FIG. 4. Time course of the effect of mercury (50 µg/L) on phosphorylated tau levels in the presence or absence of a 12-h melatonin preincubation of SHSY5Y cells. Data are mean ± SEM (bars) values of nine observations (from triplicate independent assays). The mercury-treated cells showed significantly higher phosphorylated tau levels compared with controls and melatonin plus mercury (Mel + Mel)- and melatonin-treated cells (p < 0.001 by Mann-Whitney U test with Bonferroni's multiple comparison).