Rajan R
Department of Physiology, Monash University, Monash, VIC 3800, Australia.
J Neurophysiol. 2001 Sep;86(3):1277-88. doi: 10.1152/jn.2001.86.3.1277.
Priming/conditioning the cochlea with moderately loud sound can reduce damage caused by subsequent loud sound. This study examined immediate effects of short-term priming with monaural broadband noise on temporary threshold shifts (TTSs) in hearing caused by a subsequent loud high-frequency tone and the role of centrifugal olivocochlear pathways. Priming caused delay-dependent changes in tone-induced TTSs, particularly or only at frequencies higher than the peak tone-affected frequency, through two general effects: a short-lasting increase in cochlear susceptibility to loud sound and longer-lasting complex end effects of centrifugal pathways. The results indicated the following points. Priming noise had "pure" cochlear effects, outlasting its presentation and declining with delay, that exacerbated tone-induced TTSs at frequencies higher than the peak tone-affected frequency. The centrifugal uncrossed medial olivocochlear system (UMOCS) could prevent this noise exacerbation and as this noise effect declined, could even reduce tone-induced TTSs below those to the unprimed tone. For longer delays, when priming noise no longer had any exacerbative "pure" cochlear effects on TTSs, UMOCS exacerbated TTSs above those to the unprimed tone. The crossed medial olivocochlear system (CMOCS) appeared to show a gradual "build-up" of effects postpriming. A parallel study showed it exercised no end effect on TTSs when noise and tone were concurrent. With priming, CMOCS effects were observed. For the shortest priming delay, the CMOCS blocked a UMOCS effect preventing noise exacerbation of tone-induced TTSs. For longer delays, CMOCS end effects, when present, reduced tone-induced TTSs below those to the unprimed tone. The CMOCS may oscillate between producing these effects and exerting no end-effect. With increasing delay CMOCS protection occurred in a greater proportion of animals. Finally, with a delay of 600 s between primer and loud tone, all these systems appeared to have reset to normal so that TTSs were similar to those in the unprimed condition. Thus the effects of short-term priming are not simple and do not suggest that centrifugal pathways act automatically as a protective system during such priming.
用适度响亮的声音对耳蜗进行预处理/调节可以减少后续响亮声音造成的损伤。本研究考察了单耳宽带噪声短期预处理对后续响亮高频音调引起的听力暂时阈移（TTS）的即时影响以及离心性橄榄耳蜗通路的作用。预处理通过两种一般效应导致音调诱发的TTS出现延迟依赖性变化，特别是或仅在高于峰值音调影响频率的频率上：耳蜗对响亮声音的易感性短暂增加以及离心通路的持续时间更长的复杂终末效应。结果表明以下几点。预处理噪声具有“纯粹”的耳蜗效应，持续时间超过其呈现时间并随延迟而下降，在高于峰值音调影响频率的频率上加剧了音调诱发的TTS。离心性未交叉内侧橄榄耳蜗系统（UMOCS）可以防止这种噪声加剧，并且随着这种噪声效应的下降，甚至可以将音调诱发的TTS降低到低于未预处理音调的水平。对于更长的延迟，当预处理噪声不再对TTS产生任何加剧性的“纯粹”耳蜗效应时，UMOCS使TTS高于未预处理音调的水平。交叉内侧橄榄耳蜗系统（CMOCS）在预处理后似乎表现出逐渐的“累积”效应。一项平行研究表明，当噪声和音调同时出现时，它对TTS没有终末效应。在进行预处理时，观察到了CMOCS效应。对于最短的预处理延迟，CMOCS阻断了UMOCS防止噪声加剧音调诱发TTS的效应。对于更长的延迟，CMOCS的终末效应（如果存在）将音调诱发的TTS降低到低于未预处理音调的水平。CMOCS可能在产生这些效应和不产生终末效应之间振荡。随着延迟增加，CMOCS保护作用在更大比例的动物中出现。最后，在预处理噪声和响亮音调之间延迟600秒时，所有这些系统似乎都已重置为正常状态，因此TTS与未预处理状态下的相似。因此，短期预处理的效应并不简单，也不表明离心通路在这种预处理过程中会自动作为保护系统起作用。
