Haloperidol versus risperidone on rat "early onset" vacuous chewing

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 1mg/kg of haloperidol were compared with those induced by 1, 4, and
10mg/kg of risperidone, respectively. These doses of the two antipsychotics were
then administered twice a day for 4 weeks and VCMs scored after 12h, 5 days, or 3
weeks of drug withdrawal. Among the haloperidol-treated groups, only those rats
injected with 0.5 and 1mg/kg showed high levels of VCMs after 12h 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 10mg/kg and after 12h 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