Somatostatin (Som), one of the most concentrated neuropeptides in the brain, is highly expressed in the olfactory bulb (OB). However, the temporal profile by which OB somatostatin-expressing (Som+) interneurons are produced and the molecular mechanisms controlling this profile are totally unknown. Using the5-bromo-2’-deoxyuridine (BrdU) birth dating method, combined with immunostaining, we showed that the generation of Som+interneurons in the mouse and rat OB is confined to the later embryonic and earlier postnatal stages. Within the mouse OB, the production of Som+interneurons is maximal during late embryogenesis and decreases postnatally, whereas the generation of Som+interneurons is low during embryogenesis and increases postnatally in the rat OB. Interestingly, all the Som+interneurons in the mouse external plexiform layer (EPL) and the rat glomerular layer (GL) express the transcription factor Sp8. Genetic ablation of Sp8by cre/loxP-based recombination severely reduces the number of Som+interneurons in the EPL of the mouse OB. Taken together, these results suggest that Sp8is required for the normal production of Som+interneurons in the EPL of the mouse OB. |