Frontiers in Pain Research

Background: Pressure pain threshold (PPT) is commonly assessed using pressure algometry. Self-administered algometry could reduce examiner involvement and may facilitate repeated assessment outside specialist settings. Objective: To examine the concurrent agreement of a previously described syringe-based pneumatic algometer with a commercially available comparator during self-administered PPT measurement in healthy adults. Methods: Thirty healthy volunteers completed researcher-administered and self-administered pain threshold measurements utilizing an AMF-500 device and the syringe-based pneumatic algometer. Results: During self-administration, measurements from the two devices were strongly correlated (r = 0.82, p < 0.05); the mean paired difference was 6.01 N (95% CI, -0.58 to 12.59 N). Self-administered test values were lower than researcher-administered test values in the fixed-order comparison (p = 0.0029). Conclusion: According to our findings the proposed device is a valid tool for autoalgometry and may potentially be introduced as an element of routine self-assessment of PPT.

Phantom limb pain (PLP) is common after amputation, yet why poor sleep becomes pain in only some individuals is unknown. We hypothesized that a regulatory response is interpretable only against the reserve sustaining it, and thus we tested whether autonomic capacity relative to demand moderates the sleep-pain relationship in 121 amputee adults. Sleep was assessed with the Pittsburgh Sleep Quality Index; PLP, residual limb pain (RLP), and phantom limb sensation (PLS) on 0-10 scales. Heart rate variability was summarized as autonomic reserve (log-transformed SDNN, RMSSD, total and high-frequency power) and autonomic drive (normalized low-frequency power). Poorer sleep was associated with greater PLP and RLP, but not PLS. No single HRV index moderated these associations, but the sleep x reserve x drive interaction did for PLP (b =-0.51, p = 0.026). Poor sleep predicted pain most strongly under high drive with reduced reserve. PLP vulnerability reflects autonomic capacity relative to demand, instead of any single HRV marker alone.

Background: Chronic musculoskeletal pain (CMP) is a common and debilitating symptom of Long COVID (LC), which shares several clinical features with Fibromyalgia Syndrome (FMS). Aims: This longitudinal study investigated whether the symptom overlap between LC-CMP and FMS persists over time, whether patterns differ according to pre-COVID CMP history, and the extent to which neuropathic pain features are present. Methods: Individuals with LC completed questionnaires assessing the symptom-based component of the 2010 American College of Rheumatology criteria for FMS and the presence of neuropathic pain features (PainDetect Questionnaire, PDQ) at baseline, 6- and 12-month follow-ups. Participants were grouped according to pre-COVID CMP history. Group differences were analysed using mixed-effects logistic regression. Results: 240 individuals completed the baseline assessment at a mean of 2.61 years after LC onset, including 131 (100 females) with new-onset CMP and 94 (87 females) with pre-existing CMP. The prevalence of participants meeting the symptom-based criteria for FMS remained high across follow-up (67.5-78.6%), with 50.0-61.0% of those with complete follow-up data fulfilling criteria at all timepoints. No significant subgroup differences were observed (OR = 0.43, 95% CI [0.14 1.39], p = 0.160). Across follow-up, 22.2-36.1% of participants reported likely neuropathic pain features, with significantly higher odds in the pre-existing CMP group (OR = 3.17, 95% CI [1.22 8.18], p = 0.017). Conclusions: FMS-like symptoms remain highly prevalent several years after acute COVID-19 and persist over a further 12 months, suggesting that LC-CMP frequently represents a persistent long-term condition with substantial overlap with FMS. These findings support closer integration of LC and chronic pain rehabilitation services and add to the wider literature linking post-infectious processes with FMS-like symptoms.

