A Morphometric Study on Postnatal Development of the External Granular Layer of Mice Cerebella, Focusing on Local Difference

The external granular layer (EGL) of the cerebellum thickens, thins and disappears in its developmental process. We examined the thickness of the EGL, both intralobule differences and interlobule differences, in the whole midline sections of mouse cerebella for the entire postnatal period up to disappearance. The thinnest site in each lobule was located at the outer apex throughout the observation period, the thickest site was the portion facing the inner apex during early period, and that facing the convexity where the EGL curved in the later period. The observed interlobular differences of the EGL thickness were statistically divided into three groups, referred to as the early developing group (EDG), the late developing group (LDG), and the mixed-type group (MTG). The EDG consisted of the whole anterior lobe and a site in lobule VI facing the fissura prima. These sites thickened earlier, and showed a similar thickness on each observation day. The LDG was composed of all sites in the posterior lobe, with the exception of two sites where lobules VIII and IX confronted each other as well as the site included in the EDG. The sites in the LDG thickened later. They demonstrated a similar thickness during thickening, but varied during thinning. The MTG, consisting of two sites where lobules VIII and IX facied each other, showed features similar to the EDG in the mitotic zone and the LDG in the premigratry zone. These data may serve as the basis for studies on regional differentiation of the cerebellum.