THE DISCRIMINATIVE STIMULUS PROPERTIES OF BUSPIRONE INVOLVE DOPAMINE-2 RECEPTOR ANTAGONIST ACTIVITY

To investigate a dopaminergic component in the discriminative stimulus properties of buspirone, rats were trained to discriminate 2.5 mg/kg buspirone from saline, using a two lever, food-rewarded, fixed ratio 10 operant procedure. To test the dopamine-2 (D2) antagonist action of buspirone, a second group of rats was trained to discriminate 0.16 mg/kg apomorphine from saline. In addition to a complete generalization to 8-OH-DPAT, the D2 antagonists haloperidol, R 79598 and sulpiride showed a partial generalization to buspirone. The benzodiazepine ligands chlordiazepoxide and bretazenil did not generalize to the buspirone cue. Buspirone (2.0 mg/kg) completely blocked the apomorphine cue in the apomorphine trained rats. Haloperidol, R 79895 and sulpiride also blocked the apomorphine cue, although at doses much smaller than the doses needed to evoke buspirone responding in the buspirone trained group. 8-OH-DPAT did not antagonize apomorphine. It was concluded that the D2 action of buspirone partially contributes to its discriminative stimulus properties. Mediation of the buspirone cue by 5-HT1a receptor activation seemed predominant. Further, buspirone can act as a full D2 antagonist in drug discrimination. A model was proposed suggesting a compound discriminative stimulus complex of buspirone with a dominant 5-HT1a component that overshadows a less pronounced D2 component.