Figure 3

Degeneration of axons occurs first in regions of the optic nerve proximal to the laminar region. A series of 16 photomicrographs are shown of 4 different optic nerves in different stages of degeneration based on the DiI-labeling pattern. The distal and proximal segments of each nerve were sectioned longitudinally and silver stained. The individual nerves are oriented from left to right, with their respective score shown at the top. Photomicrographs taken from each nerve are oriented from the laminar region (top panels) through to a region in the middle of the proximal segment (bottom panels). A normal nerve (left panels – score of 1) contains bundles of axons flanking columns of cells in the laminar region. Immediately posterior to this region, the axons separate from the bundles and anastomose along the entire length of the nerve. A nerve with moderate degeneration (panels second from the left – score of 3) also contains relatively normal appearing bundles of axons in the lamina. Small regions of degenerating axons are found along nerve posterior to the lamina, especially in the mid-region of the distal segment and the proximal segment. These regions are exemplified by swollen axons and axon fragments. Nerves with severe degeneration (panels third and fourth from the left) show much more extensive axonal degeneration and loss, gliosis, and scar tissue deposition. Bar = 15 μm.