[Effects of psychotropic drugs and the roles of the noradrenergic and dopaminergic systems in the lateral hypothalamic self-stimulation behavior]

Abstract

A bipolar electrode was stereotaxically implanted in or near the medial forebrain bundle at the level of the posterior lateral hypothalamus of male albino Wistar-Imamichi rats. 1) Two electrode sites implanted in a rat both in the lateral hypothalamus and in the dorsal noradrenaline bundle supported self-stimulation (SS) behavior. 2) Methamphetamine facilitated the SS dose-dependently in the "threshold"-intensity reinforcement. The pretreatment of imipramine enhanced the effects of methamphetamine, but that of chlorpromazine inhibited those effects. Methamphetamine facilitated the SS also in the moderate-intensity reinforcement. Imipramine had no significant effects. On the other hand, chlorpromazine inhibited markedly the SS behavior. 3) FLA63 and U-14,624, dopamine beta-hydroxylase inhibitors, suppressed the SS behavior. Both drugs significantly reduced brain norepinephrine levels. FLA63 significantly increased the levels of dopamine, but the increase with U-14,624 was not significant. 4) Apomorphine, stimulant of dopamine receptor, did not facilitate, but rather suppressed the SS in the "threshold"-intensity reinforcement. 5) l-Norepinephrine injected into the lateral ventricle facilitated the rate of SS, dose-dependently. On the other hand, dopamine had no detectable effects. 7) These results suggest that the noradrenergic system in the brain plays a more important role in the positive reinforcement of the lateral hypothalamic SS behavior than does the dopaminergic system.