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Aggressive and non-aggressive dogs differ in beta-diversity using the weighted UniFrac metric. Visualization of the phylogenetic differences in fecal microbiota of aggressive (green) and nonaggressive (purple) dogs using principal coordinates analysis (PCoA) of OTU abundances and weighted UniFrac distance. The separation between aggressive and non-aggressive samples in the PCoA plot was confirmed with an environmental fit analysis (p = 0.0250, R 2 = 0.1297), which supports aggression status as being a variable that is separating the microbial composition of the samples. The gut microbiome structure of aggressive and non-aggressive dogs is also significantly different with the weighted UniFrac metric using PERMANOVA (p = 0.0346, R 2 = 0.0349). Ellipses are based on 95% confidence intervals and standard error. Full-size DOI: 10.7717/peerj.6103/fig-1
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Aggression is a serious behavioral disorder in domestic dogs that endangers both dogs and humans. The underlying causes of canine aggression are poorly resolved and require illumination to ensure effective therapy. Recent research links the compositional diversity of the gut microbiome to behavioral and psychological regulation in other mammals, su...
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... microbial composition between aggressive and non-aggressive dogs, we compared stool microbiomes that were sampled from 21 aggressive dogs and 10 non-aggressive dogs. A Principal Coordinates Analysis (PCoA) using the weighted UniFrac metric shows separation of the aggressive and non-aggressive samples based on 95% confidence interval ellipses ( Fig. 1; Figs. S1; S2). The separation between aggressive and non-aggressive samples in the PCoA plot was confirmed by environmental fit (p = 0.0250, R 2 = 0.1297) and PERMANOVA (p = 0.0346, R 2 = 0.0349) analyses. Alternative measures of beta-diversity marginally support these results. For example, using a Bray-Curtis dissimilarity metric finds a similar ...
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The microbes in the gut and the chemicals they produce by metabolism have been linked to brain function. In earlier work, we showed that infection with two viruses, HIV and HCV, changed the gut microbes and metabolism in ways that were associated with a lifetime history of major depressive disorder. Here, we extend this analysis looking at a measur...
Citations
... Specifically, five studies detected an increase related to the genus Bacteroides [39] or specific species within the genus [35,[41][42][43], the most common of which was B. uniformis. Similarly, a study comparing the gut microbiota composition of aggressive and non-aggressive dogs determined a different abundance of members of the genus Bacteroides in these two groups [56]. In some studies, the increased levels of the genus Bacteroides were associated with neuropsychiatric diseases such as major depressive disorder and autism spectrum disease [57,58]. ...
The impact of the microbiome on brain function and behavior has recently become an important research topic. We searched for a link between the gut microbiome and impulsive and violent behavior. We focused on critical factors influencing the microbiome establishment that may affect human health later in life, i.e., delivery mode, early-life feeding, and early antibiotic exposure. We searched PubMed, Web of Science, and the Cochrane Library. We included original human studies examining adults and children with impulsive and/or violent behavior that assessed the gut microbiota composition of participants, delivery mode, infant feeding mode, or early antibiotic exposure. Bibliographic searches yielded 429 articles, and 21 met the eligibility criteria. Two studies reported data on patients with schizophrenia with violent behavior, while 19 studies reported data on patients with attention-deficit hyperactivity disorder (ADHD). The results showed several bacterial taxa associated with ADHD symptomatology and with violent behavior in patients with schizophrenia. No association was found between delivery mode and impulsive behavior, nor did any articles relate infant feeding mode to violent human behavior. Those studies investigating early antibiotic exposure yielded ambiguous results. The heterogeneity of the data and the different methodologies of the included studies limited the external validity of the results. We found few studies that addressed the possible microbiome involvement in the pathophysiology of impulsive and violent behavior in humans. Our review revealed a gap in knowledge regarding links between the gut microbiome and these extreme behavioral patterns.
... Gut dysbacteriosis with leaky gut seems to play a vital role in the pathophysiology. Even though there are four animal-based studies revealing the link between aggressive behaviors and gut microbiota [22][23][24][25], only one patient-based clinical study preliminarily pointed to the possible correlation among aggression onset and gut dysbacteriosis [26]. In this study enrolling 42 ScZ patients (26 with violence and 16 without violence) without antipsychotics discontinuation before samples collecting, no significantly statistical difference in fecal microbiota richness, α-diversity and β-diversity were presented between the two groups [26]. ...
