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: P8 through P9.
Unlabeled cells in the lower half of the molecular layer are now commonly seen throughout the entire cerebellum. These are basket cells that were generated before P8. Only a few labeled basket cells are in the lower molecular layer, mostly in superficial parts of lobules in the anterodorsal and central lobes. Consequently, by the morning of P8, neurogenesis in the basket cell population is waning. A fair number of unlabeled cells are in the upper half of the molecular layer throughout the cerebellum, most noticeably in the lingula, centralis, nodulus, and in deep parts of all other lobules; these are stellate cells generated before the morning of P8. Nearly all cells in the GRANULAR LAYER are still heavily labeled in superficial lobules of the anterodorsal and central lobes, but a fair number of unlabeled granule cells are scattered in the lingula, centralis, nodulus, and in deep parts of the other lobules. These are granule cells generated before the morning of P8.
Most probable composition of the external germinal layer (egl):
1 There are many fewer basket cell precursors.
2. Stellate cell precursors are in their final "neurogenetic production" generation.
3. Most of the egl is populated with granule cell precursors, especially in the superficial parts of lobules in the anterodorsal and central lobes.
4. Measurements of the egl in developing cerebella indicate that its superficial proliferative zone is thinning as more and more neurons are being generated and migrate out.