Figure 2.

Cardinal features of inflammation in CPIP mice.

(A) The hindpaws showed obvious but transient swelling at 30 minutes and 1 day after establishment of the CPIP model. The arrow indicates the ipsilateral side. (B) Statistical analysis showing that the ipsilateral paw thickness was transiently increased after CPIP establishment (n = 8 mice/group). **P < 0.01 and ****P < 0.0001, vs. control ipsilateral hindpaw. (C) The temperature of the ipsilateral hindlimbs was transiently increased after CPIP establishment (n = 6 mice/group). **P < 0.01, vs. control ipsilateral hindpaw. (D–G) Punctate mechanical hyperalgesia and heat hyperalgesia were observed in the bilateral hindpaws of CPIP mice (n = 7 mice/group). *P < 0.05, **P < 0.01, ***P < 0.001 and ****P < 0.0001, vs. control group. (H) Schematic of the CPP assay. (I) Schematic of the CPP protocol for CPIP mice. (J) Representative CPP traces from mice injected with vehicle, morphine, or clonidine. CPIP mouse activity was clearly increased in morphine- and clonidine-paired chambers compared with vehicle-paired chambers. (K) CPP results in CPIP mice treated with morphine or clonidine (n = 5 mice/group). *P < 0.05 and **P < 0.01, vs. vehicle group. (L–N) The distance traveled (L) and velocity of mice (M) in the open field test were reduced at the late stage of CPIP. The time spent (N) in the center in the open field did not change in CPIP mice (n = 6 mice for Control group; n = 5 mice for CPIP group). **P < 0.01, vs. control group. (O) The immobile time during the tail suspension did not change in CPIP mice (n = 6 mice for Control group; n = 7 mice for CPIP group). (P) The expression of ATF3 (green, Alexa Fluor 488) was increased in the ipsilateral DRG neurons of SNI mice on days 3, 7, and 14, but not in control and CPIP mice (n = 3 mice/group). Scale bar: 100 μm. All data are presented as the mean ± SEM, and were analyzed by two-way analysis of variance followed by Bonferroni post hoc test (B–G and L–O) or one-way analysis of variance followed by Bonferroni post hoc test (K). Detailed statistical information is shown in Additional Table 2 ^{(125.3KB, pdf)} and Additional file 1 ^{(136.8KB, pdf)} . ATF3: Activating transcription factor 3; BL: baseline; Control: the ankles of mice were surrounded by a cut-O-ring; CPIP: mice were submitted to chronic postischemia pain; CPP: conditional place preference; Vehicle: mice were submitted to chronic postischemia pain and injected with normal saline; Morphine: mice were submitted to chronic postischemia pain and injected with morphine; Clonidine: mice were submitted to chronic postischemia pain and injected with clonidine; DRG: dorsal root ganglion; SNI: mice were submitted to spared nerve injury.