Serotonergic Mechanisms Regulating the GI Tract: Experimental Evidence and Therapeutic Relevance

Butyrate as a potential therapeutic agent for neurodegenerative disorders

Maintaining an optimum microbial community within the gastrointestinal tract is intricately linked to human metabolic, immune and brain health. Disturbance to these microbial populations perturbs the production of vital bioactive compounds synthesised by the gut microbiome, such as short-chain fatty acids (SCFAs). Of the SCFAs, butyrate is known to be a major source of energy for colonocytes and has valuable effects on the maintenance of intestinal epithelium and blood brain barrier integrity, gut motility and transit, anti-inflammatory effects, and autophagy induction. Inducing endogenous butyrate production is likely to be beneficial for gut-brain homeostasis and for optimal neuronal function. For these reasons, butyrate has gained interest as a potential therapy for not only metabolic and immunological disorders, but also conditions related to the brain, including neurodegenerative diseases. While direct and indirect sources of butyrate, including prebiotics, probiotics, butyrate pro-drugs and glucosidase inhibitors, offer a promising therapeutic avenue, their efficacy and dosage in neurodegenerative conditions remain largely unknown. Here, we review current literature on effects of butyrate relevant to neuronal function, the impact of butyrate in a range of neurodegenerative diseases and related treatments that may have potential for the treatment of neurodegenerative diseases.

Co-Supplementation of Baobab Fiber and Arabic Gum Synergistically Modulates the In Vitro Human Gut Microbiome Revealing Complementary and Promising Prebiotic Properties

Arabic gum, a high molecular weight heteropolysaccharide, is a promising prebiotic candidate as its fermentation occurs more distally in the colon, which is the region where most chronic colonic diseases originate. Baobab fiber could be complementary due to its relatively simple structure, facilitating breakdown in the proximal colon. Therefore, the current study aimed to gain insight into how the human gut microbiota was affected in response to long-term baobab fiber and Arabic gum supplementation when tested individually or as a combination of both, allowing the identification of potential complementary and/or synergetic effects. The validated Simulator of the Human Intestinal Microbial Ecosystem (SHIME®), an in vitro gut model simulating the entire human gastrointestinal tract, was used. The microbial metabolic activity was examined, and quantitative 16S-targeted Illumina sequencing was used to monitor the gut microbial composition. Moreover, the effect on the gut microbial metabolome was quantitatively analyzed. Repeated administration of baobab fiber, Arabic gum, and their combination had a significant effect on the metabolic activity, diversity index, and community composition of the microbiome present in the simulated proximal and distal colon with specific impacts on Bifidobacteriaceae and Faecalibacterium prausnitzii. Despite the lower dosage strategy (2.5 g/day), co-supplementation of both compounds resulted in some specific synergistic prebiotic effects, including a biological activity throughout the entire colon, SCFA synthesis including a synergy on propionate, specifically increasing abundance of Akkermansiaceae and Christensenellaceae in the distal colon region, and enhancing levels of spermidine and other metabolites of interest (such as serotonin and ProBetaine).

Combination of vitamin D3 and fructooligosaccharides upregulates colonic vitamin D receptor in C57BL/6J mice and affects anxiety-related behavior in a sex-specific manner

Depression and anxiety disorders are among the most common mental health disorders that affect US adults today, frequently related to vitamin D (VD) insufficiency. Along with VD, growing evidence suggests gut microbiota likely play a role in neuropsychiatric disorders. Here, we investigated if modulation of gut microbiota would disrupt host VD status and promote behaviors related to depression and anxiety in adult mice. Six-week-old male and female C57BL/6J mice (n = 10/mice/group) were randomly assigned to receive (1) control diet (CTR), control diet treated with antibiotics (AB), control diet with total 5000 IU of VD (VD), VD treated with antibiotics (VD + AB), VD supplemented with 5% w/w fructooligosaccharides (FOS; VF), and VF diet treated with antibiotics (VF + AB), respectively, for 8 weeks. Our study demonstrated that VD status was not affected by antibiotic regimen. VD alone ameliorates anxiety-related behavior in female mice, and that combination with FOS (i.e., VF) did not further improve the outcome. Male mice, in contrast, exhibit greater anxiety with VF, but not VD, when compared with CTR mice. Colonic VD receptor was elevated in VF-treated mice in both sexes, compared with CTR, which was positively correlated to colonic TPH1, a rate-limiting enzyme for serotonin synthesis. Taken together, our data indicate that the effect of VF on anxiety-related behavior is sex-specific, which may partially be attributed to the activation of colonic VD signaling and subsequent serotonin synthesis. The synergistic or additive effect of VD and FOS on mood disorders remained to be investigated.

Serotonin regulation of mitochondria in kidney diseases

Serotonin, while conventionally recognized as a neurotransmitter in the CNS, has recently gained attention for its role in the kidney. Specifically, serotonin is not only synthesized in the kidney, but it also regulates glomerular function, vascular resistance, and mitochondrial homeostasis. Because of serotonin's importance to mitochondrial health, this review is focused on the role of serotonin and its receptors in mitochondrial function in the context of acute kidney injury, chronic kidney disease, and diabetic kidney disease, all of which are characterized by mitochondrial dysfunction and none of which has approved pharmacological treatments. Evidence indicates that activation of certain serotonin receptors can stimulate mitochondrial biogenesis (MB) and restore mitochondrial homeostasis, resulting in improved renal function. Serotonin receptor agonists that induce MB are therefore of interest as potential therapeutic strategies for renal injury and disease. SIGNIFICANCE STATEMENT: Mitochondrial dysfunction is associated with many human renal diseases such as acute kidney injury, chronic kidney disease, and diabetic kidney disease, which are associated with increased morbidity and mortality. Unfortunately, none of these pathologies has an FDA-approved pharmacological intervention, underscoring the urgency of identifying new therapeutics for such disorders. Studies show that induction of mitochondrial biogenesis via serotonin (5-hydroxytryptamine, 5-HT) receptors reduces kidney injury markers, restores mitochondrial and renal function after kidney injury, and decreases mortality, suggesting that targeting 5-HT receptors may be a promising therapeutic avenue for mitochondrial dysfunction in kidney diseases. While numerous reviews describe the importance of mitochondria and mitochondrial quality control mechanisms in kidney disease, the relevance of 5-HT receptor-mediated mitochondrial metabolic modulation in the kidney has yet to be thoroughly explored.

Addressing Combative Behaviour in Spanish Bulls by Measuring Hormonal Indicators

The fighting bull is characterised by its natural aggressiveness, but the physiological mechanisms that underlie its aggressive behaviour are poorly studied. This study determines the hormonal component of aggressiveness in fighting bulls by analysing their behaviour during a fight and correlating it to their serotonin, dopamine and testosterone levels. We also determine whether aggressive behaviour can be estimated in calves. Using 195 animals, samples were obtained when the animals were calves and after 5 years. Aggressiveness scores were obtained by an observational method during bullfights, and serotonin, dopamine and testosterone levels were determined in all animals using validated enzyme immunoassay kits. The results revealed a strong correlation of serotonin and dopamine levels with aggressiveness scores in bulls during fights, but no correlation was found with respect to testosterone. These correlations led to established cut-off point and linear regression curves to obtain expected aggressiveness scores for calves at shoeing. There were no significant differences between the expected scores obtained in calves and the observed scores in bulls. Therefore, this study demonstrates that hormone determination in calves may be a great indicator of combativeness in bulls and can reliably be used in the selection of fighting bulls.

Serotonin Transporter Deficiency Induces Metabolic Alterations in the Ileal Mucosa

Serotonin transporter (SERT) deficiency has been implicated in metabolic syndrome, intestinal inflammation, and microbial dysbiosis. Interestingly, changes in microbiome metabolic capacity and several alterations in host gene expression, including lipid metabolism, were previously observed in SERT-/- mice ileal mucosa. However, the precise host or microbial metabolites altered by SERT deficiency that may contribute to the pleiotropic phenotype of SERT KO mice are not yet understood. This study investigated the hypothesis that SERT deficiency impacts lipid and microbial metabolite abundances in the ileal mucosa, where SERT is highly expressed. Ileal mucosal metabolomics was performed by Metabolon on wild-type (WT) and homozygous SERT knockout (KO) mice. Fluorescent-activated cell sorting (FACS) was utilized to measure immune cell populations in ileal lamina propria to assess immunomodulatory effects caused by SERT deficiency. SERT KO mice exhibited a unique ileal mucosal metabolomic signature, with the most differentially altered metabolites being lipids. Such changes included increased diacylglycerols and decreased monoacylglycerols in the ileal mucosa of SERT KO mice compared to WT mice. Further, the ileal mucosa of SERT KO mice exhibited several changes in microbial-related metabolites known to play roles in intestinal inflammation and insulin resistance. SERT KO mice also had a significant reduction in the abundance of ileal group 3 innate lymphoid cells (ILC3). In conclusion, SERT deficiency induces complex alterations in the ileal mucosal environment, indicating potential links between serotonergic signaling, gut microbiota, mucosal immunity, intestinal inflammation, and metabolic syndrome.

