3H-thymidine injection on E14, survival to E15
Figure 28 shows a sagittal-slice of an E15 embryo 24 hrs after its mother was injected with 3H‑thymidine on E14. The neurons that were generated before E14 are unlabeled—a large clump is beneath the basal telencephalic and basal ganglionic neuroepithelium (NEP) and subventricular zone (SVZ). But heavily labeled cells generated on E14 have migrated into these areas. The neuroepithelim just anterior to the basal telencephalic NEP can be identified as the olfactory bulb NEP; by now, the olfactory nerve contacts a large area of the brain surface that will probably evaginate into the olfactory bulb. The neurons in this area are either unlabeled (possibly AOB output neurons) or are heavily labeled (unidentified neurons generated on E14). No lamination is recognizable in the presumptive olfactory bulb. The olfactory epithelium is continuing to invaginate and most cells are heavily labeled. There is a large accumulation of presumptive glial precursors surrounding mostly indistinct fascicles of the olfactory nerve.