Longitudinal change in perceptual and brain activation response to visceral stimuli in irritable bowel syndrome patients

Exploring the potential targets of Biling Weitong Granules on visceral hypersensitivity through integration of network pharmacology and in vivo analysis

ETHNOPHARMACOLOGICAL RELEVANCE

Biling Weitong Granules(BLWTG) are a newly developed traditional Chinese medicine prescription based on the ancient prescription Jinlingzi San and Zuojin Wan. It is used for the treatment of functional gastrointestinal disorders (FGIDs) featured as visceral hypersensitivity(VH). However, its active ingredients and protein targets involved still remain unknown.

AIM OF THE STUDY

To explore the potential targets of BLWTG for the treatment of visceral hypersensitivity.

MATERIALS AND METHODS

Active components and their protein targets of BLWTG were screened from TCMSP database and the component-target network were constructed with Cytoscape software. Irritable bowel syndrome (IBS) was the representative disease in this study and information on its linked pathways was obtained from NCBI, Drugbank and Genecard. Target pathways of BLWTG were analyzed through KEGG to verify the correlation with IBS related pathways.Then, the VH mouse models was induced by maternal separation(MS), randomly divided into normal saline(NS),BLWTG1(low-dosage) and BLWTG2(high-dosage) group. After intervention, threshold intensity of colorectal distension (CRD) and body weight were measured to evaluate relief of IBS symptoms. Elisa was performed to evaluate 5-HT concentration changes of colon tissues. Flow cytometry was performed to assess changes of colon eosinophils and mast cells proportion. Transcriptome sequencing was employed to analyze changes of pathways and differential genes.

RESULTS

199 protein targets and 132 active components of BLWTG were identified. KEGG analysis revealed the overlap between BLWTG target pathways and IBS related pathways such as neuroactive ligand-receptor interaction, tryptophan metabolism and inflammatory reaction. 34 genes were not only BLWTG target proteins but also recognized targets for treating IBS. After maternal separation(MS), the mice showed a significant decrease in threshold intensity of CRD, a progressive decrease in body weight and an increase of 5-HT concentration of colon tissue. The proportion of mast cells and eosinophils in the colon increased. Differential genes including Hp,Ido1 and Aqp7 were significantly increased in MS mice group and IBS-related pathways were upregulated. After treatment of BLWTG, threshold intensity of CRD and body weight were significantly improved and IBS related pathways were downregulated. In addition, among BLWTG protein targets, Il1b,Tnf,Adrb1 and Nos2 were found upregulated in MS + NS mice and downregulated after BLWTG intervention through combination of transcriptome sequencing.

CONCLUSIONS

In maternal separation-induced mouse models, BLWTG could alleviate visceral hypersensitivity, possibly through downregulation of 5-HT concentration and eosinophils and mast cells proportion in colon and critical pathways such as neuroactive ligand-receptor pathway. Potential targets of BLWTG including Il1b,Tnf,Adrb1 and Nos2 were found through integration of network pharmacology database and transcriptome sequencing, providing evidence for further study on mechanisms underlying visceral hypersensitivity.

Altered resting-state brain activity in functional dyspepsia patients: a coordinate-based meta-analysis

Background

Neuroimaging studies have identified aberrant activity patterns in multiple brain regions in functional dyspepsia (FD) patients. However, due to the differences in study design, these previous findings are inconsistent, and the underlying neuropathological characteristics of FD remain unclear.

Methods

Eight databases were systematically searched for literature from inception to October 2022 with the keywords "Functional dyspepsia" and "Neuroimaging." Thereafter, the anisotropic effect size signed the differential mapping (AES-SDM) approach that was applied to meta-analyze the aberrant brain activity pattern of FD patients.

Results

A total of 11 articles with 260 FD patients and 202 healthy controls (HCs) were included. The AES-SDM meta-analysis demonstrated that FD patients manifested increased activity in the bilateral insula, left anterior cingulate gyrus, bilateral thalamus, right precentral gyrus, left supplementary motor area, right putamen, and left rectus gyrus and decreased functional activity in the right cerebellum compared to the HCs. Sensitivity analysis showed that all these above regions were highly reproducible, and no significant publication bias was detected.

Conclusion

The current study demonstrated that FD patients had significantly abnormal activity patterns in several brain regions involved in visceral sensation perception, pain modulation, and emotion regulation, which provided an integrated insight into the neuropathological characteristics of FD.

Factors influencing rectal hypersensitivity in irritable bowel syndrome: A systematic review and meta-analysis

BACKGROUND

A frequent, although not universal, feature of irritable bowel syndrome (IBS) is heightened sensitivity to mechanical stimulation of the rectum, termed rectal hypersensitivity (RH). Differences in RH-based on sex, IBS subtype, IBS diagnostic criteria and age of population studied are incompletely understood. We aimed to determine whether IBS population had lower pain thresholds than healthy controls.

METHODS

We searched MEDLINE and EMBASE databases (1970-2021). Prospective studies that compared pain/discomfort thresholds to mechanical rectal stimuli in IBS and healthy controls were included. Data were pooled for meta-analyses and effect sizes were calculated with 95% confidence interval (CIs).

RESULTS

Our search strategy identified 809 studies of which 32 studies met the inclusion criteria. Reduced rectal pain thresholds was more common in IBS patients compared to healthy controls with an effect size of 1.00 95% CIs (0.77-1.24) (p < 0.0001) (I²  = 78.6%). The pediatric IBS population had lower pain thresholds than adult IBS populations (p = 0.05) but no difference based on IBS diagnostic criteria, subtype or sex.

CONCLUSION & INFERENCES

The results suggest that reduced rectal pain threshold to experimental stimulation is far more common in IBS patients than healthy controls. Further research is required to understand the pathophysiological and therapeutic implications of rectal sensitivity such as its role in measuring response to treatment and prognosis in IBS.

The interaction between obesity and visceral hypersensitivity

Obesity has been a worldwide problem associated with numerous chronic diseases such as cardiovascular disease, type 2 diabetes, and metabolic disorders. It may also play a role in visceral hypersensitivity, contributing to irritable bowel syndrome. (i) Adipose tissue secretes various inflammatory mediators, causing intestinal hyperpermeability and nerve endings activation. (ii) Obesity and gastrointestinal microbiota could affect each other, and microbial metabolites can increase sensitivity of the colon. (iii) Vitamin D deficiency contributes to both fat accumulation and disruption of the intestinal mucosal barrier. (iv) Brain-gut axis may be another bridge from obesity to visceral hypersensitivity.

Electrophysiology as a Tool to Decipher the Network Mechanism of Visceral Pain in Functional Gastrointestinal Disorders

Abdominal pain, including visceral pain, is prevalent in functional gastrointestinal (GI) disorders (FGIDs), affecting the overall quality of a patient's life. Neural circuits in the brain encode, store, and transfer pain information across brain regions. Ascending pain signals actively shape brain dynamics; in turn, the descending system responds to the pain through neuronal inhibition. Pain processing mechanisms in patients are currently mainly studied with neuroimaging techniques; however, these techniques have a relatively poor temporal resolution. A high temporal resolution method is warranted to decode the dynamics of the pain processing mechanisms. Here, we reviewed crucial brain regions that exhibited pain-modulatory effects in an ascending and descending manner. Moreover, we discussed a uniquely well-suited method, namely extracellular electrophysiology, that captures natural language from the brain with high spatiotemporal resolution. This approach allows parallel recording of large populations of neurons in interconnected brain areas and permits the monitoring of neuronal firing patterns and comparative characterization of the brain oscillations. In addition, we discussed the contribution of these oscillations to pain states. In summary, using innovative, state-of-the-art methods, the large-scale recordings of multiple neurons will guide us to better understanding of pain mechanisms in FGIDs.

The neurobiology of irritable bowel syndrome

Irritable bowel syndrome (IBS) is the most prevalent disorder of brain-gut interactions that affects between 5 and 10% of the general population worldwide. The current symptom criteria restrict the diagnosis to recurrent abdominal pain associated with altered bowel habits, but the majority of patients also report non-painful abdominal discomfort, associated psychiatric conditions (anxiety and depression), as well as other visceral and somatic pain-related symptoms. For decades, IBS was considered an intestinal motility disorder, and more recently a gut disorder. However, based on an extensive body of reported information about central, peripheral mechanisms and genetic factors involved in the pathophysiology of IBS symptoms, a comprehensive disease model of brain-gut-microbiome interactions has emerged, which can explain altered bowel habits, chronic abdominal pain, and psychiatric comorbidities. In this review, we will first describe novel insights into several key components of brain-gut microbiome interactions, starting with reported alterations in the gut connectome and enteric nervous system, and a list of distinct functional and structural brain signatures, and comparing them to the proposed brain alterations in anxiety disorders. We will then point out the emerging correlations between the brain networks with the genomic, gastrointestinal, immune, and gut microbiome-related parameters. We will incorporate this new information into a systems-based disease model of IBS. Finally, we will discuss the implications of such a model for the improved understanding of the disorder and the development of more effective treatment approaches in the future.

