Blood-to-brain communication in the hypothalamus for energy intake regulation.

The arcuate nucleus (Arc) integrates circulating hormonal and metabolic signals to control energy expenditure and intake. One of the most important routes that enables the Arc to sense circulating molecules is through the median eminence (ME), which lacks a typical blood-brain barrier. However, the mechanism by which circulating molecules reach the Arc neurons remains unclear. This review focuses on what is known to date regarding the special structure and permeability of the ME vasculature and active transport of circulating molecules from the ME to the Arc. Recent studies have demonstrated that the ME displays angiogenic behavior that is expected to provide high vascular permeability. Parenchymal diffusion of circulating molecules from the ME vasculature is size-dependent, and tanycytes actively transport circulating molecules from the ME to the Arc. Finally, we highlight structural plasticity of the Arc and ME as playing an important role in maintaining energy balance homeostasis.