Light microscopic radioautographic study on DNA synthesis of nerve cells in the cerebella of aging mice.

The morphological change and DNA synthesis of nerve cells in the cerebella of the aging mice were investigated by light microscopic radioautography using tritiated thymidine injection in vivo. During a period ranging from late fetal life to certain postnatal stages, 9 groups of mice were used. The labelled nuclei, which involved both the precursors of neurons and the glioblasts, were observed in the external granular layer of the cerebellum from embryonic day 19 to postnatal day 14. It disappeared completely at 1 month. A peak of labeling index was observed at postnatal day 3. The glioblasts of the external granular layer migrated inward, some of them forming the Bergmann glia cells located between Purkinje cells, this at postnatal day 8, some penetrating in the internal granular layer. Labelled nuclei in the internal granular layer were also observed and a maximum of the labeling was seen at postnatal day 3, similarly to the external granular layer. With the development and the expansion of the cerebellum, the endothelial cells of the cerebellar vessels were progressively labelled, reaching a maximum during the first postnatal week. The obtained results provided consequently some data on the age-related changes of DNA synthesis of mouse cerebellum from later embryonic stages to postnatal stages. Different investigations will be necessary to explain these irregular sequences of labeling.