Haloperidol and apomorphine effects on ethanol reinforcement in free feeding rats

Free feeding male Long Evans rats were trained to lever press on a Fixed Ratio 8 schedule for 10% ethanol reinforcement. Mean ethanol intake in 30-minute sessions was 0.38 g/kg. Subcutaneous apomorphine (APO: 0.025 to 0.5 mg/kg) and haloperidol (HAL: 0.005 to 0.0625 mg/kg) administered 15 minutes before sessions dose-dependently reduced responding, but only APO reduced momentary response rates. Low doses of HAL reduced the effect of 0.3 but not 0.05 mg/kg APO. When the rats were food-restricted, control response rates decreased, and APO (0.025 and 0.05 mg/kg) had no further effect. Results were discussed in terms of dopamine involvement in the mechanism of ethanol reinforcement.