EFFECT OF PROLONGED TREATMENT WITH HALOPERIDOL ON EMOTIONAL DEFECATION AND MOVEMENT IN RATS IN A WELL-HABITUATED ENVIRONMENT

Sixteen adult male Wistar rats were administered either haloperidol (n = 8), 0.5 mg/kg, or saline (placebo) (n = 8) by subcutaneous injectio n three times per week for 6 weeks, and were again injected after a 6- week drug-free period. The study was conducted in a well-habituated, d istinctive environment to which the rats were introduced 1 hour before the injection on each occasion. The fecal bolus counts I hour before and 2 hours after drug injection were obtained, as well as movement co unts repeatedly in epochs of 90 seconds upon introduction to the cages and after the injections. Haloperidol produced an overall increase in defecation in the 2 hours after drug injection compared with placebo. The postdrug bolus counts for haloperidol-treated rats were lower in week 2 compared with week 1, but the difference from placebo for this reduction was not significant, and it did not persist beyond week 4. T he haloperidol-treated group showed a significant increase in the pred rug bolus counts from week 5, suggesting a conditioned response to the cage environment. The haloperidol-treated rats were markedly less mob ile than the placebo-treated rats, and with repeated exposure to halop eridol, they tended to develop hypomotility earlier. No tolerance to t he movement effect was observed. The defecation and movement effects o f haloperidol at 12 weeks were no different from those at week 1. This study supports earlier work indicating that haloperidol produces a dy sphoric effect in rats, and it suggests that this effect does not habi tuate over 6 weeks of repeated administration. It does not replicate t he motor aspect of akathisia seen in humans.