Nodes of Ranvier during development and repair in the CNS

Nodes of Ranvier are unmyelinated domains that enable fast saltatory propagation of action potentials along myelinated axons. This Review describes the organization and function of CNS nodes of Ranvier and considers how these nodes change in demyelinating and remyelinating disorders. Saltatory conduction of action potentials along myelinated axons depends on the nodes of Ranvier - small unmyelinated axonal domains where voltage-gated sodium channels are concentrated. Our knowledge of the complex molecular composition of these axonal domains continues to accumulate, although the mechanisms of nodal assembly, which have been elucidated in the PNS, remain only partially understood in the CNS. Besides the key role of the nodes in accelerating conduction, nodal variations are thought to allow the fine tuning of axonal conduction speed to meet information processing needs. In addition, through their multiple glial contacts, nodes seem to be important for neuron-glia interactions. As we highlight in this Review, the disorganization of axonal domains has been implicated in the pathophysiology of various neurological diseases. In multiple sclerosis, for example, nodal and perinodal disruption following demyelination, with subsequent changes in ion channel distribution, leads to altered axonal conduction and integrity. The nodal clusters regenerate concurrently with but also prior to remyelination, allowing the restoration of axonal conduction. In this article, we review current knowledge of the organization and function of nodes of Ranvier in the CNS. We go on to discuss dynamic changes in the nodes during demyelination and remyelination, highlighting the impact of these changes on neuronal physiology in health and disease as well as the associated therapeutic implications.