Effects of pimozide on nordiscriminated and discriminated performance in the pigeon.

The effects of pimozide (0.06, 0.18, 0.30 mg/kg), a dopamine receptor blocker, on nondiscriminated and discriminated performance were assessed in pigeons using a Latin Square design. In Experiment 1 a dose-dependent decrease in responding was observed with a variable interval 3-min schedule of reinforcement. More detailed analyses showed that total response rate, running response rate, and post-reinforcement pause all showed the same dose-dependent relationship. In Experiment 2 a successive discrimination task was employed to determine if pimozide affects a previously learned association between environmental stimuli. Each pigeon was first trained on the discrimination and then injected with the same doses as in Experiment 1. Although pimozide reduced responding in a dose-related fashion, a corresponding decrease in accuracy of responding was not evident. It was concluded that pimozide has a general response debilitating effect and that dopaminergic neurons probably are not involved in subserving associative processes.