Inhibition of electroacupuncture on nociceptive responses of dorsal horn neurons evoked by noxious colorectal distention in an intensity-dependent manner

Understanding of Spinal Wide Dynamic Range Neurons and Their Modulation on Pathological Pain

The spinal dorsal horn (SDH) transmits sensory information from the periphery to the brain. Wide dynamic range (WDR) neurons within this relay site play a critical role in modulating and integrating peripheral sensory inputs, as well as the process of central sensitization during pathological pain. This group of spinal multi-receptive neurons has attracted considerable attention in pain research due to their capabilities for encoding the location and intensity of nociception. Meanwhile, transmission, processing, and modulation of incoming afferent information in WDR neurons also establish the underlying basis for investigating the integration of acupuncture and pain signals. This review aims to provide a comprehensive examination of the distinctive features of WDR neurons and their involvement in pain. Specifically, we will examine the regulation of diverse supraspinal nuclei on these neurons and analyze their potential in elucidating the mechanisms of acupuncture analgesia.

The efficacy and neural mechanism of acupuncture therapy in the treatment of visceral hypersensitivity in irritable bowel syndrome

Irritable Bowel Syndrome (IBS) is a complex functional gastrointestinal disorder primarily characterized by chronic abdominal pain, bloating, and altered bowel habits. Chronic abdominal pain caused by visceral Hypersensitivity (VH) is the main reason why patients with IBS seek medication. Significant research effort has been devoted to the efficacy of acupuncture as a non-drug alternative therapy for visceral-hyperalgesia-induced IBS. Herein, we examined the central and peripheral analgesic mechanisms of acupuncture in IBS treatment. Acupuncture can improve inflammation and relieve pain by reducing 5-hydroxytryptamine and 5-HT3A receptor expression and increasing 5-HT4 receptor expression in peripheral intestinal sensory endings. Moreover, acupuncture can also activate the transient receptor potential vanillin 1 channel, block the activity of intestinal glial cells, and reduce the secretion of local pain-related neurotransmitters, thereby weakening peripheral sensitization. Moreover, by inhibiting the activation of N-methyl-D-aspartate receptor ion channels in the dorsal horn of the spinal cord and anterior cingulate cortex or releasing opioids, acupuncture can block excessive stimulation of abnormal pain signals in the brain and spinal cord. It can also stimulate glial cells (through the P2X7 and prokinetic protein pathways) to block VH pain perception and cognition. Furthermore, acupuncture can regulate the emotional components of IBS by targeting hypothalamic-pituitary-adrenal axis-related hormones and neurotransmitters via relevant brain nuclei, hence improving the IBS-induced VH response. These findings provide a scientific basis for acupuncture as an effective clinical adjuvant therapy for IBS pain.

Spinal cord astrocyte P2X7Rs mediate the inhibitory effect of electroacupuncture on visceral hypersensitivity of rat with irritable bowel syndrome

