Inhibition of HDAC activity attenuates cell loss following optic nerve crush (ONC). Total cell counts in the ganglion cell layer (GCL) were performed to determine the protective effect of HDAC inhibition with trichostatin A (TSA) following ONC. (A) Histograph showing cell loss in the GCL in crush eyes as a percentage of cells in the contralateral control eyes at 2 weeks post ONC. Mean ± SE is shown (n = 6-10 retinas per treatment condition). Mice that received no injection or an injection of DMSO exhibited a 36.4 and 31.2% cell loss, respectively. Mice that were given a TSA injection prior to ONC only exhibited a 14.4% cell loss, which was significantly less than that seen with no injection or DMSO (*P = 0.005 vs. crush alone, P = 0.01 vs. DMSO). (B) Representative Nissl stained whole mounts of the mid-peripheral region of mouse retinas 2 weeks after ONC. Retinas after ONC, crush alone (crush) or crush with DMSO (DMSO), exhibited a loss of cells compared to fellow control eyes (control). TSA treated mice (TSA) exhibited less cell loss after ONC, although cells in these retinas appeared smaller due to atrophy associated with optic nerve lesion, as described by others . Scale bar = 20 μm.