Novel aspects of enteric serotonergic signaling in health and brain-gut disease

An open window: the crucial role of the gut-brain axis in neurodevelopmental outcomes post-neurocritical illness

Among patients admitted to the pediatric intensive care unit, approximately 10% are discharged with a new functional morbidity. For those who were admitted with a neurocritical illness, the number can be as high as 60%. The most common diagnoses for a neurocritical illness admission include traumatic brain injury, status epilepticus, post-cardiac arrest, hypoxic ischemic encephalopathy, meningo/encephalitis, and stroke. The gut-brain axis is crucial to childhood development, particularly neurodevelopment. Alterations on either side of the bidirectional communication of the gut-brain axis have been shown to alter typical development and have been associated with autism spectrum disorder, anxiety, sleep disturbances, and learning disabilities, among others. For those patients who have experienced a direct neurologic insult, subsequent interventions may contribute to dysbiosis, which could compound injury to the brain. Increasing data suggests the existence of a critical window for both gut microbiome plasticity and neurodevelopment in which interventions could help or could harm and warrant further investigation.

Host-microbe serotonin metabolism

As a result of a long evolutionary history, serotonin plays a variety of physiological roles, including neurological, cardiovascular, gastrointestinal, and endocrine functions. While many of these activities can be accommodated within the serotoninergic activity, recent findings have revealed an unsuspected role of serotonin in orchestrating host and microbial dialogue at the tryptophan dining table, to the benefit of local and systemic homeostasis. Herein we review the dual role of serotonin at the host-microbe interface and discuss how unraveling the interconnections among the host and microbial pathways of tryptophan degradation may help to accommodate the versatility of serotonin in physiology and pathology.

Management of Refractory Functional Gastrointestinal Disorders: What Role Should Psychiatrists Have?

Currently, it has been stated that psychiatric and psychological problems are equally paramount aspects of the clinical modulation and manifestation of both the central nervous and digestive systems, which could be used to restore balance. The present narrative review aims to provide an elaborate description of the bio-psycho-social facets of refractory functional gastrointestinal disorders, psychiatrists' role, specific psychiatric approach, and the latest psychiatric and psychological perspectives on practical therapeutic management. In this respect, "psyche," "psychiatry," "psychology," "psychiatrist," "psychotropic," and "refractory functional gastrointestinal disorders" (as the keywords) were searched in relevant English publications from January 1, 1950, to March 1, 2024, in the PubMed, Web of Science, Scopus, EMBASE, Cochrane Library, and Google Scholar databases. Eventually, the narrative technique was adopted to reach a compelling story with a high level of cohesion through material synthesis. The current literature recognizes the brain-gut axis modulation as a therapeutic target for refractory functional gastrointestinal disorders and the bio-psycho-social model as an integrated framework to explain disease pathogenesis. The results also reveal some evidence to affirm the benefits of psychotropic medications and psychological therapies in refractory functional gastrointestinal disorders, even when psychiatric symptoms were absent. It seems that psychiatrists are required to pay higher levels of attention to both the assessment and treatment of patients with refractory functional gastrointestinal disorders, accompanied by educating and training practitioners who take care of these patients.

The emerging role of gut hormones

The gut is traditionally recognized as the central organ for the digestion and absorption of nutrients, however, it also functions as a significant endocrine organ, secreting a variety of hormones such as glucagon-like peptide 1, serotonin, somatostatin, and glucocorticoids. These gut hormones, produced by specialized intestinal epithelial cells, are crucial not only for digestive processes but also for the regulation of a wide range of physiological functions, including appetite, metabolism, and immune responses. While gut hormones can exert systemic effects, they also play a pivotal role in maintaining local homeostasis within the gut. This review discusses the role of the gut as an endocrine organ, emphasizing the stimuli, the newly discovered functions, and the clinical significance of gut-secreted hormones. Deciphering the emerging role of gut hormones will lead to a better understanding of gut homeostasis, innovative treatments for disorders in the gut, as well as systemic diseases.

Mouse enteric neurons control intestinal plasmacytoid dendritic cell function via serotonin-HTR7 signaling

Serotonergic neurons in the central nervous system control behavior and mood, but knowledge of the roles of serotonergic circuits in the regulation of immune homeostasis is limited. Here, we employ mouse genetics to investigate the functions of enteric serotonergic neurons in the control of immune responses and find that these circuits regulate IgA induction and boost host defense against oral, but not systemic Salmonella Typhimurium infection. Enteric serotonergic neurons promote gut-homing, retention and activation of intestinal plasmacytoid dendritic cells (pDC). Mechanistically, this neuro-immune crosstalk is achieved through a serotonin-5-HT receptor 7 (HTR7) signaling axis that ultimately facilitates the pDC-mediated differentiation of IgA+ B cells from IgD+ precursors in the gut. Single-cell RNA-seq data further reveal novel patterns of bidirectional communication between specific subsets of enteric neurons and lamina propria DC. Our findings thus reveal a close interplay between enteric serotonergic neurons and gut immune homeostasis that enhances mucosal defense.

Liangxue Tongyu prescription attenuates neuroinflammation by increasing cholecystokinin octapeptide in acute intracerebral hemorrhage rats

Inflammatory reactions after acute intracerebral hemorrhage (AICH) contribute significantly to a poor prognosis. Liangxue Tongyu Prescription (LTP) has been proven to be clinically effective in treating AICH. Numerous studies have shown that LTP suppresses brain inflammatory damage in AICH, while the internal mechanisms underlying its action remain unclear. The aim of this study was to verify the anti-inflammatory effects of LTP on an AICH rat model and investigate the potential mechanisms. The AICH rat models were created by injecting autologous blood into the right caudate nucleus. LTP markedly decreased cerebral hematoma and brain water content and recovered from neurological deficits. Meanwhile, LTP prevented microglial activation and reduced the inflammatory reaction caused by pro-inflammatory cytokines, such as tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β) and interleukin-6 (IL-6). Notably, the expression of cholecystokinin octapeptide (CCK-8) in the brain and intestine was increased by LTP or CCK-8 treatment. LTP further suppressed nuclear factor kappa B (NF-κB) in the brains of rats with AICH. Moreover, LTP increased the protein and mRNA expression of Occludin and Claudin-1 in the intestine and decreased the levels of lipopolysaccharide (LPS) and diamine oxidase (DAO) in serum. Furthermore, the results showed that LTP increased the protein and mRNA expression of Claudin-5 and zonula occludens-1 (ZO-1) in the brain. CCK-8 receptor antagonists increased the expression of NF-κB and the concentration of pro-inflammatory cytokines. These findings suggested that LTP attenuated neuroinflammation by increasing CCK-8 in the brain and intestine, and its mechanism might be related to alterations in the gut-brain axis (GBA).

