Paternal immune activation (PIA), including via the viral mimic polyinosinic:polycytidylic acid (poly I:C), impacts offspring physiology and behaviour. A previous model employing low molecular weight (LMW) poly I:C showed alterations in the sperm small non-coding RNA (sncRNA) profile and offspring phenotypes. High molecular weight (HMW) poly I:C increases translatability by eliciting a robust sickness response accompanied by a significant increase of key cytokines. Here, male C57BL/6J mice (F0) were intraperitoneally injected with 12 mg/kg HMW poly I:C and mated with naïve females four weeks later. Adult offspring (F1) displayed reduced somatosensory cortex and corpus callosum thickness, and altered social-interaction behaviour. Male offspring displayed a reduction in gross striatum weight, reduced striatal microglia numbers and disruption to Pavlovian associative learning, while female offspring displayed increased striatal and corpus callosum microglia activation. The F0 sperm sncRNA profile showed upregulation of miR-141-3p and miR-200a-3p among 29 dysregulated sncRNAs. These results are distinct from previous LMW poly I:C administration studies, demonstrating sperm epigenome changes and subsequent offspring phenotypes may be highly specific to particular immune pathways and activation states. Our present data provide new insights into how PIA may be able to modulate brain development and function. These new findings contribute to our understanding of how paternal viral-like immune activation affects sperm and offspring phenotypes, with implications for the future prevention of the detrimental effects of such epigenetic inheritance.

MicroRNAs (miRNAs) play crucial roles in regulating gene expression and have been implicated in the pathophysiology of depression. Among them, miR-124-3p is one of the most abundant brain-enriched miRNAs and has emerged as a potential therapeutic target for mood disorders. This study aimed to evaluate the antidepressant-like effects of an acute administration of miR-124-3p and to identify associated molecular and neuronal changes across key brain regions. Female C57BL/6 mice received intracerebroventricular injections of a miR-124-3p mimic or a control oligonucleotide. Affective-like behavioural responses were assessed using the Porsolt swim test (PST) and the light-dark box test (LDB). Proteomic alterations in the hippocampus, hypothalamus and prefrontal cortex were analysed by liquid chromatography-tandem mass spectrometry (LC-MS/MS), and stress-related neuronal activity was evaluated using c-Fos immunofluorescence. Mice treated with the miR-124-3p mimic exhibited reduced immobility in the PST, indicative of an antidepressant-like effect and enhanced active stress coping. Proteomic profiling revealed region-specific changes, including downregulation of immune- and stress-related proteins in the hypothalamus and hippocampus, and upregulation of synaptic and metabolic proteins in the prefrontal cortex. c-Fos analyses showed decreased stress-induced neuronal activation in the hypothalamic paraventricular and periventricular nuclei, alongside increased activity in the hippocampal dentate gyrus. Collectively, these findings suggest that miR-124-3p mimic treatment is associated with antidepressant-like effects by reducing neuroimmune activation and enhancing neuronal plasticity. Our results support a model in which miR-124-3p promotes stress resilience through coordinated modulation of inflammatory and plasticity-related processes across distinct brain circuits.

Paternal pre-conceptual exposure to pathogenic infection can alter offspring phenotypes via changes to sperm epigenetics, including small non-coding RNAs (ncRNAs). This phenomenon occurs even in the absence of infection when pathogen mimetics trigger paternal immune activation (PIA). While this implicates a shared component of the immune response, the specific mechanisms responsible remain unknown. Cytokines are a key component of innate immunity and are highly upregulated following exposure to both pathogens and their mimetics. Here we investigate whether paternal administration of the pro-inflammatory cytokines interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α) recapitulates alterations to sperm small ncRNAs and offspring phenotypic changes from other models of PIA. C57BL/6J male mice were administered a single dose of IL-1β, TNF-α, or vehicle, prior to mating with naïve female mice, to produce offspring. Offspring from IL-1β-treated fathers exhibited altered fasting responses and female-specific alterations to stress-coping behavior. In response to paternal TNF-α, male offspring showed increased anxiety-like behavior. Analysis of paternal sperm small ncRNA revealed that IL-1β significantly downregulated several transfer RNA-derived small RNAs (tsRNAs) and P-element-induced wimpy testis (PIWI)-interacting RNA (piRNA) clusters. Surprisingly, paternal TNF-α only slightly altered small ncRNAs, downregulating a single piRNA cluster. These results partially recapitulate offspring phenotypic changes following paternal exposure to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2, in a COVID-19 mouse model) and polyinosinic:polycytidylic acid (poly I:C, a viral mimetic). Ultimately, we provide the first evidence that cytokines have intergenerational effects on brain and behavior, and that they contribute to altered offspring phenotypes in viral-like PIA. This study demonstrates that paternal cytokines are causally involved in a mechanism of epigenetic inheritance following PIA, and highlights the importance of PIA as a pre-conceptual factor that may modulate offspring health, including risk of neuropsychiatric disorders.

