Abstract
Background Transcutaneous electrical nerve stimulation (TENS) is often used for management of chronic pain.
Objective The purpose of this study was to investigate whether TENS altered postincisional allodynia, substance P, and proinflammatory cytokines in a rat model of skin-muscle incision and retraction (SMIR).
Design This was an experimental study.
Methods High-frequency (100-Hz) TENS therapy began on postoperative day 3 and was administered for 20 minutes daily to SMIR-operated rats by self-adhesive electrodes delivered to skin innervated via the ipsilateral dorsal rami of lumbar spinal nerves L1–L6 for the next 27 days. The expressions of substance P, tumor necrosis factor alpha (TNF-α), interleukin-6 (IL-6), and interleukin-1beta (IL-1β) in the spinal cord and mechanical sensitivity to von Frey stimuli (4g and 10g) were evaluated.
Results The SMIR-operated rats displayed a marked hypersensitivity to von Frey stimuli on postoperative day 3. In contrast to the SMIR-operated rats, SMIR-operated rats after TENS administration showed a quick recovery of mechanical hypersensitivity. On postoperative days 3, 16, and 30, SMIR-operated rats exhibited an upregulation of substance P and cytokines (TNF-α, IL-6, and IL-1β) in the spinal cord, whereas SMIR-operated rats after TENS therapy inhibited that upregulation. By contrast, the placebo TENS following SMIR surgery did not alter mechanical hypersensitivity and the levels of spinal substance P, TNF-α, IL-6, and IL-1β.
Limitations The experimental data are limited to animal models and cannot be generalized to postoperative pain in humans.
Conclusions The results revealed that TENS attenuates prolonged postoperative allodynia following SMIR surgery. Increased levels of spinal substance P and proinflammatory cytokines, activated after SMIR surgery, are important in the processing of persistent postsurgical allodynia. The protective effect of TENS may be related to the suppression of spinal substance P and proinflammatory cytokines in SMIR-operated rats.
Footnotes
Dr Chen, Dr Hung, and Dr Wang provided concept/idea/research design. Dr Chen, Dr Tzeng, and Dr Hung provided writing. Dr Tzeng and Ms Lin provided data collection. Dr Chen, Dr Tzeng, Ms Lin, and Dr Hung provided data analysis and consultation (including review of manuscript before submission). Dr Chen and Dr Hung provided project management and fund procurement. Dr Hung provided facilities/equipment, institutional liaisons, and administrative support.
The authors acknowledge the financial support provided by grants NSC 100-2314-B-039-017-MY3 and NSC 101-2314-B-006-037-MY3 from the National Science Council, Taiwan.
- Received July 17, 2013.
- Accepted August 28, 2014.
