慢性氟中毒对大鼠脑组织Phospho—Elk-1表达的影响

Influence of chronic fluorosis on expression of phospho-Elk-1 in rat brains

目的 观察慢性氟中毒大鼠脑组织中细胞外调节蛋白激酶（ERK1/2）信号转导通路下游作用底物三元复合物因子Phospho-Elk-1的表达和分布,探讨慢性氟中毒所致学习记忆损害的发生机制.方法 SD 大鼠72只,体质量100～120 g,按体质量随机分为3组,每组24只,雌雄各半.对照组饮用自来水（含氟量〈0.5 mg/L）,低氟组和高氟组饮用加入氟化钠的自来水（P质量浓度分别为5.0、50.0 mg/L）.6个月后,称取大鼠体质量,观察氟斑牙发生情况,用氟离子选择电极法检测大鼠尿氟及骨氟;用Morris水迷宫方法的定向航行实验检测大鼠学习能力,空间探索实验检测大鼠记忆能力;用免疫组织化学方法检测大鼠脑组织中Phospho-Elk-1在蛋白水平的表达和分布.结果 低氟组和高氟组大鼠体质量[（449.2±77.1）、（312.8 ±89.7）g]较对照组[（635.5±76.2）g]显著下降（P均〈0.05）,出现不同程度氟斑牙（x2=7.83,P〈0.05）,尿氟[（2.56±0.91）、（5.73±3.14）mg/L]及骨氟[（709.2±37.4）、（1306.3 ±102.4）mg/kg]较对照组[（0.92±0.30）mg/L、（348.5 ±89.2）mg/kg]明显升高（P均〈0.05）.低氟组和高氟组大鼠逃避潜伏期[（7.4±4.1）、（12.2±5.7）s]较对照组[（4.8±2.7）s]明显延长（P均〈0.05）,第1次穿越平台区时同[（4.18±1.10）、（5.89±0.56）s]较对照组[（1.17±0.75）s]显著延长（P均〈0.05）,均以高氟组尤为明显（P均〈0.05）.低氟组和高氟组大鼠海马CA1区（167.4±8.3、163.2±9.4）、CA2区（175.7±5.0、183.3±4.2）、CA3区（165.2±11.6、162.9±4.4）、CA4 区（168.7±6.9、169.5±5.3）、齿状回（185.2 ±4.0、193.1±6.1）及尾壳核（181.4±3.8、179.8±5.5）神经细胞Phospho-Elk-1表达水平较对照组（142.4±8.1、144.9±8.4、143.6±5.8、116.8±9.1、140.2±7.8、163.1±13.1）显著增加（P均〈0.05）.结论 慢性氟中毒可引起大鼠脑组织海马及尾壳核区域Pbospho-Elk-1表达水平升高,这种改变可能与大鼠学习记忆能力下降机制有一定关系.

Objective To investigate the expression and distribution of the downstream substrate of extracellular regulated protein kinase（ERK1/2） pathway, ternary complex factor phospho-Elk-1, in rat brains with chronic fluorosis, and reveal the mechanism of the impaired learning and memory ability caused by chronic fluorosis. Methods Seventy-two SD rats, weighing 100 - 120 g, were randomly divided into 3 groups, 24 in each group （half male and half female）. The rats in control group were fed with tap water （fluoride 〈 0.5 mg/L）; low- and high-dose fluoride groups were fed with tap water with different concentrations of NaF（5.0,50.0 mg/L F-, respectively）. After 6 months, body weight was weighed, dental fluorosis was determined by observation and urinary fluoride and bone fluoride were detected by fluorine ion-selective electrode; the learning ability of rats was measured by navigation test of Morris water maze, and memory ability by spatial probe test in Morris water maze; the expression and distribution of phospho-Elk-1 in different brain regions were detected by immunohistochemistry method. Results In low- and high-fluoride groups, the body weight of rat[（449.2 ± 77.1）, （312.8 ± 89.7）g] was significantly decreased than that of control [（635.5 ± 76.2 ）g, all P〈 0.05], the varying degrees of dental fluorosis were observed（x2 = 7.83, P〈0.05）, urinary fluoride[（2.56 ±0.91）,（5.73 ±3.14）mg/L] and bone fluoride[（709.2 ± 37.4） ,（1306.3 ± 102.4） mg/kg] were significantly higher than those in controls[（0.92 ± 0.30）mg/L,（348.5 ± 89.2）mg/kg, all P〈 0.05]. The escape latency of low- and high-fluoride groups[ （7.4 ± 4.1）, （12.2 ± 5.7）s] was longer than that of control [（4.8 ± 2.7 ）s, all P 〈 0.05] and the escape latency in high-fluoride group was significantly longer than that in other groups （all P 〈 0.05）; in spatial probe test, the time of first crossing platform was longer in rats with fluorosis [（4.18 ± 1.10）,（5.89 ± 0.56）s] as compared to control[（1.17 ± 0.75）s, all P〈 0.05]. Expressions of phospho-Elk-1 in the hippocampus CA1（167.4 ± 8.3,163.2 ± 9.4）, CA2（175.7 ± 5.0,183.3 ± 4.2）, CA3（165.2 ± 11.6,162.9 ± 4.4）, CA4（168.7± 6.9,169.5 ±5.3）, fascia dentate （185.2 ±4.0,193.1 ±6.1） and caudate putamen（ 181.4 ± 3.8, 179.8 ± 5.5） in low- and high-fluoride groups were higher than those of controls（142.4 ± 8.1,144.9 ± 8.4,143.6 ± 5.8, 116.8 ± 9.1,140.2 ± 7.8,163.1 ± 13.1, all P〈 0.05）. Conclusion Chronic fluorosis can cause increased expression of phospho-Elk-1 in the hippocampus and caudate putamen region of rat brains, which might be related to the mechanisms of decreased learning and memory ability of rats overexposed to fluoride.