The Increased Level of Depression and Anxiety in Irritable Bowel Syndrome Patients Compared with Healthy Controls: Systematic Review and Meta-analysis

Effects of a high fat diet on gut microbiome dysbiosis in a mouse model of Gulf War Illness

Gulf War Illness (GWI) is a chronic health condition that appeared in Veterans after returning home from the Gulf War. The primary symptoms linked to deployment are posttraumatic stress disorder, mood disorders, GI problems and chronic fatigue. At first glance, these symptoms are difficult to ascribe to a single pathological mechanism. However, it is now clear that each symptom can be linked individually to alterations in the gut microbiome. The primary objective of the present study was to determine if gut microbiome dysbiosis was evident in a mouse model of GWl. Because the majority of Gulf War Veterans are overweight, a second objective was to determine if a high fat diet (HF) would alter GWI outcomes. We found that the taxonomic structure of the gut microbiome was significantly altered in the GWI model and after HF exposure. Their combined effects were significantly different from either treatment alone. Most treatment-induced changes occurred at the level of phylum in Firmicutes and Bacteroidetes. If mice fed HF were returned to a normal diet, the gut microbiome recovered toward normal levels in both controls and GWI agent-treated mice. These results add support to the hypotheses that dysbiosis in the gut microbiome plays a role in GWI and that life-style risk factors such as an unhealthy diet can accentuate the effects of GWI by impacting the gut microbiome. The reversibility of the effect of HF on the gut microbiome suggests new avenues for treating GWI through dietary intervention.

Tryptophan Metabolites Along the Microbiota-Gut-Brain Axis: An Interkingdom Communication System Influencing the Gut in Health and Disease

The ‘microbiota-gut-brain axis’ plays a fundamental role in maintaining host homeostasis, and different immune, hormonal, and neuronal signals participate to this interkingdom communication system between eukaryota and prokaryota. The essential aminoacid tryptophan, as a precursor of several molecules acting at the interface between the host and the microbiota, is fundamental in the modulation of this bidirectional communication axis. In the gut, tryptophan undergoes 3 major metabolic pathways, the 5-HT, kynurenine, and AhR ligand pathways, which may be directly or indirectly controlled by the saprophytic flora. The importance of tryptophan metabolites in the modulation of the gastrointestinal tract is suggested by several preclinical and clinical studies; however, a thorough revision of the available literature has not been accomplished yet. Thus, this review attempts to cover the major aspects on the role of tryptophan metabolites in host-microbiota cross-talk underlaying regulation of gut functions in health conditions and during disease states, with particular attention to 2 major gastrointestinal diseases, such as irritable bowel syndrome (IBS) and inflammatory bowel disease (IBD), both characterized by psychiatric disorders. Research in this area opens the possibility to target tryptophan metabolism to ameliorate the knowledge on the pathogenesis of both diseases, as well as to discover new therapeutic strategies based either on conventional pharmacological approaches or on the use of pre- and probiotics to manipulate the microbial flora.

Bladder-bowel interactions: Do we understand pelvic organ cross-sensitization? International Consultation on Incontinence Research Society (ICI-RS) 2018

AIMS

Mounting evidence from experimental animal and human studies suggests that cross-sensitization exists between different organs. Lower urinary tract (LUT) and bowel dysfunction commonly overlap, and the role of cross-sensitization between pelvic visceral organs is uncertain.

METHODS

At the International Consultation on Incontinence Research Society (ICI-RS) meeting in 2018, a panel of clinicians participated in a discussion on bladder and bowel interactions in the context of pelvic organ cross-sensitization.

RESULTS

Bladder and bowel problems commonly co-occur in adults and children across different disorders, and the mechanism responsible for overlapping dysfunction is uncertain in most instances. At a neuronal level, cross-sensitization occurs as a result of afferent signaling from the LUT and lower bowel through different central and peripheral mechanisms. Studies in animals and humans have demonstrated evidence for cross-organ sensitization following experimental inflammation or distension of the lower bowel, affecting the LUT. Nerve stimulation is an effective treatment for different functional LUT and bowel disorders, and whether this treatment may influence cross-organ sensitization remains uncertain. The role of physiologically dormant C-fibers, the bladder-gut-brain axis, and gut microbiome in cross-sensitization are speculative.

CONCLUSION

Recommendations for research were made to explore the role of cross-organ sensitization in the pathogenesis of co-occurring LUT and bowel dysfunction in humans.

Antidepressants in inflammatory bowel disease

Gut-brain dysregulation has been recognized by the scientific community as being crucial to the understanding of chronic gastrointestinal conditions, and this has translated into the practice of a newly established discipline, psychogastroenterology. Along with psychotherapy, antidepressants (a subtype of central neuromodulators) have been proposed as treatments for gut-brain disorders that might benefit both psychological and gastrointestinal health. Antidepressants have been found to be effective for the treatment of comorbid anxiety and depression, pain and impaired sleep. Although the efficacy of antidepressants is well established in disorders of gut-brain interaction (DGBI), evidence is only now emerging in IBD. This Perspective discusses the use of antidepressants in DGBI and IBD, focusing on how what we have learnt about the role of antidepressants in DGBI could be applied to help optimize the management of IBD.

Clinical Management of the Microbiome in Irritable Bowel Syndrome

Background

A growing body of evidence suggests that dysbiosis contributes to the onset and symptomatology of irritable bowel syndrome (IBS) and other functional bowel disorders. Changes to the gastrointestinal microbiome may contribute to the underlying pathophysiology of IBS.

Methods

The present review summarizes the potential effects of microbiome changes on GI transit, intestinal barrier function, immune dysregulation and inflammation, gut–brain interactions and neuropsychiatric function.

Results

A multimodal approach to IBS management is recommended in accordance with current Canadian guidelines. Pharmacologic treatments are advised to target the presumed underlying pathophysiological mechanism, such as dysregulation of GI transit, peristalsis, intestinal barrier function and pain signalling. The management plan for IBS may also include treatments directed at dysbiosis, including dietary modification and use of probiotics, which may promote the growth of beneficial bacteria, affect intestinal gas production and modulate the immune response; and the administration of periodic short courses of a nonsystemic antibiotic such as rifaximin, which may re-establish microbiota diversity and improve IBS symptoms.

Conclusion

Dysregulated host–microbiome interactions are complex and the use of microbiome-directed therapies will necessarily be empiric in individual patients. A management algorithm comprising microbiome- and nonmicrobiome-directed therapies is proposed.

