Regulation of the brain-gut axis by group III metabotropic glutamate receptors

The emerging roles of neuroactive components produced by gut microbiota

BACKGROUND

As a multifunctional ecosystem, the human digestive system contains a complex network of microorganisms, collectively known as gut microbiota. This consortium composed of more than 1013 microorganisms and Firmicutes and Bacteroidetes are the dominant microbes. Gut microbiota is increasingly recognized for its critical role in physiological processes beyond digestion. Gut microbiota participates in a symbiotic relationship with the host and takes advantage of intestinal nutrients and mutually participates in the digestion of complex carbohydrates and maintaining intestinal functions.

METHOD AND RESULT

We reviewed the neuroactive components produced by gut microbiota. Interestingly, microbiota plays a crucial role in regulating the activity of the intestinal lymphatic system, regulation of the intestinal epithelial barrier, and maintaining the tolerance to food immunostimulating molecules. The gut-brain axis is a two-way communication pathway that links the gut microbiota to the central nervous system (CNS) and importantly is involved in neurodevelopment, cognition, emotion and synaptic transmissions. The connections between gut microbiota and CNS are via endocrine system, immune system and vagus nerve.

CONCLUSION

The gut microbiota produces common neurotransmitters and neuromodulators of the nervous system. These compounds play a role in neuronal functions, immune system regulation, gastrointestinal homeostasis, permeability of the blood brain barrier and other physiological processes. This review investigates the essential aspects of the neurotransmitters and neuromodulators produced by gut microbiota and their implications in health and disease.

Interrogation of the mammalian gut-brain axis using LC-MS/MS-based targeted metabolomics with in vitro bacterial and organoid cultures and in vivo gnotobiotic mouse models

Interest in the communication between the gastrointestinal tract and central nervous system, known as the gut-brain axis, has prompted the development of quantitative analytical platforms to analyze microbe- and host-derived signals. This protocol enables investigations into connections between microbial colonization and intestinal and brain neurotransmitters and contains strategies for the comprehensive evaluation of metabolites in in vitro (organoids) and in vivo mouse model systems. Here we present an optimized workflow that includes procedures for preparing these gut-brain axis model systems: (stage 1) growth of microbes in defined media; (stage 2) microinjection of intestinal organoids; and (stage 3) generation of animal models including germ-free (no microbes), specific-pathogen-free (complete gut microbiota) and specific-pathogen-free re-conventionalized (germ-free mice associated with a complete gut microbiota from a specific-pathogen-free mouse), and Bifidobacterium dentium and Bacteroides ovatus mono-associated mice (germ-free mice colonized with a single gut microbe). We describe targeted liquid chromatography-tandem mass spectrometry-based metabolomics methods for analyzing microbially derived short-chain fatty acids and neurotransmitters from these samples. Unlike other protocols that commonly examine only stool samples, this protocol includes bacterial cultures, organoid cultures and in vivo samples, in addition to monitoring the metabolite content of stool samples. The incorporation of three experimental models (microbes, organoids and animals) enhances the impact of this protocol. The protocol requires 3 weeks of murine colonization with microbes and ~1-2 weeks for liquid chromatography-tandem mass spectrometry-based instrumental and quantitative analysis, and sample post-processing and normalization.

The Role of Psychobiotics to Ensure Mental Health during the COVID-19 Pandemic-A Current State of Knowledge

Psychobiotics are defined as probiotics, mainly of the genus Lactobacillus and Bifidobacterium, that confer mental health benefits to the host when consumed in a particular quantity through the interaction with commensal gut microbiota. The gut microbiota, which means a diverse and dynamic population of microorganisms harboring the gastrointestinal tract, communicates with the brain and vice versa through the brain-gut axis. The mechanisms of action of psychobiotics may be divided into four groups: synthesis of neurotransmitters and neurochemicals, regulation of the HPA axis, influence on the immune system, and synthesis of metabolites. Recent years showed that the COVID-19 pandemic affected not only physical, but also mental health. Social isolation, fear of infection, the lack of adequate vaccine, disinformation, increased number of deaths, financial loss, quarantine, and lockdown are all factors can cause psychiatric problems. The aim of this review was to discuss the potential role of psychobiotic in light of the current problems, based on in vitro and in vivo studies, meta-analyses, clinical trials evidence, and registered studies assessing probiotics' therapeutic administration in the prevention or treatment of symptoms or side effects of COVID-19.

