The effect of sulpiride on amphetamine-induced disruption of overshadowing in the rat

Previous studies have demonstrated dopaminergic (DA) modulation of stimulus selection performance in the overshadowing and Kamin blocking (KB) tasks. Systemic administration of the DA agonist D-amphetamine selectively disrupted overshadowing in the rat. In the present study, we examined the ability of the selective DA D2 receptor antagonist sulpiride to reverse amphetamine-induced disruption of overshadowing, in the conditioned emotional response (CER) procedure. In the overshadowing task, two stimuli (light and tone) are presented simultaneously alongside an aversive unconditioned stimulus (CS) (mild footshock); overshadowing consists in the decrease in learning to the less salient stimulus, as compared to when it is conditioned alone. Systemic D-amphetamine (1 mg/kg, i.p.) prevented overshadowing, while having no effect on control learning. Pre-administration of sulpiride (50 and 100 mg/kg, i.p.) did not prevent the ability of D-amphetamine to impair overshadowing. In addition, sulpiride had no significant effect on overshadowing when administered alone. The results are in agreement with previous data indicating that DA modulation of stimulus selection performance is mediated by activation of the DA D1 rather than DA D2 receptor subtype.