Optic nerve (ON) histopathology and retinal ganglion cell (RGC) counts. A and B: Representative Luxol Fast Blue-stained cross sections of ONs of a wild-type Staphylococcus aureus infected rat (A) showed only small areas of demyelination, with mainly intact myelin (blue); in contrast, a cross section from a noninfected control animal (B) showed extensively demyelinated areas (purple). C and D: Representative examples of the substantially higher number of ED1 macrophages/activated microglia detected in the ON of a noninfected control animal (D), compared with an animal infected with wild-type S. aureus
(C). E and F: representative images for CD3+ T-lymphocyte counts, which were noted higher in the optic nerve of the animals from control group (F), whereas CD3-positive cells were hardly present in the optic nerve of the group infected with bacteria (E). G and H: Bielschowsky’s silver impregnation of ON cross sections revealed a higher density of axons on experimental autoimmune encephalomyelitis (EAE) day 8 in wild-type S. aureus infected animals (G) compared to noninfected control animals (H). I, J, K and L represent the quantitative data for demyelination, ED1 score, CD3-positive cells and for axonal loss, respectively. M: Represents the quantitative data for fluorogold labeled RGCs, which showed higher density in the animals infected with S. aureus compared to the noninfected control group. For optic nerve histopathology, n = 16 infected, n = 14 noninfected; for RGC counts n = 20 infected; n = 14 noninfected, where n indicates the number of eyes used for counting the RGCs; **P <0.01; ***P <0.001). Bar length for Luxol Fast Blue, ED1, CD3- = 100 μm, and for Bielschowsky’s silver impregnation = 20 μm.