A fundamental issue in current biology is the question of maintaining a critical balance between cell survival and cell death, both during development and in adulthood. In the nervous system, a family of neurotrophins which includes nerve growth factor (NGF), BDNF, and neurotrophins 3/4/5, maintains this critical balance. The best characterized of these is NGF, a neurotrophic protein which is important for the growth and survival of diverse peripheral and central neurons. It is expressed within discrete CNS areas and is secreted by tissues targeted by sympathetic and some sensory neurons. The effects of NGF on neuronal growth and survival are mediated by a high affinity cell surface receptor TrkA and a low affinity receptor p75(NTR)...