Cyproheptadine in serotonin syndrome: A retrospective study

Objective

Serotonin syndrome (SS) is an iatrogenic life-threatening condition caused by serotonergic agents. The treatment for SS involves the administration of a serotonin antagonist (cyproheptadine). However, the dosing schedule for cyproheptadine is not uniform in the literature.

Methods

We retrospectively evaluated 23 adult patients (>18 years) admitted to the Neurology Department and met the Hunter criteria for SS.

Results

The mean age was 35.2 years, and 52% were female. Ten patients were managed in the intensive care unit (ICU), whereas thirteen patients were admitted to the ward. Hyperreflexia was the most common clinical feature (100%), followed by clonus (91%), tachycardia (83%), and tremor (83%). Other common clinical features were rigidity (65%), increased bowel sound (61%), diaphoresis (48%), fever (43%), hypertension (39%), and myoclonus (30%). All but one patient received two or more serotonergic drugs. Tramadol was the most common serotonergic agent (39%), followed by sodium valproate (21%), and amitriptyline (21%). Cyproheptadine was administered to all patients. All patients admitted in the ICU received a loading dose of 12 mg followed by 2 mg every 2 h for at least 24 h. All patients admitted to the ward were given 4 mg of cyproheptadine three times each day. Every patient showed at least some response to cyproheptadine within 24 h. The total doses of cyproheptadine and the length of treatment differed between patients.

Conclusion

Any response to cyproheptadine at a therapeutic dose within 24 h, even a partial one, could be a diagnostic indicator of the existence of SS.

Unbiased serum metabolomic analysis in cats with naturally occurring chronic enteropathies before and after medical intervention

Chronic enteropathies (CE) are common disorders in cats and the differentiation between the two main underlying diseases, inflammatory bowel disease (IBD) and low-grade intestinal T-cell lymphoma (LGITL), can be challenging. Characterization of the serum metabolome could provide further information on alterations of disease-associated metabolic pathways and may identify diagnostic or therapeutic targets. Unbiased metabolomics analysis of serum from 28 cats with CE (14 cats with IBD, 14 cats with LGITL) and 14 healthy controls identified 1,007 named metabolites, of which 129 were significantly different in cats with CE compared to healthy controls at baseline. Random Forest analysis revealed a predictive accuracy of 90% for differentiating controls from cats with chronic enteropathy. Metabolic pathways found to be significantly altered included phospholipids, amino acids, thiamine, and tryptophan metabolism. Several metabolites were found to be significantly different between cats with IBD versus LGITL, including several sphingolipids, phosphatidylcholine 40:7, uridine, pinitol, 3,4-dihydroxybenzoic acid, and glucuronic acid. However, random forest analysis revealed a poor group predictive accuracy of 60% for the differentiation of IBD from LGITL. Of 129 compounds found to be significantly different between healthy cats and cats with CE at baseline, 58 remained different following treatment.

Colitis-Induced Small Intestinal Hypomotility Is Dependent on Enteroendocrine Cell Loss in Mice

BACKGROUND & AIMS

The abdominal discomfort experienced by patients with colitis may be attributable in part to the presence of small intestinal dysmotility, yet mechanisms linking colonic inflammation with small-bowel motility remain largely unexplored. We hypothesize that colitis results in small intestinal hypomotility owing to a loss of enteroendocrine cells (EECs) within the small intestine that can be rescued using serotonergic-modulating agents.

METHODS

Male C57BL/6J mice, as well as mice that overexpress (EECOVER) or lack (EECDEL) NeuroD1+ enteroendocrine cells, were exposed to dextran sulfate sodium (DSS) colitis (2.5% or 5% for 7 days) and small intestinal motility was assessed by 70-kilodalton fluorescein isothiocyanate-dextran fluorescence transit. EEC number and differentiation were evaluated by immunohistochemistry, terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling staining, and quantitative reverse-transcriptase polymerase chain reaction. Mice were treated with the 5-hydroxytryptamine receptor 4 agonist prucalopride (5 mg/kg orally, daily) to restore serotonin signaling.

RESULTS

DSS-induced colitis was associated with a significant small-bowel hypomotility that developed in the absence of significant inflammation in the small intestine and was associated with a significant reduction in EEC density. EEC loss occurred in conjunction with alterations in the expression of key serotonin synthesis and transporter genes, including Tph1, Ddc, and Slc6a4. Importantly, mice overexpressing EECs revealed improved small intestinal motility, whereas mice lacking EECs had worse intestinal motility when exposed to DSS. Finally, treatment of DSS-exposed mice with the 5-hydroxytryptamine receptor 4 agonist prucalopride restored small intestinal motility and attenuated colitis.

CONCLUSIONS

Experimental DSS colitis induces significant small-bowel dysmotility in mice owing to enteroendocrine loss that can be reversed by genetic modulation of EEC or administering serotonin analogs, suggesting novel therapeutic approaches for patients with symptomatic colitis.

Lab-on-chip technologies for exploring the gut-immune axis in metabolic disease

The continued rise in metabolic diseases such as obesity and type 2 diabetes mellitus poses a global health burden, necessitating further research into factors implicated in the onset and progression of these diseases. Recently, the gut-immune axis, with diet as a main regulator, has been identified as a possible role player in their development. Translation of conventional 2D in vitro and animal models is however limited, while human studies are expensive and preclude individual mechanisms from being investigated. Lab-on-chip technology therefore offers an attractive new avenue to study gut-immune interactions. This review provides an overview of the influence of diet on gut-immune interactions in metabolic diseases and a critical analysis of the current state of lab-on-chip technology to study this axis. While there has been progress in the development of "immuno-competent" intestinal lab-on-chip models, with studies showing the ability of the technology to provide mechanical cues, support longer-term co-culture of microbiota and maintain in vivo-like oxygen gradients, platforms which combine all three and include intestinal and immune cells are still lacking. Further, immune cell types and inclusion of microenvironment conditions which enable in vivo-like immune cell dynamics as well as host-microbiome interactions are limited. Future model development should focus on combining these conditions to create an environment capable of hosting more complex microbiota and immune cells to allow further study into the effects of diet and related metabolites on the gut-immune ecosystem and their role in the prevention and development of metabolic diseases in humans.

Dysbiosis of the gut microbiota and its effect on α-synuclein and prion protein misfolding: consequences for neurodegeneration

Abnormal behavior of α-synuclein and prion proteins is the hallmark of Parkinson's disease (PD) and prion illnesses, respectively, being complex neurological disorders. A primary cause of protein aggregation, brain injury, and cognitive loss in prion illnesses is the misfolding of normal cellular prion proteins (PrPC) into an infectious form (PrPSc). Aggregation of α-synuclein causes disruptions in cellular processes in Parkinson's disease (PD), leading to loss of dopamine-producing neurons and motor symptoms. Alteration in the composition or activity of gut microbes may weaken the intestinal barrier and make it possible for prions to go from the gut to the brain. The gut-brain axis is linked to neuroinflammation; the metabolites produced by the gut microbiota affect the aggregation of α-synuclein, regulate inflammation and immunological responses, and may influence the course of the disease and neurotoxicity of proteins, even if their primary targets are distinct proteins. This thorough analysis explores the complex interactions that exist between the gut microbiota and neurodegenerative illnesses, particularly Parkinson's disease (PD) and prion disorders. The involvement of the gut microbiota, a complex collection of bacteria, archaea, fungi, viruses etc., in various neurological illnesses is becoming increasingly recognized. The gut microbiome influences neuroinflammation, neurotransmitter synthesis, mitochondrial function, and intestinal barrier integrity through the gut-brain axis, which contributes to the development and progression of disease. The review delves into the molecular mechanisms that underlie these relationships, emphasizing the effects of microbial metabolites such as bacterial lipopolysaccharides (LPS), and short-chain fatty acids (SCFAs) in regulating brain functioning. Additionally, it looks at how environmental influences and dietary decisions affect the gut microbiome and whether they could be risk factors for neurodegenerative illnesses. This study concludes by highlighting the critical role that the gut microbiota plays in the development of Parkinson's disease (PD) and prion disease. It also provides a promising direction for future research and possible treatment approaches. People afflicted by these difficult ailments may find hope in new preventive and therapeutic approaches if the role of the gut microbiota in these diseases is better understood.

