Gender variations in clinical pain experience

TNFR1/p38αMAPK signaling in Nex + supraspinal neurons regulates estrogen-dependent chronic neuropathic pain

Upregulation of soluble tumor necrosis factor (sTNF) cytokine signaling through TNF receptor 1 (TNFR1) and subsequent neuronal hyperexcitability are observed in both animal models and human chronic neuropathic pain (CNP). Previously, we have shown that estrogen modulates sTNF/TNFR1 signaling in CNP, which may contribute to female prevalence of CNP. The estrogen-dependent role of TNFR1-mediated supraspinal neuronal circuitry in CNP remains unknown. In this study, we interrogated the intersect between supraspinal TNFR1 mediated neuronal signaling and sex specificity by selectively removing TNFR1 in Nex + neurons in adult mice (NexCreERT2::TNFR1f/f). We determined that mechanical hypersensitivity induced by chronic constriction injury (CCI) decreases over time in males, but not in females. Subsequently, we investigated two downstream pathways, p38MAPK and NF-κB, important in TNFR1 signaling and injury response. We detected p38MAPK and NF-κB activation in male cortical tissue; however, p38MAPK phosphorylation was reduced in NexCreERT2::TNFR1f/f males. We observed a similar recovery from acute pain in male mice following CCI when p38αMAPK was knocked out of supraspinal Nex + neurons (NexCreERT2::p38αMAPKf/f), while chronic pain developed in female mice. To explore the intersection between estrogen and inflammation in CNP we used a combination therapy of an estrogen receptor β (ER β) inhibitor with a sTNF/TNFR1 or general p38MAPK inhibitor. We determined both combination therapies lends therapeutic relief to females following CCI comparable to the response evaluated in male mice. These data suggest that TNFR1/p38αMAPK signaling in Nex + neurons in CNP is male-specific and lack of therapeutic efficacy following sTNF inhibition in females is due to ER β interference. These studies highlight sex-specific differences in pathways important to pain chronification and elucidate potential therapeutic strategies that would be effective in both sexes.

Sex differences in mechanisms of pain hypersensitivity

The introduction of sex-as-a-biological-variable policies at funding agencies around the world has led to an explosion of very recent observations of sex differences in the biology underlying pain. This review considers evidence of sexually dimorphic mechanisms mediating pain hypersensitivity, derived from modern assays of persistent pain in rodent animal models. Three well-studied findings are described in detail: the male-specific role of spinal cord microglia, the female-specific role of calcitonin gene-related peptide (CGRP), and the female-specific role of prolactin and its receptor. Other findings of sex-specific molecular involvement in pain are subjected to pathway analyses and reveal at least one novel hypothesis: that females may preferentially use Th1 and males Th2 T cell activity to mediate chronic pain.

Patterns of opioid use in New Zealand older adults, 2007-2018

OBJECTIVES

Opioid use has increased globally, dramatically increasing opioid overdose, dependence, abuse and mortality. Limited research is available on opioid use patterns in older adults in New Zealand and internationally. This study aims to address this gap by determining the incidence and prevalence of opioid use among older adults (age ≥65 years) in New Zealand from 2007 to 2018.

METHODS

This was a population-based retrospective cohort study conducted using New Zealand national administrative healthcare databases. The annual opioid use incidence (2008-2018) and prevalence (2007-2018) in older adults were determined and stratified by sex, age, and opioid type and strength. We used descriptive statistics to summarise the patterns of opioid dispensing. Data analysis was conducted using MS Excel, and data linking was performed using SQL software.

RESULTS

A total of 820,349 older adults were initiated on opioids during the study period. The overall incidence of opioid use in older adults showed a steady increase from 2008 to 2015; similarly, the prevalence steadily increased from 2007 to 2015, and thereafter, both rates fluctuated. A slight decrease in both prevalence and incidence rates was observed in 2018. Codeine and tramadol were the most commonly dispensed opioids during the study period. Females had a higher incidence and prevalence of all opioids than males.

CONCLUSIONS

The incidence and prevalence of opioid dispensing increased in New Zealand older adults over time. Monitoring the trends of opioid use in older adults is critical to enable clinicians and policymakers to deliver early interventions to prevent future opioid-related adverse events.

Musculoskeletal disorders and risk indicators for pain chronification among German dentists: A cross-sectional questionnaire-based study

OBJECTIVES

The aim of this study was to determine the prevalence of musculoskeletal (MS) disorders in practicing German dentists and identify risk factors for pain chronification.

METHODS

This was a cross-sectional, quantitative, questionnaire-based study in which the validated German version of the Örebro Musculoskeletal Pain Questionnaire was sent out to practicing German dentists.

RESULTS

Of the 8,072 questionnaires sent out, 576 dentists responded (60.2% men, 39.8% women; mean [SD] age, 50 [10.1] years; response rate, 7.1%). Overall, 344 dentists had current pain at 719 pain sites (point prevalence, 59.7%). The risk of chronic pain in dentists with current MS pain was high in 28.5% (n = 98), moderate in 30.5% (n = 105), and low in 41% (n = 141). The multivariate logistic regression analysis showed that specialization in restorative dentistry was associated with a significantly higher risk of experiencing pain chronification (odds ratio [OR], 3.94; P = .008), followed by specialization in pediatric dentistry (OR, 0.35; P = .048). A history of current pain, particularly current leg pain, was predictive of higher chronification risk (OR, 22.0; P < .001) and neck pain (OR, 4.51; P = .001).

CONCLUSIONS

Almost two-thirds of practicing German dentists have MS pain, and one-third of these have a moderate through high risk of developing pain chronification. These health problems have an adverse impact on their ability to successfully perform dental services, with the potential for prolonged sick leave, disability, and early retirement. Accordingly, these problems deserve greater attention from the scientific community (identification of risk factors), universities (sensitization and education), and policy makers (development and implementation of appropriate countermeasures for MS disorders in the dental profession).

PRACTICAL IMPLICATIONS

Knowing the risk factors associated with acute and chronic MS pain may help dentists take preventive measures and thereby improve their physical well-being and work-related quality of life.

Healthy women show more experimentally induced central sensitization compared with men

ABSTRACT

Women more often experience chronic pain conditions than men. Central sensitization (CS) is one key mechanism in chronic pain that can differ between the sexes. It is unknown whether CS processes are already more pronounced in healthy women than in men. In 66 subjects (33 women), a thermal CS induction protocol was applied to the dorsum of one foot and a sham protocol to the other. Spatial extent [cm 2 ] of secondary mechanical hyperalgesia (SMH) and dynamic mechanical allodynia were assessed as subjective CS proxy measures, relying on verbal feedback. Changes in nociceptive withdrawal reflex magnitude (NWR-M) and response rate (NWR-RR) recorded through surface electromyography at the biceps and rectus femoris muscles were used as objective CS proxies. The effect of the CS induction protocol on SMH was higher in women than in men (effect size 2.11 vs 1.68). Nociceptive withdrawal reflex magnitude results were statistically meaningful for women (effect size 0.31-0.36) but not for men (effect size 0.12-0.29). Differences between men and women were not meaningful. Nociceptive withdrawal reflex response rate at the rectus femoris increased in women after CS induction and was statistically different from NWR-RR in men (median differences of 13.7 and 8.4% for 120 and 140% reflex threshold current). The objective CS proxy differences indicate that dorsal horn CS processes are more pronounced in healthy women. The even larger sex differences in subjective CS proxies potentially reflect greater supraspinal influence in women. This study shows that sex differences are present in experimentally induced CS in healthy subjects, which might contribute to women's vulnerability for chronic pain.

Dexmedetomidine versus remifentanil in nasal surgery: a systematic review and meta-analysis

BACKGROUND

Nasal surgeries, addressing anatomical variations for form and function, require careful anesthesia administration, including dexmedetomidine and remifentanil. This meta-analysis evaluates their safety and efficacy variations in nasal surgeries, emphasizing patient comfort and optimal outcomes.

METHODS

Four electronic databases (PubMed, Scopus, Web of Science, and CINAHL Complete) were searched for records in English. Studies that measure the effect of dexmedetomidine versus remifentanil on patients underwent nasal surgery were included. The Cochrane Collaboration's tool was used to assess the quality of the included studies. A random-effect model was preferred and statistical analysis was performed by Stata software version 17.

RESULTS

Out of an initial pool of 63 articles, five studies were selected for this analysis. All of these chosen studies were Randomized Controlled Trials (RCTs). The meta-analysis involved a total of 302 participants, with 152 in the remifentanil group and 150 in the dexmedetomidine group. The analysis aimed to compare the effects of Dexmedetomidine and Remifentanil on heart rate (HR) and mean arterial pressure (MAP) during surgery. Both groups exhibited similar MAP and HR, with the exception of a slightly lower HR in the remifentanil group at the 15th minute of surgery (Standardized Mean Difference: -0.24 [-0.83, 0.34]). Furthermore, when evaluating the impact of these medications on post-surgery outcomes, including pain levels, the use of pain relief medications, patient-surgeon satisfaction, agitation scores, and recovery time, no significant differences were observed between the two medications in any of these aspects.

