Effects of selective dopamine D-1- and D-2-agonists and antagonists on timing performance in rats

Dopamine (DA) D-1- and D-2-agonists and antagonists were administered at fixed doses to assess putative dopaminergic involvement in timing behavior in rats performing under a peak-interval schedule. Significant shifts in response distributions to the left (consistent with the overestimation of the passage of time) were observed after treatment with the D-1- and D-2-agonists SKF 38393 and quinpirole, respectively. Both DA antagonists, eticlopride (D-2) and SCH 23390 (D-1), shifted the response distributions to the right (consistent with the underestimation of the passage of time), but neither drug produced statistically significant shifts. Based on percent shift in peak time from predrug baseline values, no significant differences were detected between agents as a function of their reported affinities for the D-1- or D-2-receptors. Results indicate the need for a systematic evaluation of each drug at various doses and a more derailed examination of the use of temporal schedules in predicting the efficacy of psychotherapeutic agents.