Enhancement of stereotypy induced by nomifensine in rats during continuous chronic haloperidol treatment.

Stereotyped behaviour induced by apomorphine (0.125 mg/kg s.c.) was inhibited in rats treated continuously for 20 months with haloperidol (1.4-1.6 mg/kg/day) while that induced by a higher dose of apomorphine (1.0 mg/kg s.c.) was enhanced. Stereotypy induced by nomifensine (3.125-25.0 mg/kg i.p.) was not inhibited at any dosage level in haloperidol-treated rats, and was enhanced by higher doses of nomifensine. The results indicate that the behavioural effects of endogenously released dopamine may not remain inhibited in rats undergoing chronic neuroleptic treatment.