[Changes in the substantia nigal self-stimulation behavior caused by intraventricular injection of norepinephrine,...

A bipolar electrode was stereotaxically implanted in the substantia nigra of male albino Wistar-Imamichi rats. Effects of l-norepinephrine (NE), dopamine (DA) and gamma-aminobutyric acid (GABA), injected into the lateral ventricle, on the substantia nigral self-stimulation (SS) behavior, and the effect of alpha- and beta-adrenergic receptor antagonists on the facilitation induced by NE were investigated. NE but not DA facilitated the SS behavior and GABA showed no constant effects on the behavior. Facilitation by NE of SS behavior was inhibited by phentolamine, but not by propranolol. These results suggest that the noradrenergic system in the brain may play a more significant role in the positive reinforcement of the substantia nigral SS behavior than does the dopaminergic or GABA-ergic system, and that the action of NE may be facilitated through alpha-receptors rather than through beta-receptors.