Cellular and molecular mechanisms of pain

Mitochondrial translocator-protein ligand etifoxine reduces pain symptoms and protects against motor dysfunction development following peripheral nerve injury in rats

Peripheral nerve injury enhances mitochondrial translocator protein (TSPO) expression in the spinal cord and dorsal root ganglia (DRG), which is associated with neuroinflammation and mitochondrial dysfunction contributing to chronic pain development. Here, we investigate the effect of TSPO ligand Etifoxine, on the development of chronic pain and motor dysfunction following sciatic nerve injury. Mechanical and thermal sensitivity, as well as motor function, were measured in rats before and after sciatic nerve crush (SNC). Rats were treated with the Etifoxine (50 mg/kg, twice daily) for one week. At the end of the experiment, RT-PCR and immunohistochemistry (IHC) were performed to assess mitochondrial stress and neuroinflammation. Additionally, high-resolution respirometry (O2k) was used to evaluate mitochondrial function in the spinal cord following mitochondrial permeability transition pore (mPTP) induction by Ca2+. Etifoxine treatment post-SNC alleviated mechanical and thermal hypersensitivity, as well as motor dysfunction in rats. In addition, Etifoxine treatment modulates neuroinflammation and mitochondrial stress. Specifically, we found a significant reduction in microglia presence and the transcription of pro-inflammatory cytokines (TNFα, IL-6, IL-1β) in the DRG and spinal cord of the SNC/etifoxine-treated group. Furthermore, Etifoxine treatment prevent the decline in mitochondrial respiration, including non-phosphorylation, ATP-linked respiration, and maximal respiration, after mPTP induction by Ca2+. Our findings suggest that TSPO-ligand Etifoxine protects against motor dysfunction and the development of chronic pain by reducing neuroinflammation and apoptosis in the DRG and spinal cord. Importantly, the beneficial effects of TSPO-ligands are reflected in the restoration of the mitochondrial function under challenging conditions.

RIN1 regulates ferroptosis and nociceptive perception via the Nrf2/HO-1 pathway in chronic constriction injury

Neuropathic pain (NP) has been a major focus of clinical research for decades. This study investigates the function of RAS- and RAB-interacting protein 1 (RIN1) in modulating NP and explore the involvement of the nuclear factor-2 erythroid factor-2 (Nrf2) and heme oxygenase 1 (HO-1) pathway in this context. A rat model of CCI was generated. The presence of mechanical and thermal hypersensitivity, as well as spontaneous pain behaviors, confirmed the successful modeling. Intrathecal injection of AAV9-shRNA targeting RIN1 attenuated nociception, reduced microglial activation in the L4-L6 spinal cord, and decreased the expression levels of c-Fos, GFAP, and IBA-1. Furthermore, the levels of NMDAR, PKC, Src, enzymes linked to neural hypersensitivity, was inhibited by RIN1 silencing. RIN1 was found to interact to Nrf2 protein, inhibiting its nuclear translocation and transcriptional activation. The RIN1 knockdown activated the Nrf2/HO-1 pathway, reducing oxidative stress and ROS levels in the spinal cord, while increasing the expression of Nrf2-target genes, including Nqo1, Gclc, and Gclm, which are key players in cellular antioxidant defense. Additionally, ferroptosis, characterized by mitochondrial damage and elevated Fe2+ levels, was reduced in RIN1 knockdown rats. Treatment with Nrf2 or HO-1 activators improved pain sensitivity and reduced inflammation, while inhibition of Nrf2 activity attenuated the protective effects of RIN1 silencing. In vitro, RIN1 silencing reduced activation LPS-treated of mouse BV2 microglial cells, leading to a decrease in the secretion of pro-inflammatory cytokines (IL-6, TNFα, and IL-1β), reduced microglial ferroptosis, and decreased the cytotoxicity of BV2 cells to co-cultured neurons. These effects were mediated by the Nrf2 pathway, as Nrf2 antagonism reversed the effects of RIN1 knockdown. These findings suggest that RIN1 plays a critical role in spinal cord hypersensitivity and pain perception by inhibiting the Nrf2/HO-1 pathway, influencing neuroinflammation and ferroptosis. Targeting RIN1 could provide a potential therapeutic strategy for managing NP and neuroinflammation.

Steroid hormones in pain: Mechanistic underpinnings and therapeutic perspectives

Pain is a complex sensory and emotional experience that severely affects an individual's quality of life and health status. Steroid hormones, as important regulatory substances in the human body, are extensively involved in various physiological and pathological processes. In recent years, remarkable progress has been made in the research of steroid hormones in the field of pain. They play a crucial role in the occurrence, development, and treatment of pain. This review comprehensively elaborates on the roles and therapeutic mechanisms of steroid hormones in pain, explores the performances of glucocorticoids, mineralocorticoids, sex hormones, etc. in different pain models, as well as the molecular mechanisms by which they regulate pain through genomic and non-genomic effects, aiming to provide a theoretical basis for the clinical treatment of pain.

Circadian disruption upon painful peripheral nerve injury in mice: Temporal effects on transcriptome in pain-regulating sensory tissues

BACKGROUND

Neuropathic pain (NP) resulting from nerve damage shows diurnal fluctuation of intensity in patients, indicating circadian regulation. However, mechanisms linking NP and circadian regulation remain unclear. This study aimed to investigate time-dependent transcriptomic changes during a 24-hour period using a spared nerve injury (SNI) mouse model of NP.

METHODS

Pain-related behaviours were assessed at baseline and on days 7, 14, and 21 after SNI and control sham surgeries in C57BL/6JRJ mice. Spinal cord (SC) and periaqueductal gray (PAG) were collected 4-hourly over 24 h upon completion of behavioural testing.

RESULTS

RNA sequencing revealed 111 up- and 21 downregulated differentially expressed genes (DEGs) in the SC, and 35 up- and 33 downregulated DEGs in the PAG, across all six time points. The large majority of DEGs, 245 in the SC and 191 in the PAG, are involved in regulation of immunity. Among the top expressed genes, five DEGs in the SC, Atf3, Anxa10, Gpr151, Cxcl10, Sprr1a, and two DEGs in the PAG, Igf2 and Wnt6, were previously reported to regulate pain. Circadian analysis using CircaCompare identified 383 SC transcripts and 261 PAG transcripts with altered rhythmicity. Variability of gene expression during circadian day was increased in the SC and decreased in the PAG from the SNI mice.

CONCLUSION

These findings suggest that NP disrupts the circadian expression of rhythmic transcripts in the SC and PAG, potentially revealing new targets for chronotherapy of NP.

Pain-on-a-Chip: A microfluidic device for neuron differentiation and functional discrimination in animal models of chronic pain

Chronic pain is a global health issue that is poorly understood and challenging to treat. Improving pain classification and treatment requires new strategies that objectively discriminate between pain conditions and minimise subjectivity associated with the perception of pain. To address this, we have developed a microfluidic biosensor - termed 'pain-on-a-chip' - that leverages recent advancements in biocompatible microfluidic technology with on-chip differentiation of nociceptor-like cells, enabling small sample volumes to be used. Following neuronal differentiation, we used on-chip live cell Ca2+ imaging to functionally validate the system. This includes characterising excitation responses in cells challenged with microfluidic perfusion of known nociceptive stimuli and biological fluids collected from different preclinical pain models. Our results demonstrate that this platform has the potential to discriminate between serum samples from distinct chronic pain models. This system has potential as an objective, and minimally invasive method for distinguishing between different subtypes of chronic pain.

Hippocampal microglial activation induces cognitive impairment and allodynia through neuronal plasticity changes in male mice with neuropathic pain

Clinical evidence indicates that cognitive impairment is a common comorbidity of chronic pain, including neuropathic pain, but the mechanism underlying this comorbidity remains unclear. Neuroinflammation plays a critical role in the development of both neuropathic pain and cognitive impairment. A previous study showed that minocycline, an inhibitor of microglia, ameliorated allodynia and cognitive impairment in partial sciatic nerve ligation (PSNL) mice. Therefore, the current study examined a potential role of brain microglia in allodynia and cognitive impairment in male mice with neuropathic pain due to PSNL. Immunohistochemistry of the microglial markers ionized calcium-binding adapter molecule 1 (Iba1), transmembrane protein 119 (TMEM119), and purinergic receptor P2Y12 (P2RY12) was performed to examine microglial status. Two weeks after PSNL, significant microglial activation was observed in the hippocampus and amygdala, but not in the perirhinal cortex. Inhibition of brain-region-specific microglia with a local microinjection of clodronate liposomes was examined to elucidate the involvement of these microglia in PSNL-induced allodynia and cognitive impairment. Local clodronate liposome microinjection to the hippocampus, but not the amygdala, ameliorated allodynia and cognitive impairment. Other changes in the hippocampus of PSNL mice, e.g., decreased hippocampal dendrite length and intersections number, were prevented by microinjection of clodronate liposomes. The current findings suggest hippocampal microglia are related to cognitive impairment and allodynia through neuronal plasticity changes observed in PSNL mice. Blocking hippocampal microglia-mediated neuroinflammation may be a novel approach for reducing comorbidities such as cognitive impairment associated with neuropathic pain.

