The Influence of Early Life Experience on Visceral Pain

Influence of Early-Life Stress on the Excitability of Dynorphin Neurons in the Adult Mouse Dorsal Horn

While early-life adversity has been associated with a higher risk of developing chronic pain in adulthood, the cellular and molecular mechanisms by which chronic stress during the neonatal period can persistently sensitize developing nociceptive circuits remain poorly understood. Here, we investigate the effects of early-life stress (ELS) on synaptic integration and intrinsic excitability in dynorphin-lineage (DYN) interneurons within the adult mouse superficial dorsal horn (SDH), which are important for inhibiting mechanical pain and itch. The administration of neonatal limited bedding between postnatal days (P)2 and P9 evoked sex-dependent effects on spontaneous glutamatergic signaling, as female SDH neurons exhibited a higher amplitude of miniature excitatory postsynaptic currents (mEPSCs) after ELS, while mEPSC frequency was reduced in DYN neurons of the male SDH. Furthermore, ELS decreased the frequency of miniature inhibitory postsynaptic currents selectively in female DYN neurons. As a result, ELS increased the balance of spontaneous excitation versus inhibition (E:I ratio) in mature DYN neurons of the female, but not male, SDH network. Nonetheless, ELS weakened the total primary afferent-evoked glutamatergic drive onto adult DYN neurons selectively in females, without modifying afferent-evoked inhibitory signaling onto the DYN population. Finally, ELS failed to significantly change the intrinsic membrane excitability of mature DYN neurons in either males or females. Collectively, these data suggest that ELS exerts a long-term influence on the properties of synaptic transmission onto DYN neurons within the adult SDH, which includes a reduction in the overall strength of sensory input onto this important subset of inhibitory interneurons. PERSPECTIVE: This study suggests that chronic stress during the neonatal period influences synaptic function within adult spinal nociceptive circuits in a sex-dependent manner. These findings yield new insight into the potential mechanisms by which early-life adversity might shape the maturation of pain pathways in the central nervous system (CNS).

Neural circuits regulating visceral pain

Visceral hypersensitivity, a common clinical manifestation of irritable bowel syndrome, may contribute to the development of chronic visceral pain, which is a major challenge for both patients and health providers. Neural circuits in the brain encode, store, and transfer pain information across brain regions. In this review, we focus on the anterior cingulate cortex and paraventricular nucleus of the hypothalamus to highlight the progress in identifying the neural circuits involved in visceral pain. We also discuss several neural circuit mechanisms and emphasize the importance of cross-species, multiangle approaches and the identification of specific neurons in determining the neural circuits that control visceral pain.

Involvement of oxidative stress in orofacial mechanical pain hypersensitivity following neonatal maternal separation in rats

Patients with persistent pain have sometimes history of physical abuse or neglect during infancy. However, the pathogenic mechanisms underlying orofacial pain hypersensitivity associated with early-life stress remain unclear. The present study focused on oxidative stress and investigated its role in pain hypersensitivity in adulthood following early-life stress. To establish an early-life stress model, neonatal pups were separated with their mother in isolated cages for 2 weeks. The mechanical head-withdrawal threshold (MHWT) in the whisker pad skin of rats received maternal separation (MS) was lower than that of non-MS rats at postnatal week 7. In MS rats, the expression of 8-hydroxy-deoxyguanosine, a marker of DNA oxidative damage, was enhanced, and plasma antioxidant capacity, but not mitochondrial complex I activity, decreased compared with that in non-MS rats. Reactive oxygen species (ROS) inactivation and ROS-sensitive transient receptor potential ankyrin 1 (TRPA1) antagonism in the whisker pad skin at week 7 suppressed the decrease of MHWT. Corticosterone levels on day 14 increased in MS rats. Corticosterone receptor antagonism during MS periods suppressed the reduction in antioxidant capacity and MHWT. The findings suggest that early-life stress potentially induces orofacial mechanical pain hypersensitivity via peripheral nociceptor TRPA1 hyperactivation induced by oxidative stress in the orofacial region.

Paraventricular Mast Cell-Derived Histamine Activates CRH Neurons to Mediate Adult Visceral Hypersensitivity Induced by Neonatal Maternal Separation

Neonatal maternal separation (NMS) is an early-life stress (ELS) that can result in adult visceral hypersensitivity, which is usually manifested as chronic visceral pain. Although mast cells and corticotropin-releasing hormone (CRH) neurons are involved in stress response, whether there is an interaction between mast cells and CRH neurons in hypothalamic paraventricular nucleus (PVN) during the ELS-induced visceral hypersensitivity remains elusive. Herein, we established an NMS model by separating neonatal mice from their mothers, and observed that these mice presented visceral hypersensitivity in adulthood, as indicated by elevated abdominal withdrawal reflex and lowered visceral pain threshold. The NMS-induced adult visceral hypersensitivity was accompanied by activation of mast cells and CRH neurons in PVN. Also, NMS increased the histamine content (an inflammatory mediator mainly released by mast cells) and histamine H2 receptor (H2R) expression of CRH neurons in PVN. Remarkably, intra-PVN administration with mast cell stabilizer attenuated the NMS-induced CRH neuronal activation and adult visceral pain, while histamine administration showed the opposite effects. Moreover, intra-PVN injection with H2R antagonist alleviated the NMS-induced CRH neuronal activation, PKA and CREB phosphorylation, and importantly, adult visceral pain. Together, our findings revealed a role of an interaction between paraventricular mast cells and CRH neurons in NMS-induced adult visceral hypersensitivity, thereby providing a perspective for the management of visceral pain.

Glutamatergic and GABAergic anteroventral BNST projections to PVN CRH neurons regulate maternal separation-induced visceral pain

Early-life stress (ELS) is thought to cause the development of visceral pain disorders. While some individuals are vulnerable to visceral pain, others are resilient, but the intrinsic circuit and molecular mechanisms involved remain largely unclear. Herein, we demonstrate that inbred mice subjected to maternal separation (MS) could be separated into susceptible and resilient subpopulations by visceral hypersensitivity evaluation. Through a combination of chemogenetics, optogenetics, fiber photometry, molecular and electrophysiological approaches, we discovered that susceptible mice presented activation of glutamatergic projections or inhibition of GABAergic projections from the anteroventral bed nucleus of the stria terminalis (avBNST) to paraventricular nucleus (PVN) corticotropin-releasing hormone (CRH) neurons. However, resilience develops as a behavioral adaptation partially due to restoration of PVN SK2 channel expression and function. Our findings suggest that PVN CRH neurons are dually regulated by functionally opposing avBNST neurons and that this circuit may be the basis for neurobiological vulnerability to visceral pain.

