Local immune response to food antigens drives meal-induced abdominal pain.

Up to 20% of people worldwide develop gastrointestinal symptoms following a meal1, leading to decreased quality of life, substantial morbidity and high medical costs. Although the interest of both the scientific and lay communities in this issue has increased markedly in recent years, with the worldwide introduction of gluten-free and other diets, the underlying mechanisms of food-induced abdominal complaints remain largely unknown. Here we show that a bacterial infection and bacterial toxins can trigger an immune response that leads to the production of dietary-antigen-specific IgE antibodies in mice, which are limited to the intestine. Following subsequent oral ingestion of the respective dietary antigen, an IgE- and mast-cell-dependent mechanism induced increased visceral pain. This aberrant pain signalling resulted from histamine receptor H1-mediated sensitization of visceral afferents. Moreover, injection of food antigens (gluten, wheat, soy and milk) into the rectosigmoid mucosa of patients with irritable bowel syndrome induced local oedema and mast cell activation. Our results identify and characterize a peripheral mechanism that underlies food-induced abdominal pain, thereby creating new possibilities for the treatment of irritable bowel syndrome and related abdominal pain disorders.

Expression and function of transient receptor potential melastatin 3 in the spinal afferent innervation of the mouse colon.

Abdominal pain is a cardinal symptom of inflammatory bowel disease (IBD). Transient receptor potential (TRP) channels contribute to abdominal pain in preclinical models of IBD, and TRP melastatin 3 (TRPM3) has recently been implicated in inflammatory bladder and joint pain in rodents. We hypothesized that TRPM3 is involved in colonic sensation and is sensitized during colitis. We used immunohistochemistry, ratiometric Ca2+ imaging, and colonic afferent nerve recordings in mice to evaluate TRPM3 protein expression in colon-projecting dorsal root ganglion (DRG) neurons, as well as functional activity in DRG neurons and colonic afferent nerves. Colitis was induced using dextran sulfate sodium (DSS) in drinking water. TRPM3 protein expression was observed in 76% of colon-projecting DRG neurons and was often colocalized with calcitonin gene-related peptide. The magnitudes of intracellular Ca2+ transients in DRG neurons in response to the TRPM3 agonists CIM-0216 and pregnenolone sulfate sodium were significantly greater in neurons from mice with colitis compared with controls. In addition, the percentage of DRG neurons from mice with colitis that responded to CIM-0216 was significantly increased. CIM-0216 also increased the firing rate of colonic afferent nerves from control and mice with colitis. The TRPM3 inhibitor isosakuranetin inhibited the mechanosensitive response to distension of wide dynamic range afferent nerve units from mice with colitis but had no effect in control mice. Thus, TRPM3 contributes to colonic sensory transduction and may be a potential target for treating pain in IBD.NEW & NOTEWORTHY This is the first study to characterize TRPM3 protein expression and function in colon-projecting DRG neurons. A TRPM3 agonist excited DRG neurons and colonic afferent nerves from healthy mice. TRPM3 agonist responses in DRG neurons were elevated during colitis. Inhibiting TRPM3 reduced the firing of wide dynamic range afferent nerves from mice with colitis but had no effect in control mice.

Co-occurring Chronic Pain and PTSD Among US Military Veterans: Prevalence, Correlates, and Functioning.

BACKGROUND: The prevalence of co-occurring chronic pain and posttraumatic stress disorder (PTSD) has yet to be established in a nationally representative sample of US veterans, and little is known about the individual contributing roles of these disorders to the psychiatric and functional burden of this comorbidity. OBJECTIVE: To determine the prevalence of chronic pain, PTSD, and co-occurring chronic pain and PTSD, and psychiatric comorbidities and psychosocial functioning in these groups. DESIGN: Data were analyzed from the National Health and Resilience in Veterans Study, which surveyed a nationally representative sample of US veterans. PARTICIPANTS: Veterans (n=4069) were classified into four groups: control (i.e., no PTSD or chronic pain), chronic pain only, PTSD only, and co-occurring chronic pain and PTSD. MAIN MEASURES: A probable PTSD diagnosis was established using the PTSD Checklist for DSM-5, and a chronic pain diagnosis using a self-report item that queried health care professional diagnoses. Psychiatric and functional status were assessed using the Patient Health Questionnaire-4, Alcohol Use Disorders Identification Test, Screen of Drug Use, Suicide Behaviors Questionnaire-Revised, Short Form Health Survey-8, Brief Inventory of Psychosocial Functioning, and Medical Outcomes Study Cognitive Functioning Scale. KEY RESULTS: A total of 3.8% of veterans reported both probable PTSD and a diagnosis of chronic pain. Relative to veterans with chronic pain alone, those with co-occurring chronic pain and probable PTSD were more likely to screen positive for psychiatric disorders (odds ratios [ORs]=2.59-9.88) and scored lower on measures of psychosocial functioning (Cohen's ds=0.38-1.43). Relative to veterans with probable PTSD only, those with co-occurring chronic pain and probable PTSD were more likely to have attempted suicide (OR=4.79; 95%CI, 1.81-12.69). CONCLUSIONS: Results underscore the importance of whole health care that considers a broad range of health and functional domains in the assessment and treatment of co-occurring chronic pain and PTSD in veterans.