The gut microbiome and psycho-cognitive traits

The idea that trillions of bacteria inhabit our gut is somewhat unnerving, yet these bacteria may have a greater influence on our behavior than previously thought. Accumulating data strongly suggest that these gut commensal organisms have a strong inter-relationship with our brain and behavior, including cognitive function, mood, and personality. In this chapter, we discuss the role of the gut microbiome in the development of human personality, mood and mood disorders, and cognition, with a particular emphasis on the current consensus and controversies in the literature surrounding the behavioral effects of bioactive metabolites, microbial ratio shifts, and neurotransmitter synthesis facilitated by the microbiome.

What impact do Rome IV criteria have on patients with IBS in China?

Background: The Rome criteria for functional gastrointestinal diseases (FGIDs) have been updated from Rome III to Rome IV. This study aimed to investigate the impact of the update on patients with irritable bowel syndrome (IBS) in China.Methods: A previous database including consecutive patients with FGIDs (according to Rome III criteria) from gastrointestinal department of a tertiary hospital in China was re-analyzed. Demographic information, clinical symptoms, psychological status (Zung self-rating scale), and sleep quality (Pittsburgh sleep quality index) were compared between patients with Rome III and Rome IV IBS.Results: Of the 946 patients with FGIDs, only 58 (6.1%) were diagnosed with Rome IV IBS [less than 292 (30.9%) under Rome III criteria] with a surge of the number of unspecified functional bowel disorders (U-FBD). All patients with IBS were divided into three groups: group A [meeting both Rome III and IV criteria, accounting for 43 (4.6%) of patients with FGIDs], group B [meeting only Rome III criteria, 249 (26.3%)], and group C [meeting only Rome IV criteria,15 (1.6%)]. Significant differences in frequency and severity of symptoms, subtypes, and sleep quality among groups (all p < .05) were found. Patients with Rome III IBS having sleep disorder tended to be more serious than those without. On the contrary, it was not the case under Rome IV criteria.Conclusions: Number of IBS patients was greatly reduced accompanied by a surge in U-FBD. Besides, the updated criteria also had great impacts on clinical parameters, sleep quality and psychological state of IBS patients.HighlightsRome IV criteria removed the description of abdominal discomfort for IBS.The updated Rome criteria had great impacts on IBS patients in our database.Our study analyzed the characteristics of IBS patients who fulfilled both criteria.Alterations in the Rome criteria also led to changes in the disease spectrum of FBD.

Chronic Diarrhea and Constipation Are More Common in Depressed Individuals

BACKGROUND AND AIMS

Depression is a major health issue in the United States and is highly comorbid with gastrointestinal conditions. We collected data from the National Health and Nutrition Examination Survey (NHANES), a representative sample of the US population, to study the relationship between depression and bowel habits.

METHODS

Using data from the NHANES (2009-2010), we identified 495 depressed and 4709 non-depressed adults who filled out the Bowel Health Questionnaire. Depression was defined according to a validated questionnaire. We used multivariable analysis, controlling for clinical and demographic variables, to evaluate the relationship between mood and bowel habits.

RESULTS

In our weighed sample, 24.6% of depressed individuals and 12.6% of non-depressed individuals reported disordered bowel habits. Chronic diarrhea was significantly more prevalent in depressed individuals (15.53%; 95% CI, 11.34%-20.90%) than non-depressed individuals (6.05%; 95% CI, 5.24%-6.98%; P = .0001). Chronic constipation was also more common in depressed individuals (9.10%; 95% CI, 7.02%-11.69%) than non-depressed individuals (6.55%; 95% CI, 5.55%-7.70% CI; P = .003). Mean depression scores in patients with chronic diarrhea (4.9 ± 5.8) and with chronic constipation (4.4 ± 4.93) were significantly higher than mean depression scores for individuals with normal bowel habits (3.2 ± 4.6) (P < .001). Moderate and severe depression were significantly associated with chronic diarrhea but not chronic constipation. Only mild depression was significantly associated with chronic constipation.

CONCLUSIONS

In an analysis of the NHANES database, we found a higher proportion of depressed individuals to have chronic diarrhea and constipation than non-depressed individuals; chronic diarrhea was more strongly associated with depression. Our findings provide support for the relationship between mood and specific bowel habits, accounting for multiple co-variables in a large sample of the general US population.

Recent advances in the pharmacological management of constipation predominant irritable bowel syndrome

Introduction: Irritable bowel syndrome (IBS) is a complex functional gut disorder that typically manifests in early adult years. More than a third of IBS patients are diagnosed with predominant constipation subtype (IBS-C). This syndrome has a distressing impact on the quality of life and is challenging both for patients and physicians.Areas covered: This review focuses on the pathophysiology of constipation in IBS and presents current management options. It also covers the latest findings that may lead to novel pharmacological options in IBS-C management. The authors intend to highlight the results of published research including abstracts, records from the clinicaltrials.gov database (second and third phases of the study) and information from original FDA documents.Expert opinion: Current therapeutic options for IBS-C treatment are based on linaclotide, lubiprostone, plecanatide, and the reintroduced tegaserod. Drugs present on the market as well as those in pre-clinical development should increase the lower esophageal sphincter pressure, promote gastric motility, accelerate gastric emptying and improve gastro-duodenal coordination. Most significantly, they shall not induce severe side effects.

Lower socioeconomic status is associated with an increased prevalence of comorbid anxiety and depression among patients with irritable bowel syndrome: results from a multicenter cohort

Background/Aims: Anxiety and depression are common comorbid psychiatric disorders in IBS patients, but the population-level determinants influencing these comorbidities in IBS patients are poorly understood. We sought to determine whether there was an association between comorbid affective disorders and socioeconomic status among irritable bowel syndrome (IBS) patients. Methods: We assembled a retrospective cohort of 1074 IBS patients with comorbid Generalized Anxiety Disorder (GAD) and/or Major Depressive Disorder (MDD) seen at two tertiary referral centers between 2007 and 2015. IBS patients with comorbid GAD and/or MDD were matched 3:1 by age, sex, and race to controls with IBS and no history of comorbid GAD and/or MDD. Socioeconomic status was approximated by patient zip codes. Results: IBS patients in the lowest socioeconomic group were more likely to be diagnosed with GAD and/or MDD compared to controls (OR = 1.38, p = .0004). The median average per capita income for comorbid GAD/MDD IBS patient cohort was also significantly lower than the control IBS patient cohort ($39,880.50 vs. $41,277.00, p = .02). Conclusions: Among IBS patients, the presence of comorbid Generalized Anxiety Disorder and/or Major Depressive Disorder is associated with lower socioeconomic status and lower average per capita income. These findings speak to a biopsychosocial model of illness, which should be considered by clinicians in the care of IBS patients.

