IMPAIRMENT BY APOMORPHINE OF ONE-TRIAL PASSIVE-AVOIDANCE LEARNING IN MICE - OPPOSING ROLES OF THE DOPAMINE AND NORADRENALINE SYSTEMS

Pretraining administration of the dopaminergic stimulant apomorphine (0.25-16 mg/kg) impaired retention performance of mice on a one-trial passive avoidance task. Only with a very high dose (16 mg/kg) of this drug did the effect seem related to an interference with memory formation processes. Of the dopamine receptor-blocking agents used, haloperidol (0.125-1 mg/kg), but not chlorpromazine or clozapine (0.25-4 mg/kg), prevented the apomorphine effect. Phenoxybenzamine (8 mg/kg), a noradrenaline [norepinephrine] receptor-blocker, antagonized the haloperidol effect and, when combined with a subeffective dose of apomorphine, impaired passive avoidance learning. The results obtained are interpreted in terms of the proposed inhibitory actions exerted by central noradrenaline on dopamine systems of the brain.