Kouyama N, Marshak D W
Department of Neurobiology and Anatomy, University of Texas Medical School, Houston 77025.
J Neurosci. 1992 Apr;12(4):1233-52. doi: 10.1523/JNEUROSCI.12-04-01233.1992.
A distinct subpopulation of bipolar cells in macaque monkey retina was labeled with antisera that recognize glycine-extended cholecystokinin precursors. The labeled bipolar cells were found throughout the retina and had dendrites contacting a subpopulation of cone pedicles and axons ramifying in the fifth stratum of the inner plexiform layer. Several lines of evidence indicate that the labeled bipolar cells are a single type despite some variations in their morphology. First, the density of perikarya and their diameters varied continuously as a function of eccentricity. Second, the positions of perikarya within the inner nuclear layer and the level at which the axons branched in the inner plexiform layer were constant at all eccentricities. Bipolar cells with similar morphology have been described previously as "blue cone bipolar cells" (Mariani, 1984b), but there was no direct evidence that this was the case. In this study, we show by light microscopy that labeled bipolar cells have dendrites ending exclusively upon presumptive blue cones labeled by Procion black dye. All blue cones were contacted by labeled bipolar cells, and virtually all bipolar cells contacted blue cones, the only exceptions being in regions where blue cones had been lost. Approximately 20% more labeled bipolar cells than blue cones were found at every eccentricity; thus, connections between blue cones and labeled bipolar cells were not strictly one to one. The mean number of cones presynaptic to each bipolar cell was 1.2, and the mean number of bipolar cells postsynaptic to each cone was 1.8. By an electron microscopic study of labeled bipolar cell dendrites, we determined that they became central elements of ribbon synapses in blue cones. Some of their ribbon synapses were unusual: in one type, a single, large labeled dendrite was postsynaptic to two or more ribbons, while in the other type, ribbons had two or more central elements. The presence of these invaginating contacts and the axonal terminals in the proximal inner plexiform layer suggest that the labeled bipolar cells depolarize to short-wavelength stimuli and function to relay information from blue cones to the inner plexiform layer. There were also other, unlabeled bipolar cell dendrites that received inputs from blue cones at basal junctions and triad-associated flat contacts, which suggests that there are additional types of bipolar cells conveying information from short-wavelength cones in the primate retina.
用识别甘氨酸延伸型胆囊收缩素前体的抗血清标记了猕猴视网膜中一个独特的双极细胞亚群。在整个视网膜中都发现了被标记的双极细胞，其树突与一部分视锥小足接触，轴突在内网状层的第五层分支。几条证据表明，尽管这些被标记的双极细胞在形态上存在一些差异，但它们属于单一类型。首先，胞体的密度及其直径随离心率连续变化。其次，胞体在内核层中的位置以及轴突在内网状层中分支的水平在所有离心率下都是恒定的。先前已将具有相似形态的双极细胞描述为“蓝锥双极细胞”（马里亚尼，1984b），但没有直接证据证明情况确实如此。在本研究中，我们通过光学显微镜显示，被标记的双极细胞的树突仅终止于用普施安黑染料标记的假定蓝锥上。所有蓝锥都与被标记的双极细胞接触，并且几乎所有双极细胞都与蓝锥接触，唯一的例外是蓝锥缺失的区域。在每个离心率下，发现被标记的双极细胞比蓝锥多约20%；因此，蓝锥与被标记的双极细胞之间的连接并非严格一对一。每个双极细胞突触前的视锥平均数量为1.2，每个视锥突触后的双极细胞平均数量为1.8。通过对被标记的双极细胞树突的电子显微镜研究，我们确定它们成为蓝锥中带状突触的中心元件。它们的一些带状突触很不寻常：在一种类型中，单个大的被标记树突是两个或更多个带状结构的突触后结构，而在另一种类型中，带状结构有两个或更多个中心元件。这些内陷接触和近端内网状层中的轴突终末的存在表明，被标记的双极细胞对短波长刺激去极化，并起到将信息从蓝锥传递到内网状层的作用。还有其他未被标记的双极细胞树突，它们在基底连接和三联体相关的扁平接触处接收来自蓝锥的输入，这表明在灵长类视网膜中存在其他类型的双极细胞，它们从短波长视锥传递信息。
