COCHLEAR BASAL AND APICAL DIFFERENCES REFLECTED IN THE EFFECTS OF COOLING ON RESPONSES OF SINGLE AUDITORY-NERVE FIBERS
COCHLEAR BASAL AND APICAL DIFFERENCES REFLECTED IN THE EFFECTS OF COOLING ON RESPONSES OF SINGLE AUDITORY-NERVE FIBERS
复制标题
DOI：
10.1016/0378-5955(94)90109-0
复制
发表时间：
1994-11-01
期刊：
影响因子：
2.8
通讯作者：
SIEGEL, JH
中科院分区：
文献类型：
--
作者：
OHLEMILLER, KK;SIEGEL, JH
在耳蜗快速、适度冷却之前和期间，检查了蒙古沙鼠单个听觉神经纤维的反应。将耳蜗温度从 35-39 摄氏度降低到 29-32 摄氏度，导致自发放电率 (SR) 和对突发音的响应发生稳定、可逆的变化，如频率调谐曲线和速率与强度曲线所表征。冷却效果的性质和程度与特征频率 (CF) 密切相关。对于 CF 低于 8 kHz 的光纤，CF 的速率阈值增加 0-15 dB，对于更高 CF 的光纤，增加 10-30 dB。尽管 SR 普遍降低，但 SR 降低的百分比却明显依赖于 CF。对于 CF 低于 4 kHz 的光纤，降低幅度不超过初始 SR 的 50%。对于较高的 CF，降低幅度始终大于 50%。对于 CF 低于和高于 3-4 kHz 的光纤，冷却对强度曲线形状的影响有质的不同。对于较低的 CF，曲线的斜率平均降低了 50%，但对于较高的 CF，曲线的斜率平均没有变化。与冷却相关的 CF 阈值增加可能反映了主动机械过程的损害。这些增加的 CF 依赖性表明，相对于耳蜗基部，主动机械过程在耳蜗尖部受到的损害更大，或者它们在确定基部的敏感性方面发挥着更重要的作用。由冷却引起的 SR 和速率-强度曲线形状的 CF 相关变化对应于正常温度下观察到的基底/顶端差异的增强。最好的解释是内毛细胞及其传入突触特性的纵向梯度。 SR 分布和超阈值响应特性的基底和顶端差异表明，耳蜗低频区域和高频区域的刺激编码策略不同。
Responses of single auditory nerve fibers in the Mongolian gerbil were examined before and during rapid, moderate cooling of the cochlea. Reducing cochlear temperature from 35-39 degrees C to 29-32 degrees C led to stable, reversible changes in spontaneous firing rates (SRs), and responses to tonebursts, as characterized by frequency tuning curves and rate-versus-intensity curves. The nature and extent of effects of cooling were strongly linked to characteristic frequency (CF). Rate thresholds at the CF were increased by 0-15 dB for fibers with CFs below 8 kHz, and by 10-30 dB for higher CFs. Although SRs were generally reduced, the percent reduction in SR was strikingly CF dependent. For fibers with CFs below 4 kHz, the reduction did not exceed 50% of the initial SR. For higher CFs, the reduction was always greater than 50%. The effects of cooling on intensity curve shape differed qualitatively for fibers with CFs below and above 3-4 kHz. The slope of the curve was reduced by an average of 50% for lower CFs, but on average was unchanged for higher CFs. Cooling-related increases in CF threshold probably reflect impairment of active mechanical processes. The CF dependence of these increases suggests either that active mechanical processes are more impaired in the cochlear base relative to the apex, or that they play a more crucial role in determining sensitivity in the base. The CF-dependent changes in SR and in the shape of rate-intensity curves caused by cooling correspond to an enhancement of basal/apical differences seen at normal temperatures. They are best explained by longitudinal gradients in the properties of the inner hair cells and their afferent synapses. Basal and apical differences in the distribution of SRs and in supra-threshold response properties suggest that stimulus coding strategies differ between low and high frequency regions of the cochlea.