Neuroinflammation and Central Sensitization in Chronic and Widespread Pain

Inhibition of mPFC norepinephrine improved chronic post-thoracotomy pain in adult rats

BACKGROUND

Chronic post-thoracotomy pain (CPTP) is characterized by high incidence, long duration, and severity of pain. Medial prefrontal cortex (mPFC) is a brain region closely associated with chronic pain, and norepinephrine is involved in pain regulation. But the role of mPFC norepinephrine in CPTP and its possible mechanism is unclear.

MATERIALS AND METHODS

Adult Sprague-Dawley (SD) male rats underwent sham or thoracotomy, and were microinjected with pAAV.Syn.shDβH.eGFP(AAV2/9) or vehicle into contralateral mPFC on the 3rd day after thoracotomy. The pain of rats was evaluated by mechanical withdrawal threshold and cold pain threshold around thoracotomy incision. Norepinephrine in mPFC microdialysates were determined by high performance liquid chromatography with electrochemical detection (HPLC-ECD). The mPFC was collected to assess norepinephrine synthase (dopamine beta-hydroxylase, DβH) and metabolic enzyme (monoamine oxidase A/B, MAO-A/B and catechol-O-methyltransferase, COMT), bradykinin, bradykinin receptor 2 (Bdkrb2), neuroinflammation (Iba1, IL-6 and TNF-α), Aquaporin-4 (AQP4) and IL-33.

RESULTS

Right thoracotomy reduced the mechanical withdrawal threshold and cold pain threshold around incision, the expression of AQP4 and IL-33, increased norepinephrine, DβH, bradykinin, Bdkrb2, Iba1 and IL-6, but had no impact on MAO-A, MAO-B, COMT and TNF-α in contralateral mPFC. Inhibition of norepinephrine in contralateral mPFC increased the mechanical withdrawal threshold and cold pain threshold, the expression of AQP4 and IL-33, reduced norepinephrine, DβH, Bdkrb2, Iba1 and TNF-α, but had no significant effect on bradykinin and IL-6 in contralateral mPFC after right thoracotomy.

CONCLUSIONS

Inhibition of norepinephrine in contralateral mPFC after thoracotomy improved CPTP. The potential mechanisms may include rescuing the expression of AQP4 and IL-33, as well as reducing neuroinflammation and Bdkrb2 expression.

Psychological and immunological associations with movement-evoked low back pain among older adults

Introduction

Low back pain (LBP) is a leading global factor in disability among older adults. Movement-evoked pain (MEP) is potentially an important mediator in the disability pathway but is predominantly tested in the laboratory.

Objectives

We aimed to explore MEP in the natural environment ("daily" MEP) and its correlation with laboratory MEP, along with potential psychological and immunological influences.

Method

Thirty-five older adults with persistent LBP attended a single laboratory session. Pain catastrophizing, pain-related fear of movement, and pain self-efficacy were measured by questionnaire. Resting inflammation and inflammatory reactivity to painful movement were evaluated using serum interleukin-6, tissue necrosis factor alpha, and C-reactive protein (CRP). Laboratory MEP was defined by aggregate pain intensity with a movement provocation test. Daily MEP was measured for the next 7 days using ecological momentary assessment.

Results

Laboratory MEP was strongly correlated with daily MEP (ρ = 0.780, P = <0.001). C-reactive protein (Hedges [g] = 0.266) and interleukin-6 (g = 0.433) demonstrated small to moderate reactivity to painful movement. After controlling for age and multimorbidity, pain catastrophizing and pain self-efficacy explained 24% to 37% variance in laboratory and daily MEP. Resting inflammatory markers were not associated with MEP; however, C-reactive protein reactivity to painful movement explained 19% to 25% variance in laboratory and daily MEP.

Conclusion

Preliminary indication is that laboratory and daily MEP may be proxy measures for one another, and that MEP is influenced by psychological and immunological factors. Future studies will aim to (1) validate findings among older adults with persistent LBP and (2) for clinical phenotyping, clarify complex relationships among psychological and immunological factors with disability pathway components like MEP.

Distinct functional cerebral hypersensitivity networks during incisional and inflammatory pain in rats

Although the pathophysiology of pain has been investigated tremendously, there are still many open questions with regard to specific pain entities and their pain-related symptoms. To increase the translational impact of (preclinical) animal neuroimaging pain studies, the use of disease-specific pain models, as well as relevant stimulus modalities, are critical. We developed a comprehensive framework for brain network analysis combining functional magnetic resonance imaging (MRI) with graph-theory (GT) and data classification by linear discriminant analysis. This enabled us to expand our knowledge of stimulus modalities processing under incisional (INC) and pathogen-induced inflammatory (CFA) pain entities compared to acute pain conditions. GT-analysis has uncovered specific features in pain modality processing that align well with those previously identified in humans. These include areas such as S1, M1, CPu, HC, piriform, and cingulate cortex. Additionally, we have identified unique Network Signatures of Pain Hypersensitivity (NSPH) for INC and CFA. This leads to a diminished ability to differentiate between stimulus modalities in both pain models compared to control conditions, while also enhancing aversion processing and descending pain modulation. Our findings further show that different pain entities modulate sensory input through distinct NSPHs. These neuroimaging signatures are an important step toward identifying novel cerebral pain biomarkers for certain diseases and relevant outcomes to evaluate target engagement of novel therapeutic and diagnostic options, which ultimately can be translated to the clinic.

Role of Central Sensitization Syndrome in Patients With Autonomic Symptoms

Background and Objectives

Idiosyncratic autonomic-like symptomatology, e.g., when objective autonomic tests cannot fully explain autonomic concerns, is poorly understood. We hypothesize that central sensitization plays a role in the autonomic symptoms-sings dichotomy.

Methods

This retrospective case-control study was conducted at Brigham and Women's Faulkner Hospital Autonomic Laboratory between 2022 and 2023 and analyzed patients who completed autonomic testing that included surveys (Central Sensitization Inventory [assessing central sensitization syndrome {CSS}], Compass-31 [assessing autonomic symptoms], Neuropathy Total Symptom Score-6 [assessing sensory symptoms]) and autonomic (Valsalva maneuver, deep breathing, sudomotor evaluation, and head-up tilt), cerebrovascular (cerebral blood flow velocity [CBFv]), respiratory (capnography), and neuropathic (skin biopsies for assessment of small fiber neuropathy) testing.

Results

In total, 555 patients were enrolled and 455 (78%) satisfied criteria for CSS. Patients with CSS were younger and more frequently female and had longer duration of symptoms, more comorbidities, and higher Compass-31 scores and NTSS-6 compared with non-CSS patients. Autonomic testing showed lower orthostatic end-tidal CO2 (p = 0.002) and larger orthostatic decline in CBFv (p < 0.001) in the CSS group. There was no difference in the peripheral nervous system markers (sudomotor tests and skin biopsies). The frequency of moderate autonomic failure (AF) (91.4% vs 95%, p = 0.321) was similar between the groups, but the CSS group had lower AF score (4.21 ± 3.34 vs 5.23 ± 4.08, p < 0.021).

Discussion

CSS is present in most patients with chronic autonomic concerns. Central sensitization amplifies autonomic symptoms presumably through perturbed interoceptive processing and can be an underlying mechanism driving idiosyncratic autonomic-like symptomatology. Patients with CSS had objective evidence of autonomic impairment; however, it was less severe than in non-CSS patients. Our study shows that CSS and AF coexist and both conditions need to be treated.

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.

Long-term folic acid treatment relieves chronic inflammatory pain and pain-induced anxiety by reducing MMP2 expression in rats

Chronic inflammatory pain is a top priority for arthritis patients seeking medical care. Despite the availability of NSAIDs and glucocorticoids, pain management becomes increasingly challenging due to central and peripheral sensitization. Previous studies have shown that Matrix metalloproteinase 2 (MMP2) promotes neuroinflammation by cleaving extracellular matrix proteins and activating pro-inflammatory cytokines. Folic acid acts as a promising candidate for the treatment of neuroinflammatory diseases due to its neuroprotective effects. However, the role of folic acid in inflammatory pain remains unclear. This study investigated the analgesic mechanisms of folic acid in inflammatory pain. Adult rats underwent inflammatory pain by injecting complete freund's adjuvant (CFA) into the right hindpaw. Behavioral tests were used to assess the paw withdrawal threshold (PWT) and paw withdrawal latency (PWL). The results demonstrated that CFA injection induced abnormal mechanical and thermal pain and increased MMP2 expression in L3-L5 DRG and SDH of CFA rats. MMP2 was mainly expressed in neurons rather than glial cells in L3-L5 DRG of CFA rats. We further discovered that MMP2 inhibitor auraptene or knockdown alleviated inflammatory pain in CFA rats. Interestingly, we observed that long-term folic acid treatment reversed MMP2 overexpression, resulting in sustained relief of chronic inflammatory pain. Consistently, long-term folic acid treatment also relieved pain-induced anxiety. These results indicated that folic acid had a protective role in chronic inflammatory pain and pain-induced anxiety by repressing MMP2 expression. Folic acid or auraptene might be promising therapeutic options for the treatment of chronic inflammatory pain.

