ERK was phosphorylated in the rat L4/5 spinal dorsal horn after BV injection. (A) Control p-ERK immunostaining in an L4/5 spinal cord section (16 μm) after intraplantar saline injection (50 μl). Only a few of p-ERK-IR cells were detected. (B-D) p-ERK immunostaining in L4/5 spinal cord sections (16 μm) at 2 min, 2 hr, and 2 d after intraplantar BV injection (200 μg/50 μl). p-ERK-IR cells were distributed mainly in laminae I-II of the spinal dorsal horn. Immunohistochemistry indicates a rapid increase in the number of p-ERK immunoreactive cells in the ipsilateral spinal cord at 2 min. (E) Time course of BV-evoked p-ERK labeled cells in the L4/5 dorsal horn. (n = 4 or 5 each time point, ** p < 0.001; *p < 0.05; compared with controls; one-way AVOVA). Scale bars, 50 μm in A-D. cont, control.