Killer competition: Neurons duke it out fo...( The developing nervous system makes ...),Health

The developing nervous system makes far more nerve cells than are needed to ensure target organs and tissues are properly connected to the nervous system. As nerves connect to target organs, they somehow compete with each other resulting in some living and some dying. Now, using a combination of computer modeling and molecular biology, neuroscientists at Johns Hopkins have discovered how the target tissue helps newly connected peripheral nerve cells strengthen their connections and kill neighboring nerves. The study was published in the April 18th issue of Science.

It was hard to imagine how this competition happens because the signal that leads cells to their targets also is responsible for keeping them alive, which begs the question: How do half of them die? says David Ginty, Ph.D., a professor of neuroscience and investigator of the Howard Hughes Medical Institute.

Target tissues innervated by so-called peripheral neurons coax nerves to grow toward them by releasing nerve growth factor protein, or NGF. Once the nerve reaches its target, NGF changes from a growth cue to a survival factor. In fact, when some populations of nerve cells are deprived of NGF they die. To further investigate how this NGF-dependent survival effect works the researchers looked for genes that are turned on by NGF in developing nerve cells.

They found hundreds of genes that respond to NGF genes, some of which are involved in enhancing NGFs effect. With the observation that NGF seems to control genes that improve NGF effectiveness, Gintys team hypothesized that this could be the way in which nerve cells compete with one another for survival. To test this idea the team turned to colleagues at the Mind/Brain Institute at Hopkins who specialize in computer modeling of such problems.

The computer model they built assigns each nerve cell its own mathematical equation that take into account how much NGF the cell encounters or how effective NGF can b
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