Serotonin: a mediator of the brain-gut connection

The Role of Intestinal Microbiota and Probiotics Supplementation in Multiple Sclerosis Management

Multiple sclerosis (MS) is a neurological autoimmune disorder predominantly afflicting young adults. The etiology of MS is intricate, involving a variety of environmental and genetic factors. Current research increasingly focuses on the substantial contribution of gut microbiota in MS pathogenesis. The commensal microbiota resident within the intestinal milieu assumes a central role within the intricate network recognized as the gut-brain axis (GBA), wielding beneficial impact in neurological and psychological facets. As a result, the modulation of gut microbiota is considered a pivotal aspect in the management of neural disorders, including MS. Recent investigations have unveiled the possibility of using probiotic supplements as a promising strategy for exerting a positive impact on the course of MS. This therapeutic approach operates through several mechanisms, including the reinforcement of gut epithelial integrity, augmentation of the host's resistance against pathogenic microorganisms, and facilitation of mucosal immunomodulatory processes. The present study comprehensively explains the gut microbiome's profound influence on the central nervous system (CNS). It underscores the pivotal role played by probiotics in forming the immune system and modulating neurotransmitter function. Furthermore, the investigation elucidates various instances of probiotic utilization in MS patients, shedding light on the potential therapeutic advantages afforded by this intervention.

Gut microbiota and type 2 diabetes mellitus: a focus on the gut-brain axis

Type 2 diabetes mellitus (T2DM) has become one of the most serious public healthcare challenges, contributing to increased mortality and disability. In the past decades, significant progress has been made in understanding the pathogenesis of T2DM. Mounting evidence suggested that gut microbiota (GM) plays a significant role in the development of T2DM. Communication between the GM and the brain is a complex bidirectional connection, known as the "gut-brain axis," via the nervous, neuroendocrine, and immune systems. Gut-brain axis has an essential impact on various physiological processes, including glucose metabolism, food intake, gut motility, etc. In this review, we provide an outline of the gut-brain axis. We also highlight how the dysbiosis of the gut-brain axis affects glucose homeostasis and even results in T2DM.

Membrane-Mediated Allosteric Action of Serotonin on a Noncognate G-Protein-Coupled Receptor

The structure and dynamics of the lipid membrane can affect the activity of membrane proteins. Therefore, small lipophilic molecules that alter membrane properties (such as the neurotransmitter serotonin) can potentially modulate receptor activity without binding to the receptor. Here, we investigated how the activity of neuropeptide Y type 4 receptor (Y4R, reconstituted in lipid bicelles) is modulated by serotonin, which has no known interaction with Y4R. We found a serotonin-concentration-dependent decrease (down to 0.1 mM of serotonin) in the ligand affinity of Y4R. This effect correlates with a serotonin-induced reduction of the resistance of the bilayer to indentation (measured by atomic force microscopy) and bilayer thickness (measured by solid state NMR) in two different types of zwitterionic lipid bicelles. Our findings indicate a "membrane-mediated allosteric effect" of serotonin on the activation of Y4R and suggest the potential for developing pharmacophores, which can modulate cellular signaling without directly interacting with any receptor.

Adjuvant administration of probiotic effects on sexual function in depressant women undergoing SSRIs treatment: a double-blinded randomized controlled trial

BACKGROUND

According to the Institute of Health Metrics and Evaluation's Global Health Data Exchange (2023) it is estimated that 5% of all adults will experience depressive disorder. Amongst the general loss of pleasure and interest in everyday activities that are symptoms of low mood, reduced sexual desire and sexual dysfunction can be particularly overlooked. Human sexuality is complex, but finding solutions based on scientific evidence to limit the symptoms of depressive disorder and the iatrogenic impact of antidepressant treatment to improve this outcome is an important step in promoting psychological health and general wellbeing.

OBJECTIVE

The present study aimed is to provide scientific evidence to assess the effect of oral probiotic on sexual function in women with depressive disorder treated with Selective Serotonin Reuptake Inhibitors (SSRIs) in an Iranian population.

DESIGN

This study was a double-blind randomized clinical trial. Eligible women were assigned to lactofem plus SSRIs (n = 58) or SSRIs alone (n = 54). In group A, SSRI antidepressants were prescribed together with Lactofem, and in group B, SSRI antidepressants were prescribed alone. Lactofem including Lactobacillus acidophilus 2 × 109 cfu/g, Bifidobacterium bifidus 2 × 109 cfu/g, Lactobacillus rutri 2 × 109 cfu/g, Lactobacillus fermentum 2 × 109 cfu/g; capsule weight of 500 mg bio-capsule administered orally and daily. The duration of intervention in two groups was two months. All questionnaires were completed by the patients before and after the intervention. The Female Sexual Function Index (FSFI), Hamilton Depression Rating Scale and Larson's Sexual Satisfaction Questionnaire were used to evaluate sexual function, severity of depressive disorder and sexual satisfaction, respectively.

RESULTS

Based on the results of the present study, there was a statistically significant difference in sexual satisfaction and severity of depressive disorder between the groups before and after the intervention (P < 0.05). Also, our findings showed that after eight weeks, the Lactofem plus SSRIs group showed significant improvement in FSFI domains and total scores compared to SSRIs alone group (P < 0.05).

CONCLUSIONS

The results of the present study show that taking probiotics for eight weeks may improve the severity of depressive disorder, sexual function and sexual satisfaction in depressed women treated with SSRIs.

TRIAL REGISTRATION

ClinicalTrials.govidentifier: IRCT20160524028038N14 (19/12/2022).

Host miR-129-5p reverses effects of ginsenoside Rg1 on morphine reward possibly mediated by changes in B. vulgatus and serotonin metabolism in hippocampus

Morphine addiction is closely associated with dysbiosis of the gut microbiota. miRNAs play a crucial role in regulating intestinal bacterial growth and are involved in the development of disease. Ginsenoside Rg1 exhibits an anti-addiction effect and significantly improves intestinal microbiota disorders. In pseudo-germfree mice, supplementation with Bacteroides vulgatus (B. vulgatus) synergistically enhanced Rg1 to alleviate morphine addiction. However, it is currently unknown the relationship between fecal miRNAs in morphine-exposed mice and their potential modulation of gut microbiome, as well as their role in mediating the resistance of ginsenoside Rg1 to drug addiction. Here, we studied the fecal miRNA abundance in mice treated with morphine to explore the different miRNAs expressed, their association with B. vulgatus and their role in the amelioration of morphine reward by ginsenoside Rg1. Our results indicated ginsenoside Rg1 attenuated the significant increase in miR-129-5p expression observed in the feces of morphine-treated mice. The miR-129-5p, specifically, inhibited the growth of B. vulgatus by modulating the transcript of the site-tag BVU_RS11835 and increased the levels of 5-hydroxytryptophan and indole-3-carboxaldehyde in vitro. Subsequently, we noticed that oral administration of synthetic miR-129-5p increased 5-HT levels in the hippocampus and inhibited the reversal effect of ginsenoside Rg1 both on the relative abundance of B. vulgatus in the feces and CPP effect induced by morphine exposure. In short, Ginsenoside Rg1 might play an indirect role in remodeling the B. vulgatus against morphine reward by suppressing miR-129-5p expression. These results highlight the role of miR-129-5p and B. vulgatus in morphine reward and the anti-morphine addiction of ginsenoside Rg1.

2'-Fucosyllactose (2'-FL) changes infants gut microbiota composition and their metabolism in a host-free human colonic model

BACKGROUND

Breast milk is critical for neonates, providing the necessary energy, nutrients, and bioactive compounds for growth and development. Research indicated that human milk oligosaccharides (HMOs) have been shown to shape a beneficial gut microbiota, as well as their metabolism (e.g. short-chain fatty acids). 2'-Fucosyllactose (2'-FL) is one major HMO that composed of 30% of total HMOs.

OBJECTIVES

This study aimed to understand the impact of 2'-FL on the composition and metabolism of infant gut microbiota.

METHODS

Our study utilized an in-vitro human colonic model (HCM) to investigate the host-free interactions between 2'-FL and infant gut microbiota. To simulate the infant gut microbiota, we inoculated the HCM system with eight representative bacterial species from infant gut microbiota. The effects of 2'-FL on the gut microbial composition and their metabolism were determined through real-time quantitative PCR and liquid-chromatography mass spectrometry (LC/MS). The obtained data were analyzed using Compound Discoverer 3.1 and MetaboAnalyst 4.0.

RESULTS

Our study findings suggest that the intervention of 2'-FL in HCM resulted in a significant change in the abundance of representative bacterial species. PCR analysis showed a consistent increase in the abundance of Parabacteroides. distasonis in all three colon sections. Furthermore, analysis of free fatty acids revealed a significant increase in their levels in the ascending, transverse, and descending colons, except for caproic acid, which was significantly reduced to a non-detectable level. The identification of significant extracellular polar metabolites, such as glutathione and serotonin, enabled us to distinguish between the metabolomes before and after 2'-FL intervention. Moreover, correlation analysis revealed a significant association between the altered microbes and microbial metabolites.

CONCLUSIONS

In summary, our study demonstrated the impact of 2'-FL intervention on the defined composition of infant gut microbiota and their metabolic pathways in an in vitro setting. Our findings provide valuable insights for future follow-up investigations into the role of 2'-FL in regulating the growth and development of infant gut microbiota in vivo.

