Depression from the colon
Transplantation of intestinal microflora led rats to depression
Maxim Abdulaev, "The Attic"
Scientists transplanted the feces of frightened and depressed rats to their relatives. As a result, the last of the calm animals turned into much more depressed. From this, scientists conclude that the development of depression may be associated with the activity of microflora. Anxiety was not transmitted along with excrement.
Stress, inflammation, depression and anxiety are all related. Chronic stress increases the risk of depression and post-traumatic stress disorder, and patients with depression have increased levels of interleukins. Some of these substances produced by the immune system cause inflammatory processes, and inflammatory processes in the brain cause depressive behavior in laboratory animals.
At the same time, it is known that the intestinal microflora plays a significant role in the regulation of the immune system and even mood. Neurologists from the USA conducted a study on rats to find out how anxiety, depression, inflammation, stress and microbes are related.
Scientists subjected laboratory rats to several tests. The first of them was social – in it the rats had to show how morally stable they were. To do this, scientists have found an old male whose peak of reproductive activity has already passed – such rodents are very aggressive and climb into a fight with all their neighbors. The test rats were hooked up to him, and then the time that they would last before they submitted to aggression was recorded. After that, the experimental rats were divided into two groups – vulnerable and resistant – depending on how long they endured. Besides them, there was also a control group, with which nothing was done.
Before and after the test, blood and stool tests were taken from rats to find out the composition of the microbiota. It turned out that if before the beatings it was about the same in all rats, then it changed after. In vulnerable rats, clostridia microbes began to predominate in the intestines, and lactobacilli in resistant rats.
After that, the scientists took another set of rats and divided it into four groups. One was given a suspension of feces taken from vulnerable rats through a probe, the other was given a suspension of feces from resistant rats, and the other two groups were controls, one was given a placebo (the same solution as the first two, but without feces), and nothing was done with the fourth.
After six days of such "feeding", the rats were tested in a test with an aggressive male, and on the seventh and eighth days – in another test. This time the animals had to swim. The subjects were placed in a tank of water from which it was impossible to get out on their own, and then watched how long they would flounder before they gave up.
The behavior of the group to which the feces of vulnerable rats were transplanted in the test with an angry rat did not differ in any way from the behavior of control animals. But in the test with water, the rats that were watered with a solution of the feces of the vulnerable fought for life the least.
The test with the aggressor shows, as it is believed, the level of anxiety. At least, the results of other studies demonstrate that the treatment of rats with anxiolytics improves its results. But the test with water shows, as scientists believe, the level of depression – if rats are treated with antidepressants, they take longer to get out. Thus, it can be assumed that the rats after fecal transplantation were "infected" with depression, but not anxiety.
The composition of the microbiota has also changed in the transplanted rats, especially in vulnerable ones, in which clostridium has become predominant. Apparently, the stress that the rats were subjected to created the conditions for the successful development of clostridium – there is evidence that synthetic glucocorticoids, that is, stress-causing hormones, increase the content of clostridium in the intestine.
The composition of the blood of rats to whom the feces of the vulnerable group were transplanted showed that it had a high content of the protein S100ß, which is synthesized by astrocytes, glial cells. The content of this substance in the blood shows that the permeability of the hemato-encephalic barrier has increased. In addition, the number of microglia cells in the brain of rats increased, and there was a lot of interleukin 1 beta (IL-1ß) in the blood. All together, this means that an inflammatory process was going on in the animals' brains.
Scientists have compiled such a picture of what is happening with rats: the stress of a collision with an aggressive opponent caused the release of glucocorticoids and an increase in anxiety. The rapid development of clostridium was a side reaction, but the waste products of these microbes caused the synthesis of interleukins, which triggered inflammation, and that, in turn, led to an increase in depression. Thus, anxiety affects the inhabitants of the intestine, and they can cause depression.
Scientists note that the composition of the microbiota of the stable group was dominated by lactobacilli, which may resist the action of clostridium or simply displace them, occupying their niche and protecting them from the effect of stress. The reason why harmful clostridia began to multiply in some rats as a result of beatings, and in others – useful lactobacilli, scientists could not find out.
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