Felix D, Ehrenberger K
Division of Neurobiology, University of Berne, Switzerland.
Hear Res. 1992 Dec;64(1):1-5. doi: 10.1016/0378-5955(92)90163-h.
The results of immunocytochemical, enzymatic and electrophysiological studies have indicated that acetylcholine and GABA may act as neurotransmitters in lateral olivocochlear efferent endings on inner hair cell afferent dendrites. Since spike activity can be recorded in the dendritic region of inner hair cells, microiontophoretic techniques were used testing the possible neurotransmitter candidates, acetylcholine and GABA, on spontaneous and induced firing of the afferent dendrites. The experiments were carried out in anaesthetised guinea-pigs, the third and fourth turns of the cochlea being exposed for electrode penetration. Ejection of acetylcholine resulted in a pronounced dose-dependent increase in subsynaptic spiking activity. Furthermore, acetylcholine enhanced glutamate-induced activity. In contrast, even at high doses, GABA had very little effect on the spontaneous cochlear firing rate. When the firing rate had first been enhanced by glutamate or N-methyl-D-aspartate, however, this activation could be reduced by the ejection of GABA. A similar reduction was observed when the firing rate had been enhanced with acetylcholine. The results of our studies support the hypothesis that these substances are involved in efferent neurotransmission on inner hair cell afferent fibres. It should be pointed out, however, that besides acetylcholine and GABA, several opioids such as enkephalins and dynorphins seem to be involved in efferent cochlear innervation.
免疫细胞化学、酶学及电生理学研究结果表明，乙酰胆碱和γ-氨基丁酸（GABA）可能在内侧橄榄耳蜗传出神经末梢与内毛细胞传入树突上充当神经递质。由于在内毛细胞的树突区域可记录到锋电位活动，因此采用微离子电泳技术来测试可能的神经递质候选物——乙酰胆碱和GABA，对传入树突的自发放电和诱发放电的影响。实验在麻醉的豚鼠身上进行，暴露耳蜗的第三和第四圈以进行电极插入。乙酰胆碱的微量注射导致突触后锋电位活动出现明显的剂量依赖性增加。此外，乙酰胆碱增强了谷氨酸诱导的活动。相比之下，即使在高剂量下，GABA对耳蜗自发放电率的影响也很小。然而，当放电率首先被谷氨酸或N-甲基-D-天冬氨酸增强后，GABA的微量注射可降低这种激活。当放电率被乙酰胆碱增强时，也观察到了类似的降低。我们的研究结果支持了这样一种假说，即这些物质参与了内毛细胞传入纤维上的传出神经传递。然而，应该指出的是，除了乙酰胆碱和GABA外，几种阿片类物质，如脑啡肽和强啡肽，似乎也参与了耳蜗的传出神经支配。