Antidepressant-like Effects of Representative Types of Food and Their Possible Mechanisms

Depression is a mental disorder characterized by low mood, lack of motivation, negative cognitive outlook, and sleep problems. Suicide may occur in severe cases, although suicidal thoughts are not seen in all cases. Globally, an estimated 350 million individuals grapple with depression, as reported by the World Health Organization. At present, drug and psychological treatments are the main treatments, but they produce insufficient responses in many patients and fail to work at all in many others. Consequently, treating depression has long been an important topic in society. Given the escalating prevalence of depression, a comprehensive strategy for managing its symptoms and impacts has garnered significant attention. In this context, nutritional psychiatry emerges as a promising avenue. Extensive research has underscored the potential benefits of a well-rounded diet rich in fruits, vegetables, fish, and meat in alleviating depressive symptoms. However, the intricate mechanisms linking dietary interventions to brain function alterations remain largely unexplored. This review delves into the intricate relationship between dietary patterns and depression, while exploring the plausible mechanisms underlying the impact of dietary interventions on depression management. As we endeavor to unveil the pathways through which nutrition influences mental well-being, a holistic perspective that encompasses multidisciplinary strategies gains prominence, potentially reshaping how we approach and address depression.

The efficacy and neural mechanism of acupuncture therapy in the treatment of visceral hypersensitivity in irritable bowel syndrome

Irritable Bowel Syndrome (IBS) is a complex functional gastrointestinal disorder primarily characterized by chronic abdominal pain, bloating, and altered bowel habits. Chronic abdominal pain caused by visceral Hypersensitivity (VH) is the main reason why patients with IBS seek medication. Significant research effort has been devoted to the efficacy of acupuncture as a non-drug alternative therapy for visceral-hyperalgesia-induced IBS. Herein, we examined the central and peripheral analgesic mechanisms of acupuncture in IBS treatment. Acupuncture can improve inflammation and relieve pain by reducing 5-hydroxytryptamine and 5-HT3A receptor expression and increasing 5-HT4 receptor expression in peripheral intestinal sensory endings. Moreover, acupuncture can also activate the transient receptor potential vanillin 1 channel, block the activity of intestinal glial cells, and reduce the secretion of local pain-related neurotransmitters, thereby weakening peripheral sensitization. Moreover, by inhibiting the activation of N-methyl-D-aspartate receptor ion channels in the dorsal horn of the spinal cord and anterior cingulate cortex or releasing opioids, acupuncture can block excessive stimulation of abnormal pain signals in the brain and spinal cord. It can also stimulate glial cells (through the P2X7 and prokinetic protein pathways) to block VH pain perception and cognition. Furthermore, acupuncture can regulate the emotional components of IBS by targeting hypothalamic-pituitary-adrenal axis-related hormones and neurotransmitters via relevant brain nuclei, hence improving the IBS-induced VH response. These findings provide a scientific basis for acupuncture as an effective clinical adjuvant therapy for IBS pain.

Microbiome-metabolomics analysis reveals abatement effects of itaconic acid on odorous compound production in Arbor Acre broilers

BACKGROUND

Public complaints concerning odor emissions from intensive livestock and poultry farms continue to grow, as nauseous odorous compounds have adverse impacts on the environment and human health. Itaconic acid is a metabolite from the citric acid cycle of the host and shows volatile odor-reducing effects during animal production operations. However, the specific role of itaconic acid in decreasing intestinal odorous compound production remains unclear. A total of 360 one-day-old chicks were randomly divided into 6 treatment groups: control group (basal diet) and itaconic acid groups (basal diet + 2, 4, 6, 8 and 10 g/kg itaconic acid). The feeding experiment lasted for 42 d.

RESULTS

Dietary itaconic acid supplementation linearly and quadratically decreased (P < 0.05) the cecal concentrations of indole and skatole but did not affect (P > 0.05) those of lactic, acetic, propionic and butyric acids. The cecal microbial shift was significant in response to 6 g/kg itaconic acid supplementation, in that the abundances of Firmicutes, Ruminococcus and Clostridium were increased (P < 0.05), while those of Bacteroidetes, Escherichia-Shigella and Bacteroides were decreased (P < 0.05), indicative of increased microbial richness and diversity. Furthermore, a total of 35 significantly (P < 0.05) modified metabolites were obtained by metabolomic analysis. Itaconic acid decreased (P < 0.05) the levels of nicotinic acid, nicotinamide, glucose-6-phosphate, fumatic acid and malic acid and increased (P < 0.05) 5-methoxytroptomine, dodecanoic acid and stearic acid, which are connected with the glycolytic pathway, citrate acid cycle and tryptophan metabolism. Correlation analysis indicated significant correlations between the altered cecal microbiota and metabolites; Firmicutes, Ruminococcus and Clostridium were shown to be negatively correlated with indole and skatole production, while Bacteroidetes, Escherichia-Shigella and Bacteroides were positively correlated with indole and skatole production.

CONCLUSIONS

Itaconic acid decreased cecal indole and skatole levels and altered the microbiome and metabolome in favor of odorous compound reduction. These findings provide new insight into the role of itaconic acid and expand its application potential in broilers.

Prolonged darkness attenuates imidacloprid toxicity through the brain-gut-microbiome axis in zebrafish, Danio rerio

The present study investigated the toxic effects of IMI on brain and gut of zebrafish (Danio rerio) by a combination of transcriptome and microbiome analysis. In addition, the involvement of light/dark period was also evaluated. An acute toxic test was conducted on adult zebrafish weighing 0.45 ± 0.02 g with 4 experimental groups (n = 15): 1) IMI group (Light: Dark = 12: 12 h), 2) prolonged light group (Light: Dark = 20: 4 h), 3) prolonged darkness group (Light: Dark = 4: 20 h) which received 20 mg/L of IMI, and 4) control group, which was not treated with IMI (Light: Dark = 12: 12 h). The results showed that prolonged darkness improved the survival rate of zebrafish upon IMI exposure for 96 h. In the sub-chronic test, zebrafish were divided into the same 4 groups and exposed to IMI at 1 mg/L for 14 d (n = 30). The results showed that IMI induced oxidative stress in both IMI and prolonged light groups by inhibition of antioxidant activities and accumulation of oxidative products. Transcriptome analysis revealed a compromise of antioxidation and tryptophan metabolism pathways under IMI exposure. Several genes encoding rate-limiting enzymes in serotonin and melatonin synthesis were all inhibited in both IMI and LL groups. Meanwhile, significant decrease (P < 0.5) of serotonin and melatonin levels was observed. However, there's remarkable improvement of biochemical and transcriptional status in prolonged darkness group. In addition, microbiome analysis showed great alteration of gut bacterial community structure and inhibition of tryptophan metabolism pathway. Similarly, the gut microbiota dysbiosis induced by IMI was alleviated in prolonged darkness. In summary, sub-chronic IMI exposure induced neurotoxicity and gut toxicity in zebrafish by oxidative stress and impaired the brain-gut-axis through tryptophan metabolism perturbation. Prolonged darkness could effectively attenuate the IMI toxicity probably through maintaining a normal tryptophan metabolism.

The brain-gut-microbiota axis in the treatment of neurologic and psychiatric disorders

The human gut microbiota is a complex ecosystem made of trillions of microorganisms. The composition can be affected by diet, metabolism, age, geography, stress, seasons, temperature, sleep, and medications. The increasing evidence about the existence of a close and bi-directional correlation between the gut microbiota and the brain indicates that intestinal imbalance may play a vital role in the development, function, and disorders of the central nervous system. The mechanisms of interaction between the gut-microbiota on neuronal activity are widely discussed. Several potential pathways are involved with the brain-gut-microbiota axis, including the vagus nerve, endocrine, immune, and biochemical pathways. Gut dysbiosis has been linked to neurological disorders in different ways that involve activation of the hypothalamic-pituitary-adrenal axis, imbalance in neurotransmitter release, systemic inflammation, and increase in the permeability of the intestinal and the blood-brain barrier. Mental and neurological diseases have become more prevalent during the coronavirus disease 2019pandemic and are an essential issue in public health globally. Understanding the importance of diagnosing, preventing, and treating dysbiosis is critical because gut microbial imbalance is a significant risk factor for these disorders. This review summarizes evidence demonstrating the influence of gut dysbiosis on mental and neurological disorders.

Systematic review and meta-analysis of calculating degree of comorbidity of irritable bowel syndrome with migraine

BACKGROUND

Irritable bowel syndrome (IBS) and migraines are often comorbid each other. These disorders are likely to be bidirectionally linked through the gut-brain axis and share several underlying mechanisms including central nervous system sensitization. However, quantitative analysis of comorbidity was not reported enough. The aim of this systematic review and meta-analysis was to calculate the present degree of comorbidity of these two disorders.

METHODS

A literature search was performed searching for articles describing IBS or migraine patients with the same inverse comorbidity. Pooled odds ratios (ORs) or hazard ratios (HRs) with 95% confidence intervals (CIs) were then extracted. The total effect estimates were determined and presented by random effect forest plots for the group of articles with IBS patients with migraine and the group of articles on migraine sufferers with comorbid IBS separately. The average results of these plots were compared.

RESULTS

The literature search resulted in initial 358 articles and final 22 articles for the meta-analysis. The total OR values obtained were 2.09 [1.79 - 2.43] in IBS with comorbid migraine or headache, 2.51 [1.76 - 3.58] for migraineurs with comorbid IBS and an overall HR of 1 .62 [1.29 - 2.03] was found for cohort studies of migraine sufferers with comorbid IBS. A similar expression of a selection of other comorbidities was found in IBS and migraine patients, especially for depression and fibromyalgia a strong similarity was found in their expression rate.

