Differential effects of haloperidol and clozapine on the reinforcing efficacy of food reward in an alleyway reacquisition paradigm.

Using the alleyway reacquisition procedure developed by Horvitz and Ettenberg, the present study compared the effects of a typical neuroleptic haloperidol (0.15 and 0.30 mg/kg) to those of an atypical neuroleptic clozapine (5.0 and 10 mg/kg) on running times 24 hours after a single food-rewarded trial administered during an extinction regimen. Rats that received food reward plus an injection of vehicle or 0.15 mg/kg haloperidol ran faster on the subsequent test day than did nonrewarded rats. The 0.30 mg/kg dose of haloperidol blocked this reacquisition effect, yielding results consistent with the anhedonia hypothesis. Clozapine (5.0 and 10 mg/kg), however, failed to block the reacquisition of alleyway running. Thus, unlike haloperidol, clozapine did not produce anhedonic effects in this reacquisition paradigm. These results suggest that neither motor nor anhedonic properties of neuroleptics appear to be crucial to the clinical efficacy of neuroleptics.