Objective
To evaluate the effects of high and low frequency transcutaneous electrical stimulation (TENS) on the neuropathic pain and to determine opioid-system involve to analgesia.

Method
Under pentobarbital anesthesia (55 mg/kg i.p.), twenty male Sprague-Dawley (250∼300 g) rats were operated that tibial and sural nerves were ligated and cut unilaterally. Pain sensitivity was assessed using the von Frey filament (8 mN) and acetone through behavioral test. After neuropathic pain developed, the various modes of TENS were applied to the rat with neuropathic pain and pain sensitivity was assessed to evaluate the analgesic effects. Naloxone was injected intraperitoneally to observe reversal of pain sensitivity.

Results
1) Neuropathic pain was obtained successfully through selective cut of sciatic nerve branches in the rat. 2) Neuropathic pain were reduced by more than 10 minutes stimulation of TENS. 3) The analgesic effects of TENS on mechanical and cold stimulation were sustained for 60 minutes and 30 minutes, respectively. 4) Both high and low frequency TENS showed analgesic effects. 5) Analgesic effects of TENS were reversed by the intraperitoneal administration of naloxone.

Conclusion
The results suggest that low and high frequency TENS have an analgesic effects to neuropathic pain and opioid-system was involved to reduce of neuropathic pain.