Smith P H, Joris P X, Yin T C
Department of Anatomy, University of Wisconsin Medical School, Madison, Wisconsin 53706, USA.
J Neurophysiol. 1998 Jun;79(6):3127-42. doi: 10.1152/jn.1998.79.6.3127.
We have recorded from principal cells of the medial nucleus of the trapezoid body (MNTB) in the cat's superior olivary complex using either glass micropipettes filled with Neurobiotin or horseradish peroxidase for intracellular recording and subsequent labeling or extracellular metal microelectrodes relying on prepotentials and electrode location. Labeled principal cells had cell bodies that usually gave rise to one or two primary dendrites, which branched profusely in the vicinity of the cell. At the electron microscopic (EM) level, there was a dense synaptic terminal distribution on the cell body and proximal dendrites. Up to half the measured cell surface could be covered with excitatory terminals, whereas inhibitory terminals consistently covered about one-fifth. The distal dendrites were very sparsely innervated. The thick myelinated axon originated from the cell body and innervated nuclei exclusively in the ipsilateral auditory brain stem. These include the lateral superior olive (LSO), ventral nucleus of the lateral lemniscus, medial superior olive, dorsomedial and ventromedial periolivary nuclei, and the MNTB itself. At the EM level the myelinated collaterals gave rise to terminals that contained nonround vesicles and, in the LSO, were seen terminating on cell bodies and primary dendrites. Responses of MNTB cells were similar to their primary excitatory input, the globular bushy cell (GBC), in a number of ways. The spontaneous spike rate of MNTB cells with low characteristic frequencies (CFs) was low, whereas it tended to be higher for higher CF units. In response to short tones, a low frequency MNTB cell showed enhanced phase-locking abilities, relative to auditory nerve fibers. For cells with CFs >1 kHz, the short tone response often resembled the primary-like with notch response seen in many globular bushy cells, with a well-timed onset component. Exceptions to and variations of this standard response were also noted. When compared with GBCs with comparable CFs, the latency of the MNTB cell response was delayed slightly, as would be expected given the synapse interposed between the two cell types. Our data thus confirm that, in the cat, the MNTB receives and converts synaptic inputs from globular bushy cells into a reasonably accurate reproduction of the bushy cell spike response. This MNTB cell output then becomes an important inhibitory input to a number of ipsilateral auditory brain stem nuclei.
我们使用充满神经生物素或辣根过氧化物酶的玻璃微电极进行细胞内记录及后续标记，或依靠预电位和电极位置的细胞外金属微电极，从猫上橄榄复合体中梯形体内侧核（MNTB）的主细胞进行记录。标记的主细胞具有通常发出一或两个初级树突的细胞体，这些树突在细胞附近大量分支。在电子显微镜（EM）水平，细胞体和近端树突上有密集的突触终末分布。高达一半的测量细胞表面可被兴奋性终末覆盖，而抑制性终末始终覆盖约五分之一。远端树突的神经支配非常稀疏。粗大的有髓轴突起源于细胞体，仅支配同侧听觉脑干中的核团。这些核团包括外侧上橄榄核（LSO）、外侧丘系腹侧核、内侧上橄榄核、橄榄周背内侧核和腹内侧核，以及MNTB本身。在EM水平，有髓侧支产生含有非圆形囊泡的终末，并且在LSO中，可见其终止于细胞体和初级树突上。MNTB细胞的反应在许多方面与其主要兴奋性输入——球状浓密细胞（GBC）相似。特征频率（CFs）较低的MNTB细胞的自发放电率较低，而CFs较高的单位其自发放电率往往较高。对短纯音的反应中，相对于听神经纤维，低频MNTB细胞表现出增强的锁相能力。对于CFs>1kHz的细胞，短纯音反应通常类似于许多球状浓密细胞中所见的具有切迹反应的初级样反应，具有适时的起始成分。也注意到了这种标准反应的例外情况和变化。与具有可比CFs的GBCs相比，MNTB细胞反应的潜伏期略有延迟，鉴于两种细胞类型之间存在突触，这是可以预期的。因此，我们的数据证实，在猫中，MNTB接收来自球状浓密细胞的突触输入，并将其转换为对浓密细胞动作电位反应的合理准确的再现。然后，这种MNTB细胞输出成为对许多同侧听觉脑干核团的重要抑制性输入。
