Cell proliferation refers to the division of progenitor cells located in the sgz of the dentate gyrus. Granule cell progenitors have the morphological characteristics of radial glia (Seri et al., 2001) and express glial fibrillary acidic protein (GFAP), an astroglial marker. Progenitor cells continue to express GFAP at the time of cell proliferation. Neuronal differentiation refers to the selection and emergence of a neuronal fate by some of the daughter cells. In the dentate gyrus, the majority of new cells differentiate into neurons (in the rodent, the percentage varies in the literature between 80-95%, depending on factors such as species, animal age, location of granule cells, and stage of development of cells, Cameron et al., 1993b; Cameron & McKay, 2001; Brown et al., 2003; Snyder et al., 2009). A smaller percentage (~10), differentiate into glia (Cameron et al., 1993b; Steiner et al., 2004). New glial cells continue to express GFAP while undergoing structural differentiation into mature astrocytes. New neurons stop expressing GFAP and instead express markers for immature neurons, such as doublecortin (DCX), polysialated neuronal cell adhesion molecule (PSA-NCAM) and