Belief in Living a Meaningful Life and Adjustment to Chronic Pain.

OBJECTIVE: Chronic pain is a global health concern and often interferes with multiple aspects of individuals' lives (e.g., physical activities), diminishing one's ability to engage in activities that promote meaning in life. However, it is not well understood how believing that one can live a meaningful life despite pain may contribute to improved function among individuals with chronic pain. The aim of the current study was to better understand the role that belief in living a meaningful life despite pain may have in adjustment to chronic pain. METHODS: Participants (N = 164) were individuals with chronic pain who completed baseline data from two closely related randomized clinical trials. Hierarchical regression analyses were used to examine the hypotheses that one's belief in living a meaningful life despite pain will be associated with function (pain interference and symptoms of posttraumatic stress disorder, depression, and anxiety) and that the belief in living a meaningful life despite pain would moderate the associations between pain intensity and function. RESULTS: Belief in living a meaningful life despite pain was significantly associated with less pain interference and less severe symptoms of PTSD, anxiety, and depression, supporting the potential role of this variable in adaptive adjustment to chronic pain. However, one's belief in living a meaningful life despite pain did not moderate the associations between pain intensity and function. CONCLUSIONS: Results provide important theoretical and clinical information about how believing that one can live a meaningful life despite pain may serve as an important process for adjustment to chronic pain.

Progress Toward Meaning-as-Goal and Its Association with Pain, Functioning, and Global Meaning and Purpose Among Veterans with Co-occurring Chronic Pain and PTSD.

BACKGROUND: Co-occurring chronic pain and posttraumatic stress disorder (PTSD) is associated with poorer physical and mental functioning and well-being. Treatments often incorporate goal-setting around personally meaningful behaviors; however, it is unclear whether intentionally focusing on improving meaning and purpose in life (i.e., meaning-as-goal) may also serve as a helpful treatment target. The objective of the current study is to determine whether reported progress toward meaning-as-goal at 6 months is associated with pain severity and interference, physical and mental health functioning, and global meaning and purpose at 6- and 12-months. METHODS: Data were collected as part of an evaluation effort focused on VA's Whole Health System implementation efforts. VA electronic health records were linked to survey data across three time points (baseline, 6 months, and 12 months) from Veterans with both chronic pain and PTSD across 18 VA sites. A total of 1341 Veterans met inclusion criteria (mean age = 62, SD = 11.7). RESULTS: Regression analyses showed that progress toward meaning-as-goal was significantly associated with all 6-month variables, with standardized coefficients ranging from - 0.14 (pain severity and interference) to .37 (global meaning and purpose), in addition to all 12-month variables, with standardized coefficients ranging from - .13 (pain severity and interference) to .31 (global meaning and purpose). CONCLUSIONS: Efforts to intentionally promote meaning and purpose as part of evidence-based treatment for chronic pain and PTSD may lead to decreased pain and improved physical and mental health functioning and global meaning and purpose. With coefficients ranging from small to moderate effect sizes, more work is needed to better understand how best to maximize meaning-related goals.

Risk Factors Associated with Unsuccessful High-Resolution Manometry.

