• Kathleen A Sluka, Tammy L Lisi, and Karin N Westlund.
• Physical Therapy and Rehabilitation Science Graduate Program, Neuroscience Graduate Program, Pain Research Program, University of Iowa, Iowa City, 52242, USA. kathleen-sluka@uiowa.edu
• Arch Phys Med Rehabil. 2006 Aug 1; 87 (8): 1137-40.

ObjectiveTo determine the release pattern of serotonin and noradrenaline in the spinal cord in response to transcutaneous electric nerve stimulation (TENS) delivered at low or high frequency.DesignProspective randomized allocation of 3 treatments.SettingResearch laboratory.AnimalsMale Sprague-Dawley rats (weight range, 250-350 g).InterventionKnee joints of rats were inflamed with a mixture of 3% carrageenan and 3% kaolin for 24 hours prior to placement of push-pull cannulae into the dorsal horn of the spinal cord. Push-pull samples were collected in 10-minute intervals before, during, and after treatment with low-frequency TENS (4 Hz), high-frequency TENS (100 Hz), or sham TENS. TENS was applied to the inflamed knee joint for 20 minutes at sensory intensity and 100-mus pulse duration. Push-pull samples were analyzed for serotonin and noradrenaline by high performance liquid chromatography with coulemetric detection.Main Outcome MeasuresSpinal concentrations of serotonin and noradrenaline.ResultsLow-frequency TENS significantly increased serotonin concentrations during and immediately after treatment. There was no change in serotonin with high-frequency TENS, nor was there a change in noradrenaline with low- or high-frequency TENS.ConclusionsLow-frequency TENS releases serotonin in the spinal cord to produce antihyperalgesia by activation of serotonin receptors.

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