Arcuate nucleus homeostatic systems are not altered immediately prior to the scheduled consumption of large, binge-type meals of palatable solid or liquid diet in rats and mice

Meal feeding is a critical issue in over-consumption of calories leading to human obesity. To investigate the mechanisms involved in the regulation of meal feeding in rodents, we studied a scheduled feeding regime that induces substantial food intake over short periods of time. Male Sprague-Dawley rats and C57BL6 mice were fed one of four palatable diets (45% fat pellet, 60% fat pellet or standard pellet supplemented with Ensure (EN) or 12.5% sucrose) either ad libitum or with daily 2h-scheduled access and standard pellet available for 22h. Energy balance gene expression in the hypothalamic arcuate nucleus (ARC) and nucleus accumbens (NAcc) reward gene expression were assessed by in-situ hybridisation. Rats fed ad libitum on 45% or 60% fat diet were heavier and fatter than controls, and had reduced neuropeptide Y (NPY) gene expression in the ARC. Mice fed ad libitum on any of the palatable diets were heavier, fatter and had higher blood leptin than controls, and had reduced NPY and increased cocaine-and-amphetamine-regulated transcript mRNA in the ARC. Schedule-fed rats and mice quickly adapted their feeding behaviour to 2h-access on palatable food. Three schedule-fed groups binged: the percentage of daily calories consumed in 2h on 45% fat diet, 60% fat diet or EN, respectively, was 55%, 63% and 49% in rats, and 86%, 86% and 45% in mice. However, changed feeding behaviour was not reflected in an induction of orexigenic neuropeptide or suppression of anorexigenic neuropeptide gene expression in the ARC, in the 2h-period prior to scheduled feeding. Mechanisms underlying large meal/binge-type eating may be regulated by non-homeostatic processes involving other genes in the hypothalamus or other brain areas. However, assessment of opioid and dopamine receptor gene expression in the NAcc did not reveal evidence of involvement of these genes in driving large meals, at least at the investigated time point. © 2012 British Society for Neuroendocrinology.