Schematic diagrams of the formalin model of inflammatory pain and EA stimulation. (A) Rats received EA or restriction alone before intra-plantar injection of formalin. (B) The rat received formalin injection in the left hind paw. Ipsi- or contra-lateral EA was applied to "Zusanli" and "Sanyinjiao" in the left or right leg of the rat respectively. In the last part of the study, formalin was injected to the opposite (right) paw and ipsi- or contra-lateral EA referred to EA in the right or left leg, respectively.