Acetylated histone H4 is depleted in the ganglion cell layer (GCL) nuclei following optic nerve crush (ONC). (A) Left panels, sections from a control retina and retinas after ONC were labeled for acetylated histone H4 (AcH4). Nuclei in the outer nuclear layer (not shown), inner nuclear layer (INL) and GCL of the retina were labeled. AcH4 labeling in the INL remained constant at all time points examined. Labeling in the GCL progressively decreased after ONC. Scale bar = 20 μm. Right panels, Higher magnification of cells of the GCL after ONC. All images were taken at a fixed exposure time. At 1 day post ONC, AcH4 labeling was slightly decreased. At 3 days post ONC, several nuclei showed pronounced loss of label (arrows). At 5 days post ONC, only a subset of cells in the GCL remained labeled for AcH4. Scale bar = 10 μm. (B) Quantification of AcH4 staining intensity of cells in the GCL. Staining intensity was normalized to AcH4 staining in cells of the INL for each section examined. Results are shown as the ratio of staining intensity between experimental (OS) and control (OD) eyes of the same animals (n < 99 cells counted per layer). AcH4 immunoreactivity significantly decreased during the first 5 days post ONC (*P ≤ 0.0001 OS vs. OD). By 7 days post ONC, AcH4 staining appeared to recover, but was still significantly lower than control retinas (**P = 0.041 OS vs. OD). Staining recovery may reflect an increase in the proportion of unaffected GCL amacrine cells as ganglion cells die.