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 class III beta-tubulin (Tuj1). While new neurons continue to express TuJ1 as they mature, these cells ultimately stop producing DCX and PSA-NCAM and begin to make proteins specific to mature granule cells, like Neuron specific enolase (NSE), Neuronal nuclei (NeuN) and Calbindin (Fig. 1). It should be noted that the time course of biochemical maturation of new neurons in the dentate gyrus varies among species, even within rodents. For example, new neurons in the adult rat appear to differentiate more rapidly than those in the adult mouse (Snyder et al., 2009a). In addition to biochemical changes that accompany neuronal differentiation, new neurons undergo structural and electrophysiological changes as they transition from immature to mature. Within a few weeks of mitosis, new neurons develop morphological features of granule cells. New granule cells grow characteristic dendritic trees extending toward the molecular layer (Ribak et al., 2004), elaborate axons toward the CA3 region of the hippocampus (Hastings & Gould, 1999; Zhao et al.,
