间歇性与持续性噪声暴露致大鼠焦虑抑郁样行为改变机制

Mechanism of intermittent and persistent noise exposure-induced anxiety and depression-like behavior in rats

目的 探讨间歇性与持续性噪声暴露所致大鼠焦虑抑郁样行为改变及其机制。方法 将无特定病原体级雄性SD大鼠随机分为对照组、4次/d间歇暴露组、2次/d间歇暴露组和持续暴露组,每组15只。对照组大鼠饲养于自然环境(背景噪声≤50 dB),3个暴露组大鼠每日均暴露于强度为(95±2) dB的20~20 000 Hz的噪声环境4 h,持续14 d;其中,4次/d间歇暴露组大鼠每暴露1 h进入5 h安静期,4次/d;2次/d间歇暴露组大鼠每暴露2 h进入10 h安静期,2次/d;持续暴露组每暴露4 h进入20 h安静期。暴露结束后,采用旷场实验和高架十字迷宫实验评估大鼠焦虑样行为,采用糖水偏爱实验和强迫游泳实验评价大鼠抑郁样行为;采用苏木素-伊红(HE)染色法观察大鼠海马神经元病理学改变,采用透射电子显微镜观察海马组织超微结构改变;采用化学荧光法和比色法检测大鼠海马组织中活性氧自由基(ROS)、丙二醛、谷胱甘肽(GSH)水平和超氧化物歧化酶(SOD)活力。结果 行为学实验中,与对照组比较,3个暴露组大鼠中心区运动时间百分比均下降(P值均<0.01),持续暴露组大鼠中心区运动路程和糖水偏爱指数均下降(P值均<0.01),2次/d间歇暴露组和持续暴露组大鼠开臂运动时间百分比与开臂运动路程均下降(P值均<0.01)。持续暴露组大鼠开臂运动路程短于4次/d间歇暴露组(P<0.05),不动时间分别长于对照组和4次/d间歇暴露组(P值均<0.05)。HE染色结果显示:持续暴露组大鼠海马组织CA1区神经元间距显著增宽,锥体细胞变性坏死;其余3组均未见明显神经坏死。神经元超微结构显示:2次/d间歇暴露组大鼠海马组织多数线粒体发生肿胀;持续暴露组大鼠海马组织可见部分神经元坏死,胞膜不连续,线粒体肿胀,嵴断裂、溶解甚至消失;其余2组大鼠海马组织线粒体结构较正常。与对照组比较,4次/d间歇暴露组大鼠海马组织SOD活力下降(P<0.05),2次/d间歇暴露组大鼠海马组织SOD活力和GSH水平均下降(P值均<0.05)。与其余3组比较,持续暴露组大鼠海马组织ROS和丙二醛水平均上升(P值均<0.05),SOD活力和GSH水平均下降(P值均<0.05)。结论 间歇性噪声暴露引起的大鼠焦虑抑郁样改变较持续性噪声暴露者轻;噪声可能通过氧化应激途径导致大鼠焦虑与抑郁。

Objective To investigate the effects and mechanisms of intermittent and persistent noise exposure-induced anxiety and depression-like behavior in rats. Methods The specific pathogen free male SD rats were randomly divided into control group, four times/day intermittent noise exposure group, two times/day intermittent noise exposure group and persistent noise exposure group, with 15 rats in each group. The rats in the control group were housed in natural environment(background noise ≤50 dB), and the rats in other three exposure groups were exposed to noise with intensity of(95±2) dB of 20 to 20 000 Hz noise for four hours per day for 14 days;rats in the four times/day intermittent noise exposure group entered a five-hour quiet period every one hours of noise exposure, four times/day;rats in the two times/day intermittent noise exposure group entered a 10-hour quiet period every two hours of noise exposure, two times/day;rats in the persistent noise exposure group entered a 20-hour quiet period every four hours of noise exposure. After exposure, anxiety like behavior was evaluated by open field test and elevated cross maze test. The depression like behavior was evaluated by sugar preference test and forced swimming test. The pathological changes of neurons in the hippocampus were observed by hematoxylin-eosin(HE) staining, and the ultrastructural changes of hippocampal tissues were observed by transmission electron microscope. Chemiluminescence and colorimetry were used to detect the levels of reactive oxygen species(ROS), malondialdehyde, glutathione(GSH) and the activity of superoxide dismutase(SOD). Results In the behavioral experiment, the percentage of exercise time in the central area decreased in the three noise exposure groups(all P<0.01). The exercise distance in the central area and sugar preference index decreased in the persistent noise exposure group(both P<0.01). The percentage of open arm exercise time and open arm exercise distance decreased in the two times/day intermittent noise exposure group and persistent noise exposure group compared with the control group(all P<0.01). The open arm distance of rats in the persistent noise exposure group were lower than those in the four times/day intermittent noise exposure group(P<0.05), while the immobility time was longer than in control group and the four times/day intermittent noise exposure group(both P<0.05). The HE staining showed that the neuronal spacing in CA1 area of the hippocampus of rats was significantly widened, and the pyramidal cells showed degeneration and necrosis in the persistent noise exposure group. There was no obvious necrosis found in the neurons of the other three groups. The ultrastructure of neurons showed that most mitochondria of cells in the hippocampus of rats in the two times/day intermittent noise exposure group were swollen. In the persistent noise exposure group, some neurons of the hippocampus of rats were necrotic, the cell membrane was discontinuous, the mitochondria were swollen, and the cristae were broken, dissolved or even disappeared. The mitochondrial structure of the hippocampus of rats in the other two groups was normal. The activity of SOD in the hippocampus of rats decreased in the four times/day intermittent noise exposure group(P<0.05), and the activity of SOD and the level of GSH in the hippocampus of rats decreased in the two times/day intermittent noise exposure group(both P<0.05), compared with the control group. The level of ROS and malondialdehyde in the hippocampus of rats in the persistent noise exposure group increased(all P<0.05), while the SOD activity and GSH level decreased(all P<0.05), compared with the other three groups. Conclusion Intermittent noise exposure causes less anxiety and depression-like changes in rats than persistent noise exposure. Noise may cause anxiety and depression in rats through oxidative stress pathways.