Different inhibition of conditioned avoidance response by clozapine and DA D1 and D2 antagonists in male mice

The effects of clozapine (2.5 and 5 mg/kg), SCH 23390 (0.05 and 0.1 mg/kg), and raclopride (0.1 and 0.5 mg/kg) on the acquisition and performance of a conditioned avoidance response (CAR) were studied in BALB/C mice. The high dose of clozapine decreased avoidances and crossings in acquisition and performance. SCH 23390 had no effect on acquisition, whereas a decrease of avoidances and crossings was produced by the high dose in performance. The high dose of raclopride decreased avoidances and crossings in acquisition but had no effects on performance. The results suggest that the mechanisms by which these drugs affect avoidance are not the same. This difference may reflect an action on different subtypes of DA receptors that produces different effects on motor behavior. It seems that in all cases where CAR is impaired, locomotor activity is also suppressed; therefore, a parsimonious interpretation is that the CAR procedure is sensitive to motor effects.