Figure 5. Normal ultrastructure of ribbons in the outer plexiform layer of C-terminal-binding protein 1 (CtBP1)-knockout retina. A, B: The electron micrographs show transverse sections through a rod ribbon synapse in the outer plexiform layer of wild-type (WT) and CtBP1-knockout (KO) retina. The arrow points to the ribbon, the arrowhead indicates the location of the arciform density, and the letter H marks the dendrites of horizontal cells. C, D: Electron micrographs of approximately horizontal sections through a rod ribbon synapse in WT and KO retina. The arrow indicates the ribbon, and the letter H marks the dendrites of horizontal cells.