Figure 1.
Basic AII cell networks. Vertebrate rod R and cone C signal convergence patterns onto bipolar cells, amacrine or ganglion cells, and CNS targets. (A) Non-mammalian networks display two channel types: pure cone bipolar cell (CB) and mixed rod-cone bipolar cell (MB) channels that drive sets of retinal ganglion cells (GC) projecting to CNS targets via high gain (n) glutamate signaling (black arrows). The non-mammalian rod to GC chain has a net gain of n2. (B) Mammalian networks display separate CB and rod bipolar cell (RB) channels. Only CB channels drive GCs. RB channels drive only amacrine cells (ACs), in particular the AII AC that provides low gain coupling or glycinergic signaling (open arrow) from the third stage back to stage two in the CB chain. The mammalian rod to GC chain has a net gain of n3. There is evidence for sparse rod signal leakage into the CB chain. The gray glycinergic (gly) motif in (A) is the hypothetical evolutionary precursor of the mammalian AII AC. (C) The classic AII amacrine cell network, circa 1992. The rod input is collected by rod bipolar cells (Rod BC) which drive AII cells by ionotropic glutamate receptors (iGluRs). Cone input is collected by OFF cone bipolar cells (OFF BC) that also sparsely drive AII cells by iGluRs. The AII network is extensively coupled to ON cone bipolar cells. Glycinergic output from the AII network targets OFF BCs and OFF ganglion cells (OFF GC).