Close anatomical associations between β-endorphin and luteinizing hormone-releasing hormone neuronal systems in the human diencephalon

Abstract

Endogenous opiates, such as β-endorphin, inhibit the release of luteinizing hormone (LH) release in the pituitary gland of several species including rat, pig, sheep, and human. Although it is generally believed that β-endorphin influences gonadal functions via the regulation of hypothalamic LH-releasing hormone (LHRH) release, the morphological substrate underlying this regulation in humans remains elusive. In the present series of experiments the β-endorphin-immunoreactive (IR) and LHRH-IR neural elements, utilizing single label immunohistochemistry, were mapped. Following the superimposition of the maps of these systems, the overlapping sites were identified and examined in order to verify the putative juxtapositions between the β-endorphin-IR and LHRH-IR structures. LHRH-IR elements were detected mainly in the medial basal hypothalamus, in the medial preoptic area and along the diagonal band of Broca. β-Endorphin-IR perikarya were observed in the infundibular region/median eminence, whereas β-endorphin-IR axon varicosities were detected periventricularly in the preoptic and tuberal regions, in the medial basal hypothalamus and around the mamillary bodies. Careful examination of the immunoreactive elements in the overlapping areas revealed close contacts between β-endorphin-IR and LHRH-IR structures, which have been verified in semithin plastic sections. These putative β-endorphin–LHRH juxtapositions were most numerous in the medial preoptic area and in the infundibulum/median eminence of the human diencephalon. In conclusion, the present paper is the first study that revealed close juxtapositions between the β-endorphin-IR and LHRH-IR neural elements in the human diencephalon. These β-endorphin–LHRH contacts may be functional synapses, and they may be the morphological substrate of the β-endorphin control on gonadal functions in man.