High-resolution manometry (HRM) is used to evaluate the esophageal motor function. Unfortunately, there are times when testing cannot be performed accurately. Our study aimed to quantify the occurrence of failed HRM and identify the associated risk factors. HRM tests were retrospectively collected between September 2021 and August 2022. HRM reports that could not be interpreted based on standard HRM protocol as per Chicago guidelines were classified as failed tests. Information reviewed included testing indications, patient demographics, previous medical/symptom history, and follow-up testing for failed HRM. We then compared patients with successful vs. unsuccessful HRM based on our pre-specified factors. 152 HRM tests were performed, of which 28 tests (18%) were unsuccessful. Factors associated with failed manometry included a history of nausea/vomiting, dyspepsia, and achalasia. Patients who were unable to tolerate the probe during testing were more likely to have a history of dyspepsia (OR 20.3, p = < 0.001) and/or nausea/vomiting (OR 13.8, p = < 0.001). A history of achalasia was found to have an odds ratio of 13.2 when examining failure because of curling of the manometry catheter (p = 0.012). All seven patients who had repeat HRM with endoscopic placement were successful in obtaining diagnostic information. There are two groups that have risk factors for unsuccessful HRM testing. A history of nausea/vomiting and dyspepsia symptoms were associated with being unable to tolerate the manometry probe. The second group comprises patients with a history of achalasia in whom probe curling is more common. Future research targeting these risk factors may minimize diagnostic and treatment delays.

The mediating role of posttraumatic stress disorder symptoms in pain cognitions among Veterans with chronic pain.

Symptoms of posttraumatic stress disorder (PTSD) are highly prevalent among Veterans with chronic pain. Considerable research has examined the intersection of chronic pain and PTSD symptoms. However, it remains unclear whether changes in PTSD may potentially serve a mechanistic role in improving unhelpful pain cognitions for individuals with chronic pain. The present research contributes to the foundational knowledge by addressing this question. Baseline data from a randomized controlled trial targeting pain-related disability for Veterans (n = 103; mean age 43.66; SD = 10.17) with musculoskeletal pain and depression and/or PTSD symptoms were used. Cross-sectional mediation analyses showed that PTSD symptoms mediated the relationship between pain severity and pain catastrophizing, and between pain severity and pain acceptance. After controlling for depression, the mediation involving pain catastrophizing remained significant, while the mediation for pain acceptance did not. Although limitations exist, results point to several treatment recommendations, including ensuring that depressive affect, PTSD-specific symptoms, and attention to both body and mind are included in treatment. Results also provide preliminary evidence for examining these associations longitudinally to improve our understanding of this population and corresponding treatment recommendations.

Cannabinoid 1 and mu-Opioid Receptor Agonists Synergistically Inhibit Abdominal Pain and Lack Side Effects in Mice.

While effective in treating abdominal pain, opioids have significant side effects. Recent legalization of cannabis will likely promote use of cannabinoids as an adjunct or alternative to opioids, despite a lack of evidence. We aimed to investigate whether cannabinoids inhibit mouse colonic nociception, alone or in combination with opioids at low doses. Experiments were performed on C57BL/6 male and female mice. Visceral nociception was evaluated by measuring visceromotor responses (VMR), afferent nerve mechanosensitivity in flat-sheet colon preparations, and excitability of isolated DRG neurons. Blood oxygen saturation, locomotion, and defecation were measured to evaluate side effects. An agonist of cannabinoid 1 receptor (CB1R), arachidonyl-2'-chloroethylamide (ACEA), dose-dependently decreased VMR. ACEA and HU-210 (another CB1R agonist) also attenuated colonic afferent nerve mechanosensitivity. Additionally, HU-210 concentration-dependently decreased DRG neuron excitability, which was reversed by the CB1R antagonist AM-251. Conversely, cannabinoid 2 receptor (CB2R) agonists did not attenuate VMR, afferent nerve mechanosensitivity, or DRG neuron excitability. Combination of subanalgesic doses of CB1R and µ-opioid receptor agonists decreased VMR; importantly, this analgesic effect was preserved after 6 d of twice daily treatment. This combination also attenuated afferent nerve mechanosensitivity and DRG neuron excitability, which was inhibited by neuronal nitric oxide synthase and guanylate cyclase inhibitors. This combination avoided side effects (decreased oxygen saturation and colonic transit) caused by analgesic dose of morphine. Activation of CB1R, but not CB2R, decreased colonic nociception both alone and in synergy with µ-opioid receptor. Thus, CB1R agonists may enable opioid dose reduction and avoid opioid-related side effects.SIGNIFICANCE STATEMENT One of the most cited needs for patients with abdominal pain are safe and effective treatment options. The effectiveness of opioids in the management of abdominal pain is undermined by severe adverse side effects. Therefore, strategies to replace opioids or reduce the doses of opioids to suppress abdominal pain is needed. This study in mice demonstrates that cannabinoid 1 receptor (CB1R) agonists inhibit visceral sensation. Furthermore, a combination of subanalgesic doses of µ-opioid receptor agonist and CB1R agonist markedly reduce abdominal pain without causing the side effects of high-dose opioids. Thus, CB1R agonists, alone or in combination with low-dose opioids, may be a novel and safe treatment strategy for abdominal pain.

