Histamine H2 receptors mediate morphine-induced locomotor hyperactivity of the C57BL/6J mouse

Morphine-induced locomotor hyperactivity of the C57BL/6J mouse was challenged with intracranial injections of antihistamines or the opiate antagonist naloxone. When cimetidine (H2 receptor blocker) was injected into the nucleus accumbens/stria terminalis, it significantly reduced opiate-stimulated locomotion. However, ventricular injections of cimetidine did not significantly alter either morphine or amphetamine hyperactivity, nor did cimetidine depress spontaneous locomotion. Although naloxone eliminated morphine-induced locomotion when injected into either the nucleus accumbens or the ventricles, chlorpheniramine (H1 receptor blocker) failed to reduce this behavior. These data suggest that opiate-stimulated locomotion of the C57BL/6J mouse may be partially mediated by histamine H2 receptors of the nucleus accumbens or closely adjacent structures.