Few published studies have examined whether the elevated concentrations of the nonessential toxic metal mercury (Hg) often observed in shark muscle also occur in the shark brain or whether Hg accumulation affects shark neurophysiology. Therefore, this study examined accumulation and distribution of Hg in the shark brain, as well as effects of Hg on oxidative stress in the shark central nervous system, with particular focus on the Atlantic sharpnose shark (Rhizoprionodon terraenovae). Sharks were collected along the southeastern U.S. coast throughout most of this species' U.S. geographical range. Total Hg (THg) concentrations were measured in and compared between shark muscle and brain, whereas known biomarkers of Hg-induced neurological effects, including glutathione depletion, lipid peroxidation, and concentrations of a protein marker of glial cell damage (S100b), were measured in shark cerebrospinal fluid. Brain THg concentrations were correlated with muscle THg levels but were significantly lower and did not exceed most published thresholds for neurological effects, suggesting limited potential for detrimental responses. Biomarker concentrations supported this premise, because these data were not correlated with brain THg levels. Hg speciation also was examined. Unlike muscle, methylmercury (MeHg) did not comprise a high percentage of THg in the brain, suggesting that differential uptake or loss of organic and inorganic Hg and/or demethylation of MeHg may occur in this organ. Although Hg accumulation in the shark brain generally fell below toxicity thresholds, higher THg levels were measured in the shark forebrain compared with the midbrain and hindbrain. Therefore, there is potential for selective effects on certain aspects of shark neurophysiology if brain Hg accumulation is increased.

中文翻译：

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大西洋尖嘴鲨（Rhizoprionodon terraenovae）在大脑中的汞积累和影响。

很少有发表的研究检查鲨鱼肌肉中经常观察到的非必需有毒金属汞（Hg）浓度升高是否也出现在鲨鱼大脑中，或者Hg积累是否影响鲨鱼神经生理学。因此，本研究研究了汞在鲨鱼脑中的积累和分布，以及汞对鲨鱼中枢神经系统氧化应激的影响，特别是针对大西洋尖鼻鲨（Rhizoprionodon terraenovae）。鲨鱼是在美国东南部整个美国地理范围内收集的。在鲨鱼的肌肉和大脑中测量并比较了总Hg（THg）的浓度，而已知的Hg诱导的神经系统作用的生物标志物包括谷胱甘肽耗竭，脂质过氧化，在鲨鱼脑脊髓液中测量神经胶质细胞损伤蛋白标记物（S100b）的浓度。脑THg的浓度与肌肉THg的水平相关，但显着降低，且未超过大多数公布的神经学阈值，表明有害反应的潜力有限。生物标志物的浓度支持了这一前提，因为这些数据与脑THg水平无关。还检查了汞的形态。与肌肉不同，甲基汞（MeHg）在大脑中的THg含量不高，这表明该器官中可能会发生有机和无机Hg的差异吸收或损失和/或MeHg的去甲基化。尽管鲨鱼脑中的汞积累通常低于毒性阈值，与中脑和后脑相比，鲨鱼前脑的THg水平更高。因此，如果增加脑汞的积累，可能会对鲨鱼神经生理学的某些方面产生选择性影响。