Games K D, Winer J A
Department of Physiology-Anatomy, University of California, Berkeley 94720.
Hear Res. 1988 Jul 1;34(1):1-25. doi: 10.1016/0378-5955(88)90047-0.
This study compares the form and distribution within layer V of cells projecting to the inferior colliculus with that of commissural cells of origin in adult rat auditory cortex after horseradish peroxidase injections in the ipsilateral inferior colliculus or auditory cortex. The goal of this work was to determine whether every part of layer V participates equally in both projections, and if the cortical neurons in each pathway were similar. The types of neurons were defined in Golgi-Cox preparations and matched with the profiles of retrogradely labeled cells from architectonically defined cortical area 41. Inferior colliculus and commissural neurons form two populations that differ in their distribution in layer V, in somatic area, and in the form of their apical dendritic arbors. Corticocollicular neurons include the largest pyramidal cells, whose robustly filled apical dendrites ascend into layer II or farther. Commissural cells are smaller and have a more heterogeneous form. Their apical dendrites do not usually extend above layer IV, and a few of these cells may be non-pyramidal. Small pyramidal cells and inverted pyramidal cells project to the opposite cortex, but not to the inferior colliculus. Medium-sized pyramidal cells project in both systems. In addition, certain callosal cells of origin in layers V and III were morphologically similar. More than one-third of the commissural cells originate in the superficial part of layer V, where only 7% of the inferior colliculus projection neurons arise. Most corticocollicular cells lie deeper in layer V, where there are fewer commissural neurons. These findings suggest that the efferent systems projecting to telencephalic and mesencephalic targets are morphologically distinct and spatially segregated in layer V. However, the commissural projection includes similar cells in different cortical layers. The types of these efferent neurons may be more closely related to their target than to their laminar origin.
本研究在成年大鼠听觉皮层同侧下丘或听觉皮层注射辣根过氧化物酶后，比较投射至下丘的细胞在V层内的形态和分布与起源于连合部的细胞的形态和分布。这项工作的目的是确定V层的每个部分在这两种投射中是否同等参与，以及每条通路中的皮层神经元是否相似。在高尔基-考克斯染色标本中定义神经元类型，并将其与来自结构学上定义的皮层41区的逆行标记细胞的轮廓相匹配。下丘和连合部神经元形成两个群体，它们在V层的分布、体细胞面积以及顶树突分支的形态上存在差异。皮质-皮质下神经元包括最大的锥体细胞，其充满染料的粗壮顶树突向上延伸至II层或更远。连合部细胞较小，形态更为多样。它们的顶树突通常不延伸至IV层以上，其中一些细胞可能是非锥体细胞。小锥体细胞和倒转锥体细胞投射至对侧皮层，但不投射至下丘。中等大小的锥体细胞在两个系统中均有投射。此外，V层和III层中某些起源于胼胝体的细胞在形态上相似。超过三分之一的连合部细胞起源于V层的浅层，而下丘投射神经元仅7%起源于此。大多数皮质-皮质下细胞位于V层较深部位，此处连合部神经元较少。这些发现表明，投射至端脑和中脑靶区的传出系统在形态上不同且在V层空间上分离。然而，连合部投射在不同皮层层中包括相似的细胞。这些传出神经元的类型与其靶区的关系可能比与其层状起源的关系更为密切。
