Rajan R
Department of Physiology, Monash University, Monash, VIC 3800, Australia.
J Neurophysiol. 2001 Dec;86(6):3073-6. doi: 10.1152/jn.2001.86.6.3073.
Centrifugal crossed and uncrossed medial olivocochlear systems (CMOCS and UMOCS) terminate on cochlear outer hair cells (OHCs) and exercise effects through a nicotinic cholinergic receptor. Hence their cochlear effects have not been differentiated. Recent work on protection from loud-sound-induced temporary threshold shifts (TTSs) in hearing sensitivity suggest the two OHC efferent systems may act differently. This was tested, using traumatic complex sound, to determine if such sound could activate both MOCS components and then reveal whether they exerted different effects on TTSs to such stimuli. Traumatic noise bands activated crossed and uncrossed MOCS efferents. Two different CMOCS effects were observed. For frequencies in the noise (within-band frequencies), it protected hearing sensitivity as expected. Novel findings were that at frequencies higher than the noise band range (high-side frequencies), it acted to worsen hearing sensitivity and that this was opposed by a UMOCS effect generally targeted to these frequency regions. It is proposed that the two crossed MOCS actions are extensions of a contrast-enhancement action for low-level noise bands. It is also proposed that the UMOCS plays a state-restoration role to prevent an undesired CMOCS side-effect of exacerbation of high-side TTSs to high-level noise bands.
离心交叉和不交叉内侧橄榄耳蜗系统（CMOCS和UMOCS）终止于耳蜗外毛细胞（OHC），并通过烟碱型胆碱能受体发挥作用。因此，它们对耳蜗的作用尚未得到区分。最近关于保护听力免受大声诱发的暂时性阈值偏移（TTS）影响的研究表明，这两个OHC传出系统的作用可能不同。本研究使用创伤性复合声音对此进行了测试，以确定这种声音是否能激活两个MOCS成分，然后揭示它们对这种刺激的TTS是否有不同影响。创伤性噪声带激活了交叉和不交叉的MOCS传出神经。观察到两种不同的CMOCS效应。对于噪声中的频率（带内频率），它如预期的那样保护了听力敏感性。新的发现是，在高于噪声带范围的频率（高端频率），它会使听力敏感性恶化，而UMOCS效应通常针对这些频率区域，起到了相反的作用。有人提出，两种交叉的MOCS作用是对低水平噪声带对比度增强作用的扩展。也有人提出，UMOCS起到状态恢复的作用，以防止CMOCS产生不期望的副作用，即加剧高端TTS对高水平噪声带的影响。
