Long-lasting effects of postweaning sodium butyrate exposure on social behaviors in adult mice

Gut microbiota-derived trimethylamine N-oxide involved in methamphetamine-induced depression-like behaviors of male mice

Methamphetamine (METH)-provoked psychiatric symptoms are a major health concern, with depression being a prevalent symptom among METH abusers. Recently, gut microbiota-derived metabolites have been involved in various psychosis pathogenesis, but their roles in METH-induced depression remain unclear. This study investigates the implication of gut microbiota-derived metabolite trimethylamine N-oxide (TMAO) in METH-induced depressive-like behaviors (DLBs). We examined the circulating TMAO levels post-METH exposure besides exploring the impacts of TMAO on METH-triggered DLBs. Then, potential causes of TMAO alterations were explored, along with its effects on hippocampal neuronal damage and neuroinflammation. The findings showcased that METH-treated mice displayed DLBs accompanied by increased serum TMAO levels. Similarly, introducing TMAO to the drinking water elevated serum TMAO levels and induced DLBs. Although METH exposure did not notably alter the abundance of the gut microbiota, antibiotic (ABX) therapy suppressed the increased serum TMAO levels and the onset of DLBs. Additionally, choline and L-carnitine levels were elevated following METH exposure, which may be a potential mechanism for TMAO metabolic dysregulation. Elevated TMAO levels resulted in an elevation in Nissl-positive dead cells, the number of microglia, TNF-α, and IL-1β levels, along with TLR-4, NF-κB, and MyD88 expression in the hippocampal CA3 region. Inhibition of TMAO synthesis mitigated METH-provoked neuronal damage and neuroinflammation.

Juvenile chronic social defeat stress reduces prosocial behavior in adult male mice

Exposure to stress in early life can have a significant impact on individuals. However, the effects of early-life stress (ELS) on prosocial behavior remain unclear, as do the underlying mechanisms. In this study, ICR juvenile mice were subjected to juvenile chronic social defeat stress (jCSDS) between postnatal days 32 and 41, during which body weight changes were continuously monitored. The behaviors of adult mice were evaluated using the open field test (OFT), the social interaction test (SIT), and the prosocial choice task (PCT). ELISA was used to quantify serum levels of oxytocin, serotonin, and dopamine. The density of dendritic spines in the basolateral amygdala was evaluated by Golgi staining. Behavioral test results showed that jCSDS induced anxiety-like behavior and decreased prosocial selection tendency in mice. Additionally, exposure to jCSDS increased the serum levels of oxytocin, decreased those of serotonin, and increased the density of dendritic spines in the basolateral amygdala. Correlation analysis indicated that prosocial behavior was negatively correlated with serum oxytocin levels and dendritic spine density in the basolateral amygdala. These results suggested that jCSDS reduced prosocial behavior, possibly due to changes in serum oxytocin contents and adaptive changes in amygdaloid neurons.

Genetic-epigenetic-neuropeptide associations in mood and anxiety disorders: Toward personalized medicine

Mood and anxiety disorders are complex psychiatric conditions shaped by the multifactorial interplay of genetic, epigenetic, and neuropeptide factors. This review aims to elucidate the intricate interactions among these factors and their potential in advancing personalized medicine. We examine the genetic underpinnings, emphasizing key heritability studies and specific gene associations. The role of epigenetics is discussed, focusing on how environmental factors can modify gene expression and contribute to these disorders. Neuropeptides, including substance P, CRF, AVP, NPY, galanin, and kisspeptin, are evaluated for their involvement in mood regulation and their potential as therapeutic targets. Additionally, we address the emerging role of the gut microbiome in modulating neuropeptide activity and its connection to mood disorders. This review integrates findings from genetic, epigenetic, and neuropeptide research, offering a comprehensive overview of their collective impact on mood and anxiety disorders. By highlighting novel insights and potential clinical applications, we underscore the importance of a multi-omics approach in developing personalized treatment strategies. Future research directions are proposed to address existing knowledge gaps and translate these findings into clinical practice. Our review provides a fresh perspective on the pathophysiology of mood and anxiety disorders, paving the way for more effective and individualized therapies.

