Topography and associations of luteinizing hormone-releasing hormone and neuropeptide Y-immunoreactive neuronal systems in the human diencephalon

Abstract

Neuropeptide Y (NPY) potentiates the effect of luteinizing hormone-releasing hormone (LHRH) on luteinizing hormone secretion in several species, including human. In addition to the pituitary sites, the interactions of the NPY and LHRH systems may involve diencephalic loci. However, the morphologic basis of this putative communication has not yet been elucidated in the human brain. To discover interaction sites, the distribution and connections of LHRH and NPY-immunoreactive (IR) neuronal elements in the human hypothalamus were investigated by means of light microscopic single- and double-label immunocytochemistry. NPY-IR perikarya and fibers were found to be widely distributed in the ventral diencephalon, with high densities in the preopticoseptal, periventricular, and tuberal regions. Small neuronal cell groups were infiltrated with a dense network of varicose NPY-IR fibers in the lateral preoptic area. The LHRH-IR perikarya were located mainly in the preopticoseptal region, diagonal band of Broca, lamina terminalis, and periventricular and infundibular nuclei. A few LHRH-IR neurons and fibers were scattered in the mamillary region. The overlap between the NPY and LHRH systems was apparent in the periventricular, paraventricular, and infundibular nuclei. Double-labeling immunohistochemistry showed NPY-IR axon varicosities in contact with LHRH-IR perikarya and main dendrites. The putative innervation of LHRH neurons by NPY-IR fibers was also seen in 1-microm-thick plastic sections and with confocal laser scanning microscope, thus further supporting the functional impact of NPY-IR terminals on LHRH-IR neurons. The present findings suggest that the hypophysiotropic LHRH-synthesizing neurons may be innervated by intrahypothalamic NPY-IR fibers. Confirmation by ultrastructural analysis would demonstrate that the LHRH system in the human hypothalamus is regulated by NPY, as has been demonstrated in nonhuman species.

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

“…The distribution of LHRH-IR elements were in good agreement with our previous studies (31)(32)(33)(34)(35)(36). LHRH-IR perikarya were located mainly in the medial preoptic area and in the infundibulum/median eminence (Fig.…”

“…The distribution of LHRH-IR elements is well known in the human diencephalon (31)(32)(33)(34)(35)(36). In contrast to these data, studies regarding the pattern and morphology of enkephalin system were restricted to the rat brain (27)(28)(29).…”

Immortalized neurons for the study of hypothalamic function

“…Subsequent studies linked this phenomenon to a direct regulation of the HPG axis, particularly at the level of the GnRH neuron (23,213,253,254) and specifically in the potentiation of the preovulatory GnRH-induced luteinizing hormone surge (1,14,125,217). This interaction between NPY and GnRH neurons is supported by neuroanatomic studies that found ARC NPY-and NPY receptor immunoreactive fibers in close proximity to GnRH perikarya in the preoptic area (65,66,154,166).…”

Distribution and morphology of the juxtapositions between growth hormone-releasing hormone-(ghrh)-immunoreactive neuronal elements

“…Since previous studies revealed numerous juxtapositions between LHRH neurons [21], it is a common consensus that these close associations may represent synaptic connections and they may be responsible for the pulsatile release of LHRH in numerous species. Similarly to the LHRH system, the juxtapositions described in the present paper may represent the morphological basis of the synchronized activity of the GHRH neurons.…”