Ret-RGS1 is localized to ON bipolar somas and dendrites. A, Radial section of bovine retina stained for Ret-RGS1. Staining is present in all retinal layers, most strongly in inner segments and then OPL. Staining in IPL and ganglion cell somas was somewhat variable between tissues. IS, Inner segments; ONL, outer nuclear layer; OPL, outer plexiform layer; INL, inner nuclear layer; IPL, inner plexiform layer; GCL, ganglion cell layer; NFL, nerve fiber layer. (Abbreviations apply to all Figures.) B, Double staining for Ret-RGS1 (red) and PKC (green). Rod bipolar cells marked with anti-PKC (arrows) were also stained for Ret-RGS1. Certain PKC-negative somas were Ret-RGS1 positive (arrowhead). C, Double staining for Ret-RGS1 (red) and Gαo (green). All ON bipolar cells marked by Gαo express Ret-RGS1 (arrows). D, Electron micrograph of a rod synaptic complex. The invaginating rod bipolar dendritic tip (RB) is stained for Ret-RGS1. r, Ribbon. E, Electron micrograph of a cone synaptic complex. The central element of the postsynaptic triad (CB) was stained for Ret-RGS1. H, Horizontal cell process.