Melancholic microbes or how the microbiota can affect our mood
How does the microbiota affect brain-gut communication? This is one of the questions that experts from a range of disciplines, including neurogastroenterology and psychiatry, have been trying to answer for a while. They have used different strategies in their endeavours, from probiotics to microbiota transplants. And, for now, the results point to the conclusion that the gut microbiota may modify the chemicals in the brain and consequently, our behaviour.
As shown by Professor Ted Dinan and his colleagues at University College Cork (Ireland) in the latest edition of Neurogastroenterology & Motility, several recent studies show that in animals, depression and anxiety are related to an alteration in the composition of the gut microbiota. Furthermore, the experts have no doubt that gut-brain interactions may influence gut inflammation, chronic abdominal pain, and bowel dysfunctions. Professor Dinan has also shown that in the absence of sufficient digestive bacteria, serotonin (the so-called “happiness hormone”) that is needed for regular bowel and brain functions is not properly produced both in the gut and in the brain. Understanding the relationship between emotions and the microbiota may lead to the development of “new treatments for a wide range of conditions including obesity, mood disorders and gastrointestinal complaints,” says Professor Dinan.
Previous research by gastroenterologist Premysl Bercik of McMaster University (Canada) also supports these ideas. In experiments carried out on mice, Professor Bercik found that after modifying the composition of the microbiota of mice exhibiting a passive behavioural pattern, their “personality” (explorative behaviour) changed towards exploring and they tended to look for newness and risk. More interestingly, he showed that the change was linked to chemical alterations in two emotion-related brain structures – the hippocampus and the amygdala. Specifically, the change in gut microbiota increased the expression of the brain-derived neurotrophic factor (BNDF), a substance in the brain that protects adult neurons and which is lacking in depression-like behaviour. When the microbiota returned to its original state, the mice returned to their original behaviour pattern.
“We are getting an increasingly better understanding of how the (intestinal) microbiota affects the brain and behaviour,” says Professor Dinan, who is convinced that by combining genome analysis techniques and neuroscience we will unlock the reasons why emotional disturbances may occur when communication between the brain and gut fails.