Activation of cannabinoid CB1 receptors suppresses HCN channels function in dorsal root ganglion neurons of rats

Cannabinoid receptor (CBR) and hyperpolarization-activated cyclic nucleotide-gated (HCN) channels are both critically involved in pain hypersensitivity induced by nerve injury. Both CBR and HCN channels are expressed in sensory neurons of the dorsal root ganglia (DRG). Studies have shown that HCN channel function is regulated by cAMP-PKA signaling, and the activation of cannabinoid receptor 1 (CB1R) can inhibit cAMP-PKA activity. However, it remains unclear whether the function of HCN channels is regulated by CB1R activity in DRG. In this study, we investigated the effect of ACEA, a selective agonist for CB1R, on HCN channel expression and function in the DRG of rats with chronic constriction injury (CCI) of the sciatic nerve. Mechanical allodynia was assessed by measuring the mechanical withdrawal threshold (MWT). HCN1/ HCN2 channel expression and cAMP level in lumbar 4, 5 and 6 (L4-6) DRG were detected by Western blot analysis and ELISA, respectively. As a result, MWT decreased significantly in CCI rats. HCN1/ HCN2 channel expression and cAMP level increased in the ipsilateral L4-6 DRG after CCI operation. Notably, intrathecal injection of ACEA (0.05 mg/kg) significantly decreased mechanical allodynia, HCN1/ HCN2 expression, and cAMP level in CCI rats, and this effect was blocked by the CB1R antagonist AM251. On the other hand, Ih mediated by HCN channels of DRG neurons was recorded by whole-cell patch-clamp to evaluate HCN channel activity. In this assay, ACEA (1 μM) significantly reduced the amplitude of Ih in DRG neurons (P < 0.01), while pretreatment with AM251 blocked the inhibitory effect of ACEA on Ih (P < 0.01). In addition, 8-Br-cAMP, a PKA activator, could reverse the effect of ACEA on Ih in DRG neurons (P < 0.01), indicating that CB1R activation suppresses the function of HCN channels by decreasing cAMP-PKA activity. In conclusion, these findings suggest that CB1R activation can inhibit the function of HCN channels by decreasing cAMP-PKA activity, resulting in decreased excitability of primary sensory neurons.

Oxytocin in periaqueductal gray plasticly regulates strain-dependent social recognition memory in mice, modeling social identity

Social identity differences are crucial for gregarious animals, impacting survival and social development. This is particularly evident in humans, where social stratification, cultural divides, and ethnic differences influence societal dynamics. Social recognition memory plays a central role in this process, maintaining social order by allowing individuals to distinguish familiar members within their group. Notably, social recognition memory exhibits differences: within a group, individuals form detailed memories of each member (individualized memory), while for out-group members, a more generalized memory of the entire group forms (categorized memory). Although this phenomenon has been explored in human studies, current research techniques and methods have limited investigations into the underlying neural mechanisms, especially their plasticity and regulatory mechanisms. This study utilizes mice to establish an experimental model for investigating differences in social recognition memory and its neural basis. We demonstrate that mice also exhibit social identity-driven memory recognition patterns. Mice form individualized memories for same-strain individuals but categorized memories for different strains, and the type of social recognition memory could be regulated by oxytocin level of ventrolateral periaqueductal gray. These findings demonstrate that oxytocin and its receptors in the ventrolateral periaqueductal gray are essential for constructing and plastically regulating intergroup social memory in mice.

The persistent pain enigma: Molecular drivers behind acute-to-chronic transition

The transition from acute to chronic pain is a complex and multifactorial process that presents significant challenges in both diagnosis and treatment. Key mechanisms of peripheral and central sensitization, neuroinflammation, and altered synaptic plasticity contribute to the amplification of pain signals and the persistence of pain. Glial cell activation, particularly microglia and astrocytes, is pivotal in developing chronic pain by releasing pro-inflammatory cytokines that enhance pain sensitivity. This review explores the molecular, cellular, and systemic mechanisms underlying the transition from acute to chronic pain, offering new insights into the molecular and neurobiological mechanisms involved, which are often underexplored in existing literature. It also addresses emerging therapeutic strategies beyond traditional pain management, offering valuable perspectives for future research and clinical applications.

Sculpting excitable membranes: voltage-gated ion channel delivery and distribution

The polarized and domain-specific distribution of membrane ion channels is essential for neuronal homeostasis, but delivery of these proteins to distal neuronal compartments (such as the axonal ends of peripheral sensory neurons) presents a logistical challenge. Recent developments have enabled the real-time imaging of single protein trafficking and the investigation of the life cycle of ion channels across neuronal compartments. These studies have revealed a highly regulated process involving post-translational modifications, vesicular sorting, motor protein-driven transport and targeted membrane insertion. Emerging evidence suggests that neuronal activity and disease states can dynamically modulate ion channel localization, directly influencing excitability. This Review synthesizes current knowledge on the spatiotemporal regulation of ion channel trafficking in both central and peripheral nervous system neurons. Understanding these processes not only advances our fundamental knowledge of neuronal excitability, but also reveals potential therapeutic targets for disorders involving aberrant ion channel distribution, such as chronic pain and neurodegenerative diseases.

Lidocaine-A Promising Candidate for the Treatment of Cancer-Induced Bone Pain: A Narrative Review

Pain is one of the most common symptoms in patients with cancer, with cancer-induced bone pain (CIBP) significantly affecting their quality of life. Opioids are commonly used as first-line treatments for cancer pain, but their use requires caution due to non-mechanistic analgesia and significant side effects. As a result, there is a need for new non-opioid drugs that target cancer pain through specific mechanisms. Recent studies on the anticancer effects of lidocaine have highlighted its potential benefits in both treating cancer and alleviating cancer-induced pain. This article discusses the mechanism of action and clinical applications of lidocaine in cancer pain management, and suggests new treatment approaches for patients with CIBP.

Vitamin D in the Transition from Acute to Chronic Pain: A Systematic Review

BACKGROUND

The transition from acute to chronic pain is an important clinical phenomenon that significantly impacts the healthcare system. Despite decades of research, preventing this transition remains a complex challenge. Many studies have explored the various factors that contribute to the development of chronic pain, but the underlying mechanisms are still largely unclear. In this frame, vitamin D (VD) plays an important role in pain mechanism development, with emerging evidence suggesting it influences pain perception, inflammation, and nerve function.

METHODS

A total of 14 eligible original research articles were identified.

RESULTS

Our qualitative analysis showed that VD did not directly influence the transition from acute to chronic pain, but it affected pain intensity, improving outcomes in patients at risk of developing chronic pain.

CONCLUSIONS

Additional randomized clinical trials, particularly double-blind, placebo-controlled studies, which are regarded as the gold standard in clinical research, are warranted to evaluate the role of vitamin D in the progression from acute to chronic pain.

A comprehensive review of scientifically reported phytochemicals to manage allodynia in chronic diabetes complications

BACKGROUND

The global prevalence of diabetes mellitus and its associated complications is increasing, impacting both developed and developing nations. One common complication is neuropathy and neuropathic pain, which often manifests as symptoms such as allodynia-a condition where patients experience pain from non-painful stimuli.

OBJECTIVE

This review seeks to explore scientifically validated medicinal plants and phytochemicals, presenting the findings in an organized format based on published literature.

METHODOLOGY

Data were searched in pubmed literature and only the scientifically reported phytochemicals were considered to include in this review.

KEY FINDINGS

The U.S. Food and Drug Administration (FDA) has not approved many medications targeting the root causes of neuropathy. Instead, various strategies are employed to manage the symptoms of allodynia. Research on plant-based ethno-pharmaceuticals aims to address the symptoms without affecting the disease's progression, which involves the gradual loss of nerve fibres from the extremities. This article delves into allodynia's different forms, implications, and underlying signalling mechanisms.

