孕期及哺乳期铅暴露对仔代大鼠学习记忆能力的影响及其机制

目的：探讨孕期及哺乳期铅暴露对仔代大鼠学习记忆能力和海马组织c-fos蛋白及小清蛋白（PV）表达的影响，阐明铅对仔代大鼠神经系统发育期记忆功能损害的可能机制。方法：8只孕期Wistar雌性大鼠随机分为对照组和低、中及高剂量铅暴露组。低、中和高剂量铅暴露组大鼠分别给予含0.05%、0.10%和0.20%醋酸铅的去离子水，对照组大鼠饮用去离子水。仔代大鼠出生10d后，采用Morris水迷宫法检测各仔代大鼠的学习记忆能力，原子吸收光谱法检测各组仔代大鼠血液和海马组织中铅质量浓度，生化方法测定各组仔代大鼠海马组织中一氧化氮（NO）水平和一氧化氮合酶（NOS）活性，蛋白免疫印迹法检测各组仔代大鼠海马组织中c-fos和PV蛋白表达水平，Pearson相关分析法分析仔代大鼠海马组织中c-fos和PV蛋白表达水平与学习能力指标、海马组织中NO水平及NOS活性的相关性。结果：定位航行实验，与对照组比较，中和高剂量铅暴露组仔代大鼠平均逃避潜伏期和游泳距离明显增加（P<0.05）。空间探索实验，与对照组比较，中和高剂量铅暴露组仔代大鼠目标象限停留时间和穿越次数明显减少（P<0.05）。各组仔代大鼠血液和海马组织中铅质量浓度比较差异有统计学意义（F=176.44，P<0.01；F=37.37，P<0.01）；与对照组比较，不同剂量铅暴露组仔代大鼠血液和海马组织中铅质量浓度明显升高（P<0.05）。各组仔代大鼠海马组织中NO水平和NOS活力比较差异有统计学意义（F=4.105，P<0.05；F=3.443，P<0.05）；与对照组比较，高剂量铅暴露组NO水平和NOS活力明显下降（P<0.05）。与对照组比较，不同剂量铅暴露组仔代大鼠海马组织中c-fos蛋白表达水平明显降低（P<0.05），中和高染铅暴露组仔代大鼠海马组织中PV蛋白表达水平明显升高（P<0.05）。Pearson相关分析法，仔代大鼠海马组织中c-fos蛋白表达水平与水迷宫实验中学习能力指标、海马组织中NO水平和NOS活性呈正相关关系（P<0.01），PV蛋白表达水平与水迷宫实验中学习能力指标、海马组织中NO水平和NOS活性呈负相关关系（P<0.01）。结论：孕期及哺乳期铅暴露可损伤仔代大鼠的学习记忆能力，其毒性作用机制可能与海马组织中c-fos蛋白表达水平降低和PV蛋白表达水平升高有关。

Effects of lead exposure during pregnancy and lactation periodson learning and memory abilities of offspring rats and their mechanisms

Objective: To investigate the effects of lead exposure during pregnancy and lactation periods on the learning and memory abilities and the expressions of c-fos and parvalbumin(PV) in hippocampus tissue of the offspring rats, and to clarify the possible mechanism of lead on the memory function impairment during nervous system development. Methods: Eight female Wistar rats during pregnancy period were randomly divided into control group and low,medium and high doses of lead-exposed groups. The rats in low,medium and high doses of lead-exposed groups were given deionized water containing 0.05%, 0.10%, and 0.20% lead acetate, and the rats in control group were given deionized water. Ten days after the pups were born, Morris water maze was used to measure the learning and memory abilities of the offspring rats and atomic absorption spectrometry was used to measure the blood and hippocampal lead concentrations of the offspring rats.Biochemical method was used to determine the nitric oxide (NO) levels and nitric oxide synthase (NOS) activities in hippocampus tissue of the offspring rats in various groups. The expressions of c-fos and PV proteins in hippocampus tissue of the offspring rats in various groups were detected by Western blotting method.Pearson correlation analysis was used to analyze the correlations between the expression levels of c-fos and PV proteins in hippocampus tisue of the offspring rats and the learning indexes,the NO level,and the NOS activity in hippocampus tissue. Results: In the positioning navigation test, compared with control group, the average escape latencies and the swimming distances of the offspring rats in medium and high doses lead-exposed groups were increased(P<0.05); in the space exploration experiment, the time of staying in the target quadrant and the number of crossing platform of the offspring rats in medium and high doses of lead-exposed groups were reduced(P<0.05).The blood lead and hippocampal lead concentrations of the offspring rats in various groups were statistically different (F=176.44,P<0.01;F=37.37,P<0.01); compared with control group, the blood lead and hippocampal lead concentrations of the offspring rats in low,medium and high doses of lead-exposed groups were significantly increased(P<0.05). There were statistical differences in the NO levels and the NOS activities in the hippocampus tissue of the offspring rats in various groups(F=4.105,P<0.05;F=3.443,P<0.05). Compared with control group, the NO level in hippocampus tissue of the offspring rats in high dose of lead-exposed group was significantly reduced(P<0.05), and the NOS activity was decreased (P<0.05).Compared with control group,the expression levels of c-fos protein in hippocampus tissue of the offspring rats in different doses of lead-exposed groups were decreased(P<0.05), and the expression levels of PV protein in hippocampus tissue in medium and high doses of lead-exposed groups were increased (P<0.05).The results of Pearson correlation analysis showed that the expression level of c-fos protein in hippocampus tissue of the offspring rats was positively correlated with the learning ability indexes of the water maze test and the NO level and the NOS activity in the hippocampus tissue (P<0.01); the expression level of the PV protein in hippocampus tissue of the offspring rats was negatively correlated with the learning ability indexes of the water maze test and the NO level and the NOS activity in the hippocampus tissue (P<0.01). Conclusion: Lead exposure during pregnancy and lactation periods can impair the learning and memory abilities of the offsprings rats, and the mechanism is related to the decrease of c-fos protein expression level and the increase of PV protein expression level in the hippocampus tissue.