Fasting Reduces Luteinizing Hormone Secretion in the Pekin Drake, Part I: Localization of and Effects of Fasting on Galanin-Like Peptide Expression in the Hypothalamus

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 a neuropeptide that is known to regulate feeding and reproduction, galanin-like peptide (GALP). 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 GALP-immunoreactivity (ir). Circulating LH levels were significantly (p \u3c 0.05) reduced after 24 hrs of fast. A significant increase (p \u3c 0.01) in fos-ir was found in the hypothalamic paraventricular nucleus (PVN) in fasted drakes compared to fed controls. In fed drakes, GALP-ir was localized to the infundibular nucleus (INF), the avian analog to the arcuate nucleus. There was virtually a complete loss of GALP-ir in the INF) in fasted compared to fed drakes. These data suggest that GALP neurons stimulate LH secretion and GALP peptide expression is regulated by metabolic state