Chemorepulsion of axons in the developing mammalian central nervous system.

During development of the nervous system, distinct populations of nerve cells extend specialized processes, axons and dendrites, over considerable distances to locate their targets. There is strong evidence for two general mechanisms by which these connections are made. The first involves attractive and repulsive interactions, both between cells and between them and their extracellular matrix. The second depends on the release of diffusible chemoattractants by target structures. Evidence is now provided for a mechanism of axon guidance in which diffusible chemorepulsive factors create exclusion zones for developing axons, causing them to turn away from inappropriate territory.