HALOPERIDOL, RACLOPRIDE, AND ETICLOPRIDE INDUCE MICROCATALEPSY DURINGOPERANT PERFORMANCE IN RATS, BUT CLOZAPINE AND SCH-23390 DO NOT

The purpose of this work was (1) to assess the ability of selected ant ipsychotic and comparison drugs to induce arrest of movement phenomena during operant responding and (2) to evaluate the capacity of muscari nic anitcholinergics to block such effects. The effects of haloperidol (0.02-0.12 mg/kg, IP, 45 min), raclopride (0.05-0.80 mg/kg, IP, 30 mi n) eticlopride (0.02-0.16 mg/kg, IP,45 min), clozapine (1.0-8.0 mg/kg, IP, 60 min) and SCH 23390 (0.01-0.16 mg/kg, IF, 30 min) were administ ered to rats for 4 weeks in a between-groups dosing design. Operant re sponses in 15 min and the maximum duration of the rat's muzzle entry i nto the reinforcement dipper well (the measure of arrest of movement t hat reflected microcatalepsy) were the quantitative measures of behavi or. The D-2 antagonists dose-relatedly decreased operant responding an d increased maximum muzzle duration, effects that were significantly r eversed by the anticholinergic scopolamine (0.1 mg/kg) or atropine (6. 0 mg/kg). Although the atypical antipsychotic drug clozapine and the s elective D-1 antagonist SCH 23390 both significantly reduced operant r esponding, these drugs did not produce microcatalepsy. The results sug gested that microcatalepsy expressed in the context of ongoing operant behavior may model low-dose extrapyramidal side effects.