CONCLUSION

In summary, the study compared Dexmedetomidine and Remifentanil in nasal surgeries anesthesia. No significant differences were found in heart rate, blood pressure, satisfaction, pain, agitation, or recovery time. The study had limitations, and future research should establish standardized protocols and consider various surgical factors.

Sex differences in pain catastrophizing and its relation to the transition from acute pain to chronic pain

BACKGROUND AND IMPORTANCE

Differences exist between sexes in pain and pain-related outcomes, such as development of chronic pain. Previous studies suggested a higher risk for pain chronification in female patients. Furthermore, pain catastrophizing is an important risk factor for chronification of pain. However, it is unclear whether sex differences in catastrophic thinking could explain the sex differences in pain chronification.

OBJECTIVES

The aim of this study was to examine sex differences in pain catastrophizing. Additionally, we investigated pain catastrophizing as a potential mediator of sex differences in the transition of acute to chronic pain.

DESIGN, SETTINGS AND PARTICIPANTS

Adults visiting one of the 15 participating emergency departments in the Netherlands with acute pain-related complaints. Subjects had to meet inclusion criteria and complete questionnaires about their health and pain.

OUTCOMES MEASURE AND ANALYSIS

The outcomes in this prospective cohort study were pain catastrophizing (short form pain catastrophizing) and pain chronification at 90 days (Numeric Rating Scale ≥ 1). Data was analysed using univariate and multivariable logistic regression models. Finally, stratified regression analyses were conducted to assess whether differences in pain catastrophizing accounted for observed differences in pain chronification between sexes.

MAIN RESULTS

In total 1,906 patients were included. Females catastrophized pain significantly more than males (p < 0.001). Multiple regression analyses suggested that pain catastrophizing is associated with pain chronification in both sexes.

CONCLUSIONS

This study reported differences between sexes in catastrophic cognitions in the development of chronic pain. This is possibly of clinical importance to identify high-risk patients and ensure an early intervention to prevent the transition from acute to chronic pain.

Increased Purinergic Signaling in Human Dental Pulps With Inflammatory Pain is Sex-Dependent

An enhanced understanding of neurotransmitter systems contributing to pain transmission aids in drug development, while the identification of biological variables like age and sex helps in the development of personalized pain management and effective clinical trial design. This study identified enhanced expression of purinergic signaling components specifically in painful inflammation, with levels increased more in women as compared to men. Inflammatory dental pain is common and potentially debilitating; as inflammation of the dental pulp can occur with or without pain, it provides a powerful model to examine distinct pain pathways in humans. In control tissues, P2X3 and P2X2 receptors colocalized with PGP9.5-positive nerves. Expression of the ecto-nucleotidase NTPDase1 (CD39) increased with exposure to extracellular adenosine triphosphate (ATP), implying CD39 acted as a marker for sustained elevation of extracellular ATP. Both immunohistochemistry and immunoblots showed P2X2, P2X3, and CD39 increased in symptomatic pulpitis, suggesting receptors and the ATP agonist were elevated in patients with increased pain. The increased expression of P2X3 and CD39 was more frequently observed in women than men. In summary, this study identifies CD39 as a marker for chronic elevation of extracellular ATP in fixed human tissue. It supports a role for increased purinergic signaling in humans with inflammatory dental pain and suggests the contribution of purines shows sexual dimorphism. This highlights the potential for P2X antagonists to treat pain in humans and stresses the need to consider sex in clinical trials that target pain and purinergic pathways. PERSPECTIVE: This article demonstrates an elevation of ATP-marker CD39 and of ATP receptors P2X2 and P2X3 with inflammatory pain and suggests the rise is greater in women. This highlights the potential for P2X antagonists to treat pain and stresses the consideration of sexual dimorphism in studies of purines and pain.

Pain mechanisms in the transgender individual: a review

Specific Aim

Provide an overview of the literature addressing major areas pertinent to pain in transgender persons and to identify areas of primary relevance for future research.

Methods

A team of scholars that have previously published on different areas of related research met periodically though zoom conferencing between April 2021 and February 2023 to discuss relevant literature with the goal of providing an overview on the incidence, phenotype, and mechanisms of pain in transgender patients. Review sections were written after gathering information from systematic literature searches of published or publicly available electronic literature to be compiled for publication as part of a topical series on gender and pain in the Frontiers in Pain Research.

Results

While transgender individuals represent a significant and increasingly visible component of the population, many researchers and clinicians are not well informed about the diversity in gender identity, physiology, hormonal status, and gender-affirming medical procedures utilized by transgender and other gender diverse patients. Transgender and cisgender people present with many of the same medical concerns, but research and treatment of these medical needs must reflect an appreciation of how differences in sex, gender, gender-affirming medical procedures, and minoritized status impact pain.

Conclusions

While significant advances have occurred in our appreciation of pain, the review indicates the need to support more targeted research on treatment and prevention of pain in transgender individuals. This is particularly relevant both for gender-affirming medical interventions and related medical care. Of particular importance is the need for large long-term follow-up studies to ascertain best practices for such procedures. A multi-disciplinary approach with personalized interventions is of particular importance to move forward.

Mechanisms of pain in aging and age-related conditions: Focus on caregivers

Pain is a complex, subjective experience that can significantly impact quality of life, particularly in aging individuals, by adversely affecting physical and emotional well-being. Whereas acute pain usually serves a protective function, chronic pain is a persistent pathological condition that contributes to functional deficits, cognitive decline, and emotional disturbances in the elderly. Despite substantial progress that has been made in characterizing age-related changes in pain, complete mechanistic details of pain processing mechanisms in the aging patient remain unknown. Pain is particularly under-recognized and under-managed in the elderly, especially among patients with Alzheimer's disease (AD), Alzheimer's disease-related dementias (ADRD), and other age-related conditions. Furthermore, difficulties in assessing pain in patients with AD/ADRD and other age-related conditions may contribute to the familial caregiver burden. The purpose of this article is to discuss the mechanisms and risk factors for chronic pain development and persistence, with a particular focus on age-related changes. Our article also highlights the importance of caregivers working with aging chronic pain patients, and emphasizes the urgent need for increased legislative awareness and improved pain management in these populations to substantially alleviate caregiver burden.

Social isolation consequences: lessons from COVID-19 pandemic in a context of dynamic lock-down in Chile

BACKGROUND

Chile did not adopt general and unified lockdowns for the whole nation but organized itself with dynamic and sometimes irregular lockdowns. These dynamics and consequences of social isolation could be generalized to other contexts of isolation such as those affecting minorities such as immigrants, prisoners, refugees.

METHODS

In this study, we investigated the physical and mental health symptoms associated with lifestyle changes due to lockdown among university students in Chile. We examined psychopathological variations in relation to mental health problems in a healthy young population. Our goal was to develop interventions to address these new psychosocial problems in potentially comparable post-pandemic contexts. From May 10th 2021 to June 2th 2021, 420 University students took part in an anonymous survey asking for information on habits and symptoms that emerged during the lockdown in response to the COVID-19 pandemic. Three health outcomes were assessed: digestive disorders; headache; fear of COVID-19. Covariates including conditions and lifestyle during the pandemic, SARS-CoV-2 infections in the family, financial situation and productivity were considered in the analysis.

RESULTS

Participants experienced headache and fear of COVID-19 quite frequently during the lockdown period. More than half of the sample also experienced social isolation. Female gender, sleep quality, memory difficulties, and a change in eating habits resulted associated with an increased risk of health outcomes such as headaches and digestive disorders.

CONCLUSIONS

The results of this study fit within an original pandemic context: The results of this study can help identify needs and promote solutions applicable to different contexts. Future interventions should focus on the promotion and implementation of healthy habits focused on sleep hygiene, psychoeducation on the use of mobile devices and gender medicine with the support of healthcare organizations and University.

Exploring Gender Differences in Veterans in a Secondary Analysis of a Randomized Controlled Trial of Mindfulness for Chronic Pain

Background

Although studies have documented higher rates of chronic pain among women Veterans compared to men Veterans, there remains a lack of comprehensive information about potential contributors to these disparities.

Materials and Methods

This study examined gender differences in chronic pain and its contributors among 419 men and 392 women Veterans, enrolled in a mindfulness trial for chronic pain. We conducted descriptive analyses summarizing distributions of baseline measures, obtained by survey and through the electronic health record. Comparisons between genders were conducted using chi-square tests for categorical variables and t-tests for continuous measures.

Results

Compared to men, women Veterans were more likely to have chronic overlapping pain conditions and had higher levels of pain interference and intensity. Women had higher prevalence of psychiatric and sleep disorder diagnoses, greater levels of depression, anxiety, post-traumatic stress disorder, fatigue, sleep disturbance, stress and pain catastrophizing, and lower levels of pain self-efficacy and participation in social roles and activities. However, women were less likely to smoke or have a substance abuse disorder and used more nonpharmacological pain treatment modalities.

Conclusion

Among Veterans seeking treatment for chronic pain, women differed from men in their type of pain, had greater pain intensity and interference, and had greater prevalence and higher levels of many known biopsychosocial contributors to pain. Results point to the need for pain treatment that addresses the comprehensive needs of women Veterans.

Clinical Trial Registration Number: NCT04526158. Patient enrollment began on December 4, 2020.

