Role of D-1 and D-2 receptors in apomorphine-induced pecking in chicks.

The possible involvement of subtypes of dopamine (DA) receptors in pecking induced by apomorphine (APO) in chicks was studied. D-1/D-2 agonist APO dose-dependently induced pecking in chicks. The APO response was decreased in animals pretreated with either the D-2 receptor antagonist sulpiride or the D-1 receptor antagonist SCH 23390. The inhibitory effects of both antagonists were also dose dependent. The pecking induced by APO was completely inhibited in animals pretreated with a combination of SCH 23390 and sulpiride and was potentiated with reserpine. Single administration of D-2 agonist quinpirole or D-1 agonist SKF 38393 did not induced pecking, although quinpirole, but not SKF 38393 caused considerable response in reserpine or reserpine + alpha-methyl-p-tyrosine (AMPT)-treated animals. When quinpirole was administered with SKF 38393, a slight pecking response was shown. This was also potentiated in reserpine or reserpine + AMPT-treated chicks. The results may indicate that both D-1 and D-2 DA receptors are involved in pecking induced by APO, and reserpine treatment caused the sensitization of the D-2 receptors for the induction of pecking in chicks.