“ Man and the Microbiome : A New Theory of Everything ?” — with all due respect , isn ’ t that a wee bit ambitious ?
That title is admittedly a bit overstated . But the point we are trying to make is that it isn ’ t really so odd that the microbiome is involved in everything , because the microbes were there first , and so our species has evolved in their presence . We have been able to show that growing up in a germfree environment really affects the development of the mouse brain , for example , in a variety of ways .
Our immune system is also completely shaped by microbial signals . Via that route , inflammation in our gut can affect our mood and cause symptoms of sickness behavior that are quite similar to important aspects of depression and anxiety . Many psychiatric disorders are also known to be associated with various gastrointestinal issues , though cause and effect often aren ’ t clear yet . So if you study the body , including the brain , you ignore microbes at your own peril .
Most people are on board with the idea that gut microbes affect our health , but it may be more difficult to accept that they also influence how we feel and think . How did you convince yourself this was true ?
I ’ m a stress neurobiologist , so I was trained in stress-related disorders like depression and anxiety , and my interest was really in using animal models of stress to look for novel therapeutic strategies .
Consuming microbe-rich fermented foods and microbe-supporting fibrous foods are currently the most effective ways to enrich and nourish a healthy gut microbiome .
When I moved to University College Cork in 2005 , I met a clinical researcher , Ted Dinan , and we started working together to study irritable bowel syndrome , a very common disorder that is characterized by alterations in bowel habits and abdominal pain .
That was interesting to me , as it had become very clear that this is also a stress-related disorder . So we started working on an animal model called the maternal separation model , where rat pups are separated from their moms early in life and develop a stress-like syndrome when they grow up .
Siobhain O ’ Mahony , a graduate student at the time , also wanted to look at the microbiome , and I remember telling her , “ No ! Focus , focus !” But she went ahead anyway and found a signature of this earlylife stress in the microbiome of adult rats . That was kind of a eureka moment for me .
The next part of the puzzle came when we showed that mice born in a germ-free environment have an exaggerated stress response when they grow up . So we ’ d already shown that stress was affecting the microbiome , and now we ’ d shown that the microbiome is regulating how a mouse responds to stress . It turned out that a very nice study from Japan had already shown this .
The third part of the puzzle for me was to ask whether we could alter the microbiome to alleviate some of the effects of stress . In 2011 , we were able to show that a specific strain of the bacterium Lactobacillus , when given to normal , healthy mice in a stressful situation , was able to dampen down the stress response , and that the vagus nerve connecting the gut to the brain was required for that .
These three things together , from 2006 to 2011 , really crystallized my interest in the link between the gut microbiome , brain and behavior . Since then , we ’ ve been on this magical journey to try and understand these discoveries , uncover the mechanisms and find how they translate to humans .
Can you explain what a depressed or anxious mouse
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