Glutamate stress in the caudal nucleus tractus solitarii (nTS): Impact on respiratory function and synaptic signaling in an Alzheimer's disease model

Respiratory dysfunction is a prevalent comorbidity in Alzheimer's disease (AD), yet its underlying mechanisms are poorly understood. Using the Streptozotocin (STZ) -induced rat model of AD, which replicates respiratory dysfunction and brain pathologies observed in human AD, we analyzed how these impairments relate to central neurological integration within the peripheral chemoreflex. Our focus was on glutamatergic signaling at the synapse between peripheral chemoafferents and second-order neurons in the nucleus tractus solitarii (nTS), a critical brainstem center for respiratory control. Activating the peripheral chemoreflex with potassium cyanide (KCN) increased respiratory frequency. Response magnitudes to repeated KCN injections typically decreased over time, which was exacerbated in the STZ-AD group. Similarly, repeated glutamate nanoinjections into the caudal/commissural nTS caused a pronounced reduction of respiratory frequency responses in STZ-AD. Electrophysiological analysis of nTS neurons within the peripheral chemoreflex revealed increased network activity, enhanced excitatory postsynaptic currents evoked by solitary tract stimulation (TS-EPSCs), and elevated asynchronous glutamate release following high-frequency stimulation (aEPSCs). These data were consistent with molecular evidence for astrogliosis (elevated GFAP expression), reduced astrocytic glutamate uptake (decreased EAAT2 expression), and presynaptic calcium dysregulation (increased TRPV1 expression). Additionally, presynaptic metabotropic glutamate receptors (mGluR3) were downregulated, while postsynaptic ionotropic receptor expression remained unchanged. With high-frequency solitary tract stimulation, STZ-AD rats had greater frequency-dependent TS-EPSC depression than controls, mirroring the diminished respiratory responses to KCN and glutamate nanoinjections. Our findings connect neurophysiological and molecular changes at the first nTS synapse of the peripheral chemoreflex with impaired respiratory responses to hypoxia in the STZ-AD model.

Proposition of Two Subtypes of Patients at Risk of Suicide: Pain Hypersensitive Vs. Dissociative

PURPOSE OF REVIEW

The pain-suicide relationship is one of the most debated in recent literature, but theories and clinical evidence have often reached contrasting conclusions. Through a critical overview of theoretical, meta-analytical and empirical contributions, we aimed at advancing the conversation on the pain-suicide relationship by integrating research on related concepts, specifically inflammation and dissociation, and their effects on interoceptive processes and pain perception.

RECENT FINDINGS

Ideation-to-action theories consider increased pain tolerance a key risk factor for the transition from suicidal ideation to attempt. However, several meta-analytical findings suggest that suicidal thoughts and behaviors are associated with inflammation-induced pain sensitization. On the one hand, inflammation contributes to the development and maintenance of chronic pain conditions and mood disorders, and is associated with interoceptive hypervigilance and pain hypersensitivity. Moreover, a trait of increased pain tolerance does not seem to distinguish the individuals attempting suicide among those living with suicidal thoughts. On the other, temporary hypoalgesia is often activated by dissociative experiences. Highly dissociative individuals can indeed be exposed to frequent disintegration of interoceptive processes and transitory hyposensitivity to pain. In light of this, two different patterns of responses to stress (i.e. inflammation vs. dissociation) may characterize different kinds of patients at risk of suicide, associated with specific patterns of interoceptive functioning, pain sensitivity and possibly suicidal ideation. This proposition is partially supported by neuroimaging studies on post-traumatic stress disorder and psychodynamic perspectives on neurodevelopment, as well as alternative clustering models of suicidal behavior. Theoretical, meta-analytical and neurobiological evidence highlight two opposite directions in the pain-suicide relationship: hyper- vs. hyposensitivity. Such contrasts may be explained by the existence of two tendencies in stress-response, namely inflammation and dissociation, defining two different subtypes of patients at risk of suicide. We thus propose the existence of a hypersensitive subtype, defined by underlying neuroinflammatory processes, increased vulnerability to chronic pain and mood disorders, interoceptive hypervigilance, pain hypersensitivity and potentially more persistent suicidal ideation. We further hypothesize a dissociative subtype, characterized by greater trait dissociation, vulnerability to depersonalization and derealization, frequent disintegration of interoceptive processes, transient pain hyposensitivity and abrupt peaks in suicidal ideation.

Neonatal exposure to morphine results in prolonged pain hypersensitivity during adolescence, driven by gut microbial dysbiosis and gut-brain axis-mediated inflammation

Opioids, such as morphine, are used in the Neonatal Intensive Care Unit (NICU) for pain relief in neonates. However, the available evidence concerning the benefits and harms of opioid therapy in neonates remains limited. While previous studies have reported that neonatal morphine exposure (NME) results in long-term heightened pain sensitivity, the underlying mechanisms are not well understood. This study proposes that dysbiosis of the gut microbiome contributes to pain hypersensitivity following NME. Using an adolescent female murine model, pain sensitivity was evaluated using the tail flick and hot plate assays for thermal pain and the Von Frey assay for mechanical pain. Gut microbiome composition was assessed using 16S rRNA sequencing, while transcriptomic changes in midbrain samples were investigated using bulk RNA sequencing. NME induced prolonged hypersensitivity to thermal and mechanical pain in adolescence, accompanied by persistent gut microbial dysbiosis and sustained systemic inflammation, characterized by elevated circulating cytokine levels (e.g., IL-1α, IL-12p70, IFN-γ, IL-10). Transplantation of the microbiome from NME adolescents recapitulated pain hypersensitivity in naïve adolescent mice, while neonatal probiotic intervention with Bifidobacterium infantis (B. infantis) reversed the pain hypersensitivity by preventing gut dysbiosis and associated systemic inflammation. Furthermore, transcriptomic analysis of midbrain tissues revealed that NME upregulated several genes and key signaling pathways, including those related to immune activation and excitatory signaling, which were notably mitigated with neonatal B. infantis administration. Together, these findings highlight the critical role of the gut-brain axis in modulating pain sensitivity and suggest that targeting the gut microbiome offers a promising therapeutic strategy for managing neurobiological disorders following early opioid exposure.

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.

Neuroimmune circuits in the plaque and bone marrow regulate atherosclerosis

Atherosclerosis remains the leading cause of death globally. Although its focal pathology is atheroma that develops in arterial walls, atherosclerosis is a systemic disease involving contributions by many organs and tissues. It is now established that the immune system causally contributes to all phases of atherosclerosis. Recent and emerging evidence positions the nervous system as a key modulator of inflammatory processes that underlie atherosclerosis. This neuroimmune cross-talk, we are learning, is bidirectional, and immune-regulated afferent signalling is becoming increasingly recognized in atherosclerosis. Here, we summarize data and concepts that link the immune and nervous systems in atherosclerosis by focusing on two important sites, the arterial vessel and the bone marrow.

Exploring the Role of RhoA/ROCK Signaling in Pain: A Narrative Review

Despite significant progress in understanding the mechanisms of pain and developing therapeutic agents, pain remains a challenging and unresolved clinical issue. The Ras homolog gene family member A (RhoA), a member of the small guanosine triphosphate hydrolases (GTPases) of the Ras homolog family, is involved in transmitting signals that regulate various cellular processes. RhoA exerts its effects through a range of downstream effectors, with Rho-associated kinase (ROCK) being the most extensively studied. Emerging evidence suggests that the RhoA/ROCK signaling pathway plays a crucial role in pain transmission and sensitization. Our work indicates that targeting the RhoA/ROCK signaling pathway may offer a promising therapeutic avenue for alleviating pain.

Unraveling the relationship between inflammation and cluster headache

Cluster headache (CH) is often referred to as the 'suicide headache.' Existing research suggests that the activation of the trigeminal-vascular system, increased sensitivity of nerve fibers, and the release and interaction of various neuropeptides and inflammatory mediators may contribute to neurogenic inflammation, which serves as a crucial pathophysiological basis for the development of CH. Additionally, some neuropeptides can modulate neuronal activity related to pain transmission and may increase pain perception by sensitizing central nerves. This review discusses the neuropeptides and inflammatory mediators associated with CH neuroinflammation, focusing on calcitonin gene-related peptide (CGRP), inflammatory cytokines and related signaling pathways, nitric oxide (NO), pituitary adenylate cyclase-activating peptide 38 (PACAP-38), and vasoactive intestinal peptide (VIP), incorporating both preclinical and clinical evidence to provide new insights into potential therapeutic targets for CH.

