FIG. 3. Time course of the effect of mercury (50 µg/L) on secreted Ab 1-40 and Ab 1-42 levels from SHSY5Y cells with or without a 12-h melatonin (1 µM) preincubation. A: Changes in Ab 1-40 levels. Mercury-treated cells showed significantly higher Ab 1-40 levels from 3 h of exposure through to the end of the experiment as compared with control cells (p < 0.001) and melatonin-pretreated cells (p < 0.004). Melatonin-pretreated cells exposed to mercury (Mel + Mer) also had higher levels than untreated control cells (p < 0.004). B: Changes in Ab 1-42 levels. Mercury-treated cells showed significantly higher Ab 1-42 levels between 4 and 6 h of exposure as compared with control cells and melatonin-pretreated cells (p < 0.004). Data are mean ± SEM (bars) values of nine observations (from triplicate independent assays). Statistics were calculated by Mann-Whitney U test with Bonferroni's multiple comparison.