Inhibition and potentiation of apomorphine-induced hypermotility in rats by neuroleptics

The effect of apomorphine (ap) was investigated in rats kept in a familiar cage; 0.25-5 mg/kg s.c. produced a short-lasting, abnormal hypermotility consisting mainly of locomotion and sniffing without grooming. Ap was administered to rate pretreated s.c. with various drugs. Ap hypermotility was antagonized by 12 neuroleptics from different chemical groups. The ap inhibitory effect of 5 neuroleptics was decreased when the interval between pretreatment and ap administration was increased from 0.5 to 4 hr. Clozapine was the only neuroleptic showing no inhibition but potentiation at 4 hr. Mepazine, a phenothiazine lacking antipsychotic effects, as well as the NA receptor blockers aceperone and phenoxybenzamine, did not inhibit ap hypermotility. Ap was also given 24 hr after haloperidol and clozapine. At this time both neuroleptics showed ap potentiation. The ap inhibition and potentiation after a single administration of the neuroleptics is presumable due to selective blockade and subsequent supersensitivity of some DA receptors.