NEWLY-GENERATED CELLS FROM THE ROSTRAL MIGRATORY STREAM IN THE ACCESSORY OLFACTORY-BULB OF THE ADULT-RAT

Cell proliferation in the accessory olfactory bulb of the adult rat wa s analysed after systemic injection of 5-bromo-2'-deoxyuridine, detect ed immunocytochemically at different survival times and compared with proliferating cell nuclear antigen immunostaining. As previously descr ibed in the main olfactory bulb, local cell proliferation was absent o r very limited. By contrast, starting from 15 days after bromodeoxyuri dine administration, many immunoreactive nuclei were present in the gr anular layer, and to a lesser extent, in other layers of the accessory olfactory bulb. This suggests that the newly-generated cells are migr ating elements of the rostral migratory stream which are known to reac h the olfactory bulb in 15 days.(21) By immunocytochemical detection o f the polysialylated isoform of the neural cell adhesion molecule, a w eakly-adhesive cell-surface molecule expressed by newly-generated/migr ating cells of the rostral migratory stream,(5,33) we found a high num ber of immunoreactive cells in the different layers of the accessory o lfactory bulb. Most of these cells were observed in the granular layer and showed the morphology of migrating neuroblasts. Some immunoreacti ve cells displaying neuronal morphology were also detected in the exte rnal plexiform and glomerular layers. Double labelling experiments dem onstrated that these cells are newly-generated cells. These results de monstrate the occurrence of newly-added cells in the accessory olfacto ry bulb of the adult rat, which likely correspond to the neuronal prec ursors originating from the rostral migratory stream. This could be re levant since the accessory olfactory bulb of rodents plays an importan t role in the hard wiring of a simple olfactory memory system for sexu al pheromones. (C) 1997 IBRO. Published by Elsevier Science Ltd.