Antagonism by haloperidol of locomotor depression induced by small doses of apomorphine.

Administration of 0.025--0.1 mg/kg of apomorphine i.p. to mice produced a dose-dependent locomotor depression. Haloperidol, 0.025 mg/kg, produced locomotor stimulation, whereas 0.1 mg/kg caused locomotor depression. Pretreatment with haloperidol also reversed the depression caused by apomorphine. The functional antagonism is discussed in terms of a possible agonist-antagonist interaction on dopaminergic autoreceptors.