Pimozide mitigates excessive running in the activity-stress paradigm

The present study investigated the role of dopamine in the maintenance of behaviors observed in the activity-stress paradigm. In Experiment 1, several doses (0, 0.125, 0.25, 0.50, and 1.0 mg/kg) of the dopamine D2-receptor blocker, pimozide, were administered to rats maintained on an ad lib feeding schedule. Results indicated that 0.25 mg/kg pimozide did not disrupt running activity when compared to control animals. In Experiment 2, injections of either 0, 0.25, or 0.50 mg/kg pimozide were given every 12 hours to rats subjected to the activity-stress paradigm. Although 0.25 mg/kg pimozide had no effect on dark-phase activity, it significantly suppressed light-phase activity and subsequently increased the number of survivors in the paradigm. It was concluded that dopamine plays a role in maintaining high running levels in the activity-stress paradigm.