Jäger W, Khanna S M, Flock B, Flock A
Department of Physiology and Pharmacology, Karolinska Institutet, Stockholm, Sweden.
Hear Res. 1999 Aug;134(1-2):179-85. doi: 10.1016/s0378-5955(99)00083-0.
Local anesthetics applied in the tympanic cavity have earlier been shown to affect the gross receptor potentials in reducing the cochlear microphonics and increasing the positive summating potential. To study the effects of this drug on the mechanical responses in the cochlea, vibrations were measured using laser heterodyne interferometry in an isolated in vitro temporal bone preparation from the guinea pig. Measurements were made at a set of frequencies in the fourth cochlear turn from the Hensen's cells and the outer hair cells in response to sound applied to the ear. The tuning curves of the fundamental and the second harmonic components of the vibratory responses were plotted. When 2 mM tetracaine was applied, the high frequency slope of the second harmonic curve shifted down in frequency, this caused the frequency of the maximum of second harmonic tuning to shift down. These changes were reversible when tetracaine was washed out. Observations were also made in the temporal bone preparation in vitro with a confocal microscope. Fluorescent probes were used to label various structures in the organ of Corti. Optical sections were obtained by tilting the organ permitting a view from the side like a radial section through the organ. Images were acquired before, during and after application of tetracaine and were later analyzed with a computer program. Simultaneously, cochlear microphonics and the summating potential were obtained to monitor the electrical response of the preparation. Although the cochlear microphonics and summating potential decreased when 2 mM tetracaine was applied, structural changes were not measurable in the organ of Corti. The decrease was reversible when tetracaine was washed out. It is concluded that tetracaine affected the high frequency part of the non-linear second harmonic component, possibly by lowering the stiffness of the stereocilia bundle or the body of the outer hair cells.
先前已表明，应用于鼓室的局部麻醉药会影响总体感受器电位，降低耳蜗微音电位并增加正和电位。为了研究这种药物对耳蜗机械反应的影响，在豚鼠离体颞骨标本中使用激光外差干涉测量法测量振动。在从亨森细胞和外毛细胞开始的耳蜗第四圈的一组频率下进行测量，以响应施加到耳朵的声音。绘制了振动反应的基波和二次谐波分量的调谐曲线。当应用2 mM丁卡因时，二次谐波曲线的高频斜率在频率上向下移动，这导致二次谐波调谐最大值的频率向下移动。当丁卡因被冲洗掉时，这些变化是可逆的。还使用共聚焦显微镜在体外颞骨标本中进行了观察。使用荧光探针标记柯蒂氏器中的各种结构。通过倾斜器官获得光学切片，从而可以从侧面观察，就像通过器官的径向切片一样。在应用丁卡因之前、期间和之后采集图像，随后用计算机程序进行分析。同时，获得耳蜗微音电位和总和电位以监测标本的电反应。尽管当应用2 mM丁卡因时耳蜗微音电位和总和电位降低，但在柯蒂氏器中未检测到结构变化。当丁卡因被冲洗掉时，这种降低是可逆的。得出的结论是，丁卡因可能通过降低静纤毛束或外毛细胞体的硬度来影响非线性二次谐波分量的高频部分。