CONCLUSIONS

This systematic review with meta-analysis was the first to combine data on IBS patients with comorbid migraine and migraineurs with comorbid IBS. The fact that closely related existential rates were observed between these two groups should be used as motivation for future research to further investigate these disorders for why this similarity occurs. Mechanisms involved in central hypersensitivity such as genetic risk factors, mitochondrial dysfunction and microbiota are particularly good candidates. Experimental designs in which therapeutic methods for these conditions can be exchanged or combined may also lead to the discovery of more efficient treatment methods.

Getting closer to modeling the gut-brain axis using induced pluripotent stem cells

The gut microbiome (GM), the gut barrier, and the blood-brain barrier (BBB) are key elements of the gut-brain axis (GBA). The advances in organ-on-a-chip and induced pluripotent stem cell (iPSCs) technology might enable more physiological gut-brain-axis-on-a-chip models. The ability to mimic complex physiological functions of the GBA is needed in basic mechanistic research as well as disease research of psychiatric, neurodevelopmental, functional, and neurodegenerative diseases, such as Alzheimer’s disease and Parkinson’s disease. These brain disorders have been associated with GM dysbiosis, which may affect the brain via the GBA. Although animal models have paved the way for the breakthroughs and progression in the understanding of the GBA, the fundamental questions of exactly when, how, and why still remain unanswered. The research of the complex GBA have relied on equally complex animal models, but today’s ethical knowledge and responsibilities demand interdisciplinary development of non-animal models to study such systems. In this review we briefly describe the gut barrier and BBB, provide an overview of current cell models, and discuss the use of iPSCs in these GBA elements. We highlight the perspectives of producing GBA chips using iPSCs and the challenges that remain in the field.

Changes in Tryptophan Metabolism on Serotonin and Kynurenine Pathways in Patients with Irritable Bowel Syndrome

(1) Background: L-tryptophan is a substrate for the synthesis of many biological compounds through the serotonin and kynurenine pathways. These compounds have a significant influence on gastrointestinal functions and mental processes. The aim of the study was to evaluate the urinary excretion of selected tryptophan metabolites in patients with constipation-predominant and diarrhoea-predominant irritable bowel syndrome (IBS-C and IBS-D, respectively), related to somatic and mental symptoms. (2) Methods: 120 people were included in the study and three groups were distinguished, with 40 individuals each, including healthy subjects (controls), patients with IBS-C and patients with IBS-D. The Gastrointestinal Symptoms Rating Scale (GSRS-IBS) was used to assess the severity of abdominal symptoms. The Hamilton Anxiety Rating Scale (HAM-A) and Hamilton Depression Rating Scale (HAM-D) were used to evaluate the mental state of patients. Using liquid chromatography tandem mass spectrometry (LC-MS/MS), L-tryptophan and the following metabolites in urine, related to the creatinine level, were measured: 5-hydroxyindoleacetic acid (5-HIAA), kynurenine (KYN), kynurenic acid (KYNA) and quinolinic acid (QA). (3) Results: In both groups of patients with IBS, changes in tryptophan metabolism were found as compared to the control group. We observed an increase in the activity of the serotonin pathway and a positive correlation between the 5-HIAA level and the GSRS score (p < 0.01) and HAM-A score (p < 0.001) in IBS-D patients. The IBS-C group was characterized by a higher concentration of kynurenines (KYN, QA) in urine. Moreover, the QA (p < 0.001) and KYNA (p < 0.05) levels were correlated with the HAM-D score among IBS-C patients. (4) Conclusions: Various changes in the tryptophan metabolism pathway can determine the differences in the clinical picture of irritable bowel syndrome. These results should be included in the nutritional and pharmacological treatment of this syndrome.

Meta-Analysis of the Association Between 5-Hydroxytryptamine Transporter Gene-Linked Polymorphic Region and Functional Dyspepsia and its Subtypes

Background: Association studies of variations in the 5-hydroxytryptamine (5-HT, serotonin) transporter gene-linked polymorphic region (5-HTTLPR) and functional dyspepsia (FD) have yielded contradictory results. Hence, we performed a meta-analysis to clarify inconsistencies between the 5-HTTLPR polymorphism with FD and it subtypes. Methods: We performed a literature search in PubMed, Embase, Web of Science, Cochrane Library, and CNKI, including articles published until March 2022. We calculated and pooled odds ratios (ORs) with their 95% confidence intervals (CIs) in Stata 15.0. Data extraction was performed in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines and Cochrane Handbook for Systematic Reviews of Interventions. Results: The meta-analysis included six studies, comprising 488 cases and 1513 healthy controls. We did not observe a significant association between the 5-HTTLPR polymorphism and FD in the overall population. In subgroup analyses, the 5-HTTLPR polymorphism was significantly associated with FD-subtype epigastric pain syndrome (EPS) (SS vs. LL+LS, OR = 0.620, 95% CI: 0.414-0.930; SS vs. LS, OR = 0.640, 95% CI: 0.417-0.980; S vs. L, OR = 0.655, 95% CI: 0.471-0.911). However, no association was observed with the other subtype, postprandial distress syndrome (PDS). Conclusion: While the 5-HTTLPR polymorphism had no relationship with FD overall, splitting the disease into its subtypes revealed a clear association with EPS.

Progress in Investigational Agents Targeting Serotonin-6 Receptors for the Treatment of Brain Disorders

Serotonin (5-HT) plays an important role in the regulation of several basic functions of the central and peripheral nervous system. Among the 5-HT receptors, serotonin-6 (5-HT6) receptor has been an area of substantial research. 5-HT6 receptor is a G-protein-coupled receptor mediating its effects through diverse signaling pathways. Exceptional features of the receptors fueling drug discovery efforts include unique localization and specific distribution in the brain regions having a role in learning, memory, mood, and behavior, and the affinity of several clinically used psychotropic agents. Although non-clinical data suggest that both agonist and antagonist may have similar behavioral effects, most of the agents that entered clinical evaluation were antagonists. Schizophrenia was the initial target; more recently, cognitive deficits associated with Alzheimer's disease (AD) or other neurological disorders has been the target for clinically evaluated 5-HT6 receptor antagonists. Several 5-HT6 receptor antagonists (idalopirdine, intepirdine and latrepirdine) showed efficacy in alleviating cognitive deficits associated with AD in the proof-of-concept clinical studies; however, the outcomes of the subsequent phase 3 studies were largely disappointing. The observations from both non-clinical and clinical studies suggest that 5-HT6 receptor antagonists may have a role in the management of neuropsychiatric symptoms in dementia. Masupirdine, a selective 5-HT6 receptor antagonist, reduced agitation/aggression-like behaviors in animal models, and a post hoc analysis of a phase 2 trial suggested potential beneficial effects on agitation/aggression and psychosis in AD. This agent will be assessed in additional trials, and the outcome of the trials will inform the use of 5-HT6 receptor antagonists in the treatment of agitation in dementia of the Alzheimer's type.

The Serotonergic System and Amyotrophic Lateral Sclerosis: A Review of Current Evidence

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disorder characterized by the premature death of motor neurons. Serotonin (5-HT) is a crucial neurotransmitter, and its dysfunction, whether as a contributor or by-product, has been implicated in ALS pathogenesis. Here, we summarize current evidence linking serotonergic alterations to ALS, including results from post-mortem and neuroimaging studies, biofluid testing, and studies of ALS animal models. We also discuss the possible role of 5-HT in modulating some important mechanisms of ALS (i.e. glutamate excitotoxity and neuroinflammation) and in regulating ALS phenotypes (i.e. breathing dysfunction and metabolic defects). Finally, we discuss the promise and limitations of the serotonergic system as a target for the development of ALS biomarkers and therapeutic approaches. However, due to a relative paucity of data and standardized methodologies in previous studies, proper interpretation of existing results remains a challenge. Future research is needed to unravel the mechanisms linking serotonergic pathways and ALS and to provide valid, reproducible, and translatable findings.

Lactobacillus acidophilus regulates abnormal serotonin availability in experimental ulcerative colitis

OBJECTIVES

Probiotics are known to play a beneficial role in curing irritable bowel syndrome such as ulcerative colitis. Commensal Lactobacillus species are thought to play a protective role against ulcerative colitis, as they restore homeostasis in intestinal disorders. Abnormal serotonin availability has been described in ulcerative colitis, but the underlying mechanism is still unclear. The aim of this study was to determine the anti-inflammatory role of Lactobacillus acidophilus (L. acidophilus) and its effect on serotonin expression.

METHODS

Ulcerative colitis was created with the intrarectal administration of acetic acid. A total of 40 adult male rats were divided into five groups of eight rats as control, sham, experimental colitis, treatment (Colitis + L. acidophilus) and protective group (L. acidophilus + colitis). To evaluate the effects of L. acidophilus on serotonin expression in ulcerative colitis, this bacterial strain was administered orally to the rats with acetic acid-induced colitis. After oral administration of L. acidophilus for 14 days, serotonin content was biochemically measured and serotonin expression was evaluated immunohistochemically.

RESULTS

The expression of serotonin and its protein content was significantly increased in colitis compared to the control and sham groups. Abnormal serotonin availability in the rats with acetic acid-induced colitis was significantly reduced by the L. acidophilus.

