Effects of α-endorphin, β-endorphin and (des-tyr1)-γ-endorphin on α-MPT-induced catecholamine disappearance in discrete regions of the rat brain

Abstract

Summary Following the intracerebroventricular administration of α-endorphin, β-endorphin and (des-tyrosine1)-γ-endorphin in a dose of 100 ng, the α-MPT-induced catecholamine disappearance was found to be altered in discrete regions of the rat brain. In the regions in which α-endorphin exerted an effect, it without exception caused a decrease in catecholamine disappearance. Thus, in rats treated with α-endorphin the disappearance of noradrenaline was decreased in the medial septal nucleus, dorsomedial nucleus, central amygdaloid nucleus, subiculum, the ventral part of the nucleus reticularis medullae oblongatae and the A1 region, and that of dopamine in the caudate nucleus, globus pallidus, medial septal nucleus, nucleus interstitialis striae terminalis, paraventricular nucleus, zona incerta and central amygdaloids nucleus. β-endorphin was found to decrease noradrenaline disappearance in the ventral part of the nucleus reticularis medullae oblongatae, dopamine disappearance in the lateral septal nucleus and the disappearance of both amines in the rostral part of the nucleus tractus solitarii. Dopamine disappearance was increased in the medial septal nucleus and the zona incerta following β-endorphin treatment. Following treatment with (des-tyrosine1)-γ-endorphin, noradrenaline disappearance was enhanced in the anterior hypothalamic nucleus, whereas dopamine disappearance was increased in the paraventricular nucleus, the zona incerta and the rostral part of the nucleus tractus solitarii. In addition to this the latter peptide also caused a decreased noradrenaline disappearance in the periventricular thalamus and the A7 region. The results fit well with the suggestion that endorphins act as modulators of catecholamine neurotransmission in particular brain regions. The pattern of effects of the endorphins differ from that previously observed following intracerebroventricular administration of methionine-enkephalin. This is in keeping with the notion that the enkephalin containing network in the brain and that containing β-LPH represent two independent systems with distinct differences in their projections to various brain regions.