噪声影响下纯音诱发听性脑干反应的改变

Changes in tone burst evoked auditory brainstem response by noise exposure

目的观察噪声影响下纯音诱发听性脑干反应(ABR)的改变。方法将10只成年南美栗鼠随机平均分为两组,分别暴露强度为105dB SPL窄带噪声,中心频率4kHz,2h或5h。噪声暴露前、后1h、2周及4周,测试动物对短纯音声音刺激(1、2、4、8、12以及16kHz)诱发的听神经复合动作电位(CAP)和ABR,并结合耳蜗毛细胞的损害程度和范围进行分析。结果 2h和5h的窄带噪声暴露造成南美栗鼠不同程度和范围的耳蜗毛细胞损害。与毛细胞损害部位相对应频率的CAP及ABR阈值在暴露噪声后均出现不同程度的提高。噪声暴露后4周,尽管某些动物的CAP已经发生了不可逆性永久阈移,但在某些短纯音频率诱发的ABR阈值却呈现部分恢复,甚至在个别动物的CAP测试波形中引出了低于CAP阈值的ABR波形成分。结论中枢听觉功能的重组在一定条件下可能促进脑干听觉神经元提高感知因周边耳蜗损害而引起微弱听觉输入信号的敏感性。

Objective To investigate the auditory plasticity-induced functional changes in auditory brainstem response（ABR） following the noise exposure. Methods Ten chinchillas were randomly divided into two groups, and exposed to 105 dB SPL octave band noise centered at 4 kHz for 2 or 5 hours respectively. ABR and compound action potentials （CAP） were recorded prior to noise exposure, and 1 hour, 2 weeks, 4 weeks after noise exposure. Stimuli were presented in ascending order of frequency （in octave steps from 1 kHz to 16 kHz）. Hair cell counts （cyto-cochleograms） were performed from cochlear surface preparation under light microscope. Results Exposure to 105 dB SPL narrow-band noise for a period of time caused various ranges of permanent damage in the cochlear hair cells. The thresholds of ABR and CAP in response to different frequencies tested were elevated which were consistent to the location of hair cell miss- ing. Four weeks after noise exposure, in some animals, permanent threshold shifts were detected from CAP recording, however, ABR thresholds were partially recovered in some frequencies. In one animal, ABR was detected after CAP waveform with a lower threshold than the CAP. Conclusions The plasticity and reorganization of central auditory system may enhance the sensitivity of brainstem auditory neurons to the feeble signal input from the damaged cochlea.