Neurobehavioral effects of low-dose long-term methylmercury exposures in mice

点击翻译按钮获取中文摘要

Methylmercury (MeHg) has been shown to be a neurotoxin. Since developing brain is especially sensitive to MeHg, low levels of prenatal exposure to MeHg causes several adverse effects including neurobehavioral changes. However, many questions remain to be elucidated about the long-term exposure to MeHg. To examine the neurobehavioral effects of low-dose long-term MeHg exposures, female C57BL/6Cr mice at 8 weeks old were orally given MeHg with diet containing 0, 1 or 5 ppm (as Hg) MeHg for 4 weeks before mating. The mice were continuously exposed to MeHg during gestation and lactation, and the offspring obtained were also exposed with the same diet. Neurobehavioral examinations including open field test and Morris water-maze test were performed when the offspring were at 12, 56 or 103 weeks old. In open field test at 12 weeks old, MeHg exposure significantly increased the number of urination and defecation, and decreased the locomotion activity in female mice. At this age, an abnormal pa … More ttern of extracellular glutamate mobilization could be seen at hippocampus CA3 region of male MeHg-exposed mice, suggesting that behavioral changes might be related to the biochemical changes occurred in the brain. At 56 weeks old, although MeHg exposure did not cause any significant effect in open field test, MeHg exposure again decreased the locomotion activity at 103 weeks old. In Morris water-maze test, MeHg exposure increased the time to reach to the hidden platform at 12, 56 and 103 weeks old. These results suggest that low-dose long-term MeHg exposure caused serious adverse effects on emotional behaviors and spatial learning ability ; aging unmasked the effects of MeHg exposure on the spatial learning ability, while it partially masked the effects on the emotional parameters in elderly mice. In addition, the roles of selenium, metallothionein (MT)-1,2, and growth environment were examined from the viewpoints of neurobehavioral development, respectively. Finally, the combined effects of prenatal and adulthood exposures were also examined. Less