Repeated Administrations of Polyphenolic Extracts Prevent Chronic Reflexive and Non-Reflexive Neuropathic Pain Responses by Modulating Gliosis and CCL2-CCR2/CX3CL1-CX3CR1 Signaling in Spinal Cord-Injured Female Mice

Neuropathic pain after spinal cord injury lacks any effective treatments, often leading to chronic pain. This study tested whether the daily administration of fully characterized polyphenolic extracts from grape stalks and coffee could prevent both reflexive and non-reflexive chronic neuropathic pain in spinal cord-injured mice by modulating the neuroimmune axis. Female CD1 mice underwent mild spinal cord contusion and received intraperitoneal extracts in weeks one, three, and six post-surgery. Reflexive pain responses were assessed weekly for up to 10 weeks, and non-reflexive pain was evaluated at the study's end. Neuroimmune crosstalk was investigated, focusing on glial activation and the expression of CCL2/CCR2 and CX3CL1/CX3CR1 in supraspinal pain-related areas, including the periaqueductal gray, rostral ventromedial medulla, anterior cingulate cortex, and amygdala. Repeated treatments prevented mechanical allodynia and thermal hyperalgesia, and also modulated non-reflexive pain. Moreover, they reduced supraspinal gliosis and regulated CCL2/CCR2 and CX3CL1/CX3CR1 signaling. Overall, the combination of polyphenols in these extracts may offer a promising pharmacological strategy to prevent chronic reflexive and non-reflexive pain responses by modifying central sensitization markers, not only at the contusion site but also in key supraspinal regions implicated in neuropathic pain. Overall, these data highlight the potential of polyphenolic extracts for spinal cord injury-induced chronic neuropathic pain.

CARTp/GPR160 mediates behavioral hypersensitivities in mice through NOD2

ABSTRACT

Neuropathic pain is a debilitating chronic condition that remains difficult to treat. More efficacious and safer therapeutics are needed. A potential target for therapeutic intervention recently identified by our group is the G-protein coupled receptor 160 (GPR160) and the cocaine- and amphetamine-regulated transcript peptide (CARTp) as a ligand for GPR160. Intrathecal administration of CARTp in rodents causes GPR160-dependent behavioral hypersensitivities. However, the molecular and biochemical mechanisms underpinning GPR160/CARTp-induced behavioral hypersensitivities in the spinal cord remain poorly understood. Therefore, we performed an unbiased RNA transcriptomics screen of dorsal horn spinal cord (DH-SC) tissues harvested at the time of peak CARTp-induced hypersensitivities and identified nucleotide-binding oligomerization domain-containing protein 2 ( Nod2 ) as a gene that is significantly upregulated. Nucleotide-binding oligomerization domain-containing protein 2 is a cytosolic pattern-recognition receptor involved in activating the immune system in response to bacterial pathogens. While NOD2 is well studied under pathogenic conditions, the role of NOD2-mediated responses in nonpathogenic settings is still not well characterized. Genetic and pharmacological approaches reveal that CARTp-induced behavioral hypersensitivities are driven by NOD2, with co-immunoprecipitation studies indicating an interaction between GPR160 and NOD2. Cocaine- and amphetamine-regulated transcript peptide-induced behavioral hypersensitivities are independent of receptor-interacting protein kinase 2 (RIPK2), a common adaptor protein to NOD2. Immunofluorescence studies found NOD2 co-expressed with endothelial cells rather than glial cells, implicating potential roles for CARTp/NOD2 signaling in these cells. While these findings are based only on studies with male mice, our results identify a novel pathway by which CARTp causes behavioral hypersensitivities in the DH-SC through NOD2 and highlights the importance of NOD2-mediated responses in nonpathogenic settings.

Electroacupuncture at 5/100 Hz alleviates neuropathic pain in rats by inhibiting the CCL3/CCR5 axis in the spinal cord

OBJECTIVE

Typically, neuropathic pain (NP) is difficult to manage as it is refractory to conventional medications. Electroacupuncture (EA) at 5/100 Hz has emerged as an effective and promising treatment for NP; however, its mechanism of action is still uncertain. Accordingly, this study investigated the alleviatory mechanism of EA in chronic compression injury (CCI)-induced chronic pain via the C-C chemokine ligand 3 / C-C chemokine receptor type 5 (CCL3/CCR5) axis.

METHODS

The CCI model was established in rats to induce NP. Mechanical and thermal hyperalgesia were assessed with von Frey and Hargreaves tests, respectively. From day 8 after CCI, EA (5/100 Hz) was performed for 1 week (30 min/day). CCL3 and CCR5 expression was detected with Western blotting and immunofluorescence. Glial cell activation was determined through co-labeling of neurons and glial cells with antibodies against CCL3 and CCR5. The release of interleukin (IL)-1β, IL-6 and tumor necrosis factor (TNF)-α was tested with enzyme-linked immunosorbent assay (ELISA).

RESULTS

EA markedly ameliorated CCI-induced chronic NP in rats and reduced CCL3 and CCR5 expression in the rat spinal cord. CCL3 and CCR5 were co-expressed by neurons and microglia in the central nervous system. In addition, EA also repressed the activation of glial cells and levels of IL-1β, IL-6 and TNF-α.

CONCLUSION

EA may mitigate chronic NP in rats by blocking the CCL3/CCR5 axis in the spinal cord. In addition, EA appeared to exert anti-inflammatory and analgesic effects by suppressing glial cell activation. These findings add to our understanding of the mechanism of EA-induced analgesia.

A pilot investigation on inflammatory markers and theta burst stimulation protocol interaction along a three-month recovery course following an isolated upper limb fracture

This study investigates the effects of theta burst stimulation (TBS) on inflammatory markers in patients with isolated upper limb fractures (IULF). Participants underwent a 10-day TBS intervention following a randomized matched pair design. Blood samples collected at three time points were analyzed for inflammatory biomarkers, mainly including interleukin-1 receptor antagonist (IL-1Ra), IL-1β, and IL-6. Results revealed a significant interaction between TBS and time for IL-1Ra, indicating a more pronounced decrease in IL-1Ra expression over time in the active TBS group. However, IL-6 levels decreased over time regardless of TBS intervention, suggesting a natural decline in response to injury. No significant interaction was found for IL-1β. While IL-1Ra levels were associated with higher functional disability prior to treatment initiation, active TBS intervention led to a decrease of IL-1Ra levels at both follow-up time points. These changes were not associated with alterations in pain or disability, suggesting that TBS may primarily influence recovery processes independent of pain modulation. Notably, IL-1β levels were negatively correlated with disability in the active TBS group at the 3-month follow-up. This study sheds light on the potential of TBS to modulate inflammatory responses in orthopedic trauma, emphasizing the need for further research to elucidate its therapeutic implications. Clinical Significance: TBS may offer a promising adjunctive therapy for promoting functional recovery in patients with upper limb fractures.

Preemptive Propofol Administration in Spinal Cord Injury: Effects on Pain-Induced Hypertension, Neuroinflammation, and Functional Recovery in Rats

Spinal cord injury (SCI) triggers secondary damage, including pain-induced hypertension, inflammation, and hemorrhage, impairing recovery. This study evaluated the efficacy of general anesthesia with preemptive propofol administration in mitigating secondary damage in SCI rats. SCI was induced in rats using a contusion model. Propofol (100 mg/kg) was administered intraperitoneally either 30 min before (preemptive) or 30 min after intermittent tail shock. Systolic blood pressure (SBP), body weight, food intake, inflammatory markers (interleukin-1 beta [IL-1β], interleukin-6 [IL-6]), hemorrhage markers, and serum levels of SCI biomarkers (glial fibrillary acidic protein [GFAP], myelin basic protein [MBP]) were measured. Functional recovery was assessed over 28 days using the Basso, Beattie, and Bresnahan (BBB) scale, horizontal ladder test, and rotarod test. Preemptive propofol administration effectively mitigated pain-induced hypertension, enhanced body weight and food intake, and reduced inflammatory markers to levels comparable to unstimulated SCI rats. In contrast, propofol administered post-stimulation was less effective. Preemptive administration significantly decreased GFAP levels and preserved MBP levels. Importantly, preemptive intervention reduced levels of hemoglobin and alpha hemoglobin, while post-stimulation intervention showed no significant effect on hemorrhage. Behavioral assessments demonstrated improved locomotor recovery, motor coordination, and balance in preemptively treated rats compared to delayed or no intervention. Preemptive administration of propofol effectively reduces pain-induced hypertension, inflammation, and gliosis while preserving myelin integrity and enhancing functional recovery in SCI rats. This intervention demonstrates significantly greater efficacy compared to delayed administration, underscoring the critical importance of timely treatment in mitigating secondary damage and improving outcomes after SCI.

Role of efferocytosis in chronic pain -- From molecular perspective

The complex nature of pain pathophysiology complicates the establishment of objective diagnostic criteria and targeted treatments. The heterogeneous manifestations of pain stemming from various primary diseases contribute to the complexity and diversity of underlying mechanisms, leading to challenges in treatment efficacy and undesirable side effects. Recent evidence suggests the presence of apoptotic cells at injury sites, the distal dorsal root ganglia (DRG), spinal cord, and certain brain regions, indicating a potential link between the ineffective clearance of dead cells and debris and pain persistence. This review highlights recent research findings indicating that efferocytosis plays a significant yet often overlooked role in lesion expansion while also representing a potentially reversible impairment that could be targeted therapeutically to mitigate chronic pain progression. We examine recent advances into how efferocytosis, a process by which phagocytes clear apoptotic cells without triggering inflammation, influences pain initiation and intensity in both human diseases and animal models. This review summarizes that efferocytosis contributes to pain progression from the perspective of defective and inefficient efferocytosis and its subsequent secondary necrocytosis, cascade inflammatory response, and the shift of phenotypic plasticity and metabolism. Additionally, we investigate the roles of newly discovered genetic alterations or modifications in biological signaling pathways in pain development and chronicity, providing insights into innovative treatment strategies that modulate efferocytosis, which are promising candidates and potential avenues for further research in pain management and prevention.

