3H-thymidine injections from E17 to E18 and survival to embryonic day (E)21
Figure 57. The labeling pattern in this specimen is like the one shown in Figure 41, except the labeling uptake is more intense, especially in the granule cell layers. 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 either endothelial cells or glia). The vomeronasal nerve layer is full of labeled cells, and the AOB granular layer is packed with heavily labeled cells and some definite unlabeled cells. The mitral cell layer in the main olfactory bulb (MOB) is full of unlabeled cells; there are still a few heavily labeled cells in the layer. Many small cells, and some large cells (tufted cells) are labeled in the external plexiform layer; the deep half of the layer has more unlabeled large cells than the superficial half. The internal plexiform layer has some clumps of heavily labeled cells, but many cells are unlabeled—probably late migrating mitral and tufted cells. Most cells in the MOB granule cell layer are heavily labeled and hard to distinguish from the AOB granule cells in a dorsal, crescent-shaped area (outlined).