Peripheral Serotonin Controls Dietary Fat Absorption and Chylomicron Secretion via 5-HT4 Receptor in Males

Postprandial dyslipidemia is commonly present in people with type 2 diabetes and obesity and is characterized by overproduction of apolipoprotein B48-containing chylomicron particles from the intestine. Peripheral serotonin is emerging as a regulator of energy homeostasis with profound implications for obesity; however, its role in dietary fat absorption and chylomicron production is unknown. Chylomicron production was assessed in Syrian golden hamsters by administering an olive oil gavage and IP poloxamer to inhibit lipoprotein clearance. Administration of serotonin or selective serotonin reuptake inhibitor, fluoxetine, increased postprandial plasma triglyceride (TG) and TG-rich lipoproteins. Conversely, inhibiting serotonin synthesis pharmacologically by p-chlorophenylalanine (PCPA) led to a reduction in both the size and number of TG-rich lipoprotein particles, resulting in lower plasma TG and apolipoprotein B48 levels. The effects of PCPA occurred independently of gastric emptying and vagal afferent signaling. Inhibiting serotonin synthesis by PCPA led to increased TG within the intestinal lumen and elevated levels of TG and cholesterol in the stool when exposed to a high-fat/high-cholesterol diet. These findings imply compromised fat absorption, as evidenced by reduced lipase activity in the duodenum and lower levels of serum bile acids, which are indicative of intestinal bile acids. During the postprandial state, mRNA levels for serotonin receptors (5-HTRs) were upregulated in the proximal intestine. Administration of cisapride, a 5-HT4 receptor agonist, alleviated reductions in postprandial lipemia caused by serotonin synthesis inhibition, indicating that serotonin controls dietary fat absorption and chylomicron secretion via 5-HT4 receptor.

TPH1 inhibits bladder tumorigenesis by targeting HIF-1α pathway in bladder cancer

Background

BCa is the most common cancer of the urinary system. TPH1 has been reported to be associated with distinct tumorigenesis. However, the role of TPH1 in BCa remains to be clarified.

Objectives

Our aim is to demonstrate the molecular mechanism of TPH1 in BCa carcinogenesis and development.

Methods

In research, we explored the effect of TPH1 on T24 cells. Colony formation, soft agar, and cell proliferation assays were used to determine the survival and proliferative capacity of cells. Moreover, TPH1-/- cell lines were analyzed using CRISP-CAS9, and the recovery experiment was conducted. Realtime fluorescence quantitative PCR (qPCR) and Western blot were used to detect HIF-1α mRNA levels and TPH1 protein.

Results

The TPH1 expression is lower in tumor tissues than in normal tissues. Colony formation, soft agar, and cell proliferation assays revealed that the overexpression of TPH1 declined cells survival. Moreover, the deficiency of TPH1 increased the number of clones. These results suggested that survival rate of TPH1 overexpression was repressed in cells. In addition, we found that HIF-1α activity was significantly downregulated with an increase in TPH1. The transcriptional activity of survivin was increased with TPH1-/- cells. Then, the proliferative ability of TPH1-/- cells was almost similar to the wild type levels with the treatment of LW6, TPH1 might play a major role to repress HIF-1α activity.

Conclusions

Taken together, these results suggested that increasing TPH1 activity could inhibit survival and proliferation of cells via HIF-1α pathway. TPH1 may be a potential target for human BCa therapy.

New insights into the effects of serotonin on Parkinson's disease and depression through its role in the gastrointestinal tract

Neuropsychiatric and neurodegenerative disorders are frequently associated with gastrointestinal (GI) co-pathologies. Although the central and enteric nervous systems (CNS and ENS, respectively) have been studied separately, there is increasing interest in factors that may contribute to conditions affecting both systems. There is compelling evidence that serotonin (5-HT) may play an important role in several gut-brain disorders. It is well known that 5-HT is essential for the development and functioning of the CNS. However, most of the body's 5-HT is produced in the GI tract. A deeper understanding of the specific effects of enteric 5-HT on gut-brain disorders may provide the basis for the development of new therapeutic targets. This review summarizes current data focusing on the important role of 5-HT in ENS development and motility, with particular emphasis on novel aspects of 5-HT signaling in conditions where CNS and ENS comorbidities are common, such as Parkinson's disease and depressive disorders.

Chronic intestinal pseudo-obstruction: associations with gut microbiota and genes expression of intestinal serotonergic pathway

BACKGROUND

Pediatric chronic intestinal pseudo-obstruction (PIPO) is a rare disease characterized by symptoms and radiological signs suggestive of intestinal obstruction, in the absence of lumen-occluding lesions. It results from an extremely severe impairment of propulsive motility. The intestinal endocrine system (IES) jointly with the enteric nervous system (ENS) regulates secreto-motor functions via different hormones and bioactive messengers/neurotransmitters. The neurotransmitter 5-hydroxytryptamine (5-HT) (or serotonin) is linked to intestinal peristalsis and secretory reflexes. Gut microbiota and its interplay with ENS affect 5-HT synthesis, release, and the subsequent serotonin receptor activation. To date, the interplay between 5-HT and gut microbiota in PIPO remains largely unclear. This study aimed to assess correlations between mucosa associated microbiota (MAM), intestinal serotonin-related genes expression in PIPO. To this purpose, biopsies of the colon, ileum and duodenum have been collected from 7 PIPO patients, and 7 age-/sex-matched healthy controls. After DNA extraction, the MAM was assessed by next generation sequencing (NGS) of the V3-V4 region of the bacterial RNA 16 S, on an Illumina Miseq platform. The expression of genes implicated in serotoninergic pathway (TPH1, SLC6A4, 5-HTR3 and 5-HTR4) was established by qPCR, and correlations with MAM and clinical parameters of PIPO have been evaluated.

RESULTS

Our results revealed that PIPO patients exhibit a MAM with a different composition and with dysbiosis, i.e. with a lower biodiversity and fewer less connected species with a greater number of non-synergistic relationships, compared to controls. qPCR results revealed modifications in the expression of serotonin-related intestinal genes in PIPO patients, when compared to controls. Correlation analysis do not reveal any kind of connection.

CONCLUSIONS

For the first time, we report in PIPO patients a specific MAM associated to underlying pathology and an altered intestinal serotonin pathway. A possible dysfunction of the serotonin pathway, possibly related to or triggered by an altered microbiota, may contribute to dysmotility in PIPO patients. The results of our pilot study provide the basis for new biomarkers and innovative therapies targeting the microbiota or serotonin pathways in PIPO patients.

