from competition between the two amino acids at sites of membrane transport in the brain.
D006916:5-Hydroxytryptophan / Q000008:administration & dosage / Q000494:pharmacology*; D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects*; D002262:Carboxy-Lyases / Q000037:antagonists & inhibitors*; D004305:Dose-Response Relationship, Drug; D006801:Humans; D007274:Injections, Intraperitoneal; D007980:Levodopa / Q000008:administration & dosage / Q000494:pharmacology*; D008297:Male; D051379:Mice; D009043:Motor Activity / Q000187:drug effects; D009949:Orientation / Q000187:drug effects; D013239:Stereotyped Behavior / Q000139:chemically induced; D013997:Time Factors
D007980:Levodopa; D006916:5-Hydroxytryptophan; D002262:Carboxy-Lyases