Enhancing orofacial pain relief: α-phellandrene complexed with hydroxypropyl-β-cyclodextrin mitigates orofacial nociception in rodents

Orofacial pain affects 10-15% of adults and can severely impact quality of life. Despite ongoing treatment challenges, monoterpene alpha-phellandrene (PHE) shows potential therapeutic benefits. This study aimed to develop and evaluate an inclusion complex of PHE with hydroxypropyl-beta-cyclodextrin (PHE-HPβCD) for treating orofacial pain. The PHE-HPβCD complex was created using physical mixing and characterized by differential scanning calorimetry (DSC) and high-performance liquid chromatography (HPLC) to determine encapsulation efficiency. The complex exhibited a 70.45% encapsulation efficiency. Male Swiss mice were used in models of orofacial pain induced by formalin, cinnamaldehyde, glutamate, and corneal nociception by hypertonic saline. Additionally, cytokine levels (TNF-α and IL-1β) were measured in the upper lip tissue of mice subjected to the formalin model. Both PHE and PHE-HPβCD showed significant antinociceptive effects at a 50 mg/kg dose during formalin-induced pain, reducing both neurogenic and inflammatory phases of pain. PHE-HPβCD also reduced TNF-α and IL-1β levels. For cinnamaldehyde and glutamate-induced nociception, both treatments reduced pain behavior, but only PHE-HPβCD decreased eye wipes in corneal nociception. These results suggest that PHE, especially in complexed form, alleviates orofacial pain by potentially modulating pain-related receptors (TRPA1 and TRPV1), mediators, like glutamate, and reducing pro-inflammatory cytokines. Further research is needed to explore the precise mechanisms of PHE in chronic orofacial pain models, but the study indicates promising avenues for new pain treatments.

The profile beyond leg pain: In basis of central sensitization, kinesiophobia, and body awareness in patients with chronic venous disease

Objective: Leg pain has long been underestimated despite being one of the most important symptoms of chronic venous disease (CVD). Studies investigating leg pain and psychosocial profile in CVD are limited. The study aimed to investigate leg pain, central sensitization, kinesiophobia, and body awareness in patients with CVD. Methods: The ninety-eight patients (80 female, 18 male) diagnosed with CVD were included in the study. The severity of leg pain was evaluated with the Visual Analog Scale (VAS). The patients were assessed with the Central Sensitization Inventory (CSI-A and B) for central sensitization-related symptoms and -positivity, the Body Awareness Questionnaire (BAQ) for body awareness, and the Tampa Kinesiophobia Scale (TKS) for kinesiophobia. The cut-off score was admitted as 41 for TKS. Results: The leg pain (mean (SD) = 4.3 ± 2) and body awareness (mean (SD) = 82.4 ± 22) were moderate levels in patients with CVD. Nearly half of the patients (n = 46, 46.9%) had both central sensitization positivity and elevated kinesiophobia (n = 46, 47%). The CSI was correlated with the VAS (r = 0.32, p = .001), TKS (r = 0.40, p < .001), and BAQ (r = 0.20, p = .048). Significant correlations were determined between Body Mass Index and TKS (r = 0.48, p < .001) and BAQ (r = -0.31, p = .002). Also, the patients with a TKS score ≥41-points had higher CSI-A scores (p = .002) than those with a TKS score< 41. Conclusions: Leg pain, central sensitization, and kinesiophobia are commonly seen in patients with CVD, and central sensitization seems to have a negative effect on leg pain, kinesiophobia, and body awareness. The profile beyond pain should be evaluated in detail, and various rehabilitation strategies need to be developed to manage central sensitization, interoception, kinesiophobia, and weight control in patients with CVD.

"How Do You Live the Best Life You Can With This Pain?" A Qualitative Study of Adults Living With CF and Pain in the Modulator ERA

BACKGROUND

Despite pain's high prevalence and impact on quality of life and health outcomes, no studies have examined psychosocial approaches for treating pain in CF. We interviewed adults with CF and pain about their experiences to inform development of a CF-specific psychosocial pain management intervention.

METHODS

We partnered with CF Community Voice to recruit 14 adults with CF and pain for 1.5 h individual qualitative interviews and conducted a hybrid inductive-deductive thematic analysis (NVivo 14).

RESULTS

Participants' age ranged from 23 to 64 years; Seven were taking a modulator, 4 eligible/not taking, 3 ineligible. Pain sources included lung/chest, head/sinus, joint, bone, back, neuropathic, GI; 100% reported multiple sources. Pain experience: A major theme was the close interrelationship of pain and CF. Subthemes included pain being part of life with CF, having CF leads to high pain tolerance and effects of aging with CF. Participants described CFTR modulators effect pain experiences with 3 noting improvement and 4 worsening pain. Pain centralization was common: fatigue, difficulties with cognition/sleep, increased sensitivity to nonpainful stimuli. Pain impact: Pain has a widespread negative impact on quality of life and especially mental health. Resiliency was a theme: the need for coping strategies, support and strong self-advocacy. Advice for CF Care Teams: Participants endorsed a need for increased acknowledgment of pain experiences and co-development of a treatment plan.

CONCLUSIONS

Pain remains a prominent, burdensome symptom in the modulator era, necessitating a multi-component management approach. Results informed the development and pilot of a mind-body pain intervention for adults with CF.

Youth with high-frequency headaches due to migraine are more vulnerable to non-cephalic pain complaints

We examined clinic data from a large sample of children and teens with migraine to see how common it was for these patients to also experience other types of body pain. We found that almost one quarter of youth with migraine also reported pain in an additional body location; youth with more frequent and severe headaches were more likely to have pain in body locations besides the head, with youth with constant or continuous headache being most at risk for additional body pain difficulties. Youth with migraine headaches that are severe or happen a lot of the time should be evaluated for other body pain to make sure that they get all the medical care they need to best manage pain.

BDNF Signaling and Pain Modulation

Brain-derived neurotrophic factor (BDNF) is an important neuromodulator of nervous system functions and plays a key role in neuronal growth and survival, neurotransmission, and synaptic plasticity. The effects of BDNF are mainly mediated by the activation of tropomyosin receptor kinase B (TrkB), expressed in both the peripheral and central nervous system. BDNF has been implicated in several neuropsychiatric conditions such as schizophrenia and anxio-depressive disorders, as well as in pain states. This review summarizes the evidence for a critical role of BDNF throughout the pain system and describes contrasting findings of its pro- and anti-nociceptive effects. Different cellular sources of BDNF, its influence on neuroimmune signaling in pain conditions, and its effects in different cell types and regions are described. These and endogenous BDNF levels, downstream signaling mechanisms, route of administration, and approaches to manipulate BDNF functions could explain the bidirectional effects in pain plasticity and pain modulation. Finally, current knowledge gaps concerning BDNF signaling in pain are discussed, including sex- and pathway-specific differences.

Environmental enrichment for neuropathic pain via modulation of neuroinflammation

Neuropathic pain causes tremendous biological and psychological suffering to patients worldwide. Environmental enrichment (EE) is a promising non-pharmacological strategy with high cost-effectiveness to reduce neuropathic pain and support rehabilitation therapy. Three researchers reviewed previous studies to determine the efficacy of EE for neuropathic pain to research how EE improves neuropathic pain through neuroinflammation. For this review, Embase, PubMed, and Cochran were searched. Three authors did study selection and data extraction. Out of 74 papers, 7 studies met the inclusion criteria. In the chronic constriction injury rats with acute or chronic detrimental stimulation, the change of pain behavior was influenced by environmental settings like start time, and cage size. Besides, physical EE has a larger effect than socially EE in inflammatory pain. These articles suggest employing various EE to regulate the release of pain-causing substances and changes in ion channels in the peripheral and central nerves to improve neuropathic pain behavior and depression and anxiety conditions. The existing proof provides important knowledge for upcoming preclinical investigations and the practical use of EE in clinical pain treatment. This analysis aids in the advancement of improved approaches for managing chronic pain, with a focus on internal mechanisms for controlling pain.

An Emerging Perspective on the Role of Fascia in Complex Regional Pain Syndrome: A Narrative Review

Complex Regional Pain Syndrome (CRPS) is a debilitating pain disorder involving chronic inflammation, neural sensitization and autonomic dysfunction. Fascia, a highly innervated connective tissue, is increasingly recognized for its role in pain modulation, yet its contribution to CRPS remains underexplored. This narrative review synthesizes the current evidence on fascia's involvement in CRPS pathophysiology and potential therapeutic strategies. A literature search was conducted in PubMed, Scopus and Web of Science, selecting studies on fascia, CRPS, inflammation, oxidative stress and autonomic dysfunction, with emphasis on recent experimental, anatomical and clinical research. Fascia contributes to CRPS through neuroinflammation, fibrosis and autonomic dysregulation. Its rich innervation facilitates peripheral and central sensitization, while inflammatory mediators drive fibrosis, reducing elasticity and exacerbating pain. Autonomic dysfunction worsens hypoxia and oxidative stress, fueling chronic dysfunction. Advances in sonoelastography provide new insights, while fascial manipulation and targeted therapies show promise in early studies. Fascia plays a key role in CRPS pathophysiology, yet its clinical relevance remains underexplored. Future research integrating imaging, molecular profiling and clinical trials is needed to develop evidence-based fascia-targeted interventions, potentially improving CRPS diagnosis and treatment.

