Syntaxin 3 is associated with the glutamatergic ribbon synapses of photoreceptors and bipolar cells. A–C: Labeling for syntaxin 3 and VGLUT1, a marker for ribbon synapses, colocalize extensively in the photoreceptor terminals in the OPL and in bipolar cell terminals in the IPL. Box indicates area shown in panels D–F. D–F: Examination of syntaxin 3 and VGLUT1 immunolabeling in the IPL at higher magnification confirms that all bipolar cell terminals contain syntaxin 3. Images shown are from a single optical section. IS, inner segments; ONL, Outer nuclear layer; INL, inner nuclear layer, GCL, ganglion cell layer. Scale bars = 20 μm for A–C; 10 μm for D–F.