White matter astrocytes: adrenergic mechanisms

White matter (WM) tracts contain bundles of myelinated axons and the glia that support them, namely oligodendrocytes that form the myelin and astrocytes, which provide structural and homeostatic support, together with small populations of microglia and oligodendrocyte precursor cells. Neurotransmitter signaling is prominent in WM, and there is a significant role for adrenergic signaling, together with glutamatergic and purinergic mechanisms. The site of axoglial signaling in myelinated axons is the node of Ranvier, which is the site of action potential propagation and displays many properties of synapses. Neurotransmitters released during axonal electrical activity activate receptors on perinodal astrocytes, to stimulate their release of gliotransmitters that integrate function within axon–glial–vascular networks. One of the key functions of astroglial adrenergic signaling in WM is to maintain energy supply to axons and oligodendrocytes, ensuring efficient and rapid information transfer throughout the central nervous system and maintaining WM integrity in times of energy stress.