CONCLUSIONS

In our study, it was observed that the amount of serotonin in the intestinal tissue increased excessively with ulcerative colitis. In addition, L.acidophilus has been found to reduce the abnormally increased amount of serotonin in the colon tissue, as well as reduce the inflammation in the intestinal tissue that occurs with ulcerative colitis. With our findings, it is predicted that probiotic application can be used as a treatment option in ulcerative colitis.

Are Drugs Associated with Microscopic Colitis? A Systematic Review and Meta-Analysis

There is growing evidence of the association of Microscopic Colitis (MC) with the use of specific medications such as proton pump inhibitors (PPIs), Selective serotonin reuptake inhibitors (SSRIs), Non-Steroidal anti-inflammatory drugs (NSAIDs), Statins and H2-receptor antagonists (H2RA). In our study, we calculated the pooled odds of MC in patients using these drugs. We performed a detailed search of major databases, including PubMed/Medline, Scopus, web of science, and Embase, to include the studies in which odds of MC were reported after using above mentioned drugs. A random-effects model was used to pool the estimates. Thirteen studies were included in our analysis consisting of 304,482 patients (34,194 cases and 270,018 controls). In eight studies, the control group consisted of a random population selected based on age, gender and same birth year, whereas 3 studies recruited patients who presented with diarrhea and underwent colonoscopy and biopsy to rule out MC. Two studies reported odds of MC for both diarrhea and random control groups. Patients taking PPIs were more likely to develop MC, AOR 2.65 (95% CI 1.81-3.50, I² 98.13%). Similarly, higher odds of association were found in patients taking SSRIs (OR 2.12, 95% CI 1.27-2.96, I² 96.46%), NSAIDs (OR 2.02, 95% CI 1.33-2.70, I² 92.70%) and Statins (OR 1.74, 95% CI 1.19-2.30, I² 96.36%). No difference in odds of developing MC was seen in patients using H2RA compared to the control group (OR 2.70, 95% CI 0.32-5.08, I² 98.67%). We performed a subgroup analysis based on the control group and found higher odds of MC in patients on PPIs compared to the random control group (OR 4.55, 95% CI 2.90-6.19, I² 98.13%). Similarly, higher odds of MC were noted for SSRI (OR 3.23, 95% CI 1.54-4.92, I² 98.31%), NSAIDs (OR 3.27, 95% CI 2.06-4.48, I² 95.38%), and Statins (OR 2.23, 95% CI 1.41-3.06, I² 98.11%) compared to the random control group. Contrary lower odds of MC were seen in the PPI and H2RA group compared to the diarrhea control group (OR 0.68, 95% CI 0.48-0.88, I² 7.26%), (OR 0.46, 95% CI 0.14-0.78, I² 0%) respectively. We found no difference in odds of MC in patients on SSRIs (OR 0.96, 95% CI 0.49-1.42, I² 37.89%), NSAIDs (OR 1.13, 95% CI 0.49-1.76, I² 59.37%) Statins (OR 0.91, 95% 0.66-1.17, I² 0%) and H2RA (OR 3.48, 95% CI -0.41-7.36, I² 98.89%) compared to the diarrhea control group. We also analyzed the association use of PPIs and NSAIDs with the development of collagenous colitis (CC) and lymphocytic colitis. Only the use of NSAIDs was associated with increased odds of developing collagenous colitis (OR 1.61, 95% CI 1.50-1.72, I² 0%). No increased odds of CC and LC were seen in PPI users. PPIs, NSAIDs, SSRIs, and Statins are associated with an increased risk of MC compared to the random control group. On the contrary, the use of PPIs, NSAIDs, SSRIs, and Statins is not associated with an increased risk of MC when compared to the diarrhea control group.

Mechanism and potential treatments for gastrointestinal dysfunction in patients with COVID-19

The global coronavirus disease 2019 (COVID-19) has become one of the biggest threats to the world since 2019. The respiratory and gastrointestinal tracts are the main targets for severe acute respiratory syndrome coronavirus 2 infection for they highly express angiotensin-converting enzyme-2 and transmembrane protease serine 2. In patients suffering from COVID-19, gastrointestinal symptoms have ranged from 12% to 61%. Anorexia, nausea and/or vomiting, diarrhea, and abdominal pain are considered to be the main gastrointestinal symptoms of COVID-19. It has been reported that the direct damage of intestinal mucosal epithelial cells, malnutrition, and intestinal flora disorders are involved in COVID-19. However, the underlying mechanisms remain unclear. Thus, in this study, we reviewed and discussed the correlated mechanisms that cause gastrointestinal symptoms in order to help to develop the treatment strategy and build an appropriate guideline for medical workers.

Neurotransmitters Regulation and Food Intake: The Role of Dietary Sources in Neurotransmission

Neurotransmitters (NTs) are biologically active chemicals, which mediate the electrochemical transmission between neurons. NTs control numerous organic functions particularly crucial for life, including movement, emotional responses, and the physical ability to feel pleasure and pain. These molecules are synthesized from simple, very common precursors. Many types of NTs have both excitatory and inhibitory effects. Neurotransmitters' imbalance can cause many diseases and disorders, such as Parkinson's disease, depression, insomnia, increased anxiety, memory loss, etc. Natural food sources containing NTs and/or their precursors would be a potential option to help maintain the balance of NTs to prevent brain and psychiatric disorders. The level of NTs could be influenced, therefore, by targeting dietary habits and nutritional regimens. The progressive implementation of nutritional approaches in clinical practice has made it necessary to infer more about some of the nutritional NTs in neuropsychiatry. However, the importance of the intake of nutritional NTs requires further understanding, since there are no prior significant studies about their bioavailability, clinical significance, and effects on nerve cells. Interventional strategies supported by evidence should be encouraged.

The Oncobiome in Gastroenteric and Genitourinary Cancers

Early evidence suggests a strong association of microorganisms with several human cancers, and great efforts have been made to understand the pathophysiology underlying microbial carcinogenesis. Bacterial dysbiosis causes epithelial barrier failure, immune dysregulation and/or genotoxicity and, consequently, creates a tumor-permissive microenvironment. The majority of the bacteria in our body reside in the gastrointestinal tract, known as gut microbiota, which represents a complex and delicate ecosystem. Gut microbes can reach the pancreas, stomach and colon via the bloodstream. Oral bacterial translocations can also occur. In the stomach, pancreas and colon, low microbial diversity is associated with cancer, in particular with a bad prognosis. The urogenital tract also harbors unique microbiota, distinct from the gut microbiota, which might have a role in the urinary and female/male reproductive cancers’ pathogenesis. In healthy women, the majority of bacteria reside in the vagina and cervix and unlike other mucosal sites, the vaginal microbiota exhibits low microbial diversity. Genital dysbiosis might have an active role in the development and/or progression of gynecological malignancies through mechanisms including modulation of oestrogen metabolism. Urinary dysbiosis may influence the pathogenesis of bladder cancer and prostate cancer in males. Modulation of the microbiome via pre, pro and postbiotics, fecal or vaginal microbiota transplantation and engineering bacteria might prove useful in improving cancer treatment response and quality of life. Elucidating the complex host-microbiome interactions will result in prevention and therapeutic efficacy interventions.

Real-time monitoring of serotonin with highly selective aptamer-functionalized conducting polymer nanohybrids

Adequate serotonin levels are pivotal to human well-being; thus, serotonin can be used as a biomarker because it regulates a wide range of physical and psychological functions. As an imbalance of serotonin is highly likely to initiate the pathogenesis of various disorders, monitoring serotonin levels in real time is in high demand for the early detection of disease. We fabricated a field-effect transistor (FET) biosensor based on aptamer-immobilized conducting polymer nanohybrids, which showed an instantaneous response toward serotonin in solution. The mechanism of serotonin detection was based on aptamer deformation after aptamer-ligand interaction and the consequential decrease in the charge carrier density of the FET template. Docking simulations with AutoDock/Vina and PyMOL were successfully used to investigate the binding site of serotonin in the loop structure of the aptamer. The fabricated FET template showed high sensitivity toward serotonin in the range of 10 fM to 100 nM, and the limit of detection (LOD) was exceptionally low at 10 fM. Moreover, the selectivity toward serotonin was confirmed by observing no signal after the injection of structural analogs, functional analogs and excess physiological biomolecules. The potential clinical application of this sensor was confirmed because it remained consistent when the buffer solution was exchanged for artificial serum or artificial cerebrospinal fluid (CSF). ^† S.G.L. and S.E.S. contributed equally to this work.

Ginsenoside Rg1 mitigates morphine dependence via regulation of gut microbiota, tryptophan metabolism, and serotonergic system function

BACKGROUND

Morphine dependence, a devastating neuropsychiatric condition, may be closely associated with gut microbiota dysbiosis. Ginsenoside Rg1 (Rg1), an active ingredient extracted from the roots of Panax ginseng C.A. Meyer, has potential health-promoting effects on the nervous system. However, its role in substance use disorders remains unclear. Here, we explored the potential modulatory roles of Rg1 in protection against morphine dependence.

METHODS

Conditioned place preference (CPP) was used for establishing a murine model of morphine dependence. 16S rRNA gene sequencing and metabolomics were performed for microbial and metabolite analysis. Molecular analysis was tested for evaluating the host serum and brain responses.

