The brain-to-liver mercury ratio increases with aging in mice

There was no significant change in the total amount of mercury in organs (lung, heart, kidney, brain, and liver) from male C57BL/6J mice ranging in age from 133 to 904 days of age maintained under conventional conditions with no known source of mercury exposure other than background concentrations. The lowest values were found in the liver and the highest in the brain, with considerable variation in the mercury content between individual mice for all organs examined. The ratio of mercury in the brain to that in the liver, however, was found to significantly increase with aging in an exponential manner. A similar result was found for the ratio of brain to kidney mercury. We conclude that older mice are less able to maintain low brain-to-liver ratios of mercury regardless of the total body content of mercury. Dietary mercury ranging from 200 to 20,000 ppm Hg had little or no influence on the life span of Drosophila fruit flies, suggesting that the effect of mercury is probably not on life span itself but on other factors associated with the aging process such as neurological disfunction.