Bidirectional effects of dopamine D2 receptor antagonists on responding for a conditioned reinforcer.

In general, the administration of dopamine (DA) antagonists has been shown to result in the attenuation of reward processes. Recently, however, it has been suggested that low doses of DA antagonists can enhance the incentive value of a primary reinforcer. The present study examined the effect of DA receptor antagonists on responding for a conditioned stimulus (CS) and compared their effects to that produced by d-amphetamine. For 12 days, food-deprived rats were trained to associate a CS with a food reward. In the test phase, the CS was presented following a response on one of two levers (CR), whereas responding on the other lever (NCR) had no consequence. Low doses of d-amphetamine (0.5 mg/kg), sulpiride (4 mg/kg), pimozide (0.025 mg/kg), and raclopride (0.05 mg/kg) selectively enhanced responding on CR. A low dose of haloperidol (0.01 mg/kg) led to a nonspecific increase in lever responding. Treatment with larger doses of these compounds as well as with the D1 antagonist SCH23390 attenuated responding on CR. Both CR and NCR responding were reduced following administration of higher doses of d-amphetamine. Results indicate that responding for a conditioned reinforcer is potentiated following administration of low doses of D2 receptor antagonists, suggesting that D2 receptor blockade can facilitate incentive motivation.