Interoception is described as the sensitivity to internal bodily stimuli, and plays an important role in pain perception. Heightened interoceptive sensibility (i.e. self-reported interoceptive abilities) may reinforce misinterpretation of stimuli, enhancing pain perception. This study aimed to investigate the relationship between interoceptive sensibility and acute postoperative pain. Interoceptive sensibility was measured using the Private Body Consciousness Scale in two prospective observational surgical cohorts: a Caesarean delivery cohort (C-section cohort) of 146 patients, and a lower extremity orthopaedic surgery cohort (Ortho cohort) of 70 patients. One day after surgery, patients rated pain (primary outcome) and other postoperative symptoms (secondary outcomes) on a 0-10 scale. Bonferroni corrections were applied to secondary outcomes. Interoception positively correlated with pain (C-section cohort: Spearmans rho = 0.182, P = 0.028; Ortho cohort: rho = 0.259, P = 0.031), and with dizziness (C-section cohort: rho = 0.309, P = 0.002; Ortho cohort: rho = 0.348 P = 0.041) in both cohorts. In the C-section cohort, interoception correlated with shivering (rho = 0.321, P < 0.001). In the Ortho cohort, interoception correlated with nausea (rho = 0.366, P = 0.023) and helplessness (rho = 0.363, P = 0.026); whereas no correlation with pain catastrophising was found (rho = 0.240, P = 0.539). In pooled multiple linear regression analysis (n = 216), interoception predicted pain after controlling for age, sex and anaesthetic technique (B = 0.119, 95% CI [0.027-0.210], P = 0.011). These findings highlight the potential role of interoception in identifying patients at risk for acute postsurgical pain.

Background: Although opioids are frequently prescribed for refractory chronic neuropathic pain, few data are available on baseline factors that may identify individuals more likely to respond and inform individually tailored practice. Methods: This was a post hoc, exploratory analysis of individual-level data from a placebo-controlled trial of methadone for chronic neuropathic pain (NCT05235191). Baseline clinical, psychological, psychophysical and radiological variables were tested for association with 30% or more pain reduction in the methadone group. The correlation between expectation of improvement and pain reduction was examined in both groups. Results: Of the 81 participants completing the 8-week follow-up, 28 (70%) on methadone and 14 (34.1%) on placebo achieved 30% or more pain reduction. In the methadone group, responders had higher baseline expectation of improvement (median 100 [80-100] vs. 55 [50-81]; p=0.004), which correlated moderately with percentage pain reduction (rs=0.508; p<0.001). Neither finding was observed in the placebo group (p=0.211 and p=0.161, respectively), although the correlation did not differ significantly between groups (p for interaction=0.728). Other clinical, sociodemographic, psychological and psychophysical variables were not associated with response. In the subsample with peripheral neuropathic pain and structural MRI (n=37), lower left precentral cortex volume was associated with response to methadone (p=0.041), and lower right paracentral volume with response to placebo (p=0.003). Conclusions: Baseline expectation may influence treatment outcomes, supporting its inclusion as a covariate to improve the precision of treatment effect estimates in trials, and its use in clinical practice to help tailor treatment to individual patients. These exploratory findings require confirmation in larger studies.

Non-pharmacological adjuncts are needed for chronic non-cancer pain in patients receiving long-term opioid therapy. Music listening may reduce pain, but most previous trials have used passive controls, limiting attribution of effects specifically to music. In this open-label, parallel- group, proof-of-concept randomized controlled trial, adults with chronic non-cancer pain receiving long-term opioid therapy were randomized 1:1 to four weeks of daily home-based music or audiobook listening. Analgesic outcomes included pain intensity, responder rates, quantity of pain relief, and multidimensional pain assessment; secondary outcomes included mood, quality of life, global impression of change, and safety. Of 70 participants entering the run-in period, 56 were randomized (28 per group). Adjusting for baseline pain intensity in a linear mixed-effects model, the between-group difference at end of treatment was -1.26 NRS points (95% CI -1.98 to -0.55; p<0.001; d=-0.70), favoring music. A [&ge;]30% pain-reduction criterion was met by 21.4% of participants in the music group and none in the audiobook group (p=0.023). An exploratory between-group difference in pain intensity favoring music was also observed at follow-up. Other analgesic and secondary outcomes showed no significant between-group differences, although exploratory within-group improvements in mood and health-related quality of life were observed with music. Both groups reported overall improvement in global perceived change, with ratings numerically favoring music. No intervention-related harms were observed. These findings support an analgesic benefit of music beyond the structured listening experience shared with the active comparator. Daily self-administered music listening may represent a feasible, low-cost adjunct for chronic non-cancer pain in patients receiving long-term opioid therapy.