Omics profiles of fecal and oral microbiota change in irritable bowel syndrome patients with diarrhea and symptom exacerbation

BACKGROUND

Irritable bowel syndrome (IBS) is a disorder of gut-brain interaction, including dysregulation of the hypothalamic-pituitary-adrenal axis with salivary cortisol changes. However, the role of gastrointestinal microbiota during IBS symptom exacerbation remains unclear. We tested the hypothesis that the microbial species, gene transcripts, and chemical composition of fecal and oral samples are altered during the exacerbation of IBS symptoms.

METHODS

Fecal, salivary, and dental plaque samples were collected at baseline from 43 men with IBS with diarrhea (IBS-D) and 40 healthy control (HC) men. Samples in the IBS-D patients were also collected during symptom exacerbation. The composition of the fecal microbiota was determined by analyzing the 16S rRNA gene, RNA-based metatranscriptome, and metabolites in samples from HC and IBS patients with and without symptom exacerbation. Oral samples were also analyzed using omics approaches.

RESULTS

The fecal microbiota during IBS symptom exacerbation exhibited significant differences in the phylogenic pattern and short-chain fatty acid compared with fecal samples during defecation when symptoms were not exacerbated. Although there were no significant differences in the phylogenic pattern of fecal microbiota abundance between HCs and IBS-D patients, significant differences were detected in the expression patterns of bacterial transcriptomes related to butyrate production and neuroendocrine hormones, including tryptophan-serotonin-melatonin synthesis and glutamine/GABA. The composition of plaque microbiota was different between HC and IBS-D patients during normal defecation.

CONCLUSIONS

Our findings suggest that colonic host-microbial interactions are altered in IBS-D patients during exacerbation of symptoms. There were no overlaps between feces and oral microbiomes.

Gut Microbiota Linked with Reduced Fear of Humans in Red Junglefowl Has Implications for Early Domestication

Domestication of animals can lead to profound phenotypic modifications within short evolutionary time periods, and for many species behavioral selection is likely at the forefront of this process. Animal studies have strongly implicated that the gut microbiome plays a major role in host behavior and cognition through the microbiome-gut-brain axis. Consequently, herein, it is hypothesized that host gut microbiota may be one of the earliest phenotypes to change as wild animals were domesticated. Here, the gut microbiome community in two selected lines of red junglefowl that are selected for either high or low fear of humans up to eight generations is examined. Microbiota profiles reveal taxonomic differences in gut bacteria known to produce neuroactive compounds between the two selection lines. Gut-brain module analysis by means of genome-resolved metagenomics identifies enrichment in the microbial synthesis and degradation potential of metabolites associated with fear extinction and reduces anxiety-like behaviors in low fear fowls. In contrast, high fear fowls are enriched in gut-brain modules from the butyrate and glutamate pathways, metabolites associated with fear conditioning. Overall, the results identify differences in the composition and functional potential of the gut microbiota across selection lines that may provide insights into the mechanistic explanations of the domestication process.

NDRG2 is expressed on enteric glia and altered in conditions of inflammation and oxygen glucose deprivation/reoxygenation

Enteric glial cells are more abundant than neurons in the enteric nervous system. Accumulating evidence has demonstrated that enteric glial cells share many properties with astrocytes and play pivotal roles in intestinal diseases. NDRG2 is specifically expressed in astrocytes and is involved in various diseases in the central nervous system. However, no studies have demonstrated the expression of NDRG2 in enteric glial cells. We performed immunostaining of adult mouse tissue, human colon sections, and primary enteric glial cells and the results showed that NDRG2 was widely expressed in enteric glial cells. Meanwhile, our results showed that NDRG2 was upregulated after treatment with pro-inflammatory cytokines and exposure to oxygen glucose deprivation/reoxygenation, indicating that NDRG2 might be involved in these conditions. Moreover, we determined that NDRG2 translocated to the nucleus after treatment with pro-inflammatory cytokines but not after exposure to oxygen glucose deprivation/reoxygenation. This study is the first to show the expression and distribution of NDRG2 in the enteric glia. Our results indicate that NDRG2 might be involved in the pathogenesis of enteric inflammation and ischemia/reperfusion injury. This study shows that NDRG2 might be a molecular target for enteric nervous system diseases.

