Differential effects of haloperidol and clozapine on attention

Haloperidol (0, 0.1, 0.3, or 1.0 mg/kg), the typical butyrophenone neuroleptic, decreased investigation of novel objects by gerbils following systemic injections. When given prior to apomorphine (1 or 3 mg/kg), haloperidol blocked apomorphine-induced disruption of selective attention in a dose-dependent manner. Thus, haloperidol acts like pimozide in this paradigm. In contrast, clozapine (0, 0.03, 0.1, 0.3, 1.0, or 3.0 mg/kg), the atypical dibenzodiazepine neuroleptic, increased frequency of investigation both soon after injection and 24 h later, suggesting interference with maintenance of attention. When given with apomorphine (1.0 mg/kg), clozapine did not block apomorphine effects on selective attention. The results are related to differential effects of these neuroleptics on other behaviors and to their individual pharmacological profiles.