Animal models of interstitial cystitis/bladder pain syndrome

Interstitial Cystitis/Bladder Pain Syndrome (IC/BPS) is a chronic disorder characterized by pelvic and/or bladder pain, along with lower urinary tract symptoms that have a significant impact on an individual's quality of life. The diverse range of symptoms and underlying causes in IC/BPS patients pose a significant challenge for effective disease management and the development of new and effective treatments. To facilitate the development of innovative therapies for IC/BPS, numerous preclinical animal models have been developed, each focusing on distinct pathophysiological components such as localized urothelial permeability or inflammation, psychological stress, autoimmunity, and central sensitization. However, since the precise etiopathophysiology of IC/BPS remains undefined, these animal models have primarily aimed to replicate the key clinical symptoms of bladder hypersensitivity and pain to enhance the translatability of potential therapeutics. Several animal models have now been characterized to mimic the major symptoms of IC/BPS, and significant progress has been made in refining these models to induce chronic symptomatology that more closely resembles the IC/BPS phenotype. Nevertheless, it's important to note that no single model can fully replicate all aspects of the human disease. When selecting an appropriate model for preclinical therapeutic evaluation, consideration must be given to the specific pathology believed to underlie the development of IC/BPS symptoms in a particular patient group, as well as the type and severity of the model, its duration, and the proposed intervention's mechanism of action. Therefore, it is likely that different models will continue to be necessary for preclinical drug development, depending on the unique etiology of IC/BPS being investigated.

Impact of auricular percutaneous electrical nerve field stimulation on gut microbiome in adolescents with irritable bowel syndrome: A pilot study

OBJECTIVES

Percutaneous electrical nerve field stimulation (PENFS) has documented efficacy for irritable bowel syndrome (IBS) via plausible vagal neuromodulation effects. The vagus nerve may affect gut microbiome composition via brain-gut-microbiome signaling. We aimed to investigate gut microbiome alterations by PENFS therapy in adolescent IBS patients.

METHODS

A prospective study of females with IBS aged 11-18 years receiving PENFS therapy for 4 weeks with pre- and post-intervention stool sampling was conducted. Outcome surveys completed pre-therapy, weekly, and post-therapy included IBS-Severity Scoring System (IBS-SSS), Visceral Sensitivity Index (VSI), Functional Disability Inventory (FDI), and the global symptom response scale (SRS). Bacterial DNA was extracted from stool samples followed by 16S rRNA amplification and sequencing. QIIME 2 (version 2022.2) was used for analyses of α and β diversity and differential abundance by group.

RESULTS

Twenty females aged 15.6 ± 1.62 years were included. IBS-SSS, VSI, and FDI scores decreased significantly after PENFS therapy (P < 0.0001, P = 0.0003, P = 0.0004, respectively). No intra- or interindividual microbiome changes were noted pre- versus post-therapy or between responders and non-responders. When response was defined by 50-point IBS-SSS score reduction, α diversity was higher in responders compared with non-responders at week 4 (P = 0.033). There was higher abundance of Blautia in excellent responders versus non-responders.

CONCLUSIONS

There were no substantial microbial diversity alterations with PENFS. Subjects with excellent therapeutic response showed an enrichment of relative abundance of Blautia, which may indicate that patients with specific microbial signature have a more favorable response to PENFS.

Stress-induced symptom exacerbation: Stress increases voiding frequency, somatic sensitivity, and urinary bladder NGF and BDNF expression in mice with subthreshold cyclophosphamide (CYP)

Symptom exacerbation due to stress is prevalent in many disease states, including functional disorders of the urinary bladder (e.g., overactive bladder (OAB), interstitial cystitis/bladder pain syndrome (IC/BPS)); however, the mechanisms underlying the effects of stress on micturition reflex function are unclear. In this study we designed and evaluated a stress-induced symptom exacerbation (SISE) mouse model that demonstrates increased urinary frequency and somatic (pelvic and hindpaw) sensitivity. Cyclophosphamide (CYP) (35 mg/kg; i.p., every 48 hours for a total of 4 doses) or 7 days of repeated variate stress (RVS) did not alter urinary bladder function or somatic sensitivity; however, both CYP alone and RVS alone significantly (p ≤ 0.01) decreased weight gain and increased serum corticosterone. CYP treatment when combined with RVS for 7 days (CYP+RVS) significantly (p ≤ 0.01) increased serum corticosterone, urinary frequency and somatic sensitivity and decreased weight gain. CYP+RVS exposure in mice significantly (p ≤ 0.01) increased (2.6-fold) voiding frequency as we determined using conscious, open-outlet cystometry. CYP+RVS significantly (p ≤ 0.05) increased baseline, threshold, and peak micturition pressures. We also evaluated the expression of NGF, BDNF, CXC chemokines and IL-6 in urinary bladder in CYP alone, RVS alone and CYP+RVS mouse cohorts. Although all treatments or exposures increased urinary bladder NGF, BDNF, CXC and IL-6 content, CYP+RVS produced the largest increase in all inflammatory mediators examined. These results demonstrated that CYP alone or RVS alone creates a change in the inflammatory environment of the urinary bladder but does not result in a change in bladder function or somatic sensitivity until CYP is combined with RVS (CYP+RVS). The SISE model of CYP+RVS will be useful to develop testable hypotheses addressing underlying mechanisms where psychological stress exacerbates symptoms in functional bladder disorders leading to identification of targets and potential treatments.

Spinal VGLUT3 lineage neurons drive visceral mechanical allodynia but not sensitized visceromotor reflexes

Visceral pain is among the most prevalent and bothersome forms of chronic pain, but their transmission in the spinal cord is still poorly understood. Here, we conducted focal colorectal distention (fCRD) to drive both visceromotor responses (VMRs) and aversion. We first found that spinal CCK neurons were necessary for noxious fCRD to drive both VMRs and aversion under naive conditions. We next showed that spinal VGLUT3 neurons mediate visceral allodynia, whose ablation caused loss of aversion evoked by low-intensity fCRD in mice with gastrointestinal (GI) inflammation or spinal circuit disinhibition. Importantly, these neurons were dispensable for driving sensitized VMRs under both inflammatory and central disinhibition conditions. Anatomically, a subset of VGLUT3 neurons projected to parabrachial nuclei, whose photoactivation sufficiently generated aversion in mice with GI inflammation, without influencing VMRs. Our studies suggest the presence of different spinal substrates that transmit nociceptive versus affective dimensions of visceral sensory information.

