Abstract:

BACKGROUND: Nuclear factor-kappa B (NF-κB), as a promoter of inflammatory reaction, stimulates injured parts or transcription of local inflammatory gene, promotes generation of inflammatory factors, and induces pain onset; however, the mechanism on chronic inflammatory pained spinal cord has been less reported.
OBJECTIVE: To explore the NF-κB expression in spinal dorsal horn and behavioral hyperalgesia by preparing rat models of complete Freurd’s adjuvant arthritis.
METHODS: A total of 24 SD rats were randomly divides into sham-surgery group and complete Freund’s adjuvant group, with 12 rats in each group. Adjuvant arthritis model was produced by injection of 50 μL complete Freund’s adjuvant (CFA) to the right ankle joint after anesthesia. The same volume saline was injected to the rat right ankle joint in sham-surgery group. The mechanical pain threshold, paw withdrawal thermal latency (PWTL), the diameter of ankle, and NF-κB expression in spinal dorsal horn were investigated 2 days before and 4, 7, 14, 21, and 28 days after CFA injection.
RESULTS AND CONCLUSION:  ① Three hours after CFA injection, the ankle joint appeared edema, but local inflamed and thermal symptoms were not obvious. The inflamed symptoms significantly appeared on right ankle joint and developed to food surface at 24 hours after CFA injection, while the symptoms lasted for 4 weeks. ② Diameter of right ankle was significantly increased at 4 days-4 weeks after CFA injection compared to intralateral ankle and before CFA injection (P < 0.01). ③ Compared to before injection and sham-surgery group, the mechanical pain threshold was significantly decreased at 4 days after CFA injection, and reached the lowest value at 21 days (P < 0.01). The PWTL was significantly decreased at 4 days after CFA injection and reached at the lowest level at 7 days, while the lowest level lasted for 4 weeks (P < 0.01). ④ The expression of NF-κB was significantly increased in I-VI in spinal dorsal horn in the complete Freund’s adjuvant group, which was higher than sham-surgery group (P < 0.01). The results indicated that we could gain stable monoarthritis model by injecting CFA with oil-contained water into rat ankle joint space, and the model shown prolong and significant hyperalgesia to radial thermal and mechanical pressure; meanwhile, the NF-κB expression increased significantly in lamber I-VI in spinal dorsal horn after the ankle joint arthritis.