Bugs in intestines may play role in depression

Stresses in your early life – like traumatic external events – can alter the delicate balance of your gut microbiota, something that’s linked to immune system, digestive, and mental health.

The group of mice with no gut bacteria, meanwhile, also showed the same corticosterone increase and intestine impairment, but the depressive-like behavior was interestingly absent.

Dr Premysl Bercik, from McMaster University in Canada, said: “We have shown for the first time in an established mouse model of anxiety and depression that bacteria play a crucial role in inducing this abnormal behaviour”. The germ-free mice, on the other hand, didn’t seem all that bothered by the separation, even though it altered their stress hormone levels, results reported in the Nature Communications journal showed.

The latest study looked at mice that had been exposed to a stressful experience in early life, such as being separated from their mothers. For their study, the team used two groups of mice; one group had normal gut bacteria while the other group had no gut bacteria.

Scientists at McMaster University have discovered that intestinal bacteria play an important role in inducing anxiety and depression. After the period of 3 hours were over, they were put back with their mothers.

Those specimens with a normal range of bugs displayed signs of anxiety and depression. Furthermore, these mice which had complex microbiota demonstrated gut dysfunction on account of the release of an important neurotransmitter acetylcholine.

In mice with normal gut bacteria, the team found stressed mice developed abnormal levels of the stress hormone corticosterone, alongside anxiety and depression-like behavior.

The same experiment was then repeated in germ-free conditions. This changed the bacterial composition and metabolic activity of the mice in a matter of weeks.

Gut bacteria was also transferred from the stressed mice into non-stressed, germ-free mice. “This suggests that… both host and microbial factors are required for the development of anxiety and depression-like behaviour”. The researchers thus concluded that gut microbiota trigger the behavioral signs of stress.

Bercik said this is another step in understanding how microbiota can shape host behaviour, and that it may extend the original observations into the field of psychiatric disorders.

He added: “We are starting to explain the complex mechanisms of interaction and dynamics between the gut microbiota and its host”.

Human gut, also known as alimentary canal, consists of trillions of microorganisms that perform the metabolic activities in the human body including fermentation of undigested carbohydrates and metabolizing bile acids.