Meal patterns of free feeding rats treated with clozapine, olanzapine, or haloperidol.

Selective dopamine D(2) antogonists increase meal size and decrease the rate of feeding within a meal. Three experiments investigated the extent to which the atypical antipsychotics, clozapine and olanzapine, and the prototypical antipsychotic, haloperidol, affected meal size and feeding rate. Microstructural analyses of meal patterning were made over a range of drug doses administered to free feeding male Lister hooded rats. Haloperidol and clozapine produced a short-term increase in food intake. Haloperidol (0.05-0.2 mg/kg) enhanced meal size (maximal at 0.1 mg/kg) and reduced feeding rate (monotonic decrease with increasing dose). Neither clozapine (1-10 mg/kg) nor olanzapine (0.3-3 mg/kg) enhanced meal size, although both drugs produced similar reductions in feeding rate to haloperidol. These data suggest that enhancement of meal size may be correlated with a high level of extrapyramidal side effects in an antipsychotic drug. The absence of an increase in meal size by two atypical compounds suggests that the increase in body weight associated with clinical treatment with these drugs cannot be modelled by acute stimulation of meal size in the rat.