The role of endogenous opioid neuropeptides in neurostimulation-driven analgesia

Group singing and its effect on cortisol, alpha amylase, oxytocin, and pain threshold in patients with Parkinson's disease

Background

Parkinson's disease (PD) is a neurodegenerative disorder that causes motor deficits, including rigidity and tremors. Pain is also a common problem for people with PD that may arise from their dopamine deficit. Some patients with PD experience temporary relief from pain through group singing, which has also been shown to mitigate vocal challenges related to PD. However, no work has been conducted to elucidate the neurochemical mechanisms of action on the pain threshold. Here, we examined whether the effects of group singing on cortisol, alpha amylase, and oxytocin levels are associated with changes in pain thresholds in patients with PD.

Methods

Participants with PD (n = 14) participated in a 12-week singing program involving weekly 45-min group singing sessions in the early afternoon. Data collection, involving saliva samples and pain thresholds, was performed pre- and post-session in the 2nd (Session 1), 7th (Session 2), and 12th (Session 3) weeks of the program. Saliva samples were collected before and after each session by using the passive drool method. The pain threshold was assessed before and after each session by applying pressure to the finger using a dolorimeter. Saliva samples were used to assess salivary cortisol (sCORT), alpha amylase (sAA), and oxytocin (sOXT). Pain threshold, sCORT, sAA, and sOXT change scores were calculated for each session by subtracting the pre-session value from the post-session value.

Results

Three mixed linear model analyses were performed to assess whether sCORT, sAA, and sOXT were associated with increased pain threshold. We found that group singing led to a significant reduction in sCORT and sAA. We also found that reductions in sCORT were significantly related to an increase in the pain threshold (p < 0.05). However, we did not observe any relationship between pain threshold increases and sAA or between pain threshold and sOXT.

Conclusion

Group singing significantly increases the pain threshold in patients with PD, and this increase may be mediated through a reduction in cortisol levels.

Deciphering the antinociceptive and anti-inflammatory effects of pelargonidin through L-arginine/nitric oxide/cyclic GMP/ATP-sensitive potassium channel signaling pathway and gamma-aminobutyric acid/opioidergic receptors

There are complex dysregulated pathways behind the pathogenesis of pain and inflammation. Because most of the present drugs have certain side effects or are not effective enough, providing novel multitargeting and potent therapeutic agents is of particular importance. This study investigates the antinociceptive effects of pelargonidin, an anthocyanin derived from various plants, through the modulation of the L-arginine/nitric oxide (NO)/cyclic GMP (cGMP)/ATP-sensitive potassium channel (KATP) signaling pathway. We also evaluated the anti-inflammatory role of pelargonidin passing through gamma-aminobutyric acid (GABA) and opioidergic receptors. Two experimental models were utilized. In the carrageenan model, 42 rats were divided into control, diclofenac, and three doses of pelargonidin (3, 6, and 9 mg/kg). In addition, two groups received pelargonidin 9 mg/kg + naloxone and pelargonidin 9 mg/kg + flumazenil. For the formalin model, 90 male mice were assigned to control, diclofenac, and three doses of pelargonidin, and 10 groups receiving L-arginine, S-nitroso-N-acetylpenicillamine (SNAP), N(gamma)-nitro-L-arginine methyl ester (L-NAME), glibenclamide, and sildenafil individually or alongside pelargonidin 9 mg/kg. Our results indicated that pelargonidin significantly decreased inflammation and pain in a dose-dependent manner. Notably, groups of pelargonidin 9 mg/kg + naloxone and pelargonidin 9 mg/kg + flumazenil diminished pelargonidin's anti-inflammatory effectiveness, underscoring the significant role of these receptors. Mechanistically, it was shown that the antinociceptive effects of pelargonidin were mediated by the NO signaling pathway. While L-NAME and glibenclamide reduced pelargonidin's antinociceptive efficacy, supplementation with sildenafil and SNAP enhanced the effect. This investigation demonstrated that pelargonidin possesses dose-dependent antinociceptive and anti-inflammatory actions through L-arginine/NO/cGMP/KATP pathways, and opioidergic and GABA receptors, respectively.