Necrotizing Enterocolitis and the Preterm Infant Microbiome

Preterm infants differ significantly from their term infant counterparts regarding bacterial colonization patterns related to maternal microbiota diversity, mode of delivery, feeding type, antibiotic exposure, and the environmental influences related to prolonged hospitalization in the neonatal intensive care unit (NICU). Necrotizing enterocolitis (NEC), a multifactorial intestinal disorder characterized by ischemic bowel disease, disproportionately impacts preterm infants and has a high disease burden. Recent studies in the basic, translational, and clinical scientific literature have advanced knowledge into this complex disease process. Despite the explosion of research into NEC, however, there is a still a great deal unknown about this devastating illness. Additionally, the disease morbidity and mortality for NEC remain high despite advances in therapy options. This chapter reviews the current literature into the preterm infant microbiome, pathogenesis of NEC, potential targets for altering preterm microbiome, influence of microbiome on other organ systems, long-term implications of microbiome dysbiosis, and future directions of study.

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.

Neuroprotection in metabolic syndrome by environmental enrichment. A lifespan perspective

Metabolic syndrome (MetS) is defined by the concurrence of different metabolic conditions: obesity, hypertension, dyslipidemia, and hyperglycemia. Its incidence has been increasingly rising over the past decades and has become a global health problem. MetS has deleterious consequences on the central nervous system (CNS) and neurological development. MetS can last several years or be lifelong, affecting the CNS in different ways and treatments can help manage condition, though there is no known cure. The early childhood years are extremely important in neurodevelopment, which extends beyond, encompassing a lifetime. Neuroplastic changes take place all life through - childhood, adolescence, adulthood, and old age - are highly sensitive to environmental input. Environmental factors have an important role in the etiopathogenesis and treatment of MetS, so environmental enrichment (EE) stands as a promising non-invasive therapeutic approach. While the EE paradigm has been designed for animal housing, its principles can be and actually are applied in cognitive, sensory, social, and physical stimulation programs for humans. Here, we briefly review the central milestones in neurodevelopment at each life stage, along with the research studies carried out on how MetS affects neurodevelopment at each life stage and the contributions that EE models can provide to improve health over the lifespan.

Zonulin levels are associated with cortisol, dopamine, and serotonin levels in irritable bowel syndrome

Increase intestinal permeability is one of the main mechanisms for the development of irritable bowel syndrome (IBS). The role of stress and nutrition factors is considered as key modifiable factors contributing to the development of increase intestinal permeability. Purpose of the study: to evaluate the content of a marker of increased intestinal permeability (zonulin in feces) in relation to dietary habits, levels of anxiety and depression, levels of stress hormones (cortisol in saliva) and neurotransmitters (serotonin in blood serum, dopamine in blood plasma) in patients with IBS. Materials and methods: an open cohort prospective study was conducted with the inclusion of 263 patients with an established diagnosis of IBS. The control group consisted of 40 healthy volunteers. All individuals included in the study were assessed for diet and eating habits, the severity of anxiety and depression, including the level of specific anxiety in relation to gastrointestinal symptoms, and quality of life. In addition, the levels of cortisol in the morning and evening portions of saliva, serum serotonin, plasma dopamine and fecal zonulin were assessed. Results: in patients with IBS, the marker of increased intestinal permeability (zonulin in feces) is closely related to the nature of nutrition, anxiety levels, cortisol and serotonin secretion, and is also associated with the development of abdominal pain, diarrhea, and the severity of the disease.

Unbiased characterization of the larval zebrafish enteric nervous system at a single cell transcriptomic level

The enteric nervous system (ENS) regulates many gastrointestinal functions including peristalsis, immune regulation and uptake of nutrients. Defects in the ENS can lead to severe enteric neuropathies such as Hirschsprung disease (HSCR). Zebrafish have proven to be fruitful in the identification of genes involved in ENS development and HSCR pathogenesis. However, composition and specification of enteric neurons and glial subtypes at larval stages, remains mainly unexplored. Here, we performed single cell RNA sequencing of zebrafish ENS at 5 days post-fertilization. We identified vagal neural crest progenitors, Schwann cell precursors, and four clusters of differentiated neurons. In addition, a previously unrecognized elavl3+/phox2bb-population of neurons and cx43+/phox2bb-enteric glia was found. Pseudotime analysis supported binary neurogenic branching of ENS differentiation, driven by a notch-responsive state. Taken together, we provide new insights on ENS development and specification, proving that the zebrafish is a valuable model for the study of congenital enteric neuropathies.

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.

Eating Habits, Anxiety and Depression in Patients with Irritable Bowel Syndrome: Clinical and Laboratory Comparisons

Aim: to assess the level of stress hormones (cortisol in saliva), neurotransmitters (serotonin in blood serum, dopamine in blood plasma) in relation to eating habits, anxiety and depression levels in patients with IBS.

Materials and methods. An open cohort prospective study was conducted with the inclusion of 263 patients with an established diagnosis of IBS, among them 189 (71.9 %) women and 74 (28.1 %) men. The average age of patients with IBS was 29 [25; 35] years. The control group included 40 healthy volunteers. All individuals included in the study were assessed for diet and eating habits using the WHO CINDI program questionnaire, “Information on Nutrition and Eating Behavior”, the severity of anxiety and depression according to the HADS questionnaire, the level of specific anxiety in relation to gastrointestinal symptoms according to the VSI questionnaire, quality of life according to the IBS-QoL questionnaire. In addition, the enzyme immunoassay method was used to assess the levels of cortisol in the morning and evening portions of saliva, serotonin in the blood serum and dopamine in the blood plasma.

Results. Among patients with IBS there is a statistically significantly higher level of cortisol in the morning and evening portions of saliva (U = 19.5, p < 0.001 and U = 111.5, p < 0.001, respectively), serotonin in blood serum (U = 269.0, p = 0.042) and lower plasma dopamine levels (U = 93.5, p = 0.0002) compared with controls. The mean salivary cortisol level among patients with IBS was 45.39 [29.86; 70.10] ng/ml in the morning and 19.21 [13.98; 23.50] ng/ml in the evening, while in the group of healthy individuals it was 19.0 [16.5; 21.7] and 9.7 [8.5; 10.5] ng/ml, respectively. The average content of serotonin in blood serum in patients with IBS was 188.78 [150.41; 230.32] ng/ml, among healthy individuals — 142.80 [130.52; 154.15] ng/ml. The average content of dopamine in blood plasma in patients with IBS was 28.83 [20.08; 41.54] ng/ml, in healthy individuals — 58.20 [48.15; 66.62] ng/ml.