Indole Tryptophan Metabolism and Cytokine S100B in Children with Attention-Deficit/Hyperactivity Disorder: Daily Fluctuations, Responses to Methylphenidate, and Interrelationship with Depressive Symptomatology

Background: Indole tryptophan metabolites (ITMs), mainly produced at the gastrointestinal level, participate in bidirectional gut-brain communication and have been implicated in neuropsychiatric pathologies, including attention-deficit/hyperactivity disorder (ADHD). Method: A total of 179 children, 5-14 years of age, including a healthy control group (CG, n = 49), and 107 patients with ADHD participated in the study. The ADHD group was further subdivided into predominantly attention deficit (PAD) and predominantly hyperactive impulsive (PHI) subgroups. Blood samples were drawn at 20:00 and 09:00 hours, and urine was collected between blood draws, at baseline and after 4.63 ± 2.3 months of methylphenidate treatment in the ADHD group. Levels and daily fluctuations of ITM were measured by tandem mass spectrometer, and S100B (as a glial inflammatory marker) by enzyme-linked immunosorbent assay. Factorial analysis of variance (Stata 12.0) was performed with groups/subgroups, time (baseline/after treatment), hour of day (morning/evening), and presence of depressive symptoms (DS; no/yes) as factors. Results: Tryptamine and indoleacetic acid (IAA) showed no differences between the CG and ADHD groups. Tryptamine exhibited higher evening values (p < 0.0001) in both groups. No changes were associated with methylphenidate or DS. At baseline, in comparison with the rest of study sample, PHI with DS+ group showed among them much greater morning than evening IAA (p < 0.0001), with treatment causing a 50% decrease (p = 0.002). Concerning indolepropionic acid (IPA) MPH was associated with a morning IPA decrease and restored the daily profile observed in the CG. S100B protein showed greater morning than evening concentrations (p = 0.001) in both groups. Conclusion: Variations in ITM may reflect changes associated with the presence of DS, including improvement, among ADHD patients.

Antidepressive Mechanisms of Probiotics and Their Therapeutic Potential

The accumulating knowledge of the host-microbiota interplay gives rise to the microbiota-gut-brain (MGB) axis. The MGB axis depicts the interkingdom communication between the gut microbiota and the brain. This communication process involves the endocrine, immune and neurotransmitters systems. Dysfunction of these systems, along with the presence of gut dysbiosis, have been detected among clinically depressed patients. This implicates the involvement of a maladaptive MGB axis in the pathophysiology of depression. Depression refers to symptoms that characterize major depressive disorder (MDD), a mood disorder with a disease burden that rivals that of heart diseases. The use of probiotics to treat depression has gained attention in recent years, as evidenced by increasing numbers of animal and human studies that have supported the antidepressive efficacy of probiotics. Physiological changes observed in these studies allow for the elucidation of probiotics antidepressive mechanisms, which ultimately aim to restore proper functioning of the MGB axis. However, the understanding of mechanisms does not yet complete the endeavor in applying probiotics to treat MDD. Other challenges remain which include the heterogeneous nature of both the gut microbiota composition and depressive symptoms in the clinical setting. Nevertheless, probiotics offer some advantages over standard pharmaceutical antidepressants, in terms of residual symptoms, side effects and stigma involved. This review outlines antidepressive mechanisms of probiotics based on the currently available literature and discusses therapeutic potentials of probiotics for depression.

Possible Protective Role of Melatonin in Pediatric Infectious Diseases and Neurodevelopmental Pathologies

Melatonin, produced in every cell that possesses mitochondria, acts as an endogenous free radical scavenger, and improves energetic metabolism and immune function, by complex molecular crosstalk with other intracellular compounds. There is greatly increasing evidence regarding beneficial effects of acute and chronic administration of high melatonin doses, in infectious, developmental, and degenerative pathologies, as an endothelial cell and every cell protectant.

