24 hr-survival after a single 3H-thymidine injection on E18 (anterior coronal)
Figure 93. A coronal slice through the MOB in an E19 embryo killed 24 hrs after a single exposure to 3H-thymidine on E18; note the NEP cells oozing into the ventricular lumen of the olfactory recess—typical of other E19 specimens. Labeled cells are present only in the olfactory NEP, the SVZ, and the olfactory nerve layer. Nearly all cells are unlabeled in the internal and external plexiform layers and the mitral cell layer—all generated before the morning of E18. The few labeled cells are probably locally-multiplying glia. The olfactory nerve blends with the ventral brain surface in the contact zone, obliterating the pial membrane, but the sharp decline in labeled cells in the external plexiform layer indicates the peripheral glia “know” the outer limits of the brain. The heavy label uptake in the olfactory epithelium indicates active proliferation, some parts show a separation between superficial and deep labeled cells, but other areas have homogeneous label uptake.