Changes in Bacterial Gut Composition in Parkinson's Disease and Their Metabolic Contribution to Disease Development: A Gut Community Reconstruction Approach

Parkinson's disease (PD) is a chronic and progressive neurodegenerative disease with the major symptoms comprising loss of movement coordination (motor dysfunction) and non-motor dysfunction, including gastrointestinal symptoms. Alterations in the gut microbiota composition have been reported in PD patients vs. controls. However, it is still unclear how these compositional changes contribute to disease etiology and progression. Furthermore, most of the available studies have focused on European, Asian, and North American cohorts, but the microbiomes of PD patients in Latin America have not been characterized. To address this problem, we obtained fecal samples from Colombian participants (n = 25 controls, n = 25 PD idiopathic cases) to characterize the taxonomical community changes during disease via 16S rRNA gene sequencing. An analysis of differential composition, diversity, and personalized computational modeling was carried out, given the fecal bacterial composition and diet of each participant. We found three metabolites that differed in dietary habits between PD patients and controls: carbohydrates, trans fatty acids, and potassium. We identified six genera that changed significantly in their relative abundance between PD patients and controls, belonging to the families Lachnospiraceae, Lactobacillaceae, Verrucomicrobioaceae, Peptostreptococcaceae, and Streptococcaceae. Furthermore, personalized metabolic modeling of the gut microbiome revealed changes in the predicted production of seven metabolites (Indole, tryptophan, fructose, phenylacetic acid, myristic acid, 3-Methyl-2-oxovaleric acid, and N-Acetylneuraminic acid). These metabolites are associated with the metabolism of aromatic amino acids and their consumption in the diet. Therefore, this research suggests that each individual's diet and intestinal composition could affect host metabolism. Furthermore, these findings open the door to the study of microbiome-host interactions and allow us to contribute to personalized medicine.

Beyond the Brain: Perinatal Exposure of Rats to Serotonin Enhancers Induces Long-Term Changes in the Jejunum and Liver

Serotonin (5-hydroxytryptamine, 5HT) homeostasis is essential for many physiological processes in the central nervous system and peripheral tissues. Hyperserotonemia, a measurable sign of 5HT homeostasis disruption, can be caused by 5HT-directed treatment of psychiatric and gastrointestinal diseases. Its impact on the long-term balance and function of 5HT in the peripheral compartment remains unresolved and requires further research due to possible effects on human health. We explored the effects of perinatal 5HT imbalance on the peripheral organs responsible for serotonin metabolism-the jejunum, a synthesis site, and the liver, a catabolism site-in adult rats. Hyperserotonemia was induced by subchronic treatment with serotonin precursor 5-hydroxytryptophan (5HTP) or serotonin degradation inhibitor tranylcypromine (TCP). The jejunum and liver were collected on postnatal day 70 and analyzed histomorphometrically. Relative mRNA levels of 5HT-regulating proteins were determined using qRT-PCR. Compared to controls, 5HTP- and TCP-treated rats had a reduced number of 5HT-producing cells and expression of the 5HT-synthesising enzyme in the jejunum, and an increased expression of 5HT-transporter accompanied by karyomegaly in hepatocytes, with these differences being more pronounced in the TCP-treated animals. Here, we report that perinatal 5HT disbalance induced long-term cellular and molecular changes in organs regulating 5HT-metabolism, which may have a negative impact on 5HT availability and function in the periphery. Our rat model demonstrates a link between the developmental abnormalities of serotonin homeostasis and 5HT-related changes in adult life and may be suitable for exploring the neurobiological substrates of vulnerability to behavioral and metabolic disorders, as well as for modeling the adverse effects of the prenatal exposure to 5HT enhancers in the human population.

Do the therapeutic effects of psilocybin involve actions in the gut?

The psychedelic compound psilocybin has recently emerged as a therapeutic intervention for various mental health conditions. Psilocybin is a potent agonist of serotonin (5-HT) receptors (5-HTRs), which are expressed in the brain and throughout peripheral tissues, with particularly high expression in the gastrointestinal (GI) tract. However, no studies have investigated the possibility that peripheral actions of psilocybin may contribute to improvements in mental health outcomes. This is despite strong evidence for disturbed gut-brain signalling in conditions in which psilocybin is being tested clinically. In this Opinion, we highlight the likely actions of psychedelics in the gut and provide initial support for the premise that peripheral actions may be involved in rapid and long-term therapeutic effects. A greater understanding of all sites and modes of action will guide more targeted approaches to drug development.

Quetiapine-Related Deaths: In Search of a Surrogate Endpoint

Quetiapine is a second-generation antipsychotic drug available for two and half decades. Due to increased misuse, prescription outside the approved indications, and availability on the black market, it is being encountered in medicolegal autopsies more frequently. For instance, it has been linked to increased mortality rates, most likely due to its adverse effects on the cardiovascular system. Its pharmacokinetic features and significant postmortem redistribution challenge traditional sampling in forensic toxicology. Therefore, a systematic literature review was performed, inclusive of PubMed, the Web of Science-core collection, and the Scopus databases; articles were screened for the terms "quetiapine", "death", and "autopsy" to reevaluate each matrix used as a surrogate endpoint in the forensic toxicology of quetiapine-related deaths. Ultimately, this review considers the results of five studies that were well presented (more than two matrices, data available for all analyses, for instance). The highest quetiapine concentrations were usually measured in the liver tissue. As interpreted by their authors, the results of the considered studies showed a strong correlation between some matrices, but, unfortunately, the studies presented models with poor goodness of fit. The distribution of quetiapine in distinct body compartments/tissues showed no statistically significant relationship with the length of the postmortem interval. Furthermore, this study did not confirm the anecdotal correlation of peripheral blood concentrations with skeletal muscle concentrations. Otherwise, there was no consistency regarding selecting an endpoint for analysis.

Stress in the microbiome-immune crosstalk

The gut microbiota exerts a mutualistic interaction with the host in a fragile ecosystem and the host intestinal, neural, and immune cells. Perturbations of the gastrointestinal track composition after stress have profound consequences on the central nervous system and the immune system. Reciprocally, brain signals after stress affect the gut microbiota highlighting the bidirectional communication between the brain and the gut. Here, we focus on the potential role of inflammation in mediating stress-induced gut-brain changes and discuss the impact of several immune cells and inflammatory molecules of the gut-brain dialogue after stress. Understanding the impact of microbial changes on the immune system after stress might provide new avenues for therapy.

The Importance of Visceral Hypersensitivity in Irritable Bowel Syndrome-Plant Metabolites in IBS Treatment

The visceral stimuli from the digestive tract are transmitted via afferent nerves through the spinal cord to the brain, where they are felt as pain. The overreaction observed in the brain of irritable bowel syndrome (IBS) patients may be due to increased peripheral sensitivity to stimuli from the gastrointestinal tract. Although the exact pathway is uncertain, attenuation of visceral hypersensitivity is still of interest in treating IBS. It has been shown that stress stimulates the sympathetic nervous system while inhibiting the vagus nerve (VN). In addition, stress factors lead to dysbiosis and chronic low-grade inflammation of the intestinal mucosa, which can lead to lower gastrointestinal visceral hypersensitivity. Therefore, an important goal in the treatment of IBS is the normalization of the intestinal microflora. An interesting option seems to be nutraceuticals, including Terminalia chebula, which has antibacterial and antimicrobial activity against various pathogenic Gram-positive and Gram-negative bacteria. Additionally, short-term transcutaneous vagus nerve stimulation can reduce the stress-induced increase in intestinal permeability, thereby reducing inflammation. The conducted studies also indicate a relationship between the stimulation of the vagus nerve (VN) and the activation of neuromodulatory networks in the central nervous system. Therefore, it seems reasonable to conclude that a two-way action through stimulating the VN and using nutraceuticals may become an effective therapy in treating IBS.

Characterization of gut microbiota profile in Iranian patients with bipolar disorder compared to healthy controls

Introduction

The human gut microbiota plays a crucial role in mental health through the gut-brain axis, impacting central nervous system functions, behavior, mood, and anxiety. Consequently, it is implicated in the development of neuropsychiatric disorders. This study aimed to assess and compare the gut microbiota profiles and populations of individuals with bipolar disorder and healthy individuals in Iran.

Methods

Fecal samples were collected from 60 participants, including 30 bipolar patients (BPs) and 30 healthy controls (HCs), following rigorous entry criteria. Real-time quantitative PCR was utilized to evaluate the abundance of 10 bacterial genera/species and five bacterial phyla.

