TRACK 7: The formation of the vertebrate nervous system is characterized by widespread programmed cell death, which determines cell number and appropriate target innervation during development. Neurotrophin is highly expressed during early development and has been shown to be essential for the survival of selective populations of neurons during different developmental periods. The role of neurotrophic factors is seen in the development of the nervous system. During development, neurons approaching for the growth required limited amounts of target-derived neurotrophic factors (two different receptors, the Trk receptor tyrosine kinase, and the p75 neurotrophin receptor) In this way, the nervous system molds itself to maintain only the most competitive and appropriate connections. During this development, the limited about of the receptors are required for the growth of the neurons. From these two different cases will emerge:
First, the efficacy of neuronal survival will depend upon the amounts of trophic factors produced during development. If the amount exceeds the target level, then the defects will cause.
Second, specific receptor expression in responsive cell populations will dictate neuronal responsiveness.
Depending upon these there are some neurotrophic factors which lead to both defects and growth depending upon the level of the action takes place.