Acidic QX-314 inhibited NE-induced behavioral hyperalgesia and spinal neuronal sensitization.

<p>(A) Pre-treatment with pH 5.0 QX-314 (2.5-µg/10-µl) inhibited thermal and mechanical hyperalgesia induced by intraplantar injection of NE (0.5%, 10-µl). **<i>P</i><0.01 or *<i>P</i><0.05 at 5-min to 40-min time point compared with NE or pH 7.4 QX-314+NE group, n = 8 mice in each group. (B) Pre-injection of SB366791 prevented the analgesic effect of pH 5.0 QX-314 in NE-induced thermal hyperalgesia in mice. ***<i>P</i><0.001, **<i>P</i><0.01 or *<i>P</i><0.05 at 5-min to 55-min time point compared with SB366791+pH 5.0 QX-314+NE, n = 8 mice in each group. (C) Intraplantar injection of pH 5.0 QX-314, but not pH 7.4 QX-314, attenuated the expression of spinal Fos protein induced by NE in mice, which could be abolished by pre-injection of SB366791. Representative immunohistochemical staining of Fos in the spinal cord of mice in the control group, DMSO group, NE group, pH 7.4 QX-314+NE group, pH 5.0 QX-314+NE group and SB366791+pH 5.0 QX-314+NE group. Quantitative data indicates the number of Fos positive neurons in the spinal cords of mice in each group. ***<i>P</i><0.001, NE group vs. control group or DMSO group; pH 7.4 QX-314+NE group vs. pH 5.0 QX-314+NE group, pH 5.0 QX-314+NE group vs. SB366791+pH 5.0 QX-314+NE group, n = 6 mice in each group. Scale bar = 100-µm. (D) p-ERK was examined at 10-min after pH 5.0 PBS injection. The representative western blot bands (top) and the quantitative data (bottom) for the expression of p-ERK in the spinal cord of mice are shown. The fold change for the density of p-ERK bands is calculated after normalization with control. p-ERK levels in control group were set at 1 for quantifications. **<i>P</i><0.01, NE group vs. control group or DMSO group, pH 5.0 QX-314+NE group vs. SB366791+pH 5.0 QX-314+NE group; ***<i>P</i><0.001, pH 7.4 QX-314+NE group vs. pH 5.0 QX-314+NE group, n = 6 in each group.