Key role of gut microbiota in anhedonia-like phenotype in rodents with neuropathic pain

Electro-acupuncture inhibits HDAC2 via modulating gut microbiota to ameliorate SNI-induced pain and depression-like behavior in rats

BACKGROUND

Depression and chronic pain frequent co-occur, exacerbating each other's symptoms and hindering treatment. Emerging studies have highlighted abnormal gut microbiota in both conditions. Previous studies have demonstrated the clinical effectiveness of electro-acupuncture (EA) in managing these conditions, yet the underlying mechanisms remain elusive.

METHODS

Spared nerve injury (SNI) was employed to induce chronic pain and depression-like behavior. Rats were randomly assigned to sham SNI (SS), SNI, and EA groups. SNI surgery was performed on all rats, except those in SS group, which underwent sham SNI surgery. Then EA group received 5 weeks of EA treatment. Pain and depression-like behavior were assessed through paw withdrawal threshold, sucrose-preference test, and forced swim test. Gut microbiota composition was analyzed via 16S rDNA sequencing. Brain-Derived Neurotrophic Factor (BDNF) and acetylation-related proteins in the medial prefrontal cortex (mPFC) were evaluated through enzyme-linked immunosorbent assay and western blot.

RESULTS

EA treatment significantly ameliorated pain and depression-like behavior. The 16S rDNA sequencing showed EA modulated gut microbiota composition, increased short-chain fatty acids (SCFAs)-producing bacteria, including Akkermansi, Ruminococcaceae and Lachnospiraceae family, particularly Akkermansia. Furthermore, EA increased BDNF, AcH3 and decreased HDAC2 in mPFC. Notably, SCFAs-producing bacteria exhibited a negative correlation with HDAC2 levels.

LIMITATIONS

This study exclusively investigated microbiota differences resulting from EA stimulation, without delving into the functional variations brought about by these microbial distinctions.

CONCLUSIONS

The therapeutic effects of EA on the comorbidity of chronic pain and depression may involve the modulation of the gut microbiota, resulting in histone acetylation changes and upregulation of BDNF.

Genetically predicted immune cells mediate the association between gut microbiota and neuropathy pain

BACKGROUND

Previous observational studies have indicated a complex association between gut microbiota (GM) and neuropathic pain (NP). Nonetheless, the precise biological mechanisms underlying this association remain unclear. Therefore, we adopted a Mendelian randomization (MR) approach to investigate the causal relationship between GM and neuropathic pain including post-herpetic neuralgia (PHN), painful diabetic peripheral neuropathy (PDPN), and trigeminal neuralgia (TN), as well as to explore the potential mediation effects of immune cells.

METHODS

We performed a two-step, two-sample Mendelian randomization study with an inverse variance-weighted (IVW) approach to investigate the causal role of GM on three major kinds of NP and the mediation effect of immune cells between the association of GM and NP. In addition, we determine the strongest causal associations using Bayesian weighted Mendelian randomization (BWMR) analysis. Furthermore, we will investigate the mediating role of immune cells through a two-step Mendelian randomization design.

RESULTS

We identified 53 taxonomies and pathways of gut microbiota that had significant causal associations with NP. In addition, we also discovered 120 immune cells that exhibited significant causal associations with NP. According to the BWMR and two-step Mendelian randomization analysis, we identified the following results CD4 on CM CD4 + (maturation stages of T cell) mediated 6.7% of the risk reduction for PHN through the pathway of fucose degradation (FUCCAT.PWY). CD28 + DN (CD4-CD8-) AC (Treg) mediated 12.5% of the risk reduction for PHN through the influence on Roseburia inulinivorans. CD45 on lymphocyte (Myeloid cell) mediated 11.9% of the risk increase for TN through the superpathway of acetyl-CoA biosynthesis (PWY.5173). HLA DR + CD8br %T cell (TBNK) mediated 3.2% of the risk reduction for TN through the superpathway of GDP-mannose-derived O-antigen building blocks biosynthesis (PWY.7323). IgD-CD38-AC (B cell) mediated 7.5% of the risk reduction for DPN through the pathway of thiazole biosynthesis I in E. coli (PWY.6892).

DISCUSSION

These findings provided evidence supporting the causal effect of GM with NP, with immune cells playing a mediating role. These findings may inform prevention strategies and interventions directed toward NP. Future studies should explore other plausible biological mechanisms.

The interplay between the microbiota and opioid in the treatment of neuropathic pain

Neuropathic pain (NP) is characterized by its complex and multifactorial nature and limited responses to opioid therapy; NP is associated with risks of drug resistance, addiction, difficulty in treatment cessation, and psychological disorders. Emerging research on gut microbiota and their metabolites has demonstrated their effectiveness in alleviating NP and augmenting opioid-based pain management, concurrently mitigating the adverse effects of opioids. This review addresses the following key points: (1) the current advances in gut microbiota research and the challenges in using opioids to treat NP, (2) the reciprocal effects and benefits of gut microbiota on NP, and (3) the interaction between opioids with gut microbiota, as well as the benefits of gut microbiota in opioid-based treatment of NP. Through various intricate mechanisms, gut microbiota influences the onset and progression of NP, ultimately enhancing the efficacy of opioids in the management of NP. These insights pave the way for further pragmatic clinical research, ultimately enhancing the efficacy of opioid-based pain management.

Lactobacillus Plantarum intake mitigates neuropathic pain behavior via enhancing macrophage M2 polarization in a rat model of peripheral neuropathy

Pro-inflammatory macrophages (M1-polarized) play a crucial role in neuroinflammation and neuropathic pain following nerve injury. Redirecting macrophage polarization toward anti-inflammatory (M2-polarized) phenotypes offers a promising therapeutic strategy. Recognized for their anti-inflammatory and immunomodulatory properties, probiotics are becoming a focal point of research. This study investigated the effects of Lactobacillus plantarum on macrophage polarization, nerve protection, and neuropathic pain behavior following chronic constriction injury (CCI) of the median nerve. Rats received daily oral doses of L. plantarum for 28 days before and 14 days after CCI. Subsequently, behavioral and electrophysiological assessments were performed. The M1 marker CD86 levels, M2 marker CD206 levels, and concentrations of pro-inflammatory and anti-inflammatory cytokines in the injured median nerve were assessed. L. plantarum administration effectively reduced neuropathic pain behavior and the Firmicutes to Bacteroidetes ratio after CCI. Moreover, L. plantarum treatment increased serum short-chain fatty acids (SCFAs) levels, preserved myelination of the injured median nerve, and suppressed injury-induced discharges. In CCI rats treated with L. plantarum, there was a reduction in CD86 and pro-inflammatory cytokine levels, accompanied by an increase in CD206 and the release of anti-inflammatory cytokines. Furthermore, receptors for anti-inflammatory cytokines were localized on Schwann cells, and their expression was significantly upregulated in the injured nerves of CCI rats receiving L. plantarum. In conclusion, L. plantarum shifts macrophage phenotypes from M1 to M2 by promoting the production of SCFAs and enhancing the release of anti-inflammatory cytokines. Ultimately, this process preserves nerve fiber integrity and impedes the onset of neuropathic pain.

The impact of the microbiota-gut-brain axis on endometriosis-associated symptoms: mechanisms and opportunities for personalised management strategies

Endometriosis is a chronic inflammatory condition affecting one in 10 women and those assigned female at birth, defined by the presence of endometrial-like tissue outside the uterus. It is commonly associated with pain, infertility, and mood disorders, and often comorbid with other chronic pain conditions, such as irritable bowel syndrome. Recent research has identified a key role for the microbiota-gut-brain axis in health and a range of inflammatory and neurological disorders, prompting an exploration of its potential mechanistic role in endometriosis. Increased awareness of the impact of the gut microbiota within the patient community, combined with the often-detrimental side effects of current therapies, has motivated many to utilise self-management strategies, such as dietary modification and supplements, despite a lack of robust clinical evidence. Current research has characterised the gut microbiota in endometriosis patients and animal models. However, small cohorts and differing methodology has resulted in little consensus in the data. In this narrative review, we summarise research studies that have investigated the role of gut microbiota and their metabolic products in the development and progression of endometriosis lesions, before summarising insights from research into co-morbid conditions and discussing the reported impact of self-management strategies on symptoms of endometriosis. Finally, we suggest ways in which this promising field of research could be expanded to explore the role of specific bacteria, improve access to 'microbial' phenotyping, and to develop personalised patient advice for reduction of symptoms such as chronic pain and bloating.

To analyze the relationship between gut microbiota, metabolites and migraine: a two-sample Mendelian randomization study

Background

It has been suggested in several observational studies that migraines are associated with the gut microbiota. It remains unclear, however, how the gut microbiota and migraines are causally related.

Methods

We performed a bidirectional two-sample mendelian randomization study. Genome-wide association study (GWAS) summary statistics for the gut microbiota were obtained from the MiBioGen consortium (n = 18,340) and the Dutch Microbiota Project (n = 7,738). Pooled GWAS data for plasma metabolites were obtained from four different human metabolomics studies. GWAS summary data for migraine (cases = 48,975; controls = 450,381) were sourced from the International Headache Genetics Consortium. We used inverse-variance weighting as the primary analysis. Multiple sensitivity analyses were performed to ensure the robustness of the estimated results. We also conducted reverse mendelian randomization when a causal relationship between exposure and migraine was found.