Conclusion. In patients with IBS the secretion of the stress hormone (cortisol) and neurotransmitters (serotonin, dopamine) is closely related to the nature of nutrition, the level of anxiety and depression, and is also associated with the clinical variant and severity of the course of the disease.

Mechanisms of Maternal Diet-Induced Obesity Affecting the Offspring Brain and Development of Affective Disorders

Depression and metabolic disease are common disorders that share a bidirectional relationship and continue to increase in prevalence. Maternal diet and maternal behaviour both profoundly influence the developmental trajectory of offspring during the perinatal period. At an epidemiological level, both maternal depression and obesity during pregnancy have been shown to increase the risk of neuropsychiatric disease in the subsequent generation. Considerable progress has been made to understand the mechanisms by which maternal obesity disrupts the developing offspring gut-brain axis, priming offspring for the development of affective disorders. This review outlines such mechanisms in detail, including altered maternal care, the maternal microbiome, inflammation, breast milk composition, and maternal and placental metabolites. Subsequently, offspring may be prone to developing gut-brain interaction disorders with concomitant changes to brain energy metabolism, neurotransmission, and behaviour, alongside gut dysbiosis. The gut microbiome may act as a key modifiable, and therefore treatable, feature of the relationship between maternal obesity and the offspring brain function. Further studies examining the relationship between maternal nutrition, the maternal microbiome and metabolites, and offspring neurodevelopment are warranted to identify novel therapeutic targets.

Dysfunction of the noradrenergic system drives inflammation, α-synucleinopathy, and neuronal loss in mouse colon

Clinical and pathological evidence revealed that α-synuclein (α-syn) pathology seen in PD patients starts in the gut and spreads via anatomically connected structures from the gut to the brain. Our previous study demonstrated that depletion of central norepinephrine (NE) disrupted brain immune homeostasis, producing a spatiotemporal order of neurodegeneration in the mouse brain. The purpose of this study was 1) to determine the role of peripheral noradrenergic system in the maintenance of gut immune homeostasis and in the pathogenesis of PD and 2) to investigate whether NE-depletion induced PD-like α-syn pathological changes starts from the gut. For these purposes, we investigated time-dependent changes of α-synucleinopathy and neuronal loss in the gut following a single injection of DSP-4 (a selective noradrenergic neurotoxin) to A53T-SNCA (human mutant α-syn) over-expression mice. We found DPS-4 significantly reduced the tissue level of NE and increased immune activities in gut, characterized by increased number of phagocytes and proinflammatory gene expression. Furthermore, a rapid-onset of α-syn pathology was observed in enteric neurons after 2 weeks and delayed dopaminergic neurodegeneration in the substantia nigra was detected after 3-5 months, associated with the appearance of constipation and impaired motor function, respectively. The increased α-syn pathology was only observed in large, but not in the small, intestine, which is similar to what was observed in PD patients. Mechanistic studies reveal that DSP-4-elicited upregulation of NADPH oxidase (NOX2) initially occurred only in immune cells during the acute intestinal inflammation stage, and then spread to enteric neurons and mucosal epithelial cells during the chronic inflammation stage. The upregulation of neuronal NOX2 correlated well with the extent of α-syn aggregation and subsequent enteric neuronal loss, suggesting that NOX2-generated reactive oxygen species play a key role in α-synucleinopathy. Moreover, inhibiting NOX2 by diphenyleneiodonium or restoring NE function by salmeterol (a β2-receptor agonist) significantly attenuated colon inflammation, α-syn aggregation/propagation, and enteric neurodegeneration in the colon and ameliorated subsequent behavioral deficits. Taken together, our model of PD shows a progressive pattern of pathological changes from the gut to the brain and suggests a potential role of the noradrenergic dysfunction in the pathogenesis of PD.

Probiotics, prebiotics, and synbiotics in chronic constipation: Outstanding aspects to be considered for the current evidence

This integrative aimed to evaluate the effects and the potential mechanism of action of prebiotics, probiotics, and synbiotics on constipation-associated gastrointestinal symptoms and to identify issues that still need to be answered. A literature search was performed in the PubMed database. Animal models (n = 23) and clinical trials (n = 39) were included. In animal studies, prebiotic, probiotic, and synbiotic supplementation showed a decreased colonic transit time (CTT) and an increase in the number and water content of feces. In humans, inulin is shown to be the most promising prebiotic, while B. lactis and L. casei Shirota probiotics were shown to increase defecation frequency, the latter strain being more effective in improving stool consistency and constipation symptoms. Overall, synbiotics seem to reduce CTT, increase defecation frequency, and improve stool consistency with a controversial effect on the improvement of constipation symptoms. Moreover, some aspects of probiotic use in constipation-related outcomes remain unanswered, such as the best dose, duration, time of consumption (before, during, or after meals), and matrices, as well as their effect and mechanisms on the regulation of inflammation in patients with constipation, on polymorphisms associated with constipation, and on the management of constipation via 5-HT. Thus, more high-quality randomized control trials (RCTs) evaluating these lacking aspects are necessary to provide safe conclusions about their effectiveness in managing intestinal constipation.

Decreased Gut Microbiome Tryptophan Metabolism and Serotonergic Signaling in Patients With Persistent Mental Health and Gastrointestinal Symptoms After COVID-19

INTRODUCTION

An estimated 15%-29% of patients report new gastrointestinal (GI) symptoms after coronavirus-19 disease (COVID-19) while 4%-31% report new depressive symptoms. These symptoms may be secondary to gut microbiome tryptophan metabolism and 5-hydroxytryptamine (5-HT)-based signaling.

METHODS

This study used specimens from 2 patient cohorts: (i) fecal samples from patients with acute COVID-19 who participated in a randomized controlled trial testing prebiotic fiber and (ii) blood samples from patients with acute COVID-19. Six months after recovering from COVID-19, both cohorts answered questions related to GI symptoms and anxiety or depression. Microbiome composition and function, focusing on tryptophan metabolism-associated pathways, and plasma 5-HT were assessed.

RESULTS

In the first cohort (n = 13), gut microbiome L-tryptophan biosynthesis during acute COVID-19 was decreased among those who developed more severe GI symptoms (2.0-fold lower log activity comparing those with the most severe GI symptoms vs those with no symptoms, P = 0.06). All tryptophan pathways showed decreased activity among those with more GI symptoms. The same pathways were also decreased in those with the most severe mental health symptoms after COVID-19. In an untargeted analysis, 5 additional metabolic pathways significantly differed based on subsequent development of GI symptoms. In the second cohort (n = 39), plasma 5-HT concentration at the time of COVID-19 was increased 5.1-fold in those with GI symptoms alone compared with those with mental health symptoms alone ( P = 0.02).

