Figure 1. The three rod pathways in the mammalian retina .

In the primary pathway, rods (R) transfer signals to postsynaptic rod bipolar cells (BCs; RB) and, in turn, to AII amacrine cells (ACs). The AII cells form gap junctions (gj) with ON cone BCs (CB) and inhibitory glycinergic synapses with OFF cone BCs, which pass rod signals to ON and OFF retinal gangion cells, respectively. The secondary rod pathway is formed by gap junctions between rods and cones (C), in which rod signals are passed directly to cones and then to cone BCs. The tertiary rod pathway is formed by rod synapses onto a unique type of OFF BC and possibly also to a type of ON cone BC, thereby forming complimentary ON and OFF circuits. The feedback inhibitory synapses from ACs to BC axon terminals proposed to be responsible for selective masking rod pathway signals are encircled. [Colour figure can be viewed at wileyonlinelibrary.com]