CONCLUSION

The hope is that further research on phytochemicals could lead to the development of therapies for managing various forms of allodynia in diabetic patients.

Role of the interleukin-33 (IL-33)/suppressor of tumorigenicity 2 (ST2) signaling in superoxide anion-triggered inflammation and pain behavior in mice

Reactive oxygen species such as superoxide anion have varied roles in inflammation and pain, which can be mimicked by potassium superoxide (KO2), the superoxide anion donor. Interleukin (IL)-33 has pleiotropic functions by activating its receptor suppression of tumorigenicity 2 (ST2). However, the role of IL-33/ST2 signaling in inflammatory pain initiated by reactive oxygen species (ROS) such as superoxide anion has not been investigated, which was the aim of the present study. IL-33 levels were assessed by enzyme-linked immunosorbent assay (ELISA). Mechanical and thermal hyperalgesia and overt pain were evaluated by electronic von Frey, hot plate, and abdominal writhing/paw flinching/licking, respectively. Edema and leukocyte recruitment (myeloperoxidase assay and total/differential cell count), antioxidant capacity, superoxide anion production and lipid peroxidation were assessed. Paw skin and spinal cord messenger ribonucleic acid (mRNA) expression of pro-inflammatory mediators and glial markers in the spinal cord were evaluated. Immunofluorescence was used to detect spinal glial and neuronal c-Fos activation. KO2 injection triggered IL-33 production in the paw skin and spinal cord of mice, induced hyperalgesia, edema, neutrophil recruitment to the paw tissue, overt pain-like behavior, and leukocyte recruitment to the peritoneum that were reduced in ST2 deficient mice. In the paw skin and spinal cord, KO2 triggered IL-33/ST2-dependent oxidative stress, and mRNA expression of inflammatory molecules, which were reduced by ST2 deficiency. KO2 induced spinal cord glial (at mRNA/protein levels) and neuronal activation in IL-33/ST2-dependent manner. IL-33/ST2 signaling mediates, at least in part, superoxide anion-induced inflammatory pain by modulating local and spinal inflammatory events.

A bad break: mechanisms and assessment of acute and chronic pain after bone fracture

ABSTRACT

Pain is one of the primary indicators of a bone fracture and serves both a functional and practical role in guiding recovery. However, fracture pain can persist long after the fracture itself has clinically healed. The neural and molecular mechanisms that drive acute pain postfracture, and how these mechanisms are pathologically usurped to trap patients into persistent, debilitating, and often difficult to treat, chronic pain, are not well understood. The aim of this review is to provide insight into the risk factors for pain persistence after fracture, review the physiological and pathophysiological mechanisms of fracture pain, and critically evaluate the literature around fracture pain assessment techniques/models. Taken together, the concepts covered herein will provide a strong foundation to support the development of more effective treatments to better alleviate postfracture pain.

Effect of two novel GABAA receptor positive allosteric modulators on neuropathic and inflammatory pain in mice

Loss of GABAergic inhibition in the spinal dorsal horn (SDH) is implicated in central sensitization and chronic pain. Both agonists and positive allosteric modulators (PAMs) of GABAA receptor are found to be effective in the management of chronic pain. In addition to benzodiazepines, neuroactive steroids (NASs) also act as PAMs through binding to unique sites of GABAA receptors. Thus, it is worth investigating whether these NASs can attenuate chronic pain. This study tested the antinociceptive properties of two novel NAS PAMs, ganaxolone and zuranolone, in segmental spinal nerve ligation (SNL)-induced neuropathic pain and complete Freund's adjuvant (CFA)-induced inflammation pain models. Spinally administered ganaxolone and zuranolone both exhibited dose-dependent analgesic effects but with quite different durations. This antinociceptive effect might be generated from elevated GABAergic inhibition, as the PAMs both enhanced GABA-evoked currents in SDH neurons, and the K+-Cl- cotransporter isoform 2 (KCC2) antagonist reversed the analgesic effect of the PAMs. Different from ganaxolone, zuranolone produced a durable increase in the surface expression of GABAA receptors and of the amplitude of spontaneous inhibitory currents, which may contribute to the long-lasting analgesic effect. Furthermore, the PAMs alleviated SNL-induced mechanical allodynia synergistically with diazepam or GABAA receptor activator muscimol at inactive doses, consistent with the non-competitive activity and distinct binding sites from benzodiazepines. In summary, our findings suggest that NASs may not only acutely modulate GABA receptor activity but also induce sustained metabotropic effects on GABAA receptors and thus exert long-lasting antinociceptive effects.

A Novel Compound DBZ Alleviates Chronic Inflammatory Pain and Anxiety-Like Behaviors by Targeting the JAK2-STAT3 Signaling Pathway

Chronic pain profoundly disrupts patients' daily lives and places a heavy burden on their families. Tanshinol Borneol Ester (DBZ), a novel synthetic derivative, has demonstrated anti-inflammatory and anti-atherosclerotic effects, yet its impact on the central nervous system (CNS) remains largely unexplored. This study systematically examines the CNS effects of DBZ through a combination of in vivo, in vitro, network pharmacology, and molecular docking approaches. In vivo, we utilized a mouse model of chronic inflammation induced by complete Freund's adjuvant (CFA) to evaluate DBZ's influence on pain, anxiety-like behaviors, and its modulation of inflammatory and oxidative stress markers within the anterior cingulate cortex (ACC). In vitro studies on primary mouse astrocytes assessed DBZ's effects on cell viability and inflammatory marker expression. Network pharmacology was employed to elucidate DBZ's potential molecular targets and pathways, While molecular docking provides valuable docking confirmed its interactions with key components of the JAK2-STAT3 signaling pathway. Our findings demonstrate that DBZ effectively mitigates CFA-induced chronic pain and anxiety-like behaviors. It significantly suppresses astrocytes activation, reduces levels of pro-inflammatory cytokines IL-1β, IL-6, and TNF-α, and diminishes oxidative stress markers such as ROS and MDA, while enhancing SOD levels. Moreover, DBZ modulates excitatory synaptic proteins and the JAK2-STAT3 signaling pathway in the ACC, suggesting its role in neuroprotection. These results position DBZ as a promising candidate for the treatment of chronic pain and anxiety, offering a potential foundation for the development of new therapeutic agents.

Unmasking the relationship between CGRP and glutamate: from peripheral excitation to central sensitization in migraine

The exact mechanisms that trigger the activation of the trigeminovascular system in migraine remain unclear. The involvement of calcitonin gene-related peptide (CGRP) in migraine is well-documented, and treatments aimed at blocking CGRP activity have proven successful in reducing migraine attacks for some patients. However, around one third of individuals do not respond to these therapies, which are also limited by factors like cost, side effects, and contraindications. There is growing evidence suggesting that glutamate, an excitatory neurotransmitter, plays a crucial role in the onset and maintenance of migraine pain, partially by enhancing CGRP release. Increased glutamate levels have been linked to both peripheral and central sensitization, potentially contributing to the development and persistence of chronic migraine. The relationship between CGRP and glutamate is complex, with glutamate possibly acting as an upstream trigger for CGRP release. This review examines the interplay between CGRP and glutamate, and their involvement in both peripheral and central sensitization. It also explores the therapeutic potential of targeting either glutamate or CGRP, aiming to address both peripheral and central migraine mechanisms. Finally, the role of triggers in migraine initiation at the peripheral level is discussed, offering insights into potential preventive strategies.