DISCUSSION

Acute gut microbiome-mediated reduction in 5-HT signaling may contribute to long-term GI and mental health symptoms after COVID-19. Future studies should explore modification of 5-HT signaling to reduce post-COVID symptoms.

Fluoxetine reduces organ injury and improves motor function after traumatic brain injury in mice

BACKGROUND

Traumatic brain injury (TBI) is a leading cause of morbidity and mortality in trauma patients worldwide. Brain injury is associated with significant inflammation, both within the brain and in the peripheral organs. This inflammatory response in TBI leads to a secondary injury, worsening the effects of the original brain injury. Serotonin is also linked to inflammation in the intestine and inflammatory bowel disease, but its role in the gut-brain axis is not known. We hypothesized that using fluoxetine to block serotonin reuptake would reduce organ inflammation and improve outcomes after TBI.

METHODS

C57/B6 mice were given a severe TBI using a controlled cortical impact. To measure intestinal permeability, a piece of terminal ileum was resected, the lumen was filled with 4-kDa fluorescein isothiocyanate (FITC)-dextran, and the ends were tied. The intestinal segment was submerged in buffer and fluorescence in the buffer measured over time. To measure lung permeability, 70-kDa FITC-dextran is injected retro-orbitally. Thirty minutes later, the left lung was homogenized and the fluorescence was measured. To measure performance on the rota-rod, mice were placed on a spinning rod, and the time to fall off was measured. Those treated with fluoxetine received a single dose of 5 mg/kg via intraperitoneal injection immediately after injury.

RESULTS

Traumatic brain injury was associated with an increase in intestinal permeability to FITC-dextran, increased lung vascular permeability, and worse performance on the rota-rod. Fluoxetine significantly reduced lung and intestinal permeability after TBI and improved performance on the rota-rod after TBI.

CONCLUSION

Use of fluoxetine has the potential to reduce lung injury and improve motor coordination in severe TBI patients. Further study will be needed to elucidate the mechanism behind this effect.

The Role of Plasma Membrane Sodium/Hydrogen Exchangers in Gastrointestinal Functions: Proliferation and Differentiation, Fluid/Electrolyte Transport and Barrier Integrity

The five plasma membrane Na⁺/H⁺ exchanger (NHE) isoforms in the gastrointestinal tract are characterized by distinct cellular localization, tissue distribution, inhibitor sensitivities, and physiological regulation. NHE1 (Slc9a1) is ubiquitously expressed along the gastrointestinal tract in the basolateral membrane of enterocytes, but so far, an exclusive role for NHE1 in enterocyte physiology has remained elusive. NHE2 (Slc9a2) and NHE8 (Slc9a8) are apically expressed isoforms with ubiquitous distribution along the colonic crypt axis. They are involved in pH_i regulation of intestinal epithelial cells. Combined use of a knockout mouse model, intestinal organoid technology, and specific inhibitors revealed previously unrecognized actions of NHE2 and NHE8 in enterocyte proliferation and differentiation. NHE3 (Slc9a3), expressed in the apical membrane of differentiated intestinal epithelial cells, functions as the predominant nutrient-independent Na⁺ absorptive mechanism in the gut. The new selective NHE3 inhibitor (Tenapanor) allowed discovery of novel pathophysiological and drug-targetable NHE3 functions in cystic-fibrosis associated intestinal obstructions. NHE4, expressed in the basolateral membrane of parietal cells, is essential for parietal cell integrity and acid secretory function, through its role in cell volume regulation. This review focuses on the expression, regulation and activity of the five plasma membrane Na⁺/H⁺ exchangers in the gastrointestinal tract, emphasizing their role in maintaining intestinal homeostasis, or their impact on disease pathogenesis. We point to major open questions in identifying NHE interacting partners in central cellular pathways and processes and the necessity of determining their physiological role in a system where their endogenous expression/activity is maintained, such as organoids derived from different parts of the gastrointestinal tract.

Transiently increased serotonin has modest or no effects on bone mass accrual in growing female C57BL6/J or growing male and female Lrp5A214V mice

Serotonin (5HT) is a chemical messenger with biologic activities affecting multiple organs. Within the skeletal system, studies in mice and humans suggest blood 5HT levels affect bone, with elevations impairing and reductions enhancing bone accrual. Other studies, however, have not supported this hypothesis. Recently, administering 5HT to a Piezo1 mutant mouse strain with hyposerotonemia, intestinal dysmotility, and a doubling of femoral trabecular bone mass at 2 months of age, was reported to return the animals' intestinal motility and bone mass to normal. However, whether the 5HT directly affected bone metabolism or indirectly affected metabolism by improving intestinal function was not determined. Therefore, we administered 5HT to mice with normal intestinal function. We randomized female C57BL6/J mice and male and female mice that have increased bone mass due to a missense mutation in the WNT co-receptor LRP5 (Lrp5A214V) to receive 5HT or vehicle via daily IP injection from 4 weeks to 8 weeks of age. We did not observe consistent significant changes for distal femur trabecular, midshaft femur cortical, or vertebral body trabecular bone mass between 5HT treated and vehicle treated mice of either genotype. These data are compatible with other studies that have not observed a correlation between blood 5HT level and bone mass.

Network Pharmacology Combined with Metabolomics Approach to Investigate the Toxicity Mechanism of Paclobutrazol

Paclobutrazol (PBZ) is a commonly used plant growth regulator (PGR) with good antibacterial activity. It has widespread applications in agricultural production. However, there is limited research reported on the potential risks of human health resulting from PBZ residues. In this study, using Sprague-Dawley rats, we carried out a systematic study on the hepatotoxicity and nephrotoxicity of PBZ in different doses (0.2, 0.5, and 1.0 g/kg). The metabolic profiles and network pharmacology were combined to construct a PBZ-endogenous substances-gene-hepatorenal diseases network to elucidate the underlying mechanism of PBZ's hepatorenal toxicity. At first, metabolomics analysis was done to investigate the metabolites and the related metabolic pathways associated with PBZ. Secondly, the network pharmacology approach was used in further exploration of the toxic targets. Additionally, molecular docking was carried out to investigate the interactions between PBZ and potential targets. The results indicated that PBZ showed obvious toxicity towards the liver and kidney of rats. The metabolomics analysis showed that PBZ mainly affected 4 metabolic pathways, including tryptophan metabolism, arachidonic acid metabolism, linoleic acid metabolism, and purine metabolism. Network pharmacology and molecular docking revealed that CYP1A2, CYP2A6, CYP2E1, MAOA, PLA2G2A, PTGS1, and XDH were critical targets for PBZ hepatorenal toxicity. This preliminary study revealed PBZ's hepatorenal toxicity and provided a theoretical basis for the rational and safe use of PBZ. Furthermore, it provided possible intervention targets for further research on how to avoid or reduce the damage caused by pesticides to the human body.

