Gonadotropin-inhibitory hormone (GnIH) is a hypothalamic neuropeptide that modulates the reproductive physiology of birds and mammals by inhibiting gonadotropin secretion from the anterior pituitary gland. GnIH can also directly inhibit reproductive behaviors, possibly via action within the brain. Identification of the distribution of GnIH neurons and fibers may provide us with clues to how the brain controls reproductive activities of the animal. Here, we characterized the location and connectivity of GnIH neurons in the rhesus macaque (Macaca mulatta) brain. We determined the macaque GnIH precursor mRNA, and further identified a mature GnIH peptide (SGRNMEVSLVRQVLNLPQRF-NH 2) by mass spectrometry combined with immunoaffinity purification. The majority of GnIH precursor mRNA-positive and GnIH-immunoreactive (GnIH-ir) cell bodies were localized in the intermediate periventricular nucleus (IPe) in the hypothalamus, as determined by in situ hybridization and immunocytochemistry, respectively. Abundant GnIH-ir fibers were observed in the nucleus of the stria terminalis in the telencephalon; habenular nucleus, paraventricular nucleus of the thalamus, preoptic area, paraventricular nucleus of the hypothalamus, IPe, arcuate nucleus of hypothalamus, median eminence and dorsal hypothalamic area in the diencephalon; medial region of the superior colliculus, central gray substance of the midbrain and dorsal raphe nucleus in the midbrain; and parabrachial nucleus in the pons. GnIH-ir fibers were observed in close proximity to gonadotropin-releasing hormone-I, dopamine, β-endorphin, and gonadotropin-releasing hormone-II neurons in the preoptic area, IPe, arcuate nucleus of hypothalamus, and central gray substance of midbrain, respectively. GnIH neurons might thus regulate several neural systems in addition to pituitary gonadotropin release.
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