Fig. 3.  (A, D, G ) Double confocal immunofluorescence microscopy of μ-opioid receptor (MOR; red fluorescence ) and (B, E, H ) phosphorylated p38 mitogen-activated protein kinase (MAPK; green fluorescence ) immunoreactivity in dorsal root ganglia (DRG) neurons of intraplantar vehicle (A –C ), intraplantar nerve growth factor (NGF) (D –F ), and intraplantar NGF plus intrathecal p38-MAPK inhibitor SB20358-treated animals (G–I ). (C, F, I ) Combined images showing colocalization of MOR with phosphorylated p38 MAPK (p-p38 MAPK). Note the coexistence of MOR (red) with p-p38 MAPK (green) (double arrows ) with few cells containing only MOR (single arrow ) or p-p38 MAPK (▿). After intraplantar NGF, the percentage of immunoreactive MOR neurons colocalizing with p-p38 MAPK was increased compared with intraplantar vehicle, which was attenuated after treatment with intrathecal p38-MAPK inhibitor SB203580. Bar = 20 μm.