Background
The pathophysiological mechanisms of aggression are manifold and they may closely interconnect. Current study aimed to determine the gut microbiota and its metabolites, and clarify their correlations with inflammation, oxidation, leaky gut and clinical profiles underlying aggression in schizophrenia (ScZ).
Methods
Serum and stool specimens from ScZ inpatients with (ScZ-Ag, 25 cases) and without aggression (NScZ-Ag, 25 cases) were collected. Systemic inflammation, oxidation and leaky gut biomarkers were determined by ELISA, gut microbiota by 16S rRNA sequencing, short-chain fatty acids (SCFAs) by gas chromatography-mass spectrometry analysis and neurotransmitters by liquid chromatograph mass spectrometry analysis.
Results
Significantly higher systemic pro-inflammation, pro-oxidation and leaky gut biomarkers were observed in ScZ-Ag than NScZ-Ag group (all P<0.001). Compared to NScZ-Ag group, the alpha-diversity and evenness of fecal bacterial community were much lower, the abundance of fecal genera Prevotella was significantly increased, while that Bacteroides, Faecalibacterium, Blautia, Bifidobacterium,Collinsella and Eubacterium_coprostanoligenes were remarkably reduced in ScZ-Ag group (all corrected P<0.001). Meanwhile, 6 SCFAs and 6 neurotransmitters were much lower in ScZ-Ag group (all P<0.05). Finally, a few strongly positive or negative correlations among altered gut microbiota, SCFAs, systemic pro-inflammation, leaky gut, pro-oxidation and aggression severity were detected.
Conclusions
These results demonstrate that pro-inflammation, pro-oxidation and leaky gut phenotypes relating to enteric dysbacteriosis and microbial SCFAs feature the aggression onset or severity in ScZ individuals.
... Evidence from animal model studies also reveals support for a relationship between aggressive behavior and alterations in the gut microbiota. Recently, two small studies found that the composition of the gut microbiome is associated with aggressive behavior in dogs(Kirchoff et al., 2019;Mondo et al., 2020).Researchers studying Siberian hamsters took a step further on the path from establishing correlation to figuring out causation: they investigated how manipulation of the hamsters' microbiome affected these animals' aggressive behavior(Ren et al., 2020;Sylvia et al., 2017).Sylvia et al. (2017) hypothesized that a broad-spectrum antibiotic treatment-in this case enrofloxacin-would manipulate the gut microbiome and potentially affect social behavior in male and female hamsters. After administering repeated antibiotic treatments, the male hamsters showed a decrease in aggressive behavior, but their levels of aggression returned to normal after recovery. ...
Research in biosocial criminology and other related disciplines has established links between nutrition and aggressive behavior. In addition to observational studies, randomized trials of nutritional supplements like vitamins, omega‐3 fatty acids, and folic acid provide evidence of the dietary impact on aggression. However, the exact mechanism of the diet‐aggression link is not well understood. The current article proposes that the gut microbiome plays an important role in the process, with the microbiota–gut–brain axis serving as such a mediating mechanism between diet and behavior. Based on animal and human studies, this review synthesizes a wide array of research across several academic fields: from the effects of dietary interventions on aggression, to the results of microbiota transplantation on socioemotional and behavioral outcomes, to the connections between early adversity, stress, microbiome, and aggression. Possibilities for integrating the microbiotic perspective with the more traditional, sociologically oriented theories in criminology are discussed, using social disorganization and self‐control theories as examples. To extend the existing lines of research further, the article considers harnessing the experimental potential of noninvasive and low‐cost dietary interventions to help establish the causal impact of the gut microbiome on aggressive behavior, while adhering to the high ethical standards and modern research requirements. Implications of this research for criminal justice policy and practice are essential: not only can it help determine whether the improved gut microbiome functioning moderates aggressive and violent behavior but also provide ways to prevent and reduce such behavior, alone or in combination with other crime prevention programs.
... While there have been intriguing studies from lab animal models showing a potential connection between the gut microbiome and behavior or mental health, implicating the socalled "gut-brain axis" 1,2 , there is a dearth of studies investigating the microbiome-behavior relationship in working dogs. Some recent small-scale studies in non-working dogs have found that undesirable canine behaviors (i.e., aggression, anxiety) are associated with certain characteristics of the canine gut microbiome 3,4 . However, it is critical to note when thinking about the microbiome's impact on behavior that the behavioral traits of working dogs and companion dogs have critical differences 5 . ...
