The astrocyte as a component of the node of Ranvier

Abstract

A number of recent studies have demonstrated the presence of astrocytic processes that contact the axon at nodes of Ranvier in the CNS. These studies suggest that, in addition to the axon and the myelin-forming oligodendrocyte, the perinodal astrocyte constitutes a third cell type participating in the formation of CNS nodes of Ranvier. However, the earlier studies left open the question of how the astrocyte is attached to the node. Recent immunocytochemical studies 1 have extended the observations on the perinodal astrocyte, and demonstrate that the Jl glycoprotein, a recently described 160 kDa molecule that has been postulated to play a role in cell-cell adhesion in the nervous system, is concentrated specifically at the interface between the perinodal astrocyte processes and the axons. These findings not only provide evidence for a biochemical specialization of the perinodal astrocyte processes, but also suggest a molecular mechanism by which the astrocyte interacts with the axon and its associated oligodendrocytes at the node.