Intestinal germs The intestinal flora controls thinking

A healthy intestinal flora makes an important contribution to the protection against infections, allergies and other diseases. But if it is destroyed, for example, by antibiotics, the memory also suffers. The German researchers have now found out.

Healthy intestinal flora can protect the brain
It has long been known that an intact intestinal flora makes an important contribution to the protection against infections, allergies and other diseases. However, it may also keep the brain healthy, as German researchers reported last summer in the renowned journal "Nature Neuroscience". The bacterial composition in the human gut thus has an influence on immune cells in the brain. Scientists at the Max Delbrück Center for Molecular Medicine in the Helmholtz Association (MDC) have now reported that a special strain mediates immune cells between the intestinal flora and the brain. "The findings are important for the consequences of long-term use of antibiotics, but could also help alleviate the symptoms of psychiatric illness," the MDC writes in a press release.

It has long been known that a healthy intestinal flora makes an important contribution to the protection against infections, allergies and other diseases. But it also influences thinking, as researchers have now found out. (Image: fotoliaxrender / fotolia.com)

The gut and brain "talk" to each other
As the message says, the gut and the brain "talk" to each other. And about hormones, metabolites or direct nerve connections. Another link is a specific population of immune cells from the group of monocytes, such as Dr. med. Susanne Wolf from the MDC research group led by Prof. Helmut Kettenmann together with colleagues from the University of Magdeburg, the Charité - Universitätsmedizin Berlin and the US National Institutes of Health (NIH). The experts now publish their findings in the journal "Cell Reports".

Microbiome switched off with antibiotics
To get to their findings, the researchers turned off in mice the microbiome, so the bacteria of the intestinal flora, with an antibiotic cocktail. Comparing the rodents with untreated animals, they observed significantly fewer newly formed nerve cells in the hippocampus region of the brain. According to the researchers also the memory of the mice deteriorated, because this formation of new brain cells - called "neurogenesis" - is important for certain memory achievements. When the microbiome was switched off, the number of a certain immune cell population in the brain, that of the Ly6Chi monocytes, declined significantly along with neurogenesis.

Test animals with different strategies
When Wolf and her team removed only these cells from the mice, neurogenesis decreased. When they administered Ly6Chi monocytes to antibiotic-treated animals, neurogenesis increased again. According to their own statements, the scientists cured antibiotic-treated animals with two different strategies. When the mice took a mixture of selected bacterial strains or completed voluntary training in the mouse impeller, the negative effects of the antibiotics were reversed. The monocyte count recovered as well as memory and neurogenesis. A restoration of the intestinal flora with the microbiome of untreated animals was not successful according to the experts.

Consequences for the treatment of psychiatric patients
According to Wolf, the hitherto unknown mediator function of immune cells is of particular scientific interest. "With the Ly6Chi monocytes we may have discovered a new general communication pathway from the periphery to the brain." Translated to humans, the results do not mean that all antibiotics interfere with brain function because the combination of drugs used was extremely strong. "However, similar effects on antibiotic therapies may be expected over a long period of time," says Wolf. The antibiotics also act without detours through the intestinal flora on neurogenesis, as further results of the research team show. Furthermore, the new work also has consequences for the treatment of psychiatric patients, such as schizophrenia or depression patients with impaired neurogenesis, explained Susanne Wolf: "Possibly these patients can also supplement probiotics with drugs and sports. To test that, we would like to conduct clinical pilot studies with the Charité. "(Ad)