Deiminated proteins in extracellular vesicles and serum of llama (Lama glama)-Novel insights into camelid immunity

Peptidylarginine deiminases (PADs) are phylogenetically conserved calcium-dependent enzymes which post-translationally convert arginine into citrulline in target proteins in an irreversible manner, causing functional and structural changes in target proteins. Protein deimination causes generation of neo-epitopes, affects gene regulation and also allows for protein moonlighting. Furthermore, PADs have been found to be a phylogenetically conserved regulator for extracellular vesicle (EVs) release. EVs are found in most body fluids and participate in cellular communication via transfer of cargo proteins and genetic material. In this study, post-translationally deiminated proteins in serum and serum-EVs are described for the first time in camelids, using the llama (Lama glama L. 1758) as a model animal. We report a poly-dispersed population of llama serum EVs, positive for phylogenetically conserved EV-specific markers and characterised by TEM. In serum, 103 deiminated proteins were overall identified, including key immune and metabolic mediators including complement components, immunoglobulin-based nanobodies, adiponectin and heat shock proteins. In serum, 60 deiminated proteins were identified that were not in EVs, and 25 deiminated proteins were found to be unique to EVs, with 43 shared deiminated protein hits between both serum and EVs. Deiminated histone H3, a marker of neutrophil extracellular trap formation, was also detected in llama serum. PAD homologues were identified in llama serum by Western blotting, via cross reaction with human PAD antibodies, and detected at an expected 70 kDa size. This is the first report of deiminated proteins in serum and EVs of a camelid species, highlighting a hitherto unrecognized post-translational modification in key immune and metabolic proteins in camelids, which may be translatable to and inform a range of human metabolic and inflammatory pathologies.

An infection of Enterobacter ludwigii affects development and causes age-dependent neurodegeneration in Drosophila melanogaster

The effects of teeth-blackening bacteria Enterobacter ludwigii on the physiological system were investigated using the model organism Drosophila melanogaster. The bacteria were mixed with the fly food, and its effect was checked on the growth, development and behaviour of Drosophila. Microbes generate reactive oxygen species (ROS) within the haemolymph of the larvae once it enters into the body. The increased amount of ROS was evidenced by the NBT assay and using 2',7'-dichlorofluorescin diacetate dye, which indicates the mitochondrial ROS. The increased amount of ROS resulted in a number of abnormal nuclei within the gut. Besides that larvae walking became sluggish in comparison with wild type although the larvae crawling path did not change much. Flies hatched from the infectious larvae have the posterior scutellar bristle absent from the thorax and abnormal mechanosensory hairs in the eye, and they undergo time-dependent neurodegeneration as evidenced by the geotrophic and phototrophic assays. To decipher the mechanism of neurodegeneration, flies were checked for the presence of four important bioamines: tyramine, cadaverine, putrescine and histamine. Out of these four, histamine was found to be absent in infected flies. Histamine is a key molecule required for the functioning of the photoreceptor as well as mechanoreceptors. The mechanism via which mouth infectious bacteria E. ludwigii can affect the development and cause age-dependent neurodegeneration is explained in this paper.

Targeting strategies for chemotherapy-induced peripheral neuropathy: does gut microbiota play a role?

Chemotherapy-induced peripheral neuropathy (CIPN) is a progressive, often irreversible condition that produces severe neurological deficits. Emerging data suggest that chemotherapy also exerts detrimental effects on gut microbiota composition and intestinal permeability, contributing to dysbiosis and inflammation. Compared with other complications associated with chemotherapy, such as diarrhoea and mucositis, CIPN is of particular concern because it is the most common reason for terminating or suspending treatment. However, specific and effective curative treatment strategies are lacking. In this review, we provide an update on current preclinical and clinical understandings about the role of gut microbiota in CIPN. The gut microbiota serves as an intersection between the microbiome-gut-brain and the neuroimmune-endocrine axis, forming a complex network that can directly or indirectly affect key components involved in the manifestations of CIPN. Herein, we discuss several potential mechanisms within the context of the networks and summarize alterations in gut microbiome induced by chemotherapeutic drugs, providing great potential for researchers to target pathways associated with the gut microbiome and overcome CIPN.

Glutamatergic Signaling Along The Microbiota-Gut-Brain Axis

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

Application of gastrointestinal regulation in acupuncture treatment of insomnia based on the brain-gut axis theory

Gastrointestinal function is closely related to insomnia. The brain-gut axis theory provides a new way to regulate gastrointestinal function in the treatment of insomnia. By analyzing the nervous, endocrine, immune, and intestinal flora systems of the brain-gut axis that affects brain function as well as the regulatory effect of acupuncture and the traditional theoretical basis for the relationship of the brain-gut axis with the gastrointestinal tract and insomnia, we discuss the feasibility of acupuncture treatment of insomnia by regulating the gastrointestinal tract based on the brain-gut axis theory.

