The Treasured Science review of how gut flora affects social behavior.

Social interaction includes a series of complex interactive behaviors, which can be cooperative, neutral or antagonistic.social interaction can promote mutually beneficial outcomes, such as division of labor, cooperative care and immunity enhancement. Of course, social interaction can also lead to negative outcomes, including aggression and coercion.in the colorful "animal kingdom", animals exhibit different social skills: some live in highly socialized cooperative groups such as primates, termites and bees, while others tend to live alone, such as bears.in 1973, Konrad Lorenz, Niko Tinbergen and Karl von Frisch won the Nobel Prize in physiology or medicine for their pioneering research on the genetic origin, development and social behavior patterns of mammals. Their work provides a basis for the assessment of various internal and external factors affecting social behavior.the efforts of numerous researchers have made us realize that a thorough and comprehensive understanding of the internal and external factors regulating social behavior is extremely important for revealing the mode of prosperity and development of individuals and groups, determining the reasons for the differences in communicative competence among different animals during the evolution of species, and even for elucidating the underlying causes of social behavior disorders.in clinical practice, some interesting phenomena have been found: more than 50% of patients with functional digestive diseases are associated with anxiety and depression, and most of them can achieve better therapeutic effect after being treated with psychotropic drugs; and the induction or aggravation of mental and psychological diseases is also related to digestive system diseases [1].based on this phenomenon and after years of research, scientists have gradually proposed the concepts of "brain gut axis" and "brain gut interaction"."brain gut axis" is composed of two-way communication between the central nervous system and the intestinal nervous system [2]. With the understanding of intestinal microbial composition and diversity, new findings show that intestinal microbiota can be associated with gut brain function and neurological diseases through the "brain gut axis", thus forming a new concept of "microbial gut brain axis" [3].compared with the traditional "brain gut axis" research focusing on the influence of psychological state on gastrointestinal function, the "microbial gut brain axis" pays more attention to the interaction between intestinal flora and "brain gut axis".the most important influence of intestinal flora on the "brain gut axis" is mainly reflected in the regulation of brain development and behavior performance [4]. More and more studies have found the complex relationship between animal brain social behavior and microorganisms, suggesting that microorganisms, as a means of transmitting their own genetic materials, may have affected the evolution of brain social behavior How does it affect social behavior? Recently, Professor John F. cryan, from the University of cork, Ireland, published a report entitled microbiota and the social on science Brain's review summarizes in detail the underlying mechanisms of the association between gut microbiota and brain social behavior, and describes the diversity of such connections in the animal world. It also points out that these connections may help to explain the reasons for the association between gut microbiota and social disorders, and how to target them to affect brain health.first, the mechanism of "microbial gut brain axis" more and more experimental evidence shows that many behavioral reactions observed in various animals may be regulated by intestinal flora at different stages of their life. In this mode, people pay more and more attention to clarify the communication mechanism between intestinal flora and brain. In this paper, the author introduces the influence of microorganisms on society from the following aspects Communication channels of behavior (Figure 1). Vagus nerve is the main nerve pathway connecting gastrointestinal tract and nucleus tractus solitarius in mammalian brain stem.by vagotomy and other methods, the vagal afferent has recently been proved to form synaptic connections with endocrine cells in the intestine, and promote nutritional signal communication between the intestine and the brain through glutamate neurotransmission. There is even preclinical evidence that vagus nerve can transport protein from the intestine to the brain.however, some experiments have found that the anxiety like behavior of mice caused by mild gastrointestinal infection is obvious after vagotomy, which also indicates that not all microbial signals to the brain are mediated by vagus nerve. The intestinal flora of microbial metabolites can produce a large number of metabolites, such as volatile carboxylic acids, esters, neurotransmitters (such as serotonin) and various fatty acids, some of which have been proved to affect the physiological function and behavior of the brain.for example, various short chain fatty acid (SCFA) metabolites produced by intestinal flora can regulate various physiological functions, including some central physiological processes, through their homologous free fatty acid receptor (ffar). In addition, SCFA may also affect the production of neurotransmitters in the brain by regulating the expression of enzymes involved in its biosynthesis.of course, the authors also point out that due to the short half-life of SCFA, we need more evidence to confirm that SCFA produced by intestinal flora can reach the physiologically relevant concentration of brain. Immune mechanism research shows that immunity also plays an important role in the communication between intestinal flora and brain.some preclinical evidence suggests that intestinal microflora may affect the development