Oral ethanol reinforcement: interactive effects of amphetamine, pimozide and food-restriction

Twelve male Long Evans rats, trained to lever press using 10% (v/v) oral ethanol reinforcement, were maintained with ad lib access to food and water in the home cage. After stabilization of responding, the rats were randomly divided into two groups: Group P received pimozide (PIM) injections (0.1 to 0.5 mg/kg) and Group A received d-amphetamine (DEX) injections (0.05 to 0.5 mg/kg). Following the sequence of either PIM or Dex injections, all rats were given four different combinations of PIM + DEX injections. The lower doses of amphetamine did not affect responding, but 0.5 mg/kg significantly reduced responding. All PIM doses except the lowest reduced responding. The combined PIM + DEX doses all reduced responding, in some cases further than either constituent dose alone. Next, all rats were reduced to 80% of their free feeding weights by food restriction, and tested with 0.25 mg/kg DEX, 0.1 mg/kg PIM, and 0.1 PIM + 0.25 DEX. As a result of food restriction, baseline responding increased significantly. The 0.25 mg/kg DEX dose tended to increase responding even above this baseline increase, while both PIM and PIM + DEX reduced responding.