Sex-specific patterns of discomfort in patients with restless legs syndrome

STUDY OBJECTIVES

Sex differences in the prevalence of restless legs syndrome (RLS) have been reported, with a higher prevalence in women than in men. However, sex differences in clinical presentation remain unclear. We aimed to investigate the phenotypic differences in patients with RLS between sexes by comparing clinical presentations, iron status, polysomnographic parameters, and treatment.

METHODS

We retrospectively evaluated 614 patients (225 men, 389 women) diagnosed with RLS. To enhance the robustness of the study, an age-matched control group of 179 men and 286 women without sleep disorders was also included. Information on demographics and sleep-related questionnaires were collected. Iron status was evaluated using blood samples, and polysomnography was performed to evaluate periodic leg movements and comorbid sleep disorders.

RESULTS

Our analysis revealed no sex difference in the severity of RLS but a difference in the pattern of symptoms. Women had more frequent symptoms of pain and awakening during sleep, while men had more common motor symptoms (both self-reported symptoms and periodic leg movement on polysomnography). Women with RLS also had lower iron parameters and received more frequent iron supplementation therapy than men. In contrast to women with RLS, who presented higher sleep disturbances and depressive mood, men with RLS had a higher risk of comorbidities such as hypertension and cardiovascular disease. These sex differences were notably more pronounced than in the control group.

CONCLUSIONS

This study suggests that sex differences exist in RLS phenotypes, and clinicians should consider these differences for treatment.

CITATION

Kim J, Kim JR, Park HR, Joo EY. Sex-specific patterns of discomfort in patients with restless legs syndrome. J Clin Sleep Med. 2024;20(2):253-259.

Spatial transcriptomics and single-nucleus RNA sequencing reveal a transcriptomic atlas of adult human spinal cord

Despite the recognized importance of the spinal cord in sensory processing, motor behaviors, and neural diseases, the underlying organization of neuronal clusters and their spatial location remain elusive. Recently, several studies have attempted to define the neuronal types and functional heterogeneity in the spinal cord using single-cell or single-nucleus RNA sequencing in animal models or developing humans. However, molecular evidence of cellular heterogeneity in the adult human spinal cord is limited. Here, we classified spinal cord neurons into 21 subclusters and determined their distribution from nine human donors using single-nucleus RNA sequencing and spatial transcriptomics. Moreover, we compared the human findings with previously published single-nucleus data of the adult mouse spinal cord, which revealed an overall similarity in the neuronal composition of the spinal cord between the two species while simultaneously highlighting some degree of heterogeneity. Additionally, we examined the sex differences in the spinal neuronal subclusters. Several genes, such as SCN10A and HCN1, showed sex differences in motor neurons. Finally, we classified human dorsal root ganglia (DRG) neurons using spatial transcriptomics and explored the putative interactions between DRG and spinal cord neuronal subclusters. In summary, these results illustrate the complexity and diversity of spinal neurons in humans and provide an important resource for future research to explore the molecular mechanisms underlying spinal cord physiology and diseases.

Degenerative and regenerative peripheral processes are associated with persistent painful chemotherapy-induced neuropathies in males and females

This study aimed to investigate the time course of gene expression changes during the progression of persistent painful neuropathy caused by paclitaxel (PTX) in male and female mouse hind paws and dorsal root ganglia (DRG). Bulk RNA-seq was used to investigate the gene expression changes in the paw and DRG collected at 1, 16, and 31 days post-PTX. At these time points, differentially expressed DEGs were predominantly related to reduction or increase in epithelial, skin, bone, and muscle development and to angiogenesis, myelination, axonogenesis, and neurogenesis. These processes were accompanied by regulation of DEGs related to cytoskeleton, extracellular matrix organization and cellular energy production. This gene plasticity during persistent painful neuropathy progression likely represents biological processes linked to tissue regeneration and degeneration. Unlike regeneration/degeneration, gene plasticity related to immune processes was minimal at 1-31 days post-PTX. It was also noted that despite similarities in biological processes and pain chronicity in males and females, specific DEGs showed dramatic sex-dependency. The main conclusions of this study are that gene expression plasticity in paws and DRG during PTX neuropathy progression relates to tissue regeneration and degeneration, minimally affects the immune system processes, and is heavily sex-dependent at the individual gene level.

Using Myofascial Therapy to Improve Psychological Outcomes, Quality of Life, and Sexual Function in Women with Chronic Pelvic Pain-A Case Series

(1) Background: Chronic pelvic pain represents a prevalent condition afflicting women. Research has highlighted the presence of psychological distress and sexual dysfunction in these individuals. Regrettably, myofascial pelvic pain often goes unnoticed and untreated despite its integral role in chronic pelvic pain. (2) Methods: By employing a longitudinal case series design, we studied eighteen women afflicted with chronic pelvic pain. Over a 12-week period, these participants underwent 15 sessions of myofascial therapy. Data encompassing sociodemographic particulars, the Hospital Anxiety and Depression Scale, the Medical Outcomes Study Short Form 12 questionnaire, and the Female Sexual Function Index were collected at baseline, 12 weeks post-intervention, and again at the 24-week mark. (3) Results: After a span of 12 weeks subsequent to the intervention, the participants demonstrated noteworthy enhancements (p < 0.001) in their depression and anxiety scores, their overall Mental Component scores in the Medical Outcomes Study Short Form 12, as well as sexual function. Importantly, these gains were sustained at the 24-week juncture post-therapy. (4) Conclusions: The findings stemming from our prospective case study underscore the potential utility of myofascial therapy for women grappling with chronic pelvic pain. This form of intervention yields significant advancements in alleviating anxiety, depression, health-related quality of life, and sexual function.

Association of Risk Factors and Comorbidities With Chronic Pain in the Elderly Population

INTRODUCTION/OBJECTIVE

Chronic pain disorders affect about 20% of adults in the United States, and it disproportionately affects individuals living in the neighborhoods of extreme socioeconomic disadvantage. In many instances, chronic pain has been noted to arise from an aggregation of multiple risk factors and events. Therefore, it is of importance to recognize the modifiable risk factors. The aim of this study was to investigate the comorbid medical conditions and risk factors associated with chronic pain disorders in patients aged 65 years and older.

METHODS

Our team retrospectively reviewed medical records of elderly patients (65 years and older) who were evaluated in our outpatient medicine office between July 1, 2020 and June 30, 2021 for acute problems, management of chronic medical problems, or well visits. We divided our patients into a group who suffered from chronic pain disorder, and another group who did not have chronic pain disorder. The association of variables were compared between those groups.

RESULTS

Of the 2431 patients, 493 (20.3%) had a chronic pain disorder. A higher frequency of females in the group with chronic pain disorder was found compared to the group without a chronic pain disorder (60.6% vs 55.2%; P = .033). The mean ages between the two groups were similar in the group with a chronic pain disorder compared to the group without (76.35 ± 7.5 year vs 76.81 ± 7.59 year; P = .228). There were significant associations of certain comorbidities in the group with a chronic pain disorder compared to the group without a chronic pain disorder, such as depression (21.9% vs 15.2%; P < .001), anxiety (27.0% vs 17.1%; P < .001), chronic obstructive pulmonary disease (8.7% vs 6.1%; P = .036), obstructive sleep apnea (16.8% vs 11.6%; P = .002), gastroesophageal reflux disease (40.8% vs 29.0%; P < .001), osteoarthritis (49.3% vs 26.1%; P < .001), other rheumatologic diseases (24.9% vs 19.4%; P = .006), and peripheral neuropathy (14.4% vs 5.3%; P < .001).

CONCLUSION

Female sex, depression, anxiety, chronic obstructive pulmonary disease, obstructive sleep apnea, gastroesophageal reflux disease, osteoarthritis, other rheumatologic diseases, and peripheral neuropathy were significantly associated with chronic pain disorder in elderly patients, while BMI was not associated with chronic pain disorder.

Interleukin-1beta and inflammasome expression in spinal cord following chronic constriction injury in male and female rats

Females represent a majority of chronic pain patients and show greater inflammatory immune responses in human chronic pain patient populations as well as in animal models of neuropathic pain. Recent discoveries in chronic pain research have revealed sex differences in inflammatory signaling, a key component of sensory pathology in chronic neuropathic pain, inviting more research into the nuances of these sex differences. Here we use the chronic constriction injury (CCI) model to explore similarities and differences in expression and production of Inflammatory cytokine IL-1beta in the lumbar spinal cord, as well as its role in chronic pain. We have discovered that intrathecal IL-1 receptor antagonist reverses established pain in both sexes, and increased gene expression of inflammasome NLRP3 is specific to microglia and astrocytes rather than neurons, while IL-1beta is specific to microglia in both sexes. We report several sex differences in the expression level of the genes coding for IL-1beta, as well as the four inflammasomes responsible for IL-1beta release: NLRP3, AIM2, NLRP1, and NLRC4 in the spinal cord. Total mRNA, but not protein expression of IL-1beta is greater in females than males after CCI. Also, while CCI increases all four inflammasomes in both sexes, there are sex differences in relative levels of inflammasome expression. NLRP3 and AIM2 are more highly expressed in females, whereas NLRP1 expression is greater in males.

