Effects of mediobasal hypothalamic lesion on immunoreactive ACTH/β-endorphin levels in cerebrospinal fluid, in discrete brain regions, in plasma, and in pituitary of the rat

Abstract

One week after complete destruction of the mediobasal hypothalamus, immunoreactive adrenocorticotropin (ACTH) and β-endorphin levels were determined in cerebrospinal fluid, trunk blood, as well as in brain and pituitary tissue samples collected from anaesthetized and cisternally cannulated rats. Control rats were sham operated. In lesioned rats we observed: (a) 60% decrease in the immunoreactive β-endorphin concentrations in the cerebrospinal fluid, (b) decreased immunoreactive ACTH and β-endorphin levels in the hypothalamus, in the thalamus and in the amygdala, (c) unaffected immunoreactive ACTH/β-endorphin levels in the septum and in the hippocampus, (d) decreased immunoreactive β-endorphin levels both in the anterior and neurointermediate pituitary but unchanged immunoreactive ACTH contents in the anterior lobe, and (e) unaffected immunoreactive ACTH and β-endorphin levels in the plasma under stressful conditions. From these findings the following conclusions can be drawn: (1) more than 50% of the β-endorphin-like peptide content of the cerebrospinal fluid originates from the periventricular nuclei of the hypothalamus and thalamus in the rat; (2) the loss of the hypothalamic control probably enhances the intracellular proteolytic degradation of β-endorphin both in the anterior and neurointermediate pituitary lobe; (3) rats with mediobasal hyphothalamic lesion cannot react to the stressful stimuli of either anaesthesia or cisternal cannulation with elevated plasma immunoreactive ACTH and β-endorphin levels.