Associations between postprandial symptoms, hydrogen and methane production, and transit time in irritable bowel syndrome

BACKGROUND

Abnormal oroanal transit time (OATT) and visceral hypersensitivity are key pathophysiological factors in irritable bowel syndrome (IBS). The lactulose nutrient challenge test (LNCT) has been developed to assess the postprandial symptoms and gut microbial fermentation. We aimed to investigate associations between OATT, rectal sensitivity, and LNCT in IBS patients.

METHODS

We included 263 IBS patients from two study cohorts, where the link between pathophysiology and symptoms was investigated. During the LNCT, severity of postprandial symptoms was graded, and breath hydrogen/methane concentrations were measured after ingestion of a combined lactulose nutrient drink every 15 min for 4 h. The patients underwent rectal sensitivity (rectal barostat) and OATT (radiopaque markers) investigations. Comorbid conditions (functional dyspepsia, anxiety, depression, and somatization) were assessed with questionnaires.

KEY RESULTS

After controlling for comorbid conditions, rectal sensitivity was associated with abdominal pain (p < 0.05), and more rapid OATT was associated with higher severity of abdominal discomfort, rumbling, nausea, and urgency (p < 0.05 for all) both pre- and post-prandially. Postprandial nausea, urgency, and abdominal pain changed differently over time depending on OATT (p < 0.05 for all). OATT, but not rectal sensitivity, was associated with hydrogen and methane concentrations (p = 0.002 for both). Trajectories over time of postprandial symptoms and exhaled hydrogen/methane concentrations were correlated with different correlations depending on OATT.

CONCLUSION AND INFERENCES

This study highlights the importance of oroanal transit and hydrogen and methane production in the pathophysiology of IBS and increases our understanding of pathophysiological factors involved in postprandial symptom generation. Treatments targeting oroanal transit and hydrogen and methane production may improve specific postprandial symptoms.

Effect of intracolonic volume on gastric sensory-motor responses in constipation-predominant irritable bowel syndrome

BACKGROUND

Interaction between gut stimuli may induce symptom overlap in patients with functional gastrointestinal disorders. The aim is to determine the effect of increased volumes of colonic contents on gastric sensory/motor responses and satiety in patients with constipation-predominant irritable bowel syndrome (IBS-C) and overlapping dyspeptic symptoms, and a cohort of healthy subjects.

METHODS

In 15 patients with IBS-C and 10 healthy subjects, the effect of real versus sham colonic filling with gas (1080 ml) on gastric sensitivity (measured by stepwise distensions of the stomach), gastric compliance, abdominal perception, and nutrient drink tolerance was studied on separate days.

RESULTS

In healthy subjects, colonic gas filling induced an increment in gastric sensitivity to distension (mean score 2.0 ± 0.2 before, and 3.0 ± 0.4 after; p = 0.038). In IBS, basal sensitivity was greater and remained unchanged after colonic gas filling (score 4.0 ± 0.1 and 3.8 ± 0.3, respectively; p < 0.001 vs. basal in health). Colonic gas infusion induced abdominal symptoms that were significantly greater in IBS-C (score 2.6 ± 0.1) than in health (score 1.7 ± 0.4; p = 0.027), with minor changes in gastric tone, and no changes in gastric compliance in both groups. Colonic filling produced a profound reduction in nutrient drink tolerance in IBS (791 ± 87 ml sham filling, 491 ± 58 ml gas filling; p < 0.001) but only a minor reduction in health (940 ± 70 ml sham filling, 860 ± 94 ml gas filling; p = 0.223).

CONCLUSIONS & INFERENCES

The volume of the colonic contents modulates satiety in patients with IBS-C, due to a general visceral pan-hypersensitivity. These effects should be considered in the choice of treatment for constipation in these patients.

Type of Rectal Barostat Protocol Affects Classification of Hypersensitivity and Prediction of Symptom Severity in Irritable Bowel Syndrome

Background/Aims

Visceral hypersensitivity is an important pathophysiologic mechanism in irritable bowel syndrome (IBS). We compared 2 barostat distension protocols and their ability to distinguish between IBS patients and healthy controls, identify subjects with rectal hypersensitivity, and their associations with gastrointestinal symptom severity.

Methods

We retrospectively reviewed all patients at our unit that had undergone barostat investigations 2002-2014. Protocol 1 (n = 369) used phasic isobaric distensions with stepwise increments in pressure and protocol 2 (n = 153) used pressure controlled ramp inflations. Both protocols terminated when subjects reported pain or maximum pressure was reached. Thresholds for first sensation, urgency, discomfort and pain were established. Age- and gender-matched controls were used for comparison. The gastrointestinal symptom rating scale-IBS, and the hospital anxiety and depression scale were used for symptom reports.

Results

A significantly higher proportion of patients was classified as having hypersensitivity in protocol 1 vs protocol 2 for all thresholds (P < 0.001). Patients with visceral hypersensitivity, defined based on rectal pain thresholds in protocol 1 had more severe gastrointestinal symptoms overall as well as anxiety, whereas these associations were weaker or in most cases absent when visceral hypersensitivity was defined based on rectal pain thresholds in protocol 2.

Conclusion

Our study indicates that a rectal barostat protocol using phasic isobaric distensions with stepwise pressure increments is more sensitive in IBS patients with respect to identifying subjects with rectal hypersensitivity and a link with IBS symptoms.

Altered Resting Brain Functions in Patients With Irritable Bowel Syndrome: A Systematic Review

Background

The neural activity of irritable bowel syndrome (IBS) patients in the resting state without any intervention has not been systematically studied. The purpose of this study was to compare the resting-state brain functions of IBS patients with healthy controls (HCs).

Methods

The published neuroimage studies were obtained from electronic databases including PubMed, EMBASE, PsycINFO, Web of Science Core, CNKI Database, Wanfang Database, VIP Database, and CBMdisc. Search dates were from inception to March 14th, 2022. The studies were identified by the preidentified inclusion and exclusion criteria. Two independent reviewers compiled the studies and evaluated them for quality and bias.

Results

Altogether 22 fMRI studies were included in this review. The risk of bias of the included studies was generally low. The findings indicated that in IBS patients, increased or decreased brain areas were mostly associated with visceral sensations, emotional processing, and pain processing. According to brain network research, IBS may exhibit anomalies in the DMN, CEN, and emotional arousal networks. The fluctuations in emotion (anxiety, sadness) and symptoms in IBS patients were associated with alterations in the relevant brain regions.

Conclusion

This study draws a preliminary conclusion that there are insufficient data to accurately distinguish the different neurological features of IBS in the resting state. Additional high-quality research undertaken by diverse geographic regions and teams is required to reach reliable results regarding resting-state changed brain regions in IBS.

Abnormal resting-state local spontaneous functional activity in irritable bowel syndrome patients: A meta-analysis

BACKGROUND

Irritable bowel syndrome (IBS) is a common functional gastrointestinal disorder. The current understanding of the pathogenesis underlying IBS is still unclear. Numerous studies have reported local abnormal resting state spontaneous functional activity in IBS patients in widespread brain regions. However, the results have not yet yielded consistent conclusions. Thus, we investigated common spontaneous functional activity abnormalities in patients with IBS by conducting a voxel-based meta-analysis.

METHODS

Up to December 2021, we performed a systematic search of IBS studies in five databases. These studies investigated the differences of resting state spontaneous brain activity between patients with IBS and healthy controls (HCs). The reference lists of included studies, relevant reviews and meta-analyses were investigated manually. Anisotropic effect-size signed differential mapping (AES-SDM) was applied in this meta-analysis.

RESULTS

Twelve studies encompassing 335 patients with IBS and 327 HCs were included in this meta-analysis. The local brain activities of the left calcarine fissure and surrounding cortex, right postcentral gyrus, left postcentral gyrus, left cerebellum, left inferior temporal gyrus, and left inferior frontal gyrus of triangular part in IBS patients were significantly increased compared with HCs, while the brain activities of the left anterior cingulate and paracingulate gyrus, right middle frontal gyrus, right supramarginal gyrus, left middle frontal gyrus, left precuneus, right putamen and right insula were significantly decreased compared with HCs.

CONCLUSION

The current study expands on a growing literature exploring resting state activity in IBS, which provides useful insights for understanding the underlying pathophysiology of nonorganic functional bowel disease and developing more targeted treatment and intervention strategies.