Resolvin D1 accelerates resolution of neuroinflammation by inhibiting microglia activation through the BDNF/TrkB signaling pathway

BACKGROUND

Neuropathic pain is characterized by hyperalgesia, allodynia, and inflammation and it is often resistant to treatment. The formyl peptide receptor 2 (ALX/FPR2), a G-protein-coupled receptor, has been implicated in resolving inflammation, making its agonist, Resolvin D1 (RvD1), a potential therapeutic agent. Previous studies suggest that RvD1 alleviates neuropathic pain via anti-inflammatory effects, but its mechanisms remain unclear, particularly in relation to microglial activation and the brain-derived neurotrophic factor (BDNF)/TrkB signaling pathway.

OBJECTIVE

To investigate the analgesic effects of RvD1 in a spared nerve injury (SNI) model of neuropathic pain and explore its mechanisms through the regulation of neuroinflammation and the BDNF/TrkB signaling pathway.

METHODS

SNI mice received intrathecal RvD1 at varying doses (10-40 ng) to determine its efficacy in reducing mechanical allodynia and thermal sensitivity. The anti-inflammatory effects of RvD1 were assessed using ELISA, immunofluorescence, and western blotting to measure the expression of pro-inflammatory cytokines and BDNF. The involvement of ALX/FPR2 and TrkB receptors was further examined using antagonists Boc2 and K252a.

RESULTS

RvD1 significantly reduced mechanical and thermal allodynia in SNI mice in a dose-dependent manner. RvD1 also decreased microglial activation and expression of pro-inflammatory cytokines (TNF-α, IL-1β, IL-6) and BDNF in both in vivo and in vitro models. These effects were reversed by Boc2 and K252a, confirming that the analgesic actions of RvD1 are mediated via the ALX/FPR2 receptor and inhibition of BDNF/TrkB signaling.

CONCLUSION

RvD1 alleviates neuropathic pain by reducing neuroinflammation through the ALX/FPR2 receptor and suppressing BDNF/TrkB signaling. These findings suggest RvD1 as a promising therapeutic agent for neuropathic pain management.

Ropivacaine and celecoxib-loaded injectable composite hydrogel for improved chronic pain-exacerbated myocardial ischemia-reperfusion injury

Chronic pain is a prevalent condition affecting a significant portion of the global population and is known to be associated with an increased risk of cardiovascular diseases. Despite the clinical relevance, the mechanisms underlying the link between chronic pain and myocardial ischemia-reperfusion (MI/R) injury remain poorly understood. This study aimed to investigate the role of the superior cervical ganglion (SCG) in mediating the effects of chronic pain on MI/R injury and to develop a novel therapeutic strategy. We identified that chronic pain upregulated TNF-α expression and induced hyperactivity in SCG sympathetic neurons, exacerbating MI/R injury. To address this, we engineered an injectable Pluronic/alginate-based composite hydrogel loaded with celecoxib and ropivacaine (celecoxib@Laponite-dopamine-alginate-Pluronic F-127@ropivacaine, CLDAFR). This hydrogel was designed to target the SCG, providing a localized and sustained release of the therapeutic agents, thereby mitigating neuronal inflammation and inhibiting neuronal hyperactivity. The CLDAFR hydrogel demonstrated excellent biocompatibility, heat-sensitive gelation properties, and controlled drug release in vitro. In vivo studies showed that applying CLDAFR effectively reduced MI/R injury in a chronic pain model by suppressing TNF-α expression and SCG neuronal activity. In conclusion, the CLDAFR hydrogel represents a promising therapeutic material for treating chronic pain-exacerbated MI/R injury by precisely targeting the SCG and providing a sustained anti-inflammatory and analgesic effect.

Neuropathic pain management: a focused review of current treatments and novel data from main ongoing clinical trials

INTRODUCTION

Neuropathic pain (NP) remains a significant challenge in clinical practice, requiring a sophisticated pharmacotherapeutic strategy for effective symptom management. This review provides a comprehensive analysis of the current pharmacological treatments for NP, focusing on their efficacy, mechanism of action, and therapeutic potential. Additionally, it evaluates ongoing clinical trials investigating novel drugs and therapeutic approaches, highlighting emerging trends and future directions in NP management.

AREAS COVERED

This review examines first- to third-line therapeutic modalities for NP, critically analyzing their efficacy, safety profiles, and clinical applications. It also includes an overview of ongoing clinical trials exploring innovative pharmacological therapies. A thorough literature review was conducted using the MEDLINE database without temporal limitations, offering a detailed assessment of established and emerging treatments.

EXPERT OPINION

While current pharmacological options offer significant symptom relief, their overall effectiveness in managing NP remains limited, highlighting the need for further therapeutic advancements. Staying informed about emerging therapies and clinical trials is vital to enhancing patient care and quality of life. The future of NP management lies in optimizing individualized treatment strategies, refining therapeutic approaches, and fostering interdisciplinary collaboration. Close monitoring of outcomes and continued research are essential for advancing understanding and improving the precision of NP therapies.

Rutin: a pain-relieving flavonoid

Rutin (vitamin P or rutoside) is a citrus flavonoid glycoside that has shown beneficial health effects in different organs against various conditions including inflammation and pain. The majority of rutin therapeutic benefits are ascribed to its antioxidant and anti-inflammatory properties. This review article discusses studies that investigated pain-relieving activity of rutin and summarizes the reported mechanisms of action. Rutin pain-relieving effect has been studied in streptozotocin-induced diabetes, chronic constriction injury, and oxaliplatin-, formalin-, acetic acid- and glutamate-induced nociception in mice or rats. Based on the literature, rutin analgesic effects are induced through potentiation of antioxidant arsenal, reduction of inflammatory cytokines (e.g., Tumor necrosis factor alpha (TNF-α) and interleukin-1β) levels, suppression of cyclooxygenase-2 (COX-2) and inducible nitric oxide synthase (iNOS) expressions and modulation of MAPK, NF-κB and Nrf-2/HO-1 signaling. Preclinical findings on rutin pain-relieving activity are promising, however, its safety profile needs to be more thoroughly investigated and clinical trials should be conducted to assess its analgesic effects in humans.

Noradrenergic Locus Coeruleus-CA3 Activation Alleviates Neuropathic Pain and Anxiety- and Depression-Like Behaviors by Suppressing Microglial Neuroinflammation in SNI Mice

OBJECTIVE

Neuropathic pain (NP) arises from neuroimmune interactions following nerve injury and is often accompanied by anxiety and depression. The aim of the study is to evaluate the effects of the noradrenergic locus coeruleus (LC), a key regulator of pain and emotional states, projects extensively to the hippocampus.

METHOD

We investigated the effects of chronic NP on LC integrity and its projections to the hippocampal CA3 region in spared nerve injury (SNI) mice with behavioral tests, immunohistochemistry, neurochemical analyses, and Gq-DREADD.

RESULTS

Chronic NP induced LC neuronal loss, reduced hippocampal norepinephrine (NE) release, and triggered microglial activation and neuroinflammation in CA3. Selective activation of LC-CA3 noradrenergic neurons using Gq-DREADD chemogenetics alleviated NP and comorbid anxiety- and depression-like behaviors. This intervention suppressed microglial activation, decreased proinflammatory cytokines (TNF-α and IL-1β), and restored NE levels in CA3.

CONCLUSION

Our findings highlighted the therapeutic potential of targeting LC-CA3 projections to mitigate chronic NP and its neuropsychiatric comorbidities via modulation of hippocampal neuroinflammation.

Safety and preliminary efficacy of transcutaneous auricular vagus nerve stimulation on chronic knee pain: A pilot trial

Objective

Transcutaneous auricular vagus nerve stimulation (tVNS) may be an innovative treatment for symptoms of knee osteoarthritis (OA) due to possible shared pathological mechanisms between diminished parasympathetic function, central pain mechanisms, and knee pain. Thus, we sought to test the safety and preliminary efficacy of tVNS in people with knee OA.

Design

A pilot trial in which participants received a 60-min tVNS was conducted. At baseline, immediately after, and 15 ​min after tVNS, we assessed knee pain, pressure pain threshold (PPT), temporal summation (TS), conditioned pain modulation (CPM), and high-frequency power of heart rate variability (HF). We examined the extent to which these outcome measures changed after tVNS using linear mixed models.

