Lead (Pb) is a neurotoxic heavy metal, but the mechanism of its neurotoxicity is not clearly understood. Expression of metallothioneins (MTs) is induced in response to heavy metal exposure as a protective mechanism against heavy metal toxicity. There are several isoforms of MTs (MT-1 to 4), of which MT-3 is the neuron specific isoform, which also has neurite growth inhibitory effects. Whereas, the induction of MT-1 and 2 in response to Pb has been reported, the effect of Pb on the expression of MT-3 in the brain has not been documented. This study aimed at investigating the effect of Pb exposure on the expression of MT-3 in the cerebrum and hippocampus. Wistar rat pups were exposed to Pb via their dams’ drinking water (0.2% lead acetate in deionized water) from postnatal day (PND) 0 to 21 and directly via drinking water until PND30. Expression of MT-3 was measured by Western blot and quantitative RT-PCR. MT-3 localization was done by immunohistochemistry. Divalent metal ions were analysed by atomic absorption spectrophotometry. Levels of Pb in blood and cerebrum were significantly increased, while that of copper (Cu), zinc (Zn) and manganese (Mn) were significantly decreased in the Pb-exposed rats at both PND21 and PND30. MT-3 protein was significantly increased in the cerebrum (by 2.5-fold) and in hippocampus (1.4 to 3.2-fold) in both PND21 and PND30 Pb-exposed rats over controls. MT-3 gene expression also increased in the cerebrum (by 42%), and in the hippocampus (by 65% and 43% in the PND21 and PND30 rats, respectively), in the Pb-exposed rats over controls, but the increase was statistically significant (p < 0.05) only in the PND30 rats. Pb exposure significantly increased (p < 0.05) percentage of MT-3 immunoreactive cells in Cornu Ammonis and dentate gyrus regions in the PND21 rats, and in the Cornu Ammonis 1, dentate gyrus and cortex regions in the PND30 rats. Our data thus provide convincing evidence that exposure to low levels of Pb during preweaning period increases the expression of MT-3 in the brain of rats.

铅（Pb）是一种具有神经毒性的重金属，但其神经毒性的机理尚不清楚。响应于重金属暴露诱导金属硫蛋白（MTs）的表达，作为针对重金属毒性的保护机制。MT有几种同工型（MT-1至4），其中MT-3是神经元特异性同工型，还具有抑制神经突生长的作用。尽管已经报道了响应于Pb的MT-1和2的诱导，但尚未记录Pb对大脑中MT-3表达的影响。这项研究旨在调查铅暴露对大脑和海马中MT-3表达的影响。Wistar大鼠幼崽从出生后（PND）0到21，通过其母坝的饮用水（去离子水中的乙酸铅含量为0.2％）暴露于Pb，然后直接通过饮用水暴露至PND30。通过Western印迹和定量RT-PCR测量MT-3的表达。通过免疫组织化学进行MT-3定位。通过原子吸收分光光度法分析二价金属离子。在PND21和PND30暴露于Pb的大鼠中，血液和大脑中Pb的水平显着升高，而铜（Cu），锌（Zn）和锰（Mn）的水平显着降低。在暴露于PND21和PND30 Pb的大鼠中，与对照相比，MT-3蛋白在大脑和海马中显着增加（增加了2.5倍）和在海马中增加了（1.4至3.2倍）。暴露于Pb的大鼠的大脑中MT-3基因表达在大脑中也增加了（42％），在海马体中（分别在PND21和PND30大鼠中分别增加了65％和43％），但是增加是仅在PND30大鼠中具有统计学意义（p <0.05）。在PND21大鼠的Cornu Ammonis和齿状回区域，以及在PND30大鼠的Cornu Ammonis 1，齿状回和皮质区域，Pb暴露显着增加（p <0.05）MT-3免疫反应性细胞的百分比。因此，我们的数据提供了令人信服的证据，即断奶前暴露于低水平的Pb会增加大鼠大脑中MT-3的表达。