Growth cone behavior on gradients of substratum bound laminin

We have tested the ability of a gentle gradient of neurite-promoting activity to orient the extension of embryonic growth cones. Gradients of neurite-promoting activity were made with biologically active, tritium-labeled laminin. The distributions of laminin bound to glass substrata were visualized by autoradiography and quantified with an image processing system. Embryonic chick sympathetic ganglia were explanted onto laminin gradients and cultured. No tendency for neurites to be oriented up-gradient was detected by examining the morphology of explants. Time-lapse studies of individual growth cones detected no up- or down-gradient bias in growth cone motility. These results suggest that growth cone orientation is relatively insensitive to a graded distribution of a naturally occurring neurite-promoting molecule.