RESULTS

Rg1 prevented morphine-induced CPP in mice. The 16S rRNA gene-based microbiota analysis demonstrated that Rg1 ameliorated morphine-induced gut microbiota dysbiosis, specifically for Bacteroidetes. Moreover, Rg1 also inhibited gut microbiota-derived tryptophan metabolism and reduced the serotonin, 5-hydroxytryptamine receptor 1B (5-HTR1B), and 5-hydroxytryptamine receptor 2 A (5-HTR2A) levels. However, the Rg1-induced amelioration of CPP was not observed in mice when their gut microbiome was depleted by non-absorbable antibiotics. Subsequently, gavage with Bacteroides vulgatus increased the abundance of Bacteroidetes. B. vulgatus supplementation synergistically enhanced Rg1-alleviated morphine-induced CPP in mice with microbiome knockdown. Co-treatment with B. vulgatus and Rg1 produced suppressive effects against morphine dependency by inhibiting tryptophan metabolism and reducing the serotonin and 5-HTR1B/5-HTR2A levels.

CONCLUSIONS

The gut microbiota-tryptophan metabolism-serotonin plays an important role in gut-brain signaling in morphine disorders, which may represent a novel approach for drug dependence treatment via manipulation of the gut microbial composition and tryptophan metabolite.

Serotonin modulates insect gut bacterial community homeostasis

Background

Metazoan guts are in permanent contact with microbial communities. However, the host mechanisms that have developed to manage the dynamic changes of these microorganisms and maintain homeostasis remain largely unknown.

Results

Serotonin (5-hydroxytryptamine [5-HT]) was found to modulate gut microbiome homeostasis via regulation of a dual oxidase (Duox) gene expression in both Bactrocera dorsalis and Aedes aegypti. The knockdown of the peripheral 5-HT biosynthetic gene phenylalanine hydroxylase (TPH) increased the expression of Duox and the activity of reactive oxygen species, leading to a decrease in the gut microbiome load. Moreover, the TPH knockdown reduced the relative abundance of the bacterial genera Serratia and Providencia, including the opportunistic pathogens, S. marcescens and P. alcalifaciens in B. dorsalis. Treatment with 5-hydroxytryptophan, a precursor of 5-HT synthesis, fully rescued the TPH knockdown-induced phenotype.

Conclusions

The findings reveal the important contribution of 5-HT in regulating gut homeostasis, providing new insights into gut–microbe interactions in metazoans.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12915-022-01319-x.

Effect of sumatriptan on acetic acid-induced experimental colitis in rats: a possible role for the 5-HT1B/1D receptors

Mucosal inflammation in colitis is associated with changes in the intestinal serotonin (5-HT) level. Sumatriptan, a 5-HT_1B/1D receptor agonist, has demonstrated anti-inflammatory characteristics. The purpose of this study was to determine the effects of sumatriptan in a rat model of acute experimental colitis and to elucidate the probable participation of presynaptic 5-HT_1B/1D receptors. To induce colitis, acetic acid (4%) was injected intrarectally. Treatments were given intraperitoneally (IP) once daily over 3 consecutive days starting 1-h post-induction. Sumatriptan was given at 0.5, 1, 2, and 5 mg/kg. GR-127935, a 5-HT_1B/1D receptor antagonist, was injected (0.1 and 0.3 mg/kg) 30 min prior to the most effective dose of sumatriptan (1 mg/kg). On day 4, the colon samples were isolated. Significant enhancements of the tissue tumor necrosis factor-alpha (TNF-α), myeloperoxidase (MPO), microscopic and macroscopic damages, body weight losses, and also reductions in tissue superoxide dismutase (SOD) and 5-HT were observed in colitis rats. On the other hand, sumatriptan at doses 0.5, 1, and 2 mg/kg could diminish pathologic changes in the measured biomarkers, histopathologic damages, and body weight losses. Although GR-127935 at dose 0.3 mg/kg could markedly improve the pathologic indexes, its sub-effective dose (0.1 mg/kg) reversed the protective effect of sumatriptan (1 mg/kg). Moreover, sumatriptan (1 and 5 mg/kg) and GR-127935 (0.3 mg/kg) increased the serotonin level. Post-treatment with low-dose sumatriptan demonstrated a protective impact on this peripheral inflammatory condition. Notably, this protective effect may be mediated, at least in part, through 5-HT_1B/1D receptors, as well as anti-inflammatory and anti-oxidative characteristics.

Streptozotocin-Induced Diabetes Causes Changes in Serotonin-Positive Neurons in the Small Intestine in Pig Model

Serotonin (5-hydroxytryptamine or 5-HT) is an important neurotransmitter of the central and peripheral nervous systems, predominantly secreted in the gastrointestinal tract, especially in the gut. 5-HT is a crucial enteric signaling molecule and is well known for playing a key role in sensory-motor and secretory functions in the gut. Gastroenteropathy is one of the most clinical problems in diabetic patients with frequent episodes of hyperglycemia. Changes in 5-HT expression may mediate gastrointestinal tract disturbances seen in diabetes, such as nausea and diarrhea. Based on the double immunohistochemical staining, this study determined the variability in the population of 5-HT-positive neurons in the porcine small intestinal enteric neurons in the course of streptozotocin-induced diabetes. The results show changes in the number of 5-HT-positive neurons in the examined intestinal sections. The greatest changes were observed in the jejunum, particularly within the myenteric plexus. In the ileum, both de novo 5-HT synthesis in the inner submucosal plexus neurons and an increase in the number of neurons in the outer submucosal plexus were noted. The changes observed in the duodenum were also increasing in nature. The results of the current study confirm the previous observations concerning the involvement of 5-HT in inflammatory processes, and an increase in the number of 5-HT -positive neurons may also be a result of increased concentration of the 5-HT in the gastrointestinal tract wall and affects the motor and secretory processes, which are particularly intense in the small intestines.

Mechanistic Insights into the Link between Gut Dysbiosis and Major Depression: An Extensive Review

Depression is a highly common mental disorder, which is often multifactorial with sex, genetic, environmental, and/or psychological causes. Recent advancements in biomedical research have demonstrated a clear correlation between gut dysbiosis (GD) or gut microbial dysbiosis and the development of anxiety or depressive behaviors. The gut microbiome communicates with the brain through the neural, immune, and metabolic pathways, either directly (via vagal nerves) or indirectly (via gut- and microbial-derived metabolites as well as gut hormones and endocrine peptides, including peptide YY, pancreatic polypeptide, neuropeptide Y, cholecystokinin, corticotropin-releasing factor, glucagon-like peptide, oxytocin, and ghrelin). Maintaining healthy gut microbiota (GM) is now being recognized as important for brain health through the use of probiotics, prebiotics, synbiotics, fecal microbial transplantation (FMT), etc. A few approaches exert antidepressant effects via restoring GM and hypothalamus–pituitary–adrenal (HPA) axis functions. In this review, we have summarized the etiopathogenic link between gut dysbiosis and depression with preclinical and clinical evidence. In addition, we have collated information on the recent therapies and supplements, such as probiotics, prebiotics, short-chain fatty acids, and vitamin B12, omega-3 fatty acids, etc., which target the gut–brain axis (GBA) for the effective management of depressive behavior and anxiety.

The herbal preparation STW 5 affects serotonergic pathways in the brain and colon as well as stress parameters in experimental irritable bowel syndrome

BACKGROUND

Exposure to stress has been related to disturbance in 5-hydroxytryptamine (5-HT) signaling in the brain-gut axis and is considered as a major predisposing factor for the development of irritable bowel syndrome (IBS). The present study aimed to investigate the possible involvement of 5-HT and some other stress-related parameters in the effectiveness of STW 5 against stress-induced IBS.

METHODS

Rats were subjected to restraint stress (RS) for 1 h/day for 14 consecutive days to induce IBS-like symptoms and were given STW 5 orally at the same time. At the end of the experiment, blood samples were withdrawn, then animals were euthanized and the brain hippocampi, cerebral cortices, as well as colons were isolated for biochemical and histopathological assessments.

RESULTS

RS increased the plasma corticotrophin releasing factor (CRF) with concomitant increase in hippocampal and cortical 5-HT levels, as well as mast cell inflammatory mediators, oxidative stress biomarkers, and histopathological inflammatory changes observed in rat colon. It also decreased the colonic content of 5-HT with consequent decrease in fecal pellet output (FPO). Treatment with STW 5 protected against these changes.

CONCLUSION

The protective effect of STW 5 against RS-induced IBS is related to its ability to normalize the induced changes in 5-HT in the brain-gut axis and counteract the stress-induced oxidative stress and inflammation.

Role of Serotonin in the Maintenance of Inflammatory State in Crohn’s Disease

Crohn’s disease (CD) is a chronic intestinal inflammation considered to be a major entity of inflammatory bowel diseases (IBDs), affecting different segments of the whole gastrointestinal tract. Peripheral serotonin (5-HT), a bioactive amine predominantly produced by gut enterochromaffin cells (ECs), is crucial in gastrointestinal functions, including motility, sensitivity, secretion, and the inflammatory response. These actions are mediated by a large family of serotonin receptors and specialized serotonin transporter (SERT) located on a variety of cell types in the gut. Several studies indicate that intestinal 5-HT signaling is altered in patients with inflammatory bowel disease. Paraformaldehyde-fixed intestinal tissues, obtained from fifteen patients with Crohn’s disease were analyzed by immunostaining for serotonin, Langerin/CD207, and alpha-Smooth Muscle Actin (α-SMA). As controls, unaffected (normal) intestinal specimens of seven individuals were investigated. This study aimed to show the expression of serotonin in dendritic cells (DCs) and myofibroblast which have been characterized with Langerin/CD207 and α-SMA, respectively; furthermore, for the first time, we have found the presence of serotonin in goblet cells. Our results show the correlation between different types of intestinal cells in the maintenance of the inflammatory state in CD linked to the recall of myofibroblasts.

