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

Dopamine agonists facilitate, and antagonists inhibit, conditioned preparat ory 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 effec t relative to a within-subject injection of saline vehicle bur d-amphetamin e (0.1 mg/kg), an indirect agonist, increased contact frequency without alt ering overall motor activation. To determine the relative importance of the D1 and D2 subfamilies of receptors in the amphetamine effect, separate gro ups 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, respec tively. Whereas the eticlopride-amphetamine group showed no change in conta ct frequency from baseline, co-injections of either dose of SCH23390 and am phetamine led to near total suppression of contact, as did treatment with S CH23390 (0.005 mg/kg) alone. Treatment with 0.01 mg/kg eticlopride alone in creased contact frequency while treatment with a higher dose (0.1 mg/kg) ha d no effect. Treatment with the D1-subfamily agonist SKF81297 (0.1 mg/kg) i ncreased contact frequency. Collectively, these results support the hypothe sis that dopamine mediates unconditioned preparatory behavior and suggest d iffering roles for the D1 and D2 receptor subfamilies. (C) 2000 Elsevier Sc ience B.V. All rights reserved.