Presence of radial glia in foetal mouse cerebellum.

The ventricular layer (VL) of foetal mouse cerebellum at days 13--15 of gestation was studied by light and electron microscopy. In Golgi-stained material, round or ovoid cells are located in the VL. These cells have ascending processes, which extend to the pial surface. Ultrastructurally, the ascending processes are electron-lucent, contain microfilaments, some smooth endoplasmic reticulum and scant free ribosomes. They appear to be immature glial processes, oriented radially away from the ventricle. The perikarya of these glial cells lie either in the ventricular or subventricular zones. Juxtaposed along the length of these radially oriented glial processes are unidentified cells, some of which are attached to the immature glial fibres by puncta adhaerentia. These cells are elongated or ovoid with a thin rim of cytoplasm containing few organelles. These unidentified cells may represent neuroblasts (Purkinje cells, Golgi cells, cells of the deep cerebellar nuclei) or glioblasts, (precursors of astrocytes and/or oligodendrocytes) at very early stages of development.