Regional Gray Matter Volume Changes in Brains of Patients With Ulcerative Colitis

BACKGROUND

Ulcerative colitis (UC) and Crohn's disease (CD) are 2 subtypes of inflammatory bowel disease (IBD). Several studies have reported brain abnormalities in IBD patients. This study aims to identify differences of gray matter volume (GMV) between patients with UC and healthy controls (HCs).

METHODS

Fifty-seven patients with UC and 40 HCs underwent structural magnetic resonance imaging. Voxel-based morphometry method was used to detect GMV differences. Receiver operating characteristic (ROC) curve was applied to investigate reliable biomarkers for identifying patients with UC from HCs. Regression analysis was used to examine relationships between the structure alternations and clinical symptoms.

RESULTS

Compared with HCs, patients with UC showed decreased GMV in the insula, thalamus, pregenual anterior cingulate cortex, hippocampus/parahippocampus, amygdala, and temporal pole; they showed increased GMV in the putamen, supplementary motor area, periaqueductal gray, hypothalamus, and precentral gyrus. Receiver operating characteristic analysis showed the highest classification power of thalamus. The inclusion of anxiety and depression as covariates eliminated the differences in the right insula, pregenual anterior cingulate cortex, supplementary motor area, and precentral gyrus. Most of the GMV changes were found in active patients with UC, with few changes in patients with UC in remission. We also found significantly negative correlation between UC duration and GMV in several regions.

CONCLUSION

The current neuroimaging findings were involved in visceral sensory pathways and were partially associated with the levels of anxiety and depression and clinical stage of patients with UC. This study might provide evidence for possible neuromechanisms of UC.

Temporal dynamics of fMRI signal changes during conditioned interoceptive pain-related fear and safety acquisition and extinction

Associative learning and memory mechanisms drive interoceptive signaling along the gut-brain axis, thus shaping affective-emotional reactions and behavior. Specifically, learning to predict potentially harmful, visceral pain is assumed to succeed within very few trials. However, the temporal dynamics of cerebellar and cerebral fMRI signal changes underlying early acquisition and extinction of learned fear signals and the concomitant evolvement of safety learning remain incompletely understood. 3T fMRI data of healthy individuals from three studies were uniformly processed across the whole brain and the cerebellum including an advanced normalizing method of the cerebellum. All studies employed differential delay conditioning (N=94) with one visual cue (CS⁺) being repeatedly paired with visceral pain as unconditioned stimulus (US) while a second cue remained unpaired (CS^-). During subsequent extinction (N=51), all CS were presented without US. Behavioral results revealed increased CS⁺-aversiveness and CS^--pleasantness after conditioning and diminished valence ratings for both CS following extinction. During early acquisition, the CS^- induced linearly increasing neural activation in the insula, midcingulate cortex, hippocampus, precuneus as well as cerebral and cerebellar somatomotor regions. The comparison between acquisition and extinction phases yielded a CS^--induced linear increase in the posterior cingulate cortex and precuneus during early acquisition, while there was no evidence for linear fMRI signal changes for the CS⁺ during acquisition and for both CS during extinction. Based on theoretical accounts of discrimination and temporal difference learning, these results suggest a gradual evolvement of learned safety cues that engage emotional arousal, memory, and cortical modulatory networks. As safety signals are presumably more difficult to learn and to discriminate from learned threat cues, the underlying temporal dynamics may reflect enhanced salience and prediction processing as well as increasing demands for attentional resources and the integration of multisensory information. Maladaptive responses to learned safety signals are a clinically relevant phenotype in multiple conditions, including chronic visceral pain, and can be exceptionally resistant to modification or extinction. Through sustained hypervigilance, safety seeking constitutes one key component in pain and stress-related avoidance behavior, calling for future studies targeting the mechanisms of safety learning and extinction to advance current cognitive-behavioral treatment approaches.

Functional neuroimaging in Irritable Bowel Syndrome: a systematic review highlights common brain alterations with Functional Movement Disorders

Irritable bowel syndrome (IBS) is a chronic functional gastrointestinal disorder characterized by recurring abdominal pain and altered bowel habits without detectable organic causes. This study aims to provide a comprehensive overview of the literature on functional neuroimaging in IBS and to highlight brain alterations similarities with other functional disorders - functional movement disorders in particular. We conducted the bibliographic search via PubMed in August 2020 and included 50 studies following Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) guidelines for systematic reviews. Overall, our findings showed an aberrant activation and functional connectivity of the insular, cingulate, sensorimotor and frontal cortices, the amygdala and the hippocampus, suggesting an altered activity of the homeostatic and salience network and of the autonomous nervous system. Moreover, glutamatergic dysfunction in the anterior insula and hypothalamic pituitary axis dysregulation were often reported. These alterations seem to be very similar to those observed in patients with functional movement disorders. Hence, we speculate that different functional disturbances might share a common pathophysiology and we discussed our findings in the light of a Bayesian model framework.

Gastrointestinal Interoception in Eating Disorders: Charting a New Path

PURPOSE OF REVIEW

Abnormal interoception has been consistently observed across eating disorders despite limited inclusion in diagnostic conceptualization. Using the alimentary tract as well as recent developments in interoceptive neuroscience and predictive processing as a guide, the current review summarizes evidence of gastrointestinal interoceptive dysfunction in eating disorders.

RECENT FINDINGS

Eating is a complex process that begins well before and ends well after food consumption. Abnormal prediction and prediction-error signals may occur at any stage, resulting in aberrant gastrointestinal interoception and dysregulated gut sensations in eating disorders. Several interoceptive technologies have recently become available that can be paired with computational modeling and clinical interventions to yield new insights into eating disorder pathophysiology. Illuminating the neurobiology of gastrointestinal interoception in eating disorders requires a new generation of studies combining experimental probes of gut physiology with computational modeling. The application of such techniques within clinical trials frameworks may yield new tools and treatments with transdiagnostic relevance.

Sensory Adaptation Training or Escitalopram for IBS With Constipation and Rectal Hypersensitivity: A Randomized Controlled Trial

INTRODUCTION

Rectal hypersensitivity is an important pathophysiological dysfunction in irritable bowel syndrome with predominant constipation (IBS-C), whose treatment remains challenging. In a randomized controlled trial, we compared the efficacy and safety of a novel sensori-behavioral treatment, sensory adaptation training (SAT) with escitalopram.

METHODS

Patients with IBS-C (Rome III) with rectal hypersensitivity received 6 biweekly sessions of SAT or escitalopram 10 mg daily for 3 months. SAT was performed by repetitive gradual distension of 10-cm long highly compliant rectal balloon above tolerability thresholds using barostat. Treatment effects on sensory thresholds and symptoms were compared. Coprimary outcome measures were those achieving improvements in rectal hypersensitivity (≥20% increase in ≥2/3 sensory thresholds) and pain (≥30% decrease).

RESULTS

We randomized 49 patients; 26 received SAT and 23 escitalopram. SAT significantly improved desire to defecate (Δ 13.5 ± 2.3 vs 2.2 ± 1.1 mm Hg, P = 0.0006) and maximum tolerability (Δ 14.8 ± 1.9 vs 1.6 ± 0.9 mm Hg, P < 0.0001) thresholds compared with escitalopram. There were significantly greater percentage of hypersensitivity responders with SAT than escitalopram (69% vs 17%, P < 0.001), but not pain responders (58% vs 44%, P = 0.4). Daily pain scores did not differ between groups (P = 0.8) or escitalopram (P = 0.06) but decreased with SAT (P = 0.0046) compared with baseline. SAT significantly increased rectal compliance (P < 0.019) and complete spontaneous bowel movements per week than escitalopram (P = 0.04). Five withdrew from adverse events with escitalopram and none with SAT.

DISCUSSION

SAT was significantly more efficacious in improving hypersensitivity and bowel symptoms in IBS-C than escitalopram. SAT is a promising novel treatment for IBS with rectal hypersensitivity.

