More Rapid Development of Supersensitivity of D-2 Receptors than D-1 Receptors as Examined by Rotational Behavior

Abstract

Injection of a dopamine agonist such as apomorphine induces rotation of the rat given 6-hydroxydopamine (6-OHDA) in the nigrostriatal pathway, because destruction of dopaminergic pathway causes supersensitivity of the dopaminergic receptors innervated by these fibers (Ungerstedt, 1971; Creese et al., 1977). This rotation is reported to be induced by both DA D-1 and D-2 agonists. However, whether the rotation induced by DA agonists is due to the distinct action on D-1 and D-2 receptors or synergic interaction between D-1 and D-2 receptors is unknown (Herrera-Marschitz and Ungerstedt, 1984, 1985: Arnt and Hyttel, 1984, 1985; Arnt and Perregaard, 1987; Morelli et al., 1987; Karlsson et al., 1988; Casas et al., 1989). In addition, a little is known regarding the time course of development of supersensitivity of distinct D-1 and D-2 receptors after lesion of the dopaminergic pathway. We examined the role of D-1 and D-2 receptors in rotational behavior and the time course of appearance of supersensitivity of D-1 and D-2 receptors using selective D-1 and D-2 agonists as well as antagonists.