Intracranial transection of the optic nerve in adult mice: Preliminary observations

Abstract

Between 1 and 3 days after intracranial transection of the mouse optic nerve, the number of retinal ganglion cells decreased by about 20% and the mean cross-sectional area of the cells decreased by about 25%. The decrease in number continued more slowly, to 50 to 60% of normal by 2 to 3 months, whereas the mean cell size began to recover after about 30 days, becoming nearly normal by 90 days. In the retinal stump of the optic nerve, silver-stained sections showed a core region of complete axonal degeneration extending for a distance of about 1.5 mm from the lesion toward the eye. This core, which was already present 1 day after the lesion, was probably due to ischemia of the nerve on the retinal side of the lesion. The degenerated core was surrounded by a mantle layer, about 25 to 40 μm in thickness, containing intact axons which were presumably nourished by diffusion from the surface of the nerve. The mantle layer represents about 30% of the total nerve cross section. Beginning at 8 days the degenerated core acquired a population of moderately thick fibers, which were probably constituents of connective tissue, although they could not be distinguished with certainty from regenerating axons. There was no unequivocal evidence of axonal regeneration at any time after the lesion. Some of the surviving axons in the retinal stump showed terminal bulbs, but these were less well developed than those seen on the cranial side of the lesion before the axons in the cranial stump degenerated. This suggests that axonal transport might be impaired even in the surviving axons in the retinal stump. This may be a significant factor in deterring regeneration.