Postweaning sodium citrate exposure induces long-lasting and sex-dependent effects on social behaviours in mice

BACKGROUND

Postweaning is a pivotal period for brain development and individual growth. As an important chemical used in medicines, foods and beverages, sodium citrate (SC) is commonly available. Although some effects of SC exposure on individual physiology have been demonstrated, the potential long-lasting effects of postweaning dietary SC exposure on social behaviours are still elusive.

METHODS

Both postweaning male and female C57BL/6 mice were exposed to SC through drinking water for a total of 3 weeks. A series of behavioural tests, including social dominance test (SDT), social interaction test (SIT), bedding preference test (BPT) and sexual preference test (SPT), were performed in adolescence and adulthood. After these tests, serum oxytocin (OT) levels and gut microbiota were detected.

RESULTS

The behavioural results revealed that postweaning SC exposure decreased the social dominance of male mice in adulthood and female mice in both adolescence and adulthood. SC exposure also reduced the sexual preference rates of both males and females, while it had no effect on social interaction behaviour. ELISA results indicated that SC exposure decreased the serum OT levels of females but not males. 16S rRNA sequencing analysis revealed a significant difference in β-diversity after SC exposure in both males and females. The correlation coefficient indicated the correlation between social behaviours, OT levels and dominant genera of gut microbiota.

CONCLUSION

Our findings suggest that postweaning SC exposure may have enduring and sex-dependent effects on social behaviours, which may be correlated with altered serum OT levels and gut microbiota composition.

Postweaning intermittent sleep deprivation enhances defensive attack in adult female mice via the microbiota-gut-brain axis

Sleep is one of the most important physiological activities in life and promotes the growth and development of an individual. In modern society, sleep deprivation (SD), especially among adolescents, has become a common phenomenon. However, long-term SD severely affected adolescents' neurodevelopment leading to abnormal behavioral phenotypes. Clinical studies indicated that sleep problems caused increased aggressive behavior in adolescents. Aggressive behavior was subordinate to social behaviors, in which defensive attack was often the last line for survival. Meanwhile, increasing studies shown that gut microbiota regulated social behaviors by affecting specific brain regions via the gut-brain axis. However, whether postweaning intermittent SD is related to defensive attack in adulthood, and if so, whether it is mediated by the microbiota-gut-brain axis are still elusive. Combined with microbial sequencing and hippocampal metabolomics, the present study mainly investigated the long-term effects of postweaning intermittent SD on defensive attack in adult mice. Our study demonstrated that postweaning intermittent SD enhanced defensive attack and impaired long-term memory formation in adult female mice. Moreover, microbial sequencing and LC-MS analysis showed that postweaning intermittent SD altered the gut microbial composition and the hippocampal metabolic profile in female mice, respectively. Our attention has been drawn to the neuroactive ligand-receptor interaction pathway and related metabolites. In conclusion, our findings provide a new perspective on the relationship of early-life SD and defensive attack in adulthood, and also highlight the importance of sleep in early-life, especially in females.

Effects of postweaning cadmium exposure on socioemotional behaviors in adolescent male mice

Exposure to cadmium (Cd), a toxic heavy metal classified as an environmental endocrine disruptor, can exert significant toxicity in both animals and humans. However, the potential effects of Cd exposure on socioemotional behaviors are still poorly understood, as are the underlying mechanisms. In the present study, employing a series of behavioral tests as well as 16 S rRNA sequencing analysis, we investigated the long-term effects of Cd exposure on socioemotional behaviors and their associated mechanisms in mice based on the brain-gut interaction theory. The results showed that postweaning exposure to Cd reduced the ability to resist depression, decreased social interaction, subtly altered sexual preference, and changed the composition of the gut microbiota in male mice during adolescence. These findings provided direct evidence for the deleterious effects of exposure to Cd in the postweaning period on socioemotional behaviors later in adolescence, and suggested that these effects of Cd exposure may be linked to changes in the gut microbiota.

