MeHg decreases mitochondrial mass, which is attenuated by NAD+ pretreatmemt. A, OH7193 stained with MitoTracker Green FM and treated with MeHg ± 1 mM NAD + pretreatment to measure mitochondrial mass. Data are a ratio of green to red fluorescence to normalize by worm number from five independent experiments. B, Mitochondrial DNA copy number measured from extracts of N2 worms treated with MeHg ± 1 mM NAD + pretreatment. Data are expressed as means ± SEM from seven independent experiments. *P < .05, **P < .01,***P < .001 as compared with untreated control.