Haloperidol versus risperidone on rat “early onset” vacuous chewing

Abstract Similarly to acute rat catalepsy, “early onset” vacuous chewing movements (VCMs) induced by subchronic treatment with antipsychotic have recently been proposed as a model of human extrapyramidal symptoms. In the present study, the propensities of haloperidol and risperidone in inducing rat “early onset” VCMs were compared using doses of the two antipsychotics that acutely induce similar catalepsy. Comparable rat catalepsy states were observed when the effects produced by 0.1, 0.5, and 1 mg/kg of haloperidol were compared with those induced by 1, 4, and 10 mg/kg of risperidone, respectively. These doses of the two antipsychotics were then administered twice a day for 4 weeks and VCMs scored after 12 h, 5 days, or 3 weeks of drug withdrawal. Among the haloperidol-treated groups, only those rats injected with 0.5 and 1 mg/kg showed high levels of VCMs after 12 h and 5 days of drug withdrawal when compared to vehicle-treated rats, while basal levels of VCMs were reached after 3 weeks from the last injection. High VCMs levels were observed in risperidone-treated rats only at the dose of 10 mg/kg and after 12 h of drug withdrawal, but not after 5 days or 3 weeks. The present results indicated that haloperidol possessed a much higher propensity to induce rat “early onset” VCMs than risperidone.