Psilocybin is a serotonergic psychedelic drug with emerging therapeutic applications, yet its actions under glutamatergic dysfunction, and relevance to schizophrenia and associated psychiatric disorders, remain unclear. We examined the acute and long-lasting effects of psilocybin (1 mg/kg, intraperitoneal) on behavioral and neural outcomes in the metabotropic glutamate receptor 5 (mGlu5) knockout (KO) mouse model of schizophrenia. The mGlu5 KO mice displayed psilocybin-induced hyperlocomotion, whereas wild-type (WT) mice did not. Additionally, male mGlu5 KO mice showed an amplified psilocybin-induced head-twitch response (HTR) compared with WT males, consistent with sex-dependent enhancement of 5-HT2A receptor-mediated signaling. Acute psilocybin increased c-Fos expression in the claustrum of WT but not KO mice, suggesting intact mGlu5 signaling is required for psilocybin-evoked claustral recruitment. Psilocybin did not alter anxiety-like behavior in the light-dark box and increased immobility time in the Porsolt test. Strikingly, psilocybin produced a sustained normalization in prepulse inhibition (a measure of sensorimotor gating) in female KO mice, evident nine days after treatment. Together, these findings indicate that disrupted mGlu5 signaling amplifies acute responses to psilocybin and reveals a sex-dependent long-term effect on sensorimotor gating. These results refine understanding of glutamatergic-serotonergic interactions and motivate further work evaluating psilocybin across schizophrenia-relevant endophenotypes.

Neurofibromatosis type 1 (NF1) is a genetic condition presenting with variable symptomatology, however most individuals will demonstrate cognitive and behavioural difficulties, including autism. Using a heterozygous germline knockout mouse model of NF1 (Nf1 +/-), we performed in-depth behavioural evaluations encompassing learning and memory, stereotypy, social interaction, anxiety- and depression-like behaviour. Anatomical and functional studies of the brain and gastrointestinal tract were followed by the first investigation of gut microbiota composition (via full-length 16S rRNA sequencing) in a Nf1 +/- mouse model. The cognitive and autism-like behavioural phenotype seen in Nf1 +/- mice was accompanied by a striking increase in relative brain size which is highly relevant to clinical NF1. Furthermore, brain size was correlated with behaviour, supporting a potential mechanistic link. Nf1 +/- mice showed significant alterations in gut microbiota composition vs. Nf1 +/+ wild-type controls, with males additionally showing significant changes to species abundance of the Clostridium and Blautia genera, and the Lachnospiraceae family, findings which partially overlap with those in preclinical and clinical autism. Composition of associated functional pathways was not globally altered, however +/- mice showed significant changes in a pyrimidine deoxynucleotide biosynthesis pathway. In male Nf1 +/- mice, we also identified a genotype-specific host-microbial signature, pointing towards a mechanistic link between gut microbiome composition and brain size. These findings significantly expand our understanding of brain and behavioural abnormalities in this preclinical model of NF1 and, importantly, have uncovered the gut microbiome as a highly promising new area of research and a potential therapeutic target for these symptom clusters.

Background and Hypothesis The metabotropic glutamate 5 (mGlu5) receptor is a potential therapeutic target for psychiatric disorders, including schizophrenia and substance use disorders. Indeed, mGlu5 is expressed in forebrain regions (eg, striatum, prefrontal cortex), and mGlu5 modulates N-methyl-D-aspartate receptor function and second messenger signaling. Also, male mice lacking mGlu5 display schizophrenia-like and substance use-relevant behaviors. However, there are limited investigations of sex differences or gene-dose effects in this model.Study Designs We evaluated schizophrenia-relevant and cocaine reward-relevant behaviors in adult male and female mice with heterozygous (mGlu5 HET) and homozygous (mGlu5 HOMO) mGlu5 deletion and their wildtype-like (WT) littermates. We assessed locomotion and exploration, anxiety, sensorimotor gating, novel object recognition, fear conditioning, social interaction, cocaine sensitization, and cocaine-conditioned place preference. We also examined fear memory generalization.Study Results mGlu5 HOMO mice of both sexes showed hyperlocomotion and anxiolytic-like behavior in the open field, as well as enhanced cocaine sensitization and persistent cocaine place preference. When tested for memory generalization, mGlu5 HOMO mice exhibited greater freezing to a novel context, suggesting overgeneralization of fear in these mice. mGlu5 HOMO females showed reduced sensorimotor gating. mGlu5 HET mice of both sexes showed a largely similar phenotype to sex-matched WT controls.Conclusions Our data demonstrate schizophrenia- and drug use-relevant phenotypes in mGlu5 HOMO mice, some of which are sex-dependent. These phenotypes do not occur in mGlu5 HET males and females. We also show for the first time an overgeneralization phenotype in mGlu5 HOMO mice, which may be related to poor contextual discrimination.

