Methadone, pentobarbital, pimozide and ethanol-intake.

For 28 days, water-deprived rats were given a daily, 1-hr opportunity to take a sweetened ethanol solution (ES) or water. Across days under this regimen, rats gained weight normally and increased intake of ES until they were taking considerable amounts. Across the next 13 days of the regimen, selected groups were given, before the opportunity to drink, one of five doses of methadone (from 0.5 to 8.0 mg/kg), pentobarbital (from 5 to 30 mg/kg), or their vehicles. Large doses of both agents increased intakes, with methadone (1 and 2 mg/kg) increasing only ES-intake. Subsequently, while the daily regimen continued, rats were given pimozide (0.2, 0.4, or 0.6 mg/kg) at either 1 or 4 hr before the opportunity to drink. Pimozide did not reduce ES-intake. Next, they were given a dose of pentobarbital (5.0 mg/kg) with challenge doses of naloxone (0.3, 1.0, 3.0 mg/kg). Naloxone dose-relatedly antagonized pentobarbital's potential to increase intakes.