Deciphering the Structural and Functional Effects of the R1150W Non-Synonymous Variant in SCN9A Linked to Altered Pain Perception

The SCN9A gene, a critical regulator of pain perception, encodes the voltage-gated sodium channel Nav1.7, a key mediator of pain signal transmission. This study conducts a multimodal assessment of SCN9A, integrating genetic variation, structural architecture, and molecular dynamics to elucidate its role in pain regulation. Using advanced computational methods, I-TASSER simulations generated structural decoys of the SCN9A homology domain, producing an ensemble of conformational states. SPICKER clustering identified five representative models with a C-score of -3.19 and TM-score of 0.36 ± 0.12, reflecting moderate structural similarity to experimental templates while highlighting deviations that may underpin functional divergence. Validation via ProSA-web supported model reliability, yielding a Z-score of -1.63, consistent with native-like structures. Central to the analysis was the R1150W non-synonymous variant, a potential pathogenic variant. Structural modeling revealed localized stability in the mutant conformation but disrupted hydrogen bonding and altered charge distribution. Its pathogenicity was underscored by a high MetaRNN score (0.7978498) and proximity to evolutionarily conserved regions, suggesting functional importance. Notably, the variant lies within the Sodium-Ion-Transport-Associated Domain, where perturbations could impair ion conductance and channel gating-mechanisms critical for neuronal excitability. These findings illuminate how SCN9A variants disrupt pain signaling, linking genetic anomalies to molecular dysfunction. While computational insights advance mechanistic understanding, experimental validation is essential to confirm the variant's impact on Nav1.7 dynamics and cellular physiology. By refining SCN9A's molecular blueprint and highlighting its therapeutic potential as a target for precision analgesics, this work provides a roadmap for mitigating pain-related disorders through channel-specific modulation. Integrating structural bioinformatics with functional genomics, this study deciphers SCN9A's role in pain biology, laying the groundwork for novel strategies to manage pathological pain.

Gut Microbiota: A Modulator and Therapeutic Target for Chronic Pain

Chronic pain is a prevalent condition, impacting nearly one-fifth of the global population. Despite the availability of various clinical treatments, each comes with inherent limitations, and few offer a complete cure, resulting in a significant social and economic burden. Therefore, it is important to determine the pathogenesis and causes of chronic pain. Numerous studies have shown a close link between the intestinal microflora and chronic pain. The gut microbiota can exert their effects on chronic pain through both central and peripheral mechanisms and is able to communicate with the brain through its own components or metabolites. They also can regulate chronic pain by affecting pro- and anti-inflammatory cells. This review is aimed at reviewing the connection between gut flora and different types of chronic pain, including visceral pain, neuropathic pain, inflammatory pain, musculoskeletal pain, migraine, and chronic cancer pain; exploring the central and peripheral mechanisms of the influence of gut flora on chronic pain; and attempting to provide novel treatment options for chronic pain, that is, the gut microbiota can be regulated by probiotics, fecal microbial transplantation, and natural products to treat chronic pain. By examining the intricate relationship between gut flora and chronic pain, the review sought to pave the way for new treatment strategies that target the gut microbiota, offering hope for more effective pain management.

An evaluation of distinct adeno-associated virus vector strategies for driving transgene expression in spinal inhibitory neurons of the rat

The spinal cord dorsal horn (DH) is essential for processing and transmitting nociceptive information. Its neuronal subpopulations exhibit significant heterogeneity in morphology and intrinsic properties, forming complex circuits that remain only partially understood. Under physiological and pathological conditions, inhibitory interneurons in the DH are of particular interest. These neurons modulate and refine pain-related signals entering the central nervous system. The ability to selectively target these inhibitory interneurons is key to investigating the underlying circuitry and mechanisms of pain processing, as well as to understand the specific role of inhibitory signaling within these processes. We employed a viral vector approach to deliver a fluorescent reporter protein specifically to inhibitory interneurons in the rat spinal cord. Using adeno-associated virus (AAV) vectors designed to express enhanced green fluorescent protein (EGFP) under the control of various promoters, we targeted distinct subtypes of spinal inhibitory interneurons. Through immunostaining, in situ hybridization, and confocal imaging, we evaluated the specificity and efficacy of these promoters. Our findings revealed that the promoter/vector combinations used did not achieve the desired specificity for targeting distinct interneuron populations in the DH. Despite these limitations, this work provides valuable insights into the potential and challenges of designing AAV-based approaches for selective neuronal targeting. These results emphasize the need for further refinement of promoter designs to achieve precise and reliable expression in specific spinal interneuron subtypes. Addressing these challenges will be crucial for advancing our understanding of spinal nociceptive circuits and developing targeted therapeutic approaches for pain syndromes.

An overview of the non-procedural treatment options for peripheral neuropathic pain

Peripheral neuropathic pain is common in patients with peripheral nerve injury and can significantly impact both their function and quality of life. There is a wide variety of non-interventional treatment approaches, including pharmacologic therapy, physical/occupational therapy, modalities (therapeutic, mechanical, thermal, etc.), psychology, and lifestyle modification. First line pharmacologic therapy for peripheral neuropathic pain includes gabapentinoids, tricyclic antidepressants, and serotonin-norepinephrine reuptake inhibitors. Other classes of medications, such as topical treatments, opioids, and cannabinoids, have more limited usefulness in treatment but remain part of a treatment regimen. Physical and occupational therapy, psychological interventions, and lifestyle medicine are important adjuncts in the treatment and prevention of future peripheral neuropathic pain. The strength of the evidence supporting each intervention varies, with that for pharmacologic intervention being the strongest. A combination of these options tailored to the individual needs of the patient likely will result in the best treatment outcome for peripheral neuropathic pain.

The autonomic nervous system and bone health in chronic kidney disease

Besides the well-known role of hormonal factors in mineral and bone metabolism, the sympathetic nervous system participates in this regulation by inhibiting bone formation and promoting bone resorption, primarily via β-adrenergic receptors expressed on osteoblasts. Conversely, the parasympathetic system, through cholinergic signalling, inhibits osteoclast activity, promoting bone formation and maintaining skeletal homeostasis. This review presents the role of the autonomic nervous system, with particular focus on the potential role of β-blockers, especially β1-selective blockers, in modulating bone health in people with normal kidney function and those with CKD. While early studies with non-selective β-blockers like propranolol showed mixed results, recent findings in postmenopausal women suggested that β1-selective β-blockers could enhance bone density by modulating sympathetic activity. Trial emulation using large databases and eventually randomized controlled trials are needed to test the hypothesis that β-blockade can favourably impact bone disease in patients with kidney failure.

Glial-modulating agents for the treatment of pain: a systematic review

ABSTRACT

Preclinical research supports a critical role for nervous system glia in pain pathophysiology. This systematic review of human trials of potential glia-modulating drugs for the prevention or treatment of pain followed a predefined search strategy and protocol registration. We searched for English language, randomized, double-blind trials comparing putative glia-modulating drugs to placebo or other comparators. The primary outcomes included validated participant-reported measures of pain intensity or relief and, in studies of opioid administration, measures of opioid consumption and/or opioid-related adverse effects. Twenty-six trials (2132 participants) of glial modulators (12 minocycline, 11 pentoxifylline, and 3 ibudilast) were included. Because of clinical heterogeneity related to study drug, participant population, outcome measures, and trial design, no meta-analysis was possible. Only 6 trials reported a positive effect of the treatment (pentoxifylline-4 trials; minocycline-2 trials), whereas 11 trials reported mixed results and 9 trials reported no effect. This review does not provide convincing evidence of efficacy of current pharmacological targets of nervous system glial function for pain treatment or prevention. However, in light of ample preclinical evidence of the importance of neuroimmune signalling and glial functions in pain pathophysiology, continued strategic human research is anticipated to identify (1) drugs with maximal activity as selectively targeted glial modulators, (2) the necessary timing and duration of pharmacological glial modulation needed for pain prevention or treatment for specific injuries or pain conditions, and (3) the best design of future clinical trials of glial-targeted drugs for pain treatment and/or prevention.

Investigating Mechanically Activated Currents from Trigeminal Neurons of Nonhuman Primates

Pain sensation often involves mechanical modalities. Mechanically activated (MA) ion channels on sensory neurons underly responsiveness to mechanical stimuli. MA current properties have mainly been derived from rodent sensory neurons. This study aimed to address gaps in knowledge regarding MA current properties in trigeminal (TG) neurons of a higher-order species, common marmoset nonhuman primates (NHP). MA currents triggered by a piezoactuator were recorded in patch-clamp configuration. MA responses were associated with action potential (AP) properties, such as width, dV/dt on the falling phase, and presence/absence of AP firing in NHP TG neurons. According to responsiveness to mechanical stimuli and AP properties, marmoset TG neurons were clustered into four S-type and five M-type groups. S-type TG neurons had broader AP with two dV/dt peaks on the AP falling phase. Only one S-type group of NHP TG neurons produced small MA currents. M-type TG neurons had narrow AP without two dV/dt peaks on the AP falling phase. M-type NHP TG neurons, except for one group, showed MA currents. We additionally used immunohistochemistry to confirm the presence of known sensory neuronal types such as unmyelinated peptidergic CGRP+/trpV1+, unmyelinated nonpeptidergic MrgprD+ and CGRP-/trpV1+, and myelinated peptidergic CGRP+/trpV1- and nonpeptidergic CGRP- and PV+ NHP TG neurons. Overall, marmoset TG neurons and associated MA currents have many similarities compared with reported data from mouse sensory neurons. However, there are notable differences such as lower percentage of small NHP TG neurons responding to mechanical stimuli and absence of fast inactivating MA currents.

