Long-projection astrocytes challenge canonical territorial organization in the sleep-promoting VLPO

Abstract The ventrolateral preoptic nucleus (VLPO) is a key hypothalamic hub for non-rapid eye movement sleep, yet the glial architecture supporting its circuits remains poorly understood. Here, combining genetic labeling, high-resolution imaging and calcium imaging, we uncover unexpected astrocyte diversity in the VLPO. In addition to classical protoplasmic astrocytes, we identify paired “doublet” astrocytes associated with high local proliferative activity, as revealed by EdU incorporation. We further describe a population of long-projection astrocytes extending processes far beyond canonical astrocytic territories and contacting distant cells. These projections challenge the classical territorial organization of astrocytes and resemble morphologies previously thought to be restricted to hominid brains. Notably, VLPO astrocytes display robust spontaneous Ca²⁺ activity and a highly functionally connected network compared to astrocytes in the cortex and hippocampus. Together, these findings reveal specialized astrocyte architectures and enhanced glial network integration within a sleep-promoting nucleus. Reporting summary Bellier et al. identify three astrocyte subtypes in the sleep-promoting VLPO, including long-projection astrocytes with hominid-like morphology. They uncover marked postnatal gliogenesis, distinctive spontaneous Ca²⁺ dynamics, and tightly interconnected astrocytic networks, revealing region-specific astrocyte specialization and enhanced glial communication.