Pathogenic variants in one allele of the KAT6A gene encoding the histone acetyltransferase KAT6A (MOZ, MYST3) cause Arboleda-Tham syndrome (ARTHS), characterised by developmental delay, cognitive impairment, and autism-like behaviours. As histone acetylation is reversible, and brain development continues after birth, treatments that address deficits in histone acetylation may ameliorate the condition. Here, we examined the effects of ARTHS mutations on histone acetylation in human cells and the effects of heterozygous loss of Kat6a in mice (Kat6a+/-) on learning, memory, activity, and sociability. We found that KAT6A was required for normal levels of histone H3 lysine 23 acetylation (H3K23ac) in human cells and mouse brain. Kat6a+/- mice displayed hyperactivity and learning, memory, and sociability deficits compared with WT mice. Treatment with the acetyl-donor, acetyl-L-carnitine (ALCAR) resulted in the rescue of H3K23ac levels in mouse brain and amelioration of the hyperactivity and learning impairments. Our results suggest that some individuals with ARTHS might benefit from ALCAR treatment. However, the suitability of ALCAR treatment would depend on the specific KAT6A variant and should be discussed with health professionals.

The paternal pre-conception environment has been demonstrated in preclinical models to alter the sperm epigenome and offspring phenotypes. Recent studies have reported that modulating the paternal gut microbiota through non-absorbable antibiotics altered offspring body weight, survival, brain transcriptomics and behaviour. Other paternal environmental factors including diet composition, stress and pollutant exposure have also been shown to alter the paternal gut microbiome. This review discusses current evidence on the role of the paternal gut microbiome in epigenetic inheritance and explores its potential as a target to prevent alterations in the sperm epigenome and subsequent detrimental effects on offspring outcomes. This nascent research field (at the nexus of microbiology, epigenetics and neuroscience) will facilitate the prevention and treatment of the growing challenge of ‘intergenerational epigenopathy’ in a rapidly changing world.

Background and Hypothesis Schizophrenia is a devastating psychiatric disorder characterized by positive (eg, hallucinations) and negative (eg, reduced motivation) symptoms, and cognitive deficits. Chronic gastrointestinal tract issues exist as comorbid symptoms of schizophrenia. Recent findings indicate the involvement of the microorganisms that inhabit the gut, the microbiota (and the broader microbiome which also includes microbial genomes, etc.) in schizophrenia pathogenesis. In the present study, we hypothesized that chronic administration with prebiotics fructooligosaccharide and galactooligosaccharide (FOS and GOS; a combination used clinically for other disorders) would restore gut microbiome composition of the metabotropic glutamate receptor 5 (mGlu5) knockout (KO) mouse model of schizophrenia, which we previously demonstrated to exhibit gut dysbiosis. Study Design We assessed the impact of prebiotics on gut microbiome composition and function, as well as the gastrointestinal function and schizophrenia-like phenotype of mGlu5 KO mice and wild-type littermates. We administered a combination of the prebiotics FOS and GOS, vs vehicle control administration, in both the mouse model of schizophrenia and wild-type littermates. Study Results The present study firstly corroborated the altered gut microbiome composition in the mGlu5 KO mouse model of schizophrenia. Importantly, we have revealed an altered microbial metabolic profile. We have also shown that the prebiotics we administered were not only able to rescue these gut microbiome changes but also had additional beneficial effects including cognitive enhancement and improved gastrointestinal function. Conclusion These preclinical findings indicate that prebiotics, such as the combination of FOS and GOS used in the present study, may have therapeutic potential in schizophrenia as an add-on intervention with an exceptional safety profile.

