Genetic selection for body weight in chickens has altered responses of the brain's AMPK system to food intake regulation effect of ghrelin, but not obestatin

Abstract

The effects of ghrelin and obestatin regulation of food intake are different in mammals and chickens. We investigated central effects of ghrelin and obestatin in lines of chickens selected 50 generations for high (HWS) or low (LWS) body weight. We hypothesized that the effect of ghrelin and obestatin on food intake in 5-day-old chicks is mediated by the AMP-activated protein kinase (AMPK) system and selection for body weight alters the brain's response to ghrelin and obestatin by changing the neuronal AMPK system. Although intracerebroventricular (ICV) ghrelin injection decreased food intake in both lines, the threshold for the anorexigenic effect of central ghrelin was lower in LWS than HWS chicks. Obestatin caused a linear dose-dependent increase in food intake in HWS but not LWS chicks. ICV injection of 0.4 nmol ghrelin inhibited hypothalamic AMPK related gene expression and phosphorylation of AMPK α and acetyl-CoA carboxylase (ACC) with the magnitude of inhibition different in the two lines. In contrast, ICV injection of 4 nmol obestatin did not affect mRNA expression of AMPK system or phosphorylation of AMPK and ACC in either line. These data support the premise of a lower threshold for anorexigenic effect of central ghrelin in LWS than HWS chicks, and this difference may be associated with differential hypothalamic AMPK signaling. Additionally, the hypothalamic mRNA level of ghrelin was significantly higher in LWS than HWS, which may have also contributed to the different threshold response to ghrelin in these two lines. The expression of the ghrelin receptor was also higher in the LWS line, but not until 56 days of age. In summary, selection for body weight has resulted in differences in the central ghrelin and obestatin system, and an altered brain AMPK system may contribute to the different neuronal response to ghrelin, but not obestatin.