title: Increasing intensity of TENS prevents analgesic tolerance in rats.
abstract: Transcutaneous electrical nerve stimulation (TENS) reduces hyperalgesia and pain. Both low-frequency (LF) and high-frequency (HF) TENS, delivered at the same intensity (90% motor threshold [MT]) daily, result in analgesic tolerance with repeated use by the fifth day of treatment. The current study tested 1) whether increasing intensity by 10% per day prevents the development of tolerance to repeated TENS; and 2) whether lower intensity TENS (50% MT) produces an equivalent reduction in hyperalgesia when compared to 90% MT TENS. Sprague-Dawley rats with unilateral knee joint inflammation (3% carrageenan) were separated according to the intensity of TENS used: sham, 50% LF, 50% HF, 90% LF, 90% HF, and increased intensity by 10% per day (LF and HF). The reduced mechanical withdrawal threshold following the induction of inflammation was reversed by application of TENS applied at 90% MT intensity and increasing intensity for the first 4 days. On the fifth day, the groups that received 90% MT intensity showed tolerance. Nevertheless, the group that received an increased intensity on each day still showed a reversal of the mechanical withdrawal threshold with TENS. These results show that the development of tolerance can be delayed by increasing intensity of TENS.
  
  
  CONCLUSIONS
  Our results showed that increasing intensity in both frequencies of TENS was able to prevent analgesic tolerance. Results from this study suggest that increasing intensities could be a clinical method to prevent analgesic tolerance and contribute to the effective use of TENS in reducing inflammatory pain and future clinical trials.
authors.affiliation: Physical Therapy and Rehabilitation Science, Carver College of Medicine, The University of Iowa, Iowa City, Iowa 52242, USA.
authors.forename: Karina L
authors.initials: KL
authors.lastname: Sato
authors.forename: Luciana S
authors.initials: LS
authors.lastname: Sanada
authors.forename: Barbara A
authors.initials: BA
authors.lastname: Rakel
authors.forename: Kathleen A
authors.initials: KA
authors.lastname: Sluka
mesh_terms: D000700:Analgesics / Q000009:adverse effects*; D000818:Animals; D055592:Biophysical Phenomena / Q000502:physiology*; D002351:Carrageenan / Q000633:toxicity; D004195:Disease Models, Animal; D004361:Drug Tolerance / Q000502:physiology; D007249:Inflammation / Q000139:chemically induced / Q000150:complications* / Q000188:drug therapy / Q000473:pathology; D007719:Knee Joint / Q000187:drug effects / Q000503:physiopathology; D008297:Male; D010146:Pain / Q000188:drug therapy* / Q000209:etiology*; D010147:Pain Measurement; D017288:Pain Threshold / Q000187:drug effects / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley; D013997:Time Factors; D004561:Transcutaneous Electric Nerve Stimulation / Q000379:methods*
chemical_list: D000700:Analgesics; D002351:Carrageenan