Birnbacher D, Albus K
J Comp Neurol. 1987 Jul 22;261(4):543-61. doi: 10.1002/cne.902610407.
The proportions of neurons projecting via axon collaterals to two areas in the cat's occipital cortex (diverging neurons) were determined quantitatively in subcortical and cortical afferents by making use of the retrograde axonal transport of two different tracers. The proportions of diverging neurons were determined for that part of the afferent sites in which neurons filled with tracers from both injected areas occurred (overlap zone). A number of experimental variables were tested for their role in possibly influencing the results of quantitative double-label experiments, among them the types and the combinations of retrograde tracers, the position of the injections, the survival time, and the histological procedure. The most important variable was the position of the cortical injection, which had to be restricted clearly to the cortical grey matter and to one cortical area in order to avoid false-positive double labeling. Other experimental variables affected the total number of retrogradely labeled neurons and/or the ratio between neurons labeled with the two different tracers rather than the proportions of double-labeled neurons. In particular DL proportions were largely independent of the number and density of labeled neurons. They only deviated significantly from mean values in those sections in which the number of labeled neurons amounted to less than 20% of the maximal number of labeled neurons found in one section throughout the overlap zone. Our results show that divergence is common in afferents to the cat visual cortex. The amount of divergence, however, varies considerably according to the origin of the afferent projection. The proportion of diverging neurons expressed as the percentage of the total number of neurons projecting to areas 17 and 18 was 3% in the A-laminae of the dorsal part of the lateral geniculate nucleus, about 8% in the posteromedial lateral suprasylvian area, and about 15% in the C-laminae of the dorsal part of the lateral geniculate nucleus, in the medial interlaminar nucleus, in the lateral part of the lateral posterior nucleus, and in the claustrum. The proportions of diverging neurons in the afferent projections to areas 17 and 19, and to areas 18 and 19 were about 10%. Diverging neurons were also found in the projections of the intralaminar thalamic nuclei to the visual cortex.(ABSTRACT TRUNCATED AT 400 WORDS)
通过利用两种不同示踪剂的逆行轴突运输，定量测定了猫枕叶皮质中通过轴突侧支投射到两个区域的神经元（发散神经元）在皮质下和皮质传入纤维中的比例。对于传入位点中同时充满来自两个注射区域示踪剂的神经元所在部分（重叠区），测定了发散神经元的比例。测试了多个实验变量在可能影响定量双标记实验结果中的作用，其中包括逆行示踪剂的类型和组合、注射位置、存活时间以及组织学程序。最重要的变量是皮质注射的位置，必须明确将其限制在皮质灰质和一个皮质区域内，以避免假阳性双标记。其他实验变量影响逆行标记神经元的总数和/或用两种不同示踪剂标记的神经元之间的比例，而不是双标记神经元的比例。特别是双标记比例在很大程度上与标记神经元的数量和密度无关。只有在那些标记神经元数量占整个重叠区中一个切片中发现的最大标记神经元数量不到20%的切片中，它们才会显著偏离平均值。我们的结果表明，发散在猫视觉皮质的传入纤维中很常见。然而，发散的程度根据传入投射的起源有很大差异。以投射到17区和18区的神经元总数的百分比表示的发散神经元比例，在外侧膝状体背侧部分的A板层中为3%，在后内侧外侧上薛氏区约为8%，在外侧膝状体背侧部分的C板层、内侧层间核、外侧后核外侧部分和屏状核中约为15%。投射到17区和19区以及投射到18区和19区的传入纤维中发散神经元的比例约为10%。在丘脑板内核向视觉皮质的投射中也发现了发散神经元。（摘要截取自400字）
