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

Figure 124.  This slice through the olfactory peduncle includes the main olfactory bulb (MOB) medially, the accessory olfactory bulb (AOB) dorsally, and the anterior olfactory nucleus (AON) laterally.  The AOB output neurons were all generated long before the morning of E21; a few granule cells are heavily labeled, but approximately 83% have been generated by the morning of E21—about 3% of the AOB granule cells are labeled up to postnatal day 15.  A few small cells throughout the rest of the AOB layers are labeled—mainly glial and endothelial cells.  Labeling patterns in the MOB are nearly identical to the patterns in the more anterior slice in Figure 123; the infiltration of MOB granule cells at the base of the mitral cell layer is especially prominent.  Many labeled young neurons and neuronal precursor cells in the rostral migratory stream are migrating into the MOB granular layer and periglomerular layers (arrows).  Most of the tiny cells in the rostral migratory stream are going to the anterior MOB.  Nearly all pars externa and superficial cells in the AON pars lateralis are unlabeled on the morning of E21, but a few heavily-labeled deep cells in the pars lateralis are intermingled with unlabeled cells.