Opioid-Induced Pronociceptive Signaling in the Gastrointestinal Tract Is Mediated by Delta-Opioid Receptor Signaling.

Opioid tolerance (OT) leads to dose escalation and serious side effects, including opioid-induced hyperalgesia (OIH). We sought to better understand the mechanisms underlying this event in the gastrointestinal tract. Chronic in vivo administration of morphine by intraperitoneal injection in male C57BL/6 mice evoked tolerance and evidence of OIH in an assay of colonic afferent nerve mechanosensitivity; this was inhibited by the δ-opioid receptor (DOPr) antagonist naltrindole when intraperitoneally injected in previous morphine administration. Patch-clamp studies of DRG neurons following overnight incubation with high concentrations of morphine, the µ-opioid receptors (MOPr) agonist [D-Ala2, N-Me-Phe4, Gly5-ol]-Enkephalin (DAMGO) or the DOPr agonist [D-Ala2, D-Leu5]-Enkephalin evoked hyperexcitability. The pronociceptive actions of these opioids were blocked by the DOPr antagonist SDM25N but not the MOPr antagonist D-Pen-Cys-Tyr-D-Trp-Orn-Thr-Pen-Thr-NH2 The hyperexcitability induced by DAMGO was reversed after a 1 h washout, but reapplication of low concentrations of DAMGO or [D-Ala2, D-Leu5]-Enkephalin restored the hyperexcitability, an effect mediated by protein kinase C. DOPr-dependent DRG neuron hyperexcitability was blocked by the endocytosis inhibitor Pitstop 2, and the weakly internalizing DOPr agonist ARM390 did not cause hyperexcitability. Bioluminescence resonance energy transfer studies in HEK cells showed no evidence of switching of G-protein signaling from Gi to a Gs pathway in response to either high concentrations or overnight incubation of opioids. Thus, chronic high-dose opioid exposure leads to opioid tolerance and features of OIH in the colon. This action is mediated by DOPr signaling and is dependent on receptor endocytosis and downstream protein kinase C signaling.SIGNIFICANCE STATEMENT Opioids are effective in the treatment of abdominal pain, but escalating doses can lead to opioid tolerance and potentially opioid-induced hyperalgesia. We found that δ-opioid receptor (DOPr) plays a central role in the development of opioid tolerance and opioid-induced hyperalgesia in colonic afferent nociceptors following prolonged exposure to high concentrations of MOPr or DOPr agonists. Furthermore, the role of DOPr was dependent on OPr internalization and activation of a protein kinase C signaling pathway. Thus, targeting DOPr or key components of the downstream signaling pathway could mitigate adverse side effects by opioids.

Analysis of the spinal and vagal afferent innervation of the mouse colon using neuronal retrograde tracers.

The gut-brain axis has received increasing attention recently due to evidence that colonic microbes can affect brain function and behavior. However, little is known about the innervation of the colon by a major component of the gut-brain axis, vagal afferent neurons. Furthermore, it is currently unknown whether individual NG neurons or DRG neurons innervate both the proximal and distal colon. We aimed to quantify the number of vagal and spinal afferent neurons that innervate the colon; and determine whether these individual neurons simultaneously innervate the mouse proximal and distal colon. C57Bl/6 mice received injections of a combination of retrograde tracers that were either injected into the muscularis externa of the proximal or the distal colon: fast blue, DiI and DiO. Five to seven percent of lumbosacral and thoracolumbar spinal afferent neurons, and 25% of vagal afferent neurons were labelled by injections of DiI and DiO into the colon. We also found that approximately 8% of NG neurons innervate the distal colon. Ten percent of labeled thoracolumbar and 15% of labeled lumbosacral DRG neurons innervate both the distal and proximal colon. Eighteen percent of labeled NG neurons innervated both the distal and proximal colon. In conclusion, vagal afferent innervation of the distal colon is less extensive than the proximal colon, whereas a similar gradient was not observed for the spinal afferent innervation. Furthermore, overlap appears to exist between the receptive fields of vagal and spinal afferent neurons that innervate the proximal and distal colon.

