Glial proliferation in the irradiated rat spinal cord.

The identity of mitotic cells in the ventral half of the irradiated spinal cord in 13-day-old rats was studied by light and electron microscopy. At this post-irradiation interval, astrocytes as well as oligodendrocytes are markedly reduced in both gray and white matter, and few myelin sheaths are present. Earlier studies showed incorporation of 3H-thymidine into cells identified light-microscopically as neuroglia. In the present study, a number of mitotic cells were identified in thick plastic sections. When adjacent thin sections were examined by electron microscopy, these mitotic cells were identified ultrastructurally as astroglia on the basis of the bundles of filaments in their cytoplasm and the irregular outline of the cell body and its processes. It is apparent from this study that astroglia proliferate prior to the delayed myelination that occurs later in the glial cell deprived ventral irradiated cord.