Effects of intracerebroventricular and intra-accumbens melanin-concentrating hormone agonism on food intake and energy expenditure.

The brain melanin-concentrating hormone (MCH) system represents an anabolic system involved in energy balance regulation through influences exerted on the homeostatic and nonhomeostatic controls of food intake and energy expenditure. The present study was designed to further delineate the effect of the MCH system on energy balance regulation by assessing the actions of the MCH receptor 1 (MCHR1) agonism on both food intake and energy expenditure after intracerebroventricular (third ventricle) and intra-nucleus-accumbens-shell (intraNAcSH) injections of a MCHR1 agonist. Total energy expenditure and substrate oxidation were assessed following injections in male Wistar rats using indirect calorimetry. Food intake was also measured. Pair-fed groups were added to evaluate changes in thermogenesis that would occur regardless of the meal size and its thermogenic response. Using such experimental conditions, we were able to demonstrate that acute MCH agonism in the brain, besides its orexigenic effect, induced a noticeable change in the utilization of the main metabolic fuels. In pair-fed animals, MCH significantly reduced lipid oxidation when it was injected in the third ventricle. Such an effect was not observed following the injection of MCH in the NAcSH, where MCH nonetheless strongly stimulated appetite. The present results further delineate the influence of MCH on energy expenditure and substrate oxidation while confirming the key role of the NAcSH in the effects of the MCH system on food intake.