Lee Charles C, Winer Jeffery A
Division of Neurobiology, Department of Molecular and Cell Biology, University of California at Berkeley, Berkeley, California 94720-3200, USA.
J Comp Neurol. 2008 Apr 20;507(6):1901-19. doi: 10.1002/cne.21614.
The commissural projections between 13 areas of cat auditory cortex (AC) were studied using retrograde tracers. Areal and laminar origins were characterized as part of a larger study of thalamic input and cortical origins of projections to each area. Cholera toxin beta subunit (CTbeta) and cholera toxin beta subunit gold-conjugate (CTbetaG) were injected separately within an area or in different areas in an experiment. The areas were identified independently with SMI-32, which revealed differences in neurofilament immunoreactivity in layers III, V, and VI. Each area received convergent AC input from 3 to 6 (mean, 5) contralateral areas. Most of the projections (>75%) were homotopic and from topographically organized loci in the corresponding area. Heterotopic projections (>1 mm beyond the main homotopic projection) constituted approximately 25% of the input. Layers III and V contained >95% of the commissural neurons. Commissural projection neurons were clustered in all areas. Commissural divergence, assessed by double labeling, was less than 3% in each area. This sparse axonal branching is consistent with the essentially homotopic connectivity of the commissural system. The many heterotopic origins represent unexpected commissural influences converging on an area. Areas more dorsal on the cortical convexity have commissural projections originating in layers III and V; more ventral areas favor layer III at the expense of layer V, to its near-total exclusion in some instances. Some areas have almost entirely layer III origins (temporal cortex and area AII), whereas others have a predominantly layer V input (anterior auditory field) or dual contributions from layers III and V (the dorsal auditory zone). A topographic distribution of commissural cells of origin is consistent with the order observed in thalamocortical and corticocortical projections, and which characterizes all extrinsic projection systems (commissural, corticocortical, and thalamocortical) in all AC areas. Thus, laminar as well as areal differences in projection origin distinguish the auditory cortical commissural system.
使用逆行示踪剂研究了猫听觉皮层（AC）13个区域之间的连合投射。作为对每个区域丘脑输入和皮层投射起源的更大规模研究的一部分，对区域和层状起源进行了特征描述。在实验中，霍乱毒素β亚基（CTβ）和霍乱毒素β亚基金偶联物（CTβG）分别注射到一个区域内或不同区域。使用SMI-32独立识别这些区域，SMI-32揭示了III、V和VI层中神经丝免疫反应性的差异。每个区域从3至6个（平均5个）对侧区域接收汇聚的AC输入。大多数投射（>75%）是同位的，并且来自相应区域中按地形组织的位点。异位投射（超出主要同位投射>1毫米）约占输入的25%。III层和V层包含>95%的连合神经元。连合投射神经元聚集在所有区域。通过双重标记评估的连合发散在每个区域中小于3%。这种稀疏的轴突分支与连合系统基本同位的连接性一致。许多异位起源代表了汇聚到一个区域的意外连合影响。皮层凸面更靠背侧的区域具有起源于III层和V层的连合投射；更靠腹侧的区域以牺牲V层为代价而倾向于III层，在某些情况下几乎完全排除V层。一些区域几乎完全起源于III层（颞叶皮层和AII区），而其他区域主要有V层输入（前听区）或来自III层和V层的双重贡献（背听区）。连合起源细胞的地形分布与在丘脑皮层和皮层皮层投射中观察到的顺序一致，并且这是所有AC区域中所有外在投射系统（连合、皮层皮层和丘脑皮层）的特征。因此，投射起源的层状以及区域差异区分了听觉皮层连合系统。
