Spontaneous axonal regeneration after optic nerve injury in adult rat.

Optic nerves of adult rats were crushed 2 mm behind the eye to examine the ability of retinal ganglion cells (RGCs) to regenerate their axons. Some animals were treated with the immunophilin ligands FK 506 or GPI 1046 for up to 4 weeks. After 10 days to 16 months, regenerating RGC axons were visualized using anterograde tracing and/or electron microscopy. A small proportion of RGC axons regenerated across the lesion site and grew very slowly along the entire optic nerve. Immunophilin ligands had no obvious effect. The regenerating axons were about 0.2 microm in diameter, and usually in clusters surrounded by astrocyte processes. Thus, some CNS axons can spontaneously regenerate long distances within degenerate white matter and this slow regeneration is not accelerated by immunophilin ligands.