Enteric ganglia are surrounded by a protective myenteric plexus barrier. Schematic drawing shows experimental design of FITC-dextran assays, where wild-type C57BL/6 mice receive intravenous FITC-dextran (50 mg/mL) and are killed 10, 45, and 60 minutes later (A). At 10 minutes after FITC-dextran loading, scattered green fluorescence is present in the lamina propria (B, arrow) but not the muscularis propria (B, dashed line). Most F4/80+ macrophages in the colon do not contain FITC particles (C, arrows), but some do (C, arrowheads). At 45 minutes after injection, diffuse FITC signal appears in the mucosa and submucosa (D and E). Strong FITC signal is also present around the enteric ganglia but not within them (F–F’). At 60 minutes, F4/80+ macrophages contain FITC (G, arrowheads). MyMs expressing FITC are seen in the PGS (H-H”, arrowheads; I, arrows), and FITC-loaded IGMs have entered into the intraganglionic compartment (I–I’, arrowhead).