Neural signalling of gut mechanosensation in ingestive and digestive processes

Eating and drinking generate sequential mechanosensory signals along the digestive tract. These signals are communicated to the brain for the timely initiation and regulation of diverse ingestive and digestive processes - ranging from appetite control and tactile perception to gut motility, digestive fluid secretion and defecation - that are vital for the proper intake, breakdown and absorption of nutrients and water. Gut mechanosensation has been investigated for over a century as a common pillar of energy, fluid and gastrointestinal homeostasis, and recent discoveries of specific mechanoreceptors, contributing ion channels and the well-defined circuits underlying gut mechanosensation signalling and function have further expanded our understanding of ingestive and digestive processes at the molecular and cellular levels. In this Review, we discuss our current understanding of the generation of mechanosensory signals from the digestive periphery, the neural afferent pathways that relay these signals to the brain and the neural circuit mechanisms that control ingestive and digestive processes, focusing on the four major digestive tract parts: the oral and pharyngeal cavities, oesophagus, stomach and intestines. We also discuss the clinical implications of gut mechanosensation in ingestive and digestive disorders.

The increase in urinary serotonin and decrease in salivary cortisol concentrations following direct inhalations of concentrated essential oils is not induced by non-specific effects

Objectives. The effectiveness of exogenously triggered serotonin (e.g., dietary supplements, drugs) increase is varied. However, since urinary serotonin concentrations were found to correlate with those in the cerebrospinal fluid, the olfactory system might be an efficient and testable pathway to quickly elevate serotonin levels due to its fast-acting central neurophysiological and peripheral pathways. However, little research has been devoted to investigate this assumption. This paper extends previous findings of parasympathetic activation of a specially designed essential oil inhaler (AromaStick® Balance) by experimentally testing its impact on urine serotonin and saliva cortisol excretion. Method. Two experiments involving healthy individuals were conducted to test the efficacy of essential oil application to the nose by employing different inhalation protocols and control conditions. Results. In the pilot study (n=8), serotonin urine excretion was increased after six inhalations (effect size Cohen's d=0.7). In the second experiment (n=80), inhalations proved superior to both the natural control condition and the pseudo placebo condition after three and six inhalation cycles (0.6<d<1.8). In addition, there was a large reduction of cortisol saliva levels after three inhalations (d=0.9). Conclusion. Short and deep inhalations of essential oil scents directly delivered to the olfac-tory system appear to result in an enhanced serotonin and a reduced cortisol release in healthy individuals of both sexes.

Crosstalk Between Intestinal Serotonergic System and Pattern Recognition Receptors on the Microbiota-Gut-Brain Axis

Disruption of the microbiota-gut-brain axis results in a wide range of pathologies that are affected, from the brain to the intestine. Gut hormones released by enteroendocrine cells to the gastrointestinal (GI) tract are important signaling molecules within this axis. In the search for the language that allows microbiota to communicate with the gut and the brain, serotonin seems to be the most important mediator. In recent years, serotonin has emerged as a key neurotransmitter in the gut-brain axis because it largely contributes to both GI and brain physiology. In addition, intestinal microbiota are crucial in serotonin signaling, which gives more relevance to the role of the serotonin as an important mediator in microbiota-host interactions. Despite the numerous investigations focused on the gut-brain axis and the pathologies associated, little is known regarding how serotonin can mediate in the microbiota-gut-brain axis. In this review, we will mainly discuss serotonergic system modulation by microbiota as a pathway of communication between intestinal microbes and the body on the microbiota-gut-brain axis, and we explore novel therapeutic approaches for GI diseases and mental disorders.

Distribution of α-synuclein in normal human jejunum and its relations with the chemosensory and neuroendocrine system

Alpha-synuclein (α-syn) is a presynaptic neuronal protein and its structural alterations play an important role in the pathogenesis of neurodegenerative diseases, such as Parkinson’s disease (PD). It has been originally described in the brain and aggregated α-syn has also been found in the peripheral nerves including the enteric nervous system (ENS) of PD patients. ENS is a network of neurons and glia found in the gut wall which controls gastrointestinal function independently from the central nervous system. Moreover, two types of epithelial cells are crucial in the creation of an interface between the lumen and the ENS: they are the tuft cells and the enteroendocrine cells (EECs). In addition, the abundant enteric glial cells (EGCs) in the intestinal mucosa play a key role in controlling the intestinal epithelial barrier. Our aim was to localize and characterize the presence of α-syn in the normal human jejunal wall. Surgical specimens of proximal jejunum were collected from patients submitted to pancreaticoduodenectomy and intestinal sections underwent immunohistochemical procedure. Alpha-syn has been found both at the level of the ENS and the epithelial cells. To characterize α-syn immunoreactive epithelial cells, we used markers such as choline acetyltransferase (ChAT), useful for the identification of tuft cells. Then we evaluated the co-presence of α-syn with serotonin (5-HT), expressed in EECs. Finally, we used the low-affinity nerve growth factor receptor (p75NTR), to detect peripheral EGCs. The presence of α-syn has been demonstrated in EECs, but not in the tuft cells. Additionally, p75NTR has been highlighted in EECs of the mucosal layer and co-localized with α-syn in EECs but not with ChAT-positive cells. These findings suggest that α-syn could play a possible role in synaptic transmission of the ENS and may contribute to maintain the integrity of the epithelial barrier of the small intestine through EECs.

Cardiovascular serotonergic system: Evolution, receptors, transporter, and function

The serotonergic system, serotonin (5HT), serotonin transporter (SERT), and serotonin receptors (5HT-x), is an evolutionarily ancient system that has clear physiological advantages to all life forms from bacteria to humans. This review focuses on the role of platelet/plasma serotonin and the cardiovascular system with minor references to its significant neurotransmitter function. Platelets transport and store virtually all plasma serotonin in dense granules. Stored serotonin is released from activated platelets and can bind to serotonin receptors on platelets and cellular components of the vascular wall to augment aggregation and induce vasoconstriction or vasodilation. The vascular endothelium is critical to the maintenance of cardiovascular homeostasis. While there are numerous ligands, neurological components, and baroreceptors that effect vascular tone it is proposed that serotonin and nitric oxide (an endothelium relaxing factor) are major players in the regulation of systemic blood pressure. Signals not fully defined, to date, that direct serotonin binding to one of the 15 identified 5HT receptors versus the transporter, and the role platelet/plasma serotonin plays in regulating hypertension within the cardiovascular system remain important issues to better understand many diseases and to develop new drugs. Also, expanded research of these pathways in lower life-forms may serve as important model systems to further our understanding of the evolution and mechanisms of action of serotonin.

