ABSTRACT
The first neurotrophic factor to be discovered, nerve growth factor promotes the survival of sensory neurons in the dorsal root ganglia and sympathetic neurons. Several other neurotrophins, such as brain derived neurotrophic factor and neurotrophins 3-6, promote the survival of central neurons. Variable regions containing exposed basic amino acid residues provide for the specificity shown by individual neurotrophins. The tyrosine kinase superfamily of receptors is large and together with receptors for neurotrophins, includes receptors for growth factors, insulin and the Eph receptor for ephrin. Different classes of sensory neurons in the dorsal root ganglia require different neurotrophins for their survival. About half of all neurons that are born undergo programmed cell death, apoptosis, during development. Apoptosis is very different from necrosis, the cell death that follows acute injury. Numerous genes, many of which are involved in the regulation of the cell cycles, are implicated in the control of apoptosis.