Reduction of Prostate Cancer Risk: Role of Frequent Ejaculation-Associated Mechanisms

Prostate cancer (PCa) accounts for roughly 15% of diagnosed cancers among men, with disease incidence increasing worldwide. Age, family history and ethnicity, diet, physical activity, and chemoprevention all play a role in reducing PCa risk. The prostate is an exocrine gland that is characterized by its multi-functionality, being involved in reproductive aspects such as male ejaculation and orgasmic ecstasy, as well as playing key roles in the regulation of local and systemic concentrations of 5α-dihydrotestosterone. The increase in androgen receptors at the ventral prostate is the first elevated response induced by copulation. The regulation of prostate growth and function is mediated by an androgen-dependent mechanism. Binding 5-DHT to androgen receptors (AR) results in the formation of a 5α-DHT:AR complex. The interaction of the 5α-DHT:AR complex with the specific DNA enhancer element of androgen-regulated genes leads to the regulation of androgen-specific target genes to maintain prostate homeostasis. Consequently, ejaculation may play a significant role in the reduction of PCa risk. Thus, frequent ejaculation in the absence of risky sexual behavior is a possible approach for the prevention of PCa. In this review, we provide an insight into possible mechanisms regulating the impact of frequent ejaculation on reducing PCa risk.

Application of Transcutaneous Electrical Acupoint Stimulation (TEAS) for Management of Postoperative Pain After Gynecological Surgeries: A Meta-Analysis

PURPOSE

Transcutaneous Electrical Acupoint Stimulation (TEAS) is a noninvasive technique that involves the application of electrical stimulation to specific acupoints on the skin. This meta-analysis aimed to evaluate the clinical efficacy of TEAS in alleviating postoperative pain after gynecological surgeries.

METHOD

A systematic search of multiple electronic databases was carried out to identify relevant studies that investigated the use of TEAS for postoperative pain management in gynecological surgery settings.

RESULTS

After screening and data extraction, a total of 10 randomized controlled trials (RCTs) were included in the meta-analysis. The results of the meta-analysis showed that TEAS was associated with reduction in postoperative pain intensity compared to control interventions, such as sham stimulation or conventional analgesics. However, this reduction was statistically insignificant (p > .05). Additionally, TEAS was found to be effective in reducing the consumption of analgesic medications and improving patient satisfaction with pain management. The assessment of certainty of evidence revealed a grading of low to moderate.

CONCLUSIONS

Overall, the findings of this meta-analysis suggest that TEAS may be a promising adjunctive therapy for alleviating postoperative pain in gynecological surgery patients. However, caution should be exercised when interpreting the results and making clinical recommendations based on the low to moderate quality of the current evidence. Further high-quality studies are needed to confirm these results and establish optimal treatment protocols for TEAS in this patient population.

A Comprehensive Analysis of Fibromyalgia and the Role of the Endogenous Opioid System

Fibromyalgia represents a chronic pain disorder characterized by musculoskeletal pain, fatigue, and cognitive impairments. The exact mechanisms underlying fibromyalgia remain undefined; as a result, diagnosis and treatment present considerable challenges. On the other hand, the endogenous opioid system is believed to regulate pain intensity and emotional responses; hence, it might be expected to play a key role in the enhanced sensitivity experienced by fibromyalgia patients. One explanation for the emergence of disrupted pain modulation in individuals with fibromyalgia is a significant reduction in opioid receptor activity or an imbalance in the levels of endogenous opioid peptides. Further research is essential to clarify the complex details of the mechanisms underlying this abnormality. This complexity arises from the notion that an improved understanding could contribute to the development of innovative therapeutic strategies aimed at targeting the endogenous opioid system in the context of fibromyalgia. Although progress is being made, a complete understanding of these complexities remains a significant challenge. This paradigm has the potential to revolutionize the complex management of fibromyalgia, although its implementation may experience challenges. The effectiveness of this approach depends on multiple factors, but the implications could be profound. Despite the challenges involved in this transformation, the potential for improving patient care is considerable, as this condition has long been inadequately treated.

Effect of Neurostimulation on Chronic Pancreatic Pain: A Systematic Review

BACKGROUND

Chronic pancreatic pain is one of the most severe causes of visceral pain, and treatment response is often limited. Neurostimulation techniques have been investigated for chronic pain syndromes once there are pathophysiological reasons to believe that these methods activate descending pain inhibitory systems. Considering this, we designed this systematic literature review to investigate the evidence on neuromodulation techniques as a treatment for chronic pancreatic pain.

