Electron microscopic analysis of the rod pathway of the rat retina

Two immunocytochemical markers were used to label the rod pathway of the rat retina. Rod bipolar cells were stained with antibodies against protein kinase C and AII‐amacrine cells with antibodies against parvalbumin. The synaptic circuitry of rod bipolars in the inner plexiform layer (IPL) was studied. Rod bipolar cells make approximately 15 ribbon synapses (dyads) in the IPL. Both postsynaptic members of the dyads are amacrine cells; one is usually the process of an AII‐amacrine cell and the other one frequently provides a reciprocal synapse. No direct output from rod bipolar cells into ganglion cells was found. AII‐amacrine cells make chemical output synapses with cone bipolar cells and ganglion cells in sublamina a of the IPL. They make gap junctions with cone bipolar cells and other AII‐amacrine cells in sublamina b of the IPL. The rod pathway of the rat retina is practically identical to that of the cat and of the rabbit retina. It is very likely that this circuitry is a general feature of mammalian retinal organization. © Wiley‐Liss, Inc.