A paraventricular hypothalamic nucleus input to ventral of lateral septal nucleus controls chronic visceral pain

ABSTRACT

Irritable bowel syndrome is a functional gastrointestinal disorder characterized by chronic visceral pain with complex etiology and difficult treatment. Accumulated evidence has confirmed that the sensitization of the central nervous system plays an important role in the development of visceral pain, whereas the exact mechanisms of action of the neural pathways remain largely unknown. In this study, a distinct neural circuit was identified from the paraventricular hypothalamic (PVH) to the ventral of lateral septal (LSV) region. This circuit was responsible for regulating visceral pain. In particular, the data indicated that the PVH CaMKIIα-positive neurons inputs to the LSV CaMKIIα-positive neurons were only activated by colorectal distention rather than somatic stimulations. The PVH-LSV CaMKIIα + projection pathway was further confirmed by experiments containing a viral tracer. Optogenetic inhibition of PVH CaMKIIα + inputs to LSV CaMKIIα-positive neurons suppressed visceral pain, whereas selective activation of the PVH-LSV CaMKIIα + projection evoked visceral pain. These findings suggest the critical role of the PVH-LSV CaMKIIα + circuit in regulating visceral pain.

Chronic Pelvic Pain Profiles in Women Seeking Care in a Tertiary Pelvic Pain Clinic

OBJECTIVE

Female chronic pelvic pain (CPP) has multiple pain generators and significant psychosocial sequalae. Biopsychosocial-based phenotyping could help identify clinical heterogeneity that may inform tailored patient treatment. This study sought to identify distinct CPP profiles based on routinely collected clinical information and evaluate the validity of the profiles through associations with social histories and subsequent health care utilization.

METHODS

Women (18-77 years, n = 200) seeking care for CPP in a tertiary gynecological pelvic pain clinic between 2017 and 2020 were included. Baseline data of pain intensity, interference, catastrophizing, acceptance, overlapping pelvic pain syndromes, and co-occurring psychiatric disorders were subject to a partition around medoids clustering to identify patient profiles. Profiles were compared across social history and subsequent treatment modality, prescribed medications, and surgeries performed.

RESULTS

Two profiles with equal proportion were identified. Profile 1 was vulvodynia and myofascial pelvic pain-dominant characterized by lower pain burden and better psychological functioning. Profile 2 was visceral pain-dominant featuring higher pain interference and catastrophizing, lower pain acceptance, and higher psychiatric comorbidity. Patients in Profile 2 had 2-4 times higher prevalence of childhood and adulthood abuse history (all P < .001), were more likely to subsequently receive behavioral therapy (46% vs 27%, P = .005) and hormonal treatments (34% vs 21%, P = .04), and were prescribed more classes of medications for pain management (P = .045) compared to patients in Profile 1.

CONCLUSIONS

Treatment-seeking women with CPP could be separated into two groups distinguished by pain clusters, pain burden, pain distress and coping, and co-occurring mental health disorders.

The Implications of Mental Health and Trauma in Interstitial Cystitis

This review aims to assess the relationship between interstitial cystitis (IC) and significant traumatic events or PTSD. It was shown that there is a strong correlation between past trauma and the development of interstitial cystitis, as well as a much higher incidence of PTSD in patients diagnosed with IC. It was also established that for individuals with early traumatic experiences, the more likely the development of IC later in life, and with more severe symptoms and adverse effects on quality of life. We describe three distinct hypotheses for the possible physiologic mechanism for development of IC with relation to mental health and trauma, although definitive evidence in this area is still lacking, which poses interesting avenues for further research. This review also revealed an apparent lack of, and need for, trauma informed care and screening for PTSD in patients diagnosed with IC or other chronic pain syndromes.

Upregulation of Netrin-1 in the hippocampus mediates the formation of visceral hypersensitivity induced by maternal separation

Early adverse life events (EALs), such as maternal separation (MS), can cause visceral hypersensitivity, which is thought to be a key pathophysiological mechanism of irritable bowel syndrome (IBS). Previous studies mainly focused on EALs-induced visceral hypersensitivity in adulthood but did not consider that it may have occurred in the preadult period. We previously found that rats who experienced MS suffered from visceral hypersensitivity starting from the post-weaning period. Moreover, the hippocampus is considered to be critical in regulating the formation of visceral hypersensitivity induced by MS. But the underlying mechanisms throughout different life periods are unclear. In this study, behavioral tests, RNA-seq, lentiviral interference, and molecular biology techniques were applied to investigate the molecular mechanism in the hippocampus underlying MS-induced long-lasting visceral hypersensitivity. It was found that both visceral sensitivity and anxiety-like behaviors were significantly increased in MS rats in post-weaning, prepubertal, and adult periods, especially in the prepubertal period. Subsequently, RNA-seq targeting the hippocampus identified that the expression level of Netrin-1 was significantly increased in all periods, which was further confirmed by quantitative real-time PCR and Western blot. Knocking-down hippocampal Netrin-1 in the post-weaning period by lentivirus interference alleviated visceral hypersensitivity and anxiety-like behaviors of MS rats in the later phase of life. In addition, deleted in colorectal cancer (DCC), instead of neogenin-1(Neo-1) or uncoordinated (UNC5), was proved to be the specific functional receptor of Netrin-1 in regulating visceral hypersensitivity, whose upregulation may result in the most severe symptoms in the prepubertal period. Furthermore, the activation of the Netrin-1/DCC pathway could enhance long-term potentiation (LTP) in the hippocampus, probably via recruitment of the AMPA receptor subunit GluA1, which finally resulted in the formation of visceral hypersensitivity. These novel findings suggest that long-lasting over-expression of Netrin-1 can mediate visceral hypersensitivity and anxiety disorder from the post-weaning period to adulthood by activating DCC/GluA1 pathway in the hippocampus. Moreover, early intervention of Netrin-1 in the post-weaning period could lead to significant symptom relief afterward, which provides evidence that the Netrin-1/DCC/GluA1 signaling pathway may be a potential therapeutic target for the treatment of visceral hypersensitivity in clinics.

Chronic psychological stress alters gene expression in rat colon epithelial cells promoting chromatin remodeling, barrier dysfunction and inflammation

Chronic stress is commonly associated with enhanced abdominal pain (visceral hypersensitivity), but the cellular mechanisms underlying how chronic stress induces visceral hypersensitivity are poorly understood. In this study, we examined changes in gene expression in colon epithelial cells from a rat model using RNA-sequencing to examine stress-induced changes to the transcriptome. Following chronic stress, the most significantly up-regulated genes included Atg16l1, Coq10b, Dcaf13, Nat2, Ptbp2, Rras2, Spink4 and down-regulated genes including Abat, Cited2, Cnnm2, Dab2ip, Plekhm1, Scd2, and Tab2. The primary altered biological processes revealed by network enrichment analysis were inflammation/immune response, tissue morphogenesis and development, and nucleosome/chromatin assembly. The most significantly down-regulated process was the digestive system development/function, whereas the most significantly up-regulated processes were inflammatory response, organismal injury, and chromatin remodeling mediated by H3K9 methylation. Furthermore, a subpopulation of stressed rats demonstrated very significantly altered gene expression and transcript isoforms, enriched for the differential expression of genes involved in the inflammatory response, including upregulation of cytokine and chemokine receptor gene expression coupled with downregulation of epithelial adherens and tight junction mRNAs. In summary, these findings support that chronic stress is associated with increased levels of cytokines and chemokines, their downstream signaling pathways coupled to dysregulation of intestinal cell development and function. Epigenetic regulation of chromatin remodeling likely plays a prominent role in this process. Results also suggest that super enhancers play a primary role in chronic stress-associated intestinal barrier dysfunction.

