Smith P H, Rhode W S
Department of Neurophysiology, University of Wisconsin, Madison 53706.
J Comp Neurol. 1989 Apr 22;282(4):595-616. doi: 10.1002/cne.902820410.
We distinguish two types of large multipolar cells designated sustained (CS) and onset (OC) choppers in the anterior posteroventral cochlear nucleus (A-PVCN)/nerve root region on the basis of certain anatomical and physiological features. CS axons head into the trapezoid body, while OC axons use the intermediate acoustic stria of Held. At the electron microscopic (EM) level, collateral terminals of OC axons contain pleomorphic vesicles; CS terminals contain small round vesicles. CS dendritic trees tend to be distributed in a stellate fashion while OC dendritic trees tend to be elongated. At the EM level the sustained chopper somata are sparsely innervated while the proximal dendritic tree receives considerably more input. The OC somata are highly innervated and this heavy innervation continues out onto the proximal dendrites. Distally the dendritic innervation falls off considerably for both categories. Physiologically, members of the OC population have wider dynamic ranges at the characteristic frequency (CF), wider response areas that are typically not flanked by inhibitory sidebands, and responses to short tones that do not show the same form of regularity expressed by sustained choppers. Intracellularly the sustained choppers exhibit sustained depolarization to short tones for the duration of the stimulus with resultant regular spiking at a rate that is stimulus level dependent. The response to swept tone shows this same level-dependent regularity. In response to tones, the OC cells also show a sustained depolarization whose amplitude is stimulus-level dependent but whose range is much greater and whose onset is initiated more abruptly. Although the onset component of the OC spike output is reliably initiated by these levels of depolarization, regular firing to the sustained depolarization is not initiated at levels of depolarization that would surely generate regular firing in sustained choppers. This regularity is also absent in the swept tone response despite marked levels of excitation.
基于某些解剖学和生理学特征，我们在前庭蜗神经核（A-PVCN）/神经根区域区分出两种类型的大型多极细胞，分别称为持续型（CS）和起始型（OC）斩波器。CS轴突通向梯形体，而OC轴突则利用赫尔德中间听纹。在电子显微镜（EM）水平上，OC轴突的侧支终末含有多形性囊泡；CS终末含有小圆形囊泡。CS树突树倾向于呈星状分布，而OC树突树则倾向于拉长。在EM水平上，持续型斩波器的胞体神经支配稀疏，而近端树突树接受的输入则多得多。OC胞体神经支配丰富，这种密集的神经支配一直延续到近端树突。在远端，两类细胞的树突神经支配都显著减少。在生理学上，OC群体的成员在特征频率（CF）处具有更宽的动态范围，更宽的反应区域，通常没有抑制性边带，并且对短音的反应不表现出持续型斩波器所具有的相同形式的规律性。在细胞内，持续型斩波器在刺激持续期间对短音表现出持续去极化，并以依赖于刺激水平的速率产生规则的动作电位发放。对扫频音的反应也表现出这种依赖于水平的规律性。对音调的反应中，OC细胞也表现出持续去极化，其幅度依赖于刺激水平，但其范围大得多，起始更突然。尽管OC动作电位输出的起始成分由这些去极化水平可靠地引发，但在持续型斩波器中肯定会产生规则发放的去极化水平下，对持续去极化的规则发放并未启动。尽管有明显的兴奋水平，但在扫频音反应中也不存在这种规律性。
