ABSTRACT
Hippocampal neurogenesis consists in the generation of new neurons in the dentate gyrus of the adult brain (Kempermann et al., 2004a). Initial reports about the neurogenic process in the hippocampus derived from studies of Joseph Altman in the 1960s (Altman and Das, 1966). Further studies supported the existence of new neurons in the hippocampus during adulthood (Cameron and McKay, 1999; Gage et al., 1998; Gould et al., 1997; Gould and Tanapat, 1999; Horner et al., 2000; Kempermann et al., 1997; Kuhn et al., 1996; van Praag et al., 1999). Adult hippocampal neurogenesis originates from neural stem cells (NSCs), with the characteristics of radial glial cell (NS-RGC) (Kempermann et al., 2004a). The NS-RGC goes through asymmetric divisions to give rise to subpopulations of rapid amplifying cells and neuroblasts, cells that will form immature neurons, which at their latest stage form new neurons that incorporate into the existent brain circuits (Ge et al., 2006, 2007; Kempermann et al., 2004a,b; Nollet et al., 2012; Zhao et al., 2006b, 2008). This process occurs in the hippocampus due to the presence of a permissive microenvironment in which several populations of immature and mature cells coexist to promote neurogenesis (Palmer et al., 2000). Thus, the generation of new neurons becomes a highly regulated process in which the involvement of hormones such as melatonin has been reported (Ramirez-Rodriguez et al., 2009).