The Effect of Chronic Psychological Stress on Lower Urinary Tract Function: An Animal Model Perspective

Chronic psychological stress can affect urinary function and exacerbate lower urinary tract (LUT) dysfunction (LUTD), particularly in patients with overactive bladder (OAB) or interstitial cystitis–bladder pain syndrome (IC/BPS). An increasing amount of evidence has highlighted the close relationship between chronic stress and LUTD, while the exact mechanisms underlying it remain unknown. The application of stress-related animal models has provided powerful tools to explore the effect of chronic stress on LUT function. We systematically reviewed recent findings and identified stress-related animal models. Among them, the most widely used was water avoidance stress (WAS), followed by social stress, early life stress (ELS), repeated variable stress (RVS), chronic variable stress (CVS), intermittent restraint stress (IRS), and others. Different types of chronic stress condition the induction of relatively distinguished changes at multiple levels of the micturition pathway. The voiding phenotypes, underlying mechanisms, and possible treatments of stress-induced LUTD were discussed together. The advantages and disadvantages of each stress-related animal model were also summarized to determine the better choice. Through the present review, we hope to expand the current knowledge of the pathophysiological basis of stress-induced LUTD and inspire robust therapies with better outcomes.

Neonatal Bladder Inflammation Results in Adult Female Mouse Phenotype With Increased Frequency and Nociceptive Responses to Bladder Filling

Bladder pain and hypersensitivity to bladder filling are clinically common, but animal models examining syndromes with these features are limited. A rat model of bladder hypersensitivity produced by neonatal bladder inflammation (NBI) has been reported to have many of the clinical features of bladder pain syndromes. The present study sought to determine whether similar hypersensitivity might be induced by NBI in mice. Female C57BL6/J mice had NBI induced on postnatal days P12-14 by the intravesical administration of zymosan. As adults (12–14 weeks of age), the mice were examined for hypersensitivity of their bladders as: spontaneous voiding and evoked cystometrograms at baseline, and visceromotor responses (VMRs) to urinary bladder distension (UBD) following a secondary insult (either repeated bladder inflammation or acute stress induced by footshock). Mice that experienced NBI demonstrated hypersensitivity, when compared with control mice, manifested as increased spontaneous voiding, increased frequency of evoked voids during intravesical saline infusion, and increased vigor of VMRs to UBD following either acute bladder inflammation or acute stress. This recapitulates the hallmark features of clinical painful bladder disorders and suggest utility of this murine model for the study of these disorders while allowing methodological expansion into well-established genetic and immunological models.

Reduced Hippocampal Volume and Neurochemical Response to Adult Stress Exposure in a Female Mouse Model of Urogenital Hypersensitivity

Early life stress exposure significantly increases the risk of developing chronic pain syndromes and comorbid mood and metabolic disorders later in life. Structural and functional changes within the hippocampus have been shown to contribute to many early life stress-related outcomes. We have previously reported that adult mice that underwent neonatal maternal separation (NMS) exhibit urogenital hypersensitivity, altered anxiety- and depression-like behaviors, increased adiposity, and decreased gene expression and neurogenesis in the hippocampus. Here, we are using magnetic resonance imaging and spectroscopy (MRI and MRS) to further investigate both NMS- and acute stress-induced changes in the hippocampus of female mice. Volumetric analysis of the whole brain revealed that the left hippocampus of NMS mice was 0.038 mm3 smaller compared to naïve mice. MRS was performed only on the right hippocampus and both total choline (tCho) and total N-acetylaspartate (tNAA) levels were significantly decreased due to NMS, particularly after WAS. Phosphoethanolamine (PE) levels were decreased in naïve mice after WAS, but not in NMS mice, and WAS increased ascorbate levels in both groups. The NMS mice showed a trend toward increased body weight and body fat percentage compared to naïve mice. A significant negative correlation was observed between body weight and phosphocreatine levels post-WAS in NMS mice, as well as a positive correlation between body weight and glutamine for NMS mice and a negative correlation for naïve mice. Together, these data suggest that NMS in mice reduces left hippocampal volume and may result in mitochondrial dysfunction and reduced neuronal integrity of the right hippocampus in adulthood. Hippocampal changes also appear to be related to whole body metabolic outcomes.

Corticotropin-releasing factor receptor 1 (CRF-R1) antagonists: Promising agents to prevent visceral hypersensitivity in irritable bowel syndrome

Corticotropin-releasing factor (CRF) is a 41-amino acid polypeptide that coordinates the endocrine system, autonomic nervous system, immune system, and physiological behavior. CRF is a signaling regulator in the neuro-endocrine-immune (NEI) network that mediates visceral hypersensitivity. Rodent models to simulate changes in intestinal motility similar to those reported in the irritable bowel syndrome (IBS), demonstrate that the CRF receptor 1 (CRF-R1) mediates intestinal hypersensitivity under many conditions. However, the translation of preclinical studies into clinical trials has not been successful possibly due to the lack of sufficient understanding of the multiple variants of CRF-R1 and CRF-R1 antagonists. Investigating the sites of action of central and peripheral CRF is critical for accelerating the translation from preclinical to clinical studies.

Differential Activation of Colonic Afferents and Dorsal Horn Neurons Underlie Stress-Induced and Comorbid Visceral Hypersensitivity in Female Rats

Chronic Overlapping Pain Conditions, including irritable bowel syndrome (IBS) and temporomandibular disorder (TMD), represent a group of idiopathic pain conditions that likely have peripheral and central mechanisms contributing to their pathology, but are poorly understood. These conditions are exacerbated by stress and have a female predominance. The presence of one condition predicts the presence or development of additional conditions, making this a significant pain management problem. The current study was designed to determine if the duration and magnitude of peripheral sensitization and spinal central sensitization differs between restraint stress-induced visceral hypersensitivity (SIH) and chronic comorbid pain hypersensitivity (CPH; stress during pre-existing orofacial pain). SIH in female rats, as determined by the visceromotor response, persisted at least four but resolved by seven weeks. In contrast, CPH persisted at least seven weeks. Surprisingly, colonic afferents in both SIH and CPH rats were sensitized at seven weeks. CPH rats also had referred pain through seven weeks, but locally anesthetizing the colon only attenuated the referred pain through four weeks, suggesting a transition to colonic afferent independent central sensitization. Different phenotypes of dorsal horn neurons were sensitized in the CPH rats seven weeks post stress compared to four weeks or SIH rats. The current study suggests differential processing of colonic afferent input to the lumbosacral spinal cord contributes to visceral hypersensitivity during comorbid chronic pain conditions. PERSPECTIVE: Chronic Overlapping Pain Conditions represent a unique challenge in pain management. The diverse nature of peripheral organs hinders a clear understanding of underlying mechanisms accounting for the comorbidity. This study highlights a mismatch between the condition-dependent behavior and peripheral and spinal mechanisms that contribute to visceral pain hypersensitivity.

