Macroglial Cell Types, Lineage, and Morphology in the CNS

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Abstract
The characterization of macroglial antigenic phenotypes has provided considerable information on the classification of glial subtypes and lineage, but the picture in vivo appears to more complex than originally surmised from in vitro systems. Whether type-2 astrocytes and O-2A progenitors play a significant part in vivo remains controversial, but these questions have generated a valuable reassessment of inferences made from in vitro studies. It is not known whether disparate regions of the nervous system have different glial cell types with distinct cell lineages, but results in peripheral nerve and the cortex (see Price and colleagues, and Jessen and colleagues, this volume) suggest that this is likely the case. The heterogeneity of astrocytic form and the implied divergence of function in vivo parallel but have yet to be equated with the wide range of antigenic and electrophysiologic characteristics that can be induced in glia under certain culture conditions in vitro. Whether similar conditions prevail within the developing nervous system is not clear. The continued development of immunocytochemical markers and the use of retroviral vectors, combined with morphologic and electrophysiologic studies in vivo and in vitro, will undoubtedly answer these and other questions.