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

A role of gut-brain axis on prophylactic actions of arketamine in male mice exposed to chronic restrain stress

The gut-brain axis, which includes gut microbiota and microbiome-derived metabolites, might be implicated in depression. We reported the sustained prophylactic effects of a new antidepressant arketamine in chronic restrain stress (CRS) model of depression. In this study, we investigated the role of gut-brain axis on the prophylactic effects of arketamine in the CRS (7 days) model. Pretreatment with arketamine (10 mg/kg, 1 day prior to the CRS onset) significantly prevented CRS-induced body weight loss, increased immobility time of forced swimming test, decreased sucrose preference of sucrose preference test, and reduced expressions of synaptic proteins (GluA1 and PSD-95) in the prefrontal cortex (PFC) in the male mice. Gut microbiota analysis showed that pretreatment with arketamine might restore altered abundance of gut microbiota in CRS-exposed mice. An untargeted metabolomics analysis revealed four metabolites (e.g., L-leucine, N-acetyl-l-glutamine, 2-(2,4-dichlorophenyl)-3-[4-(dimethylamino)phenyl]acrylonitrile, L-threonine amide) that were altered between control and CRS group; however, there were found to be altered between the saline + CRS group and the arketamine + CRS group. Network analysis demonstrated correlations among synaptic proteins in the PFC and certain microbiota, and blood metabolites. These findings suggest that gut-brain axis, including its metabolites, might partially contribute to the persistent prophylactic effects of arketamine in the CRS model.

The Power of Psychobiotics in Depression: A Modern Approach through the Microbiota-Gut-Brain Axis: A Literature Review

The microbiota-gut-brain (MGB) axis is a complex communication network linking the gut, microbiota, and brain, influencing various aspects of health and disease. Dysbiosis, a disturbance in the gut microbiome equilibrium, can significantly impact the MGB axis, leading to alterations in microbial composition and function. Emerging evidence highlights the connection between microbiota alterations and neurological and psychiatric disorders, including depression. This review explores the potential of psychobiotics in managing depressive disorders, emphasizing their role in restoring microbial balance and influencing the MGB axis. Psychobiotics exhibit positive effects on the intestinal barrier, immune response, cortisol levels, and the hypothalamic-pituitary-adrenal (HPA) axis. Studies suggest that probiotics may serve as an adjunct therapy for depression, especially in treatment-resistant cases. This review discusses key findings from studies on psychobiotics interventions, emphasizing their impact on the gut-brain axis and mental health. The increasing acceptance of the expanded concept of the MGB axis underscores the importance of microorganisms in mental well-being. As our understanding of the microbiome's role in health and disease grows, probiotics emerge as promising agents for addressing mental health issues, providing new avenues for therapeutic interventions in depressive disorders.

Gut microbiome promotes mice recovery from stress-induced depression by rescuing hippocampal neurogenesis

Studies from rodents to primates and humans indicate that individuals vary in how resilient they are to stress, and understanding the basis of these variations may help improve treatments for depression. Here we explored the potential contribution of the gut microbiome to such variation. Mice were exposed to chronic unpredictable mild stress (CUMS) for 4 weeks then allowed to recover for 3 weeks, after which they were subjected to behavioral tests and categorized as showing low or high stress resilience. The two types of mouse were compared in terms of hippocampal gene expression using RNA sequencing, fecal microbiomes using 16S RNA sequencing, and extent of neurogenesis in the hippocampus using immunostaining of brain sections. Fecal microbiota were transplanted from either type of mouse into previously stress-exposed and stress-naïve animals, and the effects of the transplantation on stress-induced behaviors and neurogenesis in the hippocampus were examined. Finally, we blocked neurogenesis using temozolomide to explore the role of neurogenesis promoted by fecal microbiota transplantation in enhancing resilience to stress. Results showed that highly stress-resilient mice, but not those with low resilience, improved significantly on measures of anhedonia, behavioral despair, and anxiety after 3-week recovery from CUMS. Their feces showed greater abundance of Lactobacillus, Bifidobacterium and Romboutsia than feces from mice with low stress resilience, as well as lower abundance of Staphylococcus, Psychrobacter and Corynebacterium. Similarly, highly stress-resilient mice showed greater neurogenesis in hippocampus than animals with low stress resilience. Transplanting fecal microbiota from mice with high stress resilience into previously CUMS-exposed recipients rescued neurogenesis in hippocampus, facilitating recovery from stress-induced depression and cognitive decline. Blockade of neurogenesis with temozolomide abolished recovery of recipients from CUMS-induced depression and cognitive decline in mice transplanted with fecal microbiota from mice with high stress resilience. In conclusion, our results suggested that remodeling of the gut microbiome after stress may reverse stress-induced impairment of hippocampal neurogenesis and thereby promote recovery from stress-induced depression.

