Myelinogenesis in optic nerve. A morphological, autoradiographic, and biochemical analysis

Morphologic, autoradiographic, and biochemical methods were used to study the time of appearance, distribution, and nature of sulfated constituents in the developing rat optic nerve. Electron microscopic studies showed that myelination begins (6 days postnatal) shortly after the appearance of oligodendroglia (5 days postnatal). Over the ensuing 3 wk, myelination increased rapidly. During the 1st postnatal wk, mucopolysaccharides and glycoproteins were labelled with ³⁵S and autoradiographs showed grains over arachnoidal cells, astroglia, and the glia limitans. The results indicated that astroglia synthesize sulfated mucopolysaccharides of the glia limitans. After the onset of myelination, however, the major portion of [³⁵S]sulfate was incorporated into sulfatide. Autoradiographs showed a shift of radioactive grains from astroglia and arachnoidal cells to myelin, indicating that actively myelinating oligodendroglia incorporate [³⁵S]sulfate into myelin sulfatide; there was a concomitant increase in the activity of cerebroside sulfotransferase. In addition, the increasing amounts of proteolipid protein and myelin basic protein correspond with the morphologic appearance of myelin. These results point to a strict correlation between the structural and biochemical changes occurring during myelination. This system provides a useful model for studies designed to evaluate the effects of various perturbations on the process of myelination.