EFFECT OF REPEATED HALOPERIDOL ADMINISTRATION ON PHENCYCLIDINE DISCRIMINATION IN RATS

1. Previous research has shown that acute doses of haloperidol block m any of themotor stimulatory effects of phencyclidine (PCP) and other P CP-like drugs. In addition, when given acutely, haloperidol produces p artial attenuation of PCP's discriminative stimulus effects in rats. 2 . Haloperidol is often administered chronically in clinical situations ; hence, it is important to investigate the effects of repeated, as we ll as acute, dosing with this drug. 3. The purpose of the present stud y was to examine the effects of repeated administration of haloperidol on PCP discrimination in rats. Rats were trained to discriminate PCP (2.0 mg/kg) from saline in a two lever drug discrimination procedure a nd were tested with cumulative doses of PCP before and after repeated administration of saline and of haloperidol (0.5 mg/kg/day). 4. Discri mination training was suspended during the two 14-15-day repeated dosi ng regimens. Suspended training with repeated saline administration ha d little effect on the dose-effect curve for % PCP-lever responding. 5 . Repeated administration of haloperidol produced some diminution of P CP discrimination. After haloperidol, the ED(50) for % PGC-lever respo nding was 1.4 mg/kg, compared to the pre-haloperidol ED(50) of 0.7 mg/ kg. 6. These results are consistent with those of acute dosing studies with haloperidol in PCP-trained rats and suggest that repeated admini stration of haloperidol may disrupt PCP's discriminative stimulus effe cts, although most rats were still able to discriminate the higher dos es of PCP.