This study explored the role of P2X7 receptors in spinal cord astrocytes in the electroacupuncture-induced inhibition of visceral hypersensitivity (VH) in rats with irritable bowel syndrome (IBS). Visceral hypersensitivity of IBS was intracolonically induced by 2,4,6-trinitrobenzene sulfonic acid (TNBS). Visceromotor responses to colorectal distension (CRD-20,40,60,80 mmHg) and abdominal withdrawal reflex scoring (AWRs) were recorded after electroacupuncture at bilateral Zusanli (ST36) and Sanyinjiao (SP6) acupoints to evaluate the analgesic effect of electroacupuncture on visceral pain in rats with IBS. Fluorocitric acid (FCA), an astrocyte activity inhibitor, was injected intrathecally before electroacupuncture intervention and AWRs were recorded. Western blot and real-time qPCR were used to detect the expression of NMDA and P2X7 receptor to observe the regulation effect of electroacupuncture on NMDA receptor in the spinal cord of rats with visceral hypersensitivity. Intrathecal injection of P2X7 agonist or antagonist was administered before electroacupuncture treatment. To observe the effect of P2X7 receptor in spinal astrocytes on the inhibition of visceral hyperalgesia by electroacupuncture, the changes of AWR score, NMDA receptor in the spinal cord, and GFAP expression in astrocytes were detected. Inflammation of the colon had basically subsided at day 21 post-TNBS; persistent visceral hypersensitivity could be suppressed by electroacupuncture. This analgesic effect could be inhibited by FCA. The analgesic effect, downregulation of NMDA receptor NR1 subunit, and P2X7 protein of electroacupuncture were all reversed by FCA. P2X7 receptor antagonist A740003 can cooperate with EA to carry out analgesic effect in rats with visceral pain and downregulate the expression of NR1, NR2B, and GFAP in spinal dorsal horn. However, the P2X7 receptor agonist BzATP could partially reverse the analgesic effect of EA, inhibiting the downregulatory effect of EA on the expression of NR1, NR2B, and GFAP. These results indicate that EA may downregulate the expression of the NMDA receptor by inhibiting the P2X7 receptor in the spinal cord, thereby inhibiting spinal cord sensitization in IBS rats with visceral pain, in which astrocytes are an important medium.

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

Purpose

Spinal wide dynamic range (WDR) neurons are well studied in pain models and they play critical roles in regulating nociception. Evidence has started to accumulate that acupuncture produces a good analgesic effect via activating different primary fibers with distinct intensities. The purpose of the present study was to compare the distinct intensities of pre-electroacupuncture (pre-EA) at local muscular receptive fields (RFs), adjacent or contralateral non-RFs regulating the nociceptive discharges of spinal WDR neurons evoked by hypertonic saline (HS).

Materials and Methods

Spinal segments of electrophysiological recording were identified by neural tracers applied at the left gastrocnemius muscle. The thresholds of Aβ (T_Aβ), Aδ (T_Aδ) and C (T_C) components of WDR neurons were measured to determine the intensity of pre-EA by extracellular recording. The discharges of WDR neurons induced by distinct intensities of pre-EA and 200 µL HS (6%) injection in left gastrocnemius muscle of rats were observed by extracellular recording.

Results

The spinal segments of WDR neurons were confirmed in lumbar (L)5-6 area according to the projective segments of dorsal root ganglion. T_Aβ, T_Aδ and T_C of WDR neurons was determined to be 0.5, 1, and 2 mA, respectively. The pre-EA with intensities of T_Aβ (P < 0.05), T_Aδ (P < 0.05), T_C (P < 0.05) or 2T_C (P < 0.01) at ipsilateral adjacent non-RFs significantly reduced the discharges of WDR neurons, while at local RFs only pre-EA of T_Aδ (P < 0.05), T_C (P < 0.05) and 2T_C (P < 0.01) could inhibit the nociceptive discharges. In addition, intensity of pre-EA at contralateral non-RFs should reach at least T_C to effectively inhibit the firing rates of WDR neurons (P < 0.01).

Conclusion

Pre-EA could suppress nociceptive discharges of WDR neurons and the inhibitory effects were dependent on the distinct intensities and locations of stimulation.

Effect of acupuncture on postoperative ileus after laparoscopic elective colorectal surgery: A prospective, randomised, controlled trial

BACKGROUND

Postoperative ileus after colorectal surgery is a frequent problem that significantly delays recovery, increases perioperative costs, and negatively impacts on daily life, physical and psychosocial functioning, and wellbeing. We investigated the effect of acupuncture at different single acupoint combined with standard care on postoperative ileus.