Rectal Hypersensitivity in Inflammatory Bowel Disease: A Systematic Review and Meta-analysis

Abdominal pain is a key symptom of inflammatory bowel disease (IBD), particularly in active IBD, but also occurs in patients with quiescent disease suggesting that mechanisms other than active inflammation may be responsible. Putative hypothesis to explain chronic abdominal pain in patients with quiescent IBD includes crossover with irritable bowel syndrome where rectal hypersensitivity is common and has pathophysiological implications. In contrast, in IBD, the role of rectal hypersensitivity has not been established. We aimed to determine if rectal hypersensitivity was more common in IBD compared to a healthy control population. We searched MEDLINE and EMBASE databases (1970-2018). Prospective studies that measured pain/discomfort thresholds to mechanical rectal stimuli in IBD and healthy controls were included. Data were pooled for meta-analysis and effect sizes were calculated with 95% confidence intervals (CIs). Our search strategy identified 222 citations of which 8 met the inclusion criteria, covering 133 individuals with IBD (67 men), aged between 10 and 77 compared to 99 healthy controls (55 men), aged between 10 and 67. The prevalence of rectal hypersensitivity in IBD compared to healthy controls was similar with an effect size of 0.59 (95% CIs: -0.27 to 1.44, P = .16, I ² = 87.3%). Subgroup analysis did show a significant effect size for patients compared to healthy controls with active disease (1.32) but not for quiescent disease (-0.02). These results suggest that reduced rectal pain thresholds to experimental stimulation are not seen in IBD populations except during active flares of the disease. Further research is required to understand the pathophysiology of chronic abdominal pain in quiescent IBD populations with and without chronic abdominal pain to identify appropriate management strategies.

Left and right hemispheric lateralization of the amygdala in pain

Hemispheric asymmetries within the brain have been identified across taxa and have been extensively studied since the early 19th century. Here, we discuss lateralization of a brain structure, the amygdala, and how this lateralization is reshaping how we understand the role of the amygdala in pain processing. The amygdala is an almond-shaped, bilateral brain structure located within the limbic system. Historically, the amygdala was known to have a role in the processing of emotions and attaching emotional valence to memories and other experiences. The amygdala has been extensively studied in fear conditioning and affect but recently has been shown to have an important role in processing noxious information and impacting pain. The amygdala is composed of multiple nuclei; of special interest is the central nucleus of the amygdala (CeA). The CeA receives direct nociceptive inputs from the parabrachial nucleus (PBN) through the spino-parabrachio-amygdaloid pathway as well as more highly processed cortical and thalamic input via the lateral and basolateral amygdala. Although the amygdala is a bilateral brain region, most data investigating the amygdala's role in pain have been generated from the right CeA, which has an overwhelmingly pro-nociceptive function across pain models. The left CeA has often been characterized to have no effect on pain modulation, a dampened pro-nociceptive function, or most recently an anti-nociceptive function. This review explores the current literature on CeA lateralization and the hemispheres' respective roles in the processing and modulation of different forms of pain.

Sex as a biological variable in irritable bowel syndrome

BACKGROUND

The pathophysiology and mechanisms of irritable bowel syndrome (IBS) involve both central and peripheral mechanisms that result in altered perception, as well as changes in bowel functions. These dysfunctions are associated with motor, sensory, immune, barrier, and intraluminal perturbations, including the microbiota, and their products and endogenous molecules with bioactive properties. There is evidence that these mechanisms are altered in both females and males. However, there is also increasing evidence that sex is a biological variable that impacts a number of aspects of the mechanisms, epidemiology, and manifestations of IBS.

PURPOSE

The objective of this article is to review the evidence of the differences among genders of the following factors in IBS: the brain-gut axis and sex hormones, epidemiology, diagnostic criteria and prognosis, pain perception, colonic transit, abdominal distension, overlap with urogynecological conditions, psychologic issues, anorexia, fibromyalgia, serotonin, and responsiveness to treatment of IBS. It is important to consider the variations attributable to sex in order to enhance the management of patients with IBS and the research of mechanisms involved in IBS.

Role of brain imaging in disorders of brain-gut interaction: a Rome Working Team Report

Imaging of the living human brain is a powerful tool to probe the interactions between brain, gut and microbiome in health and in disorders of brain-gut interactions, in particular IBS. While altered signals from the viscera contribute to clinical symptoms, the brain integrates these interoceptive signals with emotional, cognitive and memory related inputs in a non-linear fashion to produce symptoms. Tremendous progress has occurred in the development of new imaging techniques that look at structural, functional and metabolic properties of brain regions and networks. Standardisation in image acquisition and advances in computational approaches has made it possible to study large data sets of imaging studies, identify network properties and integrate them with non-imaging data. These approaches are beginning to generate brain signatures in IBS that share some features with those obtained in other often overlapping chronic pain disorders such as urological pelvic pain syndromes and vulvodynia, suggesting shared mechanisms. Despite this progress, the identification of preclinical vulnerability factors and outcome predictors has been slow. To overcome current obstacles, the creation of consortia and the generation of standardised multisite repositories for brain imaging and metadata from multisite studies are required.

Visceral sensitivity remains stable over time in patients with irritable bowel syndrome, but with individual fluctuations

BACKGROUND

Visceral hypersensitivity in irritable bowel syndrome (IBS), measured with rectal balloon distensions, using a barostat, has been suggested to be a phenomenon that is reduced due to habituation at repeated investigations. We investigated the stability of rectal sensitivity in patients with IBS who had undergone a previous rectal barostat study and assessed variations in symptom pattern and severity in relation to rectal sensory function.

METHOD

Irritable bowel syndrome patients, who had previously been undergone a rectal barostat study, were included. All patients underwent a second study 8-12 years later. Symptoms were characterized by use of questionnaires.

KEY RESULTS

We included 26 subjects (17 females, median age at the index investigation 44.5 (21-61) years). Pressure and volume sensory thresholds were unchanged at the follow-up compared with the index investigation (P > 0.05 for all). At the index investigation, 8/26 patients had rectal hypersensitivity of which four were reclassified as normosensitive, and sixfrom normo- to hypersensitive, meaning that 10/26 patients were hypersensitive at the follow-up investigation. IBS-QOL had improved significantly in six of nine domains at follow-up (P < 0.05 for all). There were no differences in anxiety, depression, IBS symptom severity, or somatization (P > 0.05) at follow-up. None of these were associated with change in rectal sensitivity at follow-up.

CONCLUSIONS AND INFERENCES

Rectal hypersensitivity and IBS symptoms remained stable at the group level over 8-12 years in IBS patients, even though individual fluctuations were noted. Our findings contradict previous findings indicating that visceral hypersensitivity is an unstable trait.

Altered Functional Connectivity of the Amygdala and Sex Differences in Functional Dyspepsia

INTRODUCTION

The influence of sex on the prevalence and clinical manifestations of functional dyspepsia (FD) has recently been a topic of increasing interest. However, brain MRI pathology based on sexual dimorphism in FD has not yet been investigated. The amygdala, which plays a vital role in processing gastrointestinal signals, may be associated with the sex-related pathophysiology of FD.

METHODS

We investigated the resting-state functional connectivity (rsFC) of amygdala subregions in patients with FD and healthy subjects as well as the sex differences between male and female FD patients.

RESULTS

The results showed that FD patients manifested altered rsFC in the basolateral amygdala (BLA) and centromedial amygdala subregions compared with HS and that female FD patients showed increased BLA rsFC with the insula (INS) and decreased BLA rsFC with the medial prefrontal cortex and dorsal lateral prefrontal cortex compared with male FD patients and female HS.

DISCUSSION

Our findings suggest that FD females tend to have more severe dysfunction of cognitive-affective processing among the brain regions associated with the salience network, central executive network, and default mode network.

Gastric stimulation drives fast BOLD responses of neural origin

Functional magnetic resonance imaging (fMRI) is commonly thought to be too slow to capture any neural dynamics faster than 0.1 Hz. However, recent findings demonstrate the feasibility of detecting fMRI activity at higher frequencies beyond 0.2 Hz. The origin, reliability, and generalizability of fast fMRI responses are still under debate and await confirmation through animal experiments with fMRI and invasive electrophysiology. Here, we acquired single-echo and multi-echo fMRI, as well as local field potentials, from anesthetized rat brains given gastric electrical stimulation modulated at 0.2, 0.4 and 0.8 Hz. Such gastric stimuli could drive widespread fMRI responses at corresponding frequencies from the somatosensory and cingulate cortices. Such fast fMRI responses were linearly dependent on echo times and thus indicative of blood oxygenation level dependent nature (BOLD). Local field potentials recorded during the same gastric stimuli revealed transient and phase-locked broadband neural responses, preceding the fMRI responses by as short as 0.5 s. Taken together, these results suggest that gastric stimulation can drive widespread and rapid fMRI responses of BOLD and neural origin, lending support to the feasibility of using fMRI to detect rapid changes in neural activity up to 0.8 Hz under visceral stimulation.

Plausibility criteria for putative pathophysiological mechanisms in functional gastrointestinal disorders: a consensus of experts

BACKGROUND AND AIMS

The functional gastrointestinal disorders (FGIDs) are extremely common conditions associated with a considerable personal, social and health economic burden. Managing FGIDs in clinical practice is challenging because of the uncertainty of symptom-based diagnosis, the high frequency of overlap between these conditions and the limited efficacy of available therapies. It has often been argued that successful drug development and management of FGIDs requires knowledge of the underlying pathophysiology. Numerous and highly variable candidate pathophysiological mechanisms have been implicated in the generation of FGID symptoms, but there is no current consensus on how to best define the relevance of these disturbances.

