Figure 5.

ERK1 contributes to the onset of heat hypersensitivity after intraplantar formalin injection. A, To assess the role of ERK1 in long-term formalin-induced heat hypersensitivity, WT (n = 8) and ERK1 KO (n = 8) littermates were injected with 2% formalin subcutaneously into the plantar side of the right hindpaw. Paw withdrawal latencies were measured before and after injection and are graphed as percentage of preinjection baseline. ERK1 KO mice have reduced hypersensitivity to heat at 1 and 2 h after formalin injection in the ipsilateral paw (two-way RM ANOVA with Bonferroni's post test, *p < 0.05). B, To measure formalin-induced mechanical hypersensitivity, WT (n = 8) and ERK1 KO (n = 9) littermates were injected with 3.5% formalin. Paw withdrawal thresholds were obtained using von Frey filaments. There were no statistically significant differences between WT and ERK1 KO. Error bars reflect SEM.