Low dose-dependent sub-chronic effect of HgCl2 on levels of (a) thiobarbituric acid reactive substances (TBARS) content, (b) nitric oxide (NO) and (c) catalase activity (CAT) in the hippocampus of male Wistar rats. Data are expressed as mean ± SEM. The significance level is 0.05 with *p < 0.05, **p < 0.01, ***p < 0.001.