Results

LachnospiraceaeUCG001 (OR = 1.12, 95% CI: 1.05-1.20) was a risk factor for migraine. Blautia (OR = 0.93, 95% CI: 0.88-0.99), Eubacterium (nodatum group; OR = 0.94, 95% CI: 0.90-0.98), and Bacteroides fragilis (OR = 0.97, 95% CI: 0.94-1.00) may have a suggestive association with a lower migraine risk. Functional pathways of methionine synthesis (OR = 0.89, 95% CI: 0.83-0.95) associated with microbiota abundance and plasma hydrocinnamate (OR = 0.85, 95% CI: 0.73-1.00), which are downstream metabolites of Blautia and Bacteroides fragilis, respectively, may also be associated with lower migraine risk. No causal association between migraine and the gut microbiota or metabolites was found in reverse mendelian randomization analysis. Both significant horizontal pleiotropy and significant heterogeneity were not clearly identified.

Conclusion

This Mendelian randomization analysis showed that LachnospiraceaeUCG001 was associated with an increased risk of migraine, while some bacteria in the gut microbiota may reduce migraine risk. These findings provide a reference for a deeper comprehension of the role of the gut-brain axis in migraine as well as possible targets for treatment interventions.

Transient Receptor Potential Channels: Multiple Modulators of Peripheral Neuropathic Pain in Several Rodent Models

Neuropathic pain, a prevalent chronic condition in clinical settings, has attracted widespread societal attention. This condition is characterized by a persistent pain state accompanied by affective and cognitive disruptions, significantly impacting patients' quality of life. However, current clinical therapies fall short of addressing its complexity. Thus, exploring the underlying molecular mechanism of neuropathic pain and identifying potential targets for intervention is highly warranted. The transient receptor potential (TRP) receptors, a class of widely distributed channel proteins, in the nervous system, play a crucial role in sensory signaling, cellular calcium regulation, and developmental influences. TRP ion channels are also responsible for various sensory responses including heat, cold, pain, and stress. This review highlights recent advances in understanding TRPs in various rodent models of neuropathic pain, aiming to uncover potential therapeutic targets for clinical management.

Ginger alleviates mechanical hypersensitivity and anxio-depressive behavior in rats with diabetic neuropathy through beneficial actions on gut microbiome composition, mitochondria, and neuroimmune cells of colon and spinal cord

The relationship among gut microbiota, mitochondrial dysfunction/neuroinflammation, and diabetic neuropathic pain (DNP) has received increased attention. Ginger has antidiabetic and analgesic effects because of its anti-inflammatory property. We examined the effects of gingerols-enriched ginger (GEG) supplementation on pain-associated behaviors, gut microbiome composition, and mitochondrial function and neuroinflammation of colon and spinal cord in DNP rats. Thirty-three male rats were randomly divided into 3 groups: control group, DNP group (high-fat diet plus single dose of streptozotocin at 35 mg/kg body weight, and GEG group (DNP+GEG at 0.75% in the diet for 8 weeks). Von Frey and open field tests were used to assess pain sensitivity and anxio-depressive behaviors, respectively. Colon and spinal cord were collected for gene expression analysis. 16S rRNA gene sequencing was done from cecal samples and microbiome data analysis was performed using QIIME 2. GEG supplementation mitigated mechanical hypersensitivity and anxio-depressive behavior in DNP animals. GEG supplementation suppressed the dynamin-related protein 1 protein expression (colon) and gene expression (spinal cord), astrocytic marker GFAP gene expression (colon and spinal cord), and tumor necrosis factor-α gene expression (colon, P < .05; spinal cord, P = .0974) in DNP rats. GEG supplementation increased microglia/macrophage marker CD11b gene expression in colon and spinal cord of DNP rats. GEG treatment increased abundance of Acinetobacter, Azospirillum, Colidextribacter, and Fournierella but decreased abundance of Muribaculum intestinale in cecal feces of rats. This study demonstrates that GEG supplementation decreased pain, anxio-depression, and neuroimmune cells, and improved the composition of gut microbiomes and mitochondrial function in rats with diabetic neuropathy.

The causality between gut microbiome and chronic regional pain: a Mendelian randomization analysis

Background

Numerous investigations have underscored the causal effect between chronic pain (CP) and gut microbiota, jointly contributing to the onset and development of widespread CP. Nonetheless, there was still uncertainty about the causal effect between gut microbiota and chronic regional pain (CRP).

Methods

Genome-wide association study (GWAS) summary data of gut microbial taxa (MiBioGen Consortium: 211 microbiotas and the Dutch Microbiome Project: 207 microbiotas) and eight types of CRP were used to reveal the causal effect between persistent pain in a specific region of the body and gut microbiota. A two-sample bidirectional Mendelian randomization (MR) design was used. In order to ensure the accuracy of the results, multiple sensitivity analyses were employed.

Results

This study uncovered significant causal associations between six gut microbial taxa and three types of CRP (forward: Genus Parabacteroides for general pain; Class Bacteroidia, Order Bacteroidales, and Phylum Bacteroidetes for back pain. Reverse: knee pain for Genus Howardella and Order Coriobacteriales) by forward and reverse MR analysis. These findings had been verified by a rigorous Bonferroni correction. Furthermore, this research identified 19 microbial taxa that exhibited potential correlations with four types of CRP. There are no significant or potential gut microbiotas that were associated with other types of CRP, including fascial pain, stomach or abdominal pain, and hip pain.

Conclusion

This two-sample bidirectional MR analysis unveiled the causality between gut microbial taxa and eight CRP conditions. The findings reveal the interplay between CRP and 6 gut microbiotas while also delineating 19 potential specific microbial taxa corresponding to diverse locations of persistent pain.

Regulation of miRNA expression in the prefrontal cortex by fecal microbiota transplantation in anxiety-like mice

Background

The gut-brain axis and gut microbiota have emerged as key players in emotional disorders. Recent studies suggest that alterations in gut microbiota may impact psychiatric symptoms through brain miRNA along the gut-brain axis. However, direct evidence linking gut microbiota to the pathophysiology of generalized anxiety disorder (GAD) via brain miRNA is limited. In this study, we explored the effects of fecal microbiota transplantation (FMT) from GAD donors on gut microbiota and prefrontal cortex miRNA in recipient mice, aiming to understand the relationship between these two factors.

Methods

Anxiety scores and gut microbiota composition were assessed in GAD patients, and their fecal samples were utilized for FMT in C57BL/6J mice. Anxiety-like behavior in mice was evaluated using open field and elevated plus maze tests. High-throughput sequencing of gut microbiota 16S rRNA and prefrontal cortex miRNA was performed.

Results

The fecal microbiota of GAD patients exhibited a distinct microbial structure compared to the healthy group, characterized by a significant decrease in Verrucomicrobia and Akkermansia, and a significant increase in Actinobacteria and Bacteroides. Subsequent FMT from GAD patients to mice induced anxiety-like behavior in recipients. Detailed analysis of gut microbiota composition revealed lower abundances of Verrucomicrobia, Akkermansia, Bifidobacterium, and Butyricimonas, and higher abundances of Deferribacteres, Allobaculum, Bacteroides, and Clostridium in mice that received FMT from GAD patients. MiRNA analysis identified five key miRNAs affecting GAD pathogenesis, including mmu-miR-10a-5p, mmu-miR-1224-5p, mmu-miR-218-5p, mmu-miR-10b-5p, and mmu-miR-488-3p. Notably, mmu-miR-488-3p showed a strong negative correlation with Verrucomicrobia and Akkermansia.

Conclusion

This study demonstrates that anxiety-like behavior induced by human FMT can be transmitted through gut microbiota and is associated with miRNA expression in the prefrontal cortex. It is inferred that the reduction of Akkermansia caused by FMT from GAD patients leads to the upregulation of mmu-miR-488-3p expression, resulting in the downregulation of its downstream target gene Creb1 and interference with its related signaling pathway. These findings highlight the gut microbiota's crucial role in the GAD pathophysiology.

What we need to know about the germ-free animal models

The gut microbiota (GM), as a forgotten organ, refers to the microbial community that resides in the gastrointestinal tract and plays a critical role in a variety of physiological activities in different body organs. The GM affects its targets through neurological, metabolic, immune, and endocrine pathways. The GM is a dynamic system for which exogenous and endogenous factors have negative or positive effects on its density and composition. Since the mid-twentieth century, laboratory animals are known as the major tools for preclinical research; however, each model has its own limitations. So far, two main models have been used to explore the effects of the GM under normal and abnormal conditions: the isolated germ-free and antibiotic-treated models. Both methods have strengths and weaknesses. In many fields of host-microbe interactions, research on these animal models are known as appropriate experimental subjects that enable investigators to directly assess the role of the microbiota on all features of physiology. These animal models present biological model systems to either study outcomes of the absence of microbes, or to verify the effects of colonization with specific and known microbial species. This paper reviews these current approaches and gives advantages and disadvantages of both models.

