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Yong N. Li, Taro Tsujimura, Shoji Kawamura, John E. Dowling; Bipolar Cell-Photoreceptor Connections in the Zebrafish Retina. Invest. Ophthalmol. Vis. Sci. 2011;52(14):2573.
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Bipolar cells convey luminance, spatial and color information from photoreceptors to amacrine and ganglion cells. As many as seventeen types of bipolar cells exist in the adult zebrafish retina (Connaughton et al., 2004). In this study, we describe the photoreceptor connections of 339 bipolar cells found in the zebrafish retina.
Pulled glass electrode tips loaded with DiI crystals were inserted and broken off into the whole-mounted retinas of SWS1-GFP, LWS-GFP and XOPS-GFP transgenic zebrafish and their intercrosses (Takechi et al., 2003; Tsujimura et al, in press; Fadool, 2003; Li et al., 2009). Bipolar cells were fully labeled by DiI within two weeks. Serial confocal images of bipolar cells were taken and the dendrites, their terminals, somata and axons analyzed.
Cones are arranged in a precise mosaic in the zebrafish retina: rows of alternating blue- (B) and ultraviolet-sensitive (UV) single cones alternate with rows of red- (R) and green-sensitive (G) double cones; G cones are adjacent to UV cones, and B cones adjacent to R cones (Robinson et al., 1993). Rod terminals intersperse among cone terminals. Using SWS1-GFP, LWS-GFP and XOPS-GFP retinas whose UV, R cones and rods are GFP positive, respectively, we are able to identify the positions of the four types of cones and rods. Bipolar cells (339), identified by their morphology, were observed to make Cone-only (181), Mixed (cones and rods, 150) and Rod-only (8) connections, up to 22 different combinations. The major combinations are Cone-only: R+G (45), R+G+B (39), G (26), G+B+UV (25) and R+G+B+UV (24); Mixed: R+G+Rods (82), R+G+B+Rods (31), R+G+B+UV+Rods (14) and R+Rods (11). Certain cone-specific bipolar cells have very small dendritic spreads; in contrast, G specific bipolar cells have very large dendritic fields. Based on their axon terminal stratification, the bipolar cells could be further sub-divided into ON-, OFF-, and ON/OFF-bipolar cells.
Bipolar cells connect to photoreceptors in various combinations, suggesting complex chromaticity and luminosity information transmission by bipolar cells in the zebrafish retina.
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