New routes to the neuroendocrine hypothalamus: the extracellular space

The neuroendocrine hypothalamus integrates peripheral nutritional and hormonal cues to regulate essential physiological processes, including appetite, metabolism, and reproduction. While the mechanisms by which hormones traverse the blood-brain barrier to access the hypothalamic parenchyma are well characterized, how these signals subsequently diffuse and distribute within the brain's extracellular space and matrix remains poorly understood. Emerging evidence implicates specialized components of the extracellular matrix (ECM), such as perineuronal nets (PNNs), in modulating hormonal and nutrient bioavailability, as well as neuronal excitability and plasticity. In the hypothalamus, extracellular matrix components are highly dynamic and respond to nutritional and hormonal cues. In preclinical models of metabolic disorders involving the neuroendocrine system-such as obesity and type 2 diabetes-these components undergo maladaptive remodelling. This review discusses recent advances in our understanding of how the extracellular environment shapes neuroendocrine signaling in the hypothalamus and explores the broader implications for systemic hormonal regulation and neuroendocrine disease pathophysiology.