METHODS

A group of international experts on FGIDs developed plausibility criteria that should be fulfilled by relevant pathophysiological mechanisms in FGIDs.

RESULTS

Five criteria are proposed: (1) the presence of the abnormality in a subset of patients, (2) temporal association between proposed mechanism and symptom(s), (3) correlation between the level of impairment of the mechanism and symptom(s), (4) induction of the symptom(s) by provoking the pathophysiological abnormality in healthy subjects and (5) treatment response by a therapy specifically correcting the underlying disorder or congruent natural history of symptoms and dysfunction in the absence of specific therapy. Based on strength of evidence for these five criteria according to the Grading of Recommendations Assessment, Development and Evaluation system, a plausibility score can be calculated for each mechanism.

CONCLUSION

Evaluation of the strength of evidence for candidate pathophysiological abnormalities fulfilling these five plausibility criteria will help to identify the most relevant mechanisms to target for novel diagnostic approaches and for the development of new therapies.

The Neural Bases of Interoceptive Encoding and Recall in Healthy Adults and Adults With Depression

BACKGROUND

Theoretical models assert that the brain's interoceptive network links external stimuli with their interoceptive consequences, thereby supporting later recall of these associations to guide the selection of healthy behaviors. If these accounts are correct, previously reported interoceptive abnormalities in major depressive disorder (MDD) should lead to altered recall of associations between external stimuli and their interoceptive (somatic) consequences. To date, the processes underlying interoceptive recall have never been experimentally investigated.

METHODS

We designed and implemented the Interoceptive Encoding and Recall task to compare interoceptive and exteroceptive recall among subjects with MDD (n = 24) and healthy comparison subjects (n = 21). During the encoding phase, subjects learned to pair neutral visual cues (geometric shapes) with aversive interoceptive and exteroceptive stimuli. Later, while undergoing functional magnetic resonance imaging, subjects were prompted to recall the stimulus associated with each shape.

RESULTS

Interoceptive recall, relative to exteroceptive recall, was associated with bilateral mid-to-posterior insula activation. Relative to the healthy control participants, participants with depression exhibited marked hypoactivation of the right dorsal mid-insula during interoceptive recall.

CONCLUSIONS

In healthy control subjects, simply recalling a stimulus associated with a previous interoceptive challenge activated a key region in the brain's interoceptive network. Although previous research has linked MDD with aberrant processing of interoceptive stimuli, the current study is the first to demonstrate that individuals with MDD exhibit decreased insula activity while recalling interoceptive memories. It is possible that insula hypoactivation during interoceptive recall may affect the representation of prior interoceptive experiences in ways that contribute to depressive symptomology and the relationship between depression and systemic health.

Visceral hypersensitivity is associated with GI symptom severity in functional GI disorders: consistent findings from five different patient cohorts

OBJECTIVE

Our aim was to evaluate the association between visceral hypersensitivity and GI symptom severity in large cohorts of patients with functional GI disorder (FGID) and to adjust for psychological factors and general tendency to report symptoms.

DESIGN

We included five cohorts of patients with FGIDs (IBS or functional dyspepsia; n=1144), who had undergone visceral sensitivity testing using balloon distensions (gastric fundus, descending colon or rectum) and completed questionnaires to assess GI symptom severity, non-GI somatic symptoms, anxiety and depression. Subjects were divided into sensitivity tertiles based on pain/discomfort thresholds. GI symptom severity was compared between sensitivity tertiles in each cohort and corrected for somatisation, and anxiety and depression.

RESULTS

In all five cohorts, GI symptom severity increased gradually with increasing visceral sensitivity, with significant differences in GI symptom severity between the sensitivity tertiles (p<0.0001), with small to medium effect sizes (partial η²: 0.047-0.11). The differences between sensitivity tertiles remained significant in all cohorts after correction for anxiety and depression, and also after correction for non-GI somatic symptom reporting in all of the cohorts (p<0.05).

CONCLUSIONS

A gradual increase in GI symptom severity with increasing GI sensitivity was demonstrated in IBS and functional dyspepsia, which was consistent across several large patient groups from different countries, different methods to assess sensitivity and assessments in different parts of the GI tract. This association was independent of tendency to report symptoms or anxiety/depression comorbidity. These findings confirm that visceral hypersensitivity is a contributor to GI symptom generation in FGIDs.

Amygdala-mediated mechanisms regulate visceral hypersensitivity in adult females following early life stress: importance of the glucocorticoid receptor and corticotropin-releasing factor

Alterations in amygdala activity are apparent in women who report a history of early life stress (ELS) and those diagnosed with chronic pain disorders. Chronic stress in adulthood induces visceral hypersensitivity by alterations in glucocorticoid receptor (GR) and corticotropin-releasing factor (CRF) expression within the central amygdala (CeA). Here, we hypothesized that unpredictable ELS, previously shown to induce visceral hypersensitivity in adult female rats, alters GR and CRF expression in the CeA. After neonatal ELS, visceral sensitivity and GR and CRF gene expression were quantified in adult female rats. After unpredictable ELS, adult female rats exhibited visceral hypersensitivity and increased expression of GR and CRF in the CeA. After predictable ELS, adult female rats demonstrated normosensitive behavioral pain responses and upregulation of GR but not CRF in the CeA. After the ELS paradigms, visceral sensitivity and gene expression within the CeA were unaffected in adult male rats. The role of GR and CRF in modulating visceral sensitivity in adult female rats after ELS was investigated using oligodeoxynucleotide sequences targeted to the CeA for knockdown of GR or CRF. Knockdown of GR increased visceral sensitivity in all rats but revealed an exaggerated visceral hypersensitivity in females with a history of predictable or unpredictable ELS compared with that of controls. Knockdown of CRF expression or antagonism of CRF1R in the CeA attenuated visceral hypersensitivity after unpredictable ELS. This study highlights a shift in GR and CRF regulation within the CeA after ELS that underlies the development of visceral hypersensitivity in adulthood.

Functional Bowel Disorders Are Associated with a Central Immune Activation

Background

Subjects with depression and unexplained neurological symptoms have a high prevalence of gastrointestinal comorbidity probably related to the brain-gut communication. This study explored associations between functional gastrointestinal disorders (FGID) and inflammatory markers in subjects with these disorders.

Methods

The FGID, including irritable bowel syndrome (IBS), were classified according to the Rome III criteria, and degree of symptoms was assessed with IBS symptom severity score (IBS-SSS). A range of interleukins (IL), chemokines and growth factors, tryptophan, and kynurenine were analysed in serum and the cerebrospinal fluid (CSF), and short-chain fatty acids (SCFA) were analysed in the faeces. The results are reported as partial correlation (pc) and p values.

Results

Sixty-six subjects were included. IBS was associated with high levels of tryptophan (p = 0.048) and kynurenine (p = 0.019) and low level of IL-10 (p = 0.047) in the CSF. IBS-SSS was associated with high tumor necrosis factor and low IL-10 in the CSF; pc = 0.341 and p = 0.009 and pc = −0.299 and p = 0.023, respectively. Propionic minus butyric acid in faeces was negatively associated with IL-10 in the CSF (pc = −0.416, p = 0.005).

Conclusions

FGID were associated with a proinflammatory immune activation in the central nervous system and a disturbed tryptophan metabolism that could have been mediated by the faecal microbiota.

Biomarkers as a diagnostic tool for irritable bowel syndrome: where are we?

Irritable bowel syndrome (IBS) is a common condition in clinical practice. There are currently no objective tests to rule in the disease, but rather tests to rule out other diseases. Biomarkers in IBS may provide the tools needed for diagnosis, prognosis and therapy. These include identification of differences in microbial composition, immune activation, bile acid composition, colonic transit, and alteration in sensation in subgroups of IBS patients. Areas covered: Studies included in our review were chosen based on a PubMed search for 'biomarkers' and 'IBS'. We have reviewed the literature on biomarkers to appraise their accuracy, validity and whether they are actionable. We have not covered genetic associations as biomarkers in this review. Expert commentary: There is significant promise in the usefulness of biomarkers for IBS. The most promising actionable biomarkers are markers of changes in bile acid balance, such as elevated bile acid in the stool, and altered colonic transit. However, there is also potential for microbial studies and mucosal proteases as future actionable biomarkers.

