Proliferation of neuroglial cell lines in the degenerating optic nerve of young rats. A radioautographic study.

Wallerian degeneration was investigated in the rat optic nerve after eye enucleation at 2, 5, 8, and 20 D.P.N. (key stages), corresponding to the periods of premyelination, myelination, and postmyelination. The incorporation of tritiated thymidine, and subsequent radioautography of semithin sections, allowed the identification and enumeration of labeled cells, and the computation of labeling indices of the different cell types (glioblasts, astrocytes, oligodendrocytes, and microglia) in the operated as well as the contralateral nerve. The comparison of labeling indices and absolute numbers of labeled cells in each category suggests an increased transformation of glioblasts into astrocytes, and absence of differentiation and stabilization of oligodendrocytes due to the failure of the axonal signal, and a transformation of pericytes into interstitial microglia. The first three key stages (2, 5, and 8 D.P.N.) are characterized by the integration of reactive gliosis and more or less marked failure of myelination gliosis, whereas the last one (20 D.P.N.) shows essentially a reactive gliosis. The modifications of the neural environment interfere with the genetic program of gliogenesis, illustrating the postnatal plasticity of the central nervous system.