Fig. 4. Effect of P-p38 inhibitor on behavioral responses after skin–muscle incision retraction (SMIR). Rats were stimulated by a 15-g von Frey filament (VFH) pressed against the midplantar paw surface of the leg ipsilateral to the surgical procedure; the vertical axis plots the number of withdrawal responses per 10 VFH stimulations (mean ± SD). Intrathecal injection of 10 μg SB203580 at postoperative day (POD) 2 keeps the response level at the preoperative baseline (denoted at day 0 [D0]) and at PODs 8–13 significantly below that for the control, hyperalgesic rats that received only a vehicle injection (A ). Intrathecal injection of 10 μg SB203580 at POD 9, after hyperalgesia has developed, results in only a brief reduction of the increased response. Comparison of vehicle- and SB203580-injected rats on the same days (B ). *P < 0.05, **P < 0.01, ***P < 0.001 (one-way ANOVA).