Investigating the role of interleukin-1 beta and glutamate in inflammatory bowel disease and epilepsy using discovery browsing

BACKGROUND

Structured electronic health records are a rich resource for identifying novel correlations, such as co-morbidities and adverse drug reactions. For drug development and better understanding of biomedical phenomena, such correlations need to be supported by viable hypotheses about the mechanisms involved, which can then form the basis of experimental investigations.

METHODS

In this study, we demonstrate the use of discovery browsing, a literature-based discovery method, to generate plausible hypotheses elucidating correlations identified from structured clinical data. The method is supported by Semantic MEDLINE web application, which pinpoints interesting concepts and relevant MEDLINE citations, which are used to build a coherent hypothesis.

RESULTS

Discovery browsing revealed a plausible explanation for the correlation between epilepsy and inflammatory bowel disease that was found in an earlier population study. The generated hypothesis involves interleukin-1 beta (IL-1 beta) and glutamate, and suggests that IL-1 beta influence on glutamate levels is involved in the etiology of both epilepsy and inflammatory bowel disease.

CONCLUSIONS

The approach presented in this paper can supplement population-based correlation studies by enabling the scientist to identify literature that may justify the novel patterns identified in such studies and can underpin basic biomedical research that can lead to improved treatments and better healthcare outcomes.

Activating metabotropic glutamate receptor‑7 attenuates visceral hypersensitivity in neonatal maternally separated rats

Increasing evidence has indicated that metabotropic glutamate receptor-7 (mGluR7) is an important target for reducing anxiety and stress-associated behaviours. Notably, mood disorders exhibit high levels of comorbidity with gastrointestinal dysfunction; however, the role of mGluR7 outside of the central nervous system is currently unknown. Activating mGluR7 likely increases colonic secretory function. Therefore, the present study aimed to evaluate the possible effects of mGluR7 on the visceral hypersensitivity of irritable bowel syndrome (IBS) in rats. The expression levels of mGluR7 were assessed in the colon tissues of rats with neonatal maternal separation (NMS)-induced visceral hypersensitivity using reverse transcription-quantitative polymerase chain reaction, western blotting and immunohistochemistry. In addition, the mGluR7 agonist AMN082 (3 or 10 mg/kg; i.p.) was administered 1 h prior to the visceral hypersensitivity test, and the effects of AMN082 were then observed on the nuclear factor (NF)-κB signalling pathway. The mRNA and protein expression levels of mGluR7 were upregulated in the colon mucosa of NMS rats compared with in normal control rats. Notably, administration of AMN082 (10 mg/kg) attenuated colorectal distension (CRD)-induced visceral hypersensitivity in NMS rats. In addition, interleukin-10 and transforming growth factor-β mRNA expression levels were upregulated, whereas interferon-γ mRNA expression levels were downregulated in the NMS + AMN082 group compared with in NMS rats. The number of cluster of differentiation 3⁺ T cells in the intestinal mucosa and myeloperoxidase activity were decreased in NMS + AMN082 rats. Furthermore, AMN082 treatment reduced the protein expression levels of phosphorylated-NF-κB in the colon tissue of NMS rats. These results indicated that activation of mGluR7 may attenuate CRD-induced visceral hypersensitivity in experimental IBS and reduce the abnormal immune cytokine response. In addition, it was suggested that the role of AMN082 in modulating the inflammatory response may be partially associated with inhibiting NF-κB activation. These data suggested that targeting mGluR7 may be useful in the treatment of stress-associated IBS.

