Study in the changes of the proportions and numbers of the various glial cell types in the spinal cord of neonatal and young adult rats.

Glioblasts, astrocytes, microglia and the three classes of oligodendroyctes were enumerated in the grey and white matter of the spinal cord of rats of various ages. Both regions showed fairly similar results. Glioblasts, which made up the major glial population in the newborn rats, declined steadily with age and their number became negligible by 22 days post natum. They were absent in the young adult rats (aged 70 days). Contrary to this, the major glial types increased rapidly with age, the increase being most drastic in the oligodendrocytic population. The growth continued through about 22 days after birth and became more or less stabilized thereafter. Of the three classes of oligodendrocytes, the light cells appeared to develop first, followed by the medium dense cells and subsequently the dark ones. While there was a gradual disappearance of the light and medium dense cells with age, there was an accumulation of the dark cells, so that they were predominant in the spinal cord of the young adult rats.