Astrocytes and the modulation of sleep.

Astrocytes are being identified as having multiple roles in sleep. Initially they were shown to modulate the process of sleep homeostasis through the release of adenosine which acts on adenosine A1 receptors (A1R) to promote sleep drive. More recent studies indicate that the astrocyte also plays pivotal, sleep-dependent roles in 'cleaning the brain' during sleep. This work indicates that a glymphatic pathway that critically relies on astrocytic aquaporin 4, is able to flush solutes from the brain and that deficits in this pathway may contribute to Alzheimer's disease. Finally, astrocytes are known to play important metabolic roles and provide energy on demand to neurons through an astrocyte-neuron shuttle. Given that the time course of astrocytic function is orders of magnitude slower than that of the neuron, this non-neuronal cell is perfectly tuned to modulating slow, state-dependent changes in the brain.