Cell proliferation and DNA-synthesis in the external granular layer of the postnatal rat cerebellum: a quantitative...

The external granular layer (EGL) of the rat cerebellum can be subdivided into two morphologically distinct zones, the outer of which consists of proliferating cells, while the inner has generally been considered to contain post-mitotic cells exclusively. Two criteria, the detection of mitotic figures and the observation of nuclei labelled shortly after an injection of [3H]-thymidine, were used to locate proliferating cells. Their distribution across the layer was quantified for several ages of animal. Though most frequent superficially, cell proliferation was found to occur at all levels of the EGL. Possible explanations for the existence of a gradient of proliferative activity across the EGL are discussed.