Results

Notably, Actinobacteria and Lactobacillus exhibited the greatest fold change in BPs compared to HCs at the phylum and genus level, respectively, among the bacteria with significant population differences. Ruminococcus emerged as the most abundant genus in both groups, while Proteobacteria and Bacteroidetes showed the highest abundance in BPs and HCs, respectively, at the phylum level. Importantly, our investigation revealed a lower Firmicutes/Bacteroidetes ratio, potentially serving as a health indicator, in HCs compared to BPs.

Conclusion

This study marks the first examination of an Iranian population and provides compelling evidence of significant differences in gut microbiota composition between BPs and HCs, suggesting a potential link between brain functions and the gut microbial profile and population.

Epstein-Barr virus-acquired immunodeficiency in myalgic encephalomyelitis-Is it present in long COVID?

Both myalgic encephalomyelitis or chronic fatigue syndrome (ME/CFS) and long COVID (LC) are characterized by similar immunological alterations, persistence of chronic viral infection, autoimmunity, chronic inflammatory state, viral reactivation, hypocortisolism, and microclot formation. They also present with similar symptoms such as asthenia, exercise intolerance, sleep disorders, cognitive dysfunction, and neurological and gastrointestinal complaints. In addition, both pathologies present Epstein-Barr virus (EBV) reactivation, indicating the possibility of this virus being the link between both pathologies. Therefore, we propose that latency and recurrent EBV reactivation could generate an acquired immunodeficiency syndrome in three steps: first, an acquired EBV immunodeficiency develops in individuals with "weak" EBV HLA-II haplotypes, which prevents the control of latency I cells. Second, ectopic lymphoid structures with EBV latency form in different tissues (including the CNS), promoting inflammatory responses and further impairment of cell-mediated immunity. Finally, immune exhaustion occurs due to chronic exposure to viral antigens, with consolidation of the disease. In the case of LC, prior to the first step, there is the possibility of previous SARS-CoV-2 infection in individuals with "weak" HLA-II haplotypes against this virus and/or EBV.

Serotonin reuptake transporter deficiency promotes liver steatosis and impairs intestinal barrier function in obese mice fed a Western-style diet

BACKGROUND

Intestinal barrier dysfunctions have been associated with liver steatosis and metabolic diseases. Besides nutritional factors, like a Western-style diet (WSD), serotonin has been linked with leaky gut. Therefore, we aimed to evaluate the role of serotonin in the pathogenesis of intestinal barrier dysfunctions and liver steatosis in mice fed high-fat and high-sugar diets.

METHODS

6-8 weeks old male serotonin reuptake transporter knockout mice (SERT-/- ) and wild-type controls (SERT+/+ ) were fed either a WSD or a control diet (CD) ad libitum with or without fructose 30% (F) added to the drinking water for 12 weeks. Markers of liver steatosis and intestinal barrier function were assessed.

KEY RESULTS

SERT-/- mice showed increased weight gain compared with SERT+/+ mice when fed a WSD ± F for 12 weeks (p < 0.05), whereby SERT-/- mice exhibited reduced energy (-21%) intake. Furthermore, SERT knockout resulted in a more pronounced liver steatosis (p < 0.05), enhanced levels of endotoxin in portal vein plasma (p < 0.05), and increased liver expression of Tnf and Myd88 (p < 0.05), when mice were fed a WSD ± F. Finally, SERT-/- mice, when compared with SERT+/+ mice, had a decreased mRNA expression of Muc2 (p < 0.01), Ocln (p < 0.05), Cldn5 (p = 0.054) and 7 (p < 0.01), Defa5 (p < 0.05) and other antimicrobial peptides in the ileum. On the protein level, ZO-1 (p < 0.01) and DEFA5 protein (p < 0.0001) were decreased.

CONCLUSION AND INFERENCES

Our data demonstrate that SERT knockout causes weight gain, liver steatosis, and leaky gut, especially in mice fed a WSD. Therefore, SERT induction could be a novel therapeutic approach to improve metabolic diseases associated with intestinal barrier dysfunction.

The Impact of Microbiota on the Gut-Brain Axis: Examining the Complex Interplay and Implications

The association and interaction between the central nervous system (CNS) and enteric nervous system (ENS) is well established. Essentially ENS is the second brain, as we call it. We tried to understand the structure and function, to throw light on the functional aspect of neurons, and address various disease manifestations. We summarized how various neurological disorders influence the gut via the enteric nervous system and/or bring anatomical or physiological changes in the enteric nervous system or the gut and vice versa. It is known that stress has an effect on Gastrointestinal (GI) motility and causes mucosal erosions. In our literature review, we found that stress can also affect sensory perception in the central nervous system. Interestingly, we found that mutations in the neurohormone, serotonin (5-HT), would result in dysfunctional organ development and further affect mood and behavior. We focused on the developmental aspects of neurons and cognition and their relation to nutritional absorption via the gastrointestinal tract, the development of neurodegenerative disorders in relation to the alteration in gut microbiota, and contrariwise associations between CNS disorders and ENS. This paper further summarizes the synergetic relation between gastrointestinal and neuropsychological manifestations and emphasizes the need to include behavioral therapies in management plans.

Know your neighbors: microbial recognition at the intestinal barrier and its implications for gut homeostasis and inflammatory bowel disease

Intestinal epithelial cells (IECs) perform several physiological and metabolic functions at the epithelial barrier. IECs also play an important role in defining the overall immune functions at the mucosal region. Pattern recognition receptors (PRRs) on the cell surface and in other cellular compartments enable them to sense the presence of microbes and microbial products in the intestinal lumen. IECs are thus at the crossroads of mediating a bidirectional interaction between the microbial population and the immune cells present at the intestinal mucosa. This communication between the microbial population, the IECs and the underlying immune cells has a profound impact on the overall health of the host. In this review, we focus on the various PRRs present in different cellular compartments of IECs and discuss the recent developments in the understanding of their role in microbial recognition. Microbial recognition and signaling at the epithelial barrier have implications in the maintenance of intestinal homeostasis, epithelial barrier function, maintenance of commensals, and the overall tolerogenic function of PRRs in the gut mucosa. We also highlight the role of an aberrant microbial sensing at the epithelial barrier in the pathogenesis of inflammatory bowel disease (IBD) and the development of colorectal cancer.

New insights into irritable bowel syndrome pathophysiological mechanisms: contribution of epigenetics

Irritable bowel syndrome (IBS) is a complex multifactorial condition including alterations of the gut-brain axis, intestinal permeability, mucosal neuro-immune interactions, and microbiota imbalance. Recent advances proposed epigenetic factors as possible regulators of several mechanisms involved in IBS pathophysiology. These epigenetic factors include biomolecular mechanisms inducing chromosome-related and heritable changes in gene expression regardless of DNA coding sequence. Accordingly, altered gut microbiota may increase the production of metabolites such as sodium butyrate, a prominent inhibitor of histone deacetylases. Patients with IBS showed an increased amount of butyrate-producing microbial phila as well as an altered profile of methylated genes and micro-RNAs (miRNAs). Importantly, gene acetylation as well as specific miRNA profiles are involved in different IBS mechanisms and may be applied for future diagnostic purposes, especially to detect increased gut permeability and visceromotor dysfunctions. In this review, we summarize current knowledge of the role of epigenetics in IBS pathophysiology.

The Role of the Microbiome in First Episode of Psychosis

The relationship between the gut-brain-microbiome axis has gained great importance in the study of psychiatric disorders, as it may represent a new target for their treatment. To date, the available literature suggests that the microbiota may influence the pathophysiology of several diseases, including psychosis. The aim of this review is to summarize the clinical and preclinical studies that have evaluated the differences in microbiota as well as the metabolic consequences related to psychosis. Current data suggest that the genera Lactobacillus and Megasphaera are increased in schizophrenia (SZ), as well as alterations in the glutamate-glutamine-GABA cycle, serum levels of tryptophan, kynurenic acid (KYNA), and short-chain fatty acids (SCFAs). There are still very few studies on early-onset psychosis, thus more studies are needed to be able to propose targeted therapies for a point when the disease has just started or has not yet progressed.

Kudoa septempunctata Spores Cause Acute Gastroenteric Symptoms in Mouse and Musk Shrew Models as Evidenced In Vitro in Human Colon Cells

Kudoa septempunctata is a myxosporean parasite that infects the trunk muscles of olive flounder (Paralichthys olivaceus) and has been reported to cause foodborne illnesses in humans. However, the molecular mechanisms underlying K. septempunctata spore toxicity remain largely unknown. In this study, the gastroenteropathy of K. septempunctata was examined in human colon adenocarcinoma cells as well as experimental mice inoculated with spores. We found that K. septempunctata decreased transepithelial resistance and disrupted epithelial tight junctions by deleting ZO-1 in Caco-2 monolayers. Additionally, serotonin (5-HT), an emetic neurotransmitter, was increased in K. septempunctata-inoculated cells. In vivo, K. septempunctata spores induced diarrhea in suckling mice (80% in ddY and 70% in ICR mice), with a minimum provocative dose of 2 × 10⁵ K. septempunctata spores. In house musk shrews, K. septempunctata induced emesis within 1 h and induced serotonin secretion in the intestinal epithelium. In conclusion, K. septempunctata may induce diarrhea and emesis by increasing intestinal permeability and serotonin secretion.

