RELATIONSHIP BETWEEN NEUROPEPTIDE-Y AND LUTEINIZING-HORMONE-RELEASINGHORMONE IMMUNOREACTIVITIES IN THE HYPOTHALAMUS AND PREOPTIC REGION

The purpose of this study was to examine the anatomical relationships of perikarya and fibers containing neuropeptide Y (NPY) and luteinizin g-hormone-releasing hormone (LHRH) in the hypothalamus and preoptic re gion of female rats. In view of our previous report of stimulatory eff ects of estrogen on LHRH and NPY levels in the median eminence, animal s were bilaterally ovariectomized and subsequently implanted subcutane ously with capsules containing estradiol benzoate in oil or vehicle. F ollowing intracerebroventricular injection of colchicine, rats were pe rfused with fixative and their brains sectioned and processed for immu nohistochemical visualization of NPY and LHRH in the same section and in consecutive sections. Estrogen treatment had no discernible effect on the distribution or relationship of these peptides. NPY-immunoreact ive fibers were intimately associated with LHRH-labeled primary dendri tes and perikarya in the medial preoptic region and horizontal limb of the diagonal band of Broca. Fibers containing NPY or LHRH overlapped extensively in the lateral palisade region of the median eminence and also in the subependymal and internal zones. The external zone of the median eminence displayed relatively less overlap of these peptide sys tems. LHRH-immunoreactive axons coursed among NPY-labeled perikarya in the arcuate nucleus and appeared to contact these cells. These result s suggest that NPY-containing axons may influence LHRH-positive neuron s at the cell body and also at the site of axon termination in the med ian eminence. LHRH-containing axons appear to contact NPY-immunoreacti ve perikarya in the arcuate nucleus and may interact with terminals in the median eminence. This arrangement may provide a mechanism for com munication between NPY and LHRH neurons and for the neuroendocrine coo rdination of hypothalamic NPY and LHRH secretion before ovulation.