MATERIALS AND METHODS

We performed a literature search using the databases MEDLINE, Cochrane Central Register of Controlled Trials (CENTRAL), and Embase until April 2024. The included studies used neurostimulation techniques in participants with chronic pancreatic pain and reported pain-related outcomes, with a focus on pain scales and opioid intake. Two reviewers screened and extracted data, and a third reviewer resolved discrepancies. We assessed the risk of bias using the Jadad scale. The authors then grouped the findings by the target of the neurostimulation, cortex, spinal cord, or peripheral nerves; described the findings qualitatively in the results section, including qualitative data reported by the articles; and calculated effect sizes of pain-related outcomes.

RESULTS

A total of 22 studies were included (7 randomized clinical trials [RCTs], 14 case series, and 1 survey), including a total of 257 clinical trial participants. The two outcomes most commonly reported were pain, measured by the visual analogue scale (VAS), numeric rating scale (NRS), and pressure pain threshold scores, and opioid intake. Two RCTs investigated repetitive transcranial magnetic stimulation (rTMS), showing a reduction of 36% (±16) (d = 2.25; 95% CI, 0.66-3.83) and 27.2% (±24.5%) (d = 2.594; 95% CI, 1.303-3.885) in VAS pain scale. In another clinical trial, transcranial direct-current stimulation (tDCS) and transcranial pulsed current stimulation were not observed to effect a significant reduction in VAS pain (χ2 = 5.87; p = 0.12). However, a complete remission was reported in one tDCS case. Spinal cord stimulation (SCS) and dorsal root ganglion stimulation were performed in a survey and 11 case series, showing major pain decrease and diminished opioid use in 90% of participants after successful implantation; most studies had follow-up periods of months to years. Two noninvasive vagal nerve stimulation (VNS) RCTs showed no significant pain reduction in pain thresholds or VAS (d = 0.916; 95% CI, -0.005 to 1.838; and d = 0.17; -0.86 to 1.20; p = 0.72; respectively). Splanchnic nerve stimulation in one case report showed complete pain reduction accompanied by discontinuation of oral morphine and fentanyl lozenges and a 95% decrease in fentanyl patch use. Two RCTs investigated transcutaneous electrical nerve stimulation (TENS). One found a significant pain reduction effect with the NRS (d = 1.481; 95% CI, 1.82-1.143), and decreased opioid use, while the other RCT did not show significant benefit. Additionally, one case report with TENS showed pain improvement that was not quantitatively measured.

DISCUSSION

The neuromodulation techniques of rTMS and SCS showed the most consistent potential as a treatment method for chronic pancreatic pain. However, the studies have notable limitations, and SCS has had no clinical trials. For VNS, we have two RCTs that showed a non-statistically significant improvement; we believe that both studies had a lack of power issue and suggest a gap in the literature for new RCTs exploring this modality. Additionally, tDCS and TENS showed mixed results. Another important insight was that opioid intake decrease is a common trend among most studies included and that adverse effects were rarely reported. To further elucidate the potential of these neurostimulation techniques, we suggest the development of new clinical trials with larger samples and adequate sham controls.

Enkephalins and Pain Modulation: Mechanisms of Action and Therapeutic Perspectives

Enkephalins, a subclass of endogenous opioid peptides, play a pivotal role in pain modulation. Enkephalins primarily exert their effects through opioid receptors located widely throughout both the central and peripheral nervous systems. This review will explore the mechanisms by which enkephalins produce analgesia, emotional regulation, neuroprotection, and other physiological effects. Furthermore, this review will analyze the involvement of enkephalins in the modulation of different pathologies characterized by severe pain. Understanding the complex role of enkephalins in pain processing provides valuable insight into potential therapeutic strategies for managing pain disorders.

Pain Science in Practice (Part 7): How Is Descending Modulation of Pain Measured?

