Lack of effect of dopamine D-2 blockade on ethanol intake in selected and unselected strains of rats

Previous research has suggested that brain catecholamines may be involved in regulating ethanol intake. This study was designed to look more specifically at dopamine (DA) and whether DA D-2 receptor blockade with the antagonist pimozide would alter ethanol consumption in rats. Subjects were male Maudsley Reactive and Wistar rats, the former previously shown to consume larger amounts of ethanol than the latter. Both strains were screened for ethanol intake by presentation of ethanol solutions (free choice with water) in increasing steps from 2% to 10% (v/v) on an alternate-day schedule. Following the screening period, animals were switched to a schedule of everyday presentation of the 10% (v/v) ethanol solution (free choice with water) for 10 baseline days. Animals were then divided into high and low drinking levels according to whether their mean baseline ethanol intake (g/kg) fell within +/-0.5 SD of the mean intake of their group (Maudsley Reactives: mean = 2.55 g/kg, low drinkers <1.63, high drinkers >3.47; Wistars: mean = 2.17 g/kg, low drinkers <1.53, high drinkers >2.82). The animals were assigned to one of five treatment groups for 5 subsequent days where they received IP injections of pimozide (0.08, 0.24, or 0.48 mg/kg), tartaric acid, or saline. Following the treatment period, ethanol consumption was recorded for 5 posttreatment days. No significant differences due to treatment were observed for either intake or preference of ethanol across treatments, drinking groups, or strains. The results obtained in the present study suggested that interference in DA neurotransmission through administration of the D-2 antagonist pimozide does not significantly alter ethanol consumption in either MR or Wistar animals.