Effects of pimozide on the acquisition, maintenance, and extinction of an amphetamine-induced taste aversion.

Different groups of rats were pretreated with the dopamine receptor blocker, pimozide (0.25, 0.5, or 1.0 mg/kg), in an attempt to investigate the role of dopaminergic transmission in the acquisition, maintenance, and extinction of a taste aversion produced by d-amphetamine dulphate (1.0 or 2.0 mg/kg). In the first phase of the experiment, all doses of pimozide attenuated but did not block the acquisition of the aversion produced by 1.0 mg/kg but not by 2.0 mg/kg amphetamine. In Phase II, pimozide pretreatment was suspended to allow the attenuated groups to acquire the aversion and then reintroduced in Phase III. In this phase all groups continued to avoid the taste, indicating a failure of pimozide to affect the maintenance of the avoidance response. When amphetamine treatment was suspended in Phase IV, pimozide accelerated the extinction, especially in those groups that had previously received the 1.0 mg/kg dose of amphetamine. These results are discussed with reference to dopaminergic mechanisms in avoidance learning and a pimozide-mediated reduction in the functional strength of amphetamine as an unconditioned stimulus.