title: Increased release of serotonin in the spinal cord during low, but not high, frequency transcutaneous electric nerve stimulation in rats with joint inflammation.
abstract: OBJECTIVE
  To 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.
  
  
  METHODS
  Prospective randomized allocation of 3 treatments.
  
  
  METHODS
  Research laboratory.
  
  
  METHODS
  Male Sprague-Dawley rats (weight range, 250-350 g).
  
  
  METHODS
  Knee 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.
  
  
  METHODS
  Spinal concentrations of serotonin and noradrenaline.
  
  
  RESULTS
  Low-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.
  
  
  CONCLUSIONS
  Low-frequency TENS releases serotonin in the spinal cord to produce antihyperalgesia by activation of serotonin receptors.
authors.affiliation: Physical Therapy and Rehabilitation Science Graduate Program, Neuroscience Graduate Program, Pain Research Program, University of Iowa, Iowa City, 52242, USA. kathleen-sluka@uiowa.edu
authors.forename: Kathleen A
authors.initials: KA
authors.lastname: Sluka
authors.forename: Tammy L
authors.initials: TL
authors.lastname: Lisi
authors.forename: Karin N
authors.initials: KN
authors.lastname: Westlund
mesh_terms: D000818:Animals; D002851:Chromatography, High Pressure Liquid; D007249:Inflammation / Q000503:physiopathology / Q000534:rehabilitation*; D007719:Knee Joint / Q000503:physiopathology; D008297:Male; D009638:Norepinephrine / Q000096:biosynthesis; D011446:Prospective Studies; D011897:Random Allocation; D051381:Rats; D017207:Rats, Sprague-Dawley; D012701:Serotonin / Q000096:biosynthesis*; D013116:Spinal Cord / Q000378:metabolism*; D004561:Transcutaneous Electric Nerve Stimulation
chemical_list: D012701:Serotonin; D009638:Norepinephrine