Imaging Pain

The challenges and understanding of acute and chronic pain have been illuminated through the advancement of central neuroimaging. Through neuroimaging research, new technology and findings have allowed us to identify and understand the neural mechanisms contributing to chronic pain. Several regions of the brain are known to be of particular importance for the maintenance and amplification of chronic pain, and this knowledge provides novel targets for future research and treatment. This article reviews neuroimaging for the study of chronic pain, and in particular, the rapidly advancing and popular research tools of structural and functional MRI.

Neurobiological Mechanism of Acupuncture for Relieving Visceral Pain of Gastrointestinal Origin

It is currently accepted that the neural transduction pathways of gastrointestinal (GI) visceral pain include the peripheral and central pathways. Existing research on the neurological mechanism of electroacupuncture (EA) in the treatment of GI visceral pain has primarily been concerned with the regulation of relevant transduction pathways. The generation of pain involves a series of processes, including energy transduction of stimulatory signals in the sensory nerve endings (signal transduction), subsequent conduction in primary afferent nerve fibers of dorsal root ganglia, and transmission to spinal dorsal horn neurons, the ascending transmission of sensory signals in the central nervous system, and the processing of sensory signals in the cerebral cortex. Numerous peripheral neurotransmitters, neuropeptides, and cytokines participate in the analgesic process of EA in visceral pain. Although EA has excellent efficacy in the treatment of GI visceral pain, the pathogenesis of the disease and the analgesic mechanism of the treatment have not been elucidated. In recent years, research has examined the pathogenesis of GI visceral pain and its influencing factors and has explored the neural transduction pathways of this disease.

Neuroimaging of Central Sensitivity Syndromes: Key Insights from the Scientific Literature

Central sensitivity syndromes are characterized by distressing symptoms, such as pain and fatigue, in the absence of clinically obvious pathology. The scientific underpinnings of these disorders are not currently known. Modern neuroimaging techniques promise new insights into mechanisms mediating these postulated syndromes. We review the results of neuroimaging applied to five central sensitivity syndromes: fibromyalgia, chronic fatigue syndrome, irritable bowel syndrome, temporomandibular joint disorder, and vulvodynia syndrome. Neuroimaging studies of basal metabolism, anatomic constitution, molecular constituents, evoked neural activity, and treatment effect are compared across all of these syndromes. Evoked sensory paradigms reveal sensory augmentation to both painful and nonpainful stimulation. This is a transformative observation for these syndromes, which were historically considered to be completely of hysterical or feigned in origin. However, whether sensory augmentation represents the cause of these syndromes, a predisposing factor, an endophenotype, or an epiphenomenon cannot be discerned from the current literature. Further, the result from cross-sectional neuroimaging studies of basal activity, anatomy, and molecular constituency are extremely heterogeneous within and between the syndromes. A defining neuroimaging "signature" cannot be discerned for any of the particular syndromes or for an over-arching central sensitization mechanism common to all of the syndromes. Several issues confound initial attempts to meaningfully measure treatment effects in these syndromes. At this time, the existence of "central sensitivity syndromes" is based more soundly on clinical and epidemiological evidence. A coherent picture of a "central sensitization" mechanism that bridges across all of these syndromes does not emerge from the existing scientific evidence.

Brain white matter changes associated with urological chronic pelvic pain syndrome: multisite neuroimaging from a MAPP case-control study

Clinical phenotyping of urological chronic pelvic pain syndromes (UCPPSs) in men and women have focused on end organ abnormalities to identify putative clinical subtypes. Initial evidence of abnormal brain function and structure in male pelvic pain has necessitated large-scale, multisite investigations into potential UCPPS brain biomarkers. We present the first evidence of regional white matter (axonal) abnormalities in men and women with UCPPS, compared with positive (irritable bowel syndrome, IBS) and healthy controls. Epidemiological and neuroimaging data were collected from participants with UCPPS (n = 52), IBS (n = 39), and healthy sex- and age-matched controls (n = 61). White matter microstructure, measured as fractional anisotropy (FA), was examined by diffusion tensor imaging. Group differences in regional FA positively correlated with pain severity, including segments of the right corticospinal tract and right anterior thalamic radiation. Increased corticospinal FA was specific and sensitive to UCPPS, positively correlated with pain severity, and reflected sensory (not affective) features of pain. Reduced anterior thalamic radiation FA distinguished patients with IBS from those with UCPPS and controls, suggesting greater microstructural divergence from normal tract organization. Findings confirm that regional white matter abnormalities characterize UCPPS and can distinguish between visceral diagnoses, suggesting that regional axonal microstructure is either altered with ongoing pain or predisposes its development.

Differential Activation in Amygdala and Plasma Noradrenaline during Colorectal Distention by Administration of Corticotropin-Releasing Hormone between Healthy Individuals and Patients with Irritable Bowel Syndrome

Irritable bowel syndrome (IBS) often comorbids mood and anxiety disorders. Corticotropin-releasing hormone (CRH) is a major mediator of the stress response in the brain-gut axis, but it is not clear how CRH agonists change human brain responses to interoceptive stimuli. We tested the hypothesis that brain activation in response to colorectal distention is enhanced after CRH injection in IBS patients compared to healthy controls. Brain H₂¹⁵O- positron emission tomography (PET) was performed in 16 male IBS patients and 16 age-matched male controls during baseline, no distention, mild and intense distention of the colorectum using barostat bag inflation. Either CRH (2 μg/kg) or saline (1:1) was then injected intravenously and the same distention protocol was repeated. Plasma adrenocorticotropic hormone (ACTH), serum cortisol and plasma noradrenaline levels were measured at each stimulation. At baseline, CRH without colorectal distention induced more activation in the right amygdala in IBS patients than in controls. During intense distention after CRH injection, controls showed significantly greater activation than IBS patients in the right amygdala. Plasma ACTH and serum cortisol secretion showed a significant interaction between drug (CRH, saline) and distention. Plasma noradrenaline at baseline significantly increased after CRH injection compared to before injection in IBS. Further, plasma noradrenaline showed a significant group (IBS, controls) by drug by distention interaction. Exogenous CRH differentially sensitizes brain regions of the emotional-arousal circuitry within the visceral pain matrix to colorectal distention and synergetic activation of noradrenergic function in IBS patients and healthy individuals.

Anticipation of thermal pain in diverticular disease

BACKGROUND

The relative importance of peripheral nerve injury or central pain processing in painful diverticular disease (DD) is unclear. Functional magnetic resonance imaging (fMRI) has demonstrated that dysfunctional central pain processing predominates in irritable bowel syndrome (IBS). This study aims to identify anticipatory changes in symptomatic DD (SDD) compared to asymptomatic DD (ADD) and IBS patients.

METHODS

Gastrointestinal symptoms and somatization were evaluated via the Patient Health Question-12 Somatic Symptom and the SDD group divided into low (≤6 [LSDD]) and high (≥7 [HSDD]) somatization. Cued painful cutaneous thermal stimuli were delivered to the left hand and foot during fMRI. Fixed effect group analysis of the 'cued' anticipatory phase was performed.

KEY RESULTS

Within the right posterior insula, greater deactivation was found in the ADD compared to other groups. In emotion processing centers, anterior and middle insula, greater activation was identified in all patient compared to the ADD group, and in LSDD compared to IBS and HSDD groups. In comparison, amygdala deactivation was greater in ADD than the IBS and HSDD groups, and in LSDD vs HSDD groups. Descending nociceptive control centers, such as the superior medial frontal and orbitofrontal cortex, also showed greater deactivation in the ADD and LSDD compared to the HSDD and IBS groups.

CONCLUSIONS & INFERENCES

The HSDD group have altered anticipatory responses to thermal pain, similar to IBS group. The LSDD are similar to ADD group. This suggests underlying differences in pain pathophysiology, and the need for individualized treatment strategies to target the cause of their chronic pain.