Degradation Kinetics of 6‴-p-Coumaroylspinosin and Identification of Its Metabolites by Rat Intestinal Flora

6‴-p-Coumaroylspinosin (P-CS), a bioactive flavonoid, is typically extracted from Semen Ziziphi Spinosae (SZS). In this study, a high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) method was developed to determine P-CS for investigating the degradation characteristics of P-CS incubated with rat feces. The results showed that P-CS degraded rapidly and the degradation speeds varied depending upon the P-CS concentrations (3, 15, and 30 μg/mL). The degradation of P-CS processes follow first-order kinetics. On the basis of the mass spectrometry (MS) spectrum mode of the product ions, two main metabolites of P-CS were identified. Swertisin was the main metabolite at 3 and 15 μg/mL, while spinosin was produced when the P-CS concentration was 30 μg/mL. Spinosin and swertisin could improve mRNA transcription levels of glutamate receptor K1, K2, and K3 (GluK1, GluK2, and GluK3) subunits in rat hippocampal neurons. In addition, they showed an obvious synergistic effect in this respect. Collectively, the results can be used to explain the metabolic and pharmacological mechanisms of P-CS.

The Neuro-endocrinological Role of Microbial Glutamate and GABA Signaling

Gut microbiota provides the host with multiple functions (e.g., by contributing to food digestion, vitamin supplementation, and defense against pathogenic strains) and interacts with the host organism through both direct contact (e.g., through surface antigens) and soluble molecules, which are produced by the microbial metabolism. The existence of the so-called gut–brain axis of bi-directional communication between the gastrointestinal tract and the central nervous system (CNS) also supports a communication pathway between the gut microbiota and neural circuits of the host, including the CNS. An increasing body of evidence has shown that gut microbiota is able to modulate gut and brain functions, including the mood, cognitive functions, and behavior of humans. Nonetheless, given the extreme complexity of this communication network, its comprehension is still at its early stage. The present contribution will attempt to provide a state-of-the art description of the mechanisms by which gut microbiota can affect the gut–brain axis and the multiple cellular and molecular communication circuits (i.e., neural, immune, and humoral). In this context, special attention will be paid to the microbial strains that produce bioactive compounds and display ascertained or potential probiotic activity. Several neuroactive molecules (e.g., catecholamines, histamine, serotonin, and trace amines) will be considered, with special focus on Glu and GABA circuits, receptors, and signaling. From the basic science viewpoint, “microbial endocrinology” deals with those theories in which neurochemicals, produced by both multicellular organisms and prokaryotes (e.g., serotonin, GABA, glutamate), are considered as a common shared language that enables interkingdom communication. With regards to its application, research in this area opens the way toward the possibility of the future use of neuroactive molecule-producing probiotics as therapeutic agents for the treatment of neurogastroenteric and/or psychiatric disorders.

The Pharmacology of Visceral Pain

Visceral pain describes pain emanating from the internal thoracic, pelvic, or abdominal organs. Unlike somatic pain, visceral pain is generally vague, poorly localized, and characterized by hypersensitivity to a stimulus such as organ distension. While current therapeutics provides some relief from somatic pain, drugs used for treatment of chronic visceral pain are typically less efficacious and limited by multiple adverse side effects. Thus, the treatment of visceral pain represents a major unmet medical need. Further, more basic research into the physiology and pathophysiology of visceral pain is needed to provide novel targets for future drug development. In concert with chronic visceral pain, there is a high comorbidity with stress-related psychiatric disorders including anxiety and depression. The mechanisms linking visceral pain with these overlapping comorbidities remain to be elucidated. However, persistent stress facilitates pain perception and sensitizes pain pathways, leading to a feed-forward cycle promoting chronic visceral pain disorders. We will focus on stress-induced exacerbation of chronic visceral pain and provide supporting evidence that centrally acting drugs targeting the pain and stress-responsive brain regions may represent a valid target for the development of novel and effective therapeutics.

Expression of group III metabotropic glutamate receptors in the reproductive system of male mice

Although the presence of metabotropic glutamate (mGlu) receptors in the central nervous system is well documented, they have recently been found in peripheral and non-neuronal tissues. In the present study we investigated the expression of group III mGlu receptors in the reproductive system of male mice. Reverse transcription–polymerase chain reaction analysis revealed the presence of mGlu6, mGlu7 and mGlu8 (but not mGlu4) receptor transcripts in testes and epididymides from adult mice. In addition, expression of mGlu6 (Grm6) and mGlu8 receptor (Grm8) mRNA was detected in spermatozoa isolated from the vas deferens. The vas deferens was found to contain only mGlu7 receptor (Grm7) mRNA, which was particularly intense in 21-day-old male mice. In penile homogenates, only the mGlu7 receptor signal was detected. Genetic ablation of the mGlu7 receptor in males led to fertility disorders manifested by decreased insemination capability as well as deterioration of sperm parameters, particularly sperm motility, vitality, sperm membrane integrity and morphology, with a simultaneous increase in sperm concentration. These results indicate that constitutively expressed mGlu receptors in the male reproductive system may play an important role in ejaculation and/or erection processes, as well as in the formation and maturation of spermatozoa.

