The medial nucleus of the trapezoid body in the gerbil is more than a relay:: Comparison of pre- and postsynaptic activity
The medial nucleus of the trapezoid body in the gerbil is more than a relay:: Comparison of pre- and postsynaptic activity
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DOI：
10.1007/s10162-002-2010-5
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发表时间：
2003-03-01
影响因子：
2.4
通讯作者：
R端bsamen, R
中科院分区：
文献类型：
--
作者：
Kopp-Scheinpflug, C;Lippe, WR;R端bsamen, R
梯形体内侧核（medial nucleus of The梯形体，MNTB）在处理耳间强度差异中起着重要作用，这一特征对声源定位至关重要。一般认为，MNTB的功能主要是作为一个被动中继，将来自对侧耳蜗核（CN）的兴奋性输入转化为同侧外侧上橄榄的抑制性输入。然而，研究表明MNTB本身也是抑制输入的目标，这表明MNTB可能不仅仅具有符号转换功能。为了检查CN-MNTB突触信号传递的保真度，在沙鼠MNTB的体内细胞外记录过程中，用同一电极同时监测反映MNTB神经元兴奋性输入的突触前胼胝体电位（“prepotential”）和突触后动作电位。突触前活动与突触后活动在以下几个方面有所不同：(1)自发放电率和声诱发放电率在突触前大于突触后。(2)突触后频率调谐明显强于突触前。(3)萼端和MNTB神经元对音调刺激均表现出相-张力反应模式，但突触后开始反应的持续时间和张力成分的水平均有所降低。(4)突触后的锁相效应大于突触前的锁相效应。(5)半数MNTB神经元突触前和突触后活动的速率强度特征存在显著差异。为了验证声音诱发的MNTB神经元抑制导致突触后放电水平相对较低的假设，应用了双音刺激，其中对一个音调爆发的反应，设置在神经元的特征频率上，可以通过添加第二个“抑制性”音调来减少。抑制性音调引起的突触后活动比突触前活动的减少要大得多，这表明声音诱发的抑制性影响直接作用于MNTB单元。这些发现表明，CN-MNTB突触的传递并非以固定的一对一方式发生，MNTB神经元的反应反映了其兴奋性和抑制性输入的整合。
The medial nucleus of the trapezoid body (MNTB) plays an important role in the processing of interaural intensity differences, a feature that is critical for the localization of sound sources. It is generally believed that the MNTB functions primarily as a passive relay in converting excitatory input originating from the contralateral cochlear nucleus (CN) into an inhibitory input to the ipsilateral lateral superior olive. However, studies showing that the MNTB itself is also the target of inhibitory input suggest that the MNTB may serve more than a sign-converting function. To examine the fidelity of signal transmission at the CN-MNTB synapse, presynaptic calyceal potentials ("prepotentials"), reflecting the excitatory input to the MNTB neuron, and postsynaptic action potentials were simultaneously monitored with the same electrode during in vivo extracellular recordings from the gerbil's MNTB. Presynaptic activity differed from postsynaptic activity in several respects: (1) Spontaneous and sound-evoked discharge rates were greater presynaptically than postsynaptically. (2) Frequency tuning was sharper postsynaptically than presynaptically. (3) Calyceal terminals and MNTB neurons both showed phasic-tonic response patterns to tonal stimulation, but the duration of the onset response and the level of the tonic component were reduced postsynaptically. (4) Phase-locking to sound frequencies up to 1 kHz was greater postsynaptically than presynaptically. (5) The rate-intensity characteristics of pre- and postsynaptic activities differed significantly from each other in half of the MNTB neurons. To test the hypothesis that acoustically evoked inhibition of MNTB neurons contributed to the relatively lower levels of postsynaptic discharge, two-tone stimulation was applied, wherein the response to one tone-burst, set at the neuron's characteristic frequency, can be reduced by addition of a second "inhibitory" tone. The inhibitory tone caused a much larger reduction in post- than in presynaptic activity, indicating an acoustically evoked inhibitory influence directly on MNTB units. These findings show that transmission at the CN-MNTB synapse does not occur in a fixed one-to-one manner and that the response of MNTB neurons reflects the integration of their excitatory and inhibitory inputs.