Fig. 1.

Effects of electroacupuncture (EA) application (1-ms pulse, 2 mA, for 30 min) on pain behaviors in rats 1 day after ankle sprain. The EA period is indicated by the shaded boxes. Pain levels were determined by measuring the weight-bearing forces on the affected limb. A: point specificity of the EA-induced analgesic effect. The effect of EA (with 10 Hz) applied to the contralateral SI-6 acupoint was compared with that of the ipsilateral ST-36 acupoint. Only EA at SI-6 was effective in producing the analgesic effect on ankle sprain pain. B: frequency dependency of the EA-induced analgesic effect. EA with variable frequencies was applied to the SI-6 point. EA with 10-Hz stimulation produced a more powerful analgesic effect than either 2- or 100-Hz stimulation. C: effect of phentolamine (PE; 5 mg/kg ip) and naltrexone (Nal; 10 mg/kg ip) on EA-induced analgesia. Drugs were administered 30 min before EA application. The α-adrenoceptor antagonist PE but not the opioid receptor antagonist Nal was effective in blocking the EA-induced analgesic effect on ankle sprain pain. Data are presented as percent changes in weight-bearing forces (means ± SE) using the pre-EA (- 30 m) baseline value as zero. *Values were significantly different from the control group (no EA in A and B and EA in C).