Histochemical localization of NADPH-diaphorase in the rat accessory olfactory bulb

The distribution of NADPH-diaphroase activity was examined in the accessory olfactory bulb of the rat using a direct histochemical technique. Labeled fibers and somata were found in all layers of the accessory olfactory bulb. The entire vomeronasal nerve and all vomeronasal glomeruli were strongly labeled, contrary to the main olfactory bulb, where only dorsomedial olfactory glomeruli displayed NADPH-diaphorase activity. NADPH-diaphorase positive neurons were identified as periglomerular cells in the glomerular layer and external plexiform layer, horizontal cells in the internal plexiform layer, and granule cells and deep short-axon cells in the granule cell layer. The labeled dendrites of the granule cells formed a dense neuropile in the granule cell layer, internal plexiform layer and external plexiform layer. The staining pattern in the accessory olfactory bulb was more complex than what has been previously reported, and demonstrated both similarities and differences with the distribution of NADPH-diaphorase in the main olfactory bulb.