Background: Opioids remain the cornerstone of acute postoperative pain management but are associated with potentially serious adverse effects. We aimed to investigate the effect of oxycodone patient-controlled analgesia with adjunctive S-ketamine on pain after lumbar fusion surgery. Methods: In this secondary analysis, we examined oxycodone and S-ketamine exposure and PCA behaviour during the first 24 h. We assessed current pain versus subsequent PCA activity and whether the association between plasma oxycodone and adequate analgesia changed with postoperative time. Results: Plasma concentrations of administered drugs rose rapidly after PCA initiation, but variation was large. Metabolite concentrations accumulated over time. PCA attempt and delivered-dose rates decreased over postoperative time (RR 0.965 and 0.966 per hour, respectively; both P<0.001). Older age was associated with a lower delivered-dose rate (RR 0.905 per 10 years, 95% CI 0.829-0.987). Each 1-point higher current pain score was associated with more subsequent PCA attempts (RR 1.09, 95% CI 1.04-1.14) and delivered doses (RR 1.07, 95% CI 1.03-1.11). The oxycodone-analgesia association weakened over time [interaction P <0.001; odds ratios (Ors) per 10 ng/mL 1.16, 1.13, and 1.00 at 1, 4, and 24 h, respectively]. In active S-ketamine groups, including S-ketamine, norketamine, and 6-hydroxynorketamine concentrations left the pain-PCA association unchanged (RR 1.09 and 1.07) and preserved the time-dependent oxycodone association (ORs 1.30, 1.26, and 1.02). Conclusions: During PCA, drug exposure develops from patient-generated dosing histories while pain and recovery change. Current pain was associated with subsequent PCA activity, and the oxycodone-analgesia association was time-dependent.

Detection of postoperative pain in mice is challenging, and there is a need for unbiased, automated methods. Home-cage monitoring systems are promising, but their ability to detect mild pain remains unclear. We evaluated whether home-cage activity measures can be used to detect pain-related changes in a plantar incision model of postoperative pain. First, we confirmed the presence of local hypersensitivity using von Frey filaments on 48 C57BL/6JRj mice (24 males, 24 females). Subsequently, we pair-housed 64 mice (32 males, 32 females) and allocated them to receive either a 4 mm plantar incision on the hind paw under anaesthesia, or anaesthesia alone. Baseline locomotion and voluntary wheel-running activity were recorded over five days, followed by four days of postprocedural monitoring in the home cages. Both procedure groups (incision and anaesthesia-only) showed reduced locomotion and running wheel activity relative to baseline. However, activity measures did not differ between incised and anaesthesia-only mice, and we detected no sex-related effects. Under these conditions, home cage activity measures did not reliably discriminate pain-related behavioural changes in the model, despite the model showing local mechanical hypersensitivity in the von Frey test. Together, these findings indicate that, given the mild and localised nature of the plantar incision mouse model, commonly used home-cage metrics cannot yet reliably detect subtle pain-related behavioural changes.

Trigeminal pain produces persistent facial hypersensitivity that is difficult to treat. Ion channels contribute to the pathology of trigeminal pain, but the consequences of their modulation remain poorly understood. We previously demonstrated that voltage-gated sodium channel Nav1.7 is a therapeutic target that can be indirectly modulated via interaction with collapsin mediated response protein 2 (CRMP2) to reduce membrane expression of Nav1.7 and trigeminal ganglion neuronal excitability. We used the Foramen Rotundum Inflammatory Constriction of the Trigeminal InfraOrbital Nerve (FRICT-ION) model of trigeminal neuropathic pain to characterize behavioral and supraspinal effects of indirectly modulating the peripheral CRMP2-Nav1.7 interaction via our novel Compound 194 (C194). FRICT-ION produced mechanical and cold allodynia, which were reduced by C194, but had no effect on non-evoked affective behaviors. Despite behavioral improvement, C194 did not normalize heightened glutamatergic activity in the parabrachial nucleus (PBN), revealing a dissociation between behavioral analgesia and activity of a central pain circuit. These findings extend mechanistic studies of C194 in the trigeminal system and demonstrate efficacy of CRMP2-Nav1.7 disruption in modulating facial pain-like behavior. These results support the CRMP2-Nav1.7 axis as a promising therapeutic target while highlighting the need to define how peripheral and central adaptations interact to shape persistent facial pain.

