The catchphrase is “gut-brain axis”: How the composition of the microbial communities in the gut can also influence the brain and behavior is now illustrated again by a study: A certain bacterial strain therefore causes mothers to neglect their young. The cause may be an influence on the serotonin system, whose role in sensations is known. Even if the results have not yet been directly transferable to humans, they do make it clear how complex intestinal microbes can be, say the researchers.
Important tiny things: The health importance of bacteria in our digestive system has moved more and more into the focus of science in recent years. It was shown that the composition of the intestinal flora is not only linked to the immune system and purely physical effects, but also to neurodegenerative diseases and psychological problems. Certain features of the human microbiome have been linked to the development of Alzheimer’s, depression and anxiety. The importance of this so-called gut-brain axis is currently an important research field. Since studies on the importance of the intestinal flora are rather difficult to carry out in humans, scientists often use animals as model systems.
A special E. coli strain in sight
In the current case, the researchers led by Janelle Ayres from the Salk Institute for Biological Studies in La Jolla investigated the effects of a certain strain of the intestinal germ Escherichia coli on mice. There was evidence that this version “O16: H48 MG1655” of the widespread bacterium was linked to developmental disorders in young mice. It appeared possible that the intestinal bacteria had a negative effect on the composition of the mother’s milk. For their study, the scientists generated female mice that each carried only O16: H48 MG1655 as the only strain of E. coli in their intestines. When these test animals became mothers, they could then study the effects in detail.
It was initially shown: the young animals showed a comparatively retarded growth. As the subsequent investigations made clear, this was not due to the babies themselves or the quality of the milk – it was simply due to malnutrition. “We were able to show that the behavior of the young animals was normal and that the mother’s milk had a healthy composition and was produced in normal quantities,” says Ayres. The reason for the malnutrition, however, was neglect: “We finally found that colonization with these special bacteria led to abnormal maternal behavior: the mothers did not care enough for their young,” explains Ayres. The researchers were able to confirm this by handing the young animals over to “normal” foster mothers: With them, the little ones developed without any problems.
Complex gut-brain axis
“To the best of our knowledge, this is the first evidence in the animal model that gut microbes can play a role in the development of healthy maternal behavior,” says Ayres. “This is further evidence of the connection between the intestines and the brain and the importance of microbes for regulating the behavior of the individual who inhabit them,” says the scientist. The first author of the study, Yujung Michelle Lee, says: “It is astonishing that apparently even the establishment of a healthy mother-child relationship can be influenced by factors associated with microorganisms in the body.”
In further investigations, the scientists are now looking into the question of what could be the reason for the effect. Initial results suggest that the bacteria could affect serotonin levels in the mice. This seems plausible: Serotonin is a neurotransmitter and hormone that is associated with feelings of happiness and well-being.
So far, however, it remains unclear to what extent the study could have a specific meaning for humans. It is only known that the strain O16: H48 MG1655 can also occur in the human intestine. So far, however, there is no further information about its significance for us. “It is very difficult to study these relationships in humans because the human intestinal flora contains hundreds of different types of microorganisms,” says Ayres. “But once we understand more about the mechanisms in animal models, we may be able to apply our findings to humans to see if the microbes and their effects are comparable,” says Ayres.
Source: Salk Institute, technical article: Science Advances, doi: 10.1126 / sciadv.abe6563