Smith D J, Rubel E W
J Comp Neurol. 1979 Jul 15;186(2):213-39. doi: 10.1002/cne.901860207.
Nucleus laminaris (NL) is a third-order auditory nucleus in the avian brain stem which receives spatially-segregated binaural inputs from the second-order magnocellular nuclei. The organization of dendritic structure in NL was examined in Golgi-impregnated brains from hatchling chickens. Quantitative analyses of dendritic size and number were made from camera lucida drawings of 135 neurons sampled from throughout the nucleus. The most significant results of this study may be summarized as follows: (1) The preponderant neuron in n. laminaris may be characterized as having a cylindrical-to-ovoid cell body, about 20 micrometer in diameter. The neurons comprising NL were found to be nearly completely homogeneous in issuing their dendrites in a bipolar fashion: one group of dendrites is clustered on the dorsal surface of the cells, the other group on the ventral. The dendrites of NL are contained within the glia-free neuropil surrounding the nucleus. From the rostromedial to the caudolateral poles of NL there is a gradient of increasing extension of the dendrites, increasing number of tertiary and higher-order dendrites, and increasing distance from the somata of the occurrence of branching. (2) The total dendritic size (sum of the dorsal) and ventral dendritic lengths of the cells) increases 3-fold from the rostromedial to the caudolateral poles of NL. About 50% of the variance in dendritic size is accounted for by the position of the cells in NL, and the gradient of dendritic size increase has the same orientation across NL as the tonotopic gradient of decreasing characteristic frequency in NL. (3) From the rostromedial pole to the caudolateral pole of NL there is an 11-fold decrease in the number of primary dendrites along a gradient coinciding with the length and frequency gradients. Sixty-six percent of the variance in dendrite number is accounted for by position in the nucleus. (4) The correlation of dorsal and ventral dendritic size on a cell-by-cell basis is not high (r = 0.47), indicating a fair amount of variability on the single-cell level. On the other hand, the average dorsal dendritic length within an isofrequency band in NL correlates very highly with the average ventral dendritic length. Thus, on an areal basis, the amount of dendritic surface area offered to the dorsal and ventral afferents is tightly regulated. (5) The dorsal and ventral dendrites have separate gradients of increasing length and number across NL. The dorsal gradients are skewed toward the rostrocaudal axis, while the ventral dendritic gradients are skewed mediolaterally. (6) There was no correlation between either dendritic size or number of primary dendrites and the size of the somata in NL, which remains relatively constant throughout the nucleus. Several hypotheses about the ontogenetic control of dendritic structure are examined in light of the above data. Of these, the hypotheses that the ontogeny of dendritic size and number is largely under afferent control receives a great deal of circumstantial support.
层状核（NL）是鸟类脑干中的三级听觉核，它接收来自二级大细胞核的空间分隔的双耳输入。在孵化后小鸡的高尔基染色大脑中检查了NL中树突结构的组织。从整个核中采样的135个神经元的明场绘图对树突大小和数量进行了定量分析。本研究的最重要结果可总结如下：（1）层状核中的优势神经元的特征可能是具有圆柱形至卵形的细胞体，直径约20微米。发现组成NL的神经元在以双极方式发出树突方面几乎完全同质：一组树突聚集在细胞的背表面，另一组在腹表面。NL的树突包含在围绕核的无胶质神经毡内。从NL的吻内侧极到尾外侧极，树突的延伸增加、三级及更高阶树突的数量增加以及分支发生处与胞体的距离增加存在梯度变化。（2）从NL的吻内侧极到尾外侧极，细胞的总树突大小（背侧和腹侧树突长度之和）增加3倍。树突大小约50%的变异由细胞在NL中的位置引起，并且树突大小增加的梯度在NL中与NL中特征频率降低的音频拓扑梯度具有相同的方向。（3）从NL的吻内侧极到尾外侧极，初级树突的数量沿着与长度和频率梯度一致的梯度减少11倍。树突数量66%的变异由在核中的位置引起。（4）逐个细胞的背侧和腹侧树突大小的相关性不高（r = 0.47），表明在单细胞水平上存在相当大的变异性。另一方面，NL中同频带内的平均背侧树突长度与平均腹侧树突长度高度相关。因此，在区域基础上，提供给背侧和腹侧传入纤维的树突表面积量受到严格调节。（5）背侧和腹侧树突在NL中具有不同的长度和数量增加梯度。背侧梯度向头尾轴倾斜，而腹侧树突梯度向内外侧倾斜。（6）NL中树突大小或初级树突数量与胞体大小之间没有相关性，整个核中的胞体大小保持相对恒定。根据上述数据研究了关于树突结构个体发育控制的几个假设。其中，树突大小和数量的个体发育在很大程度上受传入控制的假设得到了大量间接支持。
