Facilitation of preparatory behavior in an artificial prey paradigm by D1-subfamily dopamine receptor activation

Dopamine agonists facilitate, and antagonists inhibit, conditioned preparatory behaviors in rats. Similar effects are demonstrated on an unconditioned preparatory behavior: predatory search and contact of a moving artificial prey stimulus. Apomorphine (0.1, 0.2 mg/kg), a direct agonist, had no effect relative to a within-subject injection of saline vehicle but d-amphetamine (0.1 mg/kg), an indirect agonist, increased contact frequency without altering overall motor activation. To determine the relative importance of the D1 and D2 subfamilies of receptors in the amphetamine effect, separate groups of animals received amphetamine co-injected with either SCH23390 (0.01 and 0.005 mg/kg) or eticlopride (0.01 mg/kg), D1 and D2 antagonists, respectively. Whereas the eticlopride-amphetamine group showed no change in contact frequency from baseline, co-injections of either dose of SCH23390 and amphetamine led to near total suppression of contact, as did treatment with SCH23390 (0.005 mg/kg) alone. Treatment with 0.01 mg/kg eticlopride alone increased contact frequency while treatment with a higher dose (0.1 mg/kg) had no effect. Treatment with the D1-subfamily agonist SKF81297 (0.1 mg/kg) increased contact frequency. Collectively, these results support the hypothesis that dopamine mediates unconditioned preparatory behavior and suggest differing roles for the D1 and D2 receptor subfamilies.