VHA Whole Health Services and Complementary and Integrative Health Therapies: a Gateway to Evidence-Based Mental Health Treatment.

BACKGROUND: Engagement in evidence-based psychotherapy (EBP) among veterans with behavioral health conditions is often low. The Veterans Health Administration (VHA) is implementing a "Whole Health (WH)" system of care, to identify veteran personal health goals, align care with those goals, and offer services designed to engage and empower veterans to achieve well-being. OBJECTIVE: To examine the relationship between veteran WH utilization and subsequent engagement in EBP. DESIGN: Retrospective analysis of VHA administrative records from 18 facilities implementing WH. SUBJECTS: Veterans (n = 265,364) with a diagnosis of depression, post-traumatic stress disorder (PTSD), and/or anxiety who had a mental healthcare encounter but no EBP use in fiscal year (FY) 2018. Among this cohort, 33,146 (12.5%) began using WH in FY2019. MAIN MEASURES: We examined use of an EBP for depression, anxiety, and/or PTSD within 1 year of the index date of WH use compared to use of an EBP anytime during FY2019 for veterans not identified as using WH. We used multiple logistic regression to examine the association between veteran WH use and EBP engagement. KEY RESULTS: Approximately 3.0% (n = 7,860) of the veterans in our overall cohort engaged in an EBP in the year following their index date. Controlling for key demographic, health, and utilization variables, WH users had 2.4 (95% CI: 2.2-2.5) times higher odds of engaging in an EBP the following year than those with no WH utilization. Associations between utilization of specific WH services (vs. no utilization of that service) and engagement in an EBP in the subsequent year ranged from 1.6 (95% CI: 1.0-2.6) to 3.5 (95% CI: 3.2-3.9) across the different types of WH services used. CONCLUSIONS: WH use was associated with increased engagement in EBPs among veterans with depression, anxiety, and/or PTSD. Future interventions intended to promote veteran engagement in EBPs may benefit from leveraging WH services and therapies.

Mechanisms of change in posttraumatic headache-related disability: A mediation model.

OBJECTIVE: To explore whether the association between change in headache management self-efficacy and posttraumatic headache-related disability is partially mediated by a change in anxiety symptom severity. BACKGROUND: Many cognitive-behavioral therapy treatments for headache emphasize stress management, which includes anxiety management strategies; however, little is currently known about mechanisms of change in posttraumatic headache-related disability. Increasing our understanding of mechanisms could lead to improvements in treatments for these debilitating headaches. METHODS: This study is a secondary analysis of veterans (N = 193) recruited to participate in a randomized clinical trial of cognitive-behavioral therapy, cognitive processing therapy, or treatment as usual for persistent posttraumatic headache. The direct relationship between headache management self-efficacy and headache-related disability, along with partial mediation through change in anxiety symptoms was tested. RESULTS: The mediated latent change direct, mediated, and total pathways were statistically significant. The path analysis supported a significant direct pathway between headache management self-efficacy and headache-related disability (b = -0.45, p < 0.001; 95% confidence interval [CI: -0.58, -0.33]). The total effect of change of headache management self-efficacy scores on change in Headache Impact Test-6 scores was significant with a moderate-to-strong effect (b = -0.57, p = 0.001; 95% CI [-0.73, -0.41]). There was also an indirect effect through anxiety symptom severity change (b = -0.12, p = 0.003; 95% CI [-0.20, -0.04]). CONCLUSIONS: In this study, most of the improvements in headache-related disability were related to increased headache management self-efficacy with mediation occurring through change in anxiety. This indicates that headache management self-efficacy is a likely mechanism of change of posttraumatic headache-related disability with decreases in anxiety explaining part of the improvement in headache-related disability.

