Food Restriction Affects the Gonadotropin Releasing Hormone Neuronal System of Male Prairie Voles (Microtus ochrogaster)

Abstract

Individuals of species inhabiting temperate and boreal latitudes optimize the timing of energetically costly processes by curtailing nonessential energetically demanding processes when environmental conditions are not favourable. One proximate environmental variable used to fine-tune moment-to-moment changes in reproductive physiology and behaviour is food intake. The neuroendocrine mechanisms by which food restriction leads to the cessation of reproduction in seasonally breeding rodent species remain largely unspecified. The present study sought to determine the effects of extended food restriction on the gonadotropin releasing hormone (GnRH) neuronal system. Male prairie voles (Microtus ochrogaster) were either fed ad libitum or were exposed to either 1, 2 or 3 weeks of moderate (70% of daily mean) food restriction. In accordance with previous studies of food restriction, gross reproductive organ masses and body mass were unaffected by food deprivation. Although 1 week of food restriction did not result in alterations in the GnRH neuronal system, food restriction for 2 weeks was associated with increased GnRH-immunoreactive (GnRH-ir) neurone soma size. Three weeks of food restriction resulted in a pronounced increase in GnRH-ir neurone numbers, as well as an increase in fibre intensity in the main fibre pathway to the median eminence. Taken together, these findings suggest that extended food restriction leads to modifications in the GnRH neuronal system, providing a means for temporary cessation of reproduction without gross alterations in reproductive physiology. This transient change in the hypothalmo-pituitary-gonadal axis, without pronounced changes in reproductive organ morphology, likely provides a mechanism for the rapid reinitiation of breeding in nature when local conditions provide adequate food availability.

Photoperiod-Independent Hypothalamic Regulation of Luteinizing Hormone Secretion in a Free-Living Sonoran Desert Bird, the Rufous-Winged Sparrow <i>(Aimophila carpalis)</i>

“…Some studies report an increase in GnRH cell body size associated with decreased plasma LH and decreased sexual behavior [Foster et al, 1988;Urbanski et al, 1991;Kriegsfeld et al, 2001;Tsai and Jones, 2005]. These studies generally interpret this as GnRH production exceeding GnRH release, causing GnRH to accumulate in the cells and cell bodies to expand.…”

Tonic Activation of Brain GnRH Immunoreactivity despite Reduction of Peripheral Reproductive Parameters in Opportunistically Breeding Zebra Finches

“…After photostimulation, circulating LH concentration can increase within 18 h of exposure to the fi rst long day [20L:4D; e.g., Meddle and Follett, 1995]. Other environmental cues, such as temperature and food availability, can also have effects at all points along the HPG axis [Bruggeman et al, 1998;Kriegsfeld et al, 2000Kriegsfeld et al, , 2001, but their neuroendocrine transduction has been less well-studied.…”

Food-deprivation-induced suppression of pituitary–testicular-axis in the tilapia Oreochromis mossambicus

“…The expression of the GtH genes was not affected by food restriction in mature female goldfish (Sohn et al 1998), whereas when food-restricted rats were given unrestricted access to food, the frequency of LH and growth hormone (GH) pulses and the mean levels of FSH increased significantly within 2 days (Sisk and Bronson 1986). Even at the hypothalamic level, although 1 week of food restriction did not result in alterations in the gonadotrophin-releasing hormone (GnRH) neuronal system, food restriction for 2-3 weeks was associated with increased GnRH-immunoreactive neuronal soma size and numbers as well as an increase in fibre intensity in the main fibre pathway to the median eminence in male prairie vole Microtus ochrogaster (Kriegsfeld et al 2001). These results suggest a stimulatory influence of starvation on hypothalamo-pituitarygonad (HPG) axis.…”