Maternal Inflammation with Elevated Kynurenine Metabolites Is Related to the Risk of Abnormal Brain Development and Behavioral Changes in Autism Spectrum Disorder

Several studies show that genetic and environmental factors contribute to the onset and progression of neurodevelopmental disorders. Maternal immune activation (MIA) during gestation is considered one of the major environmental factors driving this process. The kynurenine pathway (KP) is a major route of the essential amino acid L-tryptophan (Trp) catabolism in mammalian cells. Activation of the KP following neuro-inflammation can generate various endogenous neuroactive metabolites that may impact brain functions and behaviors. Additionally, neurotoxic metabolites and excitotoxicity cause long-term changes in the trophic support, glutamatergic system, and synaptic function following KP activation. Therefore, investigating the role of KP metabolites during neurodevelopment will likely promote further understanding of additional pathophysiology of neurodevelopmental disorders, including autism spectrum disorder (ASD). In this review, we describe the changes in KP metabolism in the brain during pregnancy and represent how maternal inflammation and genetic factors influence the KP during development. We overview the patients with ASD clinical data and animal models designed to verify the role of perinatal KP elevation in long-lasting biochemical, neuropathological, and behavioral deficits later in life. Our review will help shed light on new therapeutic strategies and interventions targeting the KP for neurodevelopmental disorders.

A portable electrochemical sensing platform for serotonin detection based on surface-modified carbon fiber microelectrodes

Serotonin (5-HT) is one of the key neurotransmitters in the human body, regulating numerous physiological functions. A disruption in 5-HT homeostasis could result in serious health problems, including neurodegenerative disorders, depression, and 5-HT syndrome. Detection of 5-HT concentrations in biological fluids, such as urine, is a potential solution for early diagnosis of these diseases. In this study, we developed a novel, simple, and low-cost electrochemical sensing platform consisting of a portable workstation with customized electrodes for 5-HT detection in artificial biological fluids. Nafion/carbon nanotubes (CNTs) and electrochemically modified carbon fiber microelectrodes (Nafion-CNT/EC CFMEs) displayed improved 5-HT sensitivity and selectivity. Together with a customized Ag/AgCl reference electrode and Pt counter electrode, the portable 5-HT sensing platform had a sensitivity of 0.074 μA μM^-1 and a limit of detection (LOD) of 140 nM. This system was also assessed to measure 5-HT spiked in artificial urine samples, showing nearly full recovery rates. These satisfactory results demonstrated that the portable system exhibits outstanding performance and confirmed the feasibility of 5-HT detection, which can be used to provide point-of-care analysis in actual biological samples.

Expression Patterns of Serotonin Receptors 5-HT1A, 5-HT2A, and 5-HT3A during Human Fetal Lung Development

We analyzed the expression of the serotonin receptors 5-HT1A, 5-HT2A, and 5-HT3A at four different stages of fetal lung development from 12 to 40 weeks of gestation, divided into four groups: the pseudoglandular stage (12-16th week of development; n = 8), the canalicular stage (16th-26th week of development; n = 7), the saccular stage (26th-36th week of development; n = 5), and the alveolar stage (36th-40th week of development; n = 5). The strongest expression of all three receptor types was found in the epithelium of the proximal airways during the pseudoglandular, canalicular, and saccular stages and in a vascular wall. 5-HT1A was also strongly expressed in the smooth muscle cells of the proximal airway. Vascular smooth muscle cells and endothelium occasionally showed a strong expression of 5-HT1A and 5-HT2A. In the alveolar stage, the expression of 5-HT1A, 5-HT2A, and 5-HT3A was detected in both type I (p1) and type II (p2) pneumocytes, with a stronger expression in p2. A significant decrease in percent the 5-HT2A area and in the integrated density was observed at the alveolar stage. On the other hand, a significant decrease in the percentage area but an increase in the integrated density was observed for 5-HT3A toward the alveolar stage, suggesting that a smaller number of cells expressed 5-HT3A but that they (p1 and p2) significantly increased their 5-HT3A expression at the alveolar stage. The results presented provided us with new data on the development and function of the serotonin system in the human fetal lung and gave us insight into their possible involvement in the pathogenesis of lung pathology, particularly that characteristic of the neonatal period.

5-HT attenuates chronic stress-induced cognitive impairment in mice through intestinal flora disruption

BACKGROUND

The microbiota-gut-brain axis plays an important role in the development of depression. The aim of this study was to investigate the effects of 5-HT on cognitive function, learning and memory induced by chronic unforeseeable mild stress stimulation (CUMS) in female mice. CUMS mice and TPH2 KO mice were used in the study. Lactococcus lactis E001-B-8 fungus powder was orally administered to mice with CUMS.

METHODS

We used the open field test, Morris water maze, tail suspension test and sucrose preference test to examine learning-related behaviours. In addition, AB-PAS staining, immunofluorescence, ELISA, qPCR, Western blotting and microbial sequencing were employed to address our hypotheses.

RESULTS

The effect of CUMS was more obvious in female mice than in male mice. Compared with female CUMS mice, extracellular serotonin levels in TPH2 KO CUMS mice were significantly reduced, and cognitive dysfunction was aggravated. Increased hippocampal autophagy levels, decreased neurotransmitter levels, reduced oxidative stress damage, increased neuroinflammatory responses and disrupted gut flora were observed. Moreover, L. lactis E001-B-8 significantly improved the cognitive behaviour of mice.

CONCLUSIONS

These results strongly suggest that L. lactis E001-B-8 but not FLX can alleviate rodent depressive and anxiety-like behaviours in response to CUMS, which is associated with the improvement of 5-HT metabolism and modulation of the gut microbiome composition.

Aqueous cinnamon extract ameliorates bowel dysfunction and enteric 5-HT synthesis in IBS rats

Cinnamon protects against irritable bowel syndrome with diarrhea (IBS-D) in humans, but its efficacy and underlying mechanism of action remain poorly understood. Maternally separated (MS) IBS-D rat model and 2,4,6-trinitrobenzene sulfonic acid (TNBS)-induced post-inflammatory IBS-D rat model are characterized by visceral hyperalgesia and diarrhea. This study used the two models to evaluate the effect of cinnamon extract (CE) on bowel symptoms. The MS rat model was also used to explore its underlying anti-IBS mechanism. cinnamon extract reduced defecation frequency and visceral hyperalgesia in MS rats in a dose-dependent manner and effectively improved visceral hyperalgesia in TNBS rats. The efficacy of cinnamon extract was comparable to the positive drug serotonin receptor 3 (5-HT3) selective antagonist, Ramosetron. Excessive 5-HT, a well-known pathogenic factor for IBS, in the colon and circulation of IBS rats was reduced after cinnamon extract intervention. Both, gene and protein levels of the colonic 5-HT synthetase, Tryptophan Hydroxylase 1 (Tph1), were also decreased in CE-treated IBS rats. In addition, a luciferase assay revealed that cinnamon extract and its major components, catechin, procyanidin B1/2, cinnamic acid, and cinnamyl alcohol, significantly inhibited Tph1 transcription activity in vitro. These findings illustrated that aqueous cinnamon extract partially attenuated bowel symptoms in IBS models by directly inhibiting Tph1 expression and controlling 5-HT synthesis. This provides a scientific viewpoint for the use of cinnamon as a folk medication to treat IBS.

The Involvement of Kynurenine Pathway in Neurodegenerative Diseases

BACKGROUND

A growing body of evidence has shown the involvement of the kynurenine pathway (KP), the primary route of tryptophan (TRP) catabolism, in the pathophysiology of neuropsychiatric disorders.

OBJECTIVE

The study aims to provide a comprehensive and critical overview of the clinical evidence on the KP involvement in the pathophysiology of Alzheimer's disease (AD) and Parkinson's disease (PD), discussing therapeutic opportunities.

METHODS

We searched for studies investigating KP metabolites in human subjects with AD and/or PD.

RESULTS

Postmortem studies showed altered levels of KP metabolites in the brain of AD and PD patients compared with controls. Cross-sectional studies have reported associations between peripheral levels (serum or plasma) of KP metabolites and cognitive function in these patients, but the results are not always concordant.

