Adult Subventricular Zone and Olfactory Bulb Neurogenesis

IN THE ADULT MAMMALIAN BRAIN, NEW NEURONS are added to the olfactory bulb (OB) throughout life. In rodents, the adult germinal region for OB neurogenesis is the subventricular zone (SVZ), a layer of cells found along the walls of the brain lateral ventricles (for review, see Alvarez-Buylla and Garcia-Verdugo 2002). Neuroblasts born in the SVZ migrate a relatively long distance into the OB where they then disperse radially and differentiate into interneurons. Most of these new OB neurons integrate into functional circuits (Belluzzi et al. 2003; Carleton et al. 2003), and about half survive long-term (Petreanu and Alvarez-Buylla 2002). SVZ cell proliferation is lifelong (Kuhn et al. 1996; Goldman et al. 1997; Molofsky et al. 2006), with thousands of new neurons generated daily for the mouse OB (Lois and Alvarez-Buylla 1994). The adult SVZ is also the birthplace of oligodendrocytes in both normal and diseased brain (Nait-Oumesmar et al. 1999; Picard-Riera et al. 2002; Menn et al. 2006; Parent et al. 2006). This profound level of continuous neurogenesis and concomitant oligodendrogliogenesis argues for the existence of a self-renewing multipotent precursor cell—or, neural stem cell (NSC)— within the SVZ. The SVZ-OB system is an attractive model in which to study neurogenesis and neuronal replacement as it includes the basic processes of NSC maintenance, progenitor cell-fate specification, migration,