Chronic psychological stress and lower urinary tract symptoms

It is well established that lower urinary tract symptoms (LUTS), particularly urinary urgency and incontinence, cause stress and anxiety for patients. However, there is mounting evidence that the relationship between these two factors is bidirectional and that chronic psychological stress itself can result in the development of symptoms such as urinary frequency, urgency, incontinence, and pelvic pain. This review considers the evidence that such a relationship exists and reviews the literature from clinical and animal studies to identify some of the mechanisms that might be involved. Inflammatory responses induced by chronic stress appear to offer the strongest link to bladder dysfunction. There is overwhelming evidence, both in patients and animal models, for a release of pro-inflammatory cytokines and chemokines during periods of chronic stress. Furthermore, cytokines have been shown to cause bladder dysfunction and pain via actions in the central nervous system and locally in the bladder. In the brain and spinal cord, pro-inflammatory cytokines influence the regulation of micturition pathways by corticotropin-releasing factor (CRF) and its receptors, while peripherally cytokines affect bladder function, directly causing detrusor hypertrophy and afferent nerve hypersensitivity. There is little information on which treatments may have most benefit for stressed/anxious patients with LUTS, but animal studies suggest traditional drugs for overactive bladder (solifenacin, mirabegron) are more effective on LUTS than anxiolytic drugs (fluoxetine, imipramine). The preliminary preclinical data for CRF receptor antagonists is not consistent. A clearer understanding of the mechanisms involved in stress-induced LUTS should provide a basis for improved treatment of this condition.

An Omega-3-rich Anti-inflammatory Diet Improved Widespread Allodynia and Worsened Metabolic Outcomes in Adult Mice Exposed to Neonatal Maternal Separation

Inflammation plays a key role in the progression and maintenance of chronic pain, which impacts the lives of millions of Americans. Despite growing evidence that chronic pain can be improved by treating underlying inflammation, successful treatments are lacking and pharmaceutical interventions are limited due to drug side effects. Here we are testing whether a 'healthy human' diet (HHD), with or without anti-inflammatory components (HHAID), improves pain-like behaviors in a preclinical model of chronic widespread hypersensitivity induced by neonatal maternal separation (NMS). The HHD and HHAID are isocaloric and macronutrient-matched, have a low glycemic index, and fat content (35 kcal%) that is high in omega-3 fatty acids, while only the HHAID includes a combination of key anti-inflammatory compounds, at clinically relevant doses. Mice on these diets were compared to mice on a control diet with a macronutrient composition commonly used in rodents (20% protein, 70% carbohydrate, 10% fat). Our results demonstrate a benefit of the HHAID on pain-like behaviors in both male and female mice, despite increased caloric intake, adiposity, and weight gain. In female mice, HHAID specifically increased measures of metabolic syndrome and inflammation compared to the HHD and control diet groups. Male mice were susceptible to worsening metabolic measures on both the HHAID and HHD. This work highlights important sexual dimorphic outcomes related to early life stress exposure and dietary interventions, as well as a potential disconnect between improvements in pain-like behaviors and metabolic measures.

Voluntary wheel running improves outcomes in an early life stress-induced model of urologic chronic pelvic pain syndrome in male mice

ABSTRACT

Patients with a history of early life stress (ELS) exposure have an increased risk of developing chronic pain and mood disorders later in life. The severity of ELS in patients with urologic chronic pelvic pain syndrome (UCPPS) is directly correlated with symptom severity and increased comorbidity, and is inversely related to likelihood of improvement. Voluntary exercise improves chronic pain symptoms, and our group and others have shown that voluntary wheel running can improve outcomes in stress-induced UCPPS models, suggesting that exercise may negate some of the outcomes associated with ELS. Here, we provide further evidence that voluntary wheel running can attenuate increased perigenital mechanical sensitivity, bladder output, and mast cell degranulation in the bladder and prostate in male mice that underwent neonatal maternal separation (NMS). Sedentary male NMS mice had reduced serum corticosterone, which was not impacted by voluntary wheel running, although stress-related regulatory gene expression in the hypothalamus and hippocampus was significantly increased after exercise. Neurogenesis in the dentate gyrus of the hippocampus was diminished in sedentary NMS mice and significantly increased in both exercised naïve and NMS mice. Sucrose consumption increased in exercised naïve but not NMS mice, and anxiety behaviors measured on an elevated plus maze were increased after exercise. Together these data suggest that voluntary wheel running is sufficient to normalize many of the UCPPS-related outcomes resulting from NMS. Exercise also increased hippocampal neurogenesis and stress-related gene expression within the hypothalamic-pituitary-adrenal axis, further supporting exercise as a nonpharmacological intervention for attenuating outcomes related to ELS exposure.

Mast cells in the paraventricular nucleus participate in visceral hypersensitivity induced by neonatal maternal separation

Early-life stress (ELS) is a high-risk factor for the development of chronic visceral pain in adulthood. Emerging evidence suggests that mast cells play a key role in the development of visceral hypersensitivity through interaction with neurons. The sensitization of corticotropin-releasing factor (CRF) neurons in the hypothalamic paraventricular nucleus (PVN) plays a pivotal role in the pathogenesis of visceral pain. However, the precise mechanism by which mast cells and CRF neurons interact in the PVN in the pathogenesis of visceral hypersensitivity remains elusive. In the present study, we used neonatal maternal separation (MS), an ELS model, and observed that neonatal MS induced visceral hypersensitivity and triggered PVN mast cell activation in adult rats, which was repressed by intra-PVN infusion of the mast cell stabilizer disodium cromoglycate (cromolyn). Wild-type (WT) mice but not mast cell-deficient KitW-sh/W-sh mice that had experienced neonatal MS exhibited chronic visceral hypersensitivity. MS was associated with an increase in the expression of proinflammatory mediators, the number of CRF+ cells and CRF protein in the PVN, which was prevented by intra-PVN infusion of cromolyn. Furthermore, we demonstrated that intra-PVN infusion of the mast degranulator compound 48/80 significantly induced mast cell activation, resulting in proinflammatory mediator release, CRF neuronal sensitization, and visceral hypersensitivity, which was suppressed by cromolyn. Overall, our findings demonstrated that neonatal MS induces the activation of PVN mast cells, which secrete numerous proinflammatory mediators that may participate in neighboring CRF neuronal activity, ultimately directly inducing visceral hypersensitivity in adulthood.