Potential Roles of Enterochromaffin Cells in Early Life Stress-Induced Irritable Bowel Syndrome

Irritable bowel syndrome (IBS) is one of the most common functional gastrointestinal disorders, also known as disorders of the gut–brain interaction; however, the pathophysiology of IBS remains unclear. Early life stress (ELS) is one of the most common risk factors for IBS development. However, the molecular mechanisms by which ELS induces IBS remain unclear. Enterochromaffin cells (ECs), as a prime source of peripheral serotonin (5-HT), play a pivotal role in intestinal motility, secretion, proinflammatory and anti-inflammatory effects, and visceral sensation. ECs can sense various stimuli and microbiota metabolites such as short-chain fatty acids (SCFAs) and secondary bile acids. ECs can sense the luminal environment and transmit signals to the brain via exogenous vagal and spinal nerve afferents. Increasing evidence suggests that an ECs-5-HT signaling imbalance plays a crucial role in the pathogenesis of ELS-induced IBS. A recent study using a maternal separation (MS) animal model mimicking ELS showed that MS induced expansion of intestinal stem cells and their differentiation toward secretory lineages, including ECs, leading to ECs hyperplasia, increased 5-HT production, and visceral hyperalgesia. This suggests that ELS-induced IBS may be associated with increased ECs-5-HT signaling. Furthermore, ECs are closely related to corticotropin-releasing hormone, mast cells, neuron growth factor, bile acids, and SCFAs, all of which contribute to the pathogenesis of IBS. Collectively, ECs may play a role in the pathogenesis of ELS-induced IBS. Therefore, this review summarizes the physiological function of ECs and focuses on their potential role in the pathogenesis of IBS based on clinical and pre-clinical evidence.

Effect of Bacillus subtilis, Enterococcus faecium, and Enterococcus faecalis supernatants on serotonin transporter expression in cells and tissues

BACKGROUND

Bacillus subtilis (B. subtilis), Enterococcus faecium (E. faecium), and Enterococcus faecalis (E. faecalis) are probiotics that are widely used in the clinical treatment of irritable bowel syndrome (IBS). Whether the supernatants of these three probiotics can improve gastrointestinal sensation and movement by regulating the serotonin transporter (SERT) expression needs to be clarified.

AIM

To investigate whether B. subtilis, E. faecium, and E. faecalis supernatants can upregulate SERT expression in vitro and in vivo.

METHODS

Caco-2 and HT-29 cells were stimulated with probiotic culture supernatants for 12 and 24 h, respectively. A male Sprague-Dawley rat model of post-infectious irritable bowel syndrome (PI-IBS) was established and the rats were treated with phosphate-buffered saline (group A) and three probiotics culture supernatants (groups B, C, and D) for 4 wk. The levels of SERT were detected by quantitative PCR and western blotting.

RESULTS

The levels of SERT at post-treatment 12 and 24 h were significantly elevated in Caco-2 cells treated with B. subtilis supernatant compared with those in the control group (^aP < 0.05). Those levels were markedly upregulated in Caco-2 cells stimulated with E. faecium and E. faecalis supernatants at 24 h (^aP < 0.05). In addition, SERT expression in groups B, C, and D was significantly higher than that in group A in the 2nd wk (^aP < 0.05). Increased SERT expression was only found in group D in the 3rd wk (^aP < 0.05). However, there was no significant difference in SERT expression between the groups in the last week (P > 0.05).

CONCLUSION

The supernatants of B. subtilis, E. faecium, and E. faecalis can upregulate SERT expression in intestinal epithelial cells and the intestinal tissues in the rat model of PI-IBS.

Electroacupuncture Attenuates Post-Inflammatory IBS-Associated Visceral and Somatic Hypersensitivity and Correlates With the Regulatory Mechanism of Epac1-Piezo2 Axis

Electroacupuncture (EA) is considered to have a therapeutic effect in the relief of irritable bowel syndrome (IBS)-associated visceral hypersensitivity via the reduction of the level of 5-hydroxytryptamine (5-HT) and 5-HT₃ receptors (5-HT₃R). However, whether Epac1/Piezo2, as the upstream of 5-HT, is involved in this process remains unclear. We investigated whether EA at the ST36 and ST37 acupoints alleviated visceral and somatic hypersensitivity in a post-inflammatory IBS (PI-IBS) model mice via the Epac1-Piezo2 axis. In this study, we used 2,4,6-trinitrobenzene sulfonic acid (TNBS)-induced PI-IBS as a mouse model. Visceral sensitivity was assessed by the abdominal withdrawal reflex test. Somatic sensitivity was evaluated by the hind paw withdrawal threshold. Quantitative real-time PCR, immunofluorescence staining, ELISA, and Western blotting were performed to examine the expressions of Epac1, Piezo2, 5-HT, and 5-HT₃R from the mouse distal colon/L5-S2 dorsal root ganglia (DRG). Our results showed that EA improved the increased visceral sensation and peripheral mechanical hyperalgesia in PI-IBS model mice, and the effects of EA were superior to the sham EA. EA significantly decreased the protein and mRNA levels of Epac1 and Piezo2, and reduced 5-HT and 5-HT₃R expressions in the distal colon. Knockdown of colonic Piezo2 eliminated the effect of EA on somatic hypersensitivity. Combined knockdown of colonic Epac1 and Piezo2 synergized with EA in relieving visceral hypersensitivity and blocked the effect of EA on somatic hypersensitivity. Additionally, protein levels of Epac1 and Piezo2 were also found to be decreased in the L5-S2 DRGs after EA treatment. Taken together, our study suggested that EA at ST36 and ST37 can alleviate visceral and somatic hypersensitivity in PI-IBS model mice, which is closely related to the regulation of the Epac1-Piezo2 axis.

Neurotransmitter and Intestinal Interactions: Focus on the Microbiota-Gut-Brain Axis in Irritable Bowel Syndrome

Irritable bowel syndrome (IBS) is a functional gastrointestinal disorder of unknown etiology. IBS is caused by a disruption in the gut-brain axis. Given the importance of the gut microbiota in maintaining local and systemic homeostasis of immunity, endocrine, and other physiological processes, the microbiota-gut-brain axis has been proposed as a key regulator in IBS. Neurotransmitters have been shown to affect blood flow regulation, intestinal motility, nutrient absorption, the gastrointestinal immune system, and the microbiota in recent studies. It has the potential role to play a function in the pathophysiology of the gastrointestinal and neurological systems. Transmitters and their receptors, including 5-hydroxytryptamine, dopamine, γ-aminobutyric acid, and histamine, play an important role in IBS, especially in visceral sensitivity and gastrointestinal motility. Studies in this field have shed light on revealing the mechanism by which neurotransmitters act in the pathogenesis of IBS and discovering new therapeutic strategies based on traditional pharmacological approaches that target the nervous system or novel therapies that target the microbiota.

Gender-specific association between the regular use of statins and the risk of irritable bowel syndrome: A population-based prospective cohort study

Introduction: In addition to lipid-lowering effects, statins might modulate the gut microbiome and alleviate systematic inflammation, which in turn, may have a protective effect against irritable bowel syndrome (IBS). The aim of our study was to evaluate the gender-specific association between statin exposure and the risk of IBS. Method: We undertook a prospective analysis based on the United Kingdom Biobank, a large ongoing cohort including 477,293 participants aged 37-73 years. We included participants based on information on their personal statin use and also those free of IBS and cancer at the baseline. We evaluated the gender-specific hazard ratio (HR) and 95% confidence interval (CI) with Cox proportional hazards regression, adjusting for demographic factors, lifestyle factors, comorbidities, and statin indications. Result: A total of 438,805 participants (206,499 males and 232,306 females) were included in the analysis. Among male participants, the regular use of statins was associated with a decreased risk of IBS (HR: 0.77; 95% CI: 0.61-0.97). This association persists across multiple sensitivity and subgroup analyses and did not show clear evidence of variance among the major types of statins. We did not find sufficient evidence of the association between the statin use and IBS risk in females (HR: 0.98; 95% CI: 0.82-1.16). Conclusion: Our study found that the regular use of statins was associated with a decreased risk of IBS in male participants. Further studies are required to confirm the beneficial effect of statins.

Buspirone in the management of refractory irritable bowel syndrome: A case report

RATIONALE

Irritable bowel syndrome (IBS) is a chronic and debilitating functional disorder of the gastrointestinal tract manifested by abdominal pain and bowel habit dysregulation. The pathophysiology is complex and management targets symptom resolution. Therapeutic interventions range from dietary modification, psychological interventions, exercise, to the use of antispasmodics, antibiotics, and antidepressants. Anecdotal reports have suggested that buspirone may be beneficial in the treatment of functional dyspepsia and IBS and its physiological effect of reducing gastric tone provides a rational for its benefit.

PATIENT CONCERNS

A 28-year-old man with unremarkable past medical and psychiatric history presented with worsening abdominal pain, bloating, and bowel movement dysregulation of over 6-year duration.

