High-frequency transcutaneous electrical nerve stimulation alters thermal but not mechanical allodynia following chronic constriction injury of the rat sciatic nerve.

Abstract

To determine if daily transcutaneous electrical nerve stimulation (TENS) can alter the thermal and mechanical allodynia that develops after chronic constriction injury (CCI) to the right sciatic nerve of rats. A completely randomized experimental design was used. Four groups of rats underwent CCI surgery to the right sciatic nerve and either were not treated with TENS or received TENS starting at different times after the CCI surgery. TENS was delivered daily for 1 hour to CCI rats through self-adhesive electrodes applied to skin innervated by the right dorsal rami of lumbar spinal nerves L1-6. Rats of different groups received daily TENS starting immediately, 20 to 30 hours, or 3 days after the CCI surgery. Thermal and mechanical pain thresholds of hind paws were assessed bilaterally in all rats twice before the CCI surgery (baseline) and then 2, 7, 12, and 14 days after surgery. Thermal and mechanical allodynia were expressed as difference scores between the pain thresholds of right and left hind paws. These values were normalized to differences that existed between the two paws at baseline. Daily TENS beginning immediately after CCI surgery prevented the development of thermal allodynia at all assessment times (p < .05). Daily TENS starting 1 day after surgery reduced thermal allodynia, but only on days 2 and 14 (p < .05). Daily TENS beginning 3 days after surgery had no effect on the development of thermal allodynia. Regardless of when it was started, daily TENS did not consistently alter mechanical allodynia in CCI rats. It appears that daily TENS can prevent thermal but not mechanical allodynia in this model. However, early intervention with the treatment is critical if it is to be effective at all.