Neuro-Nutritional Approach to Neuropathic Pain Management: A Critical Review

Pain is a significant global public health issue that can interfere with daily activities, sleep, and interpersonal relationships when it becomes chronic or worsens, ultimately impairing quality of life. Despite ongoing efforts, the efficacy of pain treatments in improving outcomes for patients remains limited. At present, the challenge lies in developing a personalized care and management plan that helps to maintain patient activity levels and effectively manages pain. Neuropathic pain is a chronic condition resulting from damage to the somatosensory nervous system, significantly impacting quality of life. It is partly thought to be caused by inflammation and oxidative stress, and clinical research has suggested a link between this condition and diet. However, these links are not yet well understood and require further investigation to evaluate the pathways involved in neuropathic pain. Specifically, the question remains whether supplementation with dietary antioxidants, such as melatonin, could serve as a potential adjunctive treatment for neuropathic pain modulation. Melatonin, primarily secreted by the pineal gland but also produced by other systems such as the digestive system, is known for its anti-inflammatory, antioxidant, and anti-aging properties. It is found in various fruits and vegetables, and its presence alongside other polyphenols in these foods may enhance melatonin intake and contribute to improved health. The aim of this review is to provide an overview of neuropathic pain and examine the potential role of melatonin as an adjunctive treatment in a neuro-nutritional approach to pain management.

The Effect of Fremanezumab on Pain in Patients with Complex Regional Pain Syndrome: Study Protocol of a Randomized, Double-Blind, Proof-of-Concept, Placebo-Controlled Trial

Background/Objectives: Complex regional pain syndrome (CRPS) is a primary pain condition that can develop in a limb after a trauma. Although the condition is rare, it may cause lifelong pain and disability. Evidence-based treatments are limited. Neurogenic inflammation induced by the release of neuropeptides, such as calcitonin gene-related peptide (CGRP), is thought to play an important role in the pathophysiology of CRPS. Recently, drugs targeting CGRP have proven to be effective and well tolerated in the treatment of migraine, but their efficacy in other pain conditions, including CRPS, is unclear. The aim of this study is to assess the efficacy of the anti-CGRP antibody fremanezumab on pain in CRPS. Methods: In this randomized, double-blind, placebo-controlled, proof-of-concept study, 60 adult patients with CRPS with a disease duration of 3-36 months are randomized to treatment for eight weeks with fremanezumab 225 mg or placebo administered subcutaneously at a 1:1 rate. The primary objective is to compare the change in pain intensity from baseline to the last week of treatment between fremanezumab and the placebo. Other objectives are to assess pain relief and differences in clinical signs between the groups and to examine if the effect can be predicted by CGRP biomarkers. Adverse events and blinding will also be assessed. Conclusions: If found effective, fremanezumab and other anti-CGRP antibodies may emerge as a mechanism-based treatment option for patients with CRPS, which could hopefully improve the overall care of patients with this devastating disease.

ANO1: central role and clinical significance in non-neoplastic and neoplastic diseases

Anoctamin 1 (ANO1), also known as TMEM16A, is a multifunctional protein that serves as a calcium-activated chloride channel (CaCC). It is ubiquitously expressed across various tissues, including epithelial cells, smooth muscle cells, and neurons, where it is integral to physiological processes such as epithelial secretion, smooth muscle contraction, neural conduction, and cell proliferation and migration. Dysregulation of ANO1 has been linked to the pathogenesis of numerous diseases. Extensive research has established its involvement in non-neoplastic conditions such as asthma, hypertension, and gastrointestinal (GI) dysfunction. Moreover, ANO1 has garnered significant attention for its role in the development and progression of cancers, including head and neck cancer, breast cancer, and lung cancer, where its overexpression correlates with increased tumor growth, metastasis, and poor prognosis. Additionally, ANO1 regulates multiple signaling pathways, including the epidermal growth factor receptor (EGFR) pathway, the mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK) pathway, and phosphatidylinositol 3-kinase (PI3K)/protein kinase B (AKT) pathway, among others. These pathways are pivotal in regulating cell proliferation, migration, and invasion. Given its central role in these processes, ANO1 has emerged as a promising diagnostic biomarker and therapeutic target. Recent advancements in ANO1 research have highlighted its potential in disease diagnosis and treatment. Strategies targeting ANO1, such as small molecule modulators or gene-silencing techniques, have shown preclinical promise in both non-neoplastic and neoplastic diseases. This review explores the latest findings in ANO1 research, focusing on its mechanistic involvement in disease progression, its regulation, and its therapeutic potential. Modulating ANO1 activity may offer novel therapeutic strategies for effectively treating ANO1-associated diseases.

Perioperative Pain Management for Mastectomy in Dogs: A Narrative Review

Mammary tumours are the most common neoplasia in adult female dogs. Mastectomy leads to moderate to severe pain. Effective pain management is crucial in veterinary medicine. This review outlines analgesic techniques for managing perioperative pain in dogs undergoing mastectomy. A literature search on dog mastectomy analgesia was conducted from January 2001 to January 2025. Pre-emptive meloxicam reduces postoperative cardiovascular changes without affecting renal function. When combined with gabapentin, it lowers the need for rescue analgesic opioids, similar to robenacoxib. With regard to tramadol, it offers contrasting analgesia in the studies considered when used alone, while its effect appears enhanced when used in combination with meloxicam/dipyrone. However, methadone provides superior pain control, especially when given preoperatively or intraoperatively. The combination of ketamine, lidocaine, and maropitant enhances pain management, while fentanyl, alone or with lidocaine and ketamine, is effective for intraoperative pain control. Local infiltration with lidocaine/bupivacaine provides effective pain control, and devices like Comfont-in® or WSC facilitate this process. Tumescent anaesthesia using lidocaine/ropivacaine allows for extensive infiltration of the mammary gland. Epidural analgesia, paravertebral blocks, and TAP blocks are beneficial in multimodal protocols. Transdermal patches containing fentanyl/buprenorphine offer prolonged analgesia, while electroacupuncture can help reduce the need for rescue analgesics. Multimodal analgesic protocols are crucial for effective pain management in dog mastectomy surgeries, minimising the need for rescue opioids.

A distributed coding logic for thermosensation and inflammatory pain

Somatosensory neurons encode detailed information about touch and temperature and are the peripheral drivers of pain1,2. Here by combining functional imaging with multiplexed in situ hybridization3, we determined how heat and mechanical stimuli are encoded across neuronal classes and how inflammation transforms this representation to induce heat hypersensitivity, mechanical allodynia and continuing pain. Our data revealed that trigeminal neurons innervating the cheek exhibited complete segregation of responses to gentle touch and heat. By contrast, heat and noxious mechanical stimuli broadly activated nociceptor classes, including cell types proposed to trigger select percepts and behaviours4-6. Injection of the inflammatory mediator prostaglandin E2 caused long-lasting activity and thermal sensitization in select classes of nociceptors, providing a cellular basis for continuing inflammatory pain and heat hypersensitivity. We showed that the capsaicin receptor TRPV1 (ref. 7) has a central role in heat sensitization but not in spontaneous nociceptor activity. Unexpectedly, the responses to mechanical stimuli were minimally affected by inflammation, suggesting that tactile allodynia results from the continuing firing of nociceptors coincident with touch. Indeed, we have demonstrated that nociceptor activity is both necessary and sufficient for inflammatory tactile allodynia. Together, these findings refine models of sensory coding and discrimination at the cellular and molecular levels, demonstrate that touch and temperature are broadly but differentially encoded across transcriptomically distinct populations of sensory cells and provide insight into how cellular-level responses are reshaped by inflammation to trigger diverse aspects of pain.

Gaussian white noise stimulation as an alternative method to excite sensory neurons

Introduction

Peripheral nerve endings of dorsal root ganglion (DRG) neurons act as nociceptors and generate action potentials in response to noxious stimuli. Primary cultures of dissociated DRG have been used extensively to study changes neuronal excitability caused by either analgesics or pathological conditions, such as inflammation. The dissociation procedure can be viewed as a form of axotomy, and one might expect a resulting increase in excitability of the neurons during the subsequent culture period. However, changes in firing properties of DRG neurons over time in vitro have not been investigated systematically.