Inferior social hierarchy is vulnerable to anxiety-like behavior in chronic pain mice: Potential role of gut microbiota and metabolites

Social dominance is a universal phenomenon among grouped animals that profoundly affects survival, health, and reproductive success by determining access to resources, and exerting a powerful influence on subsequent behavior. However, the understanding of pain and anxiety comorbidities in dominant or subordinate animals suffering from chronic pain is not well-defined. Here, we provide evidence that subordinate mice are more susceptible to pain-induced anxiety compared to dominant mice. We propose that the gut microbiota may play a mediating role in this mechanism. Our findings demonstrate that transplantation of fecal microbiota from subordinate mice with chronic inflammatory pain, but not dominant mice, into antibiotics-treated pseudo-germ-free mice significantly amplifies anxiety-like phenotypes, highlighting the critical involvement of gut microbiota in this behavioral response. Using chronic inflammatory pain model, we carried out 16S rRNA sequencing and untargeted metabolomic analyses to explore the relationship between microbiota and metabolites in a stable social hierarchy of mice. Interestingly, anxiety-like behaviors were directly associated with some microbial genera and metabolites, especially bile acid metabolism. Overall, we have demonstrated a close relationship between social status and anxiety susceptibility, highlighting the contributions of gut microbiota and the associated metabolites in the high-anxiety state of subordinate mice with chronic inflammatory pain.

Parental Social Isolation during Adolescence Alters Gut Microbiome in Rat Male Offspring

Previous work from our laboratory demonstrated that parental stress, induced by social isolation starting at puberty, leads to behavioral, endocrine, and biochemical changes in the male, but not female, offspring (ISO-O) of Sprague-Dawley rats. Here, we report alterations in the gut microbiota composition of ISO-O vs. grouped-housed offspring (GH-O), although all animals received the same diet and were housed in the same conditions. Analysis of bacterial communities by next-generation sequencing (NGS) of 16S rRNA gene revealed alterations at family and order levels within the main phyla of Bacteroides, Proteobacteria, and Firmicutes, including an almost total deficit in Limosilactobacillus reuteri (formerly Lactobacillus reuteri) and a significant increase in Ligilactobacillus murinus (formerly Lactobacillus murinus). In addition, we found an increase in the relative abundance of Rhodospirillales and Clostridiales in the families of Lachnospiraceae and Ruminococcaceae, and Bacteroidales in the family of Prevotellaceae. Furthermore, we examined plasma levels of the proinflammatory cytokines interleukin-1-beta and tumor necrosis factor-alpha, which did not differ between the two groups, while corticosterone concentrations were significantly increased in ISO-O rats. Our findings suggest that adverse environmental conditions experienced by parents may have an impact on the likelihood of disease development in the subsequent generations.

Causal association between gut microbiota and fibromyalgia: a Mendelian randomization study

Background

Fibromyalgia (FM) is a syndrome characterized by chronic and widespread musculoskeletal pain. A number of studies have implied a potential association between gut microbiota and FM. However, the casual association between gut microbiota and FM remains unknown.

Method

Mendelian randomization (MR) study was conducted using the summary statistics of genetic variants from the genome-wide association study (GWAS). Inverse variance weighted (IVW), combined with MR-Egger and weighted median were used to investigate the causal association between 119 gut microbiota genera and FM. Sensitivity analyses were performed on the MR results, including heterogeneity test, leave-one-out test and pleiotropy test.

Results

A total of 1,295 single nucleotide polymorphism (SNPs) were selected as instrumental variables (IVs), with no significant heterogeneity and pleiotropy according to the sensitivity analyses. Five gut microbiota genera were found to have significant casual association with FM. Coprococcus2 (OR = 2.317, p-value = 0.005, 95% CI: 1.289-4.167), Eggerthella (OR = 1.897, p-value = 0.001, 95% CI: 1.313-2.741) and Lactobacillus (OR = 1.576, p-value =0.020, 95% CI: 1.073-2.315) can increase the risk of FM. FamillyXIIIUCG001 (OR = 0.528, p-value = 0.038, 95% CI: 0.289-0.964) and Olsenella (OR = 0.747, p-value = 0.050, 95% CI: 0.557-1.000) can decrease the risk of FM.

Conclusion

This MR study found that gut microbiota is casually associated with FM. New insights into the mechanisms of FM mediated by gut microbiota are provided.

Opioid-induced dysbiosis of maternal gut microbiota during gestation alters offspring gut microbiota and pain sensitivity

There has been a rapid increase in neonates born with a history of prenatal opioid exposure. How prenatal opioid exposure affects pain sensitivity in offspring is of interest, as this may perpetuate the opioid epidemic. While few studies have reported hypersensitivity to thermal pain, potential mechanisms have not been described. This study posits that alterations in the gut microbiome may underly hypersensitivity to pain in prenatally methadone-exposed 3-week-old male offspring, which were generated using a mouse model of prenatal methadone exposure. Fecal samples collected from dams and their offspring were subjected to 16s rRNA sequencing. Thermal and mechanical pain were assessed using the tail flick and Von Frey assays. Transcriptomic changes in whole brain samples of opioid or saline-exposed offspring were investigated using RNA-sequencing, and midbrain sections from these animals were subjected to qPCR profiling of genes related to neuropathic and inflammatory pain pathways. Prenatal methadone exposure increased sensitivity to thermal and mechanical pain and elevated serum levels of IL-17a. Taxonomical analysis revealed that prenatal methadone exposure resulted in significant alterations in fecal gut microbiota composition, including depletion of Lactobacillus, Bifidobacterium, and Lachnospiracea sp and increased relative abundance of Akkermansia, Clostridium sensu stricto 1, and Lachnoclostridium. Supplementation of the probiotic VSL#3 in dams rescued hypersensitivity to thermal and mechanical pain in prenatally methadone-exposed offspring. Similarly, cross-fostering prenatally methadone-exposed offspring to control dams also attenuated hypersensitivity to thermal pain in opioid-exposed offspring. Modulation of the maternal and neonatal gut microbiome with probiotics resulted in transcriptional changes in genes related to neuropathic and immune-related signaling in whole brain and midbrain samples of prenatally methadone-exposed offspring. Together, our work provides compelling evidence of the gut-brain-axis in mediating pain sensitivity in prenatally opioid-exposed offspring.

Chronic restraint stress induces abnormal behaviors in pain sensitivity and cognitive function in mice: the role of Keap1/Nrf2 pathway

Stress is a series of physical and psychological responses to external and internal environmental stimuli. Growing studies have demonstrated the detrimental impacts of acute restraint stress (ARS) and chronic restraint stress (CRS) on animal behavior. However, the related pathogenesis and therapeutic mechanisms remain unclear. Hence, the present study aimed to examine whether unfolded protein response (UPR) and Kelch-like ECH-associated protein 1 (Keap1)-nuclear factor erythroid 2 related factor 2 (Nrf2) pathway are associated with ARS- and CRS- induced abnormal behaviors of pain sensitivity and cognitive function. We here used four behavioral tests to evaluate pain sensitivity and cognitive function in ARS and CRS mice. CRS markedly decreased Paw Withdrawal Mechanical Threshold (PWMT) and Tail-flick Latency (TFL) scores, whereas ARS altered TFL but had no effect on PWMT scores. Additionally, CRS, but not ARS, significantly changed behaviors in nest building behavior and MWMT. Intriguingly, the expression of Keap1 and Nrf2 protein were decreased in the spinal cord and hippocampus in CRS mice, but not in ARS mice. Moreover, neither the ARS nor the CRS groups significantly differed from the control group in terms of endoplasmic reticulum stress (ERS). Taken together, this study demonstrated that CRS could induce abnormal pain sensitivity and cognitive function probably via Keap1/Nrf2 pathway in spinal cord and hippocampus. It is therefore likely that effective intervention of Keap1/Nrf2 pathway may contribute to preventing and treating hyperalgesia and cognitive dysfunction in CRS.

Multi-omics analysis of fecal microbiota transplantation's impact on functional constipation and comorbid depression and anxiety

BACKGROUND

Depression and anxiety are common comorbid diseases of constipation. Fecal microbiota transplantation (FMT) significantly relieves gastrointestinal-related symptoms, but its impact on psychiatric symptoms remains uncharted.

METHODS

We collected fecal and serum samples before and after FMT from 4 functional constipation patients with psychiatric symptoms and corresponding donor stool samples. We categorized the samples into two groups: before FMT (Fb) and after FMT (Fa). Parameters associated with constipation, depression, and anxiety symptoms were evaluated. Metagenomics and targeted neurotransmitter metabolomics were performed to investigate the gut microbiota and metabolites. 5-hydroxytryptamine (5-HT) biosynthesis was detected in patients' fecal supernatants exposed to the QGP-1 cell model in vitro.

RESULTS

Our study demonstrated that patient's constipation, depression, and anxiety were improved after FMT intervention. At the genus level, relative abundance of g_Bacteroides and g_Klebsiella decreased in the Fa group, while g_Lactobacillus, and g_Selenomonas content increased in the same group. These observations suggest a potential involvement of these genera in the pathogenesis of constipation with psychiatric symptoms. Metabolomics analysis showed that FMT intervention decreased serum 5-HT levels. Additionally, we found that species, including s_Klebsiella sp. 1_1_55, s_Odoribacter splanchnicus, and s_Ruminococcus gnavus CAG:126, were positively correlated with 5-HT levels. In contrast, s_Acetobacterium bakii, s_Enterococcus hermanniensis, s_Prevotella falsenii, s_Propionispira arboris, s_Schwartzia succinivorans, s_Selenomonas artemidis, and s_Selenomonas sp. FC4001 were negatively correlated with 5-HT levels. Furthermore, we observed that patients' fecal supernatants increased 5-HT biosynthesis in QGP-1 cells.

CONCLUSION

FMT can relieve patients' constipation, depression, and anxiety symptoms by reshaping gut microbiota. The 5-HT level was associated with an altered abundance of specific bacteria or metabolites. This study provides specific evidence for FMT intervention in constipation patients with psychiatric symptoms.

