This is a slice of the midline vermis in the cerebellum of a 60-day-old rat that was injected with 3H-thymidine on 2 consecutive days: P12 and P13.
Most cells in the MOLECULAR LAYER that are judged to be neurons are unlabeled throughout the entire cerebellum. These are basket and stellate cells that were generated before P12. The larger labeled cells are often endothelial cells, and the smaller labeled cells are glia. Only a few labeled stellate cells are in the upper molecular layer, mostly in superficial parts of lobules in the anterodorsal and central lobes. Consequently, by the morning of P12, aneurogenesis in the stellate cell population is very close to complete. Unlabeled cells in the GRANULAR LAYER predominate in the lingula, centralis, nodulus, and in deep parts of the other lobules. Labeled granule cells still predominate in superficial lobules of the central lobe--especially in the declive, tuber, and pyramis. All unlabeled granule cells were generated before the morning of P12. But since many more unlabeled granule cells are present compared to the P10-11 group, many of these were generated on P10 and P11.
Most probable composition of the external germinal layer (egl):
1. Basket cell precursors are absent.
2. Very few to no stellate cell precursors are present; those still there are in their final neurogenetic division.
3. All of the remaining and shrinking egl is populated with granule cell precursors.