Anxiety and depression in irritable bowel syndrome: Exploring the interaction with other symptoms and pathophysiology using multivariate analyses

BACKGROUND

Anxiety or depression, in other words, psychological distress, are common comorbidities in patients with irritable bowel syndrome (IBS), but their interaction with pathophysiological factors and other symptoms are unclear.

METHODS

Patients with IBS (Rome III criteria), thoroughly characterized regarding pathophysiology (colonic transit time, visceral sensitivity, and autonomic nervous system [ANS] function), symptom profile (IBS severity, somatic symptoms, gastrointestinal [GI]-specific anxiety and fatigue), and quality of life, were explored for differences regarding pathophysiology and symptoms between patients with and without reported psychological distress in univariate and multivariate analyses (Principal Component Analysis [PCA] with Hotelling's T² and Orthogonal Partial Least Squares-Discriminant Analysis [OPLS-DA]).

KEY RESULTS

When using Hospital Anxiety and Depression Scale score ≥8 as cut-off score, including both borderline and clinically significant cases, 345 (44.9%) out of 769 IBS patients reported anxiety, and 198 (25.7%) depression. In univariate analyses, patients reporting psychological distress demonstrated more severe GI and non-GI symptoms, fatigue, GI-specific anxiety and lower quality of life, and differences for some pathophysiological measures. IBS patients with and without reported psychological distress showed significant differences between the multivariate means in symptom reporting (PCA; both P < 0.001), and in pathophysiological measures in patients with and without anxiety (P = 0.018). Visceral hypersensitivity, altered ANS function, more severe GI-specific anxiety, fatigue, and higher somatic non-GI symptoms were the factors that most strongly separated patients with and without psychological distress (OPLS-DA).

CONCLUSIONS AND INFERENCES

Reported anxiety and depression are common in IBS patients, and our study demonstrates that they are interwoven in the complex pathophysiological and clinical picture of IBS.

Effects of Serotonin and Slow-Release 5-Hydroxytryptophan on Gastrointestinal Motility in a Mouse Model of Depression

BACKGROUND & AIMS

Mood disorders and constipation are often comorbid, yet their shared etiologies have rarely been explored. The neurotransmitter serotonin (5-HT) regulates central nervous system and enteric nervous system (ENS) development and long-term functions, including gastrointestinal (GI) motility and mood. Therefore, defects in neuron production of 5-HT might result in brain and intestinal dysfunction. Tryptophan hydroxylase 2 (TPH2) is the rate-limiting enzyme in 5-HT biosynthesis. A variant of TPH2 that encodes the R441H substitution (TPH2-R441H) was identified in individuals with severe depression. We studied mice with an analogous mutation (TPH2-R439H), which results in a 60%-80% decrease in levels of 5-HT in the central nervous system and behaviors associated with depression in humans. Feeding chow that contains 5-HTP slow release (5-HTP SR) to TPH2-R439H mice restores levels of 5-HT in the central nervous system and reduces depressive-like behaviors.

METHODS

We compared the effects of feeding chow, with or without 5-HTP SR, to mice with the TPH2-R439H mutation and without this mutation (control mice). Myenteric and submucosal plexuses were isolated from all 4 groups of mice, and immunocytochemistry was used to quantify total enteric neurons, serotonergic neurons, and 5-HT-dependent subsets of neurons. We performed calcium imaging experiments to evaluate responses of enteric neurons to tryptamine-evoked release of endogenous 5-HT. In live mice, we measured total GI transit, gastric emptying, small intestinal transit, and propulsive colorectal motility. To measure colonic migrating motor complexes (CMMCs), we isolated colons and constructed spatiotemporal maps along the proximodistal length to quantify the frequency, velocity, and length of CMMCs. We measured villus height, crypt perimeter, and relative densities of enterochromaffin and enteroendocrine cells in small intestinal tissue.

RESULTS

Levels of 5-HT were significantly lower in enteric neurons from TPH2-R439H mice than from control mice. TPH2-R439H mice had abnormalities in ENS development and ENS-mediated GI functions, including reduced motility and intestinal epithelial growth. Total GI transit and propulsive colorectal motility were slower in TPH2-R439H mice than controls, and CMMCs were slower and less frequent. Villus height and crypt perimeter were significantly decreased in colon tissues from TPH2-R439H mice compared with controls. Administration of 5-HTP SR to adult TPH2-R439H mice restored 5-HT to enteric neurons and reversed these abnormalities. Adult TPH2-R439H mice given oral 5-HTP SR had normalized numbers of enteric neurons, total GI transit, and colonic motility. Intestinal tissue from these mice had normal measures of CMMCs and enteric epithelial growth CONCLUSIONS: In studies of TPH2-R439H mice, we found evidence for reduced release of 5-HT from enteric neurons that results in defects in ENS development and GI motility. Our findings indicate that neuron production of 5-HT links constipation with mood dysfunction. Administration of 5-HTP SR to mice restored 5-HT to the ENS and normalized GI motility and growth of the enteric epithelium. 5-HTP SR might be used to treat patients with intestinal dysfunction associated with low levels of 5-HT.

Cumulative Effects of Psychologic Distress, Visceral Hypersensitivity, and Abnormal Transit on Patient-reported Outcomes in Irritable Bowel Syndrome

BACKGROUND & AIMS

Little is known about the link between pathophysiologic factors and symptoms of irritable bowel syndrome (IBS), or whether these factors have cumulative effects on patient-reported outcomes (PROs). We investigated whether pathophysiologic alterations associated with IBS have cumulative or independent effects on PROs.

METHODS

We performed a retrospective analysis of data from 3 cohorts of patients with IBS (n = 407; 74% female; mean age, 36 ± 12 years), based on Rome II or Rome III criteria, seen at a specialized unit for functional gastrointestinal disorders in Sweden from 2002 through 2014. All patients underwent assessments of colonic transit time (radiopaque markers); compliance, allodynia, and hyperalgesia (rectal barostat); anxiety and depression (Hospital Anxiety and Depression scale), as pathophysiologic factors. Dysfunction was defined by available normal values. PROs included IBS symptom severity, somatic symptom severity, and disease-specific quality of life.

