EFFECTS OF CLOZAPINE AND HALOPERIDOL ON BASE-LINE LEVELS OF VACUOUS JAW MOVEMENTS IN AGED RATS

Some studies have indicated that aged rats have elevated basal levels of vacuous jaw movements and these vacuous jaw movements are exacerbat ed by classic neuroleptic drugs like haloperidol, but the effects of t he atypical antipsychotic clozapine on vacuous jaw movements in aged r ats has not previously been studied. Aged rats were administered daily intraperitoneal injections of either haloperidol (0.04, 0.1 or 0.4 mg /kg), clozapine (0.4, 1.0, 4.0 mg/kg) or 0.3% tartaric acid vehicle fo r 22 days. On days 1, 8, 15 and 22 these rats were placed in an observ ation tube and vacuous jaw movements were recorded by two trained obse rvers. Vacuous jaw movements were present in the aged rats receiving v ehicle. Haloperidol produced a dose-dependent increase in vacuous jaw movements while clozapine produced a dose-dependent attenuation of vac uous jaw movements, relative to the vehicle-treated rats. These result s indicate that screening for vacuous jaw movements may provide a usef ul behavioral assay for atypical antipsychotic drugs which do not prod uce extrapyramidal side effects and that clozapine's resistance to the se side effects may extend to populations of elderly human patients. ( C) 1997 Elsevier Science B.V.