24 hr survival after a 3H-thymidine injection on E15 (sagittal)
Figure 44. This sagittal slice through the most prominent part of the evaginating olfactory bulb on E16 shows heavy label uptake after a 3H-thymidine exposure on the morning of E15. Unlabeled cells were generated before the morning of E15. The unlabeled cells in the parenchyma outside the olfactory neuroepithelium (NEP) are AOB output neurons and the few mitral cells generated before E15. Heavily labeled cells are probably mitral cells infiltrating the parenchyma in a migratory path (arrows) streaming out of the basal telencephalic NEP. There is no lamination in the olfactory bulb itself, and one cannot distinguish an MOB from an AOB. The olfactory nerve is full of large cells, some unlabeled and many labeled that coalesce with the brain surface where the bulb is evaginating. The presumptive olfactory epithelium—as in all cells lining the nasal cavity—are actively proliferating and have heavy label uptake.