Role of the gut-brain axis via the subdiaphragmatic vagus nerve in stress resilience of 3,4-methylenedioxymethamphetamine in mice exposed to chronic restrain stress

3,4-Methylenedioxymethamphetamine (MDMA) is the most widely used illicit substance worldwide. Nevertheless, recent observational studies demonstrated that lifetime MDMA use among U.S. adults was associated with a lower risk of depression and suicide thoughts. We recently reported that the gut-brain axis may contribute to MDMA-induced stress resilience in mice. To further explore this, we investigated the effects of subdiaphragmatic vagotomy (SDV) in modulating the stress resilience effects of MDMA in mice subjected to chronic restrain stress (CRS). Pretreatment with MDMA (10 mg/kg/day for 14 days) blocked anhedonia-like behavior and reduced expression of synaptic proteins and brain-derived neurotrophic factor in the prefrontal cortex (PFC) of CRS-exposed mice. Interestingly, SDV blocked the beneficial effects of MDMA on these alterations in CRS-exposed mice. Analysis of gut microbiome revealed alterations in four measures of α-diversity between the sham + MDMA + CRS group and the SDV + MDMA + CRS group. Moreover, specific microbes differed between the vehicle + CRS group and the MDMA + CRS group, and further differences in microbial composition were observed among all four groups. Untargeted metabolomics analysis showed that SDV prevented the increase in plasma levels of three compounds [lactic acid, 1-(2-hydroxyethyl)-2,2,6-tetramethyl-4-piperidinol, 8-acetyl-7-hydroxyvumaline] observed in the sham + MDMA + CRS group. Interestingly, positive correlations were found between the plasma levels of two of these compounds and the abundance of several microbes across all groups. In conclusion, our data suggest that the gut-brain axis via the subdiaphragmatic vagus nerve might contribute to the stress resilience of MDMA.

The critical role of gut-brain axis microbiome in mental disorders

The Gut-brain axis is a bidirectional neural and humoral signaling that plays an important role in mental disorders and intestinal health and connects them as well. Over the past decades, the gut microbiota has been explored as an important part of the gastrointestinal tract that plays a crucial role in the regulation of most functions of various human organs. The evidence shows several mediators such as short-chain fatty acids, peptides, and neurotransmitters that are produced by the gut may affect the brain's function directly or indirectly. Thus, dysregulation in this microbiome community can give rise to several diseases such as Parkinson's disease, depression, irritable bowel syndrome, and Alzheimer's disease. So, the interactions between the gut and the brain are significantly considered, and also it provides a prominent subject to investigate the causes of some diseases. In this article, we reviewed and focused on the role of the largest and most repetitive bacterial community and their relevance with some diseases that they have mentioned previously.

Microbiota-Accessible Boron-Containing Compounds in Complex Regional Pain Syndrome

The microbiota-gut-brain axis has garnered increasing attention in recent years for its role in various health conditions, including neuroinflammatory disorders like complex regional pain syndrome (CRPS). CRPS is a debilitating condition characterized by chronic neuropathic pain, and its etiology and pathophysiology remain elusive. Emerging research suggests that alterations in the gut microbiota composition and function could play a significant role in CRPS development and progression. Our paper explores the implications of microbiota in CRPS and the potential therapeutic role of boron (B). Studies have demonstrated that individuals with CRPS often exhibit dysbiosis, with imbalances in beneficial and pathogenic gut bacteria. Dysbiosis can lead to increased gut permeability and systemic inflammation, contributing to the chronic pain experienced in CRPS. B, an essential trace element, has shown promise in modulating the gut microbiome positively and exerting anti-inflammatory effects. Recent preclinical and clinical studies suggest that B supplementation may alleviate neuropathic pain and improve CRPS symptoms by restoring microbiota balance and reducing inflammation. Our review highlights the complex interplay between microbiota, inflammation, and neuropathic pain in CRPS and underscores the potential of B as a novel therapeutic approach to target the microbiota-gut-brain axis, offering hope for improved management of this challenging condition.

Reproducible microbiome composition signatures of anxiety and depressive symptoms

The gut microbiome is a significant contributor to mental health, with growing evidence linking its composition to anxiety and depressive disorders. Gut microbiome composition is associated with signs of anxiety and depression both in clinically diagnosed mood disorders and subclinically in the general population and may be influenced by dietary fibre intake and the presence of chronic pain. We provide an update of current evidence on the role of gut microbiome composition in depressive and anxiety disorders or symptoms by reviewing available studies. Analysing data from three independent cohorts (osteoarthritis 1 (OA1); n = 46, osteoarthritis 2 (OA2); n = 58, and healthy controls (CON); n = 67), we identified microbial composition signatures of anxiety and depressive symptoms at genus level and cross-validated our findings performing meta-analyses of our results with results from previously published studies. The genera Bifidobacterium (fixed-effect beta (95% CI) = -0.22 (-0.34, -0.10), p = 3.90e-04) and Lachnospiraceae NK4A136 group (fixed-effect beta (95% CI) = -0.09 (-0.13, -0.05), p = 2.53e-06) were found to be the best predictors of anxiety and depressive symptoms, respectively, across our three cohorts and published literature taking into account demographic and lifestyle covariates, such as fibre intake. The association with anxiety was robust in accounting for heterogeneity between cohorts and supports previous observations of the potential prophylactic effect of Bifidobacterium against anxiety symptoms.

Disordered gut microbiota and changes in short-chain fatty acids and inflammatory processes in stress-vulnerable mice

Long-term exposure to chronic stress increases the incidence of depression. However, chronic stress is an associated risk factor in only a subset of individuals. Inflammation has been identified as a putative mechanism promoting stress vulnerability. Because of the gut microbiota's potential role as a source of inflammatory substances, short-chain fatty acids (SCFAs) may exert their influence on inflammation, emotional states, and cognition via the gut-brain axis. In this study, Classic behavioral tests were used to categorize C57BL/6 J mice into a CUMS-vulnerable and a CUMS-resilient group after they were exposed to chronic unpredictable mild stress (CUMS). We compared the 16S ribosomal RNA (rRNA) gene sequences retrieved from fecal samples between control, CUMS-vulnerable, and CUMS-resilient mice. SCFAs in fecal samples were detected by liquid chromatography and gas chromatography-mass spectrometry. Hippocampal cytokine production and TLR4/MYD88/NF-κB inflammatory pathway activation were evaluated using enzyme-linked immunosorbent assays (ELISAs) and western blotting. Then, we supplemented SCFAs in CUMS mice. we observed depression-like behavior and the expression of TLR4/MYD88/NF-κB inflammatory pathway in hippocampus of SCFAs supplementation mice. Susceptible mice to CUMS showed more severe symptoms of depression and anxiety, α diversity was significantly different, as well as higher expression of interleukin (IL)-1β and TLR4/MYD88/NF-κB inflammatory pathway components in the hippocampus. SCFA levels in the feces were significantly higher in CUMS-resilient mice than in control mice. Depressive behavior was reversed in CUMS-SCFAs group, and the protein level of TLR4/MYD88/NF-κB in hippocampus was decreased. Overall, these results provide new light on the possible involvement of the microbiome in the gut-brain axis development in depressive disorder and provide a theoretical basis for identifying novel therapeutic targets.

Global Trends in Research of Pain-Gut-Microbiota Relationship and How Nutrition Can Modulate This Link

INTRODUCTION

The link between gut microbiota and chronic painful conditions has recently gained attention. Nutrition, as a common intervention in daily life and medical practice, is closely related to microbiota and pain. However, no published bibliometric reports have analyzed the scientific literature concerning the link.

METHODS AND RESULTS

We used bibliometrics to identify the characteristics of the global scientific output over the past 20 years. We also aimed to capture and describe how nutrition can modulate the abovementioned link. Relevant papers were searched in the Web of Science database. All necessary publication and citation data were acquired and exported to Bibliometrix for further analyses. The keywords mentioned were illustrated using visualization maps. In total, 1551 papers shed light on the relationship from 2003 to 2022. However, only 122 papers discussed how nutritional interventions can modulate this link. The citations and attention were concentrated on the gut microbiota, pain, and probiotics in terms of the pain-gut relationship. Nutritional status has gained attention in motor themes of a thematic map.

CONCLUSIONS

This bibliometric analysis was applied to identify the scientific literature linking gut microbiota, chronic painful conditions, and nutrition, revealing the popular research topics and authors, scientific institutions, countries, and journals in this field. This study enriches the evidence moving boundaries of microbiota medicine as a clinical medicine.

Fecal Microbiota Transplantation Alleviated Paclitaxel-Induced Peripheral Neuropathy by Interfering with Astrocytes and TLR4/p38MAPK Pathway in Rats

Purpose

Paclitaxel-induced peripheral neuropathy (PIPN) constitutes a refractory and progressive adverse consequence of paclitaxel treatment, causing pain and sensory anomalies in cancer survivors. Although the gut-brain axis is involved in multiple disorders including cancer, its impact on peripheral pain conditions remains elusive. Thus, we assessed the importance of gut microbiota and related mechanisms in PIPN.

Methods

By implementing fecal microbiota transplantation (FMT) in a rat PIPN model (ie, rats treated with paclitaxel; hereafter as PIPN rats), we explored the effect of gut microbiota on PIPN rats using multiple methods, including different behavioral tests, 16S ribosomal DNA (rDNA) sequencing, and biochemical techniques.

