The Involvement of Descending Pain Inhibitory System in Electroacupuncture-Induced Analgesia

Abstract

Chronic pain is a major health problem, which can impair quality of life and reduce productivity. Electroacupuncture (EA), a modality of medicine based on the theories of Traditional Chinese Medicine (TCM), presents great therapeutic effects on chronic pain. Its clinical application has gained increasing popularity, and in parallel, more research has been performed on the mechanisms of EA-induced analgesia. The past decades have seen enormous advances both in neuronal circuitry of needle-insertion and in its molecular mechanism. EA may block pain by activating the descending pain inhibitory system, which originates in the brainstem and terminates at the spinal cord. This review article synthesizes corresponding studies to elucidate how EA alleviate pain via the mediation of this descending system. Much emphasis has been put on the implication of descending serotonergic and noradrenergic pathways in the process of pain modulation. Also, other important transmitters and supraspinal regions related to analgesic effects of EA have been demonstrated. Finally, it should be noticed that there exist some shortcomings involved in the animal experimental designed for EA, which account for conflicting results obtained by different studies.

Pain Relief Dependent on IL-17–CD4+ T Cell–β-Endorphin Axis in Rat Model of Brachial Plexus Root Avulsion After Electroacupuncture Therapy

“…As a modified approach of acupuncture, electroacupuncture (EA) employs electrical stimulation. Besides, many clinical trials have shown that acupuncture or EA stimulation also plays a critical role in the management and therapy of immune-related disorders, such as allergic disorders, infections, autoimmune diseases, and immunodeficiency syndromes ( Wang et al, 2017 ; Lv et al, 2019 ). Nowadays, increasing evidence has shown that the analgesic effects of acupuncture are tightly associated with immune regulation.…”

Electroacupuncture Modulates Spinal BDNF/TrκB Signaling Pathway and Ameliorates the Sensitization of Dorsal Horn WDR Neurons in Spared Nerve Injury Rats

“…It is well known that electroacupuncture (EA), developed from traditional acupuncture, has been widely used in China and some Asian countries for clinical practice due to its considerable fewer side effects [ 21 , 22 ]. Evidence showed that EA stimulation has an effectiveness on neuropathic pain [ 23 , 24 ].…”

The Endocannabinoid System Contributes to Electroacupuncture Analgesia

“…Interestingly, CB 1 receptor antagonism is a promising strategy in the treatment of obesity. However, CNS side effects associated with rimonabant and other CB 1 receptor antagonists emphasized the need for new classes of peripherally acting CB 1 receptor antagonists that do not affect the intricate balance between central and peripheral physiological signaling ( Sharma et al, 2015 ; Lv et al, 2019 ). Ongoing efforts to develop safer selective peripherally acting CB 1 receptor antagonists, potent novel CB 1 receptor antagonists or inverse agonists may eventually result in therapeutics that target CB 1 receptors with reduced CNS side effects ( Sharma et al, 2015 ; Yadav and Murumkar, 2018 ; Khan N. et al, 2019 ; Micale et al, 2019 ).…”

“…The pathophysiology of pain has been thoroughly researched by many in-depth papers and reviews ( Loeser and Melzack, 1999 ; Raffaeli and Arnaudo, 2017 ; Chen et al, 2020 ). Among the brain and spinal cord areas, the descending pain modulatory pathway is critical in pain perception and acupuncture analgesia ( Lv et al, 2019 ). This system arises in the PAG, where transmitters are activated that contact the rostroventromedial medulla and project to the raphe nuclei in the brainstem, and to inhibitory synapses in the SDH ( Lai et al, 2019 ; Lv et al, 2019 ).…”

“…Among the brain and spinal cord areas, the descending pain modulatory pathway is critical in pain perception and acupuncture analgesia ( Lv et al, 2019 ). This system arises in the PAG, where transmitters are activated that contact the rostroventromedial medulla and project to the raphe nuclei in the brainstem, and to inhibitory synapses in the SDH ( Lai et al, 2019 ; Lv et al, 2019 ). Local administration of GABA agonists into the ventrolateral area of the PAG (vlPAG) promotes pain, while local administration of GABA antagonists produces antinociceptive effects by reducing inhibitory neurotransmission ( Zhu et al, 2019 ).…”