Recent research reveals that astrocytes, a key type of non-neuronal brain cell, undergo significant volume fluctuations synchronized with the sleep-wake cycle. Using advanced in vivo imaging, scientists discovered that these cells expand during wakefulness and shrink during sleep, reaching their smallest size during the REM stage. This structural remodeling is primarily driven by the neurotransmitter norepinephrine acting on $\alpha$1-adrenergic receptors. When norepinephrine levels rise during arousal, astrocytes swell, which subsequently constricts the interstitial space and likely limits the brain's waste-clearing glymphatic flow. Conversely, the reduction of astrocytic volume during sleep opens up the pathways between cells, potentially facilitating the removal of metabolic toxins. These findings establish a direct link between neuromodulatory tone and the physical geometry of the brain's cellular environment.

References:

• Deng S, Hu Y, Chen X, et al. Astrocyte cell volume dynamics across cortical states and transitions[J]. Neuron, 2026.