Effect of des-tyr 1-γ-endorphin and des-tyr 1-α-endorphin on α-MPT-induced catecholamine disappearance in rat brain nuclei: A dose-response study

Abstract

The effect of des-Tyr 1-γ-endorphin (ß-LPH 62–77, DTγE) and des-Tyr 1-α-endorphin (ß-LPH 62–76, DTαE), administered intracerebroventricularly (icv) in doses of 0.01, 0.1, 1 and 10 μg, was studied on the α-methyl-p-tyrosine- (α-MPT) induced disappearance of catecholamines in a number of microdissected rat brain regions, which were selected on the basis of the neuroanatomy of the dopamine systems in the brain and of previous observations. A dose-dependent increase in the disappearance of dopamine in α-MPT-pretreated rats was observed following icv administration of DTγE in the nucleus interstitialis striae terminalis, the paraventricular nucleus, the anterior hypothalamic nucleus and the zona incerta. In these same brain regions a decrease in the α-MPT-induced disappearance of dopamine was found following the administration of DTαE, but only after doses of 0.01, 0.1 and 1 μg. In none of these regions were effects observed after 10 μg of DTαE. No effects were seen on dopamine utilization in the nucleus accumbens, caudate nucleus and median eminence after any of the doses of DTγE or DTαE. The α-MPT-induced disappearance of noradrenaline was significantly enhanced in the anterior hypothalamic nucleus of rats treated with DTγE. It is concluded that DTγE and DTγE induce opposite changes in the utilization of dopamine selectively in brain regions which are predominantly innervated byneurons belonging to the intradiencephalic dopamine systems.