NGF and ischemia: The levels of gene expression of multifarious neural trophic factors such as nerve growth factor (NGF), brain-derived neurotropic factor (BDNF), and neurotrophin-3 (NT-3) increase significantly in vitro NSCs culture and in vivo NSCs transplantation; these trophic factors can not only promote grafted NSCs to better adapt to ischemia microenvironment and facilitate homeostasis in brain, but also protect remaining endogenous brain cells against further damage [8, 9].