Interleukin-17: A Putative Novel Pharmacological Target for Pathological Pain

Pathological pain imposes a huge burden on the economy and the lives of patients. At present, drugs used for the treatment of pathological pain have only modest efficacy and are also plagued by adverse effects and risk for misuse and abuse. Therefore, understanding the mechanisms of pathological pain is essential for the development of novel analgesics. Several lines of evidence indicate that interleukin-17 (IL-17) is upregulated in rodent models of pathological pain in the periphery and central nervous system. Besides, the administration of IL-17 antibody alleviated pathological pain. Moreover, IL-17 administration led to mechanical allodynia which was alleviated by the IL-17 antibody. In this review, we summarized and discussed the therapeutic potential of targeting IL-17 for pathological pain. The upregulation of IL-17 promoted the development of pathological pain by promoting neuroinflammation, enhancing the excitability of dorsal root ganglion neurons, and promoting the communication of glial cells and neurons in the spinal cord. In general, the existing research shows that IL-17 is an attractive therapeutic target for pathologic pain, but the underlying mechanisms still need to be investigated.

Validity and Reliability of the Persian Version of Barriers to Physical Activity Questionnaire for People With Mobility Impairments

BACKGROUND

Although physical activity (PA) is an important determinant of health, physically disabled individuals tend to have a sedentary lifestyle. The Barriers to Physical Activity Questionnaire for People with Mobility Impairments (BPAQ-MI) is a self-report instrument evaluating PA barriers. This study was intended to evaluate the validity and reliability of the Persian version of BPAQ-MI (P-BPAQ-MI) and to report the prevalence and severity of PA barriers among Persian-speaking individuals.

METHODS

The translation and back translation of the BPAQ-MI was conducted according to an internationally accepted guideline and tested on 163 participants to assess its reliability and validity. Internal consistency and test-retest reliability were analyzed using Cronbach alpha and Spearman correlation coefficient. Convergent construct validity was established by comparing the scores of P-BPAQ-MI and The Baecke Habitual Physical Activity Questionnaire. Known-groups construct validity was assessed with regard to type of assistive device and sex of the individual. Prevalence and severity of the barriers were reported by computing the percentage and means of "yes" answers.

RESULTS

The P-BPAQ-MI domains demonstrated very good internal consistency (Cronbach alpha of .77-.95) and excellent test-retest reliability (Spearman rho of .73-.96) with a significant inverse small correlation with Baecke Habitual Physical Activity Questionnaire indexes. The P-BPAQ-MI successfully discriminated between individuals with different assistive devices and sex. Community Built Environment barriers were the most prevalent and severe.

CONCLUSIONS

The P-BPAQ-MI is a valid and reliable instrument to assess the PA barriers of people with physical disability. The community barriers were the most frequently reported obstacles to PA.

Disparity in sex in ankle fracture treatment

BACKGROUND

Literature has shown implicit bias in the treatment between non-operative and surgical treatment in patients with certain types of ankle fractures, which comprise 7.6% of all adult fractures. An understanding of any bias across all ankle fracture management may prove to be critical for the understanding of potential correlations between treatment methods and outcomes of patients with ankle fractures. Therefore, this study aimed to determine whether there is a sex-based bias in the operative and non-operative treatment of all ankle fractures.

METHODS

A retrospective study of 1175 adult patients with ankle fractures was conducted. Data extracted included sex, race, age, type of treatment (non-operative/operative), fracture type (displaced/non-displaced), fracture class, BMI, and length of hospital stay. Odds ratio (OR), Chi-squared, t-test, and Pearson's correlation tests were used with p < 0.05 considered significant.

RESULTS

The study population consisted of 750 females (63.8%) and 425 males (36.2%). The study demonstrated a sex-based disparity in operative and non-operative treatment revealing that women are less likely than men to receive operative treatment for displaced ankle fractures (OR = 0.7, 95% CI: 0.5-0.9, p = 0.01). Of the 750 females, 417 (55.6%) underwent non-operative treatment, while 333 (44.4%) females had an operation. Of the 425 males, 204 (48%) had non-operative treatment, while 221 (52%) underwent operative treatment. The distribution of ankle fracture classes between both sexes was similar, suggesting fracture class did not influence the observed disparity.

CONCLUSION

Our results suggest sex correlates with the treatment type for ankle fractures, with women more likely to receive non-operative treatment for displaced fractures. As post-treatment outcomes often reflect the chosen form of treatment, it is imperative to determine if a disparity in sex explicates differences in clinical outcomes.

Gastrointestinal functioning and menstrual cycle phase in emerging young adult women: a cross-sectional study

BACKGROUND

Women experience more severe gastrointestinal (GI) symptoms compared to men. The onset of puberty and the menstrual cycle may influence these differences. Additionally, health anxiety is an important construct that has been shown to play a role in increased symptomatology across many medical conditions. Using standardized clinical measures often employed to assess disorders of gut-brain interaction (DGBI) we aimed to identify differences of GI functioning across menstrual cycle phases and to evaluate the role of health anxiety in this relationship.

METHODS

Six hundred three participants completed a survey including functional GI assessment scales (PROMIS-GI®), an abdominal pain scale and map, and a health anxiety measure. They were grouped by menstrual cycle phases (Menses, Follicular, Early-Luteal, and Premenstrual) based on self-reported start date of most recent period. Multivariate analyses of covariance were conducted to identify differences between menstrual cycle phase and scores on the symptom scales. Heath anxiety was included as a covariate in all analyses.

RESULTS

No significant differences were found between menstrual cycle group and PROMIS-GI scores. Higher GI-symptom and pain levels were found as health anxiety increased. Pain in the hypogastric region of the abdomen was significantly higher during the Menses phase when compared to Early-Luteal and Premenstrual phases. A subset of participants with DGBI diagnoses demonstrated significantly higher GI-symptom severity on several PROMIS-GI scales when compared to matched controls who did not have those diagnoses. In addition, participants with DGBI diagnoses reported significantly greater pain across multiple abdominal regions than their non-diagnosed counterparts.

CONCLUSIONS

GI symptom levels as measured by the PROMIS-GI scales in otherwise healthy women were not dependent on menstrual cycle phase. Yet, the PROMIS-GI scales were sensitive to symptom differences in women with DGBI diagnoses. Overall, this study demonstrated that the PROMIS-GI measures are unlikely to be affected by gynecological functioning in healthy young women. We argue that the abdominal pain map is an essential addition to classification and diagnosis.

Contribution of sex and gender roles to the incidence of post-infectious irritable bowel syndrome in a prospective study

Post-infectious irritable bowel syndrome (PI-IBS) occurs in about 10% of cases following gastroenteritis. The incidence of IBS is higher in females. However, it is not clear whether this is due to biological or psychosocial factors. We aimed to investigate the influence of gender roles on the incidence of PI-IBS, alongside traditional risk factors. Our study included 231 patients diagnosed with gastroenteritis who were hospitalized and treated with antibiotics between 2018 and 2021. The Korean Sex Role Inventory-Short Form (KSRI-SF), based on the Bem Sex Role Inventory (BSRI) was used to categorize patients (androgynous, masculine, feminine, and undifferentiated types). Six months after treatment, we conducted a telephone survey to confirm the presence of PI-IBS using the ROME IV criteria. Among the patients, 43.3% were female, and the mean age was 43.67 ± 16.09 years. After 6 months, 34 patients developed PI-IBS. Univariate analysis revealed that younger age, female sex, KSRI-SF undifferentiated type, and longer duration of antibiotic use independently influenced the occurrence of PI-IBS. Multivariate analysis showed that PI-IBS was associated with the KSRI-SF undifferentiated type and higher C-reactive protein (CRP) levels. Our study showed that the KSRI-SF undifferentiated type and high CRP levels at initial infection were associated with PI-IBS.

Effect of gender on presentation and outcome of renal colic

OBJECTIVES

To examine gender-related differences in the presentation, management, and outcomes of patients admitted to the emergency department ED with ureteral stones.

METHODS

Retrospective analysis of all patients admitted to the ED at our institution, found to have a ureteral stone on CT. Clinical, laboratory, imaging parameters, and outcomes were collected.

RESULTS

778 patients were admitted with ureteral stones between January 2018 and December 2020. 78% (n = 609) were males and 22% (n = 169) were females. The mean ages were 49.4 (SD 14.4) and 51.6 (SD 15.7) in males and females, respectively (p = 0.08). Female patients presented with a higher body temperature (p = 0.01), pulse rate (p < 0.0001), nausea and vomiting (p < 0.0001), elevated serum C-reactive protein (CRP) (p = 0.002) compared to males. The prevalence of elevated serum creatinine was higher in males (p < 0.0001). Alpha-blockers were recommended on discharge in 54.8% (334) of males, compared to only 29.6% (50) of females (p < 0.0001). Spontaneous stone expulsion was significantly higher in males compared to females (p = 0.01).

CONCLUSIONS

Our results demonstrate that gender does effect presentation and outcome of patients presenting with renal colic. Females were found to have elevated infectious parameters, more nausea and vomiting and a higher incidence of positive urine cultures. Males admitted to the ED were found to have significantly higher serum creatinine levels. Medical expulsive therapy (MET) with alpha-blockers was prescribed significantly less in female patients, which may have resulted in a lower spontaneous stone expulsion rate.