Mechanisms Underlying Mammalian Hybrid Sterility in Two Feline Interspecies Models

The phenomenon of male sterility in interspecies hybrids has been observed for over a century, however, few genes influencing this recurrent phenotype have been identified. Genetic investigations have been primarily limited to a small number of model organisms, thus limiting our understanding of the underlying molecular basis of this well-documented "rule of speciation." We utilized two interspecies hybrid cat breeds in a genome-wide association study employing the Illumina 63 K single-nucleotide polymorphism array. Collectively, we identified eight autosomal genes/gene regions underlying associations with hybrid male sterility (HMS) involved in the function of the blood-testis barrier, gamete structural development, and transcriptional regulation. We also identified several candidate hybrid sterility regions on the X chromosome, with most residing in close proximity to complex duplicated regions. Differential gene expression analyses revealed significant chromosome-wide upregulation of X chromosome transcripts in testes of sterile hybrids, which were enriched for genes involved in chromatin regulation of gene expression. Our expression results parallel those reported in Mus hybrids, supporting the "Large X-Effect" in mammalian HMS and the potential epigenetic basis for this phenomenon. These results support the value of the interspecies feline model as a powerful tool for comparison to rodent models of HMS, demonstrating unique aspects and potential commonalities that underpin mammalian reproductive isolation.

Relationship between brain-gut axis and inflammatory bowel disease

Inflammatory bowel disease (IBD), including ulcerative colitis (UC) and Crohn's disease (CD), is a chronic relapsing inflammatory disease affecting the gastrointestinal tract. The incidence of IBD has increased dramatically year by year in China. Currently, the IBD research is focused on genetically predisposed factors, immune response, environmental triggers and infections. However, the etiology of IBD is still unclear. Recently, more attention has been paid to the research of neural regulation affecting the progression of IBD. Previous research has revealed that psycho-neuro-endocrine-immune modulation through the brain-gut axis plays a crucial role in the pathogenesis of IBD. It is important to explore other psychotherapies applied to adjutant therapy in IBD. This review reviews the recent advances in understanding the relationship between the brain-gut axis and inflammatory bowel disease.

Influence of JuA in evoking communication changes between the small intestines and brain tissues of rats and the GABAA and GABAB receptor transcription levels of hippocampal neurons

ETHNOPHARMACOLOGICAL RELEVANCE

Jujuboside A (JuA) is a main active ingredient of semen ziziphi spinosae, which can significantly reduce spontaneous activity in mammals, increase the speed of falling asleep, prolong the sleeping time as well as improve the sleeping efficiency. In this study, the mechanism and the pathway of the sedative and hypnotic effect of JuA were investigated.

MATERIALS AND METHODS

After being treated with JuA (in vitro), the rat׳s small intestine tissues cultures were used to stimulate the brain tissues. Then 27 cytokine levels were detected in the two kinds of tissue culture via liquid protein chip technology; In addition, the cultured hippocampal neurons of rat were treated with JuA, and γ-aminobutyric acid (GABA) receptor subunits (GABAAα1, GABAAα5, GABAAβ1 and GABABR1) mRNAs were evaluated by Real-time PCR.

RESULTS

The levels of IL-1α, MIP-1α, IL-1β and IL-2 were reduced significantly after 3h of treating the small intestine tissues with JuA (200µl/ml), and the concentration change rates, in order, were -59.3%, -3.59%, -50.1% and -49.4%; these cytokines were transmitted to brain tissues 2h later, which could lead to significant levels of reduction of IL-1α, IFN-γ, IP-10 and TNF-α; the concentration change rates were -62.4%, -25.7%, -55.2% and -38.5%, respectively. Further, the intercellular communication network diagram was mapped out, which could suggest the mechanism and the pathway of the sedative and hypnotic effect of JuA. The results also indicated that JuA (50µl/ml) increased significantly GABAAα1 receptor mRNAs and reduced GABABR1, mRNAs in hippocampal neurons after 24h of stimulation; however, all the mRNA transcription levels of GABAAα1,GABAAα5, GABAAβ1 and GABABR1 receptors increased significantly after 48h.

