2 hr survival after a 3H-thymidine injection on E18 (medial sagittal)
Figure 78 is a medial sagittal slice through the olfactory bulb and nasal cavity in an E18 embryo exposed to 3H-thymidine 2 hrs before death. The NEP is still the most active central proliferation zone throughout all parts of the forebrain. Labeled cells outside the NEPs are locally multiplying neuronal and glial precursors in the various SVZs—the most active SVZ is outside the basal ganglionic NEP. Isolated labeled cells scattered in the brain parenchyma are locally-multiplying glia. Layers in the parenchyma have already been described in Figure 74. Locally-multiplying glia in the olfactory nerve also have heavy label uptake; these cells nurture the growing olfactory nerve fibers. The olfactory epithelium is actively proliferating with label uptake bordering the lumen of the nasal cavity and an outer layer of proliferating cells. These two different regions of label uptake indicate two different populations of proliferating cells. The sensory epithelium in Jacobson’s organ shows some indication of superficial/deep label uptake as well.