Oxycodone: A Current Perspective on Its Pharmacology, Abuse, and Pharmacotherapeutic Developments

Oxycodone, a semisynthetic derivative of naturally occurring thebaine, an opioid alkaloid, has been available for more than 100 years. Although thebaine cannot be used therapeutically due to the occurrence of convulsions at higher doses, it has been converted to a number of other widely used compounds that include naloxone, naltrexone, buprenorphine, and oxycodone. Despite the early identification of oxycodone, it was not until the 1990s that clinical studies began to explore its analgesic efficacy. These studies were followed by the pursuit of several preclinical studies to examine the analgesic effects and abuse liability of oxycodone in laboratory animals and the subjective effects in human volunteers. For a number of years oxycodone was at the forefront of the opioid crisis, playing a significant role in contributing to opioid misuse and abuse, with suggestions that it led to transitioning to other opioids. Several concerns were expressed as early as the 1940s that oxycodone had significant abuse potential similar to heroin and morphine. Both animal and human abuse liability studies have confirmed, and in some cases amplified, these early warnings. Despite sharing a similar structure with morphine and pharmacological actions also mediated by the μ-opioid receptor, there are several differences in the pharmacology and neurobiology of oxycodone. The data that have emerged from the many efforts to analyze the pharmacological and molecular mechanism of oxycodone have generated considerable insight into its many actions, reviewed here, which, in turn, have provided new information on opioid receptor pharmacology. SIGNIFICANCE STATEMENT: Oxycodone, a μ-opioid receptor agonist, was synthesized in 1916 and introduced into clinical use in Germany in 1917. It has been studied extensively as a therapeutic analgesic for acute and chronic neuropathic pain as an alternative to morphine. Oxycodone emerged as a drug with widespread abuse. This article brings together an integrated, detailed review of the pharmacology of oxycodone, preclinical and clinical studies of pain and abuse, and recent advances to identify potential opioid analgesics without abuse liability.

Pain after emergency treatments of symptomatic irreversible pulpitis and symptomatic apical periodontitis in the permanent dentition: a systematic review of randomized clinical trials

Background

Symptomatic irreversible pulpitis (SIP) or symptomatic apical periodontitis (SAP) are two painful conditions often warranting emergency treatment. The most common emergency treatments supported by evidence are pulpotomy and pulpectomy and are normally performed under time-constrained circumstances. However, there is no strong evidence of which treatment suggested in literature a clinician can use to reduce endodontic pain effectively. Therefore, the aim of this systematic review is to investigate the present knowledge on postoperative pain related to the two types of emergency treatments available for treating SIP and SAP.

Methods

Randomized controlled trials investigating postoperative pain after emergency treatments (pulpotomy and/or pulpectomy) on permanent dentition with signs and symptoms of SIP and/or SAP were searched in three major databases from 1978 until 2022. Risk of bias was assessed with Cochrane's tool.

Results

Only five studies fulfilled the inclusion criteria. The included studies indicated that pulpotomy and pulpectomy are both suitable treatment options for SAP and SIP, as they provide sufficient alleviation of pain in permanent dentition. However, inconsistent results were found between the included trials on which emergency treatment is more effective in reducing pain. Cochrane's tool revealed that the studies had a low risk of bias. Limitations found in the design of the included randomized control trials decreased the level of evidence. None of the included studies accounted for essential confounding variables, such as factors affecting pain (including the psychological aspects). Moreover, possible non-odontogenic pain was not assessed, and therefore, it was not excluded; hence, affecting the internal validity of the studies.

Conclusion

There are controversies within the available randomized control trials on which treatment is most effective in reducing emergency pain. This could be due to some weaknesses in the design of the clinical trials. Thus, further well-designed studies are warranted to draw conclusions on which emergency treatment is more effective in reducing pain.

Systematic Review Registration

PROSPERO (CRD42023422282).

Resilience to Pain-Related Depression in σ1 Receptor Knockout Mice Is Associated with the Reversal of Pain-Induced Brain Changes in Affect-Related Genes

Mice lacking the σ1 receptor chaperone (σ1R-/-) are resilient to depressive-like behaviors secondary to neuropathic pain. Examining the resilience's brain mechanisms could help develop conceptually novel therapeutic strategies. We explored the diminished motivation for a natural reinforcer (white chocolate) in the partial sciatic nerve ligation (PSNL) model in wild-type (WT) and σ1R-/- mice. In the same mice, we performed a comprehensive reverse transcription quantitative PCR (qPCR) analysis across ten brain regions of seven genes implicated in pain regulation and associated affective disorders, such as anxiety and depression. PSNL induced anhedonic-like behavior in WT but not in σ1R-/- mice. In WT mice, PSNL up-regulated dopamine transporter (DAT) and its rate-limiting enzyme, tyrosine hydroxylase (Th), in the ventral tegmental area (VTA) and periaqueductal gray (PAG) as well as the serotonin transporters (SERT) and its rate-limiting enzyme tryptophan hydroxylase 2 (Tph2) in VTA. In addition, μ-opioid receptor (MOR) and σ1R were up-regulated in PAG, and MOR was also elevated in the somatosensory cortex (SS) but down-regulated in the striatum (STR). Finally, increased BDNF was found in the medial prefrontal cortex (mPFC) and hypothalamus (HPT). Sham surgery also produced PSNL-like expression changes in VTA, HPT, and STR. Genetic deletion of the σ1R in mice submitted to PSNL or sham surgery prevented changes in the expression of most of these genes. σ1R is critically involved in the supraspinal gene expression changes produced by PSNL and sham surgery. The changes in gene expression observed in WT mice may be related to pain-related depression, and the absence of these changes observed in σ1R-/- mice may be related to resilience.

Macrophages and microglia in inflammation and neuroinflammation underlying different pain states

Pain is a main symptom in inflammation, and inflammation induces pain via inflammatory mediators acting on nociceptive neurons. Macrophages and microglia are distinct cell types, representing immune cells and glial cells, respectively, but they share similar roles in pain regulation. Macrophages are key regulators of inflammation and pain. Macrophage polarization plays different roles in inducing and resolving pain. Notably, macrophage polarization and phagocytosis can be induced by specialized pro-resolution mediators (SPMs). SPMs also potently inhibit inflammatory and neuropathic pain via immunomodulation and neuromodulation. In this review, we discuss macrophage signaling involved in pain induction and resolution, as well as in maintaining physiological pain. Microglia are macrophage-like cells in the central nervous system (CNS) and drive neuroinflammation and pathological pain in various inflammatory and neurological disorders. Microglia-produced inflammatory cytokines can potently regulate excitatory and inhibitory synaptic transmission as neuromodulators. We also highlight sex differences in macrophage and microglial signaling in inflammatory and neuropathic pain. Thus, targeting macrophage and microglial signaling in distinct locations via pharmacological approaches, including immunotherapies, and non-pharmacological approaches will help to control chronic inflammation and chronic pain.

Deep RNA-seq of male and female murine sensory neuron subtypes after nerve injury

ABSTRACT

Dorsal root ganglia (DRG) neurons have been well described for their role in driving both acute and chronic pain. Although nerve injury is known to cause transcriptional dysregulation, how this differs across neuronal subtypes and the impact of sex is unclear. Here, we study the deep transcriptional profiles of multiple murine DRG populations in early and late pain states while considering sex. We have exploited currently available transgenics to label numerous subpopulations for fluorescent-activated cell sorting and subsequent transcriptomic analysis. Using bulk tissue samples, we are able to circumvent the issues of low transcript coverage and drop-outs seen with single-cell data sets. This increases our power to detect novel and even subtle changes in gene expression within neuronal subtypes and discuss sexual dimorphism at the neuronal subtype level. We have curated this resource into an accessible database for other researchers ( https://livedataoxford.shinyapps.io/drg-directory/ ). We see both stereotyped and unique subtype signatures in injured states after nerve injury at both an early and late timepoint. Although all populations contribute to a general injury signature, subtype enrichment changes can also be seen. Within populations, there is not a strong intersection of sex and injury, but previously unknown sex differences in naïve states-particularly in Aβ-RA + Aδ-low threshold mechanoreceptors-still contribute to differences in injured neurons.

Different logics of pain: the gendered dimension of chronic pain in a relational setting

This study aims to increase our understanding of the gendered dimension of living with chronic pain within a relational context. The empirical setting for this study is Sweden, a country widely recognised for its long history of gender equality. Interview responses from 21 women and 12 men were analysed using the feminist notion of the marriage contract, outlining the terms for women and men living together in a relationship. The result shows how living with chronic pain leads to processes of grief and altered priorities. Respondents emphasize the importance of equality. However, men and women apply different logics when deciding which tasks to prioritise. Although there is no distinct pattern regarding whether or not couples share housework equally, the allocation of responsibilities appears to follow a particular pattern: men tend to prioritise their rehabilitation to become good fathers, women are grateful and prioritise the family before her own well-being. The study indicates that while attitudes and the allocation of household chores may have changed in the past few decades, the marriage contract still restricts women from employment and rehabilitation.

