Figure 4

Immunolabeling of substance P and phosphorylated ERK in the dorsal root ganglia (DRG) and spinal cord at day 21. (a) Quantification of labeling intensity for the neurotransmitter substance P (red) and the MAP kinase pERK (purple) in cells with MAP-2 (green) positive labeling shows elevated expression after collagenase (5 rats) injection relative to vehicle (3 rats) injection for both substance P (Wilcoxon test; *p < 0.001) and pERK (Wilcoxon test; *p < 0.001) regardless of neuronal size (see Supplementary Fig. S1 online). White arrows indicate exemplary neurons identified as small (S), medium (M), or large (L) diameter neurons. Data points superimposed on box plots in (a) represent the mean for each rat (n = 5–7 images/rat; n = 10 cells/image). (b) Intra-articular collagenase (6 rats) also induces increased positive labeling for substance P (red) and pERK (purple) in the superficial dorsal horn. Spinal substance P (Wilcoxon test; *p = 0.039) is significantly greater after collagenase injection than after injection of the vehicle (2 rats), but the same increase is not detected with pERK expression (Wilcoxon test; p = 0.147). Spinal cord images show regions of the superficial dorsal horn (700 × 300 pixels) where immunolabels were quantified; insets show higher magnification of regions (white stars) to demonstrate positive substance P labeling. Individual data points on boxplots in (b) represent the mean value per rat quantified for 6–8 images/rat. For both panels, box-and-whisker plots show horizontal lines representing the first (lower) quartile, median, and third (upper) quartile of the data and whiskers represent the minimum and maximum values of the data set.