Locomotion and conditioned place preference produced by acute intravenous amphetamine: role of dopamine receptors and individual differences in amphetamine self-administration.

Although previous studies have shown that dopamine (DA) antagonists block amphetamine reward, these studies have utilized animal models that involve repeated exposures to amphetamine. The present investigation examined the effect of DA antagonists on single-trial conditioned place preference (CPP) produced by acute intravenous (i.v.) amphetamine in rats. In the first experiment, rats were prepared with a jugular catheter and then received an acute i.v. injection of amphetamine (0.1-3 mg/kg) paired with one compartment of a CPP apparatus. Relative to sham controls (no i.v. catheter), amphetamine produced a dose-dependent increase in locomotor activity and CPP. Two further experiments demonstrated that both effects of amphetamine were completely blocked by pretreating rats with the D1 DA antagonist SCH-23390 (0.025 and 0.25 mg/kg) or the D2 DA antagonist eticlopride (0.2 and 2 mg/kg) on the conditioning trial. In a final experiment, single-trial amphetamine CPP did not predict subsequent self-administration of i.v. amphetamine (10-50 micrograms/infusion) using either a fixed ratio (FR) 1 or progressive ratio (PR) schedule of reinforcement. Thus, while sharing a similar DA receptor mechanism, the present results indicate that single-trial CPP and self-administration are dissociable effects of i.v. amphetamine.