Stem cell niches and neurogenesis in the adult brain

The discovery of undifferentiated, actively proliferating neural stem cells (NSCs) in the mature brain opens a brand new chapter in contemporary neuroscience. Adult neurogenesis appears to occur in specific brain regions throughout life in all mammalian species. This unique phenomenon is considered to be important in the processes of memory, learning and neural plasticity. Recently formulated hypotheses suggest that impaired adult neurogenesis is related to the pathogenesis of mental and neurological disorders e. g. depression, schizophrenia, Alzheimer's and Parkinson's diseases. In the adult mammalian brain, neural stem cells are located in the subgranular zone (SGZ) of the hippocampal dentate gyrus and in the subventricular zone (SVZ) of the lateral ventricle ependymal wall. The neural progenitors of the SGZ area migrate to the granular layer of the dentate gyrus. The SVZ stem cells creating the rostral migratory stream (RMS) go to the olfactory bulb, where they differentiate into interneurons. However, the pluripotency of adult NSCs seems to be limited in time and space. The proliferation, maturation and mobility of adult neural stem cells are precisely and constantly regulated by many substances deriving from their cell niche, such as growth and neurotrophic factors, e. g., FGF, VEGF, EGF, IGF-1, CNTF, BDNF, LIF, and also by numerous agents from outside of this zone, e. g., neurotransmitters, neuromodulators, hormones and drugs.