Tsukamoto Yoshihiko, Omi Naoko
Studio Retina Nishinomiya, Japan ; Department of Biology, Hyogo College of Medicine Nishinomiya, Japan.
Department of Biology, Hyogo College of Medicine Nishinomiya, Japan.
Front Neuroanat. 2014 Sep 26;8:105. doi: 10.3389/fnana.2014.00105. eCollection 2014.
This study compared the types of OFF bipolar cells found in the macaque retina with those found in the mouse retina and determined whether these OFF bipolar cells make direct contacts with both rods and cones by serial section transmission electron microscopy. We performed scatter plots and cluster analysis of the morphological variables of their axon terminals such as the stratification level, the arbor thickness, the arbor area, and the number of ribbons. Five OFF bipolar cell types, including the recently discovered DB3b type, were identified in the macaque retina. The macaque OFF bipolar cell types FMB, DB1, DB2, DB3a, and DB3b corresponded to the mouse OFF bipolar cell types 2, 1, 4, 3a, and 3b, respectively. In addition to contacting rod bipolar cells, ~7% of rods in the macaque retina made basal contacts exclusively with one cell type, DB3b, whereas 18% of rods in the mouse retina made basal contacts with one or two of types, 3a, 3b, and 4. Approximately 3% of mouse rods were divergently connected to two OFF bipolar cells of different types, but macaque rods were solely connected to one OFF bipolar cell. Rod-rod gap junctions were localized at rod cell bodies and axons in the outer nuclear layer in both macaque and mouse retinas. The direct rod-OFF bipolar connection system is slightly more developed in the mouse retina than in the macaque retina, possibly as a fine-tuned adaptation to nocturnal conditions. This one-step direct synaptic pathway from rods to OFF bipolar cells may enhance the response speed to OFF light stimuli compared with more indirect pathways via rod-cone gap junctions (a two-step pathway) and via rod bipolar and AII amacrine cells (a three-step pathway).
本研究比较了猕猴视网膜中发现的 OFF 双极细胞类型与小鼠视网膜中的类型，并通过连续切片透射电子显微镜确定这些 OFF 双极细胞是否与视杆细胞和视锥细胞都有直接接触。我们对其轴突终末的形态学变量进行了散点图和聚类分析，这些变量包括分层水平、树突厚度、树突面积和突触带数量。在猕猴视网膜中鉴定出了五种 OFF 双极细胞类型，包括最近发现的 DB3b 型。猕猴的 OFF 双极细胞类型 FMB、DB1、DB2、DB3a 和 DB3b 分别对应于小鼠的 OFF 双极细胞类型 2、1、4、3a 和 3b。除了与视杆双极细胞接触外，猕猴视网膜中约 7%的视杆细胞仅与一种细胞类型 DB3b 形成基底接触，而小鼠视网膜中 18%的视杆细胞与 3a、3b 和 4 中的一种或两种类型形成基底接触。约 3%的小鼠视杆细胞发散性地连接到两种不同类型的 OFF 双极细胞，但猕猴视杆细胞仅连接到一个 OFF 双极细胞。视杆 - 视杆间隙连接定位于猕猴和小鼠视网膜外核层中的视杆细胞体和轴突处。直接的视杆 - OFF 双极连接系统在小鼠视网膜中比在猕猴视网膜中略发达，这可能是对夜间条件的一种精细调节适应。与通过视杆 - 视锥间隙连接（两步途径）以及通过视杆双极细胞和 AII 无长突细胞（三步途径）的更间接途径相比，这种从视杆细胞到 OFF 双极细胞的一步直接突触途径可能会提高对 OFF 光刺激的反应速度。
