Supraspinal neural mechanisms of the analgesic effect produced by transcutaneous electrical nerve stimulation

Comparative Analysis of High-Frequency and Low-Frequency Transcutaneous Electrical Stimulation of the Right Median Nerve in the Regression of Clinical and Neurophysiological Manifestations of Generalized Anxiety Disorder

Background/Objectives: The anxiolytic effect of transcutaneous electrical nerve stimulation (TENS) is associated with the activation of endogenous inhibitory mechanisms in the central nervous system. Both low-frequency, high-amplitude TENS (LF-TENS) and high-frequency, low-amplitude TENS (HF-TENS) are capable of activating opioid, GABA, serotonin, muscarinic, and cannabinoid receptors. However, there has been no comparative analysis of the effectiveness of HF-TENS and LF-TENS in the treatment of GAD. The purpose of our research was to study the effectiveness of direct HF-TENS and LF-TENS of the right median nerve in the treatment of patients with GAD compared with sham TENS. Methods: The effectiveness of direct HF-TENS and LF-TENS of the right median nerve in the treatment of GAD was studied using Generalized Anxiety Disorder 7-item scale (GAD-7) and the Hamilton Anxiety Rating Scale (HAM-A). 40 patients underwent sham TENS, 40 patients passed HF-TENS (50 Hz-50 μs-sensory response) and 41 patients completed LF -TENS (1 Hz-200 μs-motor response) for 30 days daily. After completion of treatment, half of the patients received weekly maintenance therapy for 6 months. Electroencephalography was performed before and after treatment. Results: Our study showed that a significant reduction in the clinical symptoms of GAD as assessed by GAD-7 and HAM-A was observed after HF-TENS and LF-TENS by an average of 42.4%, and after sham stimulation only by 13.5% for at least 2 months after the end of treatment. However, LF-TENS turned out to be superior in effectiveness to HF-TENS by 51% and only on electroencephalography leads to an increase in PSD for the alpha rhythm in the occipital regions by 24% and a decrease in PSD for the beta I rhythm in the temporal and frontal regions by 28%. The prolonged effect of HF-TENS and LF-TENS was maintained without negative dynamics when TENS treatment was continued weekly throughout the entire six-month observation period. Conclusions: A prolonged anxiolytic effect of direct TENS of the right median nerve has been proven with greater regression of clinical and neurophysiological manifestations of GAD after LF-TENS compared to HF-TENS. Minimal side effects, low cost, safety, and simplicity of TENS procedures are appropriate as a home treatment modality.

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.

Enhancing pain modulation: the efficacy of synchronous combination of virtual reality and transcutaneous electrical nerve stimulation

Introduction

Virtual reality (VR) and transcutaneous electrical nerve stimulation (TENS) have emerged as effective interventions for pain reduction. However, their standalone applications often yield limited analgesic effects, particularly in certain painful conditions.

Aims

Our hypothesis was that the combination of VR with TENS in a synchronous manner could produce the best analgesic effect among the four experimental conditions.

Methods

To address this challenge, we proposed a novel pain modulation strategy that synchronously combines VR and TENS, aiming to capitalise on both techniques' complementary pain modulation mechanisms. Thirty-two healthy subjects participated in the study and underwent three types of interventions: VR alone, a combination of VR with conventional TENS, and a combination of VR with synchronous TENS. Additionally, a control condition with no intervention was included. Perceived pain intensity, pain unpleasantness, positive and negative affect scores, and electroencephalographic (EEG) data were collected before and after the interventions. To delve into the potential moderating role of pain intensity on the analgesic efficacy of VR combined with synchronous TENS, we incorporated two distinct levels of painful stimuli: one representing mild to moderate pain (ie, low pain) and the other representing moderate to severe pain (ie, high pain).