Objective: To identify demographic and daily cognitive, affective, and contextual predictors of headache-related interference with activity and concentration in a smartphone-based migraine cohort, using statistical models appropriate to the ordinal structure of patient-reported interference. Background: Migraine burden extends beyond headache to encompass cognitive and affective disturbance, yet most disability instruments summarize functioning retrospectively and cannot capture day-to-day variability in interference. Ecological momentary assessment addresses this limitation, yet few studies have examined cognitive and affective correlates of interference independent of pain intensity or have modeled interference using methods that respect its ordinal, non-equal-interval structure. Methods: From May 2025 to April 2026, adult participants were enrolled in this prospective, decentralized observational study via specialty clinics and social media campaigns. Eligibility required fulfilling ICHD-3 diagnostic criteria for migraine using a validated electronic survey and experiencing between 3 and 20 monthly headache days. Enrolled individuals recorded daily smartphone diary entries and performed three brief cognitive tests over a 30-day monitoring period. Daily interference with activities and concentration were captured on 5-point ordinal scales and analyzed via cumulative link mixed-effects models incorporating participant-specific random intercepts. Predictor selection across nested specifications relied on likelihood ratio testing and Akaike Information Criterion (AIC) metrics, prioritizing the more parsimonious model when goodness-of-fit was comparable. Results: The analytic sample comprised 1,267 headache-day observations from 143 participants. In the final models, brain fog (OR = 2.49 for activity, 3.19 for concentration), forgetfulness (OR = 1.48, 1.65), and mood disturbance (OR = 1.19, 1.31) were each independently associated with both outcomes (all p < 0.01), while age, sex, and employment status showed no significant association with either. Sleep quality (OR = 0.86) and anticipated next-day enjoyment (OR = 0.81) provided additional explanatory value for activity interference (p < 0.05) but not for concentration interference, for which the three-predictor model of brain fog, forgetfulness, and mood alone was retained as the most parsimonious final model. Conclusions: Cognitive and affective symptoms, rather than demographic or socioeconomic characteristics, are the primary correlates of headache-related functional interference in this cohort. Activity and concentration interference are explained by partially distinct sets of daily influences, supporting the clinical value of assessing cognitive and affective symptoms alongside conventional pain-focused evaluation.

Introduction: Neuroinflammation is a known pathophysiologic mechanism in multiple sclerosis and a proposed mechanism in fibromyalgia and myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS). Positron Emission Tomography (PET) imaging of the translocator protein (TSPO) has been widely used to measure neuroinflammation, though second-generation ligands are highly sensitive to a single nucleotide polymorphism, rs6971, resulting in high, mixed, and low affinity binders. It is unknown whether this polymorphism is associated with neuroinflammatory disorders. Materials and Methods: Eighty-six total participant genotypes for TSPO binding affinity were identified through Sanger sequencing (30 fibromyalgia, 21 ME/CFS, 11 multiple sclerosis, and 24 healthy controls). Associations between patient group and genotype were assessed with Fishers Exact test. Associations between genotype and symptom severity from self-report questionnaires were assessed with Kruskal-Wallis tests. Results: In the present study individuals with fibromyalgia, (ME/CFS), or multiple sclerosis were more likely to have a mixed- or low-affinity genotypes compared to healthy controls. Presence of the low or mixed genotypes were also associated with greater self-reported fatigue severity and depressive symptoms. Discussion: These findings should be confirmed in larger samples but suggest functional consequences of rs6971 polymorphism that may be related to the pathophysiology of pain and fatigue illnesses.

Importance: Pain varies in its intensity and course, yet much of our understanding of pain is based on cross-sectional assessments or longitudinal studies of selected clinical populations. Routinely collected electronic health record data may enable characterization of longitudinal pain patterns at scale. Objective: To identify longitudinal pain profiles among U.S. Veterans and characterize their clinical and polygenic correlates. Design: Cohort study using electronic health record and genomic data from the Million Veteran Program, with up to 16 years of pain assessments collected between 2000 to 2025. Setting: U.S. Department of Veterans Affairs health care system. Participants: Million Veteran Program participants assigned to African-like, Admixed American-like, East Asian-like, European-like, or South Asian-like genetically inferred ancestry groups who have at least three years of outpatient numeric rating scale pain records. Exposures: Outpatient pain ratings and polygenic scores for psychiatric, sleep, and substance use traits. Main Outcomes and Measures: Pain profiles were identified using Gaussian finite mixture modeling of pain intensity, directional change, and within-person variability. Profiles were characterized by pain, psychiatric and substance use diagnoses, opioid exposure, body mass index, and polygenic scores. Results: Among 624,996 participants (Mean [SD] age at first pain rating=53.4 [13.5] years; 568,833 [91.0%] male), 51,731,567 outpatient pain ratings were analyzed. Three profiles were identified: stable no pain, stable mild pain, and mild-to-moderate increasing pain. Compared with the stable no pain profile, the increasing pain profile had higher odds of chronic pain (OR=21.14 [95% CI: 18.96-23.57]), opioid use disorder (OR=9.32 [95% CI: 8.31-10.45]), opioid exposure (OR=8.61 [95% CI: 8.41-8.83]), major depressive disorder (OR=3.77 [95% CI: 3.67-3.87]), and posttraumatic stress disorder (OR=3.72 [95% CI: 3.61-3.84]). Associations were attenuated but remained after adjustment for mean pain severity. Polygenic scores for depression, insomnia, attention-deficit/hyperactivity disorder, and tobacco use disorder were the most consistent predictors of increasing pain across the three largest genetically inferred ancestry groups. Conclusions and Relevance: Longitudinal modeling of routinely collected pain scores identified pain profiles associated with clinical burden and polygenic liability. These profiles captured clinically meaningful information beyond mean pain severity alone, highlighting the value of longitudinal pain phenotyping in electronic health record data.

