2.5.4 Complete freund’s adjuvant (CFA)-induced inflammatory pain model

Adult male SD rats (180–200 g) were placed in a glass coverslip of 56 × 16 × 30 cm for 30 min to adapt to the environment before testing pain thresholds. The thermal paw withdrawal latency was measured by use of a full-automatic plantar heat stimulation (KW-600, Nanjing Calvin). Each rat was measured three times with an interval of 5 min. The mean value of the three measurements was defined as the thermosensitive threshold. Rats with a threshold of less than 5 s were eliminated. If there was no licking reaction in mice within 30s, it was recorded as 30s.

500 μL Complete Freund’s adjuvant (CFA) and 500 μL isotonic saline were pumped and mixed in the syringe until they became a milky white and sticky liquid. The skin of the right hind paw of the rats was wiped with a cotton ball moistened with 75% ethanol. Then, the CFA model was made by subcutaneous injection of configured CFA (20 μL/paw) into the right hind paw. After 48 h CFA injection, we tested the thermal paw withdrawal latency to observe if the pain model was successfully made. The negative control group was injected with isotonic saline and the positive control group was injected with aspirin (20 mg/kg intraperitoneally). C10 (20 μM) and C9 (4 μM) were injected respectively in the experimental group with a content of 0.2 mL/10 g. On the first day of administration, the thermosensitive threshold was measured 30, 60, 90 and 120 min after drug administration to determine the optimal drug onset time. All the drugs were continuously administered for 5 days.