DIAGNOSES

Physical examination revealed mild distension and discomfort on deep palpation. Thorough blood investigations, stool analysis and culture, and imaging were unremarkable except for the detection of mucus with stool. The patient was diagnosed with irritable bowel syndrome with mixed habits.

INTERVENTIONS

Dietary adjustment and a range of medications (mebeverine, simethicone, loperamide, rifaximin, sertraline and amitriptyline) yielded unsatisfactory response of were not tolerated. Buspirone was eventually introduced.

OUTCOMES

Buspirone was associated with a significant and sustained improvement in IBS symptoms and quality of life.

LESSONS

This case suggests that buspirone was effective in treating refractory IBS. Further research is needed to assess the role of buspirone in IBS management.

Migraine and Its Equivalents: What Do They Share? A Narrative Review on Common Pathophysiological Patterns

Migraine is the first in order of frequency of the neurological disorders, affecting both adult and paediatric populations. It is also the first cause of primary headaches in children. Migraine equivalents are periodic disorders that can be associated with migraine or considered as prognostic features of a future migraine manifestation. Despite the mechanisms underlying migraine and its equivalents are not entirely clear, several elements support the hypothesis of common pathophysiological patterns shared by these conditions. The aim of this review is thus to analyze the literature in order to highlight which currently known mechanisms may be common between migraine and its equivalents.

Immunohistochemical Inflammation in Histologically Normal Appendices in Patients with Right Iliac Fossa Pain

BACKGROUND

Histologically normal appendices resected for right iliac fossa pain in children demonstrate immunohistochemical markers of inflammation. We aimed to establish if subclinical inflammation was present in histologically normal appendices resected from adults with right iliac fossa pain.

METHODS

Immunohistochemistry was performed on formalin-fixed paraffin-embedded appendices for tumour necrosis factor (TNF)-α, interleukin (IL)-6, IL-2R and serotonin in four groups: Group I (n = 120): uncomplicated appendicitis, Group II (n = 118): complicated appendicitis (perforation or gangrene), Group III (n = 104): histologically normal appendices resected for right iliac fossa pain and Group IV (n = 106) appendices resected at elective colectomy. Expression was quantified using the H-scoring system.

RESULTS

Median, interquartile range expression of TNF-α was increased in Groups I (5.9, 3.1-9.8), II (6.8, 3.6-12.1) and III (9.8, 6.2-15.2) when compared with Group IV (3.0, 1.4-4.7, p < 0.01). Epithelial expression of IL-6 in Groups II (44.0, 8.0-97.0) and III (71.0, 18.5-130.0) was increased when compared with Group IV (9.5, 1.0-60.2, p < 0.01). Expression of mucosal IL-2R in Groups I (47.4, 34.8-69.0), II (37.8, 25.4-60.4) and III (18.4, 10.1-34.7) was increased when compared with Group IV (2.8, 1.2-5.7, p < 0.01). Serotonin content in Groups I (3.0, 0-30.0) and II (0, 0-8.5) was decreased when compared with Groups III (49.7, 16.7-107.5) and IV (43.5, 9.5-115.8, p < 0.01).

CONCLUSION

Histologically normal appendices resected from symptomatic patients exhibited increased proinflammatory cytokine expression on immunohistochemistry suggesting the presence of an inflammatory process not detected on conventional microscopy.

Residual effects of abomasal 5-hydroxytryptophan administration on serotonin metabolism in cattle

Studies of serotonin in animal husbandry has received growing interest. However, there is limited information about serotonin manipulation using 5-HTP administered postruminally and its residual effects in cattle. The objective of this study was to evaluate the effectiveness of 5-HTP infused into the abomasum for enhancing circulating serotonin in cattle. Four Holstein steers (487 ± 7.6 kg) fitted with ruminal cannulas were used in a 4 × 4 Latin Square design experiment. The treatments were intra-abomasal infusion of 5-HTP at 0, 0.25, 0.5, and 1 mg/kg BW. Blood was collected from the jugular vein of each steer at -60, -30, 0, 30, 60, 120, 240, and 480 min from 5-HTP infusion for basal and short term evaluation and, at 1, 2, 4, and 7 d after 5-HTP infusion for long term evaluation. Dry matter intake was not affected (P > 0.05) by intra-abomasal infusions. The half-life of 5-HTP was dose-independent (128 min). The serum 5-HTP, serotonin, and 5-hydroxyindoleacetic acid area under the curve increased (P < 0.05) linearly with an increased dose of 5-HTP. Serum 5-HTP reached peak concentration in approximately 30 min after dosing while serum and plasma serotonin peaked after 240 min postinfusion. Serotonin was greater than control for all 5-HTP doses 1 d and 2 d after infusion in serum and plasma, respectively. Intra-abomasal infusion of 5-HTP at doses up to 1 mg/ kg BW increases circulating serotonin for up 2 days.

Of bowels, brain and behavior: A role for the gut microbiota in psychiatric comorbidities in irritable bowel syndrome

BACKGROUND

The gastrointestinal microbiota has emerged as a key regulator of gut-brain axis signalling with important implications for neurogastroenterology. There is continuous bidirectional communication between the gut and the brain facilitated by neuronal, endocrine, metabolic, and immune pathways. The microbiota influences these signalling pathways via several mechanisms. Studies have shown compositional and functional alterations in the gut microbiota in stress-related psychiatric disorders. Gut microbiota reconfigurations are also a feature of irritable bowel syndrome (IBS), a gut-brain axis disorder sharing high levels of psychiatric comorbidity including both anxiety and depression. It remains unclear how the gut microbiota alterations in IBS align with both core symptoms and these psychiatric comorbidities.

METHODS

In this review, we highlight common and disparate features of these microbial signatures as well as the associated gut-brain axis signalling pathways. Studies suggest that patients with either IBS, depression or anxiety, alone or comorbid, present with alterations in gut microbiota composition and harbor immune, endocrine, and serotonergic system alterations relevant to the common pathophysiology of these comorbid conditions.

KEY RESULTS

Research has illustrated the utility of fecal microbiota transplantation in animal models, expanding the evidence base for a potential causal role of disorder-specific gut microbiota compositions in symptom set expression. Moreover, an exciting study by Constante and colleagues in this issue highlights the possibility of counteracting this microbiota-associated aberrant behavioral phenotype with a probiotic yeast, Saccharomyces boulardii CNCM I-745.

CONCLUSIONS AND INFERENCES

Such data highlights the potential for therapeutic targeting of the gut microbiota as a valuable strategy for the management of comorbid psychiatric symptoms in IBS.

The role of serotonin in the control of esophageal sensitivity assessed by multimodal stimulation in health

BACKGROUND

Esophageal hypersensitivity is considered an important pathophysiological mechanism in refractory gastroesophageal reflux disease (GERD) patients. Serotonin (5-HT) plays an important role in the regulation of GI (gastrointestinal) secretion, motility and sensitivity. Previous studies found that altered 5-HT availability has no clear effects on esophageal/GI sensations. Our aim was therefore to investigate the role of 5-HT in esophageal sensitivity in healthy volunteers (HV).

METHODS

Esophageal sensitivity to thermal, mechanical, electrical, and chemical stimuli was assessed in 3 different placebo-controlled studies. In the first study, the effect of citalopram (40 mg; 5-HT reuptake inhibitor; intravenous) was investigated (n = 14). In the second study, the effect of buspirone (20 mg; 5HT1A agonist; oral) was investigated (n = 10). In the third study, acute tryptophan depletion (ATD) was used to decrease 5-HT levels to investigate the effect of reduced 5-HT availability on esophageal sensitivity (n = 15).

KEY RESULTS

No difference was observed in esophageal sensitivity after the administration of citalopram or buspirone (all p > 0.06). In contrast, pain perception threshold to chemical stimulation was increased after ATD (p = 0.017, Cohen's d+ = 0.67). No effect was found on the first perception or pain tolerance threshold. ATD had no influence on esophageal sensitivity to thermal, mechanical, and electrical stimulation compared with placebo.

CONCLUSIONS AND INFERENCES

ATD, which induces 5-HT depletion, significantly decreased pain perception threshold during chemical stimulation, without affecting sensitivity to mechanical, thermal, or electrical stimulation. These findings confirm the involvement of 5-HT in the control of esophageal acid sensitivity, but identifying the receptors involved requires more ligands and studies.

Does Intravenous Ondansetron Affect the Intestinal Motility Pattern in Healthy Donkeys (Equus asinus)?

The current study was undertaken to investigate the effect of intravenous administration of ondansetron on the small and large intestinal motility in donkeys (Equus asinus) using non-invasive transabdominal ultrasonography. The current prospective, randomized, placebo-controlled, crossover study was conducted on thirty healthy donkeys (15 males and 15 females). The selected donkeys underwent two trials; the first was performed by intravenous administration of saline solution as a placebo, while the second was carried out by intravenous administration of ondansetron hydrochloride. The contractility of selected portions of both the small intestine (duodenum and jejunum) and the large intestine (left colon, right colon, and cecum) was counted over a period of 3 minutes before administration (zero time) and at 15, 30, 60, 90, 120, 180, and 240 minutes after administration. The results of this study showed that ondansetron significantly altered the small and large intestinal contractility compared to normal saline. Intravenous administration of ondansetron induced a significant decrease in the duodenal, jejunal and cecal contractility compared to placebo at 30, 60, 90, and 120 minutes after administration. Likewise, ondansetron induced a significant decrease in the left colon and right colon contractility when compared with placebo at 30, 60, 90, 120, and 180 minutes following administration. Ondansetron can be used as a highly specific and selective serotonin 5-HT₃ receptor antagonist for reducing the small and large intestinal motility in donkeys, and is therefore highly suggested for treating spasmodic colic in equine.