Results

Our findings revealed that both combination interventions exhibited superior analgesic effects compared with the VR-alone intervention when exposed to low and high pain stimuli. Notably, the combination of VR with synchronous TENS demonstrated greater analgesic efficacy than the combination of VR with conventional TENS. EEG data further supported these results, indicating that both combination interventions elicited a greater reduction in event-related potential magnitude compared with the VR-alone intervention during exposure to low and high pain stimuli. Moreover, the synchronous combination intervention induced a more significant reduction in N2 amplitude than the VR-alone intervention during exposure to low pain stimuli. No significant differences in EEG response changes were detected between the two combination interventions. Both combination interventions resulted in a greater reduction in negative affect compared with the VR-alone intervention.

Conclusions

Altogether, our study highlights the effectiveness of the synchronous combination of VR and TENS in enhancing pain modulation. These findings offer valuable insights for developing innovative pain treatments, emphasising the importance of tailored and multifaceted therapeutic approaches for various painful conditions.

Using TENS for Pain Control: Update on the State of the Evidence

Transcutaneous electrical nerve stimulation (TENS) is a non-pharmacological intervention used in the treatment of acute and chronic pain conditions. The first clinical studies on TENS were published over 50 years ago, when effective parameters of stimulation were unclear and clinical trial design was in its infancy. Over the last two decades, a better understanding of the mechanisms underlying TENS efficacy has led to the development of an adequate dose and has improved outcome measure utilization. The continued uncertainty about the clinical efficacy of TENS to alleviate pain, despite years of research, is related to the quality of the clinical trials included in systematic reviews. This summary of the evidence includes only trials with pain as the primary outcome. The outcomes will be rated as positive (+), negative (−), undecided (U), or equivalent to other effective interventions (=). In comparison with our 2014 review, there appears to be improvement in adverse events and parameter reporting. Importantly, stimulation intensity has been documented as critical to therapeutic success. Examinations of the outcomes beyond resting pain, analgesic tolerance, and identification of TENS responders remain less studied areas of research. This literature review supports the conclusion that TENS may have efficacy for a variety of acute and chronic pain conditions, although the magnitude of the effect remains uncertain due to the low quality of existing literature. In order to provide information to individuals with pain and to clinicians treating those with pain, we suggest that resources for research should target larger, high-quality clinical trials including an adequate TENS dose and adequate timing of the outcome and should monitor risks of bias. Systematic reviews and meta-analyses should focus only on areas with sufficiently strong clinical trials that will result in adequate sample size.

Characteristics of Zusanli Dorsal Root Ganglion Neurons in Rats and Their Receptor Mechanisms in Response to Adenosine

Neural systems play important roles in the functions of acupuncture. But the unclear structure and mechanism of acupoints hinder acupuncture standardization and cause the acupuncture effects to be varying or even paradoxical. It has been broadly assumed that the efficacy of acupuncture depends on the biological signals triggered at acupoints and passed up along neural systems. However, as the first station to transmit such signals, the characters of the dorsal root ganglia (DRG) neurons innervating acupoints are still not well elucidated. We adopted Zusanli (ST36) as a representative acupoint and found most DRG neurons innervating ST36 acupoint are middle-size neurons with a single spike firing pattern. This suggests that proprioceptive neurons take on greater possibility than small size nociceptive neurons do to mediate the acupuncture signals. Moreover, we found that adenosine injected into ST36 acupoints could dose- and acupoint-dependently mimic the analgesic effect of acupuncture. However, adenosine could not elicit action potentials in the acutely isolated ST36 DRG neurons, but it inhibited I_D currents and increased the areas of overshoots. Further, we found that 4 types of adenosine receptors were all expressed by ST36 DRG neurons, and A1, A2b, and A3 receptors were the principal reactors to adenosine. PERSPECTIVE: This study provides the major characteristics of ST36 DRG neurons, which will help to analyze the neural pathway of acupuncture signals. At the same time, these findings could provide a new possible therapy for pain relief, such as injecting adenosine or corresponding agonists into acupoints.

Meta-Analysis on the Effects of Electric Acupuncture on Neural Functional Recovery and Related Pathways of Rats after Spinal Cord Injury

Background

Spinal cord injury (SCI) is a type of damage to the central nervous system (CNS) caused by various factors. The secondary injury of SCI is more complicated. Studies have found that electroacupuncture can help the recovery of nerve function during spinal cord injury. Therefore, this study explored the efficacy of electroacupuncture on complications after spinal cord injury through meta-analysis.