RESULTS

Allodynia was observed in 36% of patients, hyperalgesia in 22%, accelerated colonic transit in 18%, delayed transit in 7%, anxiety in 52%, and depression in 24%: each of these factors was associated with severity of at least 1 symptom of IBS. Rectal compliance was not associated with more severe symptoms of IBS. At least 3 pathophysiologic factors were present in 20% of patients, 2 in 30%, 1 in 31%, and none in 18%. With increasing number of pathophysiologic abnormalities, there was a gradual increase in IBS symptom severity (P < .0001) and somatic symptom severity (P < .0001), and a gradual reduction in quality of life (P < .0001).

CONCLUSION

Visceral hypersensitivity, including allodynia and hyperalgesia, abnormal colonic transit, and psychologic factors are all associated with IBS symptoms. These factors have a cumulative effect on gastrointestinal and nongastrointestinal symptoms, as well as on quality of life, in patients with IBS and are therefore relevant treatment targets.

Relief of irritable bowel syndrome by fecal microbiota transplantation is associated with changes in diversity and composition of the gut microbiota

OBJECTIVE

To evaluate the efficacy and safety of fecal microbiota transplantation (FMT) for refractory irritable bowel syndrome (IBS).

METHODS

Microbiota suspensions from feces of the donors were injected into the intestines of 30 Chinese patients with refractory IBS. Microbiota composition analysis and genomic DNA extraction of fecal samples obtained from these patients at baseline and 1 month after FMT were performed. Clinical efficacy and safety of FMT were assessed using questionnaires covering four aspects of IBS therapeutic efficacy and assessment of adverse effects during a 6-month follow-up.

RESULTS

FMT improved IBS gastrointestinal symptoms and alleviated depression and anxiety, as shown by the improved IBS-QOL, IBS-SSS, GSRS, HAMA and HAMD scores at 1 month and 3 months after FMT. A total adverse event rate of FMT was 6.7% (2/30). Gut microbiota analysis revealed that FMT responders had a significantly higher Shannon diversity index before FMT than non-responders. In addition, analysis of differences in bacterial composition before and after FMT in responders showed specific abundance of the phyla Verrucomincrobia and Euryarchaeota at 1 month after FMT. At the genus level, Methanobrevibacter and Akkermansia were the most abundant fecal microbiota 1 month after FMT compared with those before FMT.

CONCLUSIONS

FMT may be an effective and safe therapeutic strategy for treating IBS that achieves a sustained clinical response 3-6 months after the first procedure. Changes in the diversity and dominant flora may contribute to its therapeutic effect.

Does Irritable Bowel Syndrome Exist? Identifiable and Treatable Causes of Associated Symptoms Suggest It May Not

Significant shortcomings in irritable bowel syndrome (IBS) diagnosis and treatment may arise from IBS being an “umbrella” diagnosis that clusters several underlying identifiable and treatable causes for the same symptom presentation into one classification. This view is compatible with the emerging understanding that the pathophysiology of IBS is heterogeneous with varied disease mechanisms responsible for the central pathological features. Collectively, these converging views of the pathophysiology, assessment and management of IBS render the traditional diagnosis and treatment of IBS less relevant; in fact, they suggest that IBS is not a disease entity per se and posit the question “does IBS exist?” The aim of this narrative review is to explore identifiable and treatable causes of digestive symptoms, including lifestyle, environmental and nutritional factors, as well as underlying functional imbalances, that may be misinterpreted as being IBS.

Systematic review with meta-analysis: the prevalence of anxiety and depression in patients with irritable bowel syndrome

BACKGROUND

Irritable bowel syndrome (IBS) is a common and potential disabling functional gastrointestinal disorder. Studies have revealed a possible association between IBS and psychological problems, such as anxiety and depression. Existing systematic reviews have addressed only the levels of anxiety or depression in patients with IBS.

AIM

To investigate systematically the prevalence of anxiety or depression in IBS patients METHODS: A literature search was conducted using the related keywords from the bibliographic databases of Embase, PubMed, Scopus, Web of Science and POPLINE published until 1 January 2019 with no language restriction. Studies reporting the prevalence of anxiety/depressive symptoms/disorders in adult (≥15 years) IBS patients were evaluated. The pooled prevalence, odds ratio (OR) and 95% CI were calculated using stata software.

RESULTS

A total of 14 926 articles were initially screened, and finally 73 papers were included. The prevalence rates of anxiety symptoms and disorders in IBS patients were 39.1% (95% CI: 32.4-45.8) and 23% (95% CI: 17.2-28.8) respectively. The ORs for anxiety symptoms and disorders in IBS patients compared with healthy subjects were 3.11 (95% CI: 2.43-3.98) and 2.52 (95% CI: 1.99-3.20) respectively. The prevalence estimates of depressive symptoms and disorders in IBS patients were 28.8% (95% CI: 23.6-34) and 23.3% (95% CI: 17.2-29.4) respectively. The ORs for depressive symptoms and disorders in IBS patients compared to healthy subjects were 3.04 (95% CI: 2.37-3.91) and 2.72 (95% CI: 2.45-3.02) respectively.

CONCLUSION

Patients with IBS have a three-fold increased odds of either anxiety or depression, compared to healthy subjects.

Chronic colitis-induced visceral pain is associated with increased anxiety during quiescent phase

