Origins, functions, and potential of adult neural stem cells

In recent years, the existence of neural stem cells (NSCs) in the adult mam malian brain has been confirmed. The generation of new neurons from these c ells is regulated by growth factors, hormones, and environmental cues; howe ver, the function of newly generated neurons in the adult brain remains elu sive. Two recent articles emphasize the impact of motor activity and learni ng on in situ hippocampal neurogenesis,((1,2)) suggesting a close link to h ippocampal function. Adult NSCs can be isolated and expanded in vitro. It w as presumed that the origins of the NSCs were within subependyma of the lat eral ventricle; however, new evidence suggests that the "real" stem cells m ay reside in the ependymal lining.((3)) In a related study, these same cell s were transplanted into irradiated mice and were able to integrate into th e bone marrow and produce various blood cell types,((4)) challenging the li mits of neural cell fate determination. BioEssays 21.625-630, 1999. (C) 199 9 John Wiley & Sons, Inc.