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Topography and Associations of Leu-Enkephalin and Luteinizing Hormone-Releasing Hormone Neuronal Systems in the Human Diencephalon

Department of Pharmacology and Experimental Therapeutics (B.D.), Loyola University Chicago, Strich School of Medicine, Maywood, Illinois 60153; and Women’s Health Research Institute (I.M.), Wyeth Research, Collegeville, Pennsylvania 19426

Address all correspondence and requests for reprints to: Bertalan Dudas, M.D., Department of Pharmacology and Experimental Therapeutics, Loyola University Chicago Stritch School of Medicine, 2160 South First Avenue, Maywood, Illinois 60153. E-mail: bdudas{at}lumc.edu.

Although several studies indicated that leu-enkephalin controls gonadal function, the morphological substrate of this modulation is unknown. To reveal potential interaction sites between leu-enkephalin and LH-releasing hormone (LHRH) in the hypothalamus, the distribution and connections of leu-enkephalin-immunoreactive (IR) and LHRH-IR systems were examined in the human diencephalon using double-label immunohistochemistry. First the leu-enkephalin-IR and LHRH-IR neural elements were mapped, then the maps of the two different neurotransmitter systems were superimposed unveiling the overlapping areas. The putative juxtapositions between leu-enkephalin-IR and LHRH-IR structures were revealed with double label immunocytochemistry. Close contacts were detected in the medial preoptic area and in the infundibulum/median eminence. In these areas, diaminobenzidine-silver-intensified, black leu-enkephalin-IR fibers abutted fusiform, brown, diaminobenzidine-labeled LHRH neurons often forming multiple contacts. Examination of semithin sections of these close associations with the aid of oil immersion revealed no cleft between the contacting LHRH-IR and leu-enkephalin-IR elements.

Our findings indicate that the juxtapositions between LHRH-IR and leu enkephalin-IR neurons may be functional synapses forming the morphological substrate of the leu-enkephalin-modulated LHRH secretion in the human diencephalon. Moreover, the wide distribution of leu-enkephalin-IR elements suggests leu-enkephalin control of other diencephalic functions as well.

Abbreviations: DAB, Diaminobenzidine; IR, immunoreactive; LHRH, LH-releasing hormone; MPOA, medial preoptic area; PRL, prolactin; TIDA, tuberoinfundibular dopaminergic.

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