Syntaxins 1 through 4 are differentially distributed in the synaptic layers of the retina. A: Syntaxin 1 is localized to amacrine cell bodies (A) and processes in the inner plexiform layer (IPL). B: Syntaxin 2 also is localized to amacrine cell bodies (A), but shows a more restricted, punctate distribution in the IPL. C: Syntaxin 3 is localized to the glutamatergic ribbon synapses of photoreceptor and bipolar cell terminals in the outer plexiform layer (OPL) and IPL, respectively. Labeling is also present in the cell bodies of the photoreceptors and their inner segments (IS) and in bipolar cell bodies (B) and axons. D: Syntaxin 4 shows a very restricted, punctate distribution in the OPL and IPL. In the OPL, clusters of syntaxin 4 processes are associated with cone terminals (arrows). In the IPL, a distinct lamina of syntaxin 4 positive puncta is present at the INL/IPL border (arrowheads), with other puncta sparsely distributed deeper in the IPL (circle). E–H: Immunoblots for syntaxins 1 through 4 reveal a band at the appropriate molecular mass in membrane homogenates prepared from mouse retina and brain, confirming the expression of all four syntaxin isoforms in the mouse retina and the specificity of the antibodies and antisera. ONL, outer nuclear layer; INL, inner nuclear layer, GCL, ganglion cell layer. Scale bars = 20 μm for A–D.