Minimal important difference metrics and test-retest reliability of the PTSD Checklist for DSM-5 with a primary care sample.

The PTSD Checklist for DSM-5 (PCL-5) is a measure of posttraumatic stress disorder (PTSD) symptom severity that is widely used for clinical and research purposes. Although previous work has examined metrics of minimal important difference (MID) of the PCL-5 in veteran samples, no work has identified PCL-5 MID metrics among adults in primary care in the United States. In this secondary analysis, data were evaluated from primary care patients (N = 971) who screened positive for PTSD and participated in a large clinical trial in federally qualified health centers in three U.S. states. Participants primarily self-identified as women (70.2%) and White (70.3%). We calculated test-retest reliability using clinic registry data and multiple distribution- and anchor-based metrics of MID using baseline and follow-up survey data. Test-retest reliability (Pearson's r, Spearman's ρ, intraclass correlation coefficient) ranged from adequate to excellent (.79-.94), with the shortest time lag demonstrating the highest reliability estimate. The MID for the PCL-5 was estimated using multiple approaches. Distribution-based approaches indicated an MID range of 8.5-12.5, and anchor-based approaches indicated an MID range of 9.8-11.7. Taken together, the MID metrics indicate that PCL-5 change scores of 9-12 likely reflect real change in PTSD symptoms and indicate at least an MID for patients, whereas PCL-5 change scores of 5 or less likely are not reliable. These findings can help inform clinicians using the PCL-5 in similar populations to track patient responses to treatment and help researchers interpret PCL-5 score changes in clinical trials.

Endosomal signaling of delta opioid receptors is an endogenous mechanism and therapeutic target for relief from inflammatory pain.

Whether G protein-coupled receptors signal from endosomes to control important pathophysiological processes and are therapeutic targets is uncertain. We report that opioids from the inflamed colon activate δ-opioid receptors (DOPr) in endosomes of nociceptors. Biopsy samples of inflamed colonic mucosa from patients and mice with colitis released opioids that activated DOPr on nociceptors to cause a sustained decrease in excitability. DOPr agonists inhibited mechanically sensitive colonic nociceptors. DOPr endocytosis and endosomal signaling by protein kinase C (PKC) and extracellular signal-regulated kinase (ERK) pathways mediated the sustained inhibitory actions of endogenous opioids and DOPr agonists. DOPr agonists stimulated the recruitment of Gαi/o and ß-arrestin1/2 to endosomes. Analysis of compartmentalized signaling revealed a requirement of DOPr endocytosis for activation of PKC at the plasma membrane and in the cytosol and ERK in the nucleus. We explored a nanoparticle delivery strategy to evaluate whether endosomal DOPr might be a therapeutic target for pain. The DOPr agonist DADLE was coupled to a liposome shell for targeting DOPr-positive nociceptors and incorporated into a mesoporous silica core for release in the acidic and reducing endosomal environment. Nanoparticles activated DOPr at the plasma membrane, were preferentially endocytosed by DOPr-expressing cells, and were delivered to DOPr-positive early endosomes. Nanoparticles caused a long-lasting activation of DOPr in endosomes, which provided sustained inhibition of nociceptor excitability and relief from inflammatory pain. Conversely, nanoparticles containing a DOPr antagonist abolished the sustained inhibitory effects of DADLE. Thus, DOPr in endosomes is an endogenous mechanism and a therapeutic target for relief from chronic inflammatory pain.

Agonist that activates the µ-opioid receptor in acidified microenvironments inhibits colitis pain without side effects.