Results

30 participants with knee OA were included, and all completed the intervention without any major side effects. Compared to baseline, knee pain was reduced by 1.27 (95 ​% CI, -1.74, -0.80) immediately after and by 1.87 (-2.33, -1.40) 15 ​min after tVNS; CPM improved by 0.11 (0.04, 0.19) and 0.07 (-0.01, 0.15); and HF improved by 213.29 (-0.38, 426.96) and 234.17 (20.49, 447.84). PPT and TS were not changed after tVNS.

Conclusions

Our preliminary data demonstrated that tVNS may be a safe pain-relieving treatment for people with knee OA. Our findings suggest that improvement of knee pain might be derived from improvement of parasympathetic function and central pain mechanisms as no local therapy was applied. A large study is needed to confirm that tVNS is a novel intervention to ameliorate knee pain in people with knee OA.

Clinical Trial

ClinicalTrials.gov (NCT05625178).

Modulating neuroplasticity for chronic pain relief: noninvasive neuromodulation as a promising approach

Chronic neuropathic pain is a debilitating neuroplastic disorder that notably impacts the quality of life of millions of people worldwide. This complex condition, encompassing various manifestations, such as sciatica, diabetic neuropathy and postherpetic neuralgia, arises from nerve damage or malfunctions in pain processing pathways and involves various biological, physiological and psychological processes. Maladaptive neuroplasticity, known as central sensitization, plays a critical role in the persistence of chronic neuropathic pain. Current treatments for neuropathic pain include pharmacological interventions (for example, antidepressants and anticonvulsants), invasive procedures (for example, deep brain stimulation) and physical therapies. However, these approaches often have limitations and potential side effects. In light of these challenges, interest in noninvasive neuromodulation techniques as alternatives or complementary treatments for neuropathic pain is increasing. These methods aim to induce analgesia while reversing maladaptive plastic changes, offering potential advantages over conventional pharmacological practices and invasive methods. Recent technological advancements have spurred the exploration of noninvasive neuromodulation therapies, such as repetitive transcranial magnetic stimulation, transcranial direct current stimulation and transcranial ultrasound stimulation, as well as innovative transformations of invasive techniques into noninvasive methods at both the preclinical and clinical levels. Here this review aims to critically examine the mechanisms of maladaptive neuroplasticity in chronic neuropathic pain and evaluate the efficacy of noninvasive neuromodulation techniques in pain relief. By focusing on optimizing these techniques, we can better assess their short-term and long-term effects, refine treatment variables and ultimately improve the quality of neuropathic pain management.

Widespread and Prolonged Pain May Reduce Brain Clearance Capacity Only via Sleep Impairment: Evidence from Participants with Knee Pain

The brain is key in the pain-sleep relationship, and sleep is needed for glymphatic clearance. However, no studies have examined how pain relates to the glymphatic system (GS). Characterizing the GS alongside sleep quality in well-characterized pain samples is essential for advancing this understanding. Non-invasive MRI techniques, such as Diffusion Tensor Imaging-Analysis aLong the Perivascular Space (DTI-ALPS), are particularly valuable as they are approved for humans. Although the relationship between the DTI-ALPS index and the GS is primarily deductive, the index may be a proxy for waste clearance capacity in deep white matter. Its sensitivity to interstitial space changes-known to be modulated by norepinephrine-offers a unique opportunity to investigate how sleep impairment and chronic pain regulation affect specific components of brain waste clearance. We thus fitted two longitudinal models linking pain, sleep quality and the DTI-ALPS index. We hypothesized that variations in pain characteristics would predict DTI-ALPS index changes, either directly or mediated by sleep quality changes. Alternatively, we hypothesized that variations in sleep quality would predict changes in pain characteristics via DTI-ALPS index modifications. Knee pain participants (n=87) completed an MRI and self-reported measures of pain and sleep impairment at baseline and two years later. We only found evidence supporting that more widespread and longer pain at baseline significantly influenced decreases in the DTI-ALPS index in the left hemisphere through increased sleep impairment two years later (p=0.039, corrected). Perspective: Findings highlight the need for research on the relationship between pain and sleep quality and its implications for brain health.

Up-regulation of MAPK14-related lncRNAs in the circulation of migraineurs

Mitogen-activated protein kinase 14 (MAPK14) has a fundamental role in the development of different inflammatory and neurodegenerative disorders. However, its roles in the pathoetiology of migraine are not clear. The current case-control study focused on expression analysis of MAPK14 and related long non-coding RNAs (lncRNAs) in the circulation of migraineurs compared with healthy controls. Data showed remarkable elevation of expression levels of MAPK14, HLA Complex Group 11 (HCG11), zinc ribbon domain-containing 1-antisense 1 (ZNRD1-AS1), RAD51 antisense RNA 1 (RAD51-AS1) and long noncoding RNA-activated by DNA damage (NORAD) in both groups of migraineurs (with aura and without aura) compared with controls. The accuracy of expression levels of MAPK14, HCG11, ZNRD1-AS1, RAD51-AS1 and NORAD for differentiating migraineurs from controls was 85.71%, 81.56%, 85.11%, 77.8% and 94.33%, respectively. Thus, MAPK14 and its related lncRNAs are putative markers for migraine and might participate in the pathogenesis of this neurologic condition.

Acute Infusion Pain Reaction Due to Anti-PD-1 Antibodies for the Treatment of Cutaneous Squamous Cell Carcinoma in Recessive Dystrophic Epidermolysis Bullosa: A Case Report and Review of the Literature

Recessive dystrophic epidermolysis bullosa (RDEB) belongs to a rare group of inherited dermatoses, which are characterised by mucosal and cutaneous fragility. Cutaneous squamous cell carcinoma (CSCC) is a common complication of RDEB. In the severe subtype of RDEB (RDEB-S), CSCC is observed in 90% of the patients by 55 years. CSCC in patients with RDEB follows an aggressive course with the median survival rate of 2.4 years. We report the case of a 51-year-old female with RDEB with recurrent aggressive CSCC of the right lateral-back. She was commenced on cemiplimab, an anti-programmed death receptor-1 (PD-1) antibody, for the management of unresectable locally advanced CSCC; however, she experienced a severe infusion reaction, manifested as back pain, requiring treatment cessation. Despite three incomplete doses, the patient demonstrated a marked response with significant regression of her tumours. Therefore, further treatment was pursued. She was successfully administered cemiplimab under intravenous sedation. This was later complicated by immune-related colitis, necessitating treatment cessation. The patient was transitioned to best supportive care. The patient required inpatient admission for end-of-life care due to her complex analgesia requirements. This case report explores the pathophysiological mechanisms of pain in RDEB and anti-PD-1 antibody therapy and highlights the unique challenges of pain management in RDEB patients.

Nitroxidative Stress, Cell-Signaling Pathways, and Manganese Porphyrins: Therapeutic Potential in Neuropathic Pain

Neuropathic pain, a debilitating condition arising from somatosensory system damage, significantly impacts quality of life, leading to anxiety, self-mutilation, and depression. Oxidative and nitrosative stress, an imbalance between reactive oxygen and nitrogen species (ROS/RNS) and antioxidant defenses, plays a crucial role in its pathophysiology. While reactive species are essential for physiological functions, excessive levels can cause cellular component damage, leading to neuronal dysfunction and pain. This review highlights the complex interactions between reactive species, antioxidant systems, cell signaling, and neuropathic pain. We discuss the physiological roles of ROS/RNS and the detrimental effects of oxidative and nitrosative stress. Furthermore, we explore the potential of manganese porphyrins, compounds with antioxidant properties, as promising therapeutic agents to mitigate oxidative stress and alleviate neuropathic pain by targeting key cellular pathways involved in pain. Further research is needed to fully understand their therapeutic potential in managing neuropathic pain in human and non-human animals.

Childhood abuse and health outcomes in patients with fibromyalgia: a cross-sectional exploratory study of the moderating effects of pain catastrophizing and mindfulness

BACKGROUND

Childhood abuse has been linked to poorer health outcomes in individuals with fibromyalgia (FM), and this relationship may be affected by cognitive processes such as pain catastrophizing and mindfulness.

OBJECTIVE

This study investigated the impact of childhood abuse on pain-related symptoms and functioning in individuals with (FM) and examined how the critical psychosocial constructs of pain catastrophizing and mindfulness might moderate this relationship. We hypothesized that childhood abuse would be linked to greater physical symptoms and lower functioning, with pain catastrophizing and mindfulness influencing these associations.

METHODS

The study sample consisted of 113 women with FM. Correlational analyses were conducted to examine the relationship between childhood abuse and health outcomes (pain severity, pain interference, fibromyalgia impact, and physical functioning). Moderation analyses were conducted to examine the impact of pain catastrophizing and mindfulness on the relationship between childhood abuse and health outcomes.

RESULTS

As expected, catastrophizing was generally associated with elevated pain-related symptomatology and reduced functioning, and higher levels of mindfulness were associated with reduced pain impact. However, contrary to our hypothesis, childhood abuse was not directly associated with pain severity, pain interference, fibromyalgia impact, or physical functioning. Pain catastrophizing and mindfulness were significant moderators of the relationship between childhood abuse and health outcomes. Specifically, childhood abuse was related to higher pain interference only at low levels of catastrophizing and was associated with greater fibromyalgia impact and reduced physical functioning only at high levels of mindfulness.