Inflammatory bowel diseases (IBD) are characterized by repetition of flares and remission periods leading to chronic postinflammatory sequelae. Among postinflammatory sequelae, one-third of patients with IBD are suffering from functional symptoms or psychological comorbidities that persist during remission. The aim of our study was to assess functional and behavioral sequelae of chronic colitis in rats with quiescent intestinal inflammation. Chronic colitis was induced by a weekly intrarectal injection of increasing concentrations of trinitrobenzene sulfonic acid (TNBS) for 3 wk (15-45 mg of TNBS) in 30 rats, whereas the control rats (n = 24) received the vehicle. At 50 days post-TNBS, visceral sensitivity was assessed by visceromotor response to colorectal distension, and transient receptor potential vanilloid type 1 (TRPV1) expression was also quantified in the colon and dorsal root ganglia. Barrier function and inflammatory response were assessed by studying intestinal permeability, tight junction protein, myeloperoxidase activity, histological score, and cytokine production (IL-6, IL-10, and TNF-α). Anxiety behavioral tests were performed from 50 to 64 days after the last TNBS injection. Chronic TNBS induced 1) a visceral hypersensitivity (P = 0.03), 2) an increased colon weight-to-length ratio (P = 0.01), 3) higher inflammatory and fibrosis scores (P = 0.0390 and P = 0.0016, respectively), and 4) a higher colonic IL-6 and IL-10 production (P = 0.008 and P = 0.005, respectively) compared with control rats. Intestinal permeability, colonic production of TNF-α, myeloperoxidase activity, and TRPV1 expression did not differ among groups. Chronic TNBS increased anxiety-related behavior in the open-field test and in the acoustic stress test. In conclusion, chronic colitis induced functional sequelae such as visceral hypersensitivity and increased anxiety with a low-grade intestinal inflammation. Development of a representative animal model will allow defining novel therapeutic approaches to achieve a better management of IBD-related sequelae. NEW & NOTEWORTHY Patients with inflammatory bowel diseases have impaired quality of life. Therapeutic progress to control mucosal inflammation provides us an opportunity to develop novel approaches to understand mechanisms behind postinflammatory sequelae. We used a chronic colitis model to study long-term sequelae on visceral pain, gut barrier function, and psychological impact. Chronic colitis induced functional symptoms and increased anxiety in the remission period. It might define novel therapeutic approaches to achieve a better inflammatory bowel disease-related sequelae management.

Painful neurotrophins and their role in visceral pain

Beyond their well-known role in embryonic development of the central and peripheral nervous system, neurotrophins, particularly nerve growth factor and brain-derived neurotrophic factor, exert an essential role in pain production and sensitization. This has mainly been studied within the framework of somatic pain, and even antibodies (tanezumab and fasinumab) have recently been developed for their use in chronic somatic painful conditions, such as osteoarthritis or low back pain. However, data suggest that neurotrophins also exert an important role in the occurrence of visceral pain and visceral sensitization. Visceral pain is a distressing symptom that prompts many consultations and is typically encountered in both 'organic' (generally inflammatory) and 'functional' (displaying no obvious structural changes in routine clinical evaluations) disorders of the gut, such as inflammatory bowel disease and irritable bowel syndrome, respectively. The present review provides a summary of neurotrophins as a molecular family and their role in pain in general and addresses recent investigations of the involvement of nerve growth factor and brain-derived neurotrophic factor in visceral pain, particularly that associated with inflammatory bowel disease and irritable bowel syndrome.

Metabolomics reveals elevated urinary excretion of collagen degradation and epithelial cell turnover products in irritable bowel syndrome patients

INTRODUCTION

Irritable bowel syndrome (IBS), the most commonly diagnosed functional gastrointestinal (GI) disorder in developed countries, is characterized by chronic abdominal pain, and altered bowel habits.

OBJECTIVES

Accurate and timely diagnosis is challenging as it relies on symptoms and an evolving set of exclusion criteria to distinguish it from other related GI disorders reflecting a complex etiology that remains poorly understood. Herein, nontargeted metabolite profiling of repeat urine specimens collected from a cohort of IBS patients (n = 42) was compared to healthy controls (n = 20) to gain insights into the underlying pathophysiology.

METHODS

An integrated data workflow for characterization of the urine metabolome with stringent quality control was developed to authenticate reliably measured (CV < 30%) and frequently detected (> 75%) metabolites using multisegment injection-capillary electrophoresis-mass spectrometry. Complementary statistical methods were then used to rank differentially excreted urinary metabolites after normalization to osmolality that were subsequently identified by high resolution tandem mass spectrometry and their electrophoretic migration behavior.

RESULTS

Our work revealed ten consistently elevated urinary metabolites in repeat samples collected from IBS patients at two different time points (q < 0.05 after age and Benjamini-Hochberg/FDR adjustment), which were associated with greater collagen degradation and intestinal mucosal turn-over processes likely due to low-grade inflammation. IBS-specific metabolites identified in urine included a series of hydroxylysine metabolites (O-glycosylgalactosyl-hydroxylysine, O-galactosyl-hydroxylysine, lysine), mannopyranosy-L-tryptophan, imidazole propionate, glutamine, serine, ornithine, dimethylglycine and dimethylguanosine. A major limitation in this retrospective case-control study was significant co-morbidity of IBS patients with other illnesses, including depression and prescribed medications as compared to healthy controls.

CONCLUSION

This work provides new mechanistic insights into the pathophysiology of IBS while also offering a convenient way to monitor patient disease progression and treatment responses to therapy based on a panel of urinary metabolites that avoids invasive blood sampling, colonoscopy and/or tissue biopsies.

Psychosocial Factors Associated With Irritable Bowel Syndrome Development in Chinese College Freshmen

Background/Aims

The role of psychosocial factors on irritable bowel syndrome (IBS) in adolescents is incompletely understood. The aim of this study is to investigate the association between the psychosocial factors and the risk of developing IBS in college freshmen.

Methods

A cross-sectional survey was conducted in a randomly selected freshmen population in Wuhan China (n = 2449). Questionnaire evaluated demographics and psychosocial risks. The population was divided into 3 groups: non-discomfort, chronic abdominal discomfort and IBS. The association between the development of IBS and psychosocial factors was analyzed by ordinal and multiple logistic regression analysis.

Results

A total of 2053 (83.8%) completed this survey (mean age, 18.2 ± 0.9 years; female, 35.6%). Among them, 82 (4.0%) fulfilled the Rome III criteria for IBS. Female (odds ratio [OR], 3.31; 95% confidence interval [CI], 2.47-4.45), experience of abuse (OR, 2.44; 95% CI, 1.10-5.56), and suicidal intention (OR, 2.17; 95% CI, 1.15-4.17) were more likely to have IBS. Compared with chronic abdominal discomfort, however, depression (OR, 5.55; 95% CI, 1.36-22.71) was the only dependent risk factor for IBS.

Conclusion

The prevalence of IBS in college freshmen is 4.0%, and to the freshmen, psychosocial factors such as experience of abuse, depression, and suicidal intention were associated with high risk of developing IBS.

