Appearance of the rat hindpaw and von Frey hyperalgesia test after intraplantar CFA or TNF-α injection. Seventy-two hours after injection of CFA, TNF-α or saline (control) into the right hindpaw of SD rats, we observed the hindpaw (A-C). Daily hyperalgesia testing was carried out for three days (D, E). Saline: 0.9% NaCl (ipsilateral) injection. Control (contra): contralateral to CFA or TNF-α. CFA (ipsi): CFA (100 μl) injected. TNF-α (ipsi): 500 ng TNF-α (30 μl) injected. Data were analyzed using one-way ANOVA followed by Tukey test and are expressed as mean ± SEM. **p < 0.01, ***p < 0.001; compared to basal (SD rats, N = 5 per group for CFA injection and N = 3 per group for TNF-α injection).