Results

Sequencing of 16S rDNA revealed that the abundance of genera Bacteroides and UCG-005 increased, while that of genera Turicibacter, Clostridium sensu stricto 1 and Corynebacterium decreased in the PIPN rats. However, when treated with FMT using fecal from normal rats, the mechanical allodynia and thermal hyperalgesia in PIPN rats were significantly alleviated. In addition, FMT treatment reduced the expression of toll-like receptor 4 (TLR4), phospho-p38 mitogen-activated protein kinase (p-p38MAPK), and the astrocytic marker glial fibrillary acidic protein in the colon and spinal dorsal horn. TAK242 (a TLR4 inhibitor) significantly alleviated the behavioral hypersensitivity of PIPN rats and inhibited the TLR4/p38MAPK pathway in astrocytes in these rats.

Conclusion

The gut microbiota played a critical role in PIPN. Future therapies treating PIPN should consider microbe-based treatment as an option.

Anxiety-like Behavior in Female Sprague Dawley Rats Associated with Cecal Clostridiales

The relationship between the microbiota profile and exposure to stress is not well understood. Therefore, we used a rat model of unpredictable chronic mild stress (UCMS) to investigate this relationship. Depressive-like behaviors were measured in Female Sprague Dawley rats using the sucrose preference test and the Porsolt swim test. Anxiety-like behaviors were measured with the light-dark box test. Fecal corticosterone, cecal microbiota (composition and organic acids), plasma gut permeability (lipopolysaccharide-binding protein, LBP) and plasma inflammation (12 cytokines) markers were measured. Atypical behaviors were observed in female rats following UCMS, but no depressive-like behaviors were observed. Circulating concentrations of cytokines granulocyte-macrophage colony-stimulating factor and cytokine-induced neutrophil chemoattractant 1 were higher in UCMS-exposed female rats; plasma LBP and cecal organic acid levels remained unchanged. Our results reflect a resilient and adaptive phenotype for female SD rats. The relative abundance of taxa from the Clostridiales order and Desulfovibrionaceae family did, however, correlate both positively and negatively with anxiety-like behaviors and plasma cytokine concentrations, regardless of UCMS exposure, supporting the brain-to-gut influence of mild anxiety with a microbiota profile that may involve inflammatory pathways.

Whey protein isolate attenuates depression-like behavior developed in a mouse model of breast tumor

Increasing evidence indicates that tryptophan (Trp) metabolism disturbance controls hippocampal 5-hydroxytryptamine (5-HT) and thereby affecting depression-like behavior, in which the gut microbiota (GM) might be involved. This study investigated the effect of Trp-rich whey protein isolate (WPI) on depressive-like behavior in 4T1 tumor-bearing mice. Female BALB/c mice were subcutaneously inoculated with murine 4T1 mammary carcinoma cells and received 2 g/kg of WPI by gavage daily for 21 days. The results showed that WPI exerted no significant effects on tumor weight and volume, but abrogated tumor-induced depression-like behavior, as evidenced by remarkably increased time and distance in the center of the open-field test, decreased immobility time in the tail suspension test, increased time and number of entries to the open arms in the elevated plus maze and sucrose preference. Moreover, WPI promoted the hippocampal Trp, 5-hydroxytryptophan (5-HTP), 5-HT, 5-hydroxyindoleacetic acid (5-HIAA) levels and inhibited kynurenine (Kyn) through up-regulating serotonin transporter (SERT) and down-regulating indoleamine 2, 3-dioxygenase (IDO). WPI showed an enriched microbial diversity indicated by increased Shannon index and decreased Simpson index, reduced the abundances of Proteobacteria, Rikenellaceae_RC9_gut_group, Alloprevotella and Prevotellaceae_UCG-001, and increased the abundance of unclassified_k__norank_d__Bacteria in tumor-bearing mice (P < 0.05). At level 3, WPI enhanced the function of microbial gene related to Trp metabolism in the KEGG pathways (P < 0.05). Our results suggest that WPI exhibits a potent antidepressant-like effect via the regulation of hippocampal Trp metabolism and alteration of GM composition and function, and it may be an effective prevention for cancer-related depression.

Molecular Mechanisms and Pathophysiological Pathways of High-Fat Diets and Caloric Restriction Dietary Patterns on Pain

Pain perception provides evolutionary advantages by enhancing the probability of survival, but chronic pain continues to be a significant global health concern in modern society. Various factors are associated with pain alteration. Accumulating evidence has revealed that obesity correlates with enhanced pain perception, especially in chronic pain individuals. Existing dietary patterns related to obesity are primarily high-fat diets (HFD) and calorie restriction (CR) diets, which induce or alleviate obesity separately. HFD has been shown to enhance nociception while CR tends to alleviate pain when measuring pain outcomes. Herein, this review mainly summarizes the current knowledge of the effects of HFD and CR on pain responses and underlying molecular mechanisms of the immunological factors, metabolic regulation, inflammatory processes, Schwann cell (SC) autophagy, gut microbiome, and other pathophysiological signaling pathways involved. This review would help to provide insights on potential nonpharmacological strategies of dietary patterns in relieving pain.

Gut Microbiota Taxon-Dependent Transformation of Microglial M1/M2 Phenotypes Underlying Mechanisms of Spatial Learning and Memory Impairment after Chronic Methamphetamine Exposure

Methamphetamine (METH) exposure may lead to cognitive impairment. Currently, evidence suggests that METH exposure alters the configuration of the gut microbiota. However, the role and mechanism of the gut microbiota in cognitive impairment after METH exposure are still largely unknown. Here, we investigated the impact of the gut microbiota on the phenotype status of microglia (microglial phenotypes M1 and microglial M2) and their secreting factors, the subsequent hippocampal neural processes, and the resulting influence on spatial learning and memory of chronically METH-exposed mice. We determined that gut microbiota perturbation triggered the transformation of microglial M2 to M1 and a subsequent change of pro-brain-derived neurotrophic factor (proBDNF)-p75NTR-mature BDNF (mBDNF)-TrkB signaling, which caused reduction of hippocampal neurogenesis and synaptic plasticity-related proteins (SYN, PSD95, and MAP2) and, consequently, deteriorated spatial learning and memory. More specifically, we found that Clostridia, Bacteroides, Lactobacillus, and Muribaculaceae might dramatically affect the homeostasis of microglial M1/M2 phenotypes and eventually contribute to spatial learning and memory decline after chronic METH exposure. Finally, we found that fecal microbial transplantation could protect against spatial learning and memory decline by restoring the microglial M1/M2 phenotype status and the subsequent proBDNF-p75NTR/mBDNF-TrkB signaling in the hippocampi of chronically METH-exposed mice. IMPORTANCE Our study indicated that the gut microbiota contributes to spatial learning and memory dysfunction after chronic METH exposure, in which microglial phenotype status plays an intermediary role. The elucidated "specific microbiota taxa-microglial M1/M2 phenotypes-spatial learning and memory impairment" pathway would provide a novel mechanism and elucidate potential gut microbiota taxon targets for the no-drug treatment of cognitive deterioration after chronic METH exposure.

Modulation of Glial Cell Functions by the Gut-Brain Axis: A Role in Neurodegenerative Disorders and Pain Transmission

Studies on host microbiota and their interactions with the central nervous system (CNS) have grown considerably in the last decade. Indeed, it has been widely demonstrated that dysregulations of the bidirectional gut-brain crosstalk are involved in the development of several pathological conditions, including chronic pain. In addition, the activation of central and peripheral glial cells is also implicated in the pathogenesis and progression of pain and other neurodegenerative disorders. Recent preclinical findings suggest that the gut microbiota plays a pivotal role in regulating glial maturation, morphology and function, possibly through the action of different microbial metabolites, including the most studied short-chain fatty acids (SCFAs). Moreover, altered microbiota composition has been reported in CNS disorders characterized by glial cell activation. In this review, we discuss recent studies showing the role of the gut microbiota and the effects of its depletion in modulating the morphology and function of glial cells (microglia and astrocytes), and we hypothesize a possible role for glia-microbiota interactions in the development and maintenance of chronic pain.

Hydrogen Sulfide Interacting with Cannabinoid 2 Receptors during Sciatic Nerve Injury-Induced Neuropathic Pain

Hydrogen sulfide (H₂S) donors make opioids more effective in inhibiting nociception during inflammatory and neuropathic pain. We examined whether the analgesic, anxiolytic and/or antidepressant actions of the cannabinoid 2 receptor (CB2R) agonist, JWH-133, might be improved by pretreatment with H₂S donors, DADS and GYY4137 in mice with sciatic nerve injury-provoked neuropathy (CCI). The reversion of the antinociceptive effects of these treatments with the CB2R antagonist, AM630, and the regulatory actions of H₂S in the phosphorylation of NF-κB inhibitor alpha (IKBα) and in the brain-derived neurotrophic factor (BDNF), CB2R, Nrf2 and heme oxygenase 1 (HO-1) levels in prefrontal cortex (PFC), ventral hippocampus (vHIP) and periaqueductal gray matter (PAG), were examined. Data showed that the analgesic effects of JWH-133, systemically and locally administered, were improved by the DADS or GYY4137 pretreatment. The co-treatment of GYY4137 with JWH-133 also stopped anxiodepressive-like activities that concur with neuropathy. Our data likewise showed that both H₂S donors normalized the inflammatory (p-IKBα), neurotrophic (BDNF) variations caused by CCI, increased the expression of CB2R and activated the Nrf2/HO-1 antioxidant pathway in PFC, v-HIP and/or PAG of animals with neuropathic pain. In addition, the blockade of the analgesia produced by high doses of DADS and GYY4137 with AM630 indicated the contribution of the endocannabinoid system in the effects of H₂S during neuropathic pain, thus supporting the positive interaction between H₂S and CB2R. Therefore, this study demonstrates the potential use of CB2R agonists combined with H₂S donors as a possible treatment for peripheral nerve injury-caused neuropathic pain and the associated emotional disturbances.