METHODS

In this single-centre, three-arm, prospective, randomised trial, we enrolled patients with primary colorectal cancer undergoing elective colorectal resection at Cancer Hospital Chinese Academy of Medical Science in Beijing, China. Patients were randomly assigned (1:1:1) to receive either electroacupuncture (EA) at ST36 or ST25 combined with standard care (two EA groups) once daily from post-operative days 1-4, or standard care alone (standard care group). The co-primary outcomes were time to first flatus and time to defecation assessed in the intention-to-treat population. This study is registered with Chictr.org.cn, ChiCTR1900027466.

FINDING

Between Nov 15, 2019, and Sep 30, 2020, 129 patients were assessed for eligibility, 105 patients (35 patients per group) were enrolled and included in the intention-to-treat analysis. After receiving EA at ST36, the time to first flatus and defecation were shorter (between-group difference -10.98 [97.5% CI -21.41 to -0.56], p = 0·02 for flatus; -25.41 [-47.89 to -2.93], p = 0·02 for defecation). However, we did not observe a significant difference in time to first flatus and defecation between the EA at ST25 group and standard care group (between-group difference -5.54 [97.5% CI -15.78 to 4.70], p = 0·26 for flatus; -17.69 [-40.33 to 4.95], p = 0·08 for defecation). There were no serious adverse events.

INTERPRETATION

Compared with standard care alone, standard care combined with EA at ST36, but not ST25, significantly enhances bowel function recovery in a postoperative setting to patients with colorectal cancer with laparoscopic elective colorectal resection.

FUNDING

The National Key R&D Program of China (No: 2019YFC1712100) and the National Science Fund for Distinguished Young Scholars (No:81825024).

Peripheral and Spinal Mechanisms Involved in Electro-Acupuncture Therapy for Visceral Hypersensitivity

One of the important characteristic features of clinically significant gastrointestinal disorders is visceral hypersensitivity (VH). Pain sensitization or VH is a big challenge for clinicians and becomes a very thorny work in clinical practices; the therapeutic efficacy for VH results in limited success. A popular second therapy that is being approved for the induction of analgesia and attenuates VH with fewer side effects includes electro-acupuncture (EA). Different peripheral and spinal neurological chemicals, including neurotransmitters, neuropeptides, and cytokines, and different signaling pathways were associated with EA treatment in VH. Despite the higher acceptance of EA, the underlying mechanism still needs to be further explored. In this paper, we review the available literature to find the peripheral and spinal mechanisms involved in EA to relieve VH.

Electroacupuncture and Transcutaneous Electrical Nerve Stimulation Induced Sensations in Bell's Palsy Patients: A Quantitative Current Intensity Analysis

Background

The intensity of electrical acupoint stimulation such as electroacupuncture (EA) and transcutaneous electrical nerve stimulation (TENS) is regulated by the observation of skin shivering or the participant’s comfort response. However, the specific intensity and spatial scope following EA or TENS stimulation are unclear.

Objective

This study aimed to test the stimulatory current intensities of lower and upper sensation thresholds in TENS- and EA-based treatment of Bell’s palsy patients. Also, the spatial scope of the stimulation at these current intensities was simulated and measured quantitatively.

Methods

A total of 19 Bell’s palsy patients were recruited. Six acupoints on the affected side of the face were stimulated by TENS and EA successively at 30-min intervals. During the stimulation, the current intensity was regulated gradually from 0 to 20 mA, and we simultaneously measured the lower (sensory) and upper (tolerability) sensations. After the treatment by TENS and EA, the modified Chinese version of the Massachusetts General Hospital Acupuncture Sensation Scales (C-MMASS) was applied to survey the de-qi sensations during stimulation. Additionally, we analyzed the correlation between current intensities and C-MMASS and comfort scores. Finite element models were established to depict the spatial distribution of electric field gradients at the lower and upper thresholds.