Early life stress elicits visceral hyperalgesia and functional reorganization of pain circuits in adult rats

Early life stress (ELS) is a risk factor for developing functional gastrointestinal disorders, and has been proposed to be related to a central amplification of sensory input and resultant visceral hyperalgesia. We sought to characterize ELS-related changes in functional brain responses during acute noxious visceral stimulation. Neonatal rats (males/females) were exposed to limited bedding (ELS) or standard bedding (controls) on postnatal days 2–9. Age 10–11 weeks, animals were implanted with venous cannulas and transmitters for abdominal electromyography (EMG). Cerebral blood flow (rCBF) was mapped during colorectal distension (CRD) using [¹⁴C]-iodoantipyrine autoradiography, and analyzed in three-dimensionally reconstructed brains by statistical parametric mapping and functional connectivity. EMG responses to CRD were increased after ELS, with no evidence of a sex difference. ELS rats compared to controls showed a greater significant positive correlation of EMG with amygdalar rCBF. Factorial analysis revealed a significant main effect of ‘ELS’ on functional activation of nodes within the pain pathway (somatosensory, insular, cingulate and prefrontal cortices, locus coeruleus/lateral parabrachial n. [LC/LPB], periaqueductal gray, sensory thalamus), as well as in the amygdala, hippocampus and hypothalamus. In addition, ELS resulted in an increase in the number of significant functional connections (i.e. degree centrality) between regions within the pain circuit, including the amygdala, LC/LPB, insula, anterior ventral cingulate, posterior cingulate (retrosplenium), and stria terminalis, with decreases noted in the sensory thalamus and the hippocampus. Sex differences in rCBF were less broadly expressed, with significant differences noted at the level of the cortex, amygdala, dorsal hippocampus, raphe, sensory thalamus, and caudate-putamen. ELS showed a sexually dimorphic effect (‘Sex x ELS’ interaction) at the LC/LPB complex, globus pallidus, hypothalamus, raphe, septum, caudate-putamen and cerebellum. Our results suggest that ELS alters functional activation of the thalamo-cortico-amydala pathway, as well as the emotional-arousal network (amygdala, locus coeruleus), with evidence that ELS may additionally show sexually dimorphic effects on brain function.

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Early life stress (ELS) elicits visceral hyperalgesia in adult offspring.

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ELS alters functional activation of the thalamo-cortico-amydala pathway.

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ELS shows a sexually dimorphic effects on brain function.

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Functional imaging-based endpoints promise improved animal-to-human translation.

Functional neuroimaging studies in functional dyspepsia patients: a systematic review

BACKGROUND

There is increasing evidence in support of the presence of abnormal central changes (compared to healthy controls) in functional dyspepsia (FD) in addition to the peripheral changes in gastrointestinal tract.

PURPOSE

This systematic review aims to provide an integrative understanding of the abnormal functional brain activity, visceral sensation, dyspeptic symptoms, and psychological changes of FD. Electronic and hand searches were conducted to identify functional neuroimaging studies involving FD patients. Sixteen studies were selected and divided into three categories: 10 resting state studies, three visceral distention studies, and three acupuncture studies. Changes were reported in several brain areas in FD patients including the frontal cortex, somatosensory cortex, insula, anterior cingulate cortex, thalamus, hippocampus, and amygdala. These brain activity changes were associated with visceral hypersensitivity, dyspeptic symptoms, poorer quality of life, anxiety, and depression. The results show that FD is associated with functional abnormalities in sensory and pain modulation, emotion, saliency, and homeostatic processing regions. The diversity of conditions, heterogeneous results, poorly standardized diagnoses of FD, and various comorbidities may be responsible for the variability in the results.

Calcitonin Gene-Related Peptide Modulates Heat Nociception in the Human Brain - An fMRI Study in Healthy Volunteers

Background

Intravenous infusion of calcitonin-gene-related-peptide (CGRP) provokes headache and migraine in humans. Mechanisms underlying CGRP-induced headache are not fully clarified and it is unknown to what extent CGRP modulates nociceptive processing in the brain. To elucidate this we recorded blood-oxygenation-level-dependent (BOLD) signals in the brain by functional MRI after infusion of CGRP in a double-blind placebo-controlled crossover study of 27 healthy volunteers. BOLD-signals were recorded in response to noxious heat stimuli in the V1-area of the trigeminal nerve. In addition, we measured BOLD-signals after injection of sumatriptan (5-HT_1B/1D antagonist).

Results

Brain activation to noxious heat stimuli following CGRP infusion compared to baseline resulted in increased BOLD-signal in insula and brainstem, and decreased BOLD-signal in the caudate nuclei, thalamus and cingulate cortex. Sumatriptan injection reversed these changes.

Conclusion

The changes in BOLD-signals in the brain after CGRP infusion suggests that systemic CGRP modulates nociceptive transmission in the trigeminal pain pathways in response to noxious heat stimuli.

Can Interoception Improve the Pragmatic Search for Biomarkers in Psychiatry?

Disrupted interoception is a prominent feature of the diagnostic classification of several psychiatric disorders. However, progress in understanding the interoceptive basis of these disorders has been incremental, and the application of interoception in clinical treatment is currently limited to panic disorder. To examine the degree to which the scientific community has recognized interoception as a construct of interest, we identified and individually screened all articles published in the English language on interoception and associated root terms in Pubmed, Psychinfo, and ISI Web of Knowledge. This search revealed that interoception is a multifaceted process that is being increasingly studied within the fields of psychiatry, psychology, neuroscience, and biomedical science. To illustrate the multifaceted nature of interoception, we provide a focused review of one of the most commonly studied interoceptive channels, the cardiovascular system, and give a detailed comparison of the most popular methods used to study cardiac interoception. We subsequently review evidence of interoceptive dysfunction in panic disorder, depression, somatic symptom disorders, anorexia nervosa, and bulimia nervosa. For each disorder, we suggest how interoceptive predictions constructed by the brain may erroneously bias individuals to express key symptoms and behaviors, and outline questions that are suitable for the development of neuroscience-based mental health interventions. We conclude that interoception represents a viable avenue for clinical and translational research in psychiatry, with a well-established conceptual framework, a neural basis, measurable biomarkers, interdisciplinary appeal, and transdiagnostic targets for understanding and improving mental health outcomes.

Topological Reorganization of the Default Mode Network in Irritable Bowel Syndrome

The aim of this study was to investigate the topological reorganization of the brain default mode network (DMN) in patients with irritable bowel syndrome (IBS) using resting-state functional magnetic resonance imaging (rs-fMRI). With approval by our ethics committee, rs-fMRI was prospectively performed in 31 IBS patients (25 male, 27 ± 8 years) and 32 healthy controls (25 male, 29 ± 9 years). The DMN was determined by unbiased seed-based functional connectivity (FC) analysis and then parcellated into several subregions. FC across all pairs of DMN subregions was computed to construct the DMN architecture, for which topological properties were characterized by graph theoretical approaches. Pearson correlation was performed between abnormal DMN inter-regional FC and network measures and clinical indices in IBS patients. Compared to healthy controls, IBS patients showed decreased DMN inter-regional FC between the anterior cingulate cortex and precuneus, the medial orbital of the superior frontal gyrus (ORBsupmed) and precuneus, and the middle temporal gyrus and precuneus. IBS patients also showed decreased DMN global efficiency (E _glob). Inclusion of anxiety and depression as covariates abolished FC between ORBsupmed and precuneus and some E _glob differences. The average DMN FC was positively correlated with average E _glob (r = 0.47, P = 0.008) and negatively correlated with symptom severity score (r = -0.37, P = 0.04) in IBS patients. In conclusion, IBS patients showed topological reorganization of the DMN to a non-optimized regularity configuration, which may partly be ascribed to high levels of anxiety and depression.

Systematic review: instruments to assess abdominal pain in irritable bowel syndrome

BACKGROUND

Consensus on standard methods to assess chronic abdominal pain in patients with irritable bowel syndrome (IBS) is currently lacking.

AIM

To systematically review the literature with respect to instruments of measurement of chronic abdominal pain in IBS patients.

METHODS

Systematic literature search was performed in PubMed/Medline databases for studies using pain measurement instruments in patients with IBS.

RESULTS

One hundred and ten publications were reviewed. A multitude of different instruments is currently used to assess chronic abdominal pain in IBS patients. The single-item methods, e.g. the validated 10-point numeric rating scale (NRS), and questionnaires assessing gastrointestinal symptoms severity, focus mostly on the assessment of only the intensity of abdominal pain. Of these questionnaires, the validated IBS-Symptom Severity Scale includes the broadest measurement of pain-related aspects. General pain questionnaires and electronic momentary symptom assessment tools have been used to study abdominal pain in IBS patients, but have not yet been validated for this purpose. The evidence for the use of provocation tests, e.g. the rectal barostat with balloon distention, for measurement of abdominal pain in IBS is weak, due to the poor correlation between visceral pain thresholds assessed by provocation tests and abdominal pain as assessed by retrospective questionnaires.

CONCLUSIONS

The multitude of different instruments to measure chronic abdominal pain in IBS makes it difficult to compare endpoints of published studies. There is need for validated instruments to assess chronic abdominal pain in IBS patients, that overcome the limitations of the currently available methods.

Towards a systems view of IBS

Despite an extensive body of reported information about peripheral and central mechanisms involved in the pathophysiology of IBS symptoms, no comprehensive disease model has emerged that would guide the development of novel, effective therapies. In this Review, we will first describe novel insights into some key components of brain-gut interactions, starting with the emerging findings of distinct functional and structural brain signatures of IBS. We will then point out emerging correlations between these brain networks and genomic, gastrointestinal, immune and gut-microbiome-related parameters. We will incorporate this new information, as well as the reported extensive literature on various peripheral mechanisms, into a systems-based disease model of IBS, and discuss the implications of such a model for improved understanding of the disorder, and for the development of more-effective treatment approaches in the future.

