Electroacupuncture and Moxibustion-Like Stimulation Relieves Inflammatory Muscle Pain by Activating Local Distinct Layer Somatosensory Afferent Fibers

Abstract

Recent studies have shown that both superficial and deep acupuncture produced clinically relevant and persistent effect on chronic pain, and several subtypes of somatic primary afferents played critical roles in acupuncture and moxibustion analgesia. However, which kind of primary afferents in the superficial and deep tissue of the acupoint is activated by acupuncture or moxibustion to relieve pain persistently remains unclear. The aim of this study is to investigate the roles of distinct peripheral afferents in different layers of the tissue (muscle or skin) in the acupoint for pain relief. Muscular A-fibers activated by deep electroacupuncture (dEA) with lower intensity (approximately 1 mA) persistently alleviated inflammatory muscle pain. Meanwhile, cutaneous C-nociceptors excited by noxious moxibustion-like stimulation (MS) and topical application of capsaicin (CAP) on local acupoint area produced durable analgesic effect. Additionally, spontaneous activity of C-fibers caused by muscular inflammation was also inhibited by dEA and CAP. Furthermore, decreases in pain behavior induced by dEA disappeared after deep A-fibers were demyelinated by cobra venom, whereas CAP failed to relieve pain following cutaneous denervation. Collectively, these results indicate that dEA and MS ameliorate inflammatory muscle pain through distinct primary afferents in different layers of somatic tissue; the former is achieved by activating muscular A-fibers, while the latter is mediated by activating cutaneous C-fibers.

The Effect of Pre-Electroacupuncture on Nociceptive Discharges of Spinal Wide Dynamic Range Neurons in Rat

“…44 In addition, the underlying mechanisms of the segmental analgesia of acupuncture have been suggested to be associated with the gate control theory. 10,16,45 In this study, pre-EA with low intensity T Aβ inhibited nociceptive discharges of WDR neurons, indicating that anti-nociceptive effects of pre-EA may also be related to the gate control theory. However, the phenomena only occurred when pre-EA with T Aβ was administered at adjacent non-RFs.…”

“…Other studies employed single-unit recording of primary afferent fibers or sensory neurons to determine the intensity. 25,45,61 In the present study, to better investigate the inhibitory effects of pre-EA on spinal WDR neurons, it was more reliable to determine the intensities of EA by thresholds of the 3 components of WDR neurons. Moreover, this measurement may reveal the integration of pre-EA and nociceptive signaling in the dorsal horn.…”

Effects and mechanisms of acupuncture analgesia mediated by afferent nerves in acupoint microenvironments

“…Even after cutaneous nerve resection, the effects of deep EA analgesia were not alleviated. Hence, muscular A fibers play a crucial role in mediating EA-induced analgesia ( Chen et al, 2021 ).…”

The immunomodulatory mechanisms for acupuncture practice

“…The physical basis for the specificity, intensity and frequency dependence of acupuncture points may be the many types of activated peripheral afferent nerve fibers (77). The frequency of EA stimulation, the position, and the strength of the acupuncture will all have a varied impact (80)(81)(82). Xin et al found that the segmental analgesia of EA at ST36 with lower intensity is partially mediated by ASIC3 receptor on Ab-fiber, whereas systemic analgesia induced by EA with higher intensity is more likely induced by TRPV1 receptor on Ad-and C-fibers (83).…”

“…The physical basis for the specificity, intensity and frequency dependence of acupuncture points may be the many types of activated peripheral afferent nerve fibers ( 77 ). The frequency of EA stimulation, the position, and the strength of the acupuncture will all have a varied impact ( 80 – 82 ). Xin et al.…”