Gut microbiota from sigma-1 receptor knockout mice induces depression-like behaviors and modulates the cAMP/CREB/BDNF signaling pathway

Introduction

Depression is a common mental disorder that affects approximately 350 million people worldwide. Much remains unknown about the molecular mechanisms underlying this complex disorder. Sigma-1 receptor (Sig-1R) is expressed at high levels in the central nervous system. Increasing evidence has demonstrated a close association between the Sig-1R and depression. Recently, research has suggested that the gut microbiota may play a crucial role in the development of depression.

Methods

Male Sig-1R knockout (Sig-1R KO) and wild-type (WT) mice were used for this study. All transgenic mice were of a pure C57BL/6J background. Mice received a daily gavage of vancomycin (100 mg/kg), neomycin sulfate (200 mg/kg), metronidazole (200 mg/kg), and ampicillin (200 mg/kg) for one week to deplete gut microbiota. Fecal microbiota transplantation (FMT) was conducted to assess the effects of gut microbiota. Depression-like behaviors was evaluated by tail suspension test (TST), forced swimming test (FST) and sucrose preference test (SPT). Gut microbiota was analyzed by 16s rRNA and hippocampal transcriptome changes were assessed by RNA-seq.

Results

We found that Sig-1R knockout induced depression-like behaviors in mice, including a significant reduction in immobility time and an increase in latency to immobility in the FST and TST, which was reversed upon clearance of gut microbiota with antibiotic treatment. Sig-1R knockout significantly altered the composition of the gut microbiota. At the genus level, the abundance of Alistipes, Alloprevotella, and Lleibacterium decreased significantly. Gut microbiota dysfunction and depression-like phenotypes in Sig-1R knockout mice could be reproduced through FMT experiments. Additionally, hippocampal RNA sequencing identified multiple KEGG pathways that are associated with depression. We also discovered that the cAMP/CREB/BDNF signaling pathway is inhibited in the Sig-1R KO group along with lower expression of neurotrophic factors including CTNF, TGF-α and NGF. Fecal bacteria transplantation from Sig-1R KO mice also inhibited cAMP/CREB/BDNF signaling pathway.

Discussion

In our study, we found that the gut-brain axis may be a potential mechanism through which Sig-1R regulates depression-like behaviors. Our study provides new insights into the mechanisms by which Sig-1R regulates depression and further supports the concept of the gut-brain axis.

Abnormal compositions of gut microbiota and metabolites are associated with susceptibility versus resilience in rats to inescapable electric stress

BACKGROUND

Increasing evidence suggests the role of gut microbiota in resilience versus vulnerability after stress. However, the role of gut microbiota and microbiome-derived metabolites in resilience versus susceptibility in rodents exposed to stress remains unclear.

METHODS

Adult male rats were exposed to inescapable electric stress under the learned helplessness (LH) paradigm. The composition of gut microbiota and metabolites in the brain and blood from control (no stress) rats, LH resilient rats, and LH susceptible rats were examined.

RESULTS

At the genus level, the relative abundances of Asaccharobacter, Eisenbergiella, and Klebsiella in LH susceptible rats were significantly higher than that of LH resilient rats. At the species level, the relative abundances of several microbiome were significantly altered between LH susceptible rats and LH resilient rats. Furthermore, there were several metabolites in the brain and blood altered between LH susceptible rats and LH resilient rats. A network analysis showed correlations between the abundance of several microbiome and metabolites in the brain (or blood).

LIMITATIONS

Detailed roles of microbiome and metabolites are unclear.

CONCLUSIONS

These findings suggest that abnormal compositions of the gut microbiota and metabolites might contribute to susceptibility versus resilience in rats subjected to inescapable electric foot shock.

Influence of mental health medication on microbiota in the elderly population in the Valencian region

Spain has an aging population; 19.93% of the Spanish population is over 65. Aging is accompanied by several health issues, including mental health disorders and changes in the gut microbiota. The gut-brain axis is a bidirectional network linking the central nervous system with gastrointestinal tract functions, and therefore, the gut microbiota can influence an individual’s mental health. Furthermore, aging-related physiological changes affect the gut microbiota, with differences in taxa and their associated metabolic functions between younger and older people. Here, we took a case–control approach to study the interplay between gut microbiota and mental health of elderly people. Fecal and saliva samples from 101 healthy volunteers over 65 were collected, of which 28 (EE|MH group) reported using antidepressants or medication for anxiety or insomnia at the time of sampling. The rest of the volunteers (EE|NOMH group) were the control group. 16S rRNA gene sequencing and metagenomic sequencing were applied to determine the differences between intestinal and oral microbiota. Significant differences in genera were found, specifically eight in the gut microbiota, and five in the oral microbiota. Functional analysis of fecal samples showed differences in five orthologous genes related to tryptophan metabolism, the precursor of serotonin and melatonin, and in six categories related to serine metabolism, a precursor of tryptophan. Moreover, we found 29 metabolic pathways with significant inter-group differences, including pathways regulating longevity, the dopaminergic synapse, the serotoninergic synapse, and two amino acids.

Brexpiprazole prevents colitis-induced depressive-like behavior through myelination in the prefrontal cortex

Patients with inflammatory bowel disease (IBD) have higher rates of psychiatric pathology including depression. The dextran sulfate sodium (DSS)-treated mice exhibit IBD- and depressive-like phenotypes. A disturbed intestinal environment causes a decrease in serotonin and abnormal myelination in the brain, along with depressive-like behavior in rodents. However, the involvement of these factors in DSS-induced depressive-like behavior in mice remains unclear. In this study, we examined whether myelin proteins in the prefrontal cortex (PFC) and hippocampi were altered in DSS-treated mice, along with the changes in the serotonergic system in the PFC by western blotting and HPLC. The effects of brexpiprazole (Brx), a serotonin modulator, on DSS-induced depressive-like behavior using the tail-suspension test were evaluated. Subsequently, we investigated Brx's effects on the levels of myelin, nodal proteins, and neurotrophic molecules in the PFC with western blotting, and examined the altered node of Ranvier formation by immunohistochemistry. DSS-treated mice showed a reduction in myelin and nodal proteins, dysfunction of the serotonergic system, and impaired formation of the nodes of Ranvier in the PFC. Brx administration prevented the DSS-induced depressive-like behavior and demyelination in the PFC. However, the Brx-mediated effects were inhibited by the selective 5-HT_1A antagonist, WAY100635, or the selective TrkB antagonist, ANA-12. Brx decreased the phosphorylation of ERK, CREB, and TrkB along with the expression of BDNF in the PFC of DSS-treated mice. Moreover, the effects of Brx were blocked by WAY100635. These findings indicated that myelination regulated by the activation of the ERK1/2-CREB-BDNF-TrkB pathway in the PFC may be involved in mediating the antidepressant effects of Brx.

Anti-depressive-like and cognitive impairment alleviation effects of Gastrodia elata Blume water extract is related to gut microbiome remodeling in ApoE-/- mice exposed to unpredictable chronic mild stress

ETHNOPHARMACOLOGY RELEVANCE

Gastrodia elata Blume (GE) is a traditional Chinese dietary therapy used to treat neurological disorders. Gastrodia elata Blume water extract (WGE) has been shown to ameliorate inflammation and improve social frustration in mice in a chronic social defeat model. However, studies on the anti-depressive-like effects and cognitive impairment alleviation related to the impact of WGE on the gut microbiome of ApoE-/- mice remain elusive.

AIM OF THE STUDY

The present study aimed to investigate the anti-depressive-like effect and cognitive impairment alleviation and mechanisms of WGE in ApoE-/- mice subjected to unpredictable chronic mild stress (UCMS), as well as its impact on the gut microbiome of the mice.

MATERIALS AND METHODS

Sixty ApoE-/- mice (6 months old) were randomly grouped into six groups: control, UCMS, WGE groups [5, 10, 20 mL WGE/kg body weight (bw) + UCMS], and a positive group (fluoxetine 20 mg/kg bw + UCMS). After four weeks of the UCMS paradigm, the sucrose preference, novel object recognition, and open field tests were conducted. The neurotransmitters serotonin (5-HT), dopamine (DA) and their metabolites were measured in the prefrontal cortex. Serum was collected to measure corticosterone and amyloid-42 (Aβ-42) levels. Feces were collected, and the gut microbiome was analyzed.

RESULTS

WGE restored sucrose preference, exploratory behavior, recognition ability, and decreased the levels of serum corticosterone and Aβ-42 in ApoE-/- mice to alleviate depressive-like behavior and cognitive impairment. Furthermore, WGE regulated the monoamine neurotransmitter via reduced the 5-HT and DA turnover rates in the prefrontal cortex. Moreover, WGE elevated the levels of potentially beneficial bacteria such as Bifidobacterium, Akkermansia, Alloprevotella, Defluviitaleaceae_UCG-011, and Bifidobacterium pseudolongum as well as balanced fecal short-chain fatty acids (SCFAs).