Glutamatergic Signaling Along The Microbiota-Gut-Brain Axis

A complex bidirectional communication system exists between the gastrointestinal tract and the brain. Initially termed the “gut-brain axis” it is now renamed the “microbiota-gut-brain axis” considering the pivotal role of gut microbiota in maintaining local and systemic homeostasis. Different cellular and molecular pathways act along this axis and strong attention is paid to neuroactive molecules (neurotransmitters, i.e., noradrenaline, dopamine, serotonin, gamma aminobutyric acid and glutamate and metabolites, i.e., tryptophan metabolites), sustaining a possible interkingdom communication system between eukaryota and prokaryota. This review provides a description of the most up-to-date evidence on glutamate as a neurotransmitter/neuromodulator in this bidirectional communication axis. Modulation of glutamatergic receptor activity along the microbiota-gut-brain axis may influence gut (i.e., taste, visceral sensitivity and motility) and brain functions (stress response, mood and behavior) and alterations of glutamatergic transmission may participate to the pathogenesis of local and brain disorders. In this latter context, we will focus on two major gut disorders, such as irritable bowel syndrome and inflammatory bowel disease, both characterized by psychiatric co-morbidity. Research in this area opens the possibility to target glutamatergic neurotransmission, either pharmacologically or by the use of probiotics producing neuroactive molecules, as a therapeutic approach for the treatment of gastrointestinal and related psychiatric disorders.

Comparison of the metabolomic profiles of irritable bowel syndrome patients with ulcerative colitis patients and healthy controls: new insights into pathophysiology and potential biomarkers

BACKGROUND

Evaluation of the metabolomic profile of patients with irritable bowel syndrome offers an opportunity to identify novel pathophysiological targets and biomarkers that could discriminate this disorder from related conditions.

AIM

To identify potential urinary biomarkers that discriminate irritable bowel syndrome patients from ulcerative colitis patients in remission and healthy controls and to explore the pathophysiology of irritable bowel syndrome using a metabolomic approach.

METHODS

Urine samples were collected from 39 irritable bowel syndrome patients, 53 ulcerative colitis patients in clinical remission and 21 healthy controls. Urinary metabolites were identified and quantified using direct infusion/liquid chromatography tandem mass spectrometry and gas-chromatography mass spectrometry.

RESULTS

Patients with irritable bowel syndrome had a unique urinary metabolome that could separate them from ulcerative colitis patients with an area under the curve = 0.99 (95% confidence interval 0.95-1.00). The most important metabolites for this separation were a group of amino acids and organic acids. In addition, subjects with irritable bowel syndrome could be discriminated from healthy controls using their metabolic fingerprints. Irritable bowel syndrome patients had lower urinary Phosphatidyl choline acyl-alkyl C38:6, dopamine and p-hydroxybenzoic acid than healthy controls. Levels of some urinary metabolites including histamine correlated significantly with irritable bowel syndrome symptom severity scores.

CONCLUSIONS

Irritable bowel syndrome patients have a unique urinary metabolomic profile compared to ulcerative colitis patients in clinical remission or healthy subjects. These data suggest that metabolomic profiling may provide important insights into pathophysiology and testable biomarkers to discriminate irritable bowel syndrome from other disorders that can mimic this condition and can be used to assess its severity and identify potential novel pathophysiological pathways.

Anhedonia in irritable bowel syndrome and in inflammatory bowel diseases and its relationship with abdominal pain

BACKGROUND

Anhedonia is the lowered ability to experience pleasure from rewarding or enjoyable activities and is considered a symptom of depression. Inflammatory bowel disease (IBD) and irritable bowel syndrome (IBS) are frequently accompanied by psychiatric disorders such as depression. However, to our knowledge, studies have yet to investigate the anhedonia in these patients. Our aim was to study the level of anhedonia in patients with IBD and IBS in comparison with healthy controls (HC), and to relate anhedonia levels with the severity of abdominal pain.

METHODS

We consecutively recruited IBD and IBS patients. All patients fulfilled the Snaith-Hamilton Pleasure Scale (SHAPS), a self-rating scale consisting of 14 items that cover the domains of social interaction, food, and drink, sensory experiences, achievement and pastimes, and the Beck Depression Inventory-II (BDI-II) to screen for depression. Moreover, we calculated abdominal pain on a (0-100) Visual Analog Scale (VAS) in all patients.

KEY RESULTS

We enrolled 120 patients (64 IBD and 56 IBS) and 81 HC. Among IBD patients, 34 had Crohn's disease and 30 ulcerative colitis. All patients as a whole had significantly higher SHAPS and BDI-II scores than HC (1.3 ± 1.5 vs 0.8 ± 0.1; P = 0.01 and 10.4 ± 7.5 vs 5.9 ± 4.9; P < 0.001, respectively), while no significant differences were found among groups. SHAPS score showed a significant correlation in only a few statements of BDI-II. In our cohort, a multivariate regression analysis showed that SHAPS score was significantly related to current abdominal pain (0-100 VAS) (P = 0.03) independent of gender and age.

CONCLUSIONS AND INFERENCES

The level of anhedonia was higher in all patients compared to healthy controls. The more the subject is anhedonic, the higher the VAS scale for abdominal pain. This study suggests that anhedonia would need to be very carefully weighed in IBD and IBS patients.

Anxiety and Depression Profile Is Associated With Eating Disorders in Patients With Irritable Bowel Syndrome

Objective: To compare the prevalence of anxiety and depression states and eating disorders (EDs) between patients with irritable bowel syndrome (IBS) and healthy volunteers without IBS. Methods: IBS patients according to Rome III criteria referred to our tertiary care center for therapeutic management and matched volunteers without IBS were prospectively included. EDs were screened by Sick, Control, One stone, Fat, Food-French version (SCOFF-F) questionnaire. IBS symptom severity (IBS symptom severity score), stool consistency (Bristol stool scale), anxiety and depression levels (Hospital Anxiety and Depression scale), and quality of life (validated Gastrointestinal Quality of Life Index) were assessed by validated self-questionnaires. Results: IBS (228) patients and healthy volunteers (228) were included. Mean age was 42.5 ± 13.9 years with mainly women (76.7%). Among IBS patients, 25.4% had positive SCOFF-F compared to 21.1% of volunteers. IBS patients more frequently had a lower body mass index (BMI) than volunteers (p < 0.0001). IBS patients with ED had poorer quality of life and more stressful life events (p = 0.02) than IBS patients without ED. The prevalence of anxiety and depression was significantly higher in IBS patients with ED than in volunteers without ED, respectively (19.0% vs 1.9%, p=0.00, and 60.3% vs 19.7%, p < 0.0001). Conclusions: The prevalence of ED assessed with positive SCOFF-F questionnaire was not significantly different between IBS patients and healthy volunteers. The combination of IBS and ED was associated with higher levels of anxiety or depression and poorer quality of life.

