While most of the self-renewal capacity characterizing its embryonic development ceases, the adult mammalian central nervous system retains at least two sites of continuous production of neurons and glial cells: the subventricular zone (SVZ) underneath the walls of the ventricles and the subgranule layer (SGL) of the dentate gyrus (DG) [For review (Alvarez-Buylla and Lim, 2004; Alvarez-Buylla et al., 2002; Lie et al., 2004)]. The SVZ is currently the most robust of the known neurogenic regions in the adult CNS, producing as many as 30,000 new neuroblasts each day in the young adult rats (Alvarez-Buylla et al., 2000). Neuroblasts migrate from the SVZ through the rostral migratory stream (RMS) and populate the olfactory bulb. Approximately 9000 neural stem cells (NSC) are produced daily (or 250,000 NSC per month) in the SGL of the DG of sexually mature, 9-10 weeks old rats, amounting to 0.1% of the population of the entire DG, with a survival rate of about 50% (Cameron and McKay, 2001). Neuroblasts born in these niches migrate out and are able to populate the olfactory bulb (OB) and the
