Tonotopic distribution of short-term adaptation properties in the cochlear nerve of normal and acoustically overexposed chicks
Tonotopic distribution of short-term adaptation properties in the cochlear nerve of normal and acoustically overexposed chicks
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DOI：
10.1007/s10162-006-0061-8
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发表时间：
2007-03-01
影响因子：
2.4
通讯作者：
Saunders, James C.
中科院分区：
文献类型：
--
作者：
Crumling, Mark A.;Saunders, James C.
尾神经适应被认为至少部分是由于毛细胞中神经递质储存的耗尽。最近，神经递质囊泡池已被确定在鸡高毛细胞，可能在适应中发挥作用。为了更好地了解适应和神经递质释放动力学之间的关系，短期适应的特点是使用单单位活动的刺激周时间直方图在鸡耳蜗神经。在特征频率（相对于阈值+20 dB）下，100 ms纯音刺激产生的适应功能被很好地描述为平均时间常数为18.6 +/- 0.8 ms（平均值+/- SEM）的单指数衰减过程。由响应的适应部分贡献的尖峰的数量增加tonotopically特征频率高达类似于0.8 kHz。已知的生理和解剖毛细胞特性的适应数据的比较表明，容易释放池的消耗是在鸡的短期适应的基础。考虑到这一点，短期适应被用作评估高毛细胞突触功能的代理后，强烈的声刺激。48小时后，暴露于一个强烈的纯音，短期适应的时间常数不变，而在适应组件的尖峰的数量增加，在特征频率和以上的曝光频率。这些数据表明，容易释放池排空率是不变的，但池的神经递质含量增加，通过暴露于强烈的声音。结果表明，增加容易释放池的大小可能是一种补偿机制，确保强度的毛细胞传入突触在面对持续的声应力。
Cochlear nerve adaptation is thought to result, at least partially, from the depletion of neurotransmitter stores in hair cells. Recently, neurotransmitter vesicle pools have been identified in chick tall hair cells that might play a role in adaptation. In order to understand better the relationship between adaptation and neurotransmitter release dynamics, short-term adaptation was characterized by using peristimulus time histograms of single-unit activity in the chick cochlear nerve. The adaptation function resulting from 100-ms pure tone stimuli presented at the characteristic frequency, +20 dB relative to threshold, was well described as a single exponential decay process with an average time constant of 18.6 +/- 0.8 ms (mean +/- SEM). The number of spikes contributed by the adapting part of the response increased tonotopically for characteristic frequencies up to similar to 0.8 kHz. Comparison of the adaptation data with known physiological and anatomical hair cell properties suggests that depletion of the readily releasable pool is the basis of short-term adaptation in the chick. With this idea in mind, short-term adaptation was used as a proxy for assessing tall hair cell synaptic function following intense acoustic stimulation. After 48 h of exposure to an intense pure tone, the time constant of short-term adaptation was unaltered, whereas the number of spikes in the adapting component was increased at characteristic frequencies at and above the exposure frequency. These data suggest that the rate of readily releasable pool emptying is unaltered, but the neurotransmitter content of the pool is increased, by exposure to intense sound. The results imply that an increase in readily releasable pool size might be a compensatory mechanism ensuring the strength of the hair cell afferent synapse in the face of ongoing acoustic stress.