... Microbiome markers were also statistically associated with motivation, aggression, cowardice, sociability, and obedience to one trainer vs many, and some of these associations agree with findings in previous studies 3,4,28 . When prediction models were developed with machine learning, the best models were for motivation, sociability, and GI issues, whereas the models that did not show predictive capability were for job performance and stress levels. ...
Dogs have a key role in law enforcement and military work, and research with the goal of improving working dog performance is ongoing. While there have been intriguing studies from lab animal models showing a potential connection between the gut microbiome and behavior or mental health there is a dearth of studies investigating the microbiome-behavior relationship in working dogs. The overall objective of this study was to characterize the microbiota of working dogs and to determine if the composition of the microbiota is associated with behavioral and performance outcomes. Freshly passed stools from each working canine (Total n = 134) were collected and subject to shotgun metagenomic sequencing using Illumina technology. Behavior, performance, and demographic metadata were collected. Descriptive statistics and prediction models of behavioral/phenotypic outcomes using gradient boosting classification based on Xgboost were used to study associations between the microbiome and outcomes. Regarding machine learning methodology, only microbiome features were used for training and predictors were estimated in cross-validation. Microbiome markers were statistically associated with motivation, aggression, cowardice/hesitation, sociability, obedience to one trainer vs many, and body condition score (BCS). When prediction models were developed based on machine learning, moderate predictive power was observed for motivation, sociability, and gastrointestinal issues. Findings from this study suggest potential gut microbiome markers of performance and could potentially advance care for working canines.
... Behavior abnormalities such as aggressiveness are most frequently observed in mentally stressed dogs that present anxiety disorders, which indicates imbalance in the gut microbial composition [68]. Indeed, transferring gut microbiota also transforms the mood of the donor. ...
Fecal microbiota transplantation (FMT) is an emerging therapeutic option for a variety of diseases, and is characterized as the transfer of fecal microorganisms from a healthy donor into the intestinal tract of a diseased recipient. In human clinics, FMT has been used for treating diseases for decades, with promising results. In recent years, veterinary specialists adapted FMT in canine patients; however, compared to humans, canine FMT is more inclined towards research purposes than practical applications in most cases, due to safety concerns. Therefore, in order to facilitate the application of fecal transplant therapy in dogs, in this paper, we review recent applications of FMT in canine clinical treatments, as well as possible mechanisms that are involved in the process of the therapeutic effect of FMT. More research is needed to explore more effective and safer approaches for conducting FMT in dogs.
... Previous studies have confirmed that the microbiota plays a role in gut-brain communication and subsequent behavior (Fischer et al., 2017;Nicholson et al., 2012;Sharon et al., 2010). Research specifically related to aggression is limited, but there is evidence of microbiota differences between aggressive and non-aggressive dogs (Kirchoff et al., 2019). Studies examining effects of antibiotics or germ-free conditions on host aggression in flies (Jia et al., 2021), mice (Watanabe et al., 2021), and hamsters (Sylvia et al., 2017) provide contradicting results, but there is evidence that Wolbachia infection in flies can increase aggression (Rohrscheib et al., 2015). ...
Aggression is a behavior common in most species; it is controlled by internal and external drivers, including hormones, environmental cues, and social interactions, and underlying pathways are understood in a broad range of species. To date, though, effects of gut microbiota on aggression in the context of gut-brain communication and social behavior have not been completely elucidated. We examine how manipulation of Drosophila melanogaster microbiota affects aggression as well as the pathways that underly the behavior in this species. Males flies treated with antibiotics exhibited significantly more aggressive behaviors. Furthermore, they had higher levels of cVA and (Z)-9 Tricosene, pheromones associated with aggression in flies, as well as higher expression of the relevant pheromone receptors and transporters OR67d, OR83b, GR32a, and LUSH. These findings suggest that aggressive behavior is, at least in part, mediated by bacterial species in flies.
... They could serve as a model of spontaneous pathologies for investigating new therapeutic pathways. In particular, Kirchoff et al. studied a cohort of 21 conspecifically aggressive dogs and showed that the composition of the gut microbiota differed between aggressive and non-aggressive dogs [123]. More precisely, Proteobacteria and Fusobacteria displayed greater relative abundances in samples from non-aggressive animals, whereas Firmicutes were more abundant in samples from aggressive dogs. ...