BNSTAV GABA-PVNCRF Circuit Regulates Visceral Hypersensitivity Induced by Maternal Separation in Vgat-Cre Mice

Visceral hypersensitivity as a common clinical manifestation of irritable bowel syndrome (IBS) may contribute to the development of chronic visceral pain. Our prior studies authenticated that the activation of the corticotropin-releasing factor (CRF) neurons in paraventricular nucleus (PVN) contributed to visceral hypersensitivity in mice, but puzzles still remain with respect to the underlying hyperactivation of corticotropin-releasing factor neurons. Herein, we employed maternal separation (MS) to establish mouse model of visceral hypersensitivity. The neuronal circuits associated with nociceptive hypersensitivity involved paraventricular nucleus CRF neurons by means of techniques such as behavioral test, pharmacology, molecular biology, retrograde neuronal circuit tracers, electrophysiology, chemogenetics and optogenetics. MS could predispose the elevated firing frequency of CRF neurons in PVN in murine adulthood, which could be annulled via the injection of exogenous GABA (0.3mM, 0.2µl) into PVN. The PVN-projecting GABAergic neurons were mainly distributed in the anterior ventral (AV) region in the bed nucleus of stria terminalis (BNST), wherein the excitability of these GABAergic neurons was reduced. Casp3 virus was utilized to induce apoptosis of GABA neurons in BNST-AV region, resulting in the activation of CRF neurons in PVN and visceral hyperalgesia. In parallel, chemogenetic and optogenetic approaches to activate GABAergic BNST_AV-PVN circuit in MS mice abated the spontaneous firing frequency of PVN CRF neurons and prevented the development of visceral hypersensitivity. A priori, PVN^CRF-projecting GABAergic neurons in BNST-AV region participated in the occurrence of visceral hypersensitivity induced by MS. Our research may provide a new insight into the neural circuit mechanism of chronic visceral pain.

The Brain-Gut-Microbiotal Axis: A framework for understanding functional GI illness and their therapeutic interventions

Functional gastrointestinal disorders (FGIDs), characterized by chronic abdominal complaints without a structural or biochemical cause, are common diseases that are frequently encountered by specialists in internal medicine. Collectively, irritable bowel syndrome (IBS) and functional dyspepsia are estimated to affect up to 22% of the population, and are often associated with additional somatic and pain complaints, all without an obvious structural source [1,2]. An appreciation of the current understanding of the mechanistic basis for these disorders is key to developing treatment goals and optimization of patient management strategies. In recent years, the brain-gut axis increasingly has been recognized as a central factor in the experience of functional abdominal pain disorders, including the most recent Rome IV guidelines which identify FGIDs as disorders of gut-brain interaction [3]. The brain-gut axis (BGA), simply defined, is a complex network of bidirectional communication between the central and enteric nervous systems. This axis broadly includes all the systems involved with communication between the GI tract and central nervous system (CNS), with principle inputs into this network occurring between the CNS, enteric nervous system (ENS), and autonomic nervous systems (ANS), but also includes interfaces with numerous other factors, including endocrine hormones and immune effector cells as well as interactions with the gut microbiota. Perturbances to this system have been found to play a critical role in the development of visceral hypersensitivity, bowel dysregulation, and mood. This review will summarize the principle processes involved in the neurologic and biologic function of the brain-gut axis, our current understanding of its role in functional GI disorders, and potential targets for therapeutic intervention.

Adverse Childhood Experiences in Women With Overactive Bladder or Interstitial Cystitis/Bladder Pain Syndrome

OBJECTIVE

The aim of the study was to compare the prevalence of adverse childhood experiences (ACEs) in women with overactive bladder (OAB) or interstitial cystitis/bladder pain syndrome (IC/BPS) to age-matched controls.

METHODS

This case-control study compared numbers and types of ACEs in women with OAB or IC/BPS compared with controls based on the Center for Disease Control's Behavioral Risk Factor Surveillance System ACE Module. Participants completed demographic forms, condition-specific symptom questionnaires, and the ACE Module (11 questions summarizing traumatic exposures occurring before the age of 18 years). Cases and controls were compared using χ2 and t tests, significance level P < 0.05.

RESULTS

Three hundred twenty-two women were enrolled from April 2018 to March 2019; OAB = 91 cases and 91 controls, IC/BPS = 70 cases and 70 controls. Overactive bladder group's mean age was 56 ± 13 years, and IC/BPS was 46 ± 13 years. Compared with controls, OAB and IC/BPS cases differed in race/ethnicity and education (P < 0.02), history of substance abuse (P ≤ 0.03), and median numbers of ACEs (OAB 3, controls 1; IC/BPS 4, controls 2, P < 0.01). Cases had increased odds of having 4 or more ACEs, a parameter known to be associated with poor health and longevity, and increased greater than 2-fold in OAB and greater than 7-fold in IC/BPS. Interstitial cystitis/bladder pain syndrome cases had notably increased odds of exposure to abuse (physical/emotional/sexual) and witnessed domestic violence (all P < 0.01).

CONCLUSIONS

Overactive bladder and IC/BPS cases reported increased ACE exposures; more than one-third of OAB and more than IC/BPS cases reported 4 or more ACES, a threshold associated with poor health outcomes. Recognition of increased childhood adversity in OAB and IC/BPS has important treatment and health implications.

Functional anatomy of the bed nucleus of the stria terminalis-hypothalamus neural circuitry: Implications for valence surveillance, addiction, feeding, and social behaviors

The bed nucleus of the stria terminalis (BNST) is a medial basal forebrain structure that modulates the hypothalamo-pituitary-adrenal (HPA) axis. The heterogeneous subnuclei of the BNST integrate inputs from mood and reward-related areas and send direct inhibitory projections to the hypothalamus. The connections between the BNST and hypothalamus are conserved across species, promote activation of the HPA axis, and can increase avoidance of aversive environments, which is historically associated with anxiety behaviors. However, BNST-hypothalamus circuitry is also implicated in motivated behaviors, drug seeking, feeding, and sexual behavior. These complex and diverse roles, as well its sexual dimorphism, indicate that the BNST-hypothalamus circuitry is an essential component of the neural circuitry that may underlie various psychiatric diseases, ranging from anorexia to anxiety to addiction. The following review is a cross-species exploration of BNST-hypothalamus circuitry. First, we describe the BNST subnuclei, microcircuitry and complex reciprocal connections with the hypothalamus. We will then discuss the behavioral functions of BNST-hypothalamus circuitry, including valence surveillance, addiction, feeding, and social behavior. Finally, we will address sex differences in morphology and function of the BNST and hypothalamus.