Roles of noradrenergic transmission within the ventral part of the bed nucleus of the stria terminalis in bidirectional brain-intestine interactions

Aims

The bed nucleus of the stria terminalis (BNST) is a limbic structure mediating autonomic and neuroendocrine responses and negative affective states such as anxiety and fear. We previously demonstrated that noradrenergic transmission via β‐adrenoceptors within the ventral part of BNST (vBNST) is involved in bidirectional interactions between the brain and the upper gastrointestinal (GI) tract. The present study aimed to examine the roles of intra‐vBNST noradrenergic transmission via β‐adrenoceptors in bidirectional interactions between the brain and lower GI tract.

Methods

In vivo microdialysis experiments were performed to examine colorectal distention (CRD)‐induced noradrenaline release within the vBNST of freely moving male Sprague‐Dawley rats. Colonic transit and abdominal pain perception were examined following intra‐vBNST injections of isoproterenol, a β‐adrenoceptor agonist, with and without co‐administration of timolol, a β‐adrenoceptor antagonist.

Results

CRD increased extracellular noradrenaline levels within the vBNST and evoked abdominal contractions in a pressure‐dependent manner (30‐60 mm Hg). Bilateral intra‐vBNST injections of isoproterenol (30 nmol/side) significantly increased CRD (30 mm Hg)‐induced abdominal contractions. Intra‐vBNST injections of isoproterenol (30 nmol/side) significantly increased colonic transit, which was reversed by co‐administration of timolol (30 nmol/side).

Conclusion

The results of this study suggest (a) the existence of a positive feedback loop between intra‐vBNST noradrenaline release and abdominal pain perception, and (b) the modulation of colonic motility by intra‐vBNST noradrenergic transmission via β‐adrenoceptors. Dysfunction of the lower GI tract may increase noradrenaline release within the vBNST, which, in turn, may exacerbate impairment of its motility and pain perception.

In vivo microdialysis experiments demonstrated that colorectal distention (CRD) increased extracellular levels of noradrenaline within the vBNST. Intra‐vBNST injections of isoproterenol, a β‐adrenoceptor agonist, induced visceral hypersensitivity to CRD and increased colonic transit, and the increase in colonic transit was reversed by co‐administration of timolol, a β‐adrenoceptor antagonist. The present findings demonstrated important roles of noradrenergic transmission via β‐adrenoceptors within the vBNST in bidirectional brain‐intestine interactions.

Guidelines on the management of irritable bowel syndrome: In memory of Professor Witold Bartnik

These guidelines constitute an update of the previous "Recommendations on the management of irritable bowel syndrome" issued in 2008. They have been developed by a Task Force organized by the Governing Board of the Polish Society of Gastroenterology. They discuss, with particular emphasis on new scientific data covering papers published since 2008, the aetiology, epidemiology, clinical presentation, diagnostic principles and criteria for the diagnosis, and recommendations for the treatment of irritable bowel syndrome (IBS). The English-language acronym for the syndrome (IBS) has become popular in medical and popular scientific language. It is also widely recognized by patients who identify with this diagnosis. Therefore, in the discussed guidelines, this is what we will use.

Comparison of comorbid depression between irritable bowel syndrome and inflammatory bowel disease: A meta-analysis of comparative studies

BACKGROUND

The prevalence of comorbid depression is high in chronic gastrointestinal disorders, including irritable bowel syndrome (IBS) and inflammatory bowel disease (IBD). For these two disorders in particular, the findings have not been consistent. This meta-analysis systematically compares the rates and severity of comorbid depression between IBS and IBD patients.

METHODS

A systematic literature search was conducted using PubMed, PsycINFO, Embase, Cochrane Library, Wan Fang, SinoMed, Chinese National Knowledge Infrastructure from their inception date to September 12, 2017 for comparative studies on IBS and IBD patients. Standardized mean differences (SMDs) and odds ratios (OR) of comorbid depression were calculated using random effect models. Data on comorbid anxiety in the included studies were also extracted and analyzed.

RESULTS

Altogether, 22 studies with 1,244 IBS and 1,048 IBD patients were included. While there was no significant group difference in the prevalence of depression (10 studies, OR = 1.18, 95%CI: 0.87-1.60, P = 0.29), the IBS group had more severe depression (pooled SMD = 0.18, 95%CI: 0.04-0.33, P = 0.01) and anxiety than the IBD group (pooled SMD = 0.31, 95%CI: 0.14-0.49, P = 0.0006). Sixteen (72.7%) studies were assessed as 'high quality' using the Newcastle-Ottawa Scale (NOS).

CONCLUSIONS

Although the prevalence of comorbid depression was similar between groups, IBS patients had more severe comorbid depressive and anxiety symptoms compared to IBD patients. Appropriate assessment and treatment of depressive and anxiety symptoms in these patient groups should be implemented.

Irritable Bowel Syndrome and Depression: A Shared Pathogenesis

It is common knowledge that dysfunction of the immune and neuroendocrine systems, in addition to neuroplasticity, is among the pathways that underlie irritable bowel syndrome (IBS) and depression. From as early as the 1950s, the association of IBS with psychiatric disease was postulated; however, the exact mechanism remains elusive. There has been considerable research into the association of IBS and depression over the last years; research into the gut-brain axis and alterations in gut microbes have gained momentum to spell out the relationship between depression and IBS. Evidence from these researchers indicate the dysfunction of homeostatic coping mechanisms; corticotropin-releasing factor appears to be at the core of this dysfunction. The multifactorial etiology of both depression and IBS hinders a universal, one-strategy-fits-all treatment approach to patients with comorbid depression and IBS. This review analyzes the pathophysiology that associates these two conditions; it explores the bidirectional communication between the brain and the gastrointestinal tract, and how these influence the endocrine and immune systems. Review articles, clinical trials and randomized controlled trials that analyzed the association of depression and IBS were identified by searching PubMed, Google Scholar, and articles in PMC databases. Full texts written in English and available via these search engines were selected for the synthesis of this review. Alterations to the gut-brain axis, intestinal microbiota, and the neuro-immune system may be the cornerstone to the association of IBS and depression. This literature review opens alternate therapeutic approaches to comorbid IBS and depression and encourages further research into this topic.

