Astrocyte Ca 2+ -evoked ATP release regulates myelinated axon excitability and conduction speed

Glia control white matter information flow The myelinated axons of the white matter mediate rapid information transmission between the brain’s processing nodes. Axonal excitability and conduction speed are key determinants of neural circuit function, but it is largely unknown how they are regulated. Lezmy et al . examined the effects of adenosine on the functional properties of myelinated axons. They observed activity-dependent calcium rise in astrocyte processes, calcium-triggered ATP release from astrocytes, activation of adenosine receptors in the axon initial segment and the nodes of Ranvier, increased cyclic AMP concentration, activation of HCN2 channels, and depolarization of axons by 5 to 10 millivolts. This molecular pathway enabled astrocytes to increase the excitability of pyramidal neurons and to profoundly decrease the axonal conduction velocity. Astrocytes thus control signaling speed in myelinated axons. —PRS