Catastrophizing and acceptance are mediators between insomnia and pain intensity-an SQRP study of more than 6,400 patients with non-malignant chronic pain conditions

Background

Sleep problems (insomnia) and chronic pain are associated. Chronic pain and insomnia/insufficient sleep quality share similar symptoms and features. Although they have a bidirectional relationship, more research is needed to understand how they interact via mediators and how moderators influence this relationship.

Aims

In this large clinical registry-based cohort study (N = 6,497), we investigate important mediators between insomnia and pain intensity in a cross-sectional sample of chronic pain patients using advanced path analysis. In addition, we investigate whether some background variables were moderators of the identified important paths or not and the correlation patterns between insomnia and pain intensity in relation to the mediators.

Methods

This study includes a cohort of adult patients with chronic non-cancer pain from the Swedish Quality Registry for Pain Rehabilitation (SQRP) with data on patient-reported outcome measures (PROMs) (2008-2016). The PROMs cover the background, pain aspects, psychological distress, pain-related cognitions, activity/participation, and health-related quality of life variables of the patients. Partial least squares structural equation modeling was used to explore the direct and indirect (via mediators) relationships between insomnia and pain intensity at baseline.

Results

In this cohort study, insomnia was prevalent at 62.3%, and both direct and indirect mediating paths were present for the insomnia-pain intensity relationship. All of the mediating effects combined were weaker than the direct effect between insomnia and pain intensity. The mediating effects via catastrophizing and acceptance showed the strongest and equal mediating paths, and mediating effects via fear avoidance were the second strongest. Insomnia showed stronger direct significant correlations with psychological distress, catastrophizing, and acceptance compared with those of pain intensity. Sex, age, education level, spatial extent of pain, or body mass index did not moderate the mediating paths.

Discussion and conclusion

This study confirms the existence of significant direct and mediating paths between reported insomnia and pain intensity. Future studies should focus on illuminating how sleep interventions influence pain intensity and other important key factors that contribute to the distress of chronic pain patients.

Evaluation of pain experienced by orthodontic patients following elastomeric separator insertion: A cross-sectional study

Objective

Pain following the insertion of separators and archwires varies with age, sex, race, ethnicity, threshold, and health status. This study aimed to evaluate the characteristics of pain in orthodontic patients after the insertion of elastomeric separators, its effects on daily life, and its association with age and sex in a population not previously studied in this regard.

Methods

A cross-sectional study of 130 patients undergoing orthodontic treatment included collecting data on demographics, pain experienced following the placement of separators, time of onset, duration, characteristics, change in dietary pattern or chewing side, intake of analgesics, and severity of pain on the Wong Baker's scale. The results are reported as counts and percentages. Associations between sex and age were evaluated using Pearson's chi-square test.

Results

Among the 130 patients, 56.2% were 9-20 years old, 63.8% experienced pain following the insertion of separators, 22.9% had their first episode of pain at 4 hours, 56.6% experienced intermittent pain, and 37.3% experienced discomfort; 18.1% males and 81.9% females experienced pain following the insertion of separators. Pearson's chi-square test showed a significant association between pain and sex (P = 0.04). Most patients (37.3%) reported "hurts little more" for pain intensity on Wong Baker's scale and 21.7% reported all four quadrants as sites of pain.

Conclusions

The pain experienced after separator insertion was associated with sex and age. Females experienced more pain than males and patients between the age range of 21 and 36 years suffered more pain during mastication than between 9 and 20 years old.

TNFR1/p38αMAPK signaling in Nex+ supraspinal neurons regulates sex-specific chronic neuropathic pain

Upregulation of soluble tumor necrosis factor (sTNF) cytokine signaling through TNF receptor 1 (TNFR1) and subsequent neuronal hyperexcitability are observed in both animal models and human chronic neuropathic pain (CNP) [1-4]. To test the hypothesis that supraspinal circuitry is critical to pain chronification, we studied the intersect between supraspinal TNFR1 mediated neuronal signaling and sex specificity by selectively removing TNFR1 in Nex + neurons in adult mice (NexCreERT2::TNFR1f/f). We determined that following chronic constriction injury (CCI), pain resolves in males; however, female acute pain transitions to chronic. Subsequently, we investigated two downstream pathways, p38MAPK and NF-κB, important in TNFR1 signaling and injury response. We detected p38αMAPK and NF-κB activation in male cortical tissue; however, p38αMAPK phosphorylation was reduced in NexCreERT2::TNFR1f/f males. We observed similar behavioral results following CCI in NexCreERT2::p38αMAPKf/f mice. Previously, we established estrogen's ability to modulate sTNF/TNFR1 signaling in CNP, which may contribute to female prevalence of CNP [5-9]. To explore the intersection between estrogen and inflammation in CNP we used a combination therapy of an estrogen receptor β (ER β) inhibitor with a sTNF/TNFR1 or general p38MAPK inhibitor. We determined both combination therapies lend "male-like" therapeutic relief to females following CCI. These data suggest that TNFR1/p38αMAPK signaling in Nex + neurons in CNP is male-specific and lack of therapeutic efficacy following sTNF inhibition in females is due to ER β interference. These studies highlight sex-specific differences in pathways important to pain chronification and elucidate potential therapeutic strategies that would be effective in both sexes.

The impact of sex and physical activity on the local immune response to muscle pain

Induction of muscle pain triggers a local immune response to produce pain and this mechanism may be sex and activity level dependent. The purpose of this study was to measure the immune system response in the muscle following induction of pain in sedentary and physically active mice. Muscle pain was produced via an activity-induced pain model using acidic saline combined with fatiguing muscle contractions. Prior to induction of muscle pain, mice (C57/BL6) were sedentary or physically active (24hr access to running wheel) for 8 weeks. The ipsilateral gastrocnemius was harvested 24hr after induction of muscle pain for RNA sequencing or flow cytometry. RNA sequencing revealed activation of several immune pathways in both sexes after induction of muscle pain, and these pathways were attenuated in physically active females. Uniquely in females, the antigen processing and presentation pathway with MHC II signaling was activated after induction of muscle pain; activation of this pathway was blocked by physical activity. Blockade of MHC II attenuated development of muscle hyperalgesia exclusively in females. Induction of muscle pain increased the number of macrophages and T-cells in the muscle in both sexes, measured by flow cytometry. In both sexes, the phenotype of macrophages shifted toward a pro-inflammatory state after induction of muscle pain in sedentary mice (M1 + M1/2) but toward an anti-inflammatory state in physically active mice (M2 + M0). Thus, induction of muscle pain activates the immune system with sex-specific differences in the transcriptome while physical activity attenuates immune response in females and alters macrophage phenotype in both sexes.

Chronic pain, chronic stress and substance use: overlapping mechanisms and implications

Chronic pain is among the most common reasons adults in the U.S. seek medical care. Despite chronic pain's substantial impact on individuals' physical, emotional, and financial wellness, the biologic underpinnings of chronic pain remain incompletely understood. Such deleterious impact on an individuals' wellness is also manifested in the substantial co-occurrence of chronic stress with chronic pain. However, whether chronic stress and adversity and related alcohol and substance misuse increases risk of developing chronic pain, and, if so, what the overlapping psychobiological processes are, is not well understood. Individuals suffering with chronic pain find alleviation through prescription opioids as well as non-prescribed cannabis, alcohol, and other drugs to control pain, and use of these substances have grown significantly. Substance misuse also increases experience of chronic stress. Thus, given the evidence showing a strong correlation between chronic stress and chronic pain, we aim to review and identify overlapping factors and processes. We first explore the predisposing factors and psychologic features common to both conditions. This is followed by examining the overlapping neural circuitry of pain and stress in order to trace a common pathophysiologic processes for the development of chronic pain and its link to substance use. Based on the previous literature and our own findings, we propose a critical role for ventromedial prefrontal cortex dysfunction, an overlapping brain area associated with the regulation of both pain and stress that is also affected by substance use, as key in the risk of developing chronic pain. Finally, we identify the need for future research in exploring the role of medial prefrontal circuits in chronic pain pathology. Critically, in order to alleviate the enormous burden of chronic pain without exacerbating the co-occurring substance misuse crisis, we emphasize the need to find better approaches to treat and prevent chronic pain.

Formalin-evoked pain triggers sex-specific behavior and spinal immune response

Mounting evidence shows sex-related differences in the experience of pain with women suffering more from chronic pain than men. Yet, our understanding of the biological basis underlying those differences remains incomplete. Using an adapted model of formalin-induced chemical/inflammatory pain, we report here that in contrast to male mice, females distinctly display two types of nocifensive responses to formalin, distinguishable by the duration of the interphase. Females in proestrus and in metestrus exhibited respectively a short-lasting and a long-lasting interphase, underscoring the influence of the estrus cycle on the duration of the interphase, rather than the transcriptional content of the dorsal horn of the spinal cord (DHSC). Additionally, deep RNA-sequencing of DHSC showed that formalin-evoked pain was accompanied by a male-preponderant enrichment in genes associated with the immune modulation of pain, revealing an unanticipated contribution of neutrophils. Taking advantage of the male-enriched transcript encoding the neutrophil associated protein Lipocalin 2 (Lcn2) and using flow cytometry, we confirmed that formalin triggered the recruitment of LCN2-expressing neutrophils in the pia mater of spinal meninges, preferentially in males. Our data consolidate the contribution of female estrus cycle to pain perception and provide evidence supporting a sex-specific immune regulation of formalin-evoked pain.