Decoding the role of the gut microbiome in gut-brain axis, stress-resilience, or stress-susceptibility: A review

Increased exposure to stress is associated with stress-related disorders, including depression, anxiety, and neurodegenerative conditions. However, susceptibility to stress is not seen in every individual exposed to stress, and many of them exhibit resilience. Thus, developing resilience to stress could be a big breakthrough in stress-related disorders, with the potential to replace or act as an alternative to the available therapies. In this article, we have focused on the recent advancements in gut microbiome research and the potential role of the gut-brain axis (GBA) in developing resilience or susceptibility to stress. There might be a complex interaction between the autonomic nervous system (ANS), immune system, endocrine system, microbial metabolites, and bioactive lipids like short-chain fatty acids (SCFAs), neurotransmitters, and their metabolites that regulates the communication between the gut microbiota and the brain. High fiber intake, prebiotics, probiotics, plant supplements, and fecal microbiome transplant (FMT) could be beneficial against gut dysbiosis-associated brain disorders. These could promote the growth of SCFA-producing bacteria, thereby enhancing the gut barrier and reducing the gut inflammatory response, increase the expression of the claudin-2 protein associated with the gut barrier, and maintain the blood-brain barrier integrity by promoting the expression of tight junction proteins such as claudin-5. Their neuroprotective effects might also be related to enhancing the expression of brain-derived neurotrophic factor (BDNF) and glucagon-like peptide (GLP-1). Further investigations are needed in the field of the gut microbiome for the elucidation of the mechanisms by which gut dysbiosis contributes to the pathophysiology of neuropsychiatric disorders.

Microbiota from Alzheimer's patients induce deficits in cognition and hippocampal neurogenesis

Alzheimer's disease is a complex neurodegenerative disorder leading to a decline in cognitive function and mental health. Recent research has positioned the gut microbiota as an important susceptibility factor in Alzheimer's disease by showing specific alterations in the gut microbiome composition of Alzheimer's patients and in rodent models. However, it is unknown whether gut microbiota alterations are causal in the manifestation of Alzheimer's symptoms. To understand the involvement of Alzheimer's patient gut microbiota in host physiology and behaviour, we transplanted faecal microbiota from Alzheimer's patients and age-matched healthy controls into microbiota-depleted young adult rats. We found impairments in behaviours reliant on adult hippocampal neurogenesis, an essential process for certain memory functions and mood, resulting from Alzheimer's patient transplants. Notably, the severity of impairments correlated with clinical cognitive scores in donor patients. Discrete changes in the rat caecal and hippocampal metabolome were also evident. As hippocampal neurogenesis cannot be measured in living humans but is modulated by the circulatory systemic environment, we assessed the impact of the Alzheimer's systemic environment on proxy neurogenesis readouts. Serum from Alzheimer's patients decreased neurogenesis in human cells in vitro and were associated with cognitive scores and key microbial genera. Our findings reveal for the first time, that Alzheimer's symptoms can be transferred to a healthy young organism via the gut microbiota, confirming a causal role of gut microbiota in Alzheimer's disease, and highlight hippocampal neurogenesis as a converging central cellular process regulating systemic circulatory and gut-mediated factors in Alzheimer's.

Comparative Genomics of Pesticide-Degrading Enterococcus Symbionts of Spodoptera frugiperda (Lepidoptera: Noctuidae) Leads to the Identification of Two New Species and the Reappraisal of Insect-Associated Enterococcus Species

Enterococcus species have been described as core members of the microbial community of Spodoptera frugiperda (Lepidoptera: Noctuidae) and have been previously reported as insecticide degrading agents. This study aimed to investigate the molecular composition of these microbial symbionts of S. frugiperda to better understand their association with the host and their potential for insecticide metabolization. Through phenotypic assays and comparative genomic analyses of several pesticide-degrading Enterococcus isolated from the gut of S. frugiperda larvae, we identified two new species: Enterococcus entomosocium n. sp. and Enterococcus spodopteracolus n. sp. Their identities as new species were confirmed by whole genome alignment, utilizing cut-offs of 95-96% for the average nucleotide identity (ANI) and 70% for the digital DNA: DNA hybridization (dDDH) values. The systematic positioning of these new species within the genus Enterococcus was resolved using genome-based analysis, revealing Enterococcus casseliflavus as a sister group of E. entomosocium n. sp., and Enterococcus mundtii as a sister group of E. spodopteracolus n. sp. Comparative genomic analyses of several isolates of E. entomosocium n. sp. and E. spodopteracolus n. sp. provided a better assessment of the interactions established in the symbiotic association with S. frugiperda and led to the discovery of misidentified new species of Enterococcus associated with insects. Our analyses indicated that the potential of E. entomosocium n. sp. and E. spodopteracolus n. sp. to metabolize different pesticides arises from molecular mechanisms that result in rapid evolution of new phenotypes in response to environmental stressors, in this case, the pesticides their host insect is exposed to.