Fig. 9.

Signaling pathway of spinal HMGB1-mediated morphine tolerance and hyperalgesia. (a) Compared to morphine plus vehicle treatment, intrathecal administration of morphine with HMGB1 siRNA inhibited the increase in NF-κB p-p65 levels and the decrease in cytoplasmic IκB-α levels. However, p-p38 and p-JNK levels were not changed by this treatment. Data are presented as the mean ± SEM and were analyzed by one-way ANOVA. * P < 0.05, ** P < 0.01 vs. vehicle (Veh: transfection regent); # P < 0.05, ## P < 0.01 vs. morphine plus vehicle or morphine plus scramble (sc) RNA group. (b, c) A single i.t. injection of recombinant HMGB1 resulted in the increased expression of p-p65, TNF-α and IL-1β in the dorsal horn at 3 hours, which persisted to 6 hours after the injection (b). These effects were partially blocked by the coinjection of HMGB1 with TAK-242 (c). * P < 0.05, ** P < 0.01 vs. control (i.t. ACSF); # P < 0.05 vs. HMGB1 plus vehicle (Veh: ACSF). (d) A bolus i.t. coinjection of morphine with HMGB1 reduced the analgesic efficacy of morphine. * P < 0.05 vs. morphine plus ACSF group. (e-f) Bolus i.t. injection of HMGB1 led to a reduction in the paw withdrawal threshold (e) and paw withdrawal latency (f) in the left hind paw, which occurred at 3 hours and persisted to 6 hours after the injection. * P < 0.05 vs. baseline; # P < 0.05 vs. ACSF group. ACSF: artificial cerebrospinal fluid. Data of (d), (e), and (f) were analyzed by Student’s t-test.