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3H-thymidine injections from E18 to E19 and survival to postnatal day (P)5 (anterior coronal)

Figure 72.  This slice is through all layers of the main olfactory bulb (MOB).  By the morning of E18, 98% of the mitral cells have been generated.  Consequently, the labeled cells in the mitral cell layer are not mitral cells, but are either endothelial cells (that can appear large depending how they lie in the slice), multiplying glia, smaller cells in the layer, or tufted cells still migrating through the layer on P5.  By the morning of E18 in the external plexiform layer, approximately 85% of tufted cells in the deep half, 40% of tufted cells in the superficial half, and 5% of interstitial tufted cells on the perimeters of the glomeruli have been generated (Bayer, 1983, Exp. Brain Res., 50: 329-340).  Nearly all cells in the granular layer and the periglomerular granule cells are labeled.  The core of the MOB is full of small labeled cells that form the terminus of the rostral migratory stream—a conduit of new neurons steadily migrating (arrows) into the olfactory bulb from the proliferating subependymal layer surrounding the olfactory recess and anterior horn of the lateral ventricle.