Results

The mean sensory and tolerability thresholds of TENS were 3.91–4.37 mA and 12.33–16.35 mA, respectively. The median sensory and tolerability thresholds of EA were 0.2 mA and 2.0–3.2 mA, respectively. We found a significant correlation between total C-MMASS scores and the current intensities at the tolerability threshold of TENS. The finite element model showed that the activated depths of TENS and EA at the lower threshold were 3.8 and 7 mm, respectively, whereas those at the upper threshold were both 13.8 mm. The cross-sectional diameter of the activated area during TENS was 2.5–4 times larger than that during EA.

Conclusion

This pilot study provided a method for exploring the current intensity at which the de-qi sensations can be elicited by TENS or EA. The finite element analysis potentially revealed the spatial scope of the electrical stimulation at a specific current intensity.

Electroacupuncture-Induced Muscular Inflammatory Pain Relief Was Associated With Activation of Low-Threshold Mechanoreceptor Neurons and Inhibition of Wide Dynamic Range Neurons in Spinal Dorsal Horn

Acupuncture is an effective alternative therapy for pain management. Evidence suggests that acupuncture relieves pain by exciting somatic afferent nerve fibers. However, the mechanism underlying the interaction between neurons in different layers of the spinal dorsal horn induced by electroacupuncture (EA) remains unclear. The aim of this study was to explore the mechanism of EA relieving inflammatory muscle pain, which was associated with activation of the spontaneous firing of low-threshold mechanoreceptor (LTM) neurons and inhibition of wide dynamic range (WDR) neuronal activities in the spinal dorsal horn of rats. Inflammatory muscle pain was induced by injecting complete Freund’s adjuvant into the right biceps femoris muscle. EA with intensity of threshold of A fibers (Ta) in Liangqiu (ST34) muscle considerably inhibited the abnormal spontaneous activities of electromyography (EMG) due to muscle inflammation. While EA with intensity of C-fiber threshold (Tc) increased the abnormal activities of EMG. EA with Ta also ameliorated the imbalance of weight-bearing behavior. A microelectrode array with 750-μm depth covering 32 channels was used to record the neuronal activities of WDR and LTM in different layers of the spinal dorsal horn. The spontaneous firing of LTM neurons was enhanced by EA-Ta, while the spontaneous firing of WDR neurons was inhibited. Moreover, EA-Ta led to a significant inverse correlation between changes in the frequency of WDR and LTM neurons (r = −0.64, p < 0.05). In conclusion, the results indicated that EA could alleviate inflammatory muscle pain, which was associated with facilitation of the spontaneous firing of LTM neurons and inhibition of WDR neuronal activities. This provides a promising evidence that EA-Ta could be applied to relieve muscular inflammatory pain in clinical practice.

The Involvement of Central Noradrenergic Pathway in the Analgesic Effect of Bee Venom Acupuncture on Vincristine-Induced Peripheral Neuropathy in Rats

Vincristine is a vinca alkaloid anti-mitotic drug with a broad spectrum of effects on solid and hematologic cancers. The major dose-limiting factor of this anti-cancer regimen is painful peripheral neuropathy. However, no gold-standard analgesic option has been used clinically. In this study, we investigated the effects and mechanism of bee venom acupuncture (BVA) to alleviate peripheral neuropathic pain induced by repeated intraperitoneal infusions of vincristine (1 mg/kg/day, days 1–5 and 8–12) in rats. Subcutaneous injection with bee venom (BV, 1.0 mg/kg) at the ST36 acupoint ameliorated cold and mechanical hypersensitivity (i.e., aberrant withdrawal responses in acetone drop and von Frey hair tests, respectively). In vivo extracellular recording demonstrated that BVA inhibited cutaneous cold (acetone) and mechanical (brush, press, and pinch) stimuli-elicited abnormal hyperexcitation of the spinal wide dynamic range (WDR) neurons in vincristine-treated rats. In addition, the microinjection of lidocaine into the ipsilateral locus coeruleus or the antagonism of the spinal α₂-adrenergic receptors clearly reversed the effects of BVA on cold and mechanical hypersensitivity, indicating a vital role of the descending noradrenergic modulation in analgesia. These findings suggest that BVA could be a potential therapeutic option for vincristine-induced peripheral neuropathy.

