Clozapine-like motor effects of the atypical antipsychotic risperidone in rats

A behavioral preparation that affords concurrent measurement of forelimb fo rce, lick rhythm, and forelimb tremor in rats was used to assess the effect s of the atypical a nti psychotic risperidone. Rats that were trained to pr ess downward on an isometric force transducer while simultaneously licking water reinforcement were administered risperidone (0.08, 0.12, and 0.16 mg/ kg). Risperidone suppressed task engagement and increased the duration of i ndividual press-hold-release bouts, effects shared with both typical and at ypical antipsychotic drugs in this task. Although risperidone did not signi ficantly affect forelimb force output as clozapine does, it did significant ly decrease tremor power in the high-frequency (10-25 Hz) band of the power spectrum. Risperidone dose-dependently decreased the dominant 6 Hz frequen cy of the power spectrum, a reflection of slowed lick rhythm which is an ef fect that is shared by other atypical antipsychotic drugs in this task. The results reported in the present study suggest that, although risperidone m ay not possess the exceptionally low extrapyramidal side-effect profile tha t clozapine does, its effects are more similar to clozapine than to the ext rapyramidal side-effect-producing haloperidol in this task. (C) 2000 Publis hed by Elsevier Science Ireland Ltd. All rights reserved.