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.

The trace amine theory of spontaneous hypertension as induced by classic monoamine oxidase inhibitors

The classic monoamine oxidase inhibitors (MAOIs) tranylcypromine (TCP) and phenelzine (PLZ) are powerful antidepressants that come with an equally powerful stigma, and are thus rarely prescribed-despite their well-established effectiveness. Some of these preconceptions appear to stem from unclarity, as the etiology of a rare but important side effect, 'spontaneous hypertension' (SH)-a significant increase in blood pressure absent dietary tyramine ingestion-remains improperly elucidated. This paper aims at uprooting some of the stigma surrounding MAOIs by advancing the trace amine (TA) theory as the causative underpinning of SH. This theory posits that SH results from the considerable influx of TAs observed following TCP- or PLZ-administration. TAs are known, albeit at greatly supraphysiological levels, to raise blood pressure on account of their propensity to exert potent indirect sympathomimetic effects; additionally, some research posits that TAs may induce vasoconstrictive effects partly or wholly separate therefrom, which would then constitute a second hypertensive mechanism. TAs are endogenous to the human body in low quantities. Both TCP and PLZ cause marked elevations of 2-phenylethylamine (PEA), meta- and para-tyramine (m-/p-TYR), octopamine (OA), and tryptamine (TRYP), following both acute and (sub)chronic administration. This paper holds that TYR plays a pivotal role in causing SH, due to its strong pressor effect. Cautious treatment of SH is advised, given its typically self-limiting nature. The risk of hypotensive overshoots must be taken into account. For severe cases, this paper urges reconsideration, following suitable confirmation trials, of antipsychotics (notably risperidone) as these agents may reduce striatal p-TYR levels.

Lactobacillus plantarum PS128 Promotes Intestinal Motility, Mucin Production, and Serotonin Signaling in Mice

Lactobacillus plantarum PS128 has been reported as a psychobiotic to improve mental health through the gut–brain axis in experimental animal models. To explore its mechanism of action in the gut, this study aimed to analyze the effects of L. plantarum PS128 ingestion on naïve and loperamide (Lop)-induced constipation mice. We found that, in the two mouse models, the weight, number, and water content of feces in the L. plantarum PS128 group were higher than those in the vehicle control group. Histological observation revealed that L. plantarum PS128 increased the level of colonic mucins including the major mucin MUC2. In addition, the charcoal meal test showed that L. plantarum PS128 significantly increased the small intestine transit in naïve mice, but not in the Lop-treated mice. Since intestinal serotonin has been found to modulate motility, we further analyzed the expression of genes related to serotonin signal transduction in the small intestine of naïve mice. The results showed that L. plantarum PS128 significantly altered the expression levels of Tph1, Chga, Slc6a4, and Htr4, but did not affect the expression levels of Tph2, Htr3a, and Maoa. Furthermore, immunohistochemistry revealed that L. plantarum PS128 significantly increased the number of serotonin-containing intestinal cells in mice. Taken together, our results suggest that L. plantarum PS128 could promote intestinal motility, mucin production, and serotonin signal transduction, leading to a laxative effect in mice.

Interactions between the microbiota and enteric nervous system during gut-brain disorders

For the last 20 years, researchers have focused their intention on the impact of gut microbiota in healthy and pathological conditions. This year (2021), more than 25,000 articles can be retrieved from PubMed with the keywords "gut microbiota and physiology", showing the constant progress and impact of gut microbes in scientific life. As a result, numerous therapeutic perspectives have been proposed to modulate the gut microbiota composition and/or bioactive factors released from microbes to restore our body functions. Currently, the gut is considered a primary site for the development of pathologies that modify brain functions such as neurodegenerative (Parkinson's, Alzheimer's, etc.) and metabolic (type 2 diabetes, obesity, etc.) disorders. Deciphering the mode of interaction between microbiota and the brain is a real original option to prevent (and maybe treat in the future) the establishment of gut-brain pathologies. The objective of this review is to describe recent scientific elements that explore the communication between gut microbiota and the brain by focusing our interest on the enteric nervous system (ENS) as an intermediate partner. The ENS, which is known as the "second brain", could be under the direct or indirect influence of the gut microbiota and its released factors (short-chain fatty acids, neurotransmitters, gaseous factors, etc.). Thus, in addition to their actions on tissue (adipose tissue, liver, brain, etc.), microbes can have an impact on local ENS activity. This potential modification of ENS function has global repercussions in the whole body via the gut-brain axis and represents a new therapeutic strategy.

Alterations in Gut Vitamin and Amino Acid Metabolism are Associated with Symptoms and Neurodevelopment in Children with Autism Spectrum Disorder

Metabolic disturbance may be implicated in the pathogenesis of autism. This study aimed to investigate the gut metabolomic profiles of autistic children and to analyze potential interaction between gut metabolites with autistic symptoms and neurodevelopment levels. We involved 120 autistic and 60 neurotypical children. Autistic symptoms and neurodevelopment levels were assessed. Fecal samples were analyzed using untargeted liquid chromatography-tandem mass spectrometry methods. Our results showed the metabolic disturbances of autistic children involved in multiple vitamin and amino acid metabolism pathways, with the strongest enrichment identified for tryptophan metabolism, retinol metabolism, cysteine-methionine metabolism, and vitamin digestion and absorption. Differential gut metabolites were correlated to autistic symptoms and neurodevelopment levels. Our findings improved the understanding of the perturbations of metabolome networks in autism.

The Microbiota-Gut-Brain Axis: From Motility to Mood

The gut-brain axis plays an important role in maintaining homeostasis. Many intrinsic and extrinsic factors influence signaling along this axis, modulating the function of both the enteric and central nervous systems. More recently the role of the microbiome as an important factor in modulating gut-brain signaling has emerged and the concept of a microbiota-gut-brain axis has been established. In this review, we highlight the role of this axis in modulating enteric and central nervous system function and how this may impact disorders such as irritable bowel syndrome and disorders of mood and affect. We examine the overlapping biological constructs that underpin these disorders with a special emphasis on the neurotransmitter serotonin, which plays a key role in both the gastrointestinal tract and in the brain. Overall, it is clear that although animal studies have shown much promise, more progress is necessary before these findings can be translated for diagnostic and therapeutic benefit in patient populations.

