Contact-guidance of neurite growth: a direct or an indirect effect of physical environment?

Experiments with dissociated chick dorsal root ganglion cells cultured in different media revealed the significance of non-neuronal cells for neurite growth along a physical boundary. The evidence presented suggests that fibrillary fibronectin deposited by non-neuronal cells guides neurites, rather than the physical boundary itself. This guidance is not a consequence of preferential neurite growth on fibronectin deposits. Apparently fibronectin exerts different effects when present in a homogeneous vs. a fibrillary form. It is concluded, that these mechanisms account for the fact that elongating nerve fibers extend parallel to scratches in the culture dish surface and maintain a distance to it, when co-cultured with non-neuronal cells.