Objective: The present study was conducted to investigate the effects of transcutaneous electrical nerve stimulation (TENS) and microcurrent electrical neuromuscular stimulation (MENS) on pain-like behaviors developed in rats with an experimental neuropathy.

Method: Neuropathic surgery was done by a unilateral ligation of L5 and L6 spinal nerves of the rat. Allodynic behavior was examined by measuring foot withdrawal frequency in response to 10 applications of a von Frey filament (2.5 g) to the plantar surface of the foot. Ongoing pain behavior was examined by measuring cumulative time in 3 min that the rat lifted its foot off a plate held at cold temperature (5^oC). TENS (square pulses; 3 Hz, 30 mA) or MENS (bipolar pulses; 10 Hz, 300 μA) was applied for 15 min or 5 min, respectively, to the skin of the affected foot.

Results: Behavioral signs of mechanical allodynia and cold-induced ongoing pain had developed after nerve injury. Either TENS or MENS, when applied once, alleviated allodynic behavior, lasting up to 2 hrs. Such an alleviation lasted much longer when TENS or MENS was applied repeatedly (once a day for 6 days); 3 days by TENS and 1 day by MENS. Cold-induced ongoing pain behavior, however, was not affected by the repeated application of either TENS or MENS.

Conclusion: The results suggest that both TENS and MENS are useful tools for the treatment of mechanical allodynia. Repeated application of TENS or MENS is more effective in alleviating mechanical allodynia than its single application. Either TENS or MENS, however, seems not effective in alleviating cold-induced ongoing pain.

Keywords :Neuropathic pain, Transcutaneous electrical nerve stimulation, Microcurrent electrical neuromuscular stimulation