Figure 2. Retinal ganglion cell survival. A-D: Graphs showing the dose-dependent effect of histone deacetylase inhibitors and erythropoietin on retinal ganglion cell (RGC) survival after 48 h in culture. Data are presented as means and standard error of the mean (each diagram summarizes four to six culture experiments; each of the experiments tested the drug in quadruplicates to hexaplicates of indicated concentrations). A: Compared with untreated controls, valproic acid (VPA) 0.1 and 0.5 mM significantly increased RGC survival to 163% (**p<0.01) and 157% (*p<0.05), respectively. Higher VPA concentrations (0.75 and 1.0 mM) had no protective effect, while VPA 2 mM significantly decreased RGC survival to 22% (p<0.001). B: Sodium butyrate (SB) 0.1 mM significantly increased RGC survival to 188% (***p<0.001), while a nonsignificant protective effect was seen with SB 0.5 mM. SB 1.0 mM did not affect RGC survival compared to controls. Higher concentrations of SB (≥5 mM) significantly decreased RGC survival. C: Trichostatin A (TSA) 0.5 and 1.0 nM had no effect on RGC survival, while TSA 5 nM and 10 nM significantly decreased RGC survival to 40% (p<0.01) and 8% (p<0.001), respectively. D: Erythropoietin (EPO) 0.05 IU/µl increased RGC survival to 164% (*p<0.05), while higher concentrations of EPO were less effective. E: Histone deacetylase inhibitors (HDACi: VPA 0.1 and 0.5 mM and SB 0.1 mM) had similar protective effects as EPO in this series of experiments (each column represents the increase in RGC survival [%] after HDACi treatment compared to individual controls [neuroprotective power=mean cell numbers treatment/mean cell numbers control*100]).