CONCLUSION

Our findings suggest that while childhood abuse did not directly impact pain-related outcomes in this sample of fibromyalgia patients, cognitive factors like pain catastrophizing and mindfulness play significant roles in moderating these effects. These results underscore the importance of assessing for cognitive and psychological factors in the management of fibromyalgia, especially for patients with a history of childhood abuse. Further research is needed to explore these relationships in more diverse samples and to develop personalized and targeted interventions for this patient population.

Distinct Roles of Astrocytes and GABAergic Neurons in the Paraventricular Thalamic Nucleus in Modulating Diabetic Neuropathic Pain

Diabetic neuropathic pain (DNP) is a common chronic complication of diabetes mellitus and a clinically common form of neuropathic pain. The thalamus is an important center for the conduction and modulation of nociceptive signals. The paraventricular thalamic nucleus (PVT) is an important midline nucleus of the thalamus involved in sensory processing, but the specific role of PVT astrocytes and GABAergic neurons in DNP remains unclear. Here, we examined the activity of PVT astrocytes and neurons at various time points during the development of DNP by fluorescence immunohistochemistry and found that the activity of PVT astrocytes was significantly increased while that of PVT neurons was significantly decreased 14 d after streptozotocin injection in male rats. The inhibition of PVT astrocytes by chemogenetic manipulation relieved mechanical allodynia in male DNP model rats, whereas the activation of PVT astrocytes induced mechanical allodynia in normal male rats. Interestingly, chemogenetic activation of GABAergic neurons in the PVT alleviated mechanical allodynia in male DNP model rats, whereas chemogenetic inhibition of GABAergic neurons in the PVT induced mechanical allodynia in normal male rats. These data demonstrate the distinct roles of PVT astrocytes and GABAergic neurons in modulating DNP, revealing the mechanism of DNP pathogenesis and the role of the PVT in pain modulation.

A Randomized Controlled Trial Assessing the Effect of Preoperative Ibuprofen Administration on Postoperative Pain Reduction Following Miniscrew Insertion

OBJECTIVE

To evaluate the impact of preoperative oral ibuprofen premedication as a preemptive analgesia protocol on postoperative pain following the insertion of a single miniscrew insert.

METHODS

A randomized, single-blind, placebo-controlled parallel-group trial design was adopted. A total of 68 patients seeking miniscrew insert placement were recruited based on inclusion and exclusion criteria. Patients were randomly assigned in a 1:1 ratio to either the ibuprofen group or the control group, with 34 patients in each group. The ibuprofen group and the control group received 300 mg of ibuprofen sustained-release capsules and a placebo, respectively, 30 min before surgery. Postoperative analgesics were administered as needed. Pain scores at 2, 4, 6, 8, 12, and 24 h postoperatively were recorded using the Numerical Rating Scale (NRS), and the postoperative analgesic consumption was documented.

RESULTS

A total of 68 patients (34 in the control group and 34 in the preemptive analgesia group) completed the trial. No adverse events such as nausea or vomiting occurred in any of the patients. The preemptive analgesia group exhibited significantly lower pain scores at 2, 4, 6, and 8 h postoperatively [2 (0,3), 0 (0,2), 0 (0,0), 0 (0,0.25), respectively] compared to the control group [3 (2,5), 3 (2,4), 2 (0.75,4), 1 (0,3), respectively] (P = 0.0396, P = 0.0067, P = 0.0111, P = 0.0299). The proportions of patients requiring additional analgesics within 2-24 h postoperatively were 17.6% (6/34) in the preemptive analgesia group and 64.7% (22/34) in the control group, with a statistically significant difference between the two groups (P = 0.013).

CONCLUSION

Preemptive analgesia with ibuprofen can effectively reduce postoperative pain following miniscrew insert placement and represents a safe and effective perioperative pain management strategy.

TRIAL REGISTRATION

The UK's Clinical Study Registry; ISRCTN68332234 (Retrospectively registered); 20/12/2024.

Exploratory study on the ascending pain pathway in patients with chronic neck and shoulder pain based on combined brain and spinal cord diffusion tensor imaging

Objective

To explore the changes in the white matter microstructure of the ascending pain conduction pathways in patients with chronic neck and shoulder pain (CNSP) using combined brain and spinal cord diffusion tensor imaging techniques, and to assess its correlation with clinical indicators and cognitive functions.

Materials and methods

A 3.0T MRI scanner was used to perform combined brain and spinal cord diffusion tensor imaging scans on 31 CNSP patients and 24 healthy controls (HCs), extracting the spinothalamic tract (STT) and quantitatively analyzing the fractional anisotropy (FA) and mean diffusivity (MD) which reflect the microstructural integrity of nerve fibers. Additionally, these differences were subjected to partial correlation analysis in relation to Visual Analog Scale (VAS) scores, duration of pain, Self-Rating Anxiety Scale (SAS), and Self-Rating Depression Scale (SDS).

Results

Compared to HCs, CNSP patients showed decreased mean FA values and increased mean MD values in bilateral intracranial STT compared to the HC group, but two-sample t-test results indicated no statistically significant differences (p > 0.05). FA values of the left STT (C2 segment, C5 segment) and right STT (C1 segment, C2 segment) were significantly decreased in bilateral cervical STTs of CNSP patients; MD values of the left STT (C1 segment, C2 segment, C5 segment) and right STT (C1 segment, C5 segment) were significantly increased (p < 0.05). Partial correlation analysis results showed that FA values of STT in CNSP patients were negatively correlated with VAS scores, duration of pain, SAS scores, and SDS scores, while MD values were positively correlated with VAS scores and duration of pain (Bonferroni p < 0.05).

Conclusion

This research identified that patients with CNSP exhibited reduced mean FA and increased mean MD in the bilateral intracranial STT, although these differences were not statistically significant (p > 0.05). Conversely, significant abnormalities were observed in specific segments of the bilateral cervical STT (p < 0.05), which were also correlated with variations in pain intensity, illness duration, and levels of anxiety and depression. These findings contribute a novel neuroimaging perspective to the evaluation and elucidation of the pathophysiological mechanisms underlying chronic pain in the ascending conduction pathways.

The role of glial cells in neuralgia: a bibliometric exploration

Neuropathic pain is a chronic pathological pain caused by nervous system damage, characterized by complex mechanisms and limited treatment efficacy. Glial cells play a pivotal role in the initiation and maintenance of neuropathic pain. This study employs bibliometric analysis to explore trends and emerging hotspots in research on the relationship between glial cells and neuropathic pain. Based on literature data from the Web of Science Core Collection spanning 2003 to 2022, the study identifies key contributors in the field, including leading countries such as China, the United States, and Japan, as well as influential institutions and journals, such as the University of California system and Pain. Keyword analysis highlights research hotspots focusing on glial cell activation, spinal cord injury, satellite glial cells, oxidative stress, and neuroinflammation. The findings suggest that these themes may shape future directions in the field. This study provides researchers with a comprehensive overview of trends and hotspot analysis, offering valuable insights for further investigation into the role of glial cells in neuropathic pain.

NRG1-ErbB4 signaling in the cerebrospinal fluid-contacting nucleus regulates thermal pain in mice

The cerebrospinal fluid-contacting nucleus(CSF-contacting nucleus) is a pair of unique nuclei in the brain parenchyma which has long been demonstrated to play an important role in pain signal processing. However, the mechanisms by which the CSF-contacting nucleus intervenes in pain is unclear. The NRG1-ErbB4 signaling plays an important role in the nervous system and has been shown to be involved in the regulation of pain. Whether there is an involvement of NRG1-ErbB4 signaling in the regulation of pain in the CSF-contacting nucleus is currently unknown. Here, our works showed that c-Fos expression in the CSF-contacting nucleus was increased in response to incisional pain. The activation of the CSF-contacting nucleus by chemogenetics could induce thermal hyperalgesia in naive mice without effecting the pain in mice suffering from incision pain. The inhibition of the CSF-contacting nucleus alleviated incision pain, but had no effect on the pain response in naive mice. With immunofluorescence staining and Western blot, the NRG1-ErbB4 signaling in the CSF-contacting nucleus showed upregulated during the acute pain phase. And, activating NRG1-ErbB4 signaling in the CSF-contacting nucleus specifically by intracranial injection of drugs, the naïve mice displayed thermal hyperalgesia while inhibiting this signaling by intracranial injection could reverse the hyperalgesia caused by CSF-contacting nucleus activation, and execute an analgesic effect during the painful phase in mice. Our study suggested that the CSF-contacting nucleus plays a regulatory role in thermal pain in mice via NRG1-ErbB4 signaling.

