A Golgi study of Bergmann glial cells in developing rat cerebellum.

In order to examine the relationship between the Bergmann glial cells and the migrating granule cells, the postnatal development of the Bergmann glial cells in the rat cerebellum was analysed by a rapid Golgi method. In newborn rats where immature Purkinje cells occupied a rather thick zone (about 8 cells thick) between the thin molecular layer and the intermediate zone, immature Bergmann glial cells were recognized by the irregularly contoured somata situated within the deep part of the zone of Purkinje cells and by several perpendicular thin fibers (filiform fibers) which traversed the external granular layer (EGL) to terminate at the pial surface. After day 2 of the postnatal age (PD2), both somata and fibers of Bergmann glial cells showed gradual or fairly abrupt changes. The somata migrated upwards toward the molecular layer on PD2 and on PD4 were situated just beneath the Purkinje cells which had become arranged in a single layer. After PD6 the distance between the pial surface and the somata situated in the Purkinje cell layer and concomitantly the length of the Bergmann glial fibers, progressively increased in accordance with the thickening of the molecular layer. Between PD0 and PD8 the somata were irregularly contoured with short protoplasmic processes extending radially. After PD8 they gradually lost these short processes and became smooth. The Bergmann glial fibers were rather smooth with a few beady enlargements and tiny bud-like excrescences on their surface between PD0 and PD8. On PD12 the bushy expansions, characteristic of matured Bergmann glial fibers, suddenly increased in number on most fibers. After PD12 they continued to augment until PD25, when most fibers were entirely covered with the expansions. The number of fibers issuing from each Bergmann glial cell and entering the EGL increased postnatally reaching a peak on PD8, and then decreased gradually. These changes in the number of Bergmann glial fibers corresponded well with those in the number of external granule cells, suggesting the presence of developmental interactions between these two kinds of cells.