Deficient habituation to repeated rectal distensions in irritable bowel syndrome patients with visceral hypersensitivity

BACKGROUND

Irritable bowel syndrome (IBS) patients show evidence of altered central processing of visceral signals. One of the proposed alterations in sensory processing is an altered engagement of endogenous pain modulation mechanisms. The aim was to test the hypothesis that IBS patients with (IBS-S) and without visceral hypersensitivity (IBS-N) differ in their ability to engage endogenous pain modulation mechanism during habituation to repeated visceral stimuli.

METHODS

Brain blood oxygen level dependent (BOLD) response was measured during repeated rectal distension and its anticipation in 33 IBS patients with and without visceral hypersensitivity and 18 healthy controls (HCs). BOLD response to early and late phase of the distension series was compared within and between groups.

KEY RESULTS

While BOLD response was similar during the early phase of the experiment, IBS-S showed greater BOLD response than IBS-N and HCs during the late phase of the distension series. IBS-S showed increasing BOLD response both to the anticipation and delivery of low intensity rectal distensions in brain regions including insula, anterior and mid cingulate cortex. IBS-N showed decreasing BOLD response to repeated rectal distensions in brain regions including insula, prefrontal cortex and amygdala.

CONCLUSIONS & INFERENCES

These findings are consistent with compromised ability of IBS-S to respond to repeated delivery of rectal stimuli, both in terms of sensitization of sensory pathways and habituation of emotional arousal. The fact that both IBS subgroups met Rome criteria, and did not differ in terms of reported symptom severity demonstrates that similar symptom patterns can result from different underlying neurobiological mechanisms.

Effect of electroacupuncture on P2X3 receptor regulation in the peripheral and central nervous systems of rats with visceral pain caused by irritable bowel syndrome

The aim of this study is to investigate the role of the purinergic receptor P2X3 in the peripheral and central nervous systems during acupuncture treatment for the visceral pain of irritable bowel syndrome (IBS). A total of 24 8-day-old Sprague-Dawley (SD) neonatal male rats (SPF grade) were stimulated using colorectal distention (CRD) when the rats were awake. The modeling lasted for 2 weeks with one stimulation per day. After 6 weeks, the rats were randomly divided into three groups of eight each: (1) the normal group (NG, n = 8); (2) the model group (MG, n = 8); and (3) the model + electroacupuncture group (EA, n = 8) that received electroacupuncture at a needling depth of 5 mm at the Shangjuxu (ST37, bilateral) and Tianshu (ST25, bilateral) acupoints. The parameters of the Han's acupoint nerve stimulator (HANS) were as follows: sparse-dense wave with a frequency of 2/100 Hz, current of 2 mA, 20 min/stimulation, and one stimulation per day; the treatment was provided for seven consecutive days. At the sixth week after the treatment, the abdominal withdrawal reflex (AWR) score was determined; immunofluorescence and immunohistochemistry were used to measure the expression of the P2X3 receptor in myenteric plexus neurons, prefrontal cortex, and anterior cingulate cortex; and, a real-time PCR assay was performed to measure the expression of P2X3 messenger RNA (mRNA) in the dorsal root ganglion (DRG) and spinal cord. After stimulation with CRD, the expression levels of the P2X3 receptor in the inter-colonic myenteric plexus, DRG, spinal cord, prefrontal cortex, and anterior cingulate cortex were upregulated, and the sensitivity of the rats to IBS visceral pain was increased. Electroacupuncture (EA) could downregulate the expression of the P2X3 receptor and ease the sensitivity to visceral pain. The P2X3 receptor plays an important role in IBS visceral pain. The different levels of P2X3 in the peripheral enteric nervous system and central nervous system mediate the effects of the EA treatment of the visceral hyperalgesia of IBS.

Esophageal acid stimulation alters insular cortex functional connectivity in gastroesophageal reflux disease

BACKGROUND

The insula plays a significant role in the interoceptive processing of visceral stimuli. We have previously shown that gastroesophageal reflux disease (GERD) patients have increased insular cortex activity during esophageal stimulation, suggesting a sensitized esophago-cortical neuraxis. However, information regarding the functional connectivity (FC) of the insula during visceral stimulation is lacking. The primary aim of this study was to investigate the FC of insular subregions during esophageal acid stimulation.

METHODS

Functional imaging data were obtained from 12 GERD patients and 14 healthy subjects during four steady state conditions: (i) presence of transnasal esophageal catheter (pre-infusion); (ii) neutral solution; (iii) acid infusion; (iv) presence of transnasal esophageal catheter following infusions (post-infusion). The insula was parcellated into six regions of interest. FC maps between each insular ROI and interoceptive regions were created. Differences in FC between GERD patients and healthy subjects were determined across the 4 study conditions.

KEY RESULTS

All GERD patients experienced heartburn during and after esophageal acidification. Significant differences between GERD patients and healthy subjects were seen in: (i) insula-thalamic FC (neutral solution infusion, acid infusion, post-infusion); (ii) insula-amygdala FC (acid infusion, post-infusion); (iii) insula-hippocampus and insula-cingulate FC (post-infusion).

CONCLUSIONS & INFERENCES

Esophageal stimulation in GERD patients revealed significant insular cortex FC differences with regions involved in viscerosensation and interoception. The results of our study provide further evidence that the insula, located at the transition of afferent physiologic information to human feelings, is essential for both visceral homeostasis and the experience of heartburn in GERD patients.

Neural circuitry of abdominal pain-related fear learning and reinstatement in irritable bowel syndrome

BACKGROUND

Altered pain anticipation likely contributes to disturbed central pain processing in chronic pain conditions like irritable bowel syndrome (IBS), but the learning processes shaping the expectation of pain remain poorly understood. We assessed the neural circuitry mediating the formation, extinction, and reactivation of abdominal pain-related memories in IBS patients compared to healthy controls (HC) in a differential fear conditioning paradigm.

METHODS

During fear acquisition, predictive visual cues (CS(+)) were paired with rectal distensions (US), while control cues (CS(-)) were presented unpaired. During extinction, only CSs were presented. Subsequently, memory reactivation was assessed with a reinstatement procedure involving unexpected USs. Using functional magnetic resonance imaging, group differences in neural activation to CS(+) vs CS(-) were analyzed, along with skin conductance responses (SCR), CS valence, CS-US contingency, state anxiety, salivary cortisol, and alpha-amylase activity. The contribution of anxiety symptoms was addressed in covariance analyses.

KEY RESULTS

Fear acquisition was altered in IBS, as indicated by more accurate contingency awareness, greater CS-related valence change, and enhanced CS(+)-induced differential activation of prefrontal cortex and amygdala. IBS patients further revealed enhanced differential cingulate activation during extinction and greater differential hippocampal activation during reinstatement. Anxiety affected neural responses during memory formation and reinstatement.

CONCLUSIONS & INFERENCES

Abdominal pain-related fear learning and memory processes are altered in IBS, mediated by amygdala, cingulate cortex, prefrontal areas, and hippocampus. Enhanced reinstatement may contribute to hypervigilance and central pain amplification, especially in anxious patients. Preventing a 'relapse' of learned fear utilizing extinction-based interventions may be a promising treatment goal in IBS.

Optimal management of constipation associated with irritable bowel syndrome

Irritable bowel syndrome (IBS) is a common chronic functional disorder of the gastrointestinal tract, meanly characterized by recurrent abdominal pain or discomfort and altered bowel habit. It is a complex disorder involving biological, environmental, and psychosocial factors. The diagnosis is achieved according to the Rome III criteria provided that organic causes have been excluded. Although IBS does not constitute a life-threatening condition, it has a remarkable prevalence and profoundly reduces the quality of life with burdening socioeconomic costs. One of the principal concerns about IBS is the lack of effective therapeutic options. Up to 40% of patients are not satisfied with any available medications, especially those suffering from chronic constipation. A correct management of IBS with constipation should evolve through a global approach focused on the patient, starting with careful history taking in order to assess the presence of organic diseases that might trigger the disorder. Therefore, the second step is to examine lifestyle, dietary habits, and psychological status. On these bases, a step-up management of disease is recommended: from fiber and bulking agents, to osmotic laxative drugs, to new molecules like lubiprostone and linaclotide. Although new promising tools for relief of bowel-movement-related symptoms are being discovered, a dedicated doctor-patient relationship still seems to be the key for success.