Dorsomedial hypothalamic NPY and energy balance control.

Neuropeptide Y (NPY) is a potent hypothalamic orexigenic peptide. Within the hypothalamus, Npy is primarily expressed in the arcuate nucleus (ARC) and the dorsomedial hypothalamus (DMH). While the actions of ARC NPY in energy balance control have been well studied, a role for DMH NPY is still being unraveled. In contrast to ARC NPY that serves as one of downstream mediators of actions of leptin in maintaining energy homeostasis, DMH NPY is not under the control of leptin. Npy gene expression in the DMH is regulated by brain cholecystokinin (CCK) and other yet to be identified molecules. The findings of DMH NPY overexpression or induction in animals with increased energy demands and in certain rodent models of obesity implicate a role for DMH NPY in maintaining energy homeostasis. In support of this view, adeno-associated virus (AAV)-mediated overexpression of NPY in the DMH causes increases in food intake and body weight and exacerbates high-fat diet-induced hyperphagia and obesity. Knockdown of NPY in the DMH via AAV-mediated RNAi ameliorates hyperphagia, obesity and glucose intolerance of Otsuka Long-Evans Tokushima Fatty rats in which DMH NPY overexpression has been proposed to play a causal role. NPY knockdown in the DMH also prevents high-fat diet-induced hyperphagia, obesity and impaired glucose homeostasis. A detailed examination of actions of DMH NPY reveals that DMH NPY specifically affects nocturnal meal size and produces an inhibitory action on within meal satiety signals. In addition, DMH NPY modulates energy expenditure likely through affecting brown adipocyte formation and thermogenic activity. Overall, the recent findings provide clear evidence demonstrating critical roles for DMH NPY in energy balance control, and also imply a potential role for DMH NPY in maintaining glucose homeostasis.