Enhanced spinal neuronal responses as a mechanism for increased number and size of active acupoints in visceral hyperalgesia

Acupuncture has been used to treat a variety of illness and involves the insertion and manipulation of needles into specific points on the body (termed “acupoints”). It has been suggested that acupoints are not merely discrete, static points, but can be dynamically changed according to the pathological state of internal organs. We investigated in a rat model of mustard oil (MO)-induced visceral hyperalgesia whether the number and size of acupoints were modified according to the severity of the colonic pain, and whether the changes were associated with enhanced activity of the spinal dorsal horn. In MO-treated rats, acupoints showing neurogenic inflammation (termed “neurogenic spots” or Neuro-Sps) were found both bilaterally and unilaterally on the leg. The number and size of these acupoints increased along with increasing doses of MO. Electroacupuncture of the acupoints generated analgesic effects on MO-induced visceral hypersensitivity. The MO-treated rats showed an increase in c-Fos expression in spinal dorsal horn neurons and displayed increased evoked activity and a prolonged after-discharge in spinal wide dynamic response (WDR) neurons in response to colorectal distension. Increased number and size of neurogenic inflammatory acupoints following MO treatment were reduced by inhibiting AMPA and NMDA receptors in the spinal cord. Our findings suggest that acupoints demonstrate increased number and size along with severity of visceral pain, which may be associated with enhanced neuronal responses in spinal dorsal horn neurons.

Electroacupuncture Inhibits Hyperalgesia by Alleviating Inflammatory Factors in a Rat Model of Migraine

Objective

Acupuncture has a therapeutic effect similar to that of prophylactic drugs and can be considered a treatment option for migraineurs. However, the mechanism of acupuncture treatment's effect on migraine is uncertain. An approach based on anti-inflammatory effects is an important treatment strategy for migraine because non-steroidal anti-inflammatory drugs (NSAIDs) are usually used during migraine attacks. Meningeal inflammation is thought to be responsible for the activation of the trigeminovascular system. Our previous study found that electroacupuncture (EA) decreased neurogenic inflammation mediator expression in the trigeminal ganglion (TG) and alleviated hyperalgesia. The present study examined whether EA would inhibit hyperalgesia by alleviating neurogenic inflammatory factors.

Methods

A rat model of migraine was established using dural electrical stimulation (DES). Five groups were analyzed in this study. The Model group received DES three times to mimic migraine attacks, a Control group had sham DES, and three groups received electroacupuncture after DES: a Non-Acu group at a non-acupuncture point, a GB20 group at GB20, and a GB20/34 group at GB20 and GB34 acupuncture points. We evaluated mechanical hyperalgesia using an electronic von Frey esthesiometer in the awake state. After sacrifice, the dura mater was analyzed using immunofluorescence. Serum calcitonin gene-related peptide, cyclooxygenase-2, brain-derived neurotrophic factor, IL-1β, IL-6, and TNF levels were determined using enzyme-linked immunosorbent assays to evaluate the anti-inflammatory effect of acupuncture.

Results

After repeated DES, we observed facial and hind paw mechanical hyperalgesia, which was inhibited by electroacupuncture. Electrical stimulation increased the number of mast cells and macrophages and serum levels of inflammatory factors. GB20 and GB20/34 electroacupuncture significantly decreased the number of mast cells and macrophages and serum levels of inflammatory factors. Moreover, electroacupuncture at GB20/34 was superior to that at GB20 alone in inhibiting hyperalgesia and alleviating inflammatory factors.

Conclusion

Electroacupuncture inhibits DES-induced hyperalgesia by alleviating inflammatory factors. Inhibition of dural mast cells, macrophages, and serum inflammatory factors may be one of the mechanisms involved in acupuncture treatment's effect on migraine.