The Role of Neuronal-Glial Cell Interaction During Brain Development

Abstract

Recent immunocytochemical studies using glial specific marker show that neuronal and glial cell classes coexist in the developing primate brain earlier than has hitherto been assumed, and that they originate from separate precursors that are present in the proliferative zones. DNA labeling indicates that one transient subclass — the radial glial cells — does not divide for about two months during the peak period of neurogenesis. During this period their elongated processes may play a crucial role in the compartmentalization of the nervous system and may serve as guides for migrating neurons as they traverse the distance between their sites of origin near the ventricular surface and their final destinations. The cellular mechanisms responsible for this movement, as well as the possible involvement of glial fibers in the formation of extracellular spaces and in the transfer of information and/or nutrients via intracytoplasmic transport during development, remain to be clarified. At somewhat later stages the astrocytes that are produced directly from glial precursors or by a morphogenetic transformation from radial glial cells, construct the membrana limitans gliae that forms the brain surface, separate differentiating neurons during synaptogenesis, and remove degenerating cells, axons, and synaptic terminals. Genetic or acquired abnomalities of glial cells may impair the completion of the normal developmental process and lead to various brain abnormalities.