The course of axons within the postnatal rabbit retina.

The course of optic axons within the postnatal rabbit retina was studied by scanning electron microscopy (SEM) of the nerve fibre layer exposed by HCl and collagenase treatment, and by freeze-fracture electron microscopy. In the first days after birth, axon bundles were found to run along a rather tortuous way in between the developing Müller cell endfeet. Later on and in adults, the axon bundles show a more straight course. Single axons running into a bundle show a very irregular course before they assume their path in parallel to the other fibres of the bundle. These results support the idea that the course of growing axons is somehow determined by free "channels" in between the endfeet of glial cells.