Yang L, Pollak G D
Department of Zoology, University of Texas at Austin, 78712, USA.
Hear Res. 1998 Aug;122(1-2):125-41. doi: 10.1016/s0378-5955(98)00088-4.
The dorsal nucleus of the lateral lemniscus (DNLL) is a binaural nucleus whose neurons are excited by stimulation of the contralateral ear and inhibited by stimulation of the ipsilateral ear. Here we report on several features of the ipsilaterally evoked inhibition in 95 DNLL neurons of the mustache bat. These features include its dependence on intensity, its tuning and the types of stimuli that are capable of evoking it. Inhibition was studied by evoking discharges with the iontophoretic application of glutamate, and then evaluating the strength and duration of the inhibition of the glutamate evoked background activity produced by stimulation of the ipsilateral ear. Excitatory responses were evoked by stimulation of the contralateral ear with best frequency (BF) tone bursts. Glutamate evoked discharges could be inhibited in all DNLL neurons and the inhibition often persisted for periods ranging from 10 to 50 ms beyond the duration of the tone burst that evoked it. The duration of the persistent inhibition increased with stimulus intensity. Stimulus duration had little influence on the duration of the persistent inhibition. Signals as short as 2 ms suppressed discharges for as long as 30 ms after the signal had ended. The frequency tuning of the total period of inhibition and the period of persistent inhibition were both closely matched to the tuning evoked by stimulation of the contralateral ear. Moreover, the effectiveness of complex signals for evoking persistent inhibition, such as brief FM sweeps and sinusoidally amplitude and frequency modulated signals, was comparable to that of tone bursts at the neuron's excitatory BF, so long as the complex signal contained frequencies at or around the neuron's excitatory BF. We also challenged DNLL cells with binaural paradigms. In one experiment, we presented a relatively long (40 ms) BF tone burst of fixed intensity to the contralateral ear, which evoked a sustained discharge, and a shorter, 10 ms signal of variable intensity to the ipsilateral ear. As the intensity of the 10 ms ipsilateral signal increased, it generated progressively longer periods of persistent inhibition and thus the discharges were suppressed for periods far longer than the 10 ms duration of the ipsilateral signal. With interaural time disparities, ipsilateral signals that led contralateral signals evoked a persistent inhibition that suppressed the responses to the trailing contralateral signals for periods of a least 15 ms. This suggests that an initial binaural sound that favors the ipsilateral ear should suppress the responses to trailing sounds that normally would be excitatory if they were presented alone. We hypothesize a circuit that generates the persistent inhibition and discuss how the results with binaural signals support that hypothesis.
外侧丘系背核（DNLL）是一个双耳核团，其神经元在对侧耳受到刺激时被兴奋，而在同侧耳受到刺激时被抑制。在此，我们报告了髯蝠95个DNLL神经元中同侧诱发抑制的几个特征。这些特征包括其对强度的依赖性、调谐特性以及能够诱发它的刺激类型。通过离子电泳施加谷氨酸诱发放电，然后评估同侧耳刺激对谷氨酸诱发的背景活动的抑制强度和持续时间，来研究抑制作用。用最佳频率（BF）的纯音脉冲刺激对侧耳诱发兴奋性反应。在所有DNLL神经元中，谷氨酸诱发的放电都能被抑制，并且抑制通常会在诱发它的纯音脉冲持续时间之后持续10到50毫秒。持续抑制的持续时间随刺激强度增加。刺激持续时间对持续抑制的持续时间影响很小。短至2毫秒的信号在信号结束后能抑制放电长达30毫秒。抑制总时长和持续抑制时长的频率调谐都与对侧耳刺激诱发的调谐紧密匹配。此外，只要复杂信号包含神经元兴奋性BF处或其附近的频率，诸如短暂调频扫描以及正弦幅度和频率调制信号等复杂信号诱发持续抑制的效果与神经元兴奋性BF处的纯音脉冲相当。我们还用双耳范式对DNLL细胞进行了测试。在一个实验中，我们向对侧耳呈现一个固定强度的相对较长（40毫秒）的BF纯音脉冲，诱发持续放电，同时向同侧耳呈现一个强度可变的较短（10毫秒）信号。随着10毫秒同侧信号强度增加，它产生的持续抑制时长逐渐变长，因此放电被抑制的时长远远超过同侧信号10毫秒的持续时间。对于双耳时间差异，先于对侧信号的同侧信号会诱发持续抑制，该抑制会抑制对后续对侧信号的反应至少15毫秒。这表明最初有利于同侧耳的双耳声音应该会抑制对后续单独呈现时通常会产生兴奋作用的声音的反应。我们推测了一个产生持续抑制的神经回路，并讨论了双耳信号的实验结果如何支持该假设。
