The role of growth factors in neuronal development and plasticity

The role of growth factors in the development of the nervous system, as well as in injury-induced plasticity, is of great interest. A neuronal growth factor is any substance that influences the growth of neurons, but two general classes of factors exist: diffusible substances and substrate-bound factors. Growth factors may affect neuronal survival as well as the extent and rate of neurite outgrowth in vitro. Although progress is slowly being made in the identification and characterization of putative growth factors, nerve growth factor (NGF) is the only identified molecule that clearly influences neuronal growth in vivo. Furthermore, although there are many examples of neuronal plasticity following injury, the role of growth factors in such rearrangements remains to be established. However, one model of collateral sprouting of axons from the peripheral nervous system (PNS) into the central nervous system (CNS) appears to involve the action of a growth factor with properties similar to NGF. The identification of specific molecules that affect neuronal growth should lead to an understanding of the etiology of degenerative neurological diseases such as Alzheimer's disease and, hopefully, to rational therapeutic approaches.