孕期至幼年期低水平铅暴露仔鼠海马锌离子平衡的变化及其发育期海马神经元的损伤

目的:探讨孕期至幼年期铅暴露对仔鼠发育期海马神经元的损伤及其与Zn2+平衡的相关机制。方法：25只母鼠随机分为对照组母鼠（n=10）和铅暴露组母鼠（n=15）。从受孕当天开始至仔鼠生后7、14和21　d时间点分别将对照组和铅暴露组仔鼠随机各分为3组(P7、P14和P21组)，每小组仔鼠8只，铅暴露组母鼠按上述时间段给予0.2%醋酸铅饮水，对照组母鼠正常饮水。在仔鼠生后上述时间点分别测定仔鼠血铅和脑铅含量，Timm’s染色观察海马苔藓纤维(MF)，并采用免疫组织化学法检测锌离子转运体-1（ZnT-1）的表达水平。结果：铅暴露组仔鼠血铅和脑铅含量显著高于对照组（P<0.01）。铅暴露组仔鼠海马CA2区、CA3区出现大量变性细胞，且细胞排列松散，细胞层数减少。Timm’s染色，正常组仔鼠生后21　d开始出现MF发芽，其吸光度(A)值为0.135　0±0.024　3；铅暴露组仔鼠生后21　d MF发芽的A值为0.096 7±0.024 2，较正常组显著降低(P<0.01)。铅暴露组生后7 d仔鼠海马ZnT-1表达水平显著低于对照组（P<0.01），生后14和21 d与对照组比较差异无统计学意义(P>0.05)。结论：孕期至幼年期低水平铅暴露可能导致仔鼠海马神经元Zn2+失衡和海马神经元胞内Zn2+水平降低，后者可能参与铅暴露导致发育期神经损伤。

Change of zinc balance in hippocampus of pup rats after lead exposure from pregnancy to juvenile stage and hippocampal neuron injury in development stage

Objective To investigate the hippocamal neuron injury in pup rats caused by lead exposure from pregnancy to juvenile stage and the mechanism related to zinc balance.Methods Twenty-five female Wistar rats were randomly divided into control group(n=10) and lead exposure group(n=15).The pup rats of each group were subdivided into three subgroups depending on different observation periods from pregnancy to postnatal 7,14,and 21 d(P7,P14 and P21 subgroups),respectively;each subgroup was composed of 8 pup rats.The female rats in lead exposure group were bred with 0.2% lead acetate in drinking water from pregnancy to P7,P14,and P21 of the pup rats,respectively,while the mothers in control group drank water consistently.The blood and brain lead contents were detected on P7,P14,and P21 of the pup rats in each subgroup.Timm's staining was used to observe the mossy fiber(MF) in hippocamspus,and immunohistochemistry assay was performed to detect the expression levels of zinc transporter 1(ZnT-1).Results The blood and brain lead contents in lead exposure subgroups were significantly higher than those in corresponding control subgroups(P<0.01).There were mass of degenerated cells in CA2 and CA3 regions of hippocampus in pup rats after lead exposure,and the nerve cell arrangement was unconsolidated,and the number of cell layers was decreased.The Timm's staining results showed that MF sprouting presented on P21 of the pups in control group,and the absorbtion(A) value was 0.135 0±0.024 3.The A value of P21 in lead exposure group was 0.096 7±0.024 2,which was significantly lower than that in control group(P<0.01).The expression of ZnT-1 was significantly decreased on P7 of the pups in lead exposure group compared with control group(P<0.01).There was no significant difference of ZnT-1 expression on P14 and P21 between lead exposure and control group.Conclusion There may exist neuronal zinc imbalance in pup rats after low-level lead exposure from pregnancy to juvenile stage,and it may cause the decrease of the intracellular Zn2+level in hippocampal neurons after lead exposure.