We previously demonstrated by both histological and ultrastructural analyses that rAION results in both axon loss and postischemic demyelination.
6,7 In the current study, ON histology using toluidine blue staining revealed increased preservation of ON axons and improvement in overall ON structure in eyes 30 days post-rAION induction followed immediately by a single IVT injection of PGJ
2 compared with PBS-injected eyes. Striking differences were seen in the TEM analysis of ONs from PBS-injected eyes compared with ONs from PGJ
2-injected eyes following rAION induction. Specifically, there were significant differences in the relative axon numbers, axon packing density, and degree of postischemic demyelination (
Fig. 5). TEM of normal, control ONs revealed axon bundles separated by thin septae (
Figs. 5A1, 5A4). The axons were of varying calibers, ranging from 0.2 to 2.0 μm in diameter. In PBS-injected eyes 30-day post-rAION induction, severe axon loss was apparent, with depletion of both large- and small-diameter axons (
Figs. 5A2, 5A5, 5B). The interaxonal septae were greatly thickened, with regions in which there were only a few surviving axons. There were also areas with demyelinated axons and nearby debris (possibly myelin breakdown products). In contrast, ONs from eyes injected with PGJ
2 immediately after rAION induction revealed many regions of relative axon preservation (
Figs. 5A3, 5A6, 5B) containing well-myelinated axons.
Stereological analysis of Brn3a+ cells in the RGC layer (presumably RGCs) in the PGJ
2-injected eyes compared with PBS-injected eyes also revealed striking differences in preservation after rAION induction (
Fig. 5C). rAION normally results in significant RGC loss at 30 days postinduction. This loss was present in all eyes injected with PBS but not in eyes injected with PGJ
2 (
Fig. 5D).