N-Methyl-D-aspartate receptor antagonists for the prevention of chronic postsurgical pain: a narrative review

The N-methyl-D-aspartate receptor (NMDAR) has been linked to the development of chronic postsurgical pain (CPSP), defined as pain after surgery that does not resolve by 3 months. Once the combination of a painful stimulus and glutamate binding activates the NMDAR, calcium influx triggers signaling cascades that lead to processes like central sensitization and CPSP. Three of the most widely studied perioperative NMDAR antagonists include ketamine, magnesium, and methadone, with ketamine having garnered the greatest amount of attention. While multiple studies have found improved analgesia in the acute postoperative period, fewer studies have focused on long-term outcomes and those that have are often underpowered for CPSP or have not included those patients at highest risk. Existing meta-analyses of ketamine for CPSP are inconsistent in their findings, and studies of magnesium and methadone are even more limited. Overall, the evidence supporting NMDAR antagonists for CPSP is weak and we recommend that future studies focus on high-risk patients and potentially include combinations of NMDAR antagonists administered together for the longest duration feasible. The results of ongoing trials could have a major influence on the overall direction of the evidence supporting NMDAR antagonists in preventing CPSP.

Mechanisms and Therapeutic Potential of GPX4 in Pain Modulation

Pain, a complex symptom encompassing both sensory and emotional dimensions, constitutes a significant global public health issue. Oxidative stress is a pivotal factor in the complex pathophysiology of pain, with glutathione peroxidase 4 (GPX4) recognized as a crucial antioxidant enzyme involved in both antioxidant defense mechanisms and ferroptosis pathways. This review systematically explores GPX4's functions across various pain models, including neuropathic, inflammatory, low back, and cancer-related pain. Specifically, the focus includes GPX4's physiological roles, antioxidant defense mechanisms, regulation of ferroptosis, involvement in signal transduction pathways, and metabolic regulation. By summarizing current research, we highlight the potential of GPX4-targeted therapies in pain management.

Repetitive Transcranial Magnetic Stimulation: Is it an Effective Treatment for Cancer Pain?

Cancer is a major public health issue, with an estimated 20 million new cases and 9.7 million cancer-related deaths worldwide in 2022. Approximately 44.5% of patients experience cancer pain, significantly impacting their quality of life and causing physical and psychological burdens. Repetitive transcranial magnetic stimulation (rTMS), a non-invasive neuromodulation technique, shows potential in managing cancer pain. This review summarizes current research on rTMS for cancer pain, focusing on pain directly caused by tumors, pain from cancer treatments, postoperative pain, and cancer-related symptoms. Additionally, rTMS shows promise in improving cancer-related fatigue, anxiety, depression, and cognitive dysfunction, which can indirectly reduce cancer pain. The analgesic mechanisms of rTMS include inhibiting nociceptive signal transmission in the spinal cord, modulating hemodynamic changes in brain regions, and promoting endogenous opioid release. High-frequency stimulation of the primary motor cortex (M1) has shown significant analgesic effects, improving patients' emotional and cognitive functions and overall quality of life. rTMS has a favorable safety profile, with most studies reporting no severe adverse events. In conclusion, rTMS holds substantial potential for cancer pain management, offering a non-invasive and multifaceted therapeutic approach. Continued research and clinical application are expected to establish rTMS as an essential component of comprehensive cancer pain treatment strategies, significantly enhancing the overall well-being of patients with cancer.

The role and treatment potential of the complement pathway in chronic pain

The role of the complement system in pain syndromes has garnered attention on the back of preclinical and clinical evidence supporting its potential as a target for new analgesic pharmacotherapies. Of the components that make up the complement system, component 5a (C5a) and component 3a (C3a) are most strongly and consistently associated with pain. Receptors for C5a are widely found in immune resident cells (microglia, astrocytes, sensory neuron-associated macrophages (sNAMs)) in the central nervous system (CNS) as well as hematogenous immune cells (mast cells, macrophages, T-lymphocytes, etc.). When active, as is often observed in chronic pain conditions, these cells produce various inflammatory mediators including pro-inflammatory cytokines. These events can trigger nervous tissue inflammation (neuroinflammation) which coexists with and potentially maintains peripheral and central sensitization. C5a has a likely critical role in initiating this process highlighting its potential as a promising non-opioid target for treating pain. This review summarizes the most up-to-date research on the role of the complement system in pain with emphasis on the C5 pathway in peripheral tissue, dorsal root ganglia (DRG) and the CNS, and explores advances in complement-targeted drug development and sex differences. A perspective on the optimal application of different C5a inhibitors for different types (e.g., neuropathic, post-surgical and chemotherapy-induced pain, osteoarthritis pain) and stages (e.g., acute, subacute, chronic) of pain is also provided to help guide future clinical trials. PERSPECTIVE: This review highlights the role and mechanisms of complement components and their receptors in physiological and pathological pain. The potential of complement-targeted therapeutics for the treatment of chronic pain is also explored with a focus on C5a inhibitors to help guide future clinical trials.

Effect of various modes of tracheal mechanical stimulation on the cough motor pattern

The relationship between the level (rate) of stimulus and the characteristics of the cough response was studied on 15 spontaneously breathing anesthetized cats. Three modes of stimulation were used to elicit cough. 'High' vs. 'low' level of stimulation was accomplished: 1st mode by 1 vs. 4 penetrations of the soft catheter through the trachea (approximately 10 cm), 2nd mode by 2 penetrations with the soft catheter equipped with 4 fine cross nylon fibers vs. 4 penetrations by the stimulator with 8 fibers, and 3rd mode by a similar stimulator with 4 cross fibers probing 4 cm of the trachea either right below the larynx or deeper under the upper part of the sternum (data were pooled) vs. stimulating both areas at the same time. 'High' stimulation rate in each stimulation mode resulted in a higher number of coughs, increased cough efforts, and shortened several temporal cough features. Mechanical stimulation resulting in higher cough afferent drive induces more vigorous coughing with shorter temporal cough characteristics. Modulation of cough afferent input affects both spatial and temporal components of the cough motor pattern, representing a crucial point in cough management.

Neuroplasticity and Pain Perception: Exploring the Complexities of Temporomandibular Disorders

Temporomandibular disorders (TMDs) are prevalent conditions affecting the temporomandibular joint (TMJ), masticatory muscles, and associated structures, leading to pain, restricted movement, and joint noises. These disorders are multifactorial in origin, involving structural, functional, and psychological components. This review delves into the neurophysiological mechanisms of pain perception in TMDs, focusing on peripheral and central processes, including the role of neural plasticity in chronic pain. Peripheral mechanisms involve nociceptors in the TMJ, activated by inflammatory mediators, mechanical stress, and tissue damage, leading to pain. Peripheral sensitization, driven by factors such as cytokines and neuropeptides, enhances nociceptor sensitivity, contributing to chronic pain states. The trigeminal nerve is pivotal in transmitting nociceptive information to the central nervous system (CNS), with C-fibers and A-delta fibers involved in pain perception. Central sensitization, a hallmark of chronic pain in TMDs, involves neuroplastic changes in the CNS, including wind-up and long-term potentiation (LTP), enhancing pain perception and facilitating pain persistence. Neuroplasticity, both central and peripheral, plays a critical role in the development of chronic pain. Central plasticity includes synaptic changes and alterations in brain connectivity, which were observed in functional imaging studies of TMD patients. Peripheral plasticity involves the upregulation of ion channels and neurotransmitters, sustaining pain signals. Additionally, neuroimmune interactions between microglia, astrocytes, and pain pathways are integral to central sensitization. Understanding these mechanisms is crucial for developing effective treatments targeting both peripheral and central pain processes. Emerging therapies, including transient receptor potential (TRP) channel blockers and neuroimmune modulators, offer new avenues for managing TMD pain, emphasizing the need for a multifaceted treatment approach.

The Efficacy of Botulinum Toxin A Injection in Pelvic Floor Muscles in Chronic Pelvic Pain Patients: A Double-Blinded Randomised Controlled Trial

OBJECTIVE

To evaluate and compare the efficacy and safety of Botulinum Toxin A (BTA) injections versus placebo injections, combined with pelvic floor muscle therapy (PFMT), in women with chronic pelvic pain (CPP).

DESIGN

Randomised, double-blinded clinical trial (January 2020-April 2023).

SETTING

This multicentre study was conducted at four hospitals in the Netherlands.

POPULATION AND SAMPLE

Ninety-four women with CPP and increased pelvic floor muscle tone despite previous PFMT, were enrolled.

METHODS

Participants received either BTA injections (100 units) or placebo injections into the pelvic floor muscle, followed by four PFMT sessions.

MAIN OUTCOMES AND MEASURES

Primary outcomes included the number of women with at least a 33% reduction in pain and those reporting (very) much improvement of their pain. Secondary outcomes covered quality of life and pelvic floor function. Follow-up visits were scheduled at 4, 8, 12, and 26 weeks post-treatment. Mixed models for repeated measurements were used for analysis.

RESULTS

A 33% reduction or more in average pain score was reported by 15 participants (33%) after BTA treatment and 9 participants (20%) after placebo treatment (odd ratio placebo/BTA 1.88; 95% CI 0.72-4.90, p = 0.19). In both groups, 8 women (17%) reported their improvement as (very) much better (odd ratio placebo/BTA 0.947; 95% CI 0.32-2.80, p = 0.92). Pelvic floor resting activity decreased significantly after BTA treatment compared to placebo (p = 0.001).

CONCLUSION

The results from this study do not support the use of BTA injections in the management of CPP in women.