Preferential stimulation of D1 or D2 receptors disrupts food-rewarded operant responding in rats.

Rats were trained to lever-press for food on a variable interval 30-sec schedule. Following stabilization of response rates, separate groups of rats were treated with saline, the nonselective DA agonists amphetamine or apomorphine, the D1 agonist SKF 38393, or the D2 agonist quinpirole prior to placement in the operant chamber. Treatment with SKF 38393 or quinpirole produced dose-dependent reductions in overall response rates which were similar to those observed with either amphetamine or apomorphine. In addition, treatment with the D2 agonist produced a gradual decline in responding within each test session. These data suggest that preferential stimulation of either D1 or D2 receptors is sufficient in disrupting food-reinforced lever-pressing; furthermore, the extinction-like intrasession decline in responding induced by the D2 agonist suggests that this drug, unlike the others, may have disrupted responding by reducing the reinforcing efficacy of the food.