Biurrun Manresa, J. | Search bioRxiv

bioRxiv2019

A New Experimental Model Of Muscle Pain In Humans Based On Short-Wave Diathermy

Experimental models of pain in humans are crucial for understanding pain mechanisms. The most often used muscle pain models involve the injection of algesic substances, such as hypertonic saline solution or nerve growth factor, or exercise-induced delayed onset muscle soreness (DOMS). However, these models are either invasive or take substantial time to develop, and the elicited level of pain/soreness is difficult to control. To overcome these shortcomings, we propose to elicit muscle pain by a localized application of short-wave diathermy (SWD). In this crossover study, SWD was administered to eighteen healthy volunteers to the wrist extensor muscle group, with a constant stimulation intensity and up to 4 minutes. We measured pressure pain threshold (PPT) and pinprick sensitivity (PPS) and performed a psychophysical evaluation of muscle soreness at baseline and at 0, 30 and 60 minutes. SWD evoked localized muscle pain/soreness in the wrist extensor muscle group and a decrease of PPT in the treated arm compared with the control arm that lasted for at least 60 minutes, reflecting ongoing hyperalgesia after SWD application. PPS was not significantly altered 30 to 60 min following SWD, suggesting a minimal contribution from skin tissue to sustained hyperalgesia.

neuroscience↗

bioRxiv2018

High frequency electrical stimulation induces a long-lasting enhancement of event-related potentials but does not change the perception elicited by intra-epidermal electrical stimuli delivered to the area of secondary mechanical hyperalgesia

High frequency electrical stimulation (HFS) of the skin induces increased pinprick sensitivity in the surrounding unconditioned skin (secondary hyperalgesia). Moreover, it has been shown that brief high intensity CO2 laser stimuli, activating both A{delta}- and C-fiber nociceptors, are perceived as more intense when delivered in the area of secondary hyperalgesia. To investigate the contribution of A-fiber nociceptors to secondary hyperalgesia the present study assessed if the perception and brain responses elicited by low-intensity intra-epidermal electrical stimulation (IES), a method preferentially activating A{delta}-fiber nociceptors, are increased in the area of secondary hyperalgesia. HFS was delivered to one of the two forearms of seventeen healthy volunteers. Mechanical pinprick stimulation and IES were delivered at both arms before HFS (T0), 20 minutes after HFS (T1) and 45 minutes after HFS (T2). In all participants, HFS induced an increase in pinprick perception at the HFS-treated arm, adjacent to the site of HFS. This increase was significant at both T1 and T2. HFS did not affect the percept elicited by IES, but did enhance the magnitude of the N2 wave of IES-evoked brain potentials, both at T1 and at T2. HFS induced a long-lasting enhancement of the N2 wave elicited by IES in the area of secondary hyperalgesia, indicating that HFS enhances the responsiveness of the central nervous system to nociceptive inputs conveyed by AMH-II nociceptors. However, we found no evidence that HFS affects the perception elicited by IES, which may suggest that AMH-II nociceptors do not contribute to HFS-induced secondary hyperalgesia.

neuroscience↗