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

A behavioral preparation that affords concurrent measurement of forelimb force, lick rhythm, and forelimb tremor in rats was used to assess the effects of the atypical antipsychotic risperidone. Rats that were trained to press 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 individual press-hold-release bouts, effects shared with both typical and atypical antipsychotic drugs in this task. Although risperidone did not significantly affect forelimb force output as clozapine does, it did significantly decrease tremor power in the high-frequency (10-25 Hz) band of the power spectrum. Risperidone dose-dependently decreased the dominant 6 Hz frequency of the power spectrum, a reflection of slowed lick rhythm which is an effect that is shared by other atypical antipsychotic drugs in this task. The results reported in the present study suggest that, although risperidone may not possess the exceptionally low extrapyramidal side-effect profile that clozapine does, its effects are more similar to clozapine than to the extrapyramidal side-effect-producing haloperidol in this task.