CONCLUSION

Given the emerging evidence of the involvement of KP in the pathophysiology of neuropsychiatric/ neurodegenerative diseases and promising results from preclinical pharmacological studies, a better understanding of the KP involvement in AD and PD is warranted. Future longitudinal studies are needed to define the direction of the observed associations and specific therapeutic targets within the KP.

Investigating Key Targets of Dajianzhong Decoction for Treating Crohn’s Disease Using Weighted Gene Co-Expression Network

Background: Crohn’s disease (CD) is an inflammatory bowel disease, cases of which have substantially increased in recent years. The classical formula Dajianzhong decoction (DD, Japanese: Daikenchuto) is often used to treat CD, but few studies have evaluated related therapeutic mechanisms. In this study, we investigated the potential targets and mechanisms of DD used for treating CD at the molecular level through the weighted gene co-expression network. Methods: The main chemical components of the three DD herbs (Zanthoxylum bungeanum Maxim., Zingiber officinale (Willd.) Rosc., and Ginseng Radix et Rhizoma) were searched for using the HERB database. The targets for each component were identified using the SwissTargetPrediction and HERB databases, whereas the disease targets for CD were retrieved from the GeneCards and DisGeNET databases. The functional enrichment analysis was performed on the common targets of DD and CD. High-throughput sequencing data for CD patients were retrieved from the Gene Expression Omnibus database, and WGCNA was performed to identify the key targets. The association between the key targets and DD ingredients was verified using molecular docking. Results: By analyzing the interaction targets between DD and CD, 196 overlapping genes were identified. The enrichment results indicated that the PI3K-AKT, TNF, MAPK, and IL-17 signaling pathways influenced the mechanism of action of DD in counteracting CD. Combined with WGCNA, four differentially expressed genes (SLC6A4, NOS2, SHBG, and ABCB1) and their corresponding 24 compounds were closely related to the occurrence of CD. Conclusions: By integrating gene co-expression network analysis, this study preliminarily reveals the internal molecular mechanism of DD in treating CD from a systematic perspective, validated by molecular docking. However, these findings require further validation.

An evaluation of the rat intestinal monoamine biogeography days following exposure to acute stress

Stress-induced abnormalities in gut monoamine levels (e.g., serotonin, dopamine, norepinephrine) have been linked to gastrointestinal (GI) dysfunction, as well as the worsening of symptoms in GI disorders. However, the influence of stress on changes across the entire intestinal monoamine biogeography has not been well-characterized, especially in the days following stress exposure. Therefore, the aim of this study was to comprehensively assess changes to monoamine neurochemical signatures across the entire rat intestinal tract days after exposure to an acute stressor. To the end, adult male F344 rats were subjected to an episode of unpredictable tail shocks (acute stress) or left undisturbed. Forty-eight hours later rats were euthanized either following a 12 h period of fasting or 30 min of food access to evaluate neurochemical profiles during the peri- and early postprandial periods. Monoamine-related neurochemicals were measured via UHPLC in regions of the small intestine (duodenum, jejunum, ileum), large intestine (cecum, proximal colon, distal colon), cecal contents, fecal contents, and liver. The results suggest a relatively wide-spread increase in measures of serotonin activity across intestinal regions can be observed 48 h after exposure to acute stress, however some evidence was found supporting localized differences in serotonin metabolization. Moreover, acute stress exposure reduced catecholamine-related neurochemical concentrations most notably in the ileum, and to a lesser extent in the cecal contents. Next, stress-related fecal serotonin concentrations were consistent with intestinal profiles. However, fecal dopamine was elevated in association with stress, which did not parallel findings in any other intestinal area. Finally, stress exposure and the food access period together only had minor effects on intestinal monoamine profiles. Taken together, these data suggest nuanced differences in monoaminergic profiles exist across intestinal regions the days following exposure to an acute stressor, highlighting the importance of assessments that consider the entire intestinal tract biogeography when investigating stress-related biological outcomes that may be relevant to GI pathophysiology.

Effect of altered gut microbiota on visceral hypersensitivity of postinfectious irritable bowel syndrome mice

OBJECTIVE

Irritable bowel syndrome (IBS) is a common functional bowel disorder characterized with visceral hypersensitivity. Previous studies indicated gut microbiota alteration associated short-chain fatty acids (SCFAs) dysregulation is associated with IBS development. The aim of the study is to explore the potential role of microbiota dysbiosis mediated visceral hypersensitivity in postinfectious-IBS (PI-IBS) mouse model.

METHODS

Four-week-old NIH mice were randomly allocated into four groups: control mice, PI-IBS mice, PI-IBS mice co-housing with normal mice, and PI-IBS mice were administrated with a cocktail of antibiotics. Trichinella spiralis infection established PI-IBS mouse model. Microbiota in cecal contents and feces were analyzed by 16S rDNA sequencing. SCFAs were detected by gas chromatography. 5-hydroxytryptamine (5-HT) was evaluated by ELISA, and N-methyl-D-aspartate receptors (NMDARs) were examined by western blot. Visceral sensitivity was determined by abdominal withdrawal reflex in response to colorectal distention.

RESULTS

Increased SCFAs were observed in cecal contents and feces in PI-IBS mice accompanied with higher 5-HT and NMDAR subunits expressions in ileum and colon. Visceral hypersensitivity was observed in PI-IBS mice compared to control mice. When administrated with antibiotics cocktails and co-housing with normal mice, PI-IBS mice showed decreased SCFAs, 5-HT, NMDAR subunits expressions, and improved visceral hypersensitivity.

CONCLUSION

Gut microbiota alteration induced increased SCFAs, 5-HT and NMDAR subunits expressions were associated with visceral hypersensitivity in PI-IBS mice. The critical role of gut microbiota in improving visceral hypersensitivity was further identified by treatment of antibiotics cocktail and co-housing.

The Microbiota–Gut–Brain Axis in Psychiatric Disorders

Modulating the gut microbiome and its influence on human health is the subject of intense research. The gut microbiota could be associated not only with gastroenterological diseases but also with psychiatric disorders. The importance of factors such as stress, mode of delivery, the role of probiotics, circadian clock system, diet, and occupational and environmental exposure in the relationship between the gut microbiota and brain function through bidirectional communication, described as “the microbiome–gut–brain axis”, is especially underlined. In this review, we discuss the link between the intestinal microbiome and the brain and host response involving different pathways between the intestinal microbiota and the nervous system (e.g., neurotransmitters, endocrine system, immunological mechanisms, or bacterial metabolites). We review the microbiota alterations and their results in the development of psychiatric disorders, including major depressive disorder (MDD), schizophrenia (SCZ), bipolar disorder (BD), autism spectrum disorder (ASD), and attention-deficit hyperactivity disorder (ADHD).

Voluntary activation of muscle in humans: does serotonergic neuromodulation matter?

Ionotropic inputs to motoneurones have the capacity to depolarise and hyperpolarise the motoneurone, whereas neuromodulatory inputs control the state of excitability of the motoneurone. Intracellular recordings of motoneurones from in vitro and in situ animal preparations have provided extraordinary insight into the mechanisms that underpin how neuromodulators regulate neuronal excitability. However, far fewer studies have attempted to translate the findings from cellular and molecular studies into a human model. In this review, we focus on the role that serotonin plays in muscle activation in humans. Serotonin (5-HT) is a potent regulator of neuronal firing rates which can influence the force that can be generated by muscles during voluntary contractions. We firstly outline structural and functional characteristics of the serotonergic system, and then describe how motoneurone discharge can be facilitated and suppressed depending on the 5-HT receptor subtype that is activated. We then provide a narrative on how 5-HT effects can influence voluntary activation during muscle contractions in humans, and detail how 5-HT may be a mediator of exercise-induced fatigue that arises from the central nervous system. Abstract figure legend Inputs to neuromodulatory receptors on motoneurones, such as those involved in the serotonergic system, modify the motoneuroneâ¿¿s responsiveness to ionotropic input. The release of serotonin (5-HT) into the spinal cord is linked to the level of motor activity being performed, where 5-HT can increase the discharge rate of motoneurones via excitatory 5-HT receptors on the soma and dendrites. This in turn can lead to increased voluntary muscle activation (VA) and maximal force generation. However, intense release of 5-HT onto motoneurones may lead to a spill over of 5-HT into extracellular compartments to activate inhibitory 5-HT receptors on the axon initial segment. This can cause a reduction in motoneurone discharge rate, thus decreasing VA and maximal force generation. To gain insight into the serotonergic contributions to muscle activation in humans, pharmacological interventions have been employed to enhance the concentration of 5-HT in the central nervous system or activate selective 5-HT receptors. This article is protected by copyright. All rights reserved.

