Models of axon guidance and bundling during development.

Diffusible chemoattractants and chemorepellants, together with contact attraction and repulsion, have been implicated in the establishment of connections between neurons and their targets. Here we study how such diffusible and contact signals can be involved in the whole sequence of events from bundling of axons, guidance of axon bundles towards their targets, to debundling and the final innervation of individual targets. By means of computer simulations, we investigate the strengths and weaknesses of a number of particular mechanisms that have been proposed for these processes.