Acupuncture has been used for treatment of numerous diseases, especially for pain control in the oriental culture. However, the mechanism of pain control by acupuncture was not clear so far.
The present study was examined that the effects of electro-acupuncture (EA) applied to the acu-point of extra-segmental area on modulation of formalin induced pain in Sprague - Dawley rats. In order to apply EA to acu-points in the plantar area of right fore paws, a pair of teflon - coated stainless steel wires were implanted in HT 7 (shin-mun) and PC 7 (dae-neong) 5 days before behavioral test. A behavioral test was performed by means of video camera after injection of 5% formalin (50 ㎕) into the lateral plantar region of left hind paw. EA was delivered by a constant current stimulator at 4∼5 ㎃, 2 ㎳, and 10 ㎐ for 30 min. The electromyographic activities were recorded in the biceps femoris muscle under chloral hydrate anesthesia. Test stimuli with 1∼9㎃ were applied to the sural nerve territory including the medial portion of the 4th toe and the lateral portion of the 5th toe.
Behavioral responses including favoring, flinching and bitting were occured in the biphasic pattern, such as the lst phase (0∼5 min) and the 2nd phase (20∼45 min) after formalin injection. However, EA (4∼5 ㎃, 2 ㎳, 10 ㎐) significantly inhibited Che behavioral responses. EMG activities of flexor reflex had a latency of 100∼300 ㎳ and thresholds of test stimuli for EMG were 4∼5 ㎃ in normal rats. Injection of formalin decreased threshold of test stimuli and increased EMG activities for 2hrs after injection. However, EA significantly inhibited EMG activities of flexor reflex increased by formalin and recovered EMG evoked thresholds.
These results suggest that contralateral extra-segmental EA inhibits the first and second phases of formalin induced pain but their mechanism be needed to examine additionally.
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