Dynamic transcriptome analysis of the muscles in high-fat diet-induced obese zebrafish (Danio rerio) under 5-HT treatment

Peripheral 5-hydroxytryptamine (5-HT, also called serotonin) is reportedly a potential therapeutic target in obesity-related metabolic diseases due to its regulatory role in energy homeostasis in mammals. However, information on the detailed effect of peripheral 5-HT on the energy metabolism in fishes, especially the lipid metabolism, and the underlying mechanism remains elusive. In this study, a diet-induced obesity model was developed in the zebrafish (Danio rerio), a prototypical animal model for metabolic disorders. The zebrafish were fed a high-fat diet for 8 weeks and were simultaneously injected with PBS, 0.1 mM and 10 mM 5-HT, intraperitoneally. The body weight was significantly lower in the zebrafish injected with 0.1 mM 5-HT (P < 0.05), however, there was no change in body length (P > 0.05) at the end of the 8-week treatment. The muscle tissues from the zebrafish treated with PBS and 5-HT were collected for transcriptomic analysis and the RNA-seq revealed 1134, 3713, and 2535 genes were screened out compared to the muscular DEGs among three groups. The enrichment analysis revealed DEGs to be significantly associated with multiple metabolic pathways, including ribosome, oxidative phosphorylation, proteasome, PPAR signaling pathway, and ferroptosis. Additionally, the qRT-PCR validated 12 DEGs out of which 10 genes exhibited consistent trends. Taken together, this data provided useful information on the transcriptional characteristics of the muscle tissue in the obese zebrafish exposed to 5-HT, offering important insights into the regulatory effect of peripheral 5-HT in teleosts, as well as novel approaches for preventing and treating obesity-related metabolic dysfunction.

High-fat diets on the enteric nervous system: Possible interactions and mechanisms underlying dysmotility

Obesity is a chronic disease that affects various physiological systems. Among them, the gastrointestinal tract appears to be a main target of this disease. High-fat diet (HFD) animal models can help recapitulate the classic signs of obesity and present a series of gastrointestinal alterations, mainly dysmotility. Because intestinal motility is governed by the enteric nervous system (ENS), enteric neurons, and glial cells have been studied in HFD models. Given the importance of the ENS in general gut physiology, this review aims to discuss the relationship between HFD-induced neuroplasticity and gut dysmotility observed in experimental models. Furthermore, we highlight components of the gut environment that might influence enteric neuroplasticity, including gut microbiota, enteric glio-epithelial unit, serotonin release, immune cells, and disturbances such as inflammation and oxidative stress.

Gut Microbiome and Neuroinflammation in Hypertension

Hypertension is a worldwide problem with major impacts on health including morbidity and mortality, as well as consumption of health care resources. Nearly 50% of American adults have high blood pressure, and this rate is rising. Even with multiple antihypertensive drugs and aggressive lifestyle modifications, blood pressure is inadequately controlled in about 1 of 5 hypertensive individuals. This review highlights a hypothesis for hypertension that suggests alternative mechanisms for blood pressure elevation and maintenance. A better understanding of these mechanisms could open avenues for more successful treatments. The hypothesis accounts for recent understandings of the involvement of gut physiology, gut microbiota, and neuroinflammation in hypertension. It includes bidirectional communication between gut microbiota and gut epithelium in the gut-brain axis that is involved in regulation of autonomic nervous system activity and blood pressure control. Dysfunction of this gut-brain axis, including dysbiosis of gut microbiota, gut epithelial dysfunction, and deranged input to the brain, contributes to hypertension via inflammatory mediators, metabolites, bacteria in the circulation, afferent information alterations, etc resulting in neuroinflammation and unbalanced autonomic nervous system activity that elevates blood pressure. This in turn negatively affects gut function and its microbiota exacerbating the problem. We focus this review on the gut-brain axis hypothesis for hypertension and possible contribution to racial disparities in hypertension. A novel idea, that immunoglobulin A-coated bacteria originating in the gut with access to the brain could be involved in hypertension, is raised. Finally, minocycline, with its anti-inflammatory and antimicrobial properties, is evaluated as a potential antihypertensive drug acting on this axis.

Predictive factors of inadequate bowel preparation for elective colonoscopy

Aim

This study aimed to evaluate the effects of factors like demographic items, comorbidities, and drug history on the inadequacy of colonic preparation before colonoscopy.

Background

Inadequate bowel preparation can lead to lower polyp detection rates, longer procedure times, and lower cecal intubation rates.

Methods

This population-based study was conducted on 2476 Iranian adults who were referred to two tertiary centers for elective colonoscopy between 2017 and 2018. Bowel preparation quality was scored by the Boston bowel preparation scale (BBPS). Univariate and multivariate logistic regressions were used to find the independent predictors of bowel preparation inadequacy.

Results

The results showed that 31.8% of patients had inadequate bowel preparation before their colonoscopy. Higher age, BMI>25, abdominal circumference>95 cm, low fruit consumption, and history of smoking were independently correlated with bowel preparation inadequacy. Additionally, using NSAIDs and SSRIs were correlated with bowel preparation adequacy in multivariate regression analysis. Finally, age, gender, ethnicity, BMI, abdominal circumference, fruit consumption, smoking, NSAIDs, SSRIs, education, constipation, physical activity, and diabetes entered the predictive model of this study. The area under the curve (AUC) reached 0.70 in the final step.

Conclusion

The independent risk factors associated with colonic preparation inadequacy were identified, and herein, a predictive model is suggested for identifying patients with a high risk of bowel preparation inadequacy before a colonoscopy so that alternative preparation techniques can be employed among high-risk groups to yield optimal preparation quality.

New Concepts of the Interplay Between the Gut Microbiota and the Enteric Nervous System in the Control of Motility

Propulsive gastrointestinal (GI) motility is critical for digestive physiology and host defense. GI motility is finely regulated by the intramural reflex pathways of the enteric nervous system (ENS). The ENS is in turn regulated by luminal factors: diet and the gut microbiota. The gut microbiota is a vast ecosystem of commensal bacteria, fungi, viruses, and other microbes. The gut microbiota not only regulates the motor programs of the ENS but also is critical for the normal structure and function of the ENS. In this chapter, we highlight recent research that has shed light on the microbial mechanisms of interaction with the ENS involved in the control of motility. Toll-like receptor signaling mechanisms have been shown to maintain the structural integrity of the ENS and the neurochemical phenotypes of enteric neurons, in part through the production of trophic factors including glia-derived neurotrophic factor. Microbiota-derived short-chain fatty acids and/or single-stranded RNA regulates the synthesis of serotonin in enterochromaffin cells, which are involved in the initiation of enteric reflexes, among other functions. Further evidence suggests a crucial role for microbial modulation of serotonin in maintaining the integrity of the ENS through enteric neurogenesis. Understanding the microbial pathways of enteric neural control sheds new light on digestive health and provides novel treatment strategies for GI motility disorders.

A multidimensional coding architecture of the vagal interoceptive system

Interoception, the ability to timely and precisely sense changes inside the body, is critical for survival^1-4. Vagal sensory neurons (VSNs) form an important body-to-brain connection, navigating visceral organs along the rostral-caudal axis of the body and crossing the surface-lumen axis of organs into appropriate tissue layers^5,6. The brain can discriminate numerous body signals through VSNs, but the underlying coding strategy remains poorly understood. Here we show that VSNs code visceral organ, tissue layer and stimulus modality-three key features of an interoceptive signal-in different dimensions. Large-scale single-cell profiling of VSNs from seven major organs in mice using multiplexed projection barcodes reveals a 'visceral organ' dimension composed of differentially expressed gene modules that code organs along the body's rostral-caudal axis. We discover another 'tissue layer' dimension with gene modules that code the locations of VSN endings along the surface-lumen axis of organs. Using calcium-imaging-guided spatial transcriptomics, we show that VSNs are organized into functional units to sense similar stimuli across organs and tissue layers; this constitutes a third 'stimulus modality' dimension. The three independent feature-coding dimensions together specify many parallel VSN pathways in a combinatorial manner and facilitate the complex projection of VSNs in the brainstem. Our study highlights a multidimensional coding architecture of the mammalian vagal interoceptive system for effective signal communication.

