Astroglial regulation of sleep homeostasis.

Mammalian sleep is regulated by two distinct mechanisms. A circadian oscillator provides timing signals that organize sleep and wake across the 24 hour day. A homeostatic mechanism increases sleep drive and sleep amounts (or intensity) as a function of prior time awake. The cellular mechanisms of sleep homeostasis are poorly defined, but are thought to be primarily neuronal. According to one view, sleep homeostasis arises from interactions between subcortical neurons that register sleep pressure and other neurons that promote either sleep or wakefulness. Alternatively, sleep drive may arise independently among neurons throughout the brain in a use-dependent fashion. Implicit in both views is the idea that sleep homeostasis is solely the product of neurons. In this article, I discuss an emerging view that glial astrocytes may play an essential role in sleep homeostasis.