AN ALTERNATIVE PATHWAY FOR SIGNAL FLOW FROM ROD PHOTORECEPTORS TO GANGLION-CELLS IN MAMMALIAN RETINA

Rod signals in the mammalian retina are thought to reach ganglion cells over the circuit rod --> rod depolarizing bipolar cell --> All amacrine cell --> cone bipolar cells --> ganglion cells, A possible alternative pathway involves gap junctions linking the rods and cones, the circuit being rod --> cone --> cone bipolar cells --> ganglion cells, It is not clear whether this second pathway indeed relays rod signals to ganglion cells. We studied signal flow in the isolated rabbit retina with a multielectrode array, which allows the activity of many identified ganglion cells to be observed simultaneously while the preparation is stimulated with light and/or exposed to drugs, When transmission between rods and rod depolarizing bipolar cells was blocked by the glutamate agonist 2-amino-4-phosphonobutyric acid (APB), rod input to all On-center and briskly responding Off-center ganglion cells was dramatically reduced as expected. Off responses persisted, however, in Off-center sluggish and On-Off direction-selective ganglion cells, Presumably these responses were generated by the alternative pathway involving rod-cone junctions, This APE-resistant pathway may carry the major rod input to Off-center sluggish and On-Off direction-selective ganglion cells.