Whitaker Christopher M, Nobles Gina, Ishibashi Munenori, Massey Stephen C
Ruiz Department of Ophthalmology and Visual Science, McGovern Medical School, University of Texas Medical School at Houston, Houston, TX, United States.
Front Cell Neurosci. 2021 May 6;15:662329. doi: 10.3389/fncel.2021.662329. eCollection 2021.
Rod and cone pathways are segregated in the first stage of the retina: cones synapse with both ON- and OFF-cone bipolar cells while rods contact only rod bipolar cells. However, there is an exception to this specific wiring in that rods also contact certain OFF cone bipolar cells, providing a tertiary rod pathway. Recently, it has been proposed that there is even more crossover between rod and cone pathways. Physiological recordings suggested that rod bipolar cells receive input from cones, and ON cone bipolar cells can receive input from rods, in addition to the established pathways. To image their rod and cone contacts, we have dye-filled individual rod bipolar cells in the rabbit retina. We report that approximately half the rod bipolar cells receive one or two cone contacts. Dye-filling AII amacrine cells, combined with subtractive labeling, revealed most of the ON cone bipolar cells to which they were coupled, including the occasional blue cone bipolar cell, identified by its contacts with blue cones. Imaging the AII-coupled ON cone bipolar dendrites in this way showed that they contact cones exclusively. We conclude that there is some limited cone input to rod bipolar cells, but we could find no evidence for rod contacts with ON cone bipolar cells. The tertiary rod OFF pathway operates direct contacts between rods and OFF cone bipolar cells. In contrast, our results do not support the presence of a tertiary rod ON pathway in the rabbit retina.
视锥细胞与ON型和OFF型视锥双极细胞都形成突触，而视杆细胞仅与视杆双极细胞接触。然而，这种特定的神经连接存在一个例外，即视杆细胞也与某些OFF型视锥双极细胞接触，形成一条三级视杆通路。最近，有人提出视杆和视锥通路之间的交叉甚至更多。生理学记录表明，除了已确定的通路外，视杆双极细胞还接收来自视锥细胞的输入，而ON型视锥双极细胞也可以接收来自视杆细胞的输入。为了成像它们的视杆和视锥接触，我们对兔视网膜中单个视杆双极细胞进行了染料填充。我们报告称，大约一半的视杆双极细胞接收一个或两个视锥细胞的接触。对AII无长突细胞进行染料填充，并结合减法标记，揭示了与它们耦合的大多数ON型视锥双极细胞，包括偶尔通过与蓝锥细胞的接触而识别出的蓝锥双极细胞。以这种方式对与AII耦合的ON型视锥双极树突进行成像表明，它们仅与视锥细胞接触。我们得出结论，视杆双极细胞有一些有限的视锥细胞输入，但我们没有发现视杆细胞与ON型视锥双极细胞接触的证据。三级视杆OFF通路通过视杆细胞与OFF型视锥双极细胞之间的直接接触起作用。相比之下，我们的结果不支持兔视网膜中存在三级视杆ON通路。