Methods

Thus, the current experiments compared action potential firing in dissociated DRG neurons after one to 7 days in culture and examined Gaussian white noise as novel stimulation paradigm. Primary cultures of DRG neurons were recorded in perforated patch current-clamp. Action potentials were evoked either by a sequence of five rectangular current pulses with increasing amplitudes or by Gaussian white noise of varying RMS amplitudes and frequencies.

Results

Conventional rectangular current injections triggered 19 ± 20 action potentials in cells when recorded within 24 h after dissociation. After 7 days in culture, DRG neurons fired 4.3 ± 0.7 action potentials in response to current pulses. Inflammatory mediators increased numbers of action potentials evoked by rectangular current pulses within 24 h after dissociation to 66 ± 54, but left those elicited after 7 days in vitro unaltered (4.3 ± 0.5). In the same set of neurons kept in culture for 7 days, Gaussian white noise stimuli triggered 1,540 ± 470 action potentials, and this number was increased to 2089 ± 685 by inflammatory mediators. The Kv7 channel activator retigabine and the paracetamol metabolite n-acetyl-p-benzoquinone imine (NAPQI) decreased numbers of action potentials triggered by Gaussian white noise, but failed to do so when rectangular current pulses were used as stimuli, both in neurons after 7 days in culture.

Discussion

These results demonstrate a decrease in the excitability of DRG neurons from day one to 7 after dissociation and reveal Gaussian white noise as reliable trigger of action potential firing in these neurons.

An accumbal microcircuit for the transition from acute to chronic pain

Persistent nociceptive inputs arising from peripheral tissues or/and nerve injuries cause maladaptive changes in neurons or neural circuits in the central nervous system, which further confer acute injury into chronic pain transitions (pain chronification) even after the injury is resolved. However, the critical brain regions and their neural mechanisms involved in this transition have not yet been elucidated. Here, we reveal an accumbal microcircuit that is essential for pain chronification. Notably, the increase of neuronal activity in the nucleus accumbens shell (NAcS) in the acute phase (<7 days) and in core (NAcC) in the chronic phase (14-21 days) was detected in a neuropathic pain mouse model. Importantly, we demonstrated that the NAcS neuronal activation in the acute phase of injury was necessary and sufficient for the development of chronic neuropathic pain. This process was mediated by the accumbal dopamine D2 receptor-expressing neuronal microcircuit from NAcS to NAcC. Thus, our findings reveal an accumbal microcircuit mechanism for pain chronification and suggest that the early intervention targeting this microcircuit may provide a therapeutic approach to pain chronification.

The primary somatosensory sensory cortex-basolateral amygdala pathway contributes to comorbid depression in spared nerve injury-induced neuropathic pain

Comorbid depression in chronic pain is a prevalent health problem, yet the underlying neural mechanisms remain largely unexplored. This study identified a dedicated neural circuit connecting the hind limb region of the primary somatosensory cortex (S1HL) to the basolateral amygdala (BLA) that mediated neuropathic pain-induced depression. We demonstrated that depressive-like behaviors in the chronic phase of a mouse neuropathic pain model were associated with heightened activity in the S1HL and BLA. Using viral tracing and RNAscope in situ hybridization, we characterized the circuit architecture of S1HL glutamatergic projections to BLA cholecystokinin (CCK) neurons (S1HLGlu → BLACCK). In vivo fiber photometry calcium imaging revealed that both the S1HL BLA-projecting afferents and the BLA S1HL-innervating neurons exhibited hyperactivity in neuropathic pain-induced depressive states. Chemogenetic inhibition of the S1HL → BLA circuit could block neuropathic pain-induced depressive-like behaviors. In addition, specific knockdown of CCK expression in BLA S1HL-innervating neurons alleviated these depressive-like behaviors. Our findings demonstrated that the cortical-amygdala circuit S1HLGlu → BLACCK drove the transition from chronic pain to depression, thus suggesting a potential neural circuit basis for treating chronic pain-related depressive disorders.

Differential modification of ascending spinal outputs in acute and chronic pain states

Pain hypersensitivity arises from the induction of plasticity in peripheral and spinal somatosensory neurons, which modifies nociceptive input to the brain, altering pain perception. We applied longitudinal calcium imaging of spinal dorsal projection neurons to determine whether and how the representation of somatosensory stimuli in the anterolateral tract, the principal pathway transmitting nociceptive signals to the brain, changes between distinct pain states. In healthy mice, we identified stable outputs selective for cooling or warming and a neuronal ensemble activated by noxious thermal and mechanical stimuli. Induction of acute peripheral sensitization by topical capsaicin transiently re-tuned nociceptive output neurons to encode low-intensity stimuli. In contrast, peripheral nerve injury resulted in a persistent suppression of innocuous spinal outputs coupled with persistent activation of a normally silent population of high-threshold neurons. These results demonstrate differential modulation of spinal outputs to the brain during nociceptive and neuropathic pain states.

Human assembloid model of the ascending neural sensory pathway

Somatosensory pathways convey crucial information about pain, touch, itch and body part movement from peripheral organs to the central nervous system1,2. Despite substantial needs to understand how these pathways assemble and to develop pain therapeutics, clinical translation remains challenging. This is probably related to species-specific features and the lack of in vitro models of the polysynaptic pathway. Here we established a human ascending somatosensory assembloid (hASA), a four-part assembloid generated from human pluripotent stem cells that integrates somatosensory, spinal, thalamic and cortical organoids to model the spinothalamic pathway. Transcriptomic profiling confirmed the presence of key cell types of this circuit. Rabies tracing and calcium imaging showed that sensory neurons connect to dorsal spinal cord neurons, which further connect to thalamic neurons. Following noxious chemical stimulation, calcium imaging of hASA demonstrated a coordinated response. In addition, extracellular recordings and imaging revealed synchronized activity across the assembloid. Notably, loss of the sodium channel NaV1.7, which causes pain insensitivity, disrupted synchrony across hASA. By contrast, a gain-of-function SCN9A variant associated with extreme pain disorder induced hypersynchrony. These experiments demonstrated the ability to functionally assemble the essential components of the human sensory pathway, which could accelerate our understanding of sensory circuits and facilitate therapeutic development.

Dual Kv7.2/3-TRPV1 modulators inhibit nociceptor hyperexcitability and alleviate pain without target-related side effects

ABSTRACT

Persistent or chronic pain is the primary reason people seek medical care, yet current therapies are either limited in efficacy or cause intolerable side effects. Diverse mechanisms contribute to the basic phenomena of nociceptor hyperexcitability that initiates and maintains pain. Two prominent players in the modulation of nociceptor hyperexcitability are the transient receptor potential vanilloid type 1 (TRPV1) ligand-gated ion channel and the voltage-gated potassium channel, Kv7.2/3, that reciprocally regulate neuronal excitability. Across many drug development programs targeting either TRPV1 or Kv7.2/3, significant evidence has been accumulated to support these as highly relevant targets; however, side effects that are poorly separated from efficacy have limited the successful clinical translation of numerous Kv7.2/3 and TRPV1 drug development programs. We report here the pharmacological profile of 3 structurally related small molecule analogues that demonstrate a novel mechanism of action (MOA) of dual modulation of Kv7.2/3 and TRPV1. Specifically, these compounds simultaneously activate Kv7.2/3 and enable unexpected specific and potent inhibition of TRPV1. This in vitro potency translated to significant analgesia in vivo in several animal models of acute and chronic pain. Importantly, this specific MOA is not associated with any previously described Kv7.2/3 or TRPV1 class-specific side effects. We suggest that the therapeutic potential of this MOA is derived from the selective and specific targeting of a subpopulation of nociceptors found in rodents and humans. This efficacy and safety profile supports the advancement of dual TRPV1-Kv7.2/3 modulating compounds into preclinical and clinical development for the treatment of chronic pain.

A Systematic Review of the Prevalence of Overactive Bladder in Women with Non-Urinary Tract Endometriosis and the Effect of Endometriosis Surgery on Symptoms of Overactive Bladder

INTRODUCTION AND HYPOTHESIS

Overactive bladder (OAB) is characterised by urinary urgency, with or without incontinence, often accompanied by daytime frequency and nocturia, in the absence of urinary tract infection or other identifiable causes. Population studies estimate the prevalence of OAB at 12.8% (EPIC study), increasing with age, reaching up to 43% after age 40. Endometriosis affects about 10% of women of reproductive age. Both OAB and endometriosis are chronic and negatively impact women's quality of life. They appear to share a common pathophysiology related to central sensitisation. We hypothesised that OAB and endometriosis might co-exist, and surgical excision of endometriosis could alleviate OAB symptoms. We aimed to assess the prevalence of OAB in patients with endometriosis and examine the effect of endometriosis surgery on OAB symptoms.

