SNL induces IL-18 upregulation in spinal microglia, but not in neurons or astrocytes. A, Double immunostaining of green reaction product for IL-18 and red product for NeuN, MAP2, or GFAP in the ipsilateral dorsal horn at day 7 after surgery. Double staining of IL-18 with NeuN and MAP2, neuronal markers, shows no colocalization. Double labeling of IL-18 with GFAP, an astrocyte marker, indicates that IL-18 is not increased in spinal astrocytes. B, Double immunofluorescence shows that IL-18 (green) is colocalized with Iba1 (red) in the superficial dorsal horn (laminae I–III) at day 7 after SNL. Scale bars, 50 μm.