Does the intestinal microbiota affect social relationships?

Many people suffer from social phobia, a disorder that causes anxiety and fear, often intense, in unfamiliar group situations where they have to interact with other people. They can suffer from it as early as childhood or adolescence and it can last for years, producing disabilities that make them avoid these situations and compromise their quality of life. How to solve it? Pharmacological treatments have been tried, but they have limitations and are often ineffective.

But now a new key is being explored that could perhaps help overcome this disorder, since it has been observed that people who suffer from social phobia have a different biological composition of their intestinal microbiota than that of healthy people who do not suffer from it. Hence, as strange as it may seem, the intestinal microbiota could be related to the processing of social relationships that takes place in the brain.

What is the intestinal microbiota? Numerous bacteria colonize the healthy human body, most of them in the gastrointestinal system, constituting a complex system called intestinal flora or microbiota. It comprises more than 1000 different types of bacteria whose composition is altered throughout life by factors such as diet, the use of antibiotics, the woman's type of childbirth and other factors of modern life. The changes and structure of the intestinal microbiota are dynamic. While the host, that is, the person's body and digestive system, provides a nutrient-rich environment, the intestinal flora or microbiota, in turn, provides metabolic, protective and structural functions independent of the person's genome. The microbiota contributes to the elimination of toxins and carcinogens, prevents the intestine from being colonized by pathogenic bacteria, contributes to the development of the immune system and regulates the inflammatory state of the body.

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Now, fecal microbiota transplants have emerged as an effective technique to understand how they can affect phenotypic changes in the recipient. When, for example, feces are transferred from an obese mouse to a thin, germ-free mouse, it becomes hyperphagic and gains body fat mass. But we do not know the mechanism by which the microbiota acts to produce this effect. The research carried out has also shown that these transplants can transfer psychological and physiological traits in cases of depression, anxiety comorbid with irritable bowel syndrome or schizophrenia, that is, it seems proven that the intestinal microbiota is capable of affecting the functioning of the brain.

Perhaps that is why it is not surprising that, recently, to investigate whether a certain intestinal microbiota could cause social fear, a team of researchers from the Karolinska Institute in Stockholm has inoculated fecal matter from humans with social phobia to male mice to see if this can cause changes. in social fear, sociability, social cognition and stress coping behaviors, as well as intestinal transit and motility in the recipient mice. The result has been that the mice that received fecal matter from humans with social phobia, although they did not show changes in their anxiety or depression behaviors, or significant alterations in prosocial hormones such as oxytocin or anti-inflammatory hormones such as cytosines that could influence their behavior against to conspecifics, they did show greater sensitivity specifically to social fear, all verified through Pavlovian classical conditioning tests. As expected, these results indicated a clear influence of the gut microbiota on the brain functioning of the mice.

Although on several occasions organs or biological matter have been transferred from animals to humans, reverse transfer, that is, transplants of human biological material to animals, is much less frequent, motivated here by the ethical and practical inconvenience of doing the same type of transplants. from person with social phobia to person without it. But, the result observed when transferring the microbiota related to that phobia to an inferior animal such as the mouse is always a good indicator that this influence could occur throughout the evolutionary chain of mammals and, therefore, it is also an indicator of what that can occur in our own human brain. It tells us, in turn, that modifying in some way the microbiota of people with social phobia could be a good way to cure or, at least, alleviate their disorder.

Gray matter

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