McCue M P, Guinan J J
Eaton-Peabody Laboratory of Auditory Physiology, Department of Otolaryngology, Massachusetts Eye and Ear Infirmary, Boston 02114.
J Neurosci. 1994 Oct;14(10):6071-83. doi: 10.1523/JNEUROSCI.14-10-06071.1994.
In the preceding article (McCue and Guinan, 1994) we described a class of vestibular primary afferent fibers in the cat that responds vigorously to sounds at moderately high sound levels. Like their cochlear homologs, vestibular afferents and their associated hair cells receive efferent projections from brainstem neurons. In this report, we explore efferent influences on the background activity and tone-burst responses of the acoustically responsive vestibular afferents. Shock-burst stimulation of efferents excited acoustically responsive vestibular afferents; no inhibition was seen. A fast excitatory component built up within 100-200 msec of shock-burst onset and decayed with a similar time course at the end of each shock burst. During repeated 400 msec shock bursts at 1.5 sec intervals, a slow excitatory component grew over 20-40 sec and then decayed, even though the shock bursts continued. Efferent stimulation excited acoustically responsive vestibular afferents without appreciably changing an afferent's sound threshold or its average sound-evoked response. This evidence supports the hypothesis that excitation is due to efferent synapses on afferent fibers rather than on hair cells. Efferent stimulation enhanced the within-cycle modulation of afferent discharges evoked by a tone; that is, it increased the "AC gain." No appreciable change was noted in the degree of phase locking to low-frequency tones as measured by the synchronization index. Little or no improvement in the bidirectionality (linearity) of transduction was seen. Vestibular afferent responses to tones normally had one peak per cycle; however, during efferent stimulation, two peaks per cycle were sometimes seen. We hypothesize that this is caused by two driving components acting at different sound phases with the components differentially affected by efferent activity. We discuss the relationship of our findings to efferent influences on acoustic responses in cochlear afferent fibers. The acoustically responsive vestibular afferents provide a mammalian model for studying purely excitatory efferent effects in a hair cell system.
在前一篇文章（麦丘和吉南，1994年）中，我们描述了猫体内一类前庭初级传入纤维，它们在中等偏高的声音强度下对声音有强烈反应。与它们的耳蜗同源物一样，前庭传入纤维及其相关的毛细胞接受来自脑干神经元的传出投射。在本报告中，我们探讨了传出神经对听觉反应性前庭传入纤维的背景活动和短纯音反应的影响。对传出神经进行冲击爆发刺激可兴奋听觉反应性前庭传入纤维；未观察到抑制作用。快速兴奋成分在冲击爆发开始后的100 - 200毫秒内形成，并在每次冲击爆发结束时以相似的时间进程衰减。在以1.5秒的间隔重复进行400毫秒的冲击爆发时，一个缓慢的兴奋成分在20 - 40秒内逐渐增强，然后衰减，即使冲击爆发仍在继续。传出神经刺激兴奋了听觉反应性前庭传入纤维，而没有明显改变传入纤维的声音阈值或其平均声音诱发反应。这一证据支持了这样的假设，即兴奋是由于传出神经在传入纤维上的突触作用，而不是在毛细胞上。传出神经刺激增强了由纯音诱发的传入放电的周期内调制；也就是说，它增加了“交流增益”。通过同步指数测量，对低频纯音的锁相程度没有明显变化。在转导的双向性（线性）方面几乎没有或没有改善。前庭传入纤维对纯音的反应通常每个周期有一个峰值；然而，在传出神经刺激期间，有时每个周期会出现两个峰值。我们假设这是由两个在不同声音相位起作用的驱动成分引起的，这些成分受传出神经活动的影响不同。我们讨论了我们的发现与传出神经对耳蜗传入纤维听觉反应的影响之间的关系。听觉反应性前庭传入纤维为研究毛细胞系统中纯粹的兴奋性传出神经效应提供了一个哺乳动物模型。
