A comparison of the effects of pimozide and nonreinforcement on discriminated operant responding in rats

Some controversy surrounds the interpretation of the effects of dopamine receptor blocking drugs on conditioned operant responding. To assess the motoric versus the reinforcement-reducing consequences of these compounds, the effects of pimozide (1.0 mg/kg) and nonreinforcement on discriminated operant responding were compared. Rats were trained extensively on a successive discrimination implemented with the use of a multiple schedule. Rats subsequently injected with pimozide showed a significantly greater decrease in responding in the nonreinforced component than control rats showing that pimozide produces a decrease in general level of behavioral arousal. Additionally, pimozide injection resulted in an extinction-like decrease in reinforced responding over three test sessions indicating a reduction in the effects of reinforcement. However, animals treated with pimozide continued to discriminate. Transfer between pimozide and nonreinforcement was not observed probably because of the differential effects of the two procedures on behavioral arousal. Dopaminergic neurons may influence both general behavioral arousal and the effects of reinforcement but not stimulus-stimulus associative learnings.