CONCLUSION

WGE demonstrates anti-depressive-like effects, cognitive impairment alleviation, and gut microbiome and metabolite regulation in ApoE-/- mice. Our results support the possibility of developing a functional and complementary medicine to prevent or alleviate depression and cognitive decline using WGE in CVDs patients.

Repeated use of 3,4-methylenedioxymethamphetamine is associated with the resilience in mice after chronic social defeat stress: A role of gut-microbiota-brain axis

3,4-Methylenedioxymethamphetamine (MDMA), the most widely used illicit compound worldwide, is the most attractive therapeutic drug for post-traumatic stress disorder (PTSD). Recent observational studies of US adults demonstrated that lifetime MDMA use was associated with lower risk of depression. Here, we examined whether repeated administration of MDMA can affect resilience versus susceptibility in mice exposed to chronic social defeat stress (CSDS). CSDS produced splenomegaly, anhedonia-like phenotype, and higher plasma levels of interleukin-6 (IL-6) in the saline-treated mice. In contrast, CSDS did not cause these changes in the MDMA-treated mice. Analysis of gut microbiome found several microbes altered between saline + CSDS group and MDMA + CSDS group. Untargeted metabolomics analysis showed that plasma levels of N-epsilon-methyl-L-lysine in the saline + CSDS group were significantly higher than those in the control and MDMA + CSDS groups. Interestingly, there were positive correlations between plasma IL-6 levels and the abundance of several microbes (or plasma N-epsilon-methyl-L-lysine) in the three groups. Furthermore, there were also positive correlations between the abundance of several microbes and N-epsilon-methyl-L-lysine in the three groups. In conclusion, these data suggest that repeated administration of MDMA might contribute to stress resilience in mice subjected to CSDS through gut-microbiota-brain axis.

Anxiety and Metabolic Disorders: The Role of Botanicals

Anxiety and anxiety-related disorders are becoming more evident every day, affecting an increasing number of people around the world. Metabolic disorders are often associated with anxiety. Furthermore, anxiety branches into metabolic disorders by playing multiple roles as a cofactor, symptom, and comorbidity. Taken together, these considerations open the possibility of integrating the therapy of metabolic disorders with specific drugs for anxiety control. However, anxiolytic compounds often cause disabling effects in patients. The main goal could be to combine therapeutic protocols with compounds capable of reducing side effects while performing multiple beneficial effects. In this article we propose a group of bioactive ingredients called botanicals as a healthy supplement for the treatment of metabolic disorders related to anxiety.

A role of gut-microbiota-brain axis via subdiaphragmatic vagus nerve in depression-like phenotypes in Chrna7 knock-out mice

The α7 subtype of the nicotinic acetylcholine receptor (α7 nAChR: coded by Chrna7) is known to regulate the cholinergic ascending anti-inflammatory pathway. We previously reported that Chrna7 knock-out (KO) mice show depression-like behaviors through abnormal composition of gut microbiota and systemic inflammation. Given the role of subdiaphragmatic vagus nerve in gut-microbiota-brain axis, we investigated whether subdiaphragmatic vagotomy (SDV) could affect depression-like behaviors, abnormal composition of gut microbiota, and microbes-derived metabolites in Chrna7 KO mice. SDV blocked depression-like behaviors and reduced expression of synaptic proteins in the medial prefrontal cortex (mPFC) of Chrna7 KO mice. LEfSe (linear discriminant analysis effect size) analysis revealed that the species Lactobacillus sp. BL302, the species Lactobacillus hominis, and the species Lactobacillus reuteri, were identified as potential microbial markers in the KO + SDV group. There were several genus and species altered among the three groups [wild-type (WT) + sham group, KO + sham group, KO + SDV group]. Furthermore, there were several plasma metabolites altered among the three groups. Moreover, there were correlations between relative abundance of several microbiome and behavioral data (or synaptic proteins). Network analysis showed correlations between relative abundance of several microbiome and plasma metabolites (or behavioral data). These data suggest that Chrna7 KO mice produce depression-like behaviors and reduced expression of synaptic proteins in the mPFC through gut-microbiota-brain axis via subdiaphragmatic vagus nerve.

Endometriosis and dysbiosis: State of art

Endometriosis is a complex and heterogeneous disease affecting approximately 10% of reproductive age women. The hypothesis that alterations in the microbiota are involved in the pathogenesis of endometriosis has been postulated. Possible explanations for the implications of dysbiosis in endometriosis include the Bacterial Contamination hypothesis and immune activation, cytokine-impaired gut function, altered estrogen metabolism and signaling. Thus, dysbiosis, disrupt normal immune function, leading to the elevation of proinflammatory cytokines, compromised immunosurveillance and altered immune cell profiles, all of which may contribute to the pathogenesis of endometriosis. The aim of this review is to summarize the available literature data about the relationship between microbiota and endometriosis.

Impact of gut-peripheral nervous system axis on the development of diabetic neuropathy

Diabetes is a chronic metabolic disease caused by a reduction in the production and/or action of insulin, with consequent development of hyperglycemia. Diabetic patients, especially those who develop neuropathy, presented dysbiosis, with an increase in the proportion of pathogenic bacteria and a decrease in the butyrate-producing bacteria. Due to this dysbiosis, diabetic patients presented a weakness of the intestinal permeability barrier and high bacterial product translocation to the bloodstream, in parallel to a high circulating levels of pro-inflammatory cytokines such as TNF-α. In this context, we propose here that dysbiosis-induced increased systemic levels of bacterial products, like lipopolysaccharide (LPS), leads to an increase in the production of pro-inflammatory cytokines, including TNF-α, by Schwann cells and spinal cord of diabetics, being crucial for the development of neuropathy.

Desulfovibrio confers resilience to the comorbidity of pain and anxiety in a mouse model of chronic inflammatory pain

BACKGROUND

Patients with chronic pain frequently suffer from anxiety symptoms. It has been well established that gut microbiota is associated with the pathogenesis of pain and anxiety. However, it is unknown whether the gut microbiota, particularly the specific bacteria, play a role in the comorbidity of chronic pain and anxiety.

METHODS

Chronic inflammatory pain was induced in mice by a single injection of complete Freund's adjuvant (CFA). Mice were then separated into anxiety-susceptible and anxiety-resilient phenotypes by hierarchical clustering analysis of behaviors. Fecal samples were collected to perform 16S rRNA gene sequencing. Chronic diazepam intervention served as a therapeutic strategy and its effect on the composition of gut microbiota was also determined.

RESULTS

α-Diversity and β-diversity both showed significant differences among the groups. A total of 12 gut bacteria were both altered after CFA injection and reversed by chronic diazepam treatment. More importantly, the pain hypersensitivity and anxiety-like behaviors were relieved by chronic diazepam treatment. Interestingly, we also found that Desulfovibrio was increased in anxiety-resilient group compared to control and anxiety-susceptible groups.

CONCLUSION

Abnormal composition of gut microbiota plays an essential role in chronic pain as well as in anxiety. Besides, the increased level of Desulfovibrio in anxiety-resilient mice indicated its therapeutic effects on the comorbidity of pain and anxiety. Collectively, targeting gut microbiota, especially increasing the Desulfovibrio level, might be effective in the alleviation of chronic pain-anxiety comorbidity.

Epigenetics in depression and gut-brain axis: A molecular crosstalk

Gut-brain axis is a dynamic, complex, and bidirectional communication network between the gut and brain. Changes in the microbiota-gut-brain axis are responsible for developing various metabolic, neurodegenerative, and neuropsychiatric disorders. According to clinical and preclinical findings, the gut microbiota is a significant regulator of the gut-brain axis. In addition to interacting with intestinal cells and the enteric nervous system, it has been discovered that microbes in the gut can modify the central nervous system through metabolic and neuroendocrine pathways. The metabolites of the gut microbiome can modulate a number of diseases by inducing epigenetic alteration through DNA methylation, histone modification, and non-coding RNA-associated gene silencing. Short-chain fatty acids, especially butyrate, are well-known histone deacetylases inhibitors. Similarly, other microbial metabolites such as folate, choline, and trimethylamine-N-oxide also regulate epigenetics mechanisms. Furthermore, various studies have revealed the potential role of microbiome dysbiosis and epigenetics in the pathophysiology of depression. Hence, in this review, we have highlighted the role of gut dysbiosis in epigenetic regulation, causal interaction between host epigenetic modification and the gut microbiome in depression and suggest microbiome and epigenome as a possible target for diagnosis, prevention, and treatment of depression.

Gut microbiome-wide association study of depressive symptoms

Depression is one of the most poorly understood diseases due to its elusive pathogenesis. There is an urgency to identify molecular and biological mechanisms underlying depression and the gut microbiome is a novel area of interest. Here we investigate the relation of fecal microbiome diversity and composition with depressive symptoms in 1,054 participants from the Rotterdam Study cohort and validate these findings in the Amsterdam HELIUS cohort in 1,539 subjects. We identify association of thirteen microbial taxa, including genera Eggerthella, Subdoligranulum, Coprococcus, Sellimonas, Lachnoclostridium, Hungatella, Ruminococcaceae (UCG002, UCG003 and UCG005), LachnospiraceaeUCG001, Eubacterium ventriosum and Ruminococcusgauvreauiigroup, and family Ruminococcaceae with depressive symptoms. These bacteria are known to be involved in the synthesis of glutamate, butyrate, serotonin and gamma amino butyric acid (GABA), which are key neurotransmitters for depression. Our study suggests that the gut microbiome composition may play a key role in depression.

