噪声暴露对大鼠听皮层兴奋性及GABA和NMDA受体表达的影响

Noise Exposure Affects Auditory Cortex Responses and Expressions of GABA and NMDA Receptive

目的观察噪声暴露对大鼠听皮层兴奋性以及听皮层γ-氨基丁酸(γ-amino butyric acid,GABA)和N-甲基-天冬氨酸(N-methyl-D-aspartic acid,NMDA)受体表达的影响。方法将14只SD大鼠随机分为噪声暴露高剂量组(3只)、中剂量组(4只)、低剂量组(4只)和正常对照组(3只),高、中、低剂量噪声暴露组大鼠分别于125dB SPL白噪声暴露2小时、120dB SPL白噪声暴露1小时和90dB SPL白噪声暴露1小时,正常对照组不给予噪声暴露;在噪声暴露前、暴露后1小时、1天、3天、1周、2周行听性脑干反应(ABR)和声诱发听皮层放电率检测;运用蛋白免疫印迹技术检测听皮层兴奋性增强的大鼠以及对照组大鼠听皮层组织中GABA和NMDA两种受体亚型(GABAA、GABAB和NR2A、NR2B)的蛋白表达水平。结果所有噪声暴露组大鼠在暴露后1小时各频率ABR反应阈较暴露前显著提高,脱离噪声环境2周后,低、中剂量噪声暴露组各频率ABR反应阈恢复至暴露前水平,高剂量噪声暴露组ABR阈移未恢复。与暴露前相比,低剂量噪声暴露后大鼠听皮层放电率在各时间点未升高;中剂量噪声暴露后1小时听皮层放电率升高,2周后降低至暴露前水平;高剂量组噪声暴露后听皮层放电率在各时间点均降低。与对照组相比,噪声暴露后听皮层放电率升高的大鼠听皮层GABAA、GABAB、NR2A、NR2B受体表达水平均降低。结论 120dB SPL噪声暴露1小时可导致大鼠听皮层兴奋性增强,这可能与听皮层通过减少GABA抑制作用增强听觉中枢兴奋性来补偿外周听觉系统信号输入的减少有关。

Objective To investigate the effects of noise exposure on auditory cortex excitability and expressions ofγ-amino butyric acid(GABA)and N-methyl-D-aspartic acid(NMDA)in rats.Methods 14 sprague-dawley rats were used in the study.3 of them were exposed to white noise at 125 dB SPL for 2 h as high-noise level group,shile another 4 at 120 dB SPL for 1 h as medium level group.4 rats at 90 dB SPL for 1 h as low noise level,and the left 3 rats without noise exposed as as normal group.The auditory brainstem response(ABR)and auditory cortex firing rate were detected before and 1 hour,1 day,3 days,1 week and 2 weeks after noise exposure.The expression of GABA and NMDA receptor subunits in auditory cortex were examined by western blotting.Results The ABR thresholds were significantly increased 1 h after exposure in all the noise-exposed groups.2 weeks after noise exposure,the ABR threshold shifts diminished boch in the low and medium noise level groups,but remained still in high noise level group.Auditory cortex firing rate in lowl noise evel group did not change at all time points,after noise exposure,but it increased 1 hour after noise expose in the medium level groups and returned to normal 2 weeks later.It decreased at all the time points after-noise exposure in high level group.Compared to the control group,expressions of GABAA,GABAB NR2A and NR2B receptor in the auditory cortex were all reduced in all the noise exposure groups.Conclusion Exposure to white noise at 120 dB SPL for 1 h results in increased auditory cortical excitability in rats,which may be related with enhancement of auditory cortical excitability to compensate the reduction in peripheral inputs by reducing cortical GABA inhibition.