METHODS

A systematic search of MEDLINE, PubMed, Embase, and CINAHL-Plus identified studies reporting on endometriosis and OAB or overlapping conditions such as interstitial cystitis. Studies on bladder or ureteric endometriosis were excluded.

RESULTS

Six studies (772 participants) were included. The prevalence of OAB in endometriosis patients ranged from 9.4% (Brazil) to 32% (France). OAB diagnosis varied, with tools such as International Consultation of Incontinence Modular Questionnaire on Female Lower Urinary Tract Symptoms, Core Lower Urinary Tract Symptom Score, Bristol Female Lower Urinary Tract Symptoms, and urodynamics. Surgical outcomes were inconsistent, with no improvement in three studies, equivocal in one, and worsened in another.

CONCLUSION

Overactive bladder and non-urinary tract endometriosis may co-occur in 20.5% of patients, with surgery showing variable effects on OAB symptoms. Further standardised global research is warranted to fill in evidence gaps such as whether pre-operative desensitisation could improve surgical and quality-of-life outcomes.

Early life microbiota colonization programs nociceptor sensitivity by regulating NGF production in mast cells

Recent evidence suggests that the gut microbiota can influence pain sensitivity, highlighting the potential for microbiota-targeted pain interventions. During early life, both the microbiota and nociceptors are fine-tuned and respond to environmental factors, however, little is known about how they interact with each other. Using germ-free and gnotobiotic models, we demonstrate that microbiota colonization controls nociceptor sensitivity, partly by modulating mast cell production of nerve growth factor (NGF). We report that germ-free mice respond less to thermal and capsaicin-induced stimulation, which correlates with reduced trafficking of TRPV1 to the cell membrane of nociceptors. In germ-free mice, mast cells express lower levels of NGF. Hyposensitivity to thermal and capsaicin-induced stimulation, reduced TRPV1 trafficking, and decreased NGF expression are reversed when mice are colonized at birth, but not when colonization occurs after weaning. Inhibition of mast cell degranulation and NGF signaling during the first weeks of life in colonized mice leads to a hyposensitive phenotype in adulthood, demonstrating a role for mast cells and NGF signaling in linking early life colonization with nociceptor sensitivity. These findings implicate the early life microbiota in shaping mast cell NGF production and nociceptor sensitivity later in life. SIGNIFICANCE STATEMENT: Nociceptors are specialized sensory neurons that detect and transduce painful stimuli. During the early postnatal period, nociceptors are influenced by sensory experiences and the environment. Our findings demonstrate that gut microbiota colonization is essential in setting the threshold of nociceptor responses to painful stimuli. We show that early-life bacterial colonization controls the production of nerve growth factor by mast cells, affecting our sensitivity to pain later in life. Our study highlights the potential for developing new pain treatments that target the gut microbiome.

Activation of GABAergic neurons in the dorsal raphe nucleus alleviates hyperalgesia induced by ovarian hormone withdrawal

ABSTRACT

Menopausal and postmenopausal women, characterized by a significant reduction in ovarian hormones, have a high prevalence of chronic pain with great pain intensity. However, the underlying mechanism of hyperalgesia induced by ovarian hormone withdrawal remains poorly understood. Here, we report that decreases in the activity and excitability of GABAergic neurons in the dorsal raphe nucleus (DRN) are associated with hyperalgesia induced by ovariectomy in mice. Supplementation with 17β-estradiol, but not progesterone, is sufficient to increase the mechanical pain threshold in ovariectomized (OVX) mice and the excitability of DRN GABAergic (DRN GABA ) neurons. Moreover, activation of the DRN GABA neurons projecting to the lateral parabrachial nucleus was critical for alleviating hyperalgesia in OVX mice. These findings show the essential role of DRN GABA neurons and their modulation by estrogen in regulating hyperalgesia induced by ovarian hormone withdrawal, providing therapeutic basis for the treatment of chronic pain in physiological or surgical menopausal women.

Established and emerging roles of protein kinases in regulating primary sensory neurons in injury-and inflammation-associated pain

INTRODUCTION

Recent seminal neuroscience research has significantly increased our knowledge on cellular and molecular responses of various cells in the pain pathway to peripheral nerve injuries and inflammatory processes. Transcriptomic and epigenetic analysis of primary sensory neurons (PSNs) in animal models of peripheral injuries revealed new insights into altered gene expression profiles and epigenetic modifications, which, via increasing spinal nociceptive input, lead to the development of pain. Among the various classes of molecules involved in driving differential gene expression, protein kinases, the enzymes that catalyze the phosphorylation of molecules, are emerging to control histone modification and chromatin remodeling needed for the alteration in transcriptional activity.

AREAS COVERED

Here, we focused on how protein kinases contribute to transcriptomic changes and pathways of induced reprogramming within PSNs upon peripheral nerve injury and inflammation. We conducted systematic literature search across multiple databases, including PubMed, NIH ClinicalTrials.gov portal and GEOData from 1980 to 2024 and compared protein kinase expression frequencies between publicly available RNA sequencing datasets of PSNs and investigated differences in protein kinase expression levels after peripheral nerve injury.

EXPERT OPINION

Novel findings support a new concept that protein kinases constitute regulatory hubs of reprogramming of PSNs, which offers novel analgesic approaches.

Painful Mondays: Exploring Weekly Sleep Variations and Pain Perception in Healthy Women-An Experimental Study

BACKGROUND

Acute experimental sleep deprivation induces pain hypersensitivity, particularly in females. While the impact of extreme sleep loss on pain perception has been largely studied, how subtle sleep fluctuations, for example, sleep variations across the week, affect pain perception remains unclear. This study investigated how weekly sleep variations affect pain perception in young healthy women.

METHODS

A sleep-monitoring headband and self-reported questionnaire were used to assess sleep. Quantitative sensory testing was conducted on Monday and Friday, including heat, cold, pressure pain thresholds, tonic pain summation and conditioned pain modulation.

RESULTS

A total of 26 healthy young (23.9 ± 0.9 years) women were included. Repeated measures ANOVAs revealed significant sleep variation across the week, including differences in N3 sleep stage duration (M = 89.2 ± 5.42 min; p = 0.022, lowest on Friday and Sunday nights), bedtime (M = 00:56 AM ± 0.29; p = 0.038, latest on Friday vs. Sunday night) and wake-up time (M = 07:04 AM ± 0.30; p = 0.007 latest on Saturday vs. Monday morning). With most changes affecting Sunday night and Monday morning, pain sensitivity was higher on Monday compared to Friday, with a lower heat pain threshold (B = -11.89; p = 0.002) and increased heat pain summation (B = 1.65; p < 0.001).

CONCLUSIONS

The results showed higher heat pain hyperalgesia on Mondays due to weekly sleep variation. Since sleep is a modifiable factor, maintaining a consistent sleep schedule throughout the week could benefit pain management, particularly in chronic pain patients with less effective pain modulatory pathways.

STATEMENT OF SIGNIFICANCE

How weekly sleep variations in real life between weekends and weekdays affect pain perception has not been studied before. This paper provides the first evidence that natural weekend-weekday sleep alterations, including shifts in bedtime and wake-up time over the weekend and the transition back on Sunday night, heighten pain sensitivity on Monday-known as the 'Monday effect'. The compromised pain pathways on Monday underscore the importance of maintaining a consistent sleep schedule throughout the week, potentially benefiting patients with chronic pain.

STUDY PREREGISTRATION STATEMENT

The authors have nothing to report.

