Smith Z D
J Comp Neurol. 1981 Dec 10;203(3):309-33. doi: 10.1002/cne.902030302.
Nucleus laminaris (NL) is a third-order auditory nucleus in the avian brain stem which receives spatially segregated binaural inputs from the second-order nuclei magnocellularis. The examination of the development of dendritic structure in NL revealed a number of events: In the initial period of dendritic growth (E 8--9) there is no gradient of dendritic morphology or apparent size. Starting about E 9--10, there is a spatiotemporal gradient of proliferation of numerous fine dendritic processes, from rostromedial to caudolateral, corresponding with the morphological lamination of NL, and possibly with the onset of cell death. This is followed by a spatiotemporal gradient of the elimination of the overproliferated processes, from rostromedial to caudolateral possibly coinciding with the cessation of cell death. A result of the spatiotemporal gradients of dendritic process proliferation and elimination is a spatial gradient in the morphology (extension, branching) of the remaining "mature" dendrites. At E 15 there is only a slight spatial gradient of total dendritic size across NL; this gradient is larger at E 19, and by P 25 there is a 13-fold change in dendritic size from rostromedial to caudolateral. Regression analyses suggest the size gradient begins to form when NL activity becomes driven by cochlear activity, at about E 14. The progressive formation of the size gradient is largely the result of two factors: the growth of dendritic trees, and the loss or primary dendrites. The growth rate of the dendritic trees of NL cells was found to be very highly correlated with the intensities of the sound frequencies to which the cells respond. From E 15 to P 25 there is a 50% loss of the "mature" primary dendrites of NL neurons. The separate dorsal and ventral dendritic size gradients seen at E 15 realign to coincide at E 19, and the moderate correlation of dorsal and ventral dendritic sizes seen at E 15 and E 19 is significantly increased at P 25, indicating a developmental process of sharpening in the relationship of the dorsal and ventral dendritic organizations in the nucleus. The data suggest that a key element in the regulation of dendritic size and structure in n. laminaris may be the activity of the afferents to the cells.
层状核（NL）是鸟类脑干中的三级听觉核，它从二级核巨细胞层接收空间上分离的双耳输入。对NL中树突结构发育的研究揭示了许多事件：在树突生长的初期（E 8 - 9），树突形态或明显大小没有梯度。大约从E 9 - 10开始，大量细小的树突状突起从吻内侧向尾外侧呈时空梯度增殖，这与NL的形态分层相对应，可能也与细胞死亡的开始有关。随后是过度增殖的突起从吻内侧向尾外侧呈时空梯度消除，这可能与细胞死亡的停止同时发生。树突状突起增殖和消除的时空梯度的结果是剩余“成熟”树突的形态（延伸、分支）存在空间梯度。在E 15时，NL中总的树突大小只有轻微的空间梯度；在E 19时这个梯度更大，到P 25时，从吻内侧到尾外侧树突大小有13倍的变化。回归分析表明，当NL活动在大约E 14时开始由耳蜗活动驱动时，大小梯度开始形成。大小梯度的逐渐形成主要是两个因素的结果：树突树的生长和初级树突的丢失。发现NL细胞的树突树生长速率与细胞所响应的声音频率强度高度相关。从E 15到P 25，NL神经元的“成熟”初级树突有50%丢失。在E 15时看到的单独的背侧和腹侧树突大小梯度在E 19时重新对齐，并且在E 15和E 19时看到的背侧和腹侧树突大小的中度相关性在P 25时显著增加，这表明该核中背侧和腹侧树突组织关系的发育过程在锐化。数据表明，层状核中树突大小和结构调节的一个关键因素可能是细胞传入纤维的活动。