Animal models of pain: Diversity and benefits

Chronic pain is a maladaptive neurological disease that remains a major health problem. A deepening of our knowledge on mechanisms that cause pain is a prerequisite to developing novel treatments. A large variety of animal models of pain has been developed that recapitulate the diverse symptoms of different pain pathologies. These models reproduce different pain phenotypes and remain necessary to examine the multidimensional aspects of pain and understand the cellular and molecular basis underlying pain conditions. In this review, we propose an overview of animal models, from simple organisms to rodents and non-human primates and the specific traits of pain pathologies they model. We present the main behavioral tests for assessing pain and investing the underpinning mechanisms of chronic pathological pain. The validity of animal models is analysed based on their ability to mimic human clinical diseases and to predict treatment outcomes. Refine characterization of pathological phenotypes also requires to consider pain globally using specific procedures dedicated to study emotional comorbidities of pain. We discuss the limitations of pain models when research findings fail to be translated from animal models to human clinics. But we also point to some recent successes in analgesic drug development that highlight strategies for improving the predictive validity of animal models of pain. Finally, we emphasize the importance of using assortments of preclinical pain models to identify pain subtype mechanisms, and to foster the development of better analgesics.

Pain in Endometriosis

Endometriosis is a chronic and debilitating condition affecting ∼10% of women. Endometriosis is characterized by infertility and chronic pelvic pain, yet treatment options remain limited. In many respects this is related to an underlying lack of knowledge of the etiology and mechanisms contributing to endometriosis-induced pain. Whilst many studies focus on retrograde menstruation, and the formation and development of lesions in the pathogenesis of endometriosis, the mechanisms underlying the associated pain remain poorly described. Here we review the recent clinical and experimental evidence of the mechanisms contributing to chronic pain in endometriosis. This includes the roles of inflammation, neurogenic inflammation, neuroangiogenesis, peripheral sensitization and central sensitization. As endometriosis patients are also known to have co-morbidities such as irritable bowel syndrome and overactive bladder syndrome, we highlight how common nerve pathways innervating the colon, bladder and female reproductive tract can contribute to co-morbidity via cross-organ sensitization.

Disinhibition of PVN-projecting GABAergic neurons in AV region in BNST participates in visceral hypersensitivity in rats

Ample evidence suggests that early life stress (ELS) is a high-risk factor for the development of visceral pain disorders, whereas the mechanism underlying neuronal circuit remains elusive. Herein, we employed neonatal colorectal distension (CRD) to induce visceral hypersensitivity in rats. A combination of electrophysiology, pharmacology, behavioral test, molecular biology, chemogenetics and optogenetics confirmed that CRD in neonatal rats could predispose the elevated firing frequency of the parvocellular corticotropin-releasing hormone (CRH) neurons in the paraventricular nucleus of hypothalamus (PVN) in adulthood, with the CRH neurons activated and the frequency of spontaneous inhibitory postsynaptic currents (sIPSC) diminished, both contributing to chronic visceral hypersensitivity. Moreover, following administration of exogenous GABA (300 mM/0.5 μL) and GABA_A receptor agonist muscimol (3 mM/0.5 μL) in PVN, visceral hyperalgesia was abrogated. In addition, the PVN-projecting GABAergic neurons were mainly distributed in the anterior ventral (AV) region in the bed nucleus of stria terminalis (BNST), and the excitability of these GABAergic neurons was weakened in visceral hypersensitivity. Specific depletion of the GABAergic neurons in AV region precipitated visceral hyperalgesia. Moreover, chemogenetic activation of the PVN-projecting neurons alleviated the visceral hypersensitivity. Photoactivation of PVN-projecting GABAergic neurons abated the visceral hypersensitivity in neonatal-CRD rats, whereas photoinhibition evoked visceral hyperalgesia in naïve rats. Our findings demonstrated that disinhibition of the PVN-projecting GABAergic neurons in AV region contributed to the excitation of CRH neurons, thereby mediating visceral hypersensitivity. Our study might provide a novel insight into the neuronal circuits involved in the ELS-induced visceral hypersensitivity.

Intrabladder PAC1 Receptor Antagonist, PACAP(6-38), Reduces Urinary Bladder Frequency and Pelvic Sensitivity in Mice Exposed to Repeated Variate Stress (RVS)

Stress causes symptom exacerbation in functional disorders of the urinary bladder. However, the potential mediators and underlying mechanisms of stress effects on micturition reflex function are unknown. We have characterized PACAP (Adcyap1) and PAC1 receptor (Adcyap1r1) signaling in stress-induced urinary bladder dysfunction in mice. We determined PACAP and PAC1 transcripts and protein expressions in the urinary bladder and lumbosacral dorsal root ganglia (DRG) and spinal cord in repeated variate stress (RVS) or control mouse (handling only) groups. RVS in mice significantly (p ≤ 0.01) increased serum corticosterone and urinary bladder NGF content and decreased weight gain. PACAP and PAC1 mRNA and protein were differentially regulated in lower urinary tract tissues with changes observed in lumbosacral DRG and spinal cord but not in urinary bladder. RVS exposure in mice significantly (p ≤ 0.01) increased (2.5-fold) voiding frequency as determined using conscious cystometry. Intrabladder administration of the PAC1 receptor antagonist, PACAP(6-38) (300 nM), significantly (p ≤ 0.01) increased infused volume (1.5-2.7-fold) to elicit a micturition event and increased the intercontraction interval (i.e., decreased voiding frequency) in mice exposed to RVS and in control mice, but changes were smaller in magnitude in control mice. We also evaluated the effect of PAC1 blockade at the level of the urinary bladder on pelvic sensitivity in RVS or control mouse groups using von Frey filament testing. Intrabladder administration of PACAP(6-38) (300 nM) significantly (p ≤ 0.01) reduced pelvic sensitivity following RVS. PACAP/receptor signaling in the CNS and PNS contributes to increased voiding frequency and pelvic sensitivity following RVS and may represent a potential target for therapeutic intervention.

Pharmacological evaluation of a novel corticotropin-releasing factor 1 receptor antagonist T-3047928 in stress-induced animal models in a comparison with alosetron

BACKGROUND

The major symptoms of irritable bowel syndrome (IBS) are changes in bowel habits and abdominal pain. Psychological stress is the major pathophysiological components of IBS. Corticotropin-releasing factor (CRF) is a well-known integrator in response to psychological stress. In this study, a novel CRF1 receptor antagonist T-3047928 was evaluated in stress-induced IBS models of rats to explore its potency for IBS.

METHODS

Plasma adrenocorticotropic hormone (ACTH) levels after intravenous oCRH challenge were measured as a pharmacodynamic marker. Efficacies of oral T-3047928 were compared with oral alosetron, a 5-HT3 antagonist, on conditioning fear stress (CFS)-induced defecation, restraint stress (RS)-induced acute visceral pain, specific alteration of rhythm in temperature (SART) stress-induced chronic visceral pain, and normal defecation.