A Systems Biology Approach to Investigating the Interaction between Serotonin Synthesis by Tryptophan Hydroxylase and the Metabolic Homeostasis

Obesity has become a global public health and economic problem. Obesity is a major risk factor for a number of complications, such as type 2 diabetes, cardiovascular disease, fatty liver disease, and cancer. Serotonin (5-hydroxytryptamine [5-HT]) is a biogenic monoamine that plays various roles in metabolic homeostasis. It is well known that central 5-HT regulates appetite and mood. Several 5-HT receptor agonists and selective serotonin receptor uptake inhibitors (SSRIs) have shown beneficial effects on appetite and mood control in clinics. Although several genetic polymorphisms related to 5-HT synthesis and its receptors are strongly associated with obesity, there is little evidence of the role of peripheral 5-HT in human metabolism. In this study, we performed a systemic analysis of transcriptome data from the Genotype-Tissue Expression (GTEX) database. We investigated the expression of 5-HT and tryptophan hydroxylase (TPH), the rate-limiting enzyme of 5-HT biosynthesis, in the human brain and peripheral tissues. We also performed differential gene expression analysis and predicted changes in metabolites by comparing gene expressions of tissues with high TPH expression to the gene expressions of tissues with low TPH expression. Our analyses provide strong evidence that serotonin plays an important role in the regulation of metabolic homeostasis in humans.

Childhood Development and the Microbiome-The Intestinal Microbiota in Maintenance of Health and Development of Disease During Childhood Development

The composition of the intestinal microbiome affects health from the prenatal period throughout childhood, and many diseases have been associated with dysbiosis. The gut microbiome is constantly changing, from birth throughout adulthood, and several variables affect its development and content. Features of the intestinal microbiota can affect development of the brain, immune system, and lungs, as well as body growth. We review the development of the gut microbiome, proponents of dysbiosis, and interactions of the microbiota with other organs. The gut microbiome should be thought of as an organ system that has important effects on childhood development. Dysbiosis has been associated with diseases in children and adults, including autism, attention deficit hyperactivity disorder, asthma, and allergies.

Molecular Mechanisms of Microbiota-Mediated Pathology in Irritable Bowel Syndrome

Irritable bowel syndrome (IBS) is one of the most prevalent functional gastrointestinal disorders, and accumulating evidence gained in both preclinical and clinical studies indicate the involvement of enteric microbiota in its pathogenesis. Gut resident microbiota appear to influence brain activity through the enteric nervous system, while their composition and function are affected by the central nervous system. Based on these results, the term “brain–gut–microbiome axis” has been proposed and enteric microbiota have become a potential therapeutic target in IBS cases. However, details regarding the microbe-related pathophysiology of IBS remain elusive. This review summarizes the existing knowledge of molecular mechanisms in the pathogenesis of IBS as well as recent progress related to microbiome-derived neurotransmitters, compounds, metabolites, neuroendocrine factors, and enzymes.

Bioaminergic Responses in an In Vitro System Studying Human Gut Microbiota-Kiwifruit Interactions

Whole kiwifruit ('Hayward' and 'Zesy002') were examined for their bioaminergic potential after being subjected to in vitro gastrointestinal digestion and colonic fermentation. Controls included the prebiotic inulin and water, a carbohydrate-free vehicle. The dopamine precursor l-dihydroxyphenylalanine (L-DOPA) and the serotonin precursor 5-hydroxytryptophan were increased in the kiwifruit gastrointestinal digesta ('Hayward' > 'Zesy002') in comparison to the water digesta. Fermentation of the digesta with human fecal bacteria for 18 h modulated the concentrations of bioamine metabolites. The most notable were the significant increases in L-DOPA ('Zesy002' > 'Hayward') and γ-aminobutyric acid (GABA) ('Hayward' > 'Zesy002'). Kiwifruit increased Bifidobacterium spp. and Veillonellaceae (correlating with L-DOPA increase), and Lachnospira spp. (correlating with GABA). The digesta and fermenta were incubated with Caco-2 cells for 3 h followed by gene expression analysis. Effects were seen on genes related to serotonin synthesis/re-uptake/conversion to melatonin, gut tight junction, inflammation and circadian rhythm with different digesta and fermenta from the four treatments. These indicate potential effects of the substrates and the microbially generated organic acid and bioamine metabolites on intestinal functions that have physiological relevance. Further studies are required to confirm the potential bioaminergic effects of gut microbiota-kiwifruit interactions.

The Vegetative Receptor-Vascular Reflex (VRVR) - A New Key to Regeneration

OBJECTIVE

We describe a potentially new physiological reflex path that has so far been neglected but which could be used for a novel therapeutic approach: The vegetative receptor-vascular reflex. This is a physiological response that starts from the connective tissue and influences the whole organism. We cross-fertilized various research areas with each other.

KEY FINDINGS

The matrix or the connective tissue forms a passive reservoir of substrate for the growth and development of cells, and functions as the primordial communication system of all living systems. It contains a continuous network of cells, such as fibroblasts, along with protein bundles made up of collagen that support electrical exchange through piezoelectric effects. This archaic vegetative system surrounds all cells, including neurons, and can thus be viewed as the primordial coordinating system in every organism. It is very likely the basis for a reflex which we describe here for the first time: the vegetative receptor vascular reflex. We also indicate some potential practical applications and test procedures.

CONCLUSION

The vegetative receptor vascular reflex describes the pathway from stimuli that originate in the connective tissue or the extracellular matrix toward organ systems. They might be chemical in nature or electrical via piezo-electric effects stimulating nerve endings, and thus can influence higher order processes such as regeneration or healing of tissue. Thus, this reflex lends itself to a novel therapeutic approach via certain types of manipulation of the connective tissue.

The Effect of Bacterial Endotoxin LPS on Serotonergic Modulation of Glutamatergic Synaptic Transmission

The release of the endotoxin lipopolysaccharides (LPS) from gram-negative bacteria is key in the induction of the downstream cytokine release from cells targeting cells throughout the body. However, LPS itself has direct effects on cellular activity and can alter synaptic transmission. Animals experiencing septicemia are generally in a critical state and are often treated with various pharmacological agents. Since antidepressants related to the serotonergic system have been shown to have a positive outcome for septicemic conditions impacting the central nervous system, the actions of serotonin (5-HT) on neurons also exposed to LPS were investigated. At the model glutamatergic synapse of the crayfish neuromuscular junction (NMJ), 5-HT primarily acts through a 5-HT2A receptor subtype to enhance transmission to the motor neurons. LPS from Serratia marcescens also enhances transmission at the crayfish NMJ but by a currently unknown mechanism. LPS at 100 µg/mL had no significant effect on transmission or on altering the response to 5-HT. LPS at 500 µg/mL increased the amplitude of the evoked synaptic excitatory junction potential, and 5-HT in combination with 500 µg/mL LPS continued to promote enhanced transmission. The preparations maintained responsiveness to serotonin in the presence of low or high concentrations of LPS.