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.

Perspective: 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.

Copyright © 2012 American Pain Society. Published by Elsevier Inc. All rights reserved.

Figures

Figure 1

Graph representing the daily intensity of TENS from animals receiving low and high frequency at different intensities. Data are represented as means ± SEM.

Figure 2

Graph representing mechanical withdrawal threshold of the paw (A) and knee joint (B) in animals that received high frequency TENS. Mechanical withdrawal thresholds are illustrated prior to induction of inflammation (baseline), before (b), and after application of TENS (a). Data are represented as means ± SEM. *Significantly different between before and after TENS stimulation (p

Figure 3

Graph representing mechanical withdrawal threshold of the paw (A) and knee joint (B) in animals that received low frequency TENS. Mechanical withdrawal thresholds are illustrated prior to induction of inflammation (baseline), before (b), and after application of TENS (a). Data are represented as means ± SEM. *Significantly different between before and after TENS stimulation (p

Figure 4

Graph representing the summary of effect of TENS in mechanical withdrawal threshold of the paw (A) and knee joint (B) from animals receiving Low and High Frequency of TENS treatment. #Significantly different from Sham and 50% of MT (p<0.005).+Significantly different from 90% of MT (p<0.005).