Alterations in short-chain fatty acids and serotonin in irritable bowel syndrome: a systematic review and meta-analysis

BACKGROUND

Short-chain fatty acids (SCFAs) and serotonin (5-hydroxytryptamine, 5-HT) may be associated with the pathogenesis of irritable bowel syndrome (IBS). There are some reports of alterations in SCFAs and 5-HT in IBS, but their results are inconsistent. We aimed to perform a meta-analysis to assess alterations in SCFAs and 5-HT in IBS patients and their potential role in the abnormal brain-gut-microbiota (BGM) axis.

METHODS

Case-control studies detecting SCFAs and 5-HT in IBS patients were identified from PubMed, Web of Science, Cochrane Library, and Scopus databases to identify relevant articles up to September 2018. The standardized mean differences (SMDs) with 95% confidence intervals (CIs) of SCFAs and 5-HT were calculated by REVIEW MANAGER 5.3 to evaluate the alterations of 5-HT and SCFAs in IBS.

RESULTS

Five studies on SCFAs and 5 on 5-HT in IBS patients were included. As compared to healthy controls (HCs), the SMDs of 5-HT in IBS patients was 2.35 (95% CI 0.46-4.24) and the SMDs of total SCFAs, acetic acid, propionic acid, and butyric acid in IBS patients were - 0.01 (95% CI - 0.57-0.55), - 0.04 (95% CI - 0.55-0.47), 0.07 (95% CI - 0.45-0.60), and - 0.00 (95% CI - 0.49-0.49), respectively.

CONCLUSIONS

There was an increase in 5-HT in blood of IBS patients, indicating the increased 5-HT in blood may be involved in IBS pathogenesis. However, there were no significant differences in SCFAs in feces between IBS patients and HCs. But the study did not differentiate between subgroups of IBS. These findings might provide insight for future studies of the BGM axis in the pathogenesis of IBS. Mei Luo and Xiaojun Zhuang contributed equally to the writing of this article.

Bile Acids as Key Modulators of the Brain-Gut-Microbiota Axis in Alzheimer's Disease

Recently, the concept of the brain-gut-microbiota (BGM) axis disturbances in the pathogenesis of Alzheimer's disease (AD) has been receiving growing attention. At the same time, accumulating data revealing complex interplay between bile acids (BAs), gut microbiota, and host metabolism have shed new light on a potential impact of BAs on the BGM axis. The crosstalk between BAs and gut microbiota is based on reciprocal interactions since microbiota determines BA metabolism, while BAs affect gut microbiota composition. Secondary BAs as microbe-derived neuroactive molecules may affect each of three main routes through which interactions within the BGM axis occur including neural, immune, and neuroendocrine pathways. BAs participate in the regulation of multiple gut-derived molecule release since their receptors are expressed on various cells. The presence of BAs and their receptors in the brain implies a direct effect of BAs on the regulation of neurological functions. Experimental and clinical data confirm that disturbances in BA signaling are present in the course of AD. Disturbed ratio of primary to secondary BAs as well as alterations in BA concertation in serum and brain samples have been reported. An age-related shift in the gut microbiota composition associated with its decreased diversity and stability observed in AD patients may significantly affect BA metabolism and signaling. Given recent evidence on BA neuroprotective and anti-inflammatory effects, new therapeutic targets have been explored including gut microbiota modulation by probiotics and dietary interventions, ursodeoxycholic acid supplementation, and use of BA receptor agonists.

Pattern of postruminal administration of l-tryptophan affects blood serotonin in cattle

Serotonin (5-HT) has many important functions in both central and peripheral nervous systems. Although it has been demonstrated that manipulation of serotonin metabolism is possible in many species, there is limited information about l-tryptophan (TRP), a serotonin precursor, in cattle, and these provide conflicting results. Furthermore, there is no study evaluating how different patterns of intra-abomasal infusion of TRP impact circulating 5-HT. The objective of this study was to evaluate if intra-abomasal infusion patterns of TRP can affect circulating 5-HT and other metabolites from TRP metabolism in the plasma and serum and circulating glucose and insulin in cattle. Eight ruminally cannulated Holstein steers were used in a replicated 4 × 4 Latin square design. Each received intra-abomasal water infusion (control) or intra-abomasal TRP infusion (50 mg/kg BW) in 3 different patterns: a pulse infusion once a day (pulse once), pulse infusion twice a day (pulse twice), or continuous infusion (continuous). For continuous treatment, the TRP dose was diluted in tap water and infused by a peristaltic pump (300 mL/h). To equalize conditions, the other treatments had a water infusion (300 mL/h). The steers were fed every 2 h, and blood was collected from a jugular vein catheter every 4 h for 24 h after the initial infusion. Urine produced during the 24 h period was collected. Serum and plasma TRP, 5-HT and kynurenine, plasma glucose, and serum insulin concentrations were analyzed. Urine was analyzed for concentrations of 5-hydroxyindoleacetic acid. Both serum TRP and kynurenine were increased (P < 0.05) by all TRP infusion treatments, but concentrations in pulse dose treatments were greater than those in continuous infusion. Serum 5-HT increased (P < 0.05) with both pulse TRP infusion treatments; however, the continuous TRP infusion did not increase the serum 5-HT. Plasma 5-HT, glucose, and insulin had a tendency to increase with TRP pulse infusions. The urinary 5-hydroxyindoleacetic acid excretion was highest for pulse dose treatments. An acute supply of TRP in 1 or 2 daily doses increases serum 5-HT and increases circulating glucose and insulin in cattle. The TRP and kynurenine concentrations are similar in plasma and serum. However, the serum 5-HT concentration is more responsive to TRP administration than plasma.

The serotonin reuptake transporter is reduced in the epithelium of active Crohn's disease and ulcerative colitis

Serotonin is a highly conserved and ubiquitous signaling molecule involved in a vast variety of biological processes. A majority of serotonin is produced in the gastrointestinal epithelium, where it is suggested to act as a prominent regulatory molecule in the inflammatory bowel diseases (IBDs) Crohn's disease (CD) and ulcerative colitis (UC). Extracellular and circulating serotonin levels are thought to be elevated during intestinal inflammation, but the underlying mechanisms have been poorly understood. The data on human material are limited, contradictory, and in need of further investigation and substantiating. In this study, we show a potent and significant downregulation of the dominant serotonin reuptake transporter (SERT) mRNA (SLC6A4) in the epithelium from active CD ileitis, CD colitis, and UC colitis, compared with healthy controls. The mRNA of tryptophan hydroxylase 1, the rate-limiting enzyme in serotonin synthesis, was unregulated. Immunohistochemistry showed expression of the SERT protein in both the epithelium and the lamina propria and localized the downregulation to the epithelial monolayer. Laser capture microdissection followed by RNA sequencing confirmed downregulation of SLC6A4 in the epithelial monolayer during intestinal inflammation. Patient-derived colon epithelial cell lines (colonoids) incubated with the proinflammatory cytokine tumor necrosis factor alpha (TNF-α) reduced SERT expression. In summary, these results show that intestinal inflammation potently reduces the expression of SERT in both CD and UC and that TNF-α alone is sufficient to induce a similar reduction in colonoids. The reduced serotonin reuptake capacity may contribute to the increased interstitial serotonin level associated with intestinal inflammation.NEW & NOTEWORTHY The serotonin reuptake transporter is potently reduced in inflamed areas of Crohn's ileitis, Crohn's colitis, and ulcerative colitis. The changes are localized to the intestinal epithelium and can be induced by TNF-α. The serotonin synthesis through tryptophan hydroxylase 1 is unchanged. This regulation is suggested as a mechanism underlying the increased extracellular serotonin levels associated with intestinal inflammation.

The Buspirone-dependent Abdominal Pain Transmission Within the Nucleus Tractus Solitarius in the Rat

Buspirone, a partial agonist of the 5-HT_1aR, due to potential antinociceptive properties can be useful for abdominal pain treatment in IBS patients. Pain-related effects of buspirone can be mediated by the 5-HT_1aRs, located within the nucleus tractus solitarius. The 5-HT_1aR involvement in pain transmission within the NTS is unclear. The objective of our study was to evaluate the involvement of the 5-HT_1aR in abdominal pain transmission within the NTS. Using a model of abdominal pain on urethane-anesthetized rats, two types of NTS pain-related neurons responding to the noxious colorectal distension (CRD) with excitatory and inhibitory sustained patterns of evoked activity were revealed. Buspirone (1.0-4.0 mg kg^-1, iv) has complex time- and dose-depended action on the CRD-induced NTS neuron responses. Buspirone inhibits the responses of the excitatory neurons and inverts the responses of the inhibitory pain-related neurons but at a dose of 4.0 buspirone, the effect on NTS pain-related neurons attenuates. The inhibitory effect of buspirone on the CRD-evoked responses of the excitatory NTS neurons is completely blocked by an intra-cerebroventricular administration of buspirone agonist WAY100,635. The inhibitory responses do not change by this agonist. The inhibitory action of buspirone is mediated by supraspinal 5-HT_1a receptors however, its excitatory effect on inhibitory neurons does not dependents on these receptors. We proposed that the NTS pain-related neurons could be involved in anti- or pronociceptive effects of buspirone on abdominal pain.