Sex-dependent and long-lasting effects of adolescent sleep deprivation on social behaviors in adult mice

Increasing evidence indicates that sleep deprivation (SD) can exert multiple negative effects on neuronal circuits, resulting in memory impairment, depression, and anxiety, among other consequences. The long-term effects of SD during early life on behavioral phenotypes in adulthood are still poorly understood. In this study, we investigated the long-lasting effects of SD in adolescence on social behaviors, including empathic ability and social dominance, and the role of the gut microbiota in these processes, using a series of behavioral paradigms in mice combined with 16S rRNA gene pyrosequencing. Behavioral assay results showed that SD in adolescence significantly reduced the frequency of licking, the total time spent licking, and the time spent sniffing during the emotional contagion test in male mice, effects that were not observed in female mice. These findings indicated that SD in adolescence exerts long-term, negative effects on empathic ability in mice and that this effect is sex-dependent. In contrast, SD in adolescence had no significant effect on locomotor activities, social dominance but decreased social interaction in male mice in adulthood. Meanwhile, 16S rRNA gene pyrosequencing results showed that gut microbial richness and diversity were significantly altered in adult male mice subjected to SD in adolescence. Our data provide direct evidence that SD in youth can induce alterations in empathic ability in adult male mice, which may be associated with changes in the gut microbiota. These findings highlight the long-lasting effects of sleep loss in adolescence on social behaviors in adulthood and the role played by the brain-gut axis.

Upregulation of Microglial Sirt6 and Inhibition of Microglial Activation by Vitamin D3 in Lipopolysaccharide-stimulated Mice and BV-2 Cells

Vitamin D3 may suppress microglial activation and neuroinflammation, which play a central role in the pathophysiology of many neurological disorders. Sirt6 can remove histone 3 lysine 9 acetylation (H3K9ac) to repress expression of pathological genes and produce anti-inflammatory effects. However, whether vitamin D3 upregulates microglial Sirt6 to exert its protective effects against microglial activation and neuroinflammation is unclear. The effects of lower, normal, and higher dosages (1, 10 and 100 μg/kg/day) of vitamin D3 on behavioral and neuromorphological changes, brain inflammatory factors, Sirt6 and H3K9ac levels, and microglial Sirt6 distribution in hippocampus were evaluated in lipopolysaccharide (LPS)-stimulated mice. In addition, the effects of vitamin D3 on inflammatory factors, reactive oxygen species, Sirt6, and H3K9ac were confirmed in LPS-stimulated BV-2 cells. We verified that vitamin D3 ameliorated the impaired sociability of LPS-stimulated mice by three-chamber test. In addition, vitamin D3 upregulated brain Sirt6 generation, reduced H3K9ac levels and inhibited generation of brain inflammatory factors. Moreover, vitamin D3 promoted microglial Sirt6 distribution and attenuated microglia displaying an activated morphology in the hippocampus of LPS-stimulated mice. Similarly, vitamin D3 upregulated Sirt6 generation and intensity, reduced H3K9ac levels, and inhibited the inflammatory activation of LPS-stimulated BV-2 cells. In conclusion, vitamin D3 may upregulate microglial Sirt6 to reduce H3K9ac and inhibit microglial activation, thereby antagonizing neuroinflammation.

Enterogenic metabolomics signatures of depression: what are the possibilities for the future

INTRODUCTION

An increasing number of studies indicate that the microbiota-gut-brain axis is an important pathway involved in the onset and progression of depression. The responses of the organism (or its microorganisms) to external cues cannot be separated from a key intermediate element: their metabolites.

