Sommer I, Lingenhöhl K, Friauf E
Department of Animal Physiology, University of Tübingen, Germany.
Exp Brain Res. 1993;95(2):223-39. doi: 10.1007/BF00229781.
The medial nucleus of the trapezoid body (MNTB) is one of several principal nuclei in the superior olivary complex (SOC) of mammals. It is classically thought to function as a relay station between the contralateral ventral cochlear nucleus and the lateral superior olive (LSO), playing a role among those brainstem nuclei that are involved in binaural hearing. In order to characterise the physiology and morphology at the cellular level of the major neuronal component of the MNTB, the principal cells, we have analysed these neurons in rats in vivo using intracellular recordings and horseradish peroxidase-labelling. Our data demonstrate that MNTB principal cells, when being stimulated acoustically via the contralateral ear, show a phasic-tonic response with an onset latency of 3.5 ms and a suppression of their spontaneous activity following stimulus offset. These neurons have an axonal morphology whose complexity has not yet been described. All cells (n = 10) projected exclusively ipsilaterally and had terminal axonal arbors in a variety of auditory brainstem nuclei. At least two and maximally seven auditory targets were innervated by an individual cell. Each cell projected into the LSO and the superior paraolivary nucleus (SPN). Additional projections that were intrinsic to the SOC were often observed in the lateral nucleus of the trapezoid body and in periolivary regions, with only one cell projecting into the medial superior olive. Most, if not all, MNTB principal cells also had projections that were extrinsic to the SOC, as their axons ascended into the lateral lemniscus. In two neurons the ascending axon formed terminal arbors in the ventral nucleus of the lateral lemniscus, and the dorsal nucleus of the lateral lemniscus could be identified as a target of one neuron. The location of the cell bodies of the MNTB principal cells correlated with the neurons' best frequencies, thereby demonstrating a tonotopic organisation of the MNTB, with high frequencies being represented medially and low frequencies laterally. The axonal projections into the LSO and the SPN were also tonotopically organised and the alignment of the tonotopically organised and the alignment of the tonotopic axes was similar to that in the MNTB. Our results confirm previous data from other species and suggest that MNTB principal cells have a great amount of physiological and morphological similarities across mammalian species. Furthermore, the complexity of the axonal projections indicates that these neurons play a role in auditory information processing which goes far beyond their previously described classical role.
梯形体内侧核（MNTB）是哺乳动物上橄榄复合体（SOC）中的几个主要核团之一。传统上认为它在对侧蜗腹侧核和外侧上橄榄核（LSO）之间起中继站的作用，在参与双耳听觉的脑干核团中发挥作用。为了在细胞水平上表征MNTB主要神经元成分即主细胞的生理学和形态学特征，我们在大鼠活体中使用细胞内记录和辣根过氧化物酶标记对这些神经元进行了分析。我们的数据表明，MNTB主细胞在通过对侧耳进行听觉刺激时，表现出相位 - 紧张性反应，起始潜伏期为3.5毫秒，刺激停止后其自发活动受到抑制。这些神经元具有尚未被描述过的轴突形态。所有细胞（n = 10）均仅向同侧投射，并且在各种听觉脑干核团中具有终末轴突分支。单个细胞支配至少两个且最多七个听觉靶点。每个细胞都投射到LSO和上橄榄旁核（SPN）。在梯形体外侧核和橄榄周区域经常观察到SOC内部的额外投射，只有一个细胞投射到内侧上橄榄核。大多数（如果不是全部的话）MNTB主细胞也有投射到SOC外部的情况，因为它们的轴突向上进入外侧丘系。在两个神经元中，上升的轴突在外侧丘系腹侧核形成终末分支，并且外侧丘系背侧核可被确定为一个神经元的靶点。MNTB主细胞的胞体位置与神经元的最佳频率相关，从而证明了MNTB的音频拓扑组织，高频在内侧代表，低频在外侧代表。进入LSO和SPN的轴突投射也呈音频拓扑组织，并且音频拓扑组织的排列和音频拓扑轴的排列与MNTB中的相似。我们的结果证实了来自其他物种的先前数据，并表明MNTB主细胞在哺乳动物物种之间具有大量的生理和形态学相似性。此外，轴突投射的复杂性表明这些神经元在听觉信息处理中发挥的作用远远超出了它们先前描述的经典作用。
