Proliferation and turnover of glial cells in the forebrain of young adult mice as studied by repeated injections of ³H‐thymidine over a prolonged period of time

The magnitude of glial cell renewal was studied on young adult mice using repeated intraperitoneal injections of 3 H‐thymidine every eight hours over a period of 30 days. Mean labeling indices one hour after the last injection were as follows: Glial cells of the subependymal layer of the lateral ventricle, 61.5%; oligodendrocytes (various sites), 24 to 36.2%; astrocytes (various sites), 14.3 to 30.8%, and satellites in the cerebral cortex, 32.7%. Since DNA synthesis time of the proliferating, immature glial cells is unknown and may be shorter than the time interval of eight hours chosen for repeated injections of 3 H‐thymidine, these results are interpreted as representing minimum values for turnover, during 30 days, of the various cell types in different areas of the forebrain. The significance of a marked proliferative activity of the glial cells as related to differentiation and possible migration of subependymal cells, is discussed.