AREAS COVERED

In recent years, with the rapid development of metabolomics, an increasing amount of metabolites has been detected and studied, especially the gut metabolites. Nevertheless, the increasing amount of metabolites described has not been reflected in a better understanding of their functions and metabolic pathways. Moreover, our knowledge of the biological interactions among metabolites is also incomplete, which limits further studies on the connections between the microbial-entero-brain axis and depression.

EXPERT OPINION

This paper summarizes the current knowledge on depression-related metabolites and their involvement in the onset and progression of this disease. More importantly, this paper summarized metabolites from the intestine, and defined them as enterogenic metabolites, to further clarify the function of intestinal metabolites and their biochemical cross-talk, providing theoretical support and new research directions for the prevention and treatment of depression.

ZeXieYin Formula alleviates TMAO-induced cognitive impairment by restoring synaptic plasticity damage

ETHNOPHARMACOLOGICAL RELEVANCE

Treating cognitive impairment is a challenging and necessary research topic. ZeXieYin Formula (ZXYF), is a traditional herbal formula documented in the book of HuangDiNeiJing. Our previous studies demonstrated the ameliorative effects of ZXYF on atherosclerosis by reducing the plasma trimethylamine oxide (TMAO) level. TMAO is a metabolite of gut microorganisms, our recent research found that the increasing level of TMAO may have adverse effects on cognitive functions.

AIM OF THE STUDY

Our study mainly focused on the therapeutic effects of ZXYF on TMAO-induced cognitive impairment in mice and explored its underlying mechanism.

MATERIALS AND METHODS

After the TMAO-induced cognitive impairment mice models were established, we applied behavioral tests to estimate the learning and memory ability of the ZXYF intervention mice. Liquid chromatography-mass spectrometry (LC-MS) was used to quantify the TMAO levels in plasma and the brain. The effects of ZXYF on the hippocampal synaptic structure and the neurons were observed by transmission electron microscopy (TEM) and Nissl staining. In addition, western-blotting (WB) and immunohistochemical (IHC) staining were used to detect the level of related proteins in the synaptic structure and further verify the changes in synaptic plasticity and the mTOR pathway after ZXYF administration.

RESULTS

Behavioral tests showed that the learning and memory ability of mice impaired after a period of TMAO intervention and ZXYF could alleviate these changes. A series of results showed that ZXYF partly restored the damage of hippocampal synapse and neurons in TMAO-induced mice, at the same time, the expression of synapse-related proteins and mTOR pathway-related proteins were significantly regulated compared with the damage caused by TMAO.

CONCLUSION

ZXYF could alleviate TMAO-induced cognitive impairment by improving synaptic function, reducing neuronal damage, regulating synapse-associated proteins, and regulating the mTOR signaling pathway.

D-beta-hydroxybutyrate protects against microglial activation in lipopolysaccharide-treated mice and BV-2 cells

Microglial activation is a key event in neuroinflammation, which, in turn, is a central process in neurological disorders. In this study, we investigated the protective effects of D-beta-hydroxybutyrate (BHB) against microglial activation in lipopolysaccharide (LPS)-treated mice and BV-2 cells. The effects of BHB in mice were assessed using behavioral testing, morphological analysis and immunofluorescence labeling for the microglial marker ionizing calcium-binding adaptor molecule 1 (IBA-1) and the inflammatory cytokine interleukin-6 (IL-6) in the hippocampus. Moreover, we examined the levels of the inflammatory IL-6 and tumor necrosis factor-α (TNF-α), as well as those of the neuroprotective brain-derived neurotrophic factor (BDNF) and transforming growth factor-β (TGF-β) in the brain. In addition, we examined the effects of BHB on IL-6, TNF-α, BDNF, TGF-β, reactive oxygen species (ROS) level and cell viability in LPS-stimulated BV-2 cells. BHB treatments attenuated behavioral abnormalities, reduced the number of IBA-1-positive cells and the intensity of IL-6 fluorescence in the hippocampus, with amelioration of microglia morphological changes in the LPS-treated mice. Furthermore, BHB inhibited IL-6 and TNF-α generation, but promoted BDNF and TGF-β production in the brain of LPS-treated mice. In vitro, BHB inhibited IL-6 and TNF-α generation, increased BDNF and TGF-β production, reduced ROS level, ameliorated morphological changes and elevated cell viability of LPS-stimulated BV-2 cells. Together, our findings suggest that BHB exerts protective effects against microglial activation in vitro and in vivo, thereby reducing neuroinflammation.