of the immune system and even the central nervous system.on the one hand, intestinal flora can affect the immune system locally, such as Peyer patch or mesenteric lymph nodes; on the other hand, bacteria can also release various immune agonists, such as lipopolysaccharide (LPS) and peptidoglycan (PGN), into the blood circulation and enter the brain. Olfactory mechanism olfaction the ability to sense odors is the basis of all animal life on earth. It enables animals to explore food and perceive potential toxins in the environment, and also facilitates social interaction.preliminary evidence suggests that both intestinal and environmental bacteria can affect olfaction. Throughout the animal kingdom, more and more attention has been paid to the relationship between intestinal flora and brain through olfaction. These species use the by-products of intestinal microorganisms, such as volatile fatty acids and esters, to regulate communication.Fig. 1 the biological pathway of intestinal flora regulating social behavior II. There is a bidirectional relationship between microorganisms and social behaviors Social social behavior can affect the spread of bacteria between many invertebrate species, and it can also shape the microbial community of many primates through the horizontal transfer of bacteria. At the same time, studies have found that microbial transfer can occur between different species.however, the authors also pointed out that although the changes of intestinal flora seem to be synchronized with the social changes of some species, this is not always the case. This may be due to different evolutionary processes caused by different selection pressures. Therefore, it is suggested that the influence of phylogeny should be considered when looking for the social characteristics of microorganisms. Communication studies have shown that for some invertebrates, the intestinal microflora can promote the communication between the same species of individuals. At the same time, the microbiota also contributes to the communication between some vertebrate species, and the microbial community of some species may play a role in identifying the same species. Social immunity collective life provides a wide range of potential benefits, but it also comes with many costs, including the increased risk of exposure to infectious agents.however, studies have found that the increased threat of exposure to a social source of infection can be offset by an increase in microbial diversity, which enables the immune system to work with the microbiota to resist harmful microorganisms.immunity and host response to invasive pathogens may also affect the microbial basis of social behavior, because the immune system acts as a conduit between intestinal symbiotic bacteria and the central nervous system through various immune signaling mechanisms. Diet and stress the positive effects of sociality on animal behavior are usually accompanied by a series of negative effects, such as social stress, which can lead to the decline of health and fertility, increase the susceptibility to diseases, and thus affect the overall health of the species.although social interaction may be harmful to the gut microbiota by increasing stress, they can also be beneficial, and the balance between this seems to depend largely on social relationships.at the same time, herbivorous or carnivorous diets and their effects on the composition of intestinal microflora may also affect the evolution of social behavior in some species.Third, intestinal microflora and social behavior defects are manifested in autism spectrum disorders (ASD), schizophrenia, social anxiety and depression and other neuropsychiatric disorders. Patients can not interact with others or quit social activities.given the complex and bidirectional effects of microbiota and brain social behavior in the animal world, it should not be surprising that there is growing evidence that gut microbiota plays an important role in human social disorders.interestingly, a number of preclinical and clinical studies have documented disorders of gastrointestinal microbiota in individuals with these neuropsychiatric disorders, including reduced bacterial diversity and the number of beneficial bacteria, which may be associated with the observed behavioral symptoms.more and more clinical findings indicate that intestinal flora is affected under conditions such as ASD. The authors also point out that future research needs to count more patients and introduce appropriate control, which may provide a deeper understanding of the pathogenesis of intestinal flora in such diseases.4. The relationship between targeted microbiota and social disorder indicates that targeting microbiota is likely to improve social behavior defects.microbial based treatment strategies have shown their potential to change social behavior in various preclinical models, and some preliminary evidence also shows its impact on human beings, such as probiotics and the regulation of intestinal flora by diet structure will affect social behavior.in conclusion, the influence of intestinal microflora on sociability and its neurobiological basis has a great potential impact on ecology, evolutionism and human biology.this connection between the microbiota and the central nervous system provides a biological framework to illustrate how complex patterns of behavior, from social to non social, have evolved throughout the animal kingdom. In addition, it raises important considerations about the impact of certain lifestyle choices (such as diet, antibiotic use, social relationships, etc.) on human health It also provides a better understanding of the neurobiological basis of some neuropsychiatric diseases and the potential development of treatment in the future.original link: plate maker: Ke ref. 1. Guo Chun, He Ping. Brain gut axis and its research progress. World latest medical information abstracts. 2017,17 (95), 89-91.2