Parkinson's Disease and the Metal-Microbiome-Gut-Brain Axis: A Systems Toxicology Approach

Parkinson's Disease (PD) is a neurodegenerative disease, leading to motor and non-motor complications. Autonomic alterations, including gastrointestinal symptoms, precede motor defects and act as early warning signs. Chronic exposure to dietary, environmental heavy metals impacts the gastrointestinal system and host-associated microbiome, eventually affecting the central nervous system. The correlation between dysbiosis and PD suggests a functional and bidirectional communication between the gut and the brain. The bioaccumulation of metals promotes stress mechanisms by increasing reactive oxygen species, likely altering the bidirectional gut-brain link. To better understand the differing molecular mechanisms underlying PD, integrative modeling approaches are necessary to connect multifactorial perturbations in this heterogeneous disorder. By exploring the effects of gut microbiota modulation on dietary heavy metal exposure in relation to PD onset, the modification of the host-associated microbiome to mitigate neurological stress may be a future treatment option against neurodegeneration through bioremediation. The progressive movement towards a systems toxicology framework for precision medicine can uncover molecular mechanisms underlying PD onset such as metal regulation and microbial community interactions by developing predictive models to better understand PD etiology to identify options for novel treatments and beyond. Several methodologies recently addressed the complexity of this interaction from different perspectives; however, to date, a comprehensive review of these approaches is still lacking. Therefore, our main aim through this manuscript is to fill this gap in the scientific literature by reviewing recently published papers to address the surrounding questions regarding the underlying molecular mechanisms between metals, microbiota, and the gut-brain-axis, as well as the regulation of this system to prevent neurodegeneration.

Targeting Mechano-Transcription Process as Therapeutic Intervention in Gastrointestinal Disorders

Mechano-transcription is a process whereby mechanical stress alters gene expression. The gastrointestinal (GI) tract is composed of a series of hollow organs, often encountered by transient or persistent mechanical stress. Recent studies have revealed that persistent mechanical stress is present in obstructive, functional, and inflammatory disorders and alters gene transcription in these conditions. Mechano-transcription of inflammatory molecules, pain mediators, pro-fibrotic and growth factors has been shown to play a key role in the development of motility dysfunction, visceral hypersensitivity, inflammation, and fibrosis in the gut. In particular, mechanical stress-induced cyclooxygenase-2 (COX-2) and certain pro-inflammatory mediators in gut smooth muscle cells are responsible for motility dysfunction and inflammatory process. Mechano-transcription of pain mediators such as nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF) may lead to visceral hypersensitivity. Emerging evidence suggests that mechanical stress in the gut also leads to up-regulation of certain proliferative and pro-fibrotic mediators such as connective tissue growth factor (CTGF) and osteopontin (OPN), which may contribute to fibrostenotic Crohn's disease. In this review, we will discuss the pathophysiological significance of mechanical stress-induced expression of pro-inflammatory molecules, pain mediators, pro-fibrotic and growth factors in obstructive, inflammatory, and functional bowel disorders. We will also evaluate potential therapeutic targets of mechano-transcription process for the management of these disorders.

The Brain-Gut-Microbiome System: Pathways and Implications for Autism Spectrum Disorder

Gastrointestinal dysfunction is one of the most prevalent physiological symptoms of autism spectrum disorder (ASD). A growing body of largely preclinical research suggests that dysbiotic gut microbiota may modulate brain function and social behavior, yet little is known about the mechanisms that underlie these relationships and how they may influence the pathogenesis or severity of ASD. While various genetic and environmental risk factors have been implicated in ASD, this review aims to provide an overview of studies elucidating the mechanisms by which gut microbiota, associated metabolites, and the brain interact to influence behavior and ASD development, in at least a subgroup of individuals with gastrointestinal problems. Specifically, we review the brain-gut-microbiome system and discuss findings from current animal and human studies as they relate to social-behavioral and neurological impairments in ASD, microbiota-targeted therapies (i.e., probiotics, fecal microbiota transplantation) in ASD, and how microbiota may influence the brain at molecular, structural, and functional levels, with a particular interest in social and emotion-related brain networks. A deeper understanding of microbiome-brain-behavior interactions has the potential to inform new therapies aimed at modulating this system and alleviating both behavioral and physiological symptomatology in individuals with ASD.

Gut microbiome and metabolome in a non-human primate model of chronic excessive alcohol drinking

A relationship between the gut microbiome and alcohol use disorder has been suggested. Excessive alcohol use produces changes in the fecal microbiome and metabolome in both rodents and humans. Yet, these changes can be observed only in a subgroup of the studied populations, and reversal does not always occur after abstinence. We aimed to analyze fecal microbial composition and function in a translationally relevant baboon model of chronic heavy drinking that also meets binge criteria (drinking too much, too fast, and too often), i.e., alcohol ~1 g/kg and blood alcohol levels (BALs) ≥ 0.08 g/dL in a 2-hour period, daily, for years. We compared three groups of male baboons (Papio anubis): L = Long-term alcohol drinking group (12.1 years); S = Short-term alcohol drinking group (2.7 years); and C = Control group, drinking a non-alcoholic reinforcer (Tang®) (8.2 years). Fecal collection took place during 3 days of Drinking (D), followed by a short period (3 days) of Abstinence (A). Fecal microbial alpha- and beta-diversity were significantly lower in L vs. S and C (p's < 0.05). Members of the commensal families Lachnospiraceae and Prevotellaceae showed a relative decrease, whereas the opportunistic pathogen Streptococcus genus showed a relative increase in L vs. S and C (p's < 0.05). Microbiota-related metabolites of aromatic amino acids, tricarboxylic acid cycle, and pentose increased in L vs. S and C (FDR-corrected p < 0.01), with the latter two suggesting high energy metabolism and enhanced glycolysis in the gut lumen in response to alcohol. Consistent with the long-term alcohol exposure, mucosal damage and oxidative stress markers (N-acetylated amino acids, 2-hydroxybutyrate, and metabolites of the methionine cycle) increased in L vs. S and C (FDR-corrected p < 0.01). Overall, S showed few differences vs. C, possibly due to the long-term, chronic alcohol exposure needed to alter the normal gut microbiota. In the three groups, the fecal microbiome barely differed between conditions D and A, whereas the metabolome shifted in the transition from condition D to A. In conclusion, changes in the fecal microbiome and metabolome occur after significant long-term excessive drinking and are only partially affected by acute forced abstinence from alcohol. These results provide novel information on the relationship between the fecal microbiome and metabolome in a controlled experimental setting and using a unique non-human primate model of chronic excessive alcohol drinking.

Symbiont-regulated serotonin biosynthesis modulates tick feeding activity

Ticks are obligate hematophagous arthropods. Blood feeding ensures that ticks obtain nutrients essential for their survival, development, and reproduction while providing routes for pathogen transmission. However, the effectors that determine tick feeding activities remain poorly understood. Here, we demonstrate that reduced abundance of the symbiont Coxiella (CHI) in Haemaphysalis longicornis decreases blood intake. Providing tetracycline-treated ticks with the CHI-derived tryptophan precursor chorismate, tryptophan, or 5-hydroxytryptamine (5-HT; serotonin) restores the feeding defect. Mechanistically, CHI-derived chorismate increases tick 5-HT biosynthesis by stimulating the expression of aromatic amino acid decarboxylase (AAAD), which catalyzes the decarboxylation of 5-hydroxytryptophan (5-HTP) to 5-HT. The increased level of 5-HT in the synganglion and midgut promotes tick feeding. Inhibition of CHI chorismate biosynthesis by treating the colonized tick with the herbicide glyphosate suppresses blood-feeding behavior. Taken together, our results demonstrate an important function of the endosymbiont Coxiella in the regulation of tick 5-HT biosynthesis and feeding.

Enteric Microbiota-Mediated Serotonergic Signaling in Pathogenesis of Irritable Bowel Syndrome

Irritable bowel syndrome (IBS) is a chronic functional disorder that affects the gastrointestinal tract. Details regarding the pathogenesis of IBS remain largely unknown, though the dysfunction of the brain-gut-microbiome (BGM) axis is a major etiological factor, in which neurotransmitters serve as a key communication tool between enteric microbiota and the brain. One of the most important neurotransmitters in the pathology of IBS is serotonin (5-HT), as it influences gastrointestinal motility, pain sensation, mucosal inflammation, immune responses, and brain activity, all of which shape IBS features. Genome-wide association studies discovered susceptible genes for IBS in serotonergic signaling pathways. In clinical practice, treatment strategies targeting 5-HT were effective for a certain portion of IBS cases. The synthesis of 5-HT in intestinal enterochromaffin cells and host serotonergic signaling is regulated by enteric resident microbiota. Dysbiosis can trigger IBS development, potentially through aberrant 5-HT signaling in the BGM axis; thus, the manipulation of the gut microbiota may be an alternative treatment strategy. However, precise information regarding the mechanisms underlying the microbiota-mediated intestinal serotonergic pathway related to the pathogenesis of IBS remains unclear. The present review summarizes current knowledge and recent progress in understanding microbiome–serotonin interaction in IBS cases.