Beyond the neuron: astroglial regulation of mammalian sleep.

The cellular substrates of sleep are incompletely described, but historically they have been thought to be neuronal. According to one view, sleep is produced by interactions between wake-promoting neurons, sleep-inducing neurons, and sleep-inducing substances released by neurons (e.g. adenosine)[1, 2]. Alternatively, sleep pressure may arise independently among subsets of neurons in a use-dependent fashion within the neocortex (i.e. 'local' sleep) [3, 4]. Implicit in both views is the notion that changes in neuronal activity (or plasticity) is the principle mechanism driving sleep homeostasis. Recent findings, however, suggest that the glial cells known as astrocytes may play critical roles in mammalian sleep.