D₂-specific discriminative stimuli: Parameters, blocking, and rebound

This study characterizes the cue properties of quinpirole (LY 171555), a selective D₂ agonist, and the blocking capabilities of spiperone, a selective D₂ antagonist. After rats were trained to discriminate 0.025 mg/kg quinpirole from distilled water, a dose-response curve and time course of the quinpirole discriminative stimulus were determined. The effectiveness of three doses of spiperone in blocking the discriminative stimulus produced by 0.02 mg/kg quinpirole was then assessed. Finally, the time course of spiperone's blocking action was determined. Given the putative selective action of these drugs on D₂ receptors and the parametric data presented here, it was predicted that following chronic treatment with spiperone, a rebound increase in quinpirole-appropriate responding would occur. Neither chronic treatment with spiperone nor chronic treatment with haloperidol produced the predicted changes. This result, however, may be confined to the specific dose and time parameters used.