Acidosis-related pain and its receptors as targets for chronic pain

Sensing acidosis is an important somatosensory function in responses to ischemia, inflammation, and metabolic alteration. Accumulating evidence has shown that acidosis is an effective factor for pain induction and that many intractable chronic pain diseases are associated with acidosis signaling. Various receptors have been known to detect extracellular acidosis and all express in the somatosensory neurons, such as acid sensing ion channels (ASIC), transient receptor potential (TRP) channels and proton-sensing G-protein coupled receptors. In addition to sense noxious acidic stimulation, these proton-sensing receptors also play a vital role in pain processing. For example, ASICs and TRPs are involved in not only nociceptive activation but also anti-nociceptive effects as well as some other non-nociceptive pathways. Herein, we review recent progress in probing the roles of proton-sensing receptors in preclinical pain research and their clinical relevance. We also propose a new concept of sngception to address the specific somatosensory function of acid sensation. This review aims to connect these acid-sensing receptors with basic pain research and clinical pain diseases, thus helping with better understanding the acid-related pain pathogenesis and their potential therapeutic roles via the mechanism of acid-mediated antinociception.

Machine learning analysis predicts a person's sex based on mechanical but not thermal pain thresholds

Sex differences in pain perception have been extensively studied, but precision medicine applications such as sex-specific pain pharmacology have barely progressed beyond proof-of-concept. A data set of pain thresholds to mechanical (blunt and punctate pressure) and thermal (heat and cold) stimuli applied to non-sensitized and sensitized (capsaicin, menthol) forearm skin of 69 male and 56 female healthy volunteers was analyzed for data structures contingent with the prior sex structure using unsupervised and supervised approaches. A working hypothesis that the relevance of sex differences could be approached via reversibility of the association, i.e., sex should be identifiable from pain thresholds, was verified with trained machine learning algorithms that could infer a person's sex in a 20% validation sample not seen to the algorithms during training, with balanced accuracy of up to 79%. This was only possible with thresholds for mechanical stimuli, but not for thermal stimuli or sensitization responses, which were not sufficient to train an algorithm that could assign sex better than by guessing or when trained with nonsense (permuted) information. This enabled the translation to the molecular level of nociceptive targets that convert mechanical but not thermal information into signals interpreted as pain, which could eventually be used for pharmacological precision medicine approaches to pain. By exploiting a key feature of machine learning, which allows for the recognition of data structures and the reduction of information to the minimum relevant, experimental human pain data could be characterized in a way that incorporates "non" logic that could be translated directly to the molecular pharmacological level, pointing toward sex-specific precision medicine for pain.

A Review of Voice-Based Pain Detection in Adults Using Artificial Intelligence

Pain is a complex and subjective experience, and traditional methods of pain assessment can be limited by factors such as self-report bias and observer variability. Voice is frequently used to evaluate pain, occasionally in conjunction with other behaviors such as facial gestures. Compared to facial emotions, there is less available evidence linking pain with voice. This literature review synthesizes the current state of research on the use of voice recognition and voice analysis for pain detection in adults, with a specific focus on the role of artificial intelligence (AI) and machine learning (ML) techniques. We describe the previous works on pain recognition using voice and highlight the different approaches to voice as a tool for pain detection, such as a human effect or biosignal. Overall, studies have shown that AI-based voice analysis can be an effective tool for pain detection in adult patients with various types of pain, including chronic and acute pain. We highlight the high accuracy of the ML-based approaches used in studies and their limitations in terms of generalizability due to factors such as the nature of the pain and patient population characteristics. However, there are still potential challenges, such as the need for large datasets and the risk of bias in training models, which warrant further research.

The basolateral amygdala-anterior cingulate pathway contributes to depression-like behaviors and comorbidity with chronic pain behaviors in male mice

While depression and chronic pain are frequently comorbid, underlying neuronal circuits and their psychopathological relevance remain poorly defined. Here we show in mice that hyperactivity of the neuronal pathway linking the basolateral amygdala to the anterior cingulate cortex is essential for chronic pain-induced depression. Moreover, activation of this pathway in naive male mice, in the absence of on-going pain, is sufficient to trigger depressive-like behaviors, as well as transcriptomic alterations that recapitulate core molecular features of depression in the human brain. These alterations notably impact gene modules related to myelination and the oligodendrocyte lineage. Among these, we show that Sema4a, which was significantly upregulated in both male mice and humans in the context of altered mood, is necessary for the emergence of emotional dysfunction. Overall, these results place the amygdalo-cingulate pathway at the core of pain and depression comorbidity, and unravel the role of Sema4a and impaired myelination in mood control.

Standing on the shoulders of bias: lack of transparency and reporting of critical rigor characteristics in pain research

ABSTRACT

Rigorous experimental design with transparent reporting in biomedical science reduces risk of bias and allows for scientists to judge the quality of the research. Basic factors of rigor such as blinding, randomization, power analysis, and inclusion of both sexes impact the reproducibility by reducing experimental bias. We designed a systematic study to analyze basic factors of rigor, inclusion of sex, and whether data were analyzed or disaggregated by sex over the past 10 years in the journal PAIN. Studies that included humans reported randomization in 81%, blinding in 48%, and the use of a power analysis calculation in 27% over the past 10 years. Studies that included mice reported randomization in 35%, blinding in 70%, and the use of a power analysis in 9%. Studies that included rats reported randomization in 38%, blinding in 63%, and the use of power analysis in 12%. This study also found that human studies consistently included both sexes over the past decade, but less than 20% of data were disaggregated or analyzed for sex differences. Although mouse and rat studies predominately used males only, there has been a slight increase in inclusion of both sexes over the past few years. Justification for single-sex studies was below 50% in both human and rodent data. In both human and animal studies, transparency in reporting of experimental design and inclusion of both sexes should be considered standard practice and will result in improved quality and reproducibility of published research.

Analysis of the factors affecting pain level during K-wire removal among pediatric elbow fractures

Our aim was, to analyze the reasons for possible increased pain during the removal of the Kirschner wires from the elbows of children. From February 2021 to December 2021, 573 patients with elbow fractures were treated. In total, 150 patients were analyzed prospectively. No action was taken to reduce pain during the removal of Kirschner wires. The pain status of the patients was evaluated according to the Wong-Baker FACES Pain Rating scoring system (WBAS), the Numeric Rating Scale (NRS) for the pain system and the pulse and oxygen saturation measured by the pulse oximeter on the finger. Measurements were performed before, during, immediately after and 30 min after the procedure. There were 119 patients with a diagnosis of supracondylar humerus fracture and 31 patients with a diagnosis of lateral condyle fracture. The mean age of treated patients was 7.1 years (1-15 years). Of the patients, 93 were boys and 57 were girls. In the measurements made according to the sex difference, it was determined that there was a statistically significant increase in the WBAS scores measured both before the procedure ( P  = 0.032) and during the removal ( P  = 0.017), and also in the pulse measurements taken 30 min after the removal in girls ( P  = 0.034). A statistically significant difference was found in both the WBAS score during removal ( P  = 0.025) and the NRS scores 30 min later ( P  = 0.048) in the procedures performed on the right elbow. We found a statistically significant increase in the pain parameters we evaluated in girls, right extremity fractures, the group over 8 years old and when both parents were with the child during the K-wire removal procedure. In light of these findings, physicians should consider the above-mentioned conditions before starting the procedure to ensure a less painful and positive experience.

Targeting Neuroinflammation with Abscisic Acid Reduces Pain Sensitivity in Females and Hyperactivity in Males of an ADHD Mice Model

Attention deficit/hyperactivity disorder (ADHD) is a neurodevelopmental syndrome characterized by dopaminergic dysfunction. In this study, we aimed to demonstrate that there is a link between dopaminergic deficit and neuroinflammation that underlies ADHD symptoms. We used a validated ADHD mice model involving perinatal 6-OHDA lesions. The animals received abscisic acid (ABA), an anti-inflammatory phytohormone, at a concentration of 20 mg/L (drinking water) for one month. We tested a battery of behavior tests, learning and memory, anxiety, social interactions, and pain thresholds in female and male mice (control and lesioned, with or without ABA treatment). Postmortem, we analyzed microglia morphology and Ape1 expression in specific brain areas related to the descending pain inhibitory pathway. In females, the dopaminergic deficit increased pain sensitivity but not hyperactivity. In contrast, males displayed hyperactivity but showed no increased pain sensitivity. In females, pain sensitivity was associated with inflammatory microglia and lower Ape1 levels in the anterior cingulate cortex (ACC) and posterior insula cortex (IC). In addition, ABA treatment alleviated pain sensitivity concomitant with reduced inflammation and normalized APE1. In males, ABA reduced hyperactivity but had no significant effect on inflammation in these areas. This is the first study proving a sex-dependent association between dopamine dysfunction and inflammation in specific brain areas, hence leading to different behavioral outcomes in a mouse model of ADHD. These findings provide new clues for potential treatments for ADHD.

