Cerebellar foliation in rats. 4. Mid-line distortion of the primary fissure in normal postnatal rats.

Two types of mid-line distortion affecting the primary fissure of the cerebellum in foetal rats were recently described (Conradi 1987a). During the postnatal period, cells of the external granular layer (EGL) in distorted regions differentiated to granule cells, forming a heterotopic granule cell layer replacing the deeper portion of the fissure. Differentiated heterotopic granule cells were seen close to normal EGL. Formation and growth of lobules V and VI, apart from the partial fusion at the mid-line, was not affected by the distortions. The findings support the previous suggestion that foliation is relatively independent of formation of a fissure. A network of capillaries was formed in the heterotopic granule cell layer and was continuous with capillaries in the molecular layer of lobules V and VI. The frequency of capillaries in the heterotopias increased in parallel with an increased activity of oxidative enzymes, simulated that in the internal granule cell layer and was higher than that in the molecular layer. These findings support the suggestion of a correlation between nerve-cell differentiation and capillary growth.