Postnatal development of the cerebellar cortex in the rat. III. Maturation of the components of the granular layer

Abstract The migration of granule cells and the maturation of the various elements of the granular layer were studied in the cerebellar cortex of rats aged 0, 3, 5, 7, 10, 12, 15, 21 and 30 days with histological, histochemical, autoradiographic and electron microscopic techniques. The bulk of the granule cells are formed during the second week, but due to the time required for their migration and the lag in the formation of dendrites, few glomerular synapses are formed with mossy fibers before the beginning of the third week and the process is still in progress at 30 days, long after the dissolution of the external germinal layer. The maturation of Golgi cells is a protracted process. Their axons synapse with granule cell dendrites as soon as the glomeruli begin to mature. Evidence was obtained that mossy fibers synapse with the dendrites of Golgi cells. Towards the end of the second week the Lugaro cells are formed and synapses appear on their somata during the third week. Among these synapses the recurrent collaterals of Purkinje cell axons were identified. The Lugaro cells may be the primary targets of the infra and supraganglionic plexuses formed by these collaterals. In conclusion it was suggested that there are three major, successive stages in the neurogenesis of the cerebellar cortex, the morphogenic, synaptogenic and gliogenic. However, in the large Purkinje cell the synaptic maturation of one region (the soma) may begin before the morphogenic and synaptogenic maturation of the entire cell (the dendrites) is completed.