Course corrections of deflected retinal axons on the tectum of the chick embryo.

Recently developed neuroanatomical staining methods utilizing transportable markers have made it possible to visualize individual, growing retinotectal axons in the chick embryo. In the present work, we used such methods to examine the behavior of mechanically deflected axons on the tectum. The deflection of axons was achieved by inserting small teflon barriers into the embryonic tectal tissue shortly before the arrival of retinal axons. All axons are laterally deflected by the teflon barrier from their original anteroposterior direction of growth. At the end of the barrier most of them correct their direction of growth. Not only do they turn again towards the posterior tectal pole, but they also approach the route they would have taken in the absence of the barrier.