New findings: How to make intestinal bacteria depressed
Years ago, scientific studies provided indications that intestinal bacteria could trigger depression. Austrian researchers have now been able to gain new insights into how intestinal bacteria, the immune system and obesity can lead to mental illness.
Only recently, German scientists reported on their study, which demonstrated the influence of intestinal bacteria on weight loss and on weight gain. In any case, it has long been known that the intestinal flora affects physical health. There are also indications that these bacteria also have an effect on the psyche. A research group from Austria has now been able to gain new insights into how intestinal bacteria cause depression.
Changes in the brain
It has long been known that there is a real medical background to the proverbial "gut feeling". As explained in an article by "scilog", the magazine of the Austrian Science Fund FWF, the intestine has its own nervous system, which due to its size and complexity is also called the "abdominal brain", and closely with the Brain is networked.
According to the experts, processes in the gut cause changes in the brain and, conversely, mental factors influence the intestine. However, it is not fully understood how far this interaction goes and how exactly it works. For example, there are indications that the gut may be involved in the development of psychiatric diseases.
A research group led by Peter Holzer, Professor of Experimental Neuro-Gastroenterology at the Medical University of Graz, is investigating the complex interplay between the intestine and the brain. Now, in a project funded by the Science Fund FWF, the team has identified some concrete factors that can trigger psychological changes in mice.  There is a strong connection between the brain and the gut
"The connection between the intestinal nervous system and the brain has long been known, but the situation has become more complex if you look at the last published work, "says project manager Peter Holzer.
" To the direct nerve conduction between the intestine and brain, of which one has long been known, come many intestinal hormones that carry messages to the brain, and In addition, a huge immune system that emits messengers on stimulation. In recent years, the microbiome of the intestine has been added as a factor. This is a huge number of unicellular organisms, which also give off substances and probably play an important role in the information system. "
According to Holzer, many people are aware of a strong connection between the brain and the gut. "But the fact that so much information reaches the brain from the intestine is usually hardly known to us. This information is fed into areas of the brain that are important to our mood and emotions. "
Sickness is triggered
The researchers from Graz spent five years studying different signaling pathways in which processes in the intestine can influence the brain. According to the information, a part of the project should clarify how certain bacteria in the intestine alert the immune system and thus trigger a feeling of sickness.
"The immune system learns early to tolerate the microorganisms in the intestine. It starts with the baby's age, "explains Holzer. "However, if some of the bacteria produced by bacteria penetrate into the intestinal wall, which produces an immune response and this is associated with the feeling that we are sick." Specifically, the research group examined the so-called "endotoxin lipopolysaccharide" (LPS), which by certain Intestinal bacteria is released and stimulates the immune system, so that we feel that we are ill.
"Those who suffer from bacterial infection feel tired, have muscle pain, lose their appetite and retreat. It's a sensible body response to dealing with the infection quickly, "says the scientist. "However, there are indications that this reaction in humans could be triggered by intestinal bacteria, if there is no infection."
The team was able to show that other bacteria-produced substances, so-called "peptidoglycans" enhance the effects of LPS. "We believe from these findings that lipopolysaccharide is only one of several factors in the development of mental illness."
Severe obesity increases the risk of depression
The neurogastroenterologist sees this physical response to "feeling sick" in the larger context Influences of the intestine on mental factors, in particular as a possible trigger for psychiatric disorders.
"From psychiatry and nutrition it is well-known that being overweight increases the risk of depression and depressive moods. And you've also known for about 15 years that the intestinal microbiome of healthy and very overweight people is very different, "says Holzer. One result of the project now provides specific information on how processes in the intestine can trigger depressive behavior.
In order to gain new insights, the scientists exposed mice to a high-fat diet and then analyzed their behavior. According to the data, not only in the brain, but also the behavioral changes associated with depression were found to be appropriate for depression.
According to Holzer, this is not easy to determine in mice, but it is possible. "Depressed people lose the joy of certain things. This anhedonic, ie listless behavior we could prove in the high-fat-fed mice. "For this purpose, the animals normal water and sugar water alternative offered. Healthy mice prefer sugar water, but the mice in Holzer's experiment did so to a much lesser degree.
In order to find out if intestinal microbes even contribute to depressive behavior after a high-fat diet, the next step was to severely restrict the intestinal microbiome with antibiotics. These results will be published shortly.
Possible signaling pathway identified
The team from Graz has also identified a possible signaling pathway for how a high-fat diet leads to depressive behavior. The hormone "leptin", which is released by fat cells, seems to play a role in this. Mice that can not produce this hormone, although they increase to the same extent as other mice when given high-fat foods, are not prone to depression-related behavior.
"The role of leptin is still in the literature not clearly clarified. In any case, we were able to show that leptin is important here, "says Holzer, who suggests that the secretion of leptin is linked to short-chain fatty acids produced by microorganisms in the gut from fiber-rich food. Consequently, the intestinal microbiome also appears to play an important role in the context of overweight depression. (ad)
- scilog: How to make intestinal bacteria depressive, (Call: 25.08.2019), scilog