Huntington's disease (HD) is an autosomal dominant neurodegenerative disorder featuring abnormal cognition, psychiatric symptoms, movement, and gastrointestinal function. It is caused by a tandem-repeat gene mutation encoding an expanded polyglutamine tract in the huntingtin protein. Our group was the first to demonstrate gut microbial disruption in both clinical HD cohorts and validated preclinical models, supporting a role for microbiota-gut-brain axis dysfunction in HD. The NLRP3 inflammasome, a key innate immune sensor that integrates microbial, metabolic, and host-derived danger signals, has been implicated in HD pathology. However, its contribution to gut health and microbiota-linked cognitive deficits in HD remains unknown. This study addressed this critical gap by investigating whether targeting NLRP3 can restore gut and brain health in HD through modulation of the microbiota-gut-brain axis. We aimed to investigate the role of the NLRP3 inflammasome in microbiota-gut-brain axis dysfunction by targeting its inhibition. Here, we assessed whether inhibiting NLRP3 can ameliorate cognitive deficits, gut abnormalities, gut microbial alteration, and associated molecular and behavioural disturbances in HD. NLRP3 inflammasome inhibitor MCC950 was administered to R6/1 transgenic HD mice and their wild-type (WT) littermate controls from 6 to 20 weeks of age. Cognitive and behavioural performance was evaluated using validated tests, alongside assessments of general health and gut function. HD mice exhibited reduced body and brain weight, increased fluid consumption, memory impairments, motor deficits, exacerbated gastrointestinal phenotype, and altered gut microbiota. Treatment with MCC950 did not affect body or brain weight, cognitive and motor performance, and it also did not affect the gut microbial profile of HD mice. However, MCC950 significantly rescued gut health, as evidenced by increased faecal output (in females) and water content (in both males and females), improved stool consistency (in both sexes), and ameliorated macroscopic gut abnormalities. Our findings highlight a promising therapeutic avenue for addressing the significant gastrointestinal anomalies observed in HD. By targeting the NLRP3 inflammasome in R6/1 HD mice, we have identified a novel strategy to improve gut health. These results support further investigation of inflammasome inhibition as a means to alleviate central and peripheral symptoms in HD and improve overall disease management.

Neurodegenerative diseases are characterized by a variety of pathogenic processes, including various forms of protein aggregation that disrupt neural homeostasis and ultimately lead to functional decline. With an aging population, the prevalence and associated economic burden of these diseases are expected to rise dramatically, underscoring the urgent need for effective therapies. Protein aggregation, a hallmark of Alzheimer’s disease (AD), Parkinson’s disease (PD) and Huntington’s disease (HD), activates microglia, the brain’s resident immune cells. While microglia help maintain homeostasis, their overactivation exacerbates synaptic loss and network disruption, making them key players in neurodegenerative pathology and potential therapeutic targets. Environmental enrichment (EE), a laboratory paradigm that enhances experience-dependent plasticity through physical, sensory and cognitive stimulation, has been shown to produce beneficial molecular, cellular, and behavioural outcomes in rodent models of neurodegeneration, including modulation of microglial activity. This review highlights current findings on the effects of EE on microglia across different neurodegenerative diseases. However, collective results remain limited due to variations in EE paradigms such as differences in duration, timing, and enrichment setup, which hinder direct comparisons. Moreover, most studies have focused on AD, with far fewer investigations in other neurodegenerative conditions. Current findings are largely descriptive, examining microglial density, activation state, morphology, and gene expression, without establishing causative relationships. Future research should determine whether microglial depletion alters the beneficial effects of EE, thereby clarifying the complex interplay between EE, microglia, and neurodegenerative pathology. Such studies will be essential for identifying therapeutic strategies that harness EE to modulate microglia, delay pathogenesis and mitigate disease progression.

Given that the SARS-CoV-2 virus, and the COVID-19 pandemic, constitutes a major environmental challenge faced by billions of people worldwide, we investigated whether paternal pre-conceptual SARS-CoV-2 infection has impacts on sperm RNA content, and intergenerational (F1) and transgenerational (F2) effects on offspring phenotypes. Using an established mouse-adapted SARS-CoV-2 (P21) preclinical model, we infected adult male mice with the virus, or performed a mock control infection, and bred them with naïve female mice four weeks later, when males were no longer infectious. Here we show that offspring of infected sires display increased anxiety-like behaviors. Additionally, the F1 offspring have significant transcriptomic changes in their hippocampus. Various sperm small noncoding RNAs, including PIWI-interacting RNAs, transfer-derived RNAs and microRNAs, are differentially altered by prior paternal SARS-CoV-2 infection. Microinjection of RNA from the sperm of SARS-CoV-2 infected males into fertilized oocytes leads to a phenotype resembling that of the naturally born F1 offspring, supporting the interpretation that sperm RNAs are contributing to the outcomes of our paternal SARS-CoV-2 model. Therefore, this study provides evidence that paternal SARS-CoV-2 infection impacts sperm and affects offspring phenotypes. These findings have public-health implications and inform further research in males affected by COVID-19, and their offspring.

