3H-thymidine injection on E14, survival to E15
Figure 29 shows a coronal-slice of an E15 embryo 24 hrs after its mother was injected with 3H‑thymidine on E14. The slice grazes the part of the anteroventral forebrain that is completely surrounded by the olfactory and vomeronasal nerve contact zones. Neurons generated before E14 are unlabeled—a ring of unlabeled cells is outside the presumptive border of the olfactory subventricular zone—many may be AOB output neurons. The thin strands of vomeronasal nerve fibers exiting Jacobsen’s organ approach the brain surface from the medial side, while the large olfactory nerve fiber bundles grow toward the brain in intermediate and lateral bundles. These incoming nerve fibers might guide AOB output neurons and MOB mitral cell migration routes. The edge of the brain is nearly indistinguishable in the nerve contact zone, especially ventrally—there are many opportunities for cellular exchange between the brain and nerve.