Taurine inhibits KDM3a production and microglia activation in lipopolysaccharide-treated mice and BV-2 cells

Microglia activation has been suggested as the key factor in neuro-inflammation and thus participates in neurological diseases. Although taurine exhibits anti-inflammatory and neuro-protective effects, its underlying epigenetic mechanism is unknown. In this study, taurine was administered to lipopolysaccharide (LPS)-treated mice and BV-2 cells. Behavioral test, morphological analyze, detection of microglia activation, and lysine demethylase 3a (KDM3a) measurements were performed to investigate the mechanism by which taurine regulates KDM3a and subsequently antagonizes microglia activation. Taurine improved the sociability of LPS-treated mice, inhibited microglia activation in the hippocampus, and reduced generation of brain inflammatory factors, such as interleukin-6, tumor necrosis factor-α, inducible nitric oxide synthase, and cyclooxygenase-2. Meanwhile, taurine suppressed the LPS-induced increase in microglial KDM3a, and increased the level of mono-, di- or tri-methylation of lysine 9 on histone H3 (H3K9me1/2/3). Furthermore, taurine inhibited the LPS-induced increase in KDM3a, elevated the H3K9me1/2/3 level, and reduced inflammatory factors and reactive oxygen species in a concentration-dependent manner in LPS-stimulated BV-2 cells. In conclusion, taurine inhibited KDM3a and microglia activation, thereby playing an anti-inflammatory role in LPS-treated mice and BV-2 cells.

Maternal exposure to triclosan during lactation alters social behaviors and the hippocampal ultrastructure in adult mouse offspring

We recently reported that exposure to triclosan (TCS), a broad-spectrum antibacterial agent, affects social behaviors in adult mice, however, the long-lasting effects of TCS exposure during early life on social behaviors are still elusive. The present study aimed to investigate the long-lasting impacts of adding TCS to the maternal drinking water during lactation on the social behaviors of adult mouse offspring and to explore the potential mechanism underlying these effects. The behavioral results showed that TCS exposure decreased body weight, increased depression-like behavior and decreased social dominance in both male and female offspring, as well as increased anxiety-like behavior and bedding preference in female offspring. In addition, enzyme-linked immunosorbent assay (ELISA) indicated that TCS exposure increased peripheral proinflammatory cytokine levels, altered serum oxytocin (OT) levels, and downregulated the expression of postsynaptic density protein 95 (PSD-95) in the hippocampus. Morphological analysis by transmission electron microscopy (TEM) demonstrated that exposure to TCS induced morphological changes to synapses and neurons in the hippocampus of offspring. These findings suggested that TCS exposure during lactation contributed to abnormal social behaviors accompanied by increased peripheral inflammation and altered hippocampal neuroplasticity, which provides a deeper understanding of the effects of TCS exposure during early life on brain function and behavioral phenotypes.

Long-lasting effects of postweaning sleep deprivation on cognitive function and social behaviors in adult mice