Psilocybin, a serotonergic compound that produces psychedelic effects primarily through activation of the 5-HT2A receptor, has shown promise in treating neuropsychiatric conditions, including obsessive-compulsive disorder (OCD). However, the effects of chronic psilocybin administration on gut function, microbiota, and behavioural phenotypes remain understudied. The present study investigated the effects of chronic psilocybin (0.1 and 1 mg/kg, oral gavage) on gut and behavioural measures in wild-type (WT) and SAPAP3 knockout (KO) mice, a model of OCD-like phenotypes. We present novel evidence that SAPAP3 KO mice exhibit social deficits, and that chronic psilocybin increases sociability in male WT mice. Although no therapeutic effects were observed at either dose on anxiety-, compulsive-, or depressive-like behaviour, chronic psilocybin also did not induce psychosis-like behaviours. A dose-dependent effect of psilocybin was observed on gut motility. Although chronic administration did not significantly alter overall gut microbiome diversity, reductions in Lactobacillus murinus, Lactobacillus animalis, and Alistipes dispar were observed in male WT mice, but not in KO mice or female mice. Integrative analysis revealed that a microbial cluster, comprising Lactobacillus and Alistipes species, correlated with locomotion, head-twitch response and gut motility, effectively differentiating psilocybin-treated mice from vehicle controls. This suggests a potential host-microbiome feedback mechanism regulating host serotonin signalling, linked to central and peripheral 5-HT2A receptor activation. Additionally, separate microbial clusters were associated with startle response and sociability, indicating that psilocybin may engage distinct neural pathways to mediate these behaviours. These findings highlight the importance of considering the microbiome and sex in future psychedelic research and open new avenues for exploring the microbiota-gut-brain axis as a target for future therapeutic strategies.

The COVID-19 pandemic caused by the coronavirus SARS-CoV-2 has highlighted the vulnerability of a globally connected population to zoonotic viruses. The FDA-approved coronavirus antiviral Paxlovid targets the essential SARS-CoV-2 main protease, Mpro. Whilst effective in the acute phase of a COVID infection, Paxlovid cannot be used by all patients, can lead to viral recurrence, and does not protect against post-acute sequelae of COVID-19 (PASC), commonly known as long COVID, an emerging significant health burden that remains poorly understood and untreated. Alternative antivirals that are addressing broader patient needs are urgently required. We here report our drug discovery efforts to target PLpro, a further essential coronaviral protease, for which we report a novel chemical scaffold that targets SARS-CoV-2 PLpro with low nanomolar activity, and which exhibits activity against PLpro of other pathogenic coronaviruses. Our lead compound shows excellent in vivo efficacy in a mouse model of severe acute disease. Importantly, our mouse model recapitulates long-term pathologies matching closely those seen in PASC patients. Our lead compound offers protection against a range of PASC symptoms in this model, prevents lung pathology and reduces brain dysfunction. This provides proof-of-principle that PLpro inhibition may have clinical relevance for PASC prevention and treatment going forward.

Recent decades have revealed increasing evidence for epigenetic inheritance through paternal environmental exposures and experiences, affecting offspring health outcomes across diverse species. Key epigenetic mediators in sperm may include DNA methylation, chromatin modifications, as well as small and long non-coding (nc)RNAs. Identified environmental influences extend beyond lifestyle factors (e.g., exercise, diet, alcohol, and nicotine use) to include stress, infections, pollutants, and other toxins. Evidence from humans, rodents, and other species suggests that various paternal exposures before conception substantially shape the phenotypes in offspring, via developmental modulation, including changes to brain and behavior, metabolism, endocrinology, and physiology. These findings raise concerns regarding human epigenetic inheritance, because the relevant environmental exposures have changed significantly in recent decades, potentially increasing the risk of future generations for various disorders (‘transgenerational epigenopathy’). Here, we integrate evidence for paternal environmental exposures affecting offspring phenotypes, and associated epigenetic mechanisms, critically discussing potential implications for medicine and other scientific fields.

