Transpoosion transmits anxiety and IBS

03 March 2017

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A number of studies have shown that individuals who complain of irritable bowel (IBS) symptoms also have changes to the spectrum of bugs that inhabit the intestine. They are also more likely than average to suffer with anxiety and depression. But are the changes in bowel bugs and mood a cause, or a consequence of IBS? Now a new study carried out in Canada has shown that IBS and mood symptoms can be transmitted between individuals by bowel bacteria.

Premysl Bercik and his team at Ontario's McMaster University, writing in Science Translational Medicine, collected stool specimens from 5 healthy human volunteers and 8 patients with IBS. These individuals had an average age of 42 and included a mixture of males and females. Bacteria from the participants were administered to so-called germ-free mice that were reared previously in a sterile environment.

Three weeks later the team measured the microbiomes - the spectrum of bugs - in the intestines of their mice as well as looking at the pattern of genes being switched on in the walls of the animals' intestines, the permeability of the intestinal lining, and the range of chemicals being produced by the bowel bugs. The animals were also tested for signs of anxiety or mood abnormalities.

Compared with mice colonised by bugs from the healthy human volunteers, the animals with IBS bacteria showed behaviours consistent with anxiety. Also like the human donor patients they had reduced intestinal transit times, meaning more frequent bowel movements and diarrhoea.

Their intestinal walls were also more permeable, and there were signs of increased immune activation with clusters of genes linked to inflammation being switched on and higher expression of an anti-bacterial chemical called beta-defensin. The affected mice also had lower levels of a chemical called phosphatidylserine, which is linked to immune regulation, and higher levels of the substance phosphatidyl choline, which plays a role in inflammation.

The mice with the greatest levels of immune activation also had the highest levels of anxiety-like behaviours. These results strongly point towards a role of the intestinal microbiome in the mood manifestations  and intestinal symptoms that are associated with IBS.

Studies on human patients have shown that certain probiotic supplements, with strains of Bifidobacteria, can reduce brain responses to certain emotional stimuli, and the same bacteria can reduce anxiety symptoms in mice. Could this, the researchers ask, point to a role for manipulation of the microbiome as a way to manage the symptoms of IBS?

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