Sleep deprivation (SD) has adverse effects on physical and mental health. Recently increasing attention has been given to SD in the early-life stage. However, the effects and mechanisms of postweaning SD on cognitive function and social behaviors are still unclear. In this study, SD was conducted in mice from postnatal Day 21 (PND21) to PND42, 6 h a day. Meanwhile, changes in body weight, food and water intake were continuously monitored. Behavioral tests were carried out in adulthood of mice. The levels of serum corticosterone, the proinflammatory cytokines interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α), and the anti-inflammatory cytokines interleukin-10 (IL-10), vasopressin (VP) and oxytocin (OT) were measured by ELISA. Golgi staining was used to calculate neural dendritic spine density in the dorsal hippocampus (dHPC) CA1 region and medial prefrontal cortex (mPFC). We found that postweaning SD increased the food intake and the weight of female mice. Behavioral results showed that postweaning SD caused cognitive impairment and lowered social dominance in adult male mice but not in female mice. ELISA results showed that SD increased the levels of serum corticosterone, VP and OT in male mice and serum OT in female mice. Golgi staining analysis showed that SD decreased neural dendritic spine density in the dHPC in male mice. These results suggest that postweaning SD has a long-term effect on social dominance and cognitive function in male mice, which may provide a new insight into the role of SD in regulating cognitive function and social behaviors.

Short chain fatty acids: Microbial metabolites for gut-brain axis signalling

The role of the intestinal microbiota as a regulator of gut-brain axis signalling has risen to prominence in recent years. Understanding the relationship between the gut microbiota, the metabolites it produces, and the brain will be critical for the subsequent development of new therapeutic approaches, including the identification of novel psychobiotics. A key focus in this regard have been the short-chain fatty acids (SCFAs) produced by bacterial fermentation of dietary fibre, which include butyrate, acetate, and propionate. Ongoing research is focused on the entry of SCFAs into systemic circulation from the gut lumen, their migration to cerebral circulation and across the blood brain barrier, and their potential to exert acute and chronic effects on brain structure and function. This review aims to discuss our current mechanistic understanding of the direct and indirect influence that SCFAs have on brain function, behaviour and physiology, which will inform future microbiota-targeted interventions for brain disorders.

Gut microbiota shapes social dominance through modulating HDAC2 in the medial prefrontal cortex

Social dominance is a ubiquitous phenomenon among social animals, including humans. To date, individual attributes leading to dominance (after a contest) remain largely elusive. Here, we report that socially dominant rats can be distinguished from subordinates based on their intestinal microbiota. When dysbiosis is induced, rats are predisposed to a subordinate state, while dysbiotic rats reclaim social dominance following microbiota transplantation. Winning hosts are characterized by core microbes, a majority of which are associated with butyrate production, and the sole colonization of Clostridium butyricum is sufficient to restore dominance. Regarding molecular aspects, a histone deacetylase, HDAC2, is responsive to microbial status and mediates competition outcome; however, this occurs only in a restricted population of cells in the medial prefrontal cortex (mPFC). Furthermore, HDAC2 acts by modulating synaptic activity in mPFC. Together, these findings uncover a link between commensals and host dominance, providing insight into the gut-brain mechanisms underlying dominance determination.

Effects of chronic triclosan exposure on social behaviors in adult mice

Triclosan (TCS), a newly identified environmental endocrine disruptor (EED) in household products, has been reported to have toxic effects on animals and humans. The effects of TCS exposure on individual social behaviors and the potential underlying mechanisms are still unknown. This study investigated the behavioral effects of 42-day exposure to TCS (0, 50, 100 mg/kg) in drinking water using the open field test (OFT), social dominance test (SDT), social interaction test (SIT), and novel object recognition task (NOR). Using 16S rRNA sequencing analysis and transmission electron microscopy (TEM), we observed the effects of TCS exposure on the gut microbiota and ultrastructure of hippocampal neurons and synapses. Behavioral results showed that chronic TCS exposure reduced the social dominance of male and female mice. TCS exposure also reduced social interaction in male mice and impaired memory formation in female mice. Analysis of the gut microbiota showed that TCS exposure increased the relative abundance of the Proteobacteria and Actinobacteria phyla in female mice. Ultrastructural analysis revealed that TCS exposure induced ultrastructural damage to hippocampal neurons and synapses. These findings suggest that TCS exposure may affect social behaviors, which may be caused by altered gut microbiota and impaired plasticity of hippocampal neurons and synapses.

