The Perinodal Astrocyte: Functional and Developmental Considerations

Abstract

Since perinodal astrocytes were first described more than two decades ago (Hildebrand 1971a,b), the presence of astrocyte processes which contact the node of Ranvier has been documented in numerous CNS tracts and in many species (Waxman and Black 1984; Hildebrand and Waxman 1984; Raine 1984; Sims et al. 1985; Bodega et al. 1987; Sims et al. 1991). Perinodal astrocytes are associated with myelinated axons in a highly specific manner at the nodes of Ranvier. Thus, each myelinated axon in the CNS is contacted by numerous perinodal astrocytes. Despite the ubiquity of these specialized cells, however, their functions remain obscure. Over the past few years, our laboratory has carried out ultrastructural, immunocytochemical, electrophysiological, and biophysical studies on astrocytes in white matter (see e.g., Black et al. 1989a,b; Minturn et al. 1990, 1992; Sontheimer et al. 1991a,b,c) which have begun to delineate the properties of these cells. Several other laboratories have also provided new information that may be relevant to the properties of perinodal astrocytes (e.g., Nowak et al. 1987; Barres et al. 1988, 1989, 1990; Bevan et al. 1985; Gray and Ritchie 1986; Ransom and Carlini 1986). The present chapter will briefly review some of the more recent studies from these laboratories which provide information about astrocyte properties, and will examine the question, What do perinodal astrocytes do?