OBJECTIVE: The effectiveness of µ-opioid receptor (MOPr) agonists for treatment of visceral pain is compromised by constipation, respiratory depression, sedation and addiction. We investigated whether a fentanyl analogue, (±)-N-(3-fluoro-1-phenethylpiperidine-4-yl)-N-phenyl propionamide (NFEPP), which preferentially activates MOPr in acidified diseased tissues, would inhibit pain in a preclinical model of inflammatory bowel disease (IBD) without side effects in healthy tissues. DESIGN: Antinociceptive actions of NFEPP and fentanyl were compared in control mice and mice with dextran sodium sulfate colitis by measuring visceromotor responses to colorectal distension. Patch clamp and extracellular recordings were used to assess nociceptor activation. Defecation, respiration and locomotion were assessed. Colonic migrating motor complexes were assessed by spatiotemporal mapping of isolated tissue. NFEPP-induced MOPr signalling and trafficking were studied in human embryonic kidney 293 cells. RESULTS: NFEPP inhibited visceromotor responses to colorectal distension in mice with colitis but not in control mice, consistent with acidification of the inflamed colon. Fentanyl inhibited responses in both groups. NFEPP inhibited the excitability of dorsal root ganglion neurons and suppressed mechanical sensitivity of colonic afferent fibres in acidified but not physiological conditions. Whereas fentanyl decreased defecation and caused respiratory depression and hyperactivity in mice with colitis, NFEPP was devoid of these effects. NFEPP did not affect colonic migrating motor complexes at physiological pH. NFEPP preferentially activated MOPr in acidified extracellular conditions to inhibit cAMP formation, recruit ß-arrestins and evoke MOPr endocytosis. CONCLUSION: In a preclinical IBD model, NFEPP preferentially activates MOPr in acidified microenvironments of inflamed tissues to induce antinociception without causing respiratory depression, constipation and hyperactivity.

Changes in signalling from faecal neuroactive metabolites following dietary modulation of IBS pain.

OBJECTIVE: Dietary therapies for irritable bowel syndrome (IBS) have received increasing interest but predicting which patients will benefit remains a challenge due to a lack of mechanistic insight. We recently found evidence of a role for the microbiota in dietary modulation of pain signalling in a humanised mouse model of IBS. This randomised cross-over study aimed to test the hypothesis that pain relief following reduced consumption of fermentable carbohydrates is the result of changes in luminal neuroactive metabolites. DESIGN: IBS (Rome IV) participants underwent four trial periods: two non-intervention periods, followed by a diet low (LFD) and high in fermentable carbohydrates for 3 weeks each. At the end of each period, participants completed questionnaires and provided stool. The effects of faecal supernatants (FS) collected before (IBS FS) and after a LFD (LFD FS) on nociceptive afferent neurons were assessed in mice using patch-clamp and ex vivo colonic afferent nerve recording techniques. RESULTS: Total IBS symptom severity score and abdominal pain were reduced by the LFD (N=25; p<0.01). Excitability of neurons was increased in response to IBS FS, but this effect was reduced (p<0.01) with LFD FS from pain-responders. IBS FS from pain-responders increased mechanosensitivity of nociceptive afferent nerve axons (p<0.001), an effect lost following LFD FS administration (p=NS) or when IBS FS was administered in the presence of antagonists of histamine receptors or protease inhibitors. CONCLUSIONS: In a subset of IBS patients with improvement in abdominal pain following a LFD, there is a decrease in pronociceptive signalling from FS, suggesting that changes in luminal mediators may contribute to symptom response.

The role of identity in chronic pain cognitions and pain-related disability within a clinical chronic pain population.

OBJECTIVE: Chronic pain has a significant impact on functioning and results in the disruption of one's assumed life trajectory, potentially altering their self-perceived identity. The present research is designed to determine whether identity-related issues are associated with common chronic pain cognitions and pain-related disability, which may help inform understanding of clinical chronic pain populations. METHOD: Ninety-eight adult chronic pain patients were assessed at a local pain clinic during a regularly scheduled appointment focusing on pain management. Multivariate hierarchal regression was used to determine whether issues related to identity and death anxiety were associated with pain catastrophizing, pain acceptance, and pain-related disability, above and beyond pain severity, fear-avoidance, and age. RESULTS: Self-concept clarity was significantly related to pain catastrophizing and pain acceptance, above and beyond death anxiety, pain severity, fear-avoidance, and age. Death anxiety was associated with pain catastrophizing, pain acceptance, and pain-related disability above and beyond pain severity, fear-avoidance, and age. CONCLUSIONS: To the best of our knowledge, the present study is the first examination of self-concept clarity and death anxiety as they relate to pain catastrophizing, pain acceptance, and pain-related disability. These descriptive results support the inclusion of identity and death anxiety within the pain experience and could serve as a foundation for future directions relevant to clinical applications.

Impact of Chronic Pain and Perceived Opioid Benefit on Value Domains.

