Bugs in your belly affect your brain

When things go amiss in your gut, they can also go amiss in your brain. Emerging research shows a link between intestinal bacteria and brains that can influence mood and behaviour — a link scientists are only beginning to understand.

Roughly 100 trillion microorganisms live here. Research suggests they "talk" to our brains. (Joey Yee, flickr.com)

Roughly 100 trillion microorganisms live here. Research suggests they “talk” to our brains. (Joey Yee, flickr.com)

For instance, up to 80 per cent of people with irritable bowel syndrome (IBS) have increased anxiety and depression. And some people with autism — a syndrome characterized by problems interacting with others —have abnormal mixes of gut bacteria.

“Many people with chronic intestinal conditions also have psychological disturbances and we never fully understood why,” says McMaster University gastroenterologist Stephen Collins.

Now, researchers such as Collins are starting to come up with answers, most of which point to the teeming community of microorganisms in our guts.

Our lower gastrointestinal tract is home to almost 100 trillion microorganisms, most of which are bacteria. They are largely “good” bacteria that help us digest food and release the energy and nutrients we need. They also crowd out “bad” bacteria that can make us sick.

But bad bacteria can sometimes take over, affecting our command and control centre for mood and behaviour: the brain.

Collins and fellow McMaster University gastroenterologist Premysl Bercik have done some of the seminal research into the bacteria-brain-behaviour connection. In one study, they changed the behaviour of mice by giving them fecal transplants of intestinal bacteria through a feeding tube.

They gave adventurous mice bacteria from timid ones, thereby inducing timid behaviour. Before the transplant, adventurous mice placed in a dark, protected enclosure spent much of their time exploring an attached bright, wide-open area. After the transplant, they rarely ventured beyond their enclosure.

The researchers also did the reverse — transplanting bacteria from adventurous mice into timid mice, which then became adventurous.

The mice’s brain chemistry gives some insight into what might be going on, says Collins. The newly adventurous mice had decreased levels of a naturally occurring chemical called brain-derived neurotrophic factor (BDNF), which is linked to anxiety.

“We can’t do experiments like this in humans. But it’s highly likely this is applicable in humans too,” says Collins.

Probing probiotics

He and Bercik have just completed a study in which they transferred gut microbes from three different groups of people into mice. The groups were divided into those who were healthy, those with irritable IBS, and those with IBS plus anxiety. The researchers found that when they transferred microbes from people with IBS plus anxiety, the mice also became anxious.

In another recently completed pilot study, Collins and Bercik tested a probiotic on people with IBS and depression. The researchers had already established that this probiotic — a mixture of beneficial microorganisms — alleviates symptoms of depression in mice.

Half of the 44 IBS study participants drank the probiotic, while the other half drank a placebo. Those who had the real thing reported reduced depression. Collins and Bercik hope to repeat their findings in a larger study.

But how exactly do bacteria alter mood and behaviour? Research shows there are three mechanisms. The first has to do with bacterial waste called metabolites. Bacteria feed on nutrients we ingest with our food, and they produce chemicals as they digest those nutrients. These chemicals may get into the blood and possibly into the brain, changing its chemistry and function. And chemical activities in the brain underlie mood and behaviour.

The second way bacteria affect the way we feel and act is by activating the body’s immune system, resulting in the release of signals that can influence the brain. The third way is through the vagus nerve, a long nerve that runs between the gut lining and brain. Gut bacteria, or their metabolites, somehow communicate with the brain over this nerve.

Regardless of how the signalling takes place, scientists hope to eventually find what constitutes bad bacteria and good bacteria, and how many good ones it takes to make a difference. “We are in the process of trying to narrow that down,” says Collins.

Tagged: Health, Nature, Technology, Blog, Stories

Share: Print

Leave Comments

Blog Posts

Indigenous art and the ‘...

