The influence of neuroleptics on the behavioural effect of 5-hydroxytryptophan

The antagonism of neuroleptics of various groups (chlorpromazine, chlorprothixene, clopenthixol, clozapine, flupenthixol, fluphenazine, haloperidol, levomepromazine, mepazine, perazine, perphenazine, pimozide, prochlorperazine, promazine, spiperone, thiopromazine, thioridazine, trifluperazine, trifluperidol, triflupromazine) towards L-5-hydroxytryptophan (5-HTP) was assessed on the basis of inhibition of characteristic head-twitches. ED50 was assayed in mice and rats. The results indicate that all investigated neuroleptics inhibit the action of 5-HTP and their ED50 values are, as a rule, lower than the values of ED50 for catalepsy. That action is for the majority of neuroleptics more pronounced in mice than in rats. The present paper disucsses possible serotonergic, dopaminergic and also noradrenergic mechanism of action of neuroleptics in the 5-HTP test.