生命早期及成年再暴露百草枯对老年小鼠运动协调能力的影响

Effects of early-life exposure and adulthood re-challenge to paraquat on motor ability of C57BL/6 mice

[背景]生命早期是神经系统对神经毒物的高敏感期,任何外来因素对神经系统发育过程的干扰都可能造成永久性的损伤。百草枯(PQ)作为一种广泛使用的除草剂,成年期暴露可引起类帕金森样的运动功能损伤症状。然而有关生命早期PQ暴露是否可加重成年暴露引起的老年运动机能异常的研究仍然有限。[目的]研究生命早期暴露于PQ对不同性别C57BL/6小鼠及成年后再次暴露于PQ对雄性C57BL/6小鼠运动协调能力的影响。[方法]将出生后5 d的C57BL/6雄鼠及雌鼠各分为两组,雄性每组16只,雌性每组8只。对照组给予生理盐水(NS),处理组给予0.8 mg·kg-1 PQ,每天1次,连续腹腔注射15 d。至8月龄时,将生命早期NS及PQ处理的雄鼠进一步各随机分为两组,共4组,每组8只。NS+NS组及PQ+NS组隔2 d进行生理盐水腹腔注射,NS+PQ组及PQ+PQ组隔2 d进行PQ(10 mg·kg-1)腹腔注射,共10次。于小鼠22月龄时,使用步态分析实验对小鼠运动协调能力进行评估。[结果]在22月龄时,生命早期暴露于PQ降低了雄鼠步序正常指数[NS组:(95.12±2.79)%;PQ组:(85.04±2.33)%]、右前肢脚印面积[NS组:(0.317±0.004)m2;PQ组:(0.272±0.010)m2]及右前肢步幅[NS组:(6.38±0.11)cm;PQ组:(5.14±0.33)cm],增加了通过总步数(NS组:18.00±1.04;PQ组:24.38±1.71)及右前肢支撑时间[NS组:(0.286±0.001)s;PQ组:(0.315±0.014)s](均P<0.05);而生命早期PQ处理的雌鼠未观察到相应的步态变化(均P>0.05)。成年期暴露后,与NS+PQ组相比,PQ+PQ组通过总步数增加(NS+PQ组:19.88±0.72;PQ+PQ组:29.00±1.52)、步序正常指数降低[NS+PQ组:(94.82±2.85)%;PQ+PQ组:(88.32±2.02)%]、右前肢支撑时间增加[NS+PQ组:(0.336±0.010)s;PQ+PQ组:(0.384±0.119)s]、右前肢脚印面积减小[NS+PQ组:(0.307±0.008)m2;PQ+PQ组:(0.260±0.114)m2]、右前肢摇摆速度降低[NS+PQ组:(38.61±1.62)cm·s-1;PQ+PQ组:(26.52±1.38)cm·s-1]和右前肢步幅降低[NS+PQ组:(6.24±0.24)cm;PQ+PQ组:(4.70±0.27)cm](均P<0.05)。[结论]生命早期暴露于低剂量PQ会对雄鼠的运动协调能力造成不可逆的损伤,成年后再次暴露于PQ会进一步加重运动功能的损伤,但生命早期接触低剂量的PQ对雌性小鼠神经行为相关指标并无明显影响,提示在PQ引起的运动神经行为失调中,雄性啮齿动物比雌性更敏感。

[Background]Animals are highly susceptible to environmental neurotoxicants during early life,and tend to sustain life-long injuries.Adulthood exposure to paraquat(PQ),a widely applied herbicide,can cause Parkinson’s disease-like impaired motor function symptoms.There are limited studies,however,on the effects of exposure to PQ during early life and re-exposure in adult life on the motor function of the elderly.[Objective]This experiment investigates the effects of early-life exposure to PQ on the motor function of male and female C57 BL/6 mice,and the effects of adult-life re-challenge to PQ on the motor function of male C57 BL/6 mice.[Methods]Male and female C57 BL/6 mice at 5 days old were divided into two groups of each sex,with 16 male mice in each male group and 8 female mice in each female group.The control groups received normal saline(NS),while the PQ groups received intraperitoneal injection of 0.8 mg·kg-1 PQ,once a day,for consecutive 15 d.At 8 months old,the male mice treated with NS or PQ in early life were further divided into two groups of each treatment,with 8 mice in each group.The NS+NS group and the PQ+NS group additionally received NS administration,and the NS+PQ group and the PQ+PQ group additionally received 10 intraperitoneal injections of PQ(10 mg·kg-1),once every other day.At 22 months old,a gait analysis system was employed to assess the motor function of the mice.[Results]Early-life exposure to PQ decreased the regularity index[male NS group:(95.12±2.79)%;male PQ group:(85.04±2.33)%],the foot area of right forelimb[male NS group:(0.317±0.004)m2;male PQ group:(0.272±0.010)m2],and the stride of right forelimb[male NS group:(6.38±0.11)cm;male PQ group:(5.14±0.33)cm]of the male mice at 22 months of age,and also increased the number of steps(male NS group:18.00±1.04;male PQ group:24.38±1.71)and the run duration of right forelimb[male NS group:(0.286±0.001)s;male PQ group:(0.315±0.014)s](P<0.05).Early-life PQ treatment had no impacts on motor function of female mice(P>0.05).After re-challenge to PQ in adulthood,compared with NS+PQ treatment,PQ+PQ treatment significantly increased the number of steps(NS+PQ group:19.88±0.72;PQ+PQ group:29.00±1.52),decreased the regularity index[NS+PQ group:(94.82±2.85)%;PQ+PQ group:(88.32±2.02)%],increased the run duration of right forelimb[NS+PQ group:(0.336±0.010)s;PQ+PQ group:(0.384±0.119)s],decreased the foot area of right forelimb[NS+PQ group:(0.307±0.008)m2;PQ+PQ group:(0.260±0.114)m2],decreased the swing speed of right forelimb[NS+PQ group:(38.61±1.62)cm·s-1;PQ+PQ group:(26.52±1.38)cm·s-1],and decreased the stride of right forelimb[NS+PQ group:(6.24±0.24)cm;PQ+PQ group:(4.70±0.27)cm](P<0.05).[Conclusion]Early-life exposure to low-dose PQ can cause irreversible motor function impairments,and enhance the vulnerability to subsequent adulthood insults in male mice,but such effects are not observed in female mice,suggesting that male rodent animals are more sensitive to PQ in regard of motor behavior defects.