Fasting Reduces Luteinizing Hormone Secretion in the Pekin Drake, Part II: Localization of and Effects of Fasting on Gonadotropin-Inhibitory Hormone Expression in the Hypothalamus

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Dr. Gregory Fraley, Hope College

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Pekin ducks are seasonal breeders that are also very sensitive to nutritional status. It is known that fasting reduces reproductive hormone secretion, however the neurobiology underlying this effect is not clear. The purpose of this study was to first confirm that fasting reduces plasma luteinizing hormone (LH) levels in male ducks. Second we set out to determine if the reduced LH levels were associated with changes in the hypothalamic expression of a neuropeptide known to regulate feeding and reproduction, gonadotropin inhibitory hormone (GnIH). Groups of adult male Pekin ducks (~60 weeks of age) were either fed or fasted for 17, 24 or 48 hours (n = 6 per group). At the end of each time point, drakes were euthanized by cervical dislocation and blood collected for plasma determination of LH levels. Brains were removed and processed for immunocytochemical detection of fos-, and/or GnIH-immunoreactivity (ir). Circulating LH levels were significantly (p < 0.05) reduced after 24 hrs of fast. As with all other avian species, GnIH-ir was localized to the hypothalamic paraventricular nucleus (PVN). A significant increase (p < 0.01) in fos-ir was found in the PVN in fasted drakes compared to fed controls. Many of the fos-ir neurons within the PVN also colocalized GnIH-ir. These data suggest that GnIH neurons are important mediators between the feeding and reproductive systems in Pekin drakes.

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