Metabolic fuels, neuropeptide Y, and estrous behavior in Syrian hamsters

Of the various environmental factors influencing reproduction, food availability plays a particularly significant role, and an insufficient supply of oxidizable metabolic fuels inhibits reproduction in female mammals. When ovariectomized, steroid-primed hamsters are food deprived for 48 h, estrous behavior is suppressed. However, the specific neuroendocrine alterations that mediate the suppression of estrous behavior are unknown. Several conditions that inhibit female sexual behavior are thought to be associated with altered neuropeptide Y (NPY) activity in the brain. Intracerebroventricular (ICV) infusion of NPY inhibits estrous behavior in ovariectomized steroid-primed rats and hamsters. Furthermore, food-deprived rats have an increase in NPY mRNA in the arcuate nucleus (ARC) of the hypothalamus. Unlike rats, studies in Syrian hamsters have failed to detect any alterations in ARC NPY mRNA following food deprivation. Here we show that ARC NPY immunoreactivity and mRNA is increased in food-deprived hamsters but not in hamsters given other metabolic challenges that inhibit estrous behavior. These findings support the hypothesis that NPY contribute to, but not be critical for, the nutritional inhibition of sexual receptivity.