Figure 6.

Ranking of synaptic contacts from RB to AII amacrine cells. A: The axon terminals of RB cells (B1–22) make ribbon synapses with the distal dendrites of AII amacrine cells (AII 1–7). The number of ribbon contacts for each RB–AII connection is shown at the periphery of a circle representing each AII amacrine cell. B: The cumulative numbers of ribbon contacts made by each RB cell (1–22) to AII amacrine cells (1–7 labeled in different colors, and unknowns in gray) are displayed in each column. The number of AII amacrine cells involved in reunions is shown by integers (2–4) above columns with brackets; e.g., common rod-driven signals of RB7 and RB8 may reunite at AII 3 (blue) and AII 2 (pink). Dominant reunion pairs of RB cells at a particular AII amacrine cell are found between RB6 and RB7 at AII 1 (blue, 64 contacts in total), RB8 and RB12 at AII 2 (pink, 68 contacts), RB17 and RB21 at AII 3 (light blue, 65 contacts), and RB9 and RB11 at AII 4 (green-yellow, 66 contacts). +, Partially reconstructed RB axon arbors. C: The number of RB ribbon contacts that could convey a common rod-driven signal to AII amacrine cells, each of which is designated by its corresponding color and plotted in descending order. The resulting weighting profile is sharpest for RB9 and RB11 (66, 24, five, and two contacts) but flattest for RB11 and RB12 (37, 33, 11, and seven contacts). Scale bar = 5 μm.