Background: Temporary 60-day percutaneous peripheral nerve stimulation (PNS) can relieve pain in refractory occipital neuralgia (ON), but whether it alters acute healthcare utilization relative to the natural trajectory of the disease is unknown, because prior studies have lacked a concurrent comparator. Methods: We performed a secondary analysis of prospectively collected data from a tertiary interventional pain center. Adults with medically refractory ON (primary diagnosis occipital neuralgia, ICD-10-CM M54.81) who underwent 60-day occipital PNS (n = 42) were compared with concurrent patients who were clinically eligible for PNS but were denied insurance authorization and continued optimized non-PNS management (usual care; n = 63). Headache-related emergency department (ED) encounters - index (occipital neuralgia) and non-index (other headache/facial-pain diagnoses) - were ascertained over the 12 months before and after the treatment window via the electronic record and the statewide health information exchange. Patients were 1:1 propensity-matched on a priori confounders (age, sex, baseline total headache-related ED utilization, HIT-6, and baseline headache-medication use). The primary analysis was a difference-in-differences (DiD) comparison of the change in headache-related ED utilization, reported as the additive difference (Hodges-Lehmann estimate, distribution-free 95% CI) and, alongside, as a multiplicative rate ratio (RR). Results: Thirty-six matched pairs were well balanced. Baseline headache-related ED utilization was nearly identical between matched groups (6.3 vs. 6.2 visits/year). Over the following year, PNS patients' utilization fell to 2.5 while usual-care patients' rose to 6.9. The DiD was 5.0 fewer headache-related ED visits per patient (95% CI 3.0-6.0; p < 0.001), corresponding to a rate ratio of 0.36 (95% CI 0.27-0.48; p < 0.001). Results were consistent in the full sample, in covariate-adjusted models, and after excluding controls denied for incomplete conservative-therapy trials. The effect was driven by non-index headache visits. Conclusions: Relative to a concurrent, matched usual-care cohort whose headache related ED utilization rose over time, 60-day occipital PNS was associated with a substantial reduction in acute-care use, strengthening the case for a role of PNS on healthcare utilization in refractory ON.

Many pathological conditions, including chronic pain (CP), can impair cognitive functions. These functions are essential for adapting and evolving in concordance with the environment, which are key processes for coping with CP. However, in CP centers, cognitive assessment is rarely included in CP patient follow-up due to a lack of time, appropriate tools, or trained health professionals. To fill this gap, our team developed EasyCog, a digital tool that enables rapid self-assessment of cognitive functions. It enables cognitive evaluation without an experimenter's help, thanks to speech recognition powered by an artificial neural network. In the initial validation steps, we established normative values for 7 cognitive functions on a cohort of 76 healthy subjects. Because EasyCog includes tests comparable to the Montreal Cognitive Assessment (MoCA) and the Mini-Mental State Examination (MMSE), we assessed its reliability against available normative values. To assess its specificity, we compared data from healthy subjects with 15 subjects with mild cognitive impairment (MCI) and 15 age-matched CP patients selected from a medical center. Finally, we tested EasyCog's test-retest reliability by repeating sessions at different time intervals. EasyCog showed excellent sensitivity to age-related decline, similar to MoCA normative values. Several cognitive functions were significantly and differentially impaired in MCI subjects and CP patients compared to normative values in healthy subjects, confirming good specificity. Finally, test-retest analysis showed no effect at a 4-month interval. In conclusion, EasyCog appears to be a convenient and reliable numeric tool for rapidly assessing and monitoring cognitive functions in patients.

