Anatomical correlations of intrinsic axon repair after partial optic nerve crush in rats

About 15% of retinal ganglion cells survive diffuse axonal injury of the optic nerve in adult rats. Following initial blindness, discrimination of visual stimuli in behavioral tests recovers within three weeks. To investigate the mechanisms promoting this functional recovery the axonal transport and the neurofilaments were studied. Intraocularly applied MiniRuby is transported until the place of crush and accumulated in enlarged axon terminals. Three weeks after lesion the anterograde transport of MiniRuby recovers distal to the place of crush. At the same point in time the retrograde transport of surviving retinal ganglion cells is restored which was visualized by horseradish peroxidase injected into the superior colliculus. The heavy neurofilament was stained immunohistochemically and analyzed statistically up to three weeks after optic nerve crush. The stained filaments in the axon fibers of retinal ganglion cells appear wavelike and/or fragmented up to day 8, but first signs of heavy neurofilament restitution in the fibers of the optic nerve are seen at day 12 after axonal injury. Because these results cannot be explained by longlasting axon regeneration, the present results provide convincing evidence for intrinsic axon repair soon after diffuse axonal injury that correlates in time with recovery of vision.