Cannabidiol and Delta-9-Tetrahydrocannabinol Interactions in Male and Female Rats With Persistent Inflammatory Pain

Cannabidiol (CBD) and delta-9-tetrahydrocannabinol (THC), 2 of the primary constituents of cannabis, are used by some individuals to self-treat chronic pain. It is unclear whether the pain-relieving effects of CBD alone and in combination with THC are consistent across genders and among types of pain. The present study compared the effects of CBD and THC given alone and in combination in male and female rats with Complete Freund's adjuvant-induced inflammatory pain. After induction of hindpaw inflammation, vehicle, CBD (0.05-2.5 mg/kg), THC (0.05-2.0 mg/kg), or a CBD:THC combination (3:1, 1:1, or 1:3 dose ratio) was administered i.p. twice daily for 3 days. Then on day 4, mechanical allodynia, thermal hyperalgesia, weight-bearing, and locomotor activity were assessed 0.5 to 4 hours after administration of the same dose combination. Hindpaw edema and open field (anxiety-like) behaviors were measured thereafter. THC alone was anti-allodynic and anti-hyperalgesic, and decreased paw thickness, locomotion, and open field behaviors. CBD alone was anti-allodynic and anti-hyperalgesic. When combined with THC, CBD tended to decrease THC effects on pain-related behaviors and exacerbate THC-induced anxiety-like behaviors, particularly in females. These results suggest that at the doses tested, CBD-THC combinations may be less beneficial than THC alone for the treatment of chronic inflammatory pain. PERSPECTIVE: The present study compared CBD and THC effects alone and in combination in male and female rats with persistent inflammatory pain. This study could help clinicians who prescribe cannabis-based medicines for inflammatory pain conditions determine which cannabis constituents may be most beneficial.

Sex Differences in Pain and Its Treatment

Pain is a highly personal experience. Pain is often considered to be a purely neurologic phenomenon, but in actuality, it is a combination of both sensory and emotional experiences. This has sometimes been translated clinically toward a more mechanistic approach to the assessment and treatment of pain instead of one that does not discount pain mechanisms, but also is more inclusive of the need for humanism - considering the individual. In today's medical environment, more than ever before there is a significant amount of attention being paid to educating clinicians to better understand that several physiological, neurophysiological, and psychosocial factors can significantly impact responses to pain. The composition of these factors will be unique to that individual's life narrative, context, sex, and prior life experiences. Thus, the concept that a templated approach to pain assessment and pharmacotherapeutic treatment planning should not be expected to provide optimal patient satisfaction and treatment outcomes in the majority. The hypotheses that there may be sex-based differences in the pain experience in a variety of ways including pain sensitivity, tolerance to pain, threshold at which something becomes painful, and the effectiveness of endogenous pain modulation systems are not new and have been well represented in the literature. This chapter reviews important key findings in the scientific literature with respect to sex-based differences in pain and pain responses to experimentally induced painful stimuli, pain experienced in commonly occurring painful medical conditions, and variations in responses to pain treatments. Possible explanations to account for observed differences or similarities will also be discussed.

Lean Mass is Associated with, but Does Not Mediate Sex Differences in Pressure Pain Sensitivity in Healthy Adults

Background

Sex differences exist in pain sensitivity, however, the underlying mechanism(s) that explain these differences are not fully understood. Pain sensitivity has been shown to be influenced by body mass index, but limited data exist on the role of body composition on pain sensitivity. The purpose was to examine the influence of body composition on pain sensitivity in males and females.

Methods

This cross-sectional study design used pressure pain thresholds (PPT) of 87 participants (45 female) who were assessed in the vastus lateralis (leg PPT) and brachioradialis (arm PPT) using a pressure algometer. Fat and lean tissue were assessed via dual-energy X-ray absorptiometry (DXA). A two group by two limb, repeated measured ANOVA was used to assess differences between limbs and sex. Spearman correlations and hierarchical regression analyses were employed to determine the association between body composition and PPT.

Results

Males had higher PPTs then females (P<0.05) and had higher DXA assessed lean and lower levels fat mass (P<0.05). Total body and limb specific lean mass was associated with PPTs (r≥0.34; P<0.05). Hierarchical regression analysis revealed lean mass was a significant predictor of 8% of the variance in arm PPT (P<0.006) and 18% of the variance in leg PPT (P<0.001). However, lean mass was not found to statistically mediate the observed sex differences in PPT.

Conclusion

This finding suggests lean mass may play a previously unknown role in sex differences in pressure pain sensitivity. Future studies are needed to confirm this finding and a larger sample size is likely required to have sufficient power to perform the mediation analysis.

Pain severity at emergency department discharge as a predictor for chronification of pain

Introduction

Inadequate pain management remains a problem in the emergency department (ED) and might increase the risk of chronic pain. Previous studies suggested that pain intensity is associated with pain chronification in specific patient groups. This study aims to study the association between pain intensity {[verbal] numeric rating scale ([V]NRS) ≥ 7} at discharge from the ED and pain chronification in the general population.

Objective

To assess whether a high pain score at discharge from the ED increases the risk of chronic pain development.

Methods

Adults who visited the ED with pain as their main complaint, and who were not hospitalized, were eligible for inclusion. Chronic pain was defined as pain with an (V)NRS score ≥1 90 days after the ED visit and with a similar location to the acute pain.

Results

We included 1906 patients, of whom 825 participants completed 90 days of follow-up. Approximately 34.1% left the ED with an (V)NRS score ≥7, and 67.8% reported an (V)NRS score of ≥1 90 at days. Of all patients leaving the ED with an (V)NRS score ≥7, 76.5% developed chronic pain vs 63.2% of patients with (V)NRS score <7 (P < 0.01). After correction, this difference was borderline statistically significant with an odds ratio of 1.45 (95% confidence interval: 0.99-2.13, P = 0.054). Various sensitivity analyses using a different (V)NRS at discharge and different definitions of chronic pain at 90 days showed a significant difference in the chronification of pain.

Conclusion

This study suggests that pain intensity at discharge from the ED, regardless of the localization or cause of pain, increased the risk of developing chronic pain. By distinguishing patients at risk and providing an effective treatment, chronic pain and the associated burden of disease might be preventable.

The Geography of Pain in the United States and Canada

Pain epidemiologists have, thus far, devoted scant attention to geospatial analyses of pain.  Both cross-national and, especially, subnational variation in pain have been understudied, even though geographic comparisons could shed light on social factors that increase or mitigate pain. This study presents the first comparative analysis of pain in the U.S. and Canada, comparing the countries in aggregate, while also analyzing variation across states and provinces. Analyses are based on cross-sectional data collected in 2020 from U.S. and Canadian adults 18 years and older (N = 4,113). The focal pain measure is a product of pain frequency and pain interference. We use decomposition and regression analyses to link socioeconomic characteristics and pain, and inverse-distance weighting spatial interpolation to map pain levels. We find significantly and substantially higher pain in the U.S. than in Canada. The difference is partly linked to Americans' worse economic conditions. Additionally, we find significant pain variability within the U.S. and Canada. U.S. states in the Deep South, Appalachia, and parts of the West stand out as pain 'hotspots' with particularly high pain levels. Overall, our findings identify areas with a high need for pain prevention and management; they also urge further scholarship on geographic factors as important covariates in population pain. PERSPECTIVE: This study documents the high pain burden in the U.S. versus Canada, and points to states in the Deep South, Appalachia, and parts of the West as having particularly high pain burden. The findings identify geographic areas with a high need for pain prevention and management.

Long-lasting visceral hypersensitivity in a model of DSS-induced colitis in rats

BACKGROUND

Persistent visceral hypersensitivity is a key component of functional and inflammatory gastrointestinal diseases. Current animal models fail to fully reproduce the characteristics of visceral pain in humans, particularly as it relates to persistent hypersensitivity. This work explores the validity of DSS-induced colitis in rats as a model to mimic chronic intestinal hypersensitivity.

METHODS

Exposure to DSS (5% for 7 days) was used to induce colitis in rats. Thereafter, changes in viscerosensitivity (visceromotor responses to colorectal distension-CRD), the presence of somatic referred pain (mechanosensitivity of the hind paws, von Frey test) and the expression (qRT-PCR) of sensory-related markers (colon, lumbosacral DRGs, and lumbosacral spinal cord) were assessed at different times during the 35 days period after colitis induction.

RESULTS

Following colitis, a sustained increase in visceromotor responses to CRD were observed, indicative of the presence of visceral hypersensitivity. Responses in animals without colitis remained stable over time. In colitic animals, somatic referred hypersensitivity was also detected. DSS-induced colitis was associated to a differential expression of sensory-related markers (with both pro- and anti-nociceptive action) in the colon, lumbosacral DRGs and lumbosacral spinal cord; indicating the presence of peripheral and central sensitization.

CONCLUSIONS AND INFERENCES

DSS-induced colitis in rats is associated to the generation of a long-lasting state of visceral (colonic) hypersensitivity, despite clinical colitis resolution. This model reproduces the changes in intestinal sensitivity characteristics of inflammatory and functional gastrointestinal disorders in humans and can be used in the characterization of new pharmacological treatments against visceral pain.