The cytokine FL and its receptor, Fms-like tyrosine kinase 3 (FLT3), contribute to chronic pain and to the maladaptive effects of morphine but the intracellular mechanisms underlying these effects remain incompletely understood. Here, we investigated the contribution of the Raf-MEK-ERK pathway to FLT3dependent nociceptive signaling and to the modulation of morphine analgesia. Using HEK293T cells expressing human or mouse FLT3, primary dorsal root ganglion (DRG) neurons, and rodent models, we examined ERK activation, TRPV1 sensitization, and behavioral responses following FLT3 activation by its ligand, FL. FL induced concentration-dependent ERK phosphorylation through FLT3, while pharmacological inhibition of FLT3, Raf, or MEK reduced this response. In primary DRG neurons, MEK inhibition attenuated FLinduced potentiation of capsaicin-evoked calcium responses, supporting a role for MEK-ERK signaling in TRPV1 sensitization. In vivo, intrathecal FL increased ERK phosphorylation in DRGs and induced mechanical hypersensitivity, both of which were reduced by Raf or MEK inhibition. In FLT3/MOR-expressing cells, morphine potentiated FL-induced ERK activation, an effect reduced by naloxone and abolished by FLT3 inhibition. In rats, MEK inhibition prevented the FL-induced reduction of morphine analgesia and subsequent mechanical hypersensitivity. Together, these findings identify Raf-MEK-ERK signaling as an important downstream pathway linking neuronal FLT3 activation to nociceptor sensitization and impaired morphine analgesic efficacy.

While progress has been made in identifying pain biomarkers using neuroimaging, the development of reliable EEG-based biomarkers remains challenging, limited by small sample sizes and the lack of adequate control conditions. We present a comprehensive dataset from 125 pain-free adults, comprising electroencephalogram (EEG) recordings, and behavioural, sociodemographic, and psychological data. Galvanic skin response and electrocardiogram data were also recorded in a subset of participants (n = 76). Participants received two sustained painful stimulations (thermal, chemical) and two sustained aversive non-painful stimulations (auditory, taste), each delivered twice (with and without continuous intensity ratings). Data are provided in Brain Imaging Data Structure format, where all physiological, stimulus-related, and behavioural data are synchronized within the EEG data files for easy access and analysis. Technical validation confirmed data integrity, with spectral and physiological analyses showing responses associated with stimulus intensity and subjective pain/unpleasantness levels. By providing multimodal physiological data across painful and non-painful aversive conditions, this initiative represents a valuable resource for developing or validating biomarkers and exploring the multidimensional nature of pain perception.

BackgroundNeuropathic pain is a common and debilitating condition with persistently poor translation from preclinical research to effective clinical therapies. Preclinical systematic reviews and meta-analyses (SRMAs) can provide more robust estimates of intervention effects and help identify sources of bias and heterogeneity, but their use is limited by the time and effort required to synthesise rapidly expanding literatures. Automation may help overcome these barriers. MethodsWe developed Neuropathic Pain - Systematic Online Living Evidence Summaries (NP-SOLES), a machine-assisted approach used in this study to support systematic identification of animal studies relevant to neuropathic pain. Using NP-SOLES, we conducted a pilot systematic review and meta-analysis of controlled animal studies assessing the effects of citrus flavonoids on thermal and mechanical pain-related outcomes in streptozotocin-induced models of painful diabetic neuropathy. ResultsIn this pilot application, machine-assisted evidence synthesis supported reduced manual screening burden, illustrating the potential of such approaches to facilitate timely preclinical SRMAs. Fourteen studies met inclusion criteria for meta-analysis on thermal pain-related outcomes. Pooled estimates suggested a reduction in thermal pain-related behaviours following flavonoid treatment; however, substantial heterogeneity and widespread methodological limitations were observed. Nine studies were eligible for qualitative analysis on mechanical pain-related outcomes, which showed an overall reduction in pain-related behaviours following treatment but had similar methodological limitations. Reporting of key measures to reduce risk of bias, including randomisation and blinding, were consistently poor, and subgroup analyses were constrained by sparse data. ConclusionsAvailable evidence from preclinical animal studies suggests a potential analgesic effect of citrus flavonoids on thermal and mechanical pain-related outcomes in diabetic neuropathy models, but confidence in this estimate is limited by significant risks of bias. More rigorously designed and transparently reported preclinical studies are required before clinical translation can be justified.