Pathophysiology and management of burn injury-induced pain

This review examines the pathophysiology and therapeutic management of burn injury-induced pain (BIP). Burn injury, occurring globally in about 11 million people, often induces the most intense pain, but its management remains suboptimal. The pain often persists even after complete wound healing and hospital discharge causing both long-term disability and neurological dysfunction. The fact that BIP persists well beyond the initial hospitalization is not well recognized and should be underscored as the pain involves even non-burned areas. The pathophysiology of the latter problem is poorly understood and needs further study. Opioids, the mainstay for moderate to severe pain relief after major burn injury, with time, have poor analgesic and serious side effects. Accurate assessment pain of BIP and its biology at different stages of treatment helps to provide effective treatments of the different etiological factors that cause BIP and their sequelae. Based on clinical and pre-clinical studies, we discuss the current knowledge on the underlying cellular and molecular mechanisms in the initiation and persistence of BIP during the acute phase and later phases of injury. Opioid receptor-mediated signaling changes per se and immune microglia responses in concert exaggerate nociceptive behavior. Both burn injury and opioids upregulate spinal NMDA receptor expression and microglia changes, which further exaggerate pain. BIP has inflammatory and neuropathic components. Pharmacological and non-pharmacological approaches currently available for management of BIP is discussed. Areas that need further study include the role of other central and peripheral factors in the exaggeration of pain well beyond wound healing. Novel non-opioid methods to rectify BIP is important to develop in view of the potential for opioid use disorder. The role of microbiome in chronic pain syndromes is an unexplored territory and its relevance to BIP needs further examination. Pruritus or itch, though very common and important in the pharmacotherapy of burns, the discussion of this topic is brief. Extensive review of this topic is beyond the scope of this review in view of the vast body of knowledge and varying and multiple treatment options.

Molecule-rich solutions for achieving novel non-opioid analgesics

Despite their efficacy, opioids have long been associated with risks of addiction, tolerance, and dependence, leaving an unmet clinical need for pain treatment. Efforts have been devoted to developing novel classes of pain-relieving medication that outperform current options in terms of pain relief, side-effect profiles, and potential for abuse, but with limited success. Recent advances in the neurobiology of pain have shed light on the potential of targeting non-opioid receptors involved in pain processing. In this review, we identify avenues, ranging from molecular-based approaches to molecule-rich solutions, for effectively identifying non-opioid analgesics free from the side effects associated with opioids.

Sensory neurons on guard: roles in pathogen defense and host immunity

The nervous system, like the immune system, constantly interfaces with the environment, encountering threats, including pathogens. Recent discoveries reveal an emerging role for sensory neurons in host defense and immunity. Sensory neurons detect infections either by directly sensing microbial signals or through immune mediators. Beyond pathogen detection, they modulate immune responses and local inflammation by interacting with immune cells, influencing inflammation and pathogen clearance. Additionally, sensory neurons trigger protective reflexes - such as pain, coughing, sneezing, and itching - that can help expel pathogens but may also facilitate their spread. Sensory neurons may also encode and shape long-term immunity. Understanding the roles of neurons in pathogen defense could offer new insights into infectious diseases and highlight therapeutic opportunities for immune modulation.

Psychological Treatment in the Management of Pain following Musculoskeletal Injury

Musculoskeletal injuries are a leading cause of pain and disability, with many patients developing chronic pain. While traditional management focuses on physical treatments, psychological interventions have emerged as a complementary approach. This study examines the role of psychological treatments in pain management after musculoskeletal injury, their efficacy, and their integration with existing treatment strategies. A review of literature, including systematic reviews and meta-analyses, was conducted to assess the effectiveness of psychological treatments such as cognitive-behavioral therapy (CBT), mindfulness-based stress reduction (MBSR), and pain neuroscience education (PNE). Studies on the impact of psychological distress on pain perception, circulating inflammatory biomarkers, and neuromuscular exercises were analyzed. Research indicates that psychological elements, particularly pain catastrophizing, anxiety, and depression, play crucial roles in determining both pain intensity and disability levels. Short-term improvements in pain intensity, functional capacity, and psychological well-being have been documented with CBT, MBSR, and PNE interventions. The integration of psychological approaches with physiotherapy demonstrates enhanced patient outcomes. Biological markers of inflammation, specifically CRP and IL-6, show potential as indicators of pain severity and treatment effectiveness. Notably, neuromuscular exercises have shown pain-reducing effects comparable to pharmaceutical interventions, though long-term efficacy data for psychological treatments remains variable. The integration of psychological interventions represents a significant advancement in musculoskeletal pain management, particularly in addressing the mental and emotional dimensions of pain experience. While current research supports their immediate benefits, additional investigation is necessary to determine long-term effectiveness and refine treatment approaches. Future research should emphasize individualized treatment protocols, technological integration, and robust longitudinal studies to maximize therapeutic outcomes.

Optogenetic activation of mechanical nociceptions to enhance implant osseointegration

Orthopedic implants with high elastic modulus often suffer from poor osseointegration due to stress shielding, a phenomenon that suppresses the expression of intracellular mechanotransduction molecules (IMM) such as focal adhesion kinase (FAK). We find that reduced FAK expression under stress shielding is also mediated by decreased calcitonin gene-related peptide (CGRP) released from Piezo2+ mechanosensitive nerves surrounding the implant. To activate these nerves minimally invasively, we develop a fully implantable, wirelessly rechargeable optogenetic device. In mice engineered to express light-sensitive channels in Piezo2+ neurons, targeted stimulation of the L2-3 dorsal root ganglia (DRG) enhances localized CGRP release near the implant. This CGRP elevation activates the Protein Kinase A (PKA)/FAK signaling pathway in bone marrow mesenchymal stem cells (BMSCs), thereby enhancing osteogenesis and improving osseointegration. Here we show that bioelectronic modulation of mechanosensitive nerves offers a strategy to address implant failure, bridging neuroregulation and bone bioengineering.

Effects of aging on experimentally induced pain perception during a distraction task

To investigate the effects of psychological (anxiety, depression, pain catastrophizing) aspects, pain sensitivity, cognitive performance and executive functions, on pain perception during a distraction task in an acute pain laboratory in young and elderly adults. Twenty-six young (age: 20.0 ± 1.6 years) and thirty-three elderly (age: 68.0 ± 3.8 years) adults completed four self-reported questionnaires (Hospital Anxiety and Depression Scale-HADS, Pain Anxiety Symptoms Scale-20-PASS/20, Pain Catastrophizing Scale-PCS, and Pittsburgh Sleep Quality Index-PSQI), pressure pain thresholds (PPTs), a battery of executive functions (working memory, cognitive flexibility, mental inhibition), and attention levels before performing two distraction tasks (1-back, 2-back). Pain was experimentally induced with a thermal stimulus applied at the non-dominant forearm to provoke moderate pain (70/100 points) before and during the distraction tasks. Age (young, elderly), psychological and psychophysical variables, and neurocognitive test performance levels (low, medium, high) were included in separate ANCOVAs to compare pain intensity at baseline and during distraction tasks. All ANOVAs revealed a main effect of distraction task, indicating that perceived pain intensity scores were lower during both distraction tasks (p < 0.001) compared to baseline. Overall, there was no significant effect of age on perceived pain intensity after distraction tasks, except for an interaction effect between the distraction task and age group depending on PPTs levels (F [2,49] = 3.7, p = 0.03). Elderly adults (with higher PPTs) reported lower perceived pain intensity during both distraction tasks compared to younger adults (lower PPTs). This study found that the hypoalgesic effect of a distraction task is not directly associated with age or neurocognitive function and attention levels in pain-free subjects, but it was related with higher PPTs (lower pressure pain hyperalgesia).

Male-Dominant Spinal Microglia Contribute to Neuropathic Pain by Producing CC-Chemokine Ligand 4 Following Peripheral Nerve Injury

Recent studies have revealed marked sex differences in pathophysiological roles of spinal microglia in neuropathic pain, with microglia contributing to pain exacerbation exclusively in males. However, the characteristics of pain-enhancing microglia, which are more prominent in males, remain poorly understood. Here, we reanalyzed a previously published single-cell RNA sequencing dataset and identified a microglial subpopulation that significantly increases in the spinal dorsal horn (SDH) of male mice following peripheral nerve injury. CC-chemokine ligand 4 (CCL4) was highly expressed in this subpopulation and its mRNA levels were increased in the SDH after partial sciatic nerve ligation (PSL) only in male mice. Notably, CCL4 expression was reduced in male mice following microglial depletion, indicating that microglia are the primary source of CCL4. Intrathecal administration of maraviroc, an inhibitor of the CCL4-CC-chemokine receptor 5 (CCR5) signaling pathway, after PSL, significantly suppressed mechanical allodynia only in male mice. Furthermore, intrathecal administration of CCL4 induced mechanical allodynia in both sexes, accompanied by increased expression of c-fos, a neuronal excitation marker, in the SDH. These findings highlight a sex-biased difference in the gene expression profile of spinal microglia following peripheral nerve injury, with elevated CCL4 expression in male mice potentially contributing to pain exacerbation.