砷暴露对大鼠学习记忆能力的影响

Effect of arsenic exposure on learning and memory in rat models and its underlying mechanisms

目的探讨出生后发育关键期低质量浓度砷暴露对大鼠学习记忆的影响及其可能机制。方法构建幼年大鼠脑快速发育期(出生4~10d)水砷暴露模型。实验分为4组(每组10~12只):正常对照组、15μg/L三氧化二砷(As2O3)组、30μg/LAs2O3组、45μg/LAs2O3组。应用水迷宫实验进行学习记忆能力测试。采用HE染色、尼氏染色检测砷暴露后不同时间点海马CA1~CA3区和齿状回dentategyrus(DG)神经元结构,免疫组织化学法检测微管相关蛋白Doublecortin(DCX),了解海马神经元的生长发育水平。结果与正常对照组比较,砷暴露组大鼠逃避潜伏期延长,正常对照组、15μg/LAs2O3组、30μg/LAs2O3组、45μg/LAs2O3组大鼠第5天平均逃避潜伏期分别为(17.00±9.53)s、(35.89±19.81)s、(26.60±18.84)s、(33.79±18.08)s,组间比较差异有统计学意义(F=3.591,P<0.05),在原目标象限停留时间缩短,分别为(38.93±8.33)s、(36.03±16.25)s、(29.85±9.27)s、(29.84±10.16)s,组间比较差异无统计学意义(F=1.681,P=0.187)。HE染色和尼氏染色显示:急性期砷暴露大鼠海马CA1区、CA2区及齿状回细胞出现水肿、变性、坏死等病理改变,砷暴露质量浓度越高,细胞结构紊乱越明显。但暴露后5周检测发现,砷暴露组海马神经元病理改变逐渐恢复正常。免疫组织化学显示:砷暴露后24h,与对照组比较,砷暴露大鼠CA1区、CA2区及齿状回DCX表达明显减少,其中45μg/LAs2O2组最为明显。砷暴露后5周,海马CA1~CA3区各组均无表达,齿状回仍有少量表达。结论出生后发育关键期低质量浓度砷暴露可影响大鼠的学习记忆,大鼠海马齿状回神经元的生发异常可能为其潜在机制。

Objective To explore the effects of arsenic exposure on learning and memory and its potential mechanism in rats. Methods Water-based arsenic-exposed rat models were established on 4-10 postnatal days.The experimental animals were divided into 4 groups (10-12 cases in each group): the control group, the 15 μg/L As2O3 water group, the 30 μg/L As2O3 water group, and the 45 μg/L As2O3 water group.Cognitive functions were examined with the Morris water maze, exploratory behavior was detected by the exploratory behavior test.The hippocampus of pups from each experimental group was sectioned at various time points after arsenic exposure.The morphologies and neurogenesis of the neurons in the hippocampus CA1-CA3 region and dentate gyrus (DG) were observed by hematoxylin-eosin staining, Nissl staining, and doublecortin (DCX) immunostaining at different time points after arsenic exposure. Results Compared with the normal control group, the escape latency of the rats in the arsenic-exposed group was prolonged.The average escape latency of the rats in the normal control group, 15 μg/L As2O3 group, 30 μg/L As2O3 group and 45 μg/L As2O3 group were (17.00±9.53) s,(35.89±19.81) s,(26.60±18.84) s, and (33.79±18.08) s, respectively, and the difference among 4 groups was statistically significant (F=3.591, P<0.05), and the residence time in the original target quadrant was shortened, respectively,(38.93±8.33) s,(36.03±16.25) s,(29.85±9.27) s, and (29.84±10.16) s, respectively, and there was no significant difference among 4 groups (F=1.681, P=0.187). HE staining and Nissl staining showed that pathological changes such as edema, degeneration and necrosis were observed in the hippocampal CA1 area and CA2 area as well as dentate gyrus cells in rats exposed to arsenic in the acute phase.The higher the concentration of arsenic exposure, the more obvious the cell structure disorder was.However, 5 weeks after exposure, the pathological changes in hippocampal neurons in the arsenic-exposed group gradually returned to normal.Immunohistochemistry showed that the expressions of DCX in the CA1, CA2 and dentate gyrus of rats exposed to arsenic decreased significantly 24 h after arsenic exposure, especially in the 45 μg/L group.Five weeks after arsenic exposure, there was no expression in the hippocampal CA1-CA3 area, and there was still a small amount of expression in the dentate gyrus. Conclusions Postnatal low-concentration arsenic exposure may impair learning and abnormal germination of neurons in the hippocampal dentate gyrus may be the underlying mechanism.