Octopamine: An Endogenous Blocker of Dopamine D-1 Receptors

Abstract

Octopamine, an important neurohormone in invertebrates ( Robertson and Juorio, 1976; Axelrod and Saavedra, 1977; David and Coulon, 1985), has been recognized as the false transmitter of adrenergic neurotransmission for a long time (Korol et al., 1968). Octopamine has been identified in mammalian brain ( Harmer and Horn, 1976; Duffield et al., 1981) and a deficiency has been found to be associated with depressive states (Sandler et al., 1983). In the animal behaviors, octopamine has been reported to increase motor activity (Hicks, 1977) and avoidance conditioning (Delacour et al., 1983). Recently, we found that octopamine induced the relaxation of mammalian intestine by an activation of dopamine DA-1 receptors (Cheng and Hsieh-Chen, 1988). In the present report we will briefly discuss some recent findings that indicate the possible role of octopamine on dopamine D-1 receptor in mammalian brain.