Magnesium-L-threonate alleviate colonic inflammation and memory impairment in chronic-plus-binge alcohol feeding mice

Magnesium-l-threonate (MgT) is considered a food supplement. Alcohol-mediated diseases (AMD) are accompanied by inflammation and memory impairment. The purpose of this study is to investigate the function of MgT in AMD. Hence, chronic-plus-binge alcohol feeding mice model and multiply bioinformatics analysis were performed. Consequently, the expression of inflammatory cytokines downregulated, while the activities of antioxidases decreased in serum, colon, and brain. Interestingly, MgT relieved gut barrier dysfunction and reshaped microbiota. The relative abundance of Akkermansia, Odoribacter, and Blautia were increased, while that of Alloprevotella and Clostridium were decreased. Metabolic analysis elucidated amino acids and glutamate metabolism were enhanced in MgT-treated mice. Furthermore, morris water maze test confirmed memory ability was enhanced. Inflammation cytokines were negatively correlated with Blautia, and Akkermansia. Collectively, MgT relieved inflammation in gut-brain axis of mice, reshaped gut microbiota, and enhanced the amino acids and glutamate metabolism. MgT may be used as a food supplement to prevent inflammation and memory impairment induced by alcohol abuse.

Exogenous microbiota-derived metabolite trimethylamine N-oxide treatment alters social behaviors: Involvement of hippocampal metabolic adaptation

Increasing evidence indicates that gut microbiota and its metabolites can influence the brain function and the related behaviors. Trimethylamine N-oxide (TMAO), an indirect metabolite of gut microbiota, has been linked to aging, cognitive impairment, and many brain disorders. However, the potential effects of TMAO on social behaviors remain elusive. The present study investigated the effects of early life systemic TMAO exposure and intra-hippocampal TMAO infusion during adulthood on social behaviors in mice. We also analyzed the effects of intra-hippocampus infusion of TMAO during adulthood on levels of metabolites. The results showed that both systemic TMAO exposure in the post-weaning period and intra-hippocampal TMAO infusion during adulthood decreased social rank and reduced sexual preference in adult mice. Data from LC-MS metabolomics analysis showed that intra-hippocampal TMAO infusion induced a total 207 differential metabolites, which belongs to several metabolic or signaling pathways, especially FoxO signaling pathway and retrograde endocannabinoid signaling pathway. These data suggest that TMAO may affect social behaviors by regulating metabolites in the hippocampus, which may provide a new insight into the role of gut microbiota in regulating social behaviors.

Repeated 3,3-Dimethyl-1-butanol exposure alters social dominance in adult mice

The influence of gut microbiota on brain function and brain disorders has been attracted more and more attention. Trimethylamine N-oxide (TMAO), an indirect metabolite of gut microbiota, has been linked to aging, cognitive impairment, and other brain disorders. However, the relationship between TMAO and social behaviors are still poorly understood. Adult male mice were exposed to drinking water containing 3,3- Dimethyl-1-butanol (DMB), an indirect inhibitors of TMAO, for 21 continuous days followed by a series of behavioral tests to detect the effect of DMB exposure on social behaviors, mainly including social dominance test (SDT), bedding preference test (BP), sexual preference test (SP), social interaction test (SI), open field test (OFT), tail suspension test (TST), forced swim test (FST), novelty suppressed feeding test (NSF), and novel object recognition (NOR) task. In the SDT, compared with the control group, the mice treated with DMB (both 0.2% and 1.0%), both high-ranked and low-ranked mice, showed a reduction in the number of victories. There is no statistical difference on sexual preference, anxiety, depression-like behavior phenotype, and memory formation. In conclusion, the present findings provide direct evidence, for the first time, that repeated DMB exposure produces significant effects on social dominance of adult mice, without any effects on sexual preference, anxiety, depression-like behavior phenotype or memory formation, highlighting the regulatory effects of gut-brain interaction on social behaviors.