SYNOPSIS: Understanding the descending pain modulatory system allows for a neuroscientific explanation of naturally occurring pain relief. Evidence from basic science and clinical studies on the effectiveness of drugs in certain patient groups led to pharmacological manipulation of the descending pain modulatory system for analgesia. Understanding mechanisms and theories helps clinicians make sense of chronic musculoskeletal pain. This editorial explains how test paradigms, including conditioned pain modulation, offset analgesia, and stress-induced analgesia work, provide an overview of a placebo analgesia circuitry, and discusses how evoking activity in the descending pain modulatory system using specific paradigms can give new insights into how specific treatments work to reduce pain. J Orthop Sports Phys Ther 2024;54(2):1-6. doi:10.2519/jospt.2024.12113.

Fast and slow: Recording neuromodulator dynamics across both transient and chronic time scales

Neuromodulators transform animal behaviors. Recent research has demonstrated the importance of both sustained and transient change in neuromodulators, likely due to tonic and phasic neuromodulator release. However, no method could simultaneously record both types of dynamics. Fluorescence lifetime of optical reporters could offer a solution because it allows high temporal resolution and is impervious to sensor expression differences across chronic periods. Nevertheless, no fluorescence lifetime change across the entire classes of neuromodulator sensors was previously known. Unexpectedly, we find that several intensity-based neuromodulator sensors also exhibit fluorescence lifetime responses. Furthermore, we show that lifetime measures in vivo neuromodulator dynamics both with high temporal resolution and with consistency across animals and time. Thus, we report a method that can simultaneously measure neuromodulator change over transient and chronic time scales, promising to reveal the roles of multi-time scale neuromodulator dynamics in diseases, in response to therapies, and across development and aging.

Periaqueductal/periventricular gray deep brain stimulation for the treatment of neuropathic facial pain

Background

The Periaqueductal gray (PAG) and the periventricular gray (PVG) are the anatomical targets for deep brain stimulation (DBS) to treat severe, refractory neuropathic pain.

Methods

Seven (four female and three male) patients were qualified for PAG/PVG DBS because of neuropathic facial pain. Frame-based unilateral implantations of DBS were conducted according to indirect planning of the PAG/PVG, contralateral to reported pain (3389, Activa SC 37603, Medtronic). The efficacy of PAG/PVG DBS on pain was measured with Numeric Pain Rating Scale (NRS) and Neuropathic Pain Symptom Inventory (NPSI) before surgery and 3, 12, and 24 months after surgery.

Results

The mean age of the group at the implantation was 43.7 years (range: 28-62; SD: 12.13). The mean duration of pain varied from 2 to 12 years (mean: 7.3; SD: 4.11). Five patients suffered from left-sided facial pain and two suffered right-sided facial pain. The etiology of pain among four patients was connected to ischemic brain stroke and in one patient to cerebral hemorrhagic stroke. Patients did not suffer from any other chronic medical condition The beginnings of ailments among two patients were related to craniofacial injury. NRS decreased by 54% at the 3 months follow-up. The efficacy of the treatment measured with mean NRS decreased at one-year follow-up to 48% and to 45% at 24 months follow-up. The efficacy of the treatment measured with NPSI decreased from 0.27 to 0.17 at 2 years follow-up (mean reduction by 38%). The most significant improvement was recorded in the first section of NPSI (Q1: burning- reduced by 53%). The records of the last section (number five) of the NPSI (paresthesia/dysesthesia- Q11/Q12) have shown aggravation of those symptoms by 10% at the two-years follow-up. No surgery- or hardware-related complications were reported in the group. Transient adverse effects related to the stimulation were eliminated during the programming sessions.

Conclusion

PAG/PVG DBS is an effective and safe method of treatment of medically refractory neuropathic facial pain. The effectiveness of the treatment tends to decrease at 2 years follow-up. The clinical symptoms which tend to respond the best is burning pain. Symptoms like paresthesia and dysesthesia might increase after DBS treatment, even without active stimulation.

Dorsal Root Ganglion Stimulation to Treat Chronic Shoulder Pain: A Case Report

A 67-year-old man presented with severe 9 of 10 intractable pain of the left shoulder joint after arthroplasty and revision surgeries, with associated weakness, atrophy, and limited range of motion in all directions. Dorsal root ganglion stimulation (DRG-S) at the left C4, C5, and C6 levels was used after failed conservative and interventional measures, resulting in significant improvement in pain, function, and quality of life measures through 6 months postimplantation. Larger studies should examine if DRG-S is effective in treating chronic arthritic joint pain as well as chronic postsurgical pain of the shoulder that is not predominantly neuropathic.