Melanin-concentrating hormone promotes feeding through the lateral septum

Feeding is necessary for survival but can be hindered by anxiety or fear, thus neural systems that can regulate anxiety states are key to elucidating the expression of food-related behaviors. Melanin-concentrating hormone (MCH) is a neuropeptide produced in the lateral hypothalamus that promotes feeding and anxiogenesis. The orexigenic actions of MCH that prolong ongoing homeostatic or hedonic feeding are context-dependent and more prominent in male than female rodents, but it is not clear where MCH acts to initiate feeding. The lateral septum (LS) promotes feeding and suppresses anxiogenesis when inhibited, and it comprises the densest projections from MCH neurons. However, it is not known whether the LS is a major contributor to MCH-mediated feeding. As MCH inhibits LS cells by MCH receptor (MCHR1) activation, MCH may promote feeding via the LS. We bilaterally infused MCH into the LS and found that MCH elicited a rapid and long-lasting increase in the consumption of standard chow and a palatable, high sugar diet in male and female mice; these MCH effects were blocked by the co-administration of a MCHR1 antagonist TC-MCH 7c. Interestingly, the orexigenic effect of MCH was abolished in a novel, anxiogenic environment even when presented with a food reward, but MCH did not induce anxiety-like behaviors. These findings indicated the LS as a novel region underlying orexigenic MCH actions, which stimulated and enhanced feeding in both sexes in a context -dependent manner that was most prominent in the homecage.