CONCLUSION

JuA performed its specific sedative and hypnotic effect through not only adjusting GABA receptors subunit mRNAs expression, but also down-regulating the secretion of relevant inflammation cytokines on the intestinal mucosal system to affect the intercellular cytokine network between nerve cells in the brain. This mechanism is similar to that of melatonin.

Metabotropic glutamate receptors as drug targets: what's new?

The question in the title: 'what's new?' has two facets. First, are 'clinical' expectations met with success? Second, is the number of CNS disorders targeted by mGlu drugs still increasing? The answer to the first question is 'no', because development program with promising drugs in the treatment of schizophrenia, Parkinson's disease, and Fragile X syndrome have been discontinued. Nonetheless, we continue to be optimistic because there is still the concrete hope that some of these drugs are beneficial in targeted subpopulations of patients. The answer to the second question is 'yes', because mGlu ligands are promising targets for 'new' disorders such as type-1 spinocerebellar ataxia and absence epilepsy. In addition, the increasing availability of pharmacological tools may push mGlu7 and mGlu8 receptors into the clinical scenario. After almost 30 years from their discovery, mGlu receptors are still alive.

Contents of amino acid neurotransmitters and expression of γ-aminobutyric acid receptor in two subtypes of irritable bowel syndrome

AIM: To explore the feasibility of using in vivo cerebral microdialysis and high performance liquid chromatography (HPLC) to determine the contents of glutamate (Glu), glycine (Gly), γ-aminobutyric acid (γ-GABA) and taurine (Tau), and to observe the protein expression of γ-aminobutyric acid receptor A (GABA_Aα1) in irritable bowel syndrome with diarrhea (IBS-D) and irritable bowel syndrome with constipation (IBS-C) to investigate the preliminary pathogenesis of these two subtypes.

METHODS: Using in vitro relative recovery and in vivo relative loss ratio as monitoring indicators, the feasibility of using cerebral microdialysis and HPLC to determine the contents of Glu, Gly, Tau and γ-GABA was first explored. IBS-C was induced by cold water administration and IBS-D by folium sennae combined with restraint. Cerebral microdialysis and HPLC were then used to determine the contents of Glu, Gly, Tau and γ-GABA in the rat brain. Western blot was used to detect the expression of GABA_Aα1 protein in brain tissue.

RESULTS: In vivo cerebral microdialysis and HPLC were feasible for determining the contents of Glu and γ-GABA; the in vitro relative recovery rates were 21.6% and 24.5%, respectively; in vivo relative loss rates were 41.8% and 32.5%. Compared with rats in the normal group, the ratio of Glu/γ-GABA in the IBS-C and IBS-D groups significantly increased (P < 0.05). GABA_Aα1 protein expression in both IBS-C and IBS-D groups were significantly higher than that in the normal group (P < 0.05). In addition, GABA_Aα1 protein expression in the IBS-D group was significantly higher than that in the IBS-C group (P < 0.05).

CONCLUSION: The pathogenesis of IBS-C and IBS-D may be related with Glu/GABA ratio and GABA_Aα1 in the brain.

VGLUTs in Peripheral Neurons and the Spinal Cord: Time for a Review

Vesicular glutamate transporters (VGLUTs) are key molecules for the incorporation of glutamate in synaptic vesicles across the nervous system, and since their discovery in the early 1990s, research on these transporters has been intense and productive. This review will focus on several aspects of VGLUTs research on neurons in the periphery and the spinal cord. Firstly, it will begin with a historical account on the evolution of the morphological analysis of glutamatergic systems and the pivotal role played by the discovery of VGLUTs. Secondly, and in order to provide an appropriate framework, there will be a synthetic description of the neuroanatomy and neurochemistry of peripheral neurons and the spinal cord. This will be followed by a succinct description of the current knowledge on the expression of VGLUTs in peripheral sensory and autonomic neurons and neurons in the spinal cord. Finally, this review will address the modulation of VGLUTs expression after nerve and tissue insult, their physiological relevance in relation to sensation, pain, and neuroprotection, and their potential pharmacological usefulness.