In pursuit of excellence in scholarly publishing, the Neuroscience editorial team shares valuable insights that are essential for authors, reviewers, and the broader scientific community. Firstly, we emphasize that impactful research is built on rigorous study design and execution. Beyond fundamental methodological safeguards such as randomization and blinded analysis, we highlight the importance of thoughtfully selecting study models, with deliberate attention to biological variables like sex and gender, as well as appropriate nomenclature. Secondly, as technological innovations reshape research landscapes, we advocate for combining methodological rigor with suitable analytical tools to ensure robust data collection and transparent reporting. Thirdly, for manuscripts reaching the revision stage, we frame the response to reviewers as a strategic process that requires objectivity, diplomacy, and evidence-based rebuttals where necessary. Finally, we call for intentional prioritization of inclusivity and diversity across all stages of scientific inquiry - from laboratory collaborations to editorial decisions - and urge stakeholders to actively counteract implicit biases in manuscript evaluation and citation practices. By embedding these principles into the scientific workflow, we argue that the research community can foster not only greater rigor but also a more equitable and innovative scholarly ecosystem.

Psilocybin is a serotonergic psychedelic with growing evidence for efficacy in mood disorders, and its therapeutic potential in obsessive—compulsive disorder (OCD) and related conditions is increasingly recognised but remains understudied. We systematically evaluated clinical and preclinical evidence on psilocybin's effects on obsessive and compulsive behaviours with attention to translational relevance. A systematic search identified 13 eligible studies (4 clinical trials and 9 preclinical investigations examining psilocybin or psilocin on obsessive—compulsive symptoms or behaviours), and reporting followed Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. In clinical studies, single doses of psilocybin led to rapid reductions in obsessive-compulsive symptoms, including in patients with OCD and body dysmorphic disorder. In wild-type mice, psilocybin acutely decreased marble-burying behaviour, although this effect was transient and not observed beyond the first day after administration. In contrast, in SAPAP3 knockout mice—a validated genetic model of compulsive behaviour—a single administration of psilocybin produced robust, enduring reductions in excessive grooming, and these lasting anti-compulsive effects were replicated across independent laboratories and doses. Additionally, chronic hallucinogenic doses of psilocybin did not improve anxiety-like or compulsive-like behaviour in SAPAP3 knockout mice; however, a separate study in Long—Evans rats found that chronic sub-hallucinogenic psilocybin reduced self-grooming and enhanced expression of synaptic markers in the paraventricular thalamus. Together, the evidence suggests that psilocybin transiently reduces obsessive—compulsive symptoms in clinical populations and produces lasting anti-compulsive effects in validated animal models. Future clinical studies should include larger placebo-controlled trials and incorporate neuroimaging to assess psilocybin's impact on fronto-striatal circuitry implicated in OCD pathophysiology.

The paternal environment prior to conception has been demonstrated to influence offspring physiology and behavior, with the sperm epigenome (including noncoding RNAs) proposed as a potential facilitator of nongenetic inheritance. Whilst the maternal gut microbiome has been established as an important influence on offspring development, the impact of the paternal gut microbiome on offspring development, health and behavior is largely unknown. Gut microbiota have major influences on immunity, and thus we hypothesized that they may be relevant to paternal immune activation (PIA) modulating epigenetic inheritance in mice. Therefore, male C57BL/6J mice (F0) were orally administered non-absorbable antibiotics via drinking water in order to substantially deplete their gut microbiome. Four weeks after administration of the antibiotics (gut microbiome depletion), F0 male mice were then mated with na & iuml;ve female mice. The F1 offspring of the microbiome-depleted males had reduced body weight as well as altered gut morphology (shortened colon length). F1 females showed significant alterations in affective behaviors, including measures of anxiety and depressive-like behaviors, indicating altered development. Analysis of small noncoding RNAs in the sperm of F0 mice revealed that gut microbiome depletion is associated with differential expression of 8 different PIWI-interacting RNAs (piRNAs), each of which has the potential to modulate the expression of multiple downstream gene targets, and thus influence epigenetic inheritance and offspring development. This study demonstrates that the gut-germline axis influences sperm small RNA profiles and offspring physiology, with specific impacts on offspring affective and/or coping behaviors. These findings may have broader implications for other animal species with comparable gut microbiota, intergenerational epigenetics and developmental biology, including humans.