Adult neurogenesis in the mammalian central nervous system: functionality and potential clinical interest.

In the past decades, much evidence has confirmed that neurogenesis occurs in the adult brain and that neural stem cells reside in the adult central nervous system, overturning the long-held dogma that we are born with a certain number of nerve cells and that the brain cannot generate new neurons and renew itself. In the adult brain, neurogenesis occurs mainly in two areas: the hippocampus and the subventricular zone, and self-renewing, multipotent neural stem cells have been isolated and characterized in vitro from various regions of the adult central nervous system. Though significant advances have been made in this field of research, the identification and function of neural stem cells in the adult central nervous system remain the source of debate and controversy. Neurogenesis is modulated by several normal and pathologic conditions, suggesting the involvement of the hippocampus and the subventricular zone in a broad range of functions, and that environmental stimuli and pathological conditions may have long-term consequences on the architecture and functioning of the central nervous system. Neurogenesis is involved in processes such as learning, memory, and depression, and may also be involved in regenerative attempts after injuries to the central nervous system. However, the contribution of neurogenesis to these phenomena remains to be elucidated. Neural stem cells also hold the promise to cure a broad range of neurological diseases and injuries. Cell therapeutic interventions may involve both cell transplantation and the stimulation of endogenous neural progenitor cells.