Depressive symptoms in patients with irritable bowel syndrome: a meta-analysis of comparative studies

Depression is common in patients with irritable bowel syndrome (IBS), but the reported prevalence across different studies is inconsistent. This meta-analysis systematically examined the presence and severity of depressive symptoms in patients with IBS. Two investigators independently performed a literature search. The pooled depressive symptom severity was calculated using a random effects model. Subgroup, sensitivity and meta-regression analyses were conducted to examine the moderating factors of the development of depressive symptoms. Twenty four studies (n=2,837) comparing depressive symptoms between IBS patients (n=1,775) and healthy controls (n=1,062) were identified; 14 (58.3%) studies were rated as high quality. Compared to healthy controls, IBS patients had more frequent (OR=9.21, 95%CI: 4.56-18.57, P<0.001; I2=76%) and more severe depressive symptoms (n=1,480, SMD=2.02, 95%CI: 1.56-2.48, P<0.001; I2=94%). Subgroup analyses revealed that patients with all IBS subtypes had more severe depressive symptoms than controls. In addition, versions of the Hamilton Depression Rating Scale (HAM-D) and IBS diagnostic criteria were significantly associated with depressive symptom severity. Meta-regression analyses revealed that female gender, younger age and small sample size were significantly associated with more severe depressive symptoms. In conclusion, meta-analytic data showed that IBS patients had more frequent and severe depressive symptoms than healthy controls. Adequate screening and treatment for depression should be developed and implemented in this patient population.

Epinephrine modulates Na+/K+ ATPase activity in Caco-2 cells via Src, p38MAPK, ERK and PGE2

Epinephrine, a key stress hormone, is known to affect ion transport in the colon. Stress has been associated with alterations in colonic functions leading to changes in water movements manifested as diarrhea or constipation. Colonic water movement is driven by the Na⁺-gradient created by the Na⁺/K⁺-ATPase. Whether epinephrine acts via an effect on the Na⁺/K⁺-ATPase hasn’t been studied before. The aim of this work was to investigate the effect of epinephrine on the Na⁺/K⁺-ATPase and to elucidate the signaling pathway involved using CaCo-2 cells as a model. The activity of the Na⁺/K⁺-ATPase was assayed by measuring the amount of inorganic phosphate released in presence and absence of ouabain, a specific inhibitor of the enzyme. Epinephrine, added for 20 minutes, decreased the activity of the Na⁺/K⁺-ATPase by around 50%. This effect was found to be mediated by α2 adrenergic receptors as it was fully abolished in the presence of yohimbine an α2-blocker, but persisted in presence of other adrenergic antagonists. Furthermore, treatment with Rp-cAMP, a PKA inhibitor, mimicked epinephrine’s negative effect and didn’t result in any additional inhibition when both were added simultaneously. Treatment with indomethacin, PP2, SB202190, and PD98059, respective inhibitors of COX enzymes, Src, p38MAPK, and ERK completely abrogated the effect of epinephrine. The effect of epinephrine did not appear also in presence of inhibitors of all four different types of PGE2 receptors. Western blot analysis revealed an epinephrine-induced increase in the phosphorylation of p38 MAPK and ERK that disappeared in presence of respectively PP2 and SB2020190. In addition, an inhibitory effect, similar to that of epinephrine’s, was observed upon incubation with PGE2. It was concluded that epinephrine inhibits the Na⁺/K⁺-ATPase by the sequential activation of α2 adrenergic receptors, Src, p38MAPK, and ERK leading to PGE2 release.

The TPH1 rs211105 gene polymorphism affects abdominal symptoms and quality of life of diarrhea-predominant irritable bowel syndrome

The gastrointestinal symptoms of irritable bowel syndrome are strongly related to impaired quality of life (QOL), especially in diarrhea-predominant. The gene polymorphisms associated with serotonin, or 5-hydroxytryptamine, alter gastrointestinal symptoms and mental status. We aimed to evaluate the effects of gene polymorphisms on gastrointestinal symptoms, psychological conditions, and QOL, and compare these between patients with diarrhea-predominant irritable bowel syndrome (n = 62) and healthy controls (n = 64). The gene polymorphisms of 5-HTTLPR, 5-HTTVNTR, TPH1 rs453773, and TPH1 rs211105 were evaluated. Gastrointestinal symptoms, depressive state, and QOL were assessed using the Gastrointestinal Symptom Rating Scale, Self-rating Depression Scale, and Short-Form-36. Gene polymorphisms did not significantly differ in frequency between the two groups. The scores for diarrhea, abdominal pain, and indigestion significantly correlated with the physical component summary score. Only the group of patients with diarrhea-predominant irritable bowel syndrome showed a significant correlation between the TPH1 rs211105 T/T genotype and lower scores for role physical and mental health, and higher scores for indigestion and diarrhea. 5-HTTLPR l/s was associated with lower score of role emotional in the diarrhea-predominant irritable bowel syndrome and higher scores in the controls. The gene polymorphisms of 5-hydroxytryptamine signaling effected gastrointestinal symptoms and QOL, especially of the patients with diarrhea-predominant irritable bowel syndrome.

Treating Depression with Transcutaneous Auricular Vagus Nerve Stimulation: State of the Art and Future Perspectives

Depression is a highly prevalent disorder, and its treatment is far from satisfactory. There is an urgent need to develop a new treatment for depression. Although still at its early stage, transcutaneous auricular vagus nerve stimulation (taVNS) has shown promising potential for treating depression. In this article, we first summarize the results of clinical studies on the treatment effect of taVNS on depression. Then, we re-analyze a previous study to identify the specific symptoms taVNS can relieve as indicated by subscores of the 24-item Hamilton Depression Scale in patients with depression. We found that taVNS can significantly reduce multiple symptoms of depression patients, including anxiety, psychomotor retardation, sleep disturbance, and hopelessness. Next, we pose several hypotheses on the mechanism of taVNS treatment of depression, including directly and indirectly modulating the activity and connectivity of key brain regions involved in depression and mood regulation; inhibiting neuro-inflammatory sensitization; modulating hippocampal neurogenesis; and regulating the microbiome-brain-gut axis. Finally, we outline current challenges and lay out the future directions of taVNS treatment of depression, which include (1) intensively comparing stimulation parameters and "dose effect" (treatment frequency and duration) to maximize the treatment effect of taVNS; (2) exploring the effect of taVNS on disorders comorbid with depression (such as chronic pain disorders, cardiovascular disorder, and autism) to provide new "two-for-one" treatment approaches for patients with these disorders; and (3) applying multiple scale methods to explore the underlying mechanism of taVNS.