Hypothalamic AGRP mRNA is elevated during natural and stress-induced anorexia

Animals can undergo periods of voluntarily reduced food intake and body weight or “animal anorexias” as part of their natural lives that are beneficial for survival or breeding such as during territorial behaviour, hibernation, migration and incubation of eggs. For incubation, a change in the defended level of body weight or “sliding set point” appears to be involved but the neural mechanisms are unknown. We investigated how neuropeptide gene expression in the arcuate nucleus of the domestic chicken responded to a 60-70% voluntary reduction in food intake measured both after incubation and after an environmental stressor involving transfer to unfamiliar housing. We hypothesized that gene expression would not change in these circumstances because the reduced food intake and body weight represented a defended level in birds with free access to food. Unexpectedly, we observed increased gene expression of the orexigenic peptide AGRP in both incubating and transferred animals compared to controls. Also POMC mRNA was higher in incubating hens and significantly increased six days after exposure to the stressor. Conversely NPY and CART gene expression were unchanged in both experimental situations. We conclude that AGRP expression remains sensitive to the level of energy stores during natural anorexias, which is of adaptive advantage, but that its normal orexigenic effects are overridden by inhibitory signals. In the case of stress-induced anorexia, increased POMC may contribute to this inhibitory role whereas, for incubation, reduced feeding may also be associated with increased expression in the hypothalamus of the anorexigenic peptide VIP.