Methods

Relevant literatures published from January 2010 to March 2022 were searched with "Electric acupuncture, Spinal cord injury, Neural functional recovery, Spinal cord injury in rats, Neuronal Signaling" as search words. The risk of bias of included references was analyzed and assessed using RevMan 5.3 software and Stata software. Heterogeneity between studies was assessed using the Q-test and heterogeneity (I 2).

Results

There was no heterogeneity among the study groups. The comparison on the therapeutic effects of electroacupuncture and conventional therapy suggested that electroacupuncture was more effective for nerve recovery after spinal cord injury than conventional therapy. It can better improve the recovery of motor function after spinal cord injury in rats. On the other hand, SCI+EA had a good inhibitory effect on the expression of RhoA protein signal in rats and had a positive effect on the signal pathway. Discussion. The results of meta-analysis confirmed that electroacupuncture was more effective than conventional therapy in inhibiting pathways.

Role of Transcutaneous Electric Nerve Stimulation in Pain and Pulmonary Function in Patients after Bariatric Surgery

Background

Changes in lifestyle, a carbohydrate-rich diet, and decreased physical activity are part of the context that led to an obesity pandemic. Treating obesity is a task that requires multidisciplinary care; however, in many cases, conventional therapy has no effect, requiring surgical intervention. This, in turn, is not without risks and causes important changes in lung function. Therefore, the aim of this study is to evaluate the effect of electroanalgesia through conventional transcutaneous electrical nerve stimulation (TENS) on the pain and lung function in the postoperative period of bariatric surgery.

Methods

This is a controlled and blinded clinical trial with 66 subjects who underwent bariatric surgery. The participants were randomized into 2 groups as follows: an intervention group treated with TENS (n = 33) and a placebo group (n = 33). The participants underwent 4 TENS sessions, and the effect on pain was assessed using a visual analogue scale (VAS pain). Lung function was measured by spirometry.

Results

There were no differences between the 2 groups regarding time of surgery and time of mechanical ventilation. Compared to placebo, TENS reduced pain in the intervention group (p = 0.001). Regarding the effect of electroanalgesia on pulmonary function, the spirometric parameters were similar between the groups. However, regarding muscle strength between the preoperative and postoperative periods, maximal inspiratory pressure (MIP) was maintained in the intervention group and decreased in the placebo group (p = 0.03). Compared with that in the intervention group, the respiratory rate in the placebo group increased during the application of TENS (p = 0.003).

Conclusion

Electroanalgesia reduces pain in patients who underwent bariatric surgery. Importantly, in these patients, the MIP is maintained between the preoperative and postoperative periods. However, electroanalgesia does not contribute to improvements in spirometric data. This trial is registered with NCT04800640.

The Distinct Functions of Dopaminergic Receptors on Pain Modulation: A Narrative Review

Chronic pain is considered an economic burden on society as it often results in disability, job loss, and early retirement. Opioids are the most common analgesics prescribed for the management of moderate to severe pain. However, chronic exposure to these drugs can result in opioid tolerance and opioid-induced hyperalgesia. On pain modulation strategies, exploiting the multitarget drugs with the ability of the superadditive or synergistic interactions attracts more attention. In the present report, we have reviewed the analgesic effects of different dopamine receptors, particularly D1 and D2 receptors, in different regions of the central nervous system, including the spinal cord, striatum, nucleus accumbens (NAc), and periaqueductal gray (PAG). According to the evidence, these regions are not only involved in pain modulation but also express a high density of DA receptors. The findings can be categorized as follows: (1) D2-like receptors may exert a higher analgesic potency, but D1-like receptors act in different manners across several mechanisms in the mentioned regions; (2) in the spinal cord and striatum, antinociception of DA is mainly mediated by D2-like receptors, while in the NAc and PAG, both D1- and D2-like receptors are involved as analgesic targets; and (3) D2-like receptor agonists can act as adjuvants of μ-opioid receptor agonists to potentiate analgesic effects and provide a better approach to pain relief.