2.2 Inflammatory pain model
We used complete Freund’s adjuvant (CFA; Sigma-Aldrich, St Louis, MO) as a model of inflammatory pain. Baseline response to thermal stimulation was determined before CFA administration. Then, animals were anesthetized through isoflurane inhalation, and 20 μl of 1 mg∙mL-1 CFA was administered via subcutaneous (s.c.) injection into the plantar surface of the left hind paw with a 1-ml tuberculin syringe (BD, Franklin Lakes, NJ). CFA-induced paw edema and thermal hypersensitivity were assessed at 24 and 48 hr post-injection.