Figure 8. Rods and rod bipolar cells remain synaptically coupled in the Dscaml1^GT/GT retina.

A, B, Sections of wild type and Dscaml1^GT/GT retinas were stained with antibodies to PKCα, to label RBCs, Bassoon, a marker of the rod presynapse, and Cacna1s, a component of the RBC postsynapse. Presynaptic and postsynaptic markers were paired in both the wild type and Dscaml1^GT/GT retina, although the number of synapses was reduced in the mutant retina. C, D, Sections of wild type and Dscaml1^GT/GT retinas were stained with antibodies to PKCα, to label RBCs, and calbindin a marker of horizontal cells (N=2). The dendrites of both wild type and Dscaml1^GT/GT RBCs colaminated with horizontal cell axons. E–H, Transmission electron microscopy was used to examine the anatomy of the Dscaml1^GT/GT ribbon synapses. Examples of ribbon synapses from wild type (E and F) and Dscaml1^GT/GT (G and H) retinas showing the photoreceptor ribbon (R) apposed to a horizontal cell (H) and invaginating bipolar cells (B, typically an ON bipolar dendrite flanked by darker OFF bipolar processes). An increase in floating ribbons was seen in the mutant (H). I–K, Electroretinography (ERG) was performed on wild type, Dscaml1^GT/GT, and Dscam^−/− mice (N≥5). Rod bipolar cells receive input from rods in the Dscaml1^GT/GT mice, as demonstrated by the robust B wave, reflecting postsynaptic bipolar cell activation, which had a greater amplitude compared to wild type and Dscam^−/− mice. The scale bar below panel (H) is equivalent to 32.4 µm in A and B, 40.9 µm in C and D and 478 nm in E–H.