3H-thymidine injections from E20 to E21 and survival to postnatal day (P)5

Figure 106.  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 E20; a few granule cells are heavily labeled, but approximately 75% have been generated by the morning of E20; a sprinkling of small cells throughout the rest of the AOB layers are labeled, but many are unlabeled.  Labeling patterns in the MOB are nearly identical to the patterns in the more anterior slice in Figure 105.  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 E20, but a few heavily-labeled deep cells in the pars lateralis are intermingled with unlabeled cells.