RESULTS

T-3047928 (1-10 mg/kg, p.o.) demonstrated a dose-dependent inhibition on oCRH-induced ACTH secretion. In disease models, T-3047928 suppressed fecal pellet output induced by CFS and improved both acute and chronic visceral hypersensitivity induced by RS and SART stress, respectively. Alosetron was also efficacious in stress-induced defecation and visceral pain models at 1 and 10 mg/kg, respectively. Alosetron, however, also suppressed normal defecation at lower those. On the other hand, T-3047928 did not change normal defecation even at higher dose than those in disease models.

CONCLUSION

T-3047928 is an orally active CRF1 antagonist that demonstrated potent inhibitory effects in stress-associated IBS models with no effect on normal defecation. Therefore, it is suggested that T-3047928 may have a potency as a novel option for IBS-D therapy with minimal constipation risk.

Reprogramming of the Immune System by Stress and Faulty Hormonal Imprinting

PURPOSE

Hormonal imprinting is taking place perinatally at the first encounter between the developing hormone receptors and their target hormones. However, in this crucial period when the developmental window for physiological imprinting is open, other molecules, such as synthetic hormones and endocrine disruptors can bind to the receptors, leading to faulty imprinting with life-long consequences, especially to the immune system. This review presents the factors of stress and faulty hormonal imprinting that lead to reprogramming of the immune system.

METHODS

Relevant publications from Pubmed since 1990 were reviewed and synthesized.

FINDINGS

The developing immune system is rather sensitive to hormonal effects. Faulty hormonal imprinting is able to reprogram the original developmental program present in a given cell, with lifelong consequences, manifested in alteration of hormone binding by receptors, susceptibility to certain (non-infectious) diseases, and triggering of other diseases. As stress mobilizes the hypothalamic-pituitary-adrenal axis if it occurred during gestation or perinatally, it could lead to faulty hormonal imprinting in the immune system, manifested later as allergic and autoimmune diseases or weakness of normal immune defenses. Hormonal imprinting is an epigenetic process and is carried to the offspring without alteration of DNA base sequences. This means that any form of early-life stress alone or in association with hormonal imprinting could be associated with the developmental origin of health and disease (DOHaD). As puberty is also a period of reprogramming, stress or faulty imprinting can change the original (developmental) program, also with life-long consequences.

IMPLICATIONS

Considering the continuous differentiation of immune cells (from blast-cells) during the whole life, there is a possibility of late-imprinting or stress-activated reprogramming in the immune system at any periods of life, with later pathogenetic consequences.

Walking the Tightrope: A Proposed Model of Chronic Pain and Stress

Pain and stress are both phenomena that challenge an individual’s homeostasis and have significant overlap in conceptual and physiological processes. Allostasis is the ability to adapt to pain and stress and maintain homeostasis; however, if either process becomes chronic, it may result in negative long-term outcomes. The negative effects of stress on health outcomes on physiology and behavior, including pain, have been well documented; however, the specific mechanisms of how stress and what quantity of stress contributes to the maintenance and exacerbation of pain have not been identified, and thus pharmacological interventions are lacking. The objective of this brief review is to: 1. identify the gaps in the literature on the impact of acute and chronic stress on chronic pain, 2. highlight future directions for stress and chronic pain research; and 3. introduce the Pain-Stress Model in the context of the current literature on stress and chronic pain. A better understanding of the connection between stress and chronic pain could provide greater insight into the neurobiology of these processes and contribute to individualized treatment for pain rehabilitation and drug development for these often comorbid conditions.

Is Stress a Cause or a Consequence of Endometriosis?

Clinical studies clearly indicate that endometriosis is a condition associated with high levels of chronic stress. The stress intensity correlates with pain severity and disease extension. However, it is unknown whether chronic stress represents a primary cause of endometriosis and, therefore, if avoiding or treating chronic stress may reduce the risk of developing endometriosis. Repeated, uncontrolled stress either before or after experimental endometriosis induction promotes disease mechanisms and accelerates lesion growth in rodents. Furthermore, patients with endometriosis have a heightened risk of other inflammatory and immune-related diseases, many of which have also been associated with stress. Here, we review the latest evidences regarding the relationship between chronic stress and endometriosis and discuss the potential bidirectional aspect of such association. Further research may clarify if endometriosis is a cause and/or a consequence of stress and whether stress-reducing therapies are effective to mitigate symptoms and slow down the development of endometriotic lesions.

Visceral Pain

Most of us live blissfully unaware of the orchestrated function that our internal organs conduct. When this peace is interrupted, it is often by routine sensations of hunger and urge. However, for >20% of the global population, chronic visceral pain is an unpleasant and often excruciating reminder of the existence of our internal organs. In many cases, there is no obvious underlying pathological cause of the pain. Accordingly, chronic visceral pain is debilitating, reduces the quality of life of sufferers, and has large concomitant socioeconomic costs. In this review, we highlight key mechanisms underlying chronic abdominal and pelvic pain associated with functional and inflammatory disorders of the gastrointestinal and urinary tracts. This includes how the colon and bladder are innervated by specialized subclasses of spinal afferents, how these afferents become sensitized in highly dynamic signaling environments, and the subsequent development of neuroplasticity within visceral pain pathways. We also highlight key contributing factors, including alterations in commensal bacteria, altered mucosal permeability, epithelial interactions with afferent nerves, alterations in immune or stress responses, and cross talk between these two adjacent organs.

Mechanisms Underlying Overactive Bladder and Interstitial Cystitis/Painful Bladder Syndrome

The bladder is innervated by extrinsic afferents that project into the dorsal horn of the spinal cord, providing sensory input to the micturition centers within the central nervous system. Under normal conditions, the continuous activation of these neurons during bladder distension goes mostly unnoticed. However, for patients with chronic urological disorders such as overactive bladder syndrome (OAB) and interstitial cystitis/painful bladder syndrome (IC/PBS), exaggerated bladder sensation and altered bladder function are common debilitating symptoms. Whilst considered to be separate pathological entities, there is now significant clinical and pre-clinical evidence that both OAB and IC/PBS are related to structural, synaptic, or intrinsic changes in the complex signaling pathways that mediate bladder sensation. This review discusses how urothelial dysfunction, bladder permeability, inflammation, and cross-organ sensitisation between visceral organs can regulate this neuroplasticity. Furthermore, we discuss how the emotional affective component of pain processing, involving dysregulation of the HPA axis and maladaptation to stress, anxiety and depression, can exacerbate aberrant bladder sensation and urological dysfunction. This review reveals the complex nature of urological disorders, highlighting numerous interconnected mechanisms in their pathogenesis. To find appropriate therapeutic treatments for these disorders, it is first essential to understand the mechanisms responsible, incorporating research from every level of the sensory pathway, from bladder to brain.