Scopolamine modulates apomorphine-induced behavior in rats treated with haloperidol or SCH 23390.

In acute experiments, scopolamine (1.0 mg/kg) potentiated apomorphine stereotypy and inhibited the antistereotypic effect of both haloperidol (0.5 mg/kg) and SCH 23390 (0.2 mg/kg). Daily administration of either haloperidol (0.5 mg/kg) or SCH 23390 (0.2 mg/kg) for 3 weeks produced enhanced stereotypic responses to apomorphine. Co-administration of scopolamine (1.0 mg/kg) with haloperidol or SCH 23390 significantly reduced the behavioral supersensitivity produced by haloperidol or SCH 23390 alone. It is suggested that both D-1 and D-2 dopamine receptors are linked to a cholinergic mechanism.