Abstract
ABSTRACT Although transcutaneous electrical nerve stimulation (TENS) has been proposed to modulate pain and the mechanisms underlying analgesia remain poorly understood, evidence of anti-inflammatory effect is more limited. The purpose of this study was to examine the opioidergic mechanisms of TENS effects in two different frequencies on pain and inflammatory edema in the ankle sprain model in rats. Threshold to mechanical stimulation was utilized to examine the changes produced by intraperitoneal injection of non-selective opioid antagonist naloxone on the antihyperalgesic effect induced by a 20-min period of 2Hz or 100Hz TENS in the ankle sprain model, produced by manually overextending the lateral ligaments. Ankle sprain induced a long-lasting reduction in paw withdrawn latency (PWL) after 30 minutes for up to 24 hours in sham TENS (SH-TENS) treated rats. The reduced PWL after the induction of ankle sprain was restored partially at 0,1,2,3 and 6, but not 24 hours, after the termination of 2 Hz-TENS (LF-TENS). In 100Hz (HF-TENS) the reduction in PWL was shorter than LF-TENS and both LF and HF effects were fully blocked in naloxone-treated rats. LF- and HF-TENS treated rats did not reach the elevation of edema and presented a progressive edema reduction for over 24 hours when compared to SH-TENS group. Both effects were reduced by naloxone. TENS-induced antihyperalgesic and anti-edematous effects observed in ankle sprain model were mediated by the endogenous opioid system.
Highlights
Transcutaneous electrical nerve stimulation (TENS) is a noninvasive treatment commonly used to manage pain
TENS has been extensively used for different purposes mainly for pain relief.,the mechanism involved in TENS analgesic effect is not completely understood[23]
We extend these observations showing that a single session of la terminación de Hz-TENS (LF-TENS) or HzTENS (LF-TENS). In 100Hz (HF-TENS) (10 or 100Hz) produced long-lasting reduction in mechanical inflammatory hyperalgesia and edema induced by ankle sprain in rat hind paw
Summary
Transcutaneous electrical nerve stimulation (TENS) is a noninvasive treatment commonly used to manage pain. Two different theories have been proposed to explain TENS-induced analgesia. TENS activates pain inhibitory pathways stimulating the release of endogenous opioids[8] and serotonin[9]. Endogenous opioid peptides such as betaendorphin activate opioid receptors both at the level of the spinal cord[10,11] and on peripheral sensory neurons at the site of inflammation[12,13]. In inflammatory pain model in rats serotonin contributes to TENS-induced analgesia via spinal 5-HT2A and 5-HT3, but not 5-HT1A receptors and 5-HT3 receptors involves GABAergic, enkephalinergic, and other classes of spinal intrinsic neurons related to gate control and descendent pain inhibitory pathways[14]
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