Colour receptors, and their synaptic connexions, in the retina of a cyprinid fish.
Colour receptors, and their synaptic connexions, in the retina of a cyprinid fish.
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鲤鱼视网膜中的颜色感受器及其突触连接。
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发表时间：
1975
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通讯作者：
J. Scholes
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作者：
J. Scholes
从形态上来说，红眼斯卡丁鱼（Scardinius erythrophamus）的视网膜中有五种视锥细胞。但其中的两个，即双视锥细胞和自由主视锥细胞，在功能上可能是等效的，而另一个稀疏的小（斜）视锥细胞群（在老年鱼中消失）不太可能对视觉光谱灵敏度做出重大贡献。因此，主视锥细胞和副视锥细胞（通常彼此配对）以及单个视锥细胞似乎是构成鱼类三色性的三种受体。使用单个视锥细胞的照相密度测量来提供证据，证明辅助视锥细胞含有吸收绿色的感光色素，而单个视锥细胞含有蓝色的。其他论据也支持这些鉴定，它们也强烈表明主锥体含有吸收红色的色素。通过电子显微镜检查高尔基体浸渍的双极细胞，以确定它们与这些不同的、解剖学上可识别的色锥体和视网膜杆形成的突触连接的特定模式。区分了三种主要安排（参见第 100 页图 69）。 (1) 杆双极细胞包含两种不同的形态类型，这两种类型都专门连接到主（红色）锥体以及树突域轮廓内的杆。 (2) 选择性视锥双极细胞，更精致的神经元，具有相当宽的树突域，连接（根据类型）到一种或其他不同颜色的视锥细胞群。分析的示例特定于附件（绿色）或单个（蓝色）锥体；没有发现双极细胞仅与红色视锥细胞连接。 (3) 混合视锥双极具有最小的树突场，并连接到视锥的组合（例如，红色和绿色，或绿色和蓝色，但不是红色和蓝色）。它们还具有来自视杆的突触输入（通常相对稀疏）。遇到了与所有三种锥体类型连接的细胞，但仅对它们进行了部分分析，并且没有详细描述。这些双极细胞类型的光学显微镜形态始终反映了每种细胞与不同受体群体的连接的详细模式（正如视锥细胞的形态反映了其感光色素的光谱特性一样）。但是，虽然它们的突触连接通常对锥体类型具有高度特异性，但它们偶尔也会与“错误”受体建立异常连接。受体双极突触存在高度分歧（第 85 页），不同种类的锥体各自连接到不同数量的双极细胞。主（红色）视锥细胞数量最多，与其他类型的视锥细胞相比，它们单独连接到更多的双极，其特有的突触发散同样与它们在视网膜中出现的频率有关。然而，视杆细胞的数量比视锥细胞多得多，因此不符合这种概括。还检查了不同锥体的突触末端通过内陷基底突连接在一起的选择性。这些突触连接不同颜色视锥细胞的相邻突触末端：具体而言，主（红色）视锥细胞基底突内陷辅助（绿色）视锥细胞蒂，反之亦然。单个（蓝色）锥体基底突仅连接到附属锥体蒂，但突触关系不是交互的。视锥细胞之间的这些突触对于双极细胞连接模式的解释具有重要影响。在他们看来，不同视锥细胞汇聚到混合视锥双极树突上所介导的颜色通道之间的相互作用，似乎重复了已经在更外围进行的过程。同样，虽然选择性视锥双极的解剖结构似乎旨在传达各个视锥细胞群的活动，但它们采样的受体的反应必定已经受到其他颜色通道活动的影响。
Morphologically speaking, there are five kinds of cone cells in the retina of the rudd (Scardinius erythrophthalmus). But two of them, the principal elements of the double cones and the free principal cones, are probably functionally equivalent, while another, sparse, population of small (oblique) cones (which disappear in older fish), is unlikely to make a significant contribution to visual spectral sensitivity. Thus, principal and accessory cones (usually paired with one another), and single cones seem to be the three receptors which underlie the fish's trichromacy. Photographic densitometry of individual cone cells was used to provide evidence that accessory cones contain a green-absorbing photopigment and the single cones a blue one. Other arguments are given in support of those identifications, and they also strongly suggest that principal cones contain the red-absorbing pigment. Golgi-impregnated bipolar cells were examined electron-microscopically to determine the specific patterns of synaptic connexion they make with these different, anatomically identifiable, colour cones and with the retinal rods. Three principal arrangements were distinguished (see figure 69, page 100). (1) Rod bipolar cells comprise two distinct morphological types, both of which connect exclusively to principal (red) cones as well as to the rods within the outlines of their dendritic fields. (2) Selective cone bipolar cells, more delicate neurons with considerably wider dendritic fields, connect (according to type) to one or other of the different colour cone populations. Examples analysed were specific for the accessory (green) or for the single (blue) cones; no bipolar cells were found connected only to red cones. (3) Mixed cone bipolars have the smallest dendritic fields, and connect to combinations of cones (for example, red and green, or green and blue, but not red and blue). They also have synaptic input (usually relatively sparse) from the rods. Cells were encountered connecting to all three cone types, but they were only partially analysed, and are not described at length. The light microscopic morphology of these bipolar cell types consistently reflects the detailed pattern of connexion each makes with the different receptor populations (just as the morphology of the cones reflects the spectral properties of their photopigment). But while their synaptic connectivity is generally highly specific for cone type, they do occasionally make anomalous connexions with the 'wrong' receptors. There is a high degree of divergence (page 85) at the receptor-bipolar synapses, and the different kinds of cones each characteristically connect to different numbers of bipolar cells. Principal (red) cones, which are the most numerous, individually connect to more bipolars than cones of other types, whose characteristic synaptic divergence is likewise related to the frequency with which they occur in the retina. However, rods, which are much more numerous than cones, do not conform with this generalization. The selectivity with which the synaptic terminals of the different cones are connected together by their invaginating basal processes was also examined. These processes link neighbouring synaptic terminals of differently coloured cones: specifically, principal (red) cone basal processes invaginate accessory (green) cone pedicles, and vice versa. Single (blue) cone basal processes connect only to accessory cone pedicles, but that synaptic relation is not reciprocated. These synapses between the cones have important bearing upon interpretation of the bipolar cell connectivity patterns. In their light, the interaction between colour channels which the convergence of different cones onto the mixed cone bipolar dendrites mediates, seems to re-iterate a process already undertaken more peripherally. Likewise, whereas the anatomy of the selective cone bipolars appears designed to convey activity from the individual cone populations, the responses of the receptors they sample must already be influenced by activity in other colour channels.