Xie D H, Henson M M, Bishop A L, Henson O W
Department of Cell Biology and Anatomy, University of North Carolina, Chapel Hill 27599.
Hear Res. 1993 Mar;66(1):81-90. doi: 10.1016/0378-5955(93)90262-y.
Efferent terminals in the cochlea of the mustached bat were stained for acetylcholinesterase (AChE) and quantitative data were obtained for the number and size of the endings on the outer hair cells (OHCs) in each row, from base to apex. From TEM micrographs and AChE-stained, surface preparations it was determined that every OHC had a single, large terminal. The mean size of the terminals was significantly different in each row, with the largest occurring in the first row (7.1 microns 2); the mean size in the second and third rows was 5.7 and 5.0 microns 2 respectively. In specific frequency processing regions, the largest mean size (8.4 microns 2) for first row OHCs was consistently found in the distal densely innervated (DDI) area. This region has afferent neurons that are sharply tuned to the second harmonic, constant frequency component of the bat's biosonar signals. Sudden changes in the size of the terminals were observed exactly at the boundaries of the DDI with adjacent sparsely innervated regions. Similar, but less striking, size changes also occurred in and adjacent to the proximal densely innervated (PDI) region, a harmonically related, sharply tuned region, which processes the bat's 91.5 kHz, third harmonic, constant frequency signals. The region of the cochlea with the smallest first row terminals (mean 5.3 microns 2) was the large, sparsely innervated region of the basal turn, a region that does not appear to process biosonar signals. Although the significance of differences in efferent terminal size is not known, the data suggest a possible correlation between OHC stimulation and sharp tuning. The potentially greater influence of the efferent fibers on the first row of OHCs, compared to other rows, is consistent with observations made on other mammals; in the latter, however, the greater influence has been suggested more by number than size. Unlike other mammals, the OHC efferents in the mustached bat have no clear base-to-apex gradient in the number or size of the efferent terminals. It is suggested that this might reflect the high frequency nature of the ear (6-120 kHz) and absence of low frequency hearing.
对髯蝠耳蜗中的传出终末进行乙酰胆碱酯酶（AChE）染色，并获取从基部到顶部每排外毛细胞（OHC）上终末数量和大小的定量数据。通过透射电子显微镜（TEM）显微照片和AChE染色的表面标本确定，每个OHC都有一个单一的大终末。每排终末的平均大小有显著差异，最大的出现在第一排（7.1平方微米）；第二排和第三排的平均大小分别为5.7和5.0平方微米。在特定频率处理区域，第一排OHC的最大平均大小（8.4平方微米）始终出现在远端密集支配（DDI）区域。该区域的传入神经元对蝙蝠生物声纳信号的二次谐波、恒频成分有敏锐的调谐。在DDI与相邻稀疏支配区域的边界处，正好观察到终末大小的突然变化。在近端密集支配（PDI）区域及其附近也发生了类似但不太明显的大小变化，PDI区域是一个与谐波相关、调谐敏锐的区域，处理蝙蝠91.5千赫兹的三次谐波恒频信号。耳蜗中第一排终末最小（平均5.3平方微米）的区域是基部转弯处的大的、稀疏支配区域，该区域似乎不处理生物声纳信号。虽然传出终末大小差异的意义尚不清楚，但数据表明OHC刺激与敏锐调谐之间可能存在相关性。与其他排相比，传出纤维对第一排OHC可能有更大的影响，这与在其他哺乳动物上的观察结果一致；然而，在其他哺乳动物中，这种更大的影响更多是由数量而非大小表明的。与其他哺乳动物不同，髯蝠的OHC传出纤维在传出终末的数量或大小上没有明显的从基部到顶部的梯度。有人认为，这可能反映了耳朵的高频特性（6至120千赫兹）以及缺乏低频听力。
