Cellular and chemical changes during myelination: Histologic, autoradiographic, histochemical and biochemical data on myelination in the pyramidal tract and corpus callosum of rat

Abstract

Abstract A quantitative study of myelination in the pyramidal tract and in the corpus callosum of rat was undertaken to establish the order and the possible correlation of various cellular and chemical changes in the tissue. Myelination was initiated by a period of thymidine‐H 3 labeling of nuclei and g±al proliferation, resulting in a rapid increase in the cell density or “myelination gliosis.” Slightly later, there was an increase in NAD‐diaphorase activity and in leucine‐H 3 uptake in both the glia cells and throughout the tissue. The formation of myelin sheaths began when myelination gliosis was established; it overlapped the periods of high enzyme activity and high leucine‐H 3 uptake. Cell proliferation continued during myelin formation after the onset of myelination gliosis; the cell density in the pyramidal tract decreased during this period, probably because the spacing of the cells increased due to the growth of the myelin sheaths. Staining of myelin sheaths was estimated with a semi‐quantitative method and paralleled an increase in biochemical assays of total cholestrol. The significance and possible interrelations between the morphological and chemical changes during myelination are discussed.