Neuropathic pain involves spinal microglial activation and metabolic changes.Forsythoside B (FB) has anti-inflammatory effects, but its role in neuropathic pain and microglial glycolysis remains unclear. We investigated the effects and mechanisms of FB in mice with chronic constriction injury (CCI) and in LPS-stimulated BV2 microglia.FB reduced mechanical allodynia and thermal hyperalgesia in CCI mice. FB also reduced the spinal levels of HIF-1, HK2, PKM2, LDHA, and CD86. It decreased the proportion of IBA1+/CD86+ cells and the levels of IL-1{beta}, IL-6, and TNF-. In LPS20 stimulated BV2 microglia, FB reduced glycolysis-related proteins, proinflammatory markers, and cytokine release. FB also reduced glycolytic activity and partly restored basal mitochondrial respiration. FB did not change Hif1a mRNA levels. However, it Manuscript Click here to access/download;Manuscript;Manuscript.docx increased HIF-1 ubiquitination and promoted its proteasome-dependent degradation. HIF-1 overexpression partly reversed the effects of FB on glycolytic enzymes, CD86 expression, and proinflammatory cytokine production. Immunoprecipitation followed by mass spectrometry and UbiBrowser analysis identified USP7 as a candidate HIF27 1-associated deubiquitinase. Molecular docking and cellular thermal shift assays supported a possible interaction between FB and USP7. FB reduced the association between USP7 and HIF-1. USP7 knockdown produced effects similar to those of FB on HIF-1 ubiquitination and downstream glycolytic and inflammatory responses.Overall, FB alleviated neuropathic pain and reduced proinflammatory microglial responses. These effects may involve the promotion of HIF-1 degradation through modulation of the USP7-HIF-1 regulatory axis.

The genetic evidence for an essential role of sodium channel Nav1.7 in human pain conditions is compelling. Unfortunately, potent selective channel blockers of Nav1.7 are not useful analgesics because they have deleterious side effects, particularly on the autonomic nervous system. Here we have evaluated the downstream mechanisms induced by Nav1.7 loss in utero. Nav1.1 compensates for loss of Nav1.7 in sensory neurons and antisense Nav1.1 oligonucleotides diminish excitability in Nav1.7 embryonic null sensory neurons. Enhanced endogenous opioid signalling contributes substantially to analgesia. This is linked to altered gene expression that potentiates opioid signalling through lowered levels of proteins that terminate G-protein signalling (RGS4 and RGS8). There is also enhanced opioid drive through increased enkephalin levels linked to lowered sodium levels in Nav1.7 null neurons. Opioid signalling is the main driver of analgesia, but enhanced potassium channel expression (KCNC4 KCNK2, KCNMB2, KCNAB3) all implicated in pain control, may also contribute to the small level of naloxone-resistant analgesia. These findings suggest a potential new route to analgesia, through mimicking the events at Nav1.7 null sensory neuron terminals. Here we demonstrate potentiation of suzetrigine-evoked analgesia with RGS antagonists alone or in combination with normally inactive doses of morphine in formalin-evoked pain and CFA-induced inflammatory pain. Intriguingly, no analgesia is observed with acute pain. Cancer pain is under investigation. These data are of potential clinical interest.

Behavioral scoring is central to preclinical pain research but is typically performed manually, which is inherently low-throughput and subject to variability between observers. Automated alternatives exist, but cost and programming expertise limit adoption beyond the laboratories that build them. Here we describe PixelPaws, an open-source platform combining a near-infrared imaging enclosure built from consumer parts for under $300, multi-camera acquisition software, a bundled pose-estimation network, and eight classifiers in a graphical user interface. We evaluated the platform across standard assays of pain, itch, and opioid withdrawal. Licking, scratching, and jumping classifiers were validated against trained human observers by leave-one-session-out evaluation. In the formalin assay, classifier-scored licking followed the expected biphasic time course and was reduced dose-dependently by oxycodone, with a phase 2 potency estimate comparable to blinded manual scoring. Chloroquine roughly tripled scratching, and naloxone precipitated a burst of jumping in oxycodone-treated mice. From the same recordings we derived a set of paw contour metrics. Contour intensity fell after formalin and tracked the oxycodone dose series, and contour area shifted toward symmetry after oxycodone in nerve-injured mice. Behavioral sequencing revealed distinct changes in the transi