A role for D-2, but not D-1, dopamine receptors in the response-reinstating effects of food reinforcement

Although the reinforcing properties of food are reduced in the presence of dopamine antagonist drugs, controversy exists about the relative roles of D-1 vs D-2 receptor subtypes in the actions of these drugs. The current experiment compared the effects of raclopride (a selective D-2 receptor antagonist) and SCH 39166 (a selective D-1 receptor antagonist) in the response-reinstating effects of food reinforcement. Hungry rats were trained to run a straight-alley for food reinforcement during single daily trials. The operant was then extinguished during consecutive daily non-reinforced trials. Subjects were then injected with one of four doses of raclopride (0.0, 1.0, 0.5, and 0.25 mg/kg, IP) or SCH 39166 (0.0, 1.0, 0.5, and 0.1 mg/kg IP) 30 min prior to a single reinforced treatment trial. Twenty-four h later, a test trial was conducted in an unbaited runway. The single reinforced trial in the midst of extinction was observed to reinstate operant runway performance. Raclopride, but not SCH 39166, dose-dependently attenuated this reinstatement. Motor control groups ruled out the possibility that these results were due to differential residual motor effects of the drugs. Results suggest that D-2, but not D-1, dopamine receptors, are involved in the response-reinstating properties of food reinforcement. (C) 1997 Elsevier Science Inc.