Dopaminergic D-1 receptors: essential role in morphine-induced hypermotility.

Administration of morphine HCl (20 mg/kg SC) to male C57Bl/6 mice evoked hypermotility. Pretreatment with low doses of the specific D-1 antagonist SCH 23390 (0.006, 0.012, 0.025 mg/kg SC) dose-dependently inhibited morphine-evoked hypermotility. The results suggest that dopamine is the essential mediator of opiate hypermotility and indicate that D-1 receptors play an important role in this effect.