Syntaxin 4-positive puncta in the distal inner plexiform layer (IPL) do not arise from dopaminergic or GABAergic CD15-positive amacrine cells. A–C: Syntaxin 4-positive puncta form a plexus along the border of the inner nuclear layer (INL) and IPL that co-stratifies with the processes of dopaminergic amacrine cells (A) labeled for tyrosine hydroxylase (TH). Syntaxin 4 and TH labeling do not colocalize (see D–F), but syntaxin 4-positive puncta contact the processes and cell bodies of the dopaminergic cells (arrowheads). Images shown from a projection of 73 optical sections with total thickness of 10.5 μm. D–F: Higher magnification image of syntaxin 4-positive puncta (arrows and arrowheads) and TH-positive dopaminergic amacrine cell processes in the IPL in a single optical plane. There is no colocalization of labels indicating that the syntaxin 4-positive puncta do not arise from the dopaminergic amacrine cells, but there is often contact between the syntaxin 4-positive puncta and the TH-positive processes (arrowheads). G–I: Syntaxin 4-positive puncta (arrows) form a distinctive plexus that co-stratifies with processes from GABAergic CD15-positive amacrine cells (A). The processes of the CD15-positive amacrine cells do not label for syntaxin 4, but there is contact between syntaxin 4-positive puncta and the processes and cell body of CD15-positive amacrine cells (arrowhead). Images shown from a projection of 57 optical sections with total thickness of 8.16 μm. J–L: Higher magnification image of syntaxin 4 and CD15 double labeling visualized in a single optical plane. Syntaxin 4-positive puncta (arrows) co-stratify with the CD15-positive plexus in the IPL and often contact CD15-positive amacrine cells at the cell body or on processes (arrowhead). Images shown from a projection of 14 optical sections with total thickness of 1.89 μm. GCL, ganglion cell layer. Scale bars = 20 μm for A–C; 10 μm for D–I; 5 μm for J–L.