Accumulating data show the involvement of intestinal microbiota in the development and maintenance of numerous diseases. Many environmental factors influence the composition and function of the gut microbiota. An animal model subjected to the same environmental constraints that will allow better characterization of the microbiota–host dialogue is awaited. The domestic dog has physiological, dietary and pathological characteristics similar to those of humans and shares the domestic environment and lifestyle of its owner. This review exposes how the domestication of dogs has brought them closer to humans based on their intrinsic and extrinsic similarities which were discerned through examining and comparing the current knowledge and data on the intestinal microbiota of humans and canines in the context of several spontaneous pathologies, including inflammatory bowel disease, obesity and diabetes mellitus.
... They could serve as a model of spontaneous pathologies for investigating new therapeutic pathways. In particular, Kirchoff et al. studied a cohort of 21 conspecifically aggressive dogs and showed that the composition of the gut microbiota differed between aggressive and non-aggressive dogs [123]. More precisely, Proteobacteria and Fusobacteria displayed greater relative abundances in samples from non-aggressive animals, whereas Firmicutes were more abundant in samples from aggressive dogs. ...
... A nutraceutical diet could positively affect the neuroendocrine parameters in dogs with behavioral problems (Sechi et al., 2017). A study targeting a small population of rescued dogs has found that the conspecific aggression was correlated to the gut microbiome (Kirchoff et al., 2019). Nevertheless, to our knowledge, there are rare scientific literatures available regarding the influences of probiotics on canine behaviors. ...
Certain strains of Lactiplantibacillus were found to have a positive impact on host neuromodulation through the gut-brain axis and thus ameliorate emotional and behavioral problems. A number of researches have been performed on humans, mice and rats; however, studies on dogs are limited. Forty-five dogs with behavioral problems were enrolled in this study, including aggression (n=22), separation anxiety (n=15), compulsive disorder (n=7) and unclassifiable inappropriate behavior (n=1, excessive barking). The behavioral diagnosis was made based on the primary behavioral consultation questionnaires and the careful interrogations at interviews. Lactiplantibacillus plantarum PS128 (PS128) probiotic was administered to these physically healthy dogs with behavioral problems over a course of two weeks to determine the probiotic effectiveness on canine behaviors. Dogs were evaluated and scored using the Evaluation of Dog’s Emotional and cognitive Disorders (EDED) scale and the Canine Behavioral Checklist (CBC) questionnaire at the visits before and after the probiotic treatment. Plasma serotonin levels were measured using high-performance liquid chromatography- electrochemical detection (HPLC-ECD) and the serotonin turnover ratios (5-HIAA/5-HT) were compared pre- and post-treatment. The results showed that the general behavioral stability was improved, and the problems of aggression and separation anxiety were ameliorated after treatment. A significant decrease in 5-HIAA/5-HT ratio was observed in dogs with separation anxiety, suggesting a serotonin-related mechanism. These results proved that PS128 was beneficial for emotional stabilization, which might be useful as a therapeutic supplement for canine aggression and separation anxiety.
... Another important aspect of nutrition is the ability to influence the microbiome of the digestive system. Recent studies link the diversity of the composition of the gut microbiome with behavioral and psychological regulation in other mammals such as mice and humans, including aggressive behavior [88][89][90][91]. A study by Kirchoff et al. [91] on dogs of the pit bull type showed a correlation between the composition of the digestive system microbiome and the incidence of aggression in dogs. ...
Aggression as a behavior is not always desirable, often ends in abandonment and/or
euthanasia. However, it is possible to prevent the occurrence of unwanted aggression in domestic dogs. Aggression is not a fully understood phenomenon. In recent years, many studies have focused on the influence of diet and physiology (including the endocrine system) on the emergence of behavioral disorders. In particular, the emphasis was put on nutritional additives such as fatty acids, amino acids, and probiotics. In addition, the possibility of using neurocognition in the observation of abnormal behavior in dogs has also been discussed, which may allow for a more detailed determination of the basis of aggressive behavior in dogs. In this review, the concepts related to aggression and its potential causes have been gathered. In addition, the possible influence of diet and hormones on aggression in dogs has been discussed, as well as the application of neurocognition in the possibility of its diagnosis
