3H-thymidine injections from E16 to E17 and survival to embryonic day (E)21
Figure 41. In the accessory olfactory bulb (AOB), the output neurons are all unlabeled; the same is true for cells in the internal and external plexiform layers (the scattered labeled cells there are endothelial cells or glia). The vomeronasal nerve layer is full of labeled cells, and the granular layer is packed with heavily labeled cells, with a few definite unlabeled cells. The mitral cell layer in the main olfactory bulb (MOB) is full of unlabeled cells and a few heavily labeled cells, always in a deep position (by the morning of E16, a little over 60% have been generated). The superficial heavily labeled cells may be tufted cells (or others) migrating into the external plexiform layer, which has more labeled cells in its superficial half. The internal plexiform layer is full of clumps of heavily labeled cells, interpreted as migrating into more superficial layers, including the mitral cell layer. Most cells in the MOB granule cell layer are labeled, as are nearly all cells in the olfactory nerve layer.