Shamim K M, Tóth P, Cook J E
Department of Anatomy and Developmental Biology, University College London, UK.
Vis Neurosci. 1997 Sep-Oct;14(5):811-26. doi: 10.1017/s095252380001155x.
Population-based studies of retinal neurons have helped to reveal their natural types in mammals and teleost fishes. In this, the first such study in a frog, labeled ganglion cells of the mesobatrachian Xenopus laevis were examined in flatmounts. Cells with large somata and thick dendrites could be divided into three mosaic-forming types, each with its own characteristic stratification pattern. These are named alpha a, alpha ab, and alpha c, following a scheme recently used for teleosts. Cells of the alpha a mosaic (approximately 0.4% of all ganglion cells) had very large somata and trees, arborizing diffusely within sublamina a (the most sclerad). Their distal dendrites were sparsely branched but achieved consistent coverage by intersecting those of their neighbors. Displaced and orthotopic cells belonged to the same mosaic, as did cells with symmetric and asymmetric trees. Cells of the alpha ab mosaic (approximately 1.2%) had large somata, somewhat smaller trees that appeared bistratified at low magnification, and dendrites that branched extensively. Their distal dendrites arborized throughout sublamina b and the vitread part of a, tessellating with their neighbors. All were orthotopic; most were symmetric. Cells of the alpha c mosaic (approximately 0.5%) had large somata and very large, sparse, flat, overlapping trees, predominantly in sublamina c. All were orthotopic; some were asymmetric. Nearest-neighbor analyses and spatial correlograms confirmed that each mosaic was regular and independent, and that spacings were reduced in juvenile frogs. Densities, proportions, sizes, and mosaic statistics are tabulated for all three types, which are compared with types defined previously by size and symmetry in Xenopus and potentially homologous mosaic-forming types in teleosts. Our results reveal strong organizational similarities between the large ganglion cells of teleosts and frogs. They also demonstrate the value of introducing mosaic analysis at an early stage to help identify characters that are useful markers for natural types and that distinguish between within-type and between-type variation in neuronal populations.
基于群体的视网膜神经元研究有助于揭示哺乳动物和硬骨鱼类中视网膜神经元的自然类型。在此，对蛙类进行的第一项此类研究中，对中蛙非洲爪蟾的标记神经节细胞进行了整装片检查。具有大细胞体和粗树突的细胞可分为三种形成镶嵌的类型，每种类型都有其独特的分层模式。按照最近用于硬骨鱼类的方案，这些类型被命名为αa、αab和αc。αa镶嵌类型的细胞（约占所有神经节细胞的0.4%）具有非常大的细胞体和树突，在a亚层（最靠巩膜侧）内呈弥散性分支。它们的远端树突分支稀疏，但通过与相邻细胞的树突相交实现了一致的覆盖。移位细胞和原位细胞属于同一镶嵌类型，具有对称和不对称树突的细胞也是如此。αab镶嵌类型的细胞（约1.2%）具有大细胞体，树突稍小，在低倍镜下呈双分层，且树突广泛分支。它们的远端树突在b亚层和a亚层的玻璃体侧部分广泛分支，与相邻细胞镶嵌排列。所有细胞都是原位的；大多数是对称的。αc镶嵌类型的细胞（约0.5%）具有大细胞体和非常大、稀疏、扁平且相互重叠的树突，主要分布在c亚层。所有细胞都是原位的；有些是不对称的。最近邻分析和空间相关图证实，每种镶嵌类型都是规则且独立的，并且幼蛙中的间距减小。列出了所有三种类型的密度、比例、大小和镶嵌统计数据，并与之前在非洲爪蟾中根据大小和对称性定义的类型以及硬骨鱼类中可能同源的形成镶嵌的类型进行了比较。我们的结果揭示了硬骨鱼类和蛙类的大型神经节细胞之间存在很强的组织相似性。它们还证明了在早期引入镶嵌分析的价值，有助于识别那些对自然类型有用的标记特征，并区分神经元群体中类型内和类型间的变异。
