3H-thymidine injection on E15, 2 hr survival
Figure 30 shows a sagittal slice of an E15 embryo 2 hrs after its mother was injected with 3H‑thymidine. All NEP areas have thick accumulations of precursor cells at their superficial borders except the tentatively identified olfactory bulb NEP. The most well-defined subventricular zone is peppered with locally multiplying cells in the basal ganglionic eminence. Heavily-labeled cells outside the NEP are most likely proliferating glial precursors. The brain parenchyma is expanding and differentiating young neurons populate all areas, including the presumptive olfactory bulb; many are AOB output neurons. The olfactory epithelium has a substantial amount of label uptake. In some parts that are cut perpendicularly, labeled nuclei are in a superficial position—like the pseudostratified NEP that lines the brain ventricles. Of course, the olfactory epithelium is also generating sensory neurons that are the source of the olfactory nerve.