Gut microbiota alterations may increase the risk of prescription opioid use, but not vice versa: A two-sample bi-directional Mendelian randomization study

INTRODUCTION

Gut microbiota alterations are strongly associated with prescription opioid use (POU) and multisite chronic pain (MCP). However, whether or not these associations are causal remains unknown. Therefore, we aim to explore the causal relationships between them comprehensively.

METHODS

A two-sample bi-directional Mendelian randomization was conducted to assess the potential associations between gut microbiota and POU/MCP using summary level Genome-wide association studies (GWASs) that were based on predominantly European ancestry.

RESULTS

Potential causal effects were identified between seven host genetic-driven traits of gut microbiota on POU, including Adlercreutzia, Allisonella, Dialister, Anaerofilum, Anaerostipes, ChristensenellaceaeR.7group, and LachnospiraceaeNC2004group at the genus level (p < 0.05) by the Inverse-variance weighted method, with significant causal effects of ChristensenellaceaeR.7group and Allisonella on POU (p < 0.025). A total of five genetically greater abundance of gut microbiota traits were identified to be possibly related to the level of MCP (p < 0.05), including genus ErysipelotrichaceaeUCG003, family Clostridiaceae1, order Gastranaerophilales, order Actinomycetales, and family Actinomycetaceae. In the other direction, no clear evidence was found to support a significant causal relationship between POU and gut microbiota, as well as MCP and gut microbiota. In addition, evidence was also provided for the relationship between triacylglycerols and diacylglycerol elevation, and an increased risk of POU and MCP. No evidence was found across various sensitivity analyses, including reverse causality, pleiotropy, and heterogeneity.

CONCLUSION

The findings from this study provide robust evidence that gut microbiota alterations may be a risk of POU/MCP, but not vice versa.

The Role of the Human Microbiome in the Pathogenesis of Pain

Understanding of the gut microbiome's role in human physiology developed rapidly in recent years. Moreover, any alteration of this microenvironment could lead to a pathophysiological reaction of numerous organs. It results from the bidirectional communication of the gastrointestinal tract with the central nervous system, called the gut-brain axis. The signals in the gut-brain axis are mediated by immunological, hormonal, and neural pathways. However, it is also influenced by microorganisms in the gut. The disturbances in the gut-brain axis are associated with gastrointestinal syndromes, but recently their role in the development of different types of pain was reported. The gut microbiome could be the factor in the central sensitization of chronic pain by regulating microglia, astrocytes, and immune cells. Dysbiosis could lead to incorrect immune responses, resulting in the development of inflammatory pain such as endometriosis. Furthermore, chronic visceral pain, associated with functional gastrointestinal disorders, could result from a disruption in the gut microenvironment. Any alteration in the gut-brain axis could also trigger migraine attacks by affecting cytokine expression. Understanding the gut microbiome's role in pain pathophysiology leads to the development of analgetic therapies targeting microorganisms. Probiotics, FODMAP diet, and fecal microbiota transplantation are reported to be beneficial in treating visceral pain.

Acceptability and feasibility of fecal microBIOME and serum metabolite sample collection in people with end-stage kidney disease and pain being treated with HemoDialysis: A pilot study (BIOME-HDp)

Pain is known to reduce hemodialysis treatment adherence, reduce quality of life, and increase mortality. The absence of effective strategies to treat pain without medications has contributed to poor health outcomes for people with end-stage kidney disease (ESKD) on hemodialysis. It is now recognized that symbiotic microbiota in the gut play a critical role in health and disease, and new evidence sheds light on the role of the microbiome in chronic pain. The pilot study protocol presented here (BIOME-HDp) employs a longitudinal repeated measures design to interrogate the effects of a nonpharmacological pain intervention on the composition and function of the gut microbiome and circulating metabolites. This pilot study is an ancillary study of the HOPE Consortium Trial to reduce pain and opioid use in hemodialysis, which is part of the NIH's Helping to End Addiction Long-term (HEAL) initiative. The BIOME-HDp pilot study will establish clinical microbiome research methods and determine the acceptability and feasibility of fecal microbiome and serum metabolite sample collection.

The modified outer membrane protein Amuc_1100 of Akkermansia muciniphila improves chronic stress-induced anxiety and depression-like behavior in mice

Akkermansia muciniphila is a next-generation probiotic. The interaction between outer membrane protein Amuc_1100 of A. muciniphila and toll-like receptor 2 (TLR2) in intestinal epithelial cells influences the level of intestinal 5-hydroxytryptamine (5-HT). Amuc_1100^Δ80 is a truncated form of Amuc_1100 lacking the first 80 N-terminal amino acids and has a higher affinity for TLR2 than the wild-type protein. Here, we report that Amuc_1100^Δ80 could significantly reduce anxiety and depression-like behavior of mice when they were exposed to chronic unpredictable mild stress (CUMS). The experimental results of the rat insulinoma cell line RIN-14B showed that Amuc_1100^Δ80 also induced a significantly higher upregulation of tryptophan hydroxylase 1 (Tph1), a rate-limiting enzyme of intestinal 5-HT synthesis. The imbalance of the gut microflora could be diminished when CUMS mice were fed with Amuc_1100^Δ80. These results reveal that Amuc_1100^Δ80 could affect the 5-HT level and the downstream 5-HTR1A-CREB-BDNF signal pathway via interacting with TLR2 and by altering the gut microbial composition. In parallel, the downregulation exerted by Amuc_1100^Δ80 on the inflammation and hyperactivated HPA axis was closely related to the improvement of depression-like symptoms in CUMS mice. This study not only provides new insights into the antidepressant effect of A. muciniphila and its outer membrane protein Amuc_1100 but also identifies new potential targets and pathways in the gut for future research and the development of antidepressant drugs.

Inhibitory effects of antibiotic-induced gut microbiota depletion on acute itch behavior in mice

BACKGROUND

The gut microbiota is known to be associated with the regulation of many neurological diseases and behaviors, including chronic pain. However, it is unclear whether the gut microbiota is critical to the itch sensation. In this study, we investigated the effects of gut microbiota depletion on acute itch.

METHODS

First, an antibiotic cocktail was orally administered to deplete the gut microbiota in male C57BL/6 mice. Then, pruritogens were intradermally injected to induce acute itch behavior. In addition, antibiotic-treated mice received transplantation of fecal microbiota from untreated mice, followed by tests for acute itch. The changes in c-Fos expression in trigeminal ganglia (TG) neurons were also investigated by immunofluorescence staining.

RESULTS

Our results indicated that chronic antibiotic treatment significantly reduced the diversity and richness of the gut microbiota of mice. Compared to vehicle-treated mice, antibiotic-treated mice showed reductions in acute itch behavior induced by compound 48/80, chloroquine (CQ), and serotonin (5-HT), respectively. Moreover, repositioning of microbiota reversed the reductions in acute itch behavior in antibiotic-treated mice. In addition, immunofluorescence staining revealed that antibiotic-treated mice displayed decreased c-Fos expression in ipsilateral TG compared to controls.

CONCLUSIONS

Our study, for the first time, discovered that antibiotic-induced gut microbiota depletion could reduce acute itch behavior, which may be connected with decreased TG neuronal activity.

The diversity and abundance of gut microbiota are associated with the pain sensation threshold in the Japanese population

Small fibre neuropathy (SFN) is an initial pathology of diabetic polyneuropathy (DPN). Serum lipopolysaccharide binding protein levels are positively correlated with the pain threshold in the foot, suggesting that the abundance of gut Gram-negative bacilli, which are a source of lipopolysaccharides, may be involved in the development of DPN. Furthermore, the abundance of the gut and oral microbiota is assumed to be involved in the pathogenesis of diabetes. Nevertheless, the association between SFN and the microbiota has not been clarified. A total of 1056 individuals were recruited in the 2018 Iwaki Health Promotion Project. Pain sensation was evaluated based on the pain threshold from intraepidermal electrical stimulation (PINT). Patients with PINT scores <0.15 mA were categorized into the low-PINT group (n = 718); otherwise, they were categorized into the high-PINT group (n = 283). Furthermore, each group was divided into the subjects with or without glucose tolerance based on HbA1c levels, fasting blood glucose levels and diabetic history. Principal coordinate analysis and α- and β-diversity of the microbiota were evaluated. The correlation between clinical and microbiota data was examined. Oral microbiota diversity showed no structural differences according to PINT scores, whereas principal coordinate analysis and α- and β-diversity revealed significant structural differences in gut microbiota (p < 0.01, p < 0.05 and p < 0.05, respectively), even after the participants with glucose intolerance were excluded (p < 0.01, p < 0.05 and p < 0.05, respectively). The relative abundance of the genus Bacteroides was significantly lower in high-PINT participants compared with low-PINT participants (10 ± 6.7% vs. 11.3 ± 7.0%, p < 0.01), even after the exclusion of subjects with diabetes and impaired fasting glucose (10.0 ± 6.5% vs. 11.2 ± 6.9%, p < 0.05). In univariate linear regression analyses, PINT was significantly correlated with metabolic syndrome parameters, eGFR, uric acid level and the abundance of Bacteroides. The correlation between Bacteroides and PINT scores remained significant after adjustment for multiple factors (β = -0.07181, p < 0.05). Changes of bacterial diversity and a low abundance of gut Bacteroides were correlated with elevated PINT scores in the Japanese population. This correlation may represent a new therapeutic option for SFN.