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3H-thymidine injections from E21 to E22 and survival to postnatal day (P)5

Figure 123.  This slice is through all layers of the main olfactory bulb (MOB).  Mitral cells were generated long before the morning of E21, so the small labeled cells in the mitral cell layer are various other cell types: endothelial cells, multiplying glia, granule cells, and cells migrating through to the external plexiform and glomerular layers.  Large labeled cells are probably interstitial tufted cells still migrating through the layer on P5.  Many granule and periglomerular granule cells are labeled.  Most of the labeled cells in the internal plexiform layer are migrating toward superficial layers to settle or they are the most superficial granule cells.  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.  The olfactory nerve layer is filled with labeled cells (glia) that surround cell-sparse circular areas where mitral and tufted cell axons contact olfactory nerve terminals.