Guinan J J, Gifford M L
Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge.
Hear Res. 1988 May;33(2):97-113. doi: 10.1016/0378-5955(88)90023-8.
In previous studies describing the effects of electrically stimulating the olivocochlear bundle, it seems possible that both medial and lateral (MOC and LOC) efferents may have been stimulated. To selectively stimulate MOC efferents, we used an electrode placed at the origin of the MOC efferents in the brainstem (MOC stimulation). For comparison, a stimulating electrode was placed in the fourth ventricle at the decussation of the crossed olivocochlear bundle where both MOC and LOC efferents are present (midline-OCB stimulation). Rate versus sound level functions from auditory-nerve fibers were obtained with and without efferent stimulation. Stimulation at either location shifted rate vs. level functions to higher sound levels and depressed the rate in the plateau. For fibers with high spontaneous rates, the level shifts and plateau depressions had slightly different distributions as a function of characteristic frequency. The average amplitudes of these effects were largest for midline-OCB stimulation, next largest for crossed MOC stimulation and smallest for uncrossed MOC stimulation. The qualitative pattern of the effects, however, did not depend on the location of the stimulus electrode. The amplitudes of the efferent-induced effects were different for auditory-nerve fibers with different spontaneous rates (by as much as a factor of three for the plateau depression). The results support several hypotheses: (1) the effects of midline-OCB stimulation are due only to the action of MOC efferents, (2) individual crossed and uncrossed MOC fibers produce similar effects, and (3) efferents differentially change the information carrying properties of auditory-nerve fibers in different spontaneous-rate categories. These results, taken together with anatomical data in the literature, are consistent with the hypothesis that, in the cat, MOC and midline-OCB stimulation have their effect solely through synapses on outer hair cells. The data are consistent with the hypothesis that the level shifts are produced by MOC efferents acting on outer hair cells to reduce the mechanical stimulus to inner hair cells. It seems likely that some other mechanism is required to produce the plateau depressions, at least for auditory-nerve fibers with high spontaneous rates.
在先前描述电刺激橄榄耳蜗束效应的研究中，似乎有可能内侧和外侧（MOC和LOC）传出神经均受到了刺激。为了选择性地刺激MOC传出神经，我们使用了一个放置在脑干中MOC传出神经起始部位的电极（MOC刺激）。作为对照，将一个刺激电极置于交叉橄榄耳蜗束交叉处的第四脑室，此处同时存在MOC和LOC传出神经（中线-OCB刺激）。在有和没有传出神经刺激的情况下，获取听神经纤维的发放率与声级函数。在这两个位置的刺激均使发放率与声级函数向更高声级偏移，并使平台期的发放率降低。对于具有高自发放电率的纤维，声级偏移和平台期降低作为特征频率的函数，具有略有不同的分布。这些效应的平均幅度对于中线-OCB刺激最大，其次是交叉MOC刺激，对于未交叉MOC刺激最小。然而，效应的定性模式并不取决于刺激电极的位置。对于具有不同自发放电率的听神经纤维，传出神经诱导效应的幅度不同（平台期降低可达三倍之多）。这些结果支持了几个假设：（1）中线-OCB刺激的效应仅归因于MOC传出神经的作用；（2）单个交叉和未交叉的MOC纤维产生相似的效应；（3）传出神经以不同方式改变不同自发放电率类别的听神经纤维的信息携带特性。这些结果与文献中的解剖学数据一起，与以下假设一致：在猫中，MOC和中线-OCB刺激仅通过对外毛细胞的突触起作用。数据与以下假设一致：声级偏移是由MOC传出神经作用于外毛细胞以减少对内毛细胞的机械刺激而产生的。似乎至少对于具有高自发放电率的听神经纤维，需要一些其他机制来产生平台期降低。