Non-pharmacological chronic pain treatments increasingly incorporate values-based approaches as an alternative to opioid therapy. Chronic pain and opioid use may differentially impact value domains such as family or work, and there is little guidance on how to implement values-based treatment to address pain and comorbid opioid use. This study aims to characterize ways in which chronic pain and values interact. Participants (N = 327) 18 or older (M = 46 years) experiencing chronic musculoskeletal pain for > 3 months and actively taking a prescription opioid completed an online, self-report survey assessing the importance of values in six domains (i.e., family, intimate relationships, friendship, work, health, growth). Participants responded to questions about pain interference with and without opioids, and subjective impact of pain within each value domain. There were significant differences between the six value domains in importance ratings. Pain interference also differed among the values with the most reported pain interference occurring in the work and health domains. Pain interference without opioids was significantly greater for work, health, and family than the other values. The subjective impact of pain interference was greatest for family, work, and health as well. Across all value domains, pain interference without opioids was significantly greater than pain interference with the use of opioids. Results highlight that value domains are differentially impacted by chronic pain and opioids are perceived as reducing pain interference across all values. These results provide an initial description from which theory and hypotheses can be developed. Clinical implications and future directions are discussed.

Deoxycholic acid activates colonic afferent nerves via 5-HT3 receptor-dependent and -independent mechanisms.

Increased bile acids in the colon can evoke increased epithelial secretion resulting in diarrhea, but little is known about whether colonic bile acids contribute to abdominal pain. This study aimed to investigate the mechanisms underlying activation of colonic extrinsic afferent nerves and their neuronal cell bodies by a major secondary bile acid, deoxycholic acid (DCA). All experiments were performed on male C57BL/6 mice. Afferent sensitivity was evaluated using in vitro extracellular recordings from mesenteric nerves in the proximal colon (innervated by vagal and spinal afferents) and distal colon (spinal afferents only). Neuronal excitability of cultured dorsal root ganglion (DRG) and nodose ganglion (NG) neurons was examined with perforated patch clamp. Colonic 5-HT release was assessed using ELISA, and 5-HT immunoreactive enterochromaffin (EC) cells were quantified. Intraluminal DCA increased afferent nerve firing rate concentration dependently in both proximal and distal colon. This DCA-elicited increase was significantly inhibited by a 5-HT3 antagonist in the proximal colon but not in the distal colon, which may be in part due to lower 5-HT immunoreactive EC cell density and lower 5-HT levels in the distal colon following DCA stimulation. DCA increased the excitability of DRG neurons, whereas it decreased the excitability of NG neurons. DCA potentiated mechanosensitivity of high-threshold spinal afferents independent of 5-HT release. Together, this study suggests that DCA can excite colonic afferents via direct and indirect mechanisms but the predominant mechanism may differ between vagal and spinal afferents. Furthermore, DCA increased mechanosensitivity of high-threshold spinal afferents and may be a mechanism of visceral hypersensitivity.NEW & NOTEWORTHY Deoxycholic acid (DCA) directly excites spinal afferents and, to a lesser extent, indirectly via mucosal 5-HT release. DCA potentiates mechanosensitivity of high-threshold spinal afferents independent of 5-HT release. DCA increases vagal afferent firing in proximal colon via 5-HT release but directly inhibits the excitability of their cell bodies.

Depression precedes, but does not follow, gestational diabetes.

OBJECTIVES: To determine whether past history of depression is associated with increased rates of gestational diabetes, and whether history of gestational diabetes is associated with increased rates of postpartum depression. RESEARCH DESIGN: Data for this case-control study consisted of de-identified chart records for 1439 women who received pregnancy care at a large university hospital between 1998 and 2017. RESULTS: A history of depression prior to pregnancy was associated with gestational diabetes requiring insulin, although not with subtler degrees of gestational hyperglycemia. Diabetes in pregnancy was not associated with an increased risk of postpartum depression. Trauma history was associated with both impaired glucose tolerance in pregnancy and postpartum depression. CONCLUSIONS: Past episodes of depression increase risk for the most severe form of gestational diabetes; however, gestational diabetes does not contribute significantly to risk for postpartum depression. This suggests a unidirectional association, unlike the bidirectional association of diabetes with depression among the general population. History of trauma increases risk for both gestational hyperglycemia and postpartum depression, suggesting important health effects of trauma that may differ measurably from those associated with depression.