Sharon Oosthoek | June 27, 2016

Gerald McMaster is fascinated by creative people who move in an out of, or are influenced by different communities and cultures. At once nomadic and connected, their experiences formed the basis of his early research. Today, the Ontario College of Art and Design University professor, curator, author, and artist is about to dive back into this area of research. He is launching a multi-year project that will examine the ways in which Indigenous and non-Indigenous cultures interact, influence and inspire one another. read more »

2016 Women’s Health Scholars

Alex Hughes | June 22, 2016

Ten outstanding Ontario university scholars are being recognized for potentially life-changing research for women in Ontario and across the globe, as they look to develop health care in the areas such as HIV-care, contraceptives, and breast cancer. The Council of Ontario Universities, with funding from the Ontario Ministry of Health and Long-Term Care introduced the Ontario Women’s Health Scholars Awards in 2001 to ensure that Ontario attracts and retains pre-eminent women’s health scholars.  The awards aim to improve women’s health. The 2016 recipients include postdoctoral, doctoral and master’s students from six Ontario universities. They each will receive scholarships of $25,000 to $50,000, along with research grants of $1,000 to $5,000. This year’s recipients and their areas of research are: Alisa Grigorovich, University of Toronto – how to create effective policies that address the sexual harassment of female workers by clients in Ontario residential long-term facilities. Jocelyn Wessels, McMaster University – how female sex hormones found in contraceptives affect vaginal health and susceptibility to sexually transmitted infections. Lori Chambers, McMaster University – the challenges and benefits to African immigrant women who are living with HIV and choose to work in prevention, treatment and advocacy for others with HIV. Komal Shaikh, York University – assessing the effects of education-based therapy in treating and rehabilitating cancer survivors with cancer-related cognitive dysfunction. Amanda D. Timmers, Queen’s University – how sexual arousal patterns vary across genders and how these variations can inform the treatment of sexual dysfunction. Kelly Coons, Laurentian University – how to improve the ability of future health care professionals to counsel pregnant women on drinking alcohol during pregnancy. Sara King-Dowling, McMaster University – how the development of girls’ motor skills affects their overall health and activity levels over time. Denise Jaworsky, University of Toronto – how living in rural and Northern areas of Canada affects the ability of women living with HIV to access care. Justin Michael, Western University – developing tools to allow for a single-visit radiation treatment for women with breast cancer to make things easier for those living far from treatment facilities. Shira Yufe, York University – how to encourage breast cancer survivors to adopt healthy lifestyle and weight management habits. Each of the researchers has spent countless hours studying topics related to women’s health and improving the lives of women in Ontario.  Their research (full descriptions available here) will contribute to the way that Ontarians (and the global community) live, work and play.  Congratulations are in order to the award recipients! Stay Curious!

Closing the cancer gap ...

Pippa Wysong | June 17, 2016

First Nations women are up to 20 times more likely to develop cervical cancer compared to women in the general Canadian population, largely because very few First Nations women undergo Pap testing. But a project focusing on this population is coming up with new ways to improve screening and help get cancer rates down. read more »

Rewriting Ottawa’s history

Chris Cline | June 13, 2016

New evidence shows an extensive Indigenous burial ground from as early as 4,900 years ago at “Hull Landing,” the present site of the Canadian Museum of History, directly across the Ottawa River from Parliament Hill. The find came to light last year thanks to the research of Carleton University journalism professor Randy Boswell and Canadian Museum of History curator, Jean-Luc Pilon. While Bytown antiquarian Edward Van Cortlandt first investigated the site in 1843, knowledge of the burial ground’s true location was lost for more than a century. That is, until Boswell's recent series of discoveries in 19th-century Ottawa newspaper archives. read more »
university classroom

Calling out racism in ...

Sharon Oosthoek | June 7, 2016

Growing up in Northern Ontario as a member of the Teme-Augama Anishnabai, Sheila Cote-Meek is no stranger to the impact of Canada's colonial history. So when she set out to study colonized classrooms for her PhD dissertation — published as a book in 2014 — she had a good idea of the kind of stories she would hear from  university students and professors. Still, even she was taken aback: "I was shocked and saddened that in this day and age,  students still have to deal with racism in overt and covert ways," she recalls. read more »
More Blogs »