Representative photomicrographs showing p-ERK-IR in the spinal DH (L4-L5) of formalin-treated rats. (A-I) p-ERK-IR in the spinal DH of the saline-pretreated and formalin treated rats. The p-ERK-IR was found exclusively in spinal DH neurons (A-C), but not in microglia (D-F) or astrocytes (G-I). (J,K) Microglia (J) and astrocytes (K) in normal rat (salinepretreated and saline-treated). Scale bar = 50 μm.