FosB/ΔFosB colocalizes with preprodynorphin in the nucleus accumbens. Representative images (magnification, 40×) showing DAPI (A and E), FosB/ΔFosB-ir (B and F), and preprodynorphin-ir (C and G) in the nucleus accumbens of mice that received repeated vehicle (top row) or THC (bottom row) treatment. FosB/ΔFosB-ir was localized to the nucleus, as demonstrated with DAPI staining, and preprodynorphin-ir was localized to the cell body. Merged images show colocalization of FosB/ΔFosB-ir (red), preprodynorphin-ir (green), and DAPI (blue) (D and H). Cell counts showed that FosB/ΔFosB-ir cells that were also positive for preprodynorphin-ir (white bars) were in the majority relative to cells positive for FosB/ΔFosB-ir only (black bars) in both vehicle- and THC-treated mice (I). Data are mean counts ± S.E.M. (n = 4 per group). ***P < 0.001 compared with FosB/ΔFosB-ir only cells. VEH, vehicle.