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   How Intestinal Bacteria May Influence Our Moods    
   CBC 07/14/14 05:00 AM ET    
   Mounting evidence that gut bacteria affect mood and behaviour has researchers   
   investigating just how much power these tiny microbes wield over our mental   
   health.    
      
   "Many people with chronic intestinal conditions also have psychological   
   disturbances and we never understood why," says McMaster University   
   gastroenterologist Dr. Stephen Collins.    
      
   Now, scientists such as Dr. Collins are starting to come up with answers.    
      
   Our lower gastrointestinal tract is home to almost 100 trillion    
   icroorganisms, most of which are bacteria. They are, by and large, "good"   
   bacteria that help us digest food and release the energy and nutrients we   
   need. They also crowd out bacteria that    
   can trigger disease.    
      
   But when things go awry in our guts, they can also go awry in our brains.    
      
   Up to 80 per cent of people with irritable bowel syndrome experience increased   
   anxiety and depression. And those with autism -- a syndrome associated with   
   problems interacting with others -- are more likely to have abnormal levels of   
   gut bacteria.    
      
   Dr. Collins and fellow McMaster gastroenterologist Premysl Bercik have done   
   some of the seminal research into the bacteria-brain-behaviour connection. In   
   a study published last year, they changed the behaviour of mice by giving them   
   fecal transplants of    
   intestinal bacteria.    
      
   It involved giving 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 Dr. Collins. The newly adventurous mice had increased levels of a   
   naturally occurring chemical called brain-derived neurotrophic factor (BDNF),   
   which is linked to reduced    
   anxiety. The newly timid mice, on the other hand, saw their BDNF levels drop.    
      
   Investigating probiotic potential    
      
   But mice are not men. Nor are they women. How well can mouse studies predict   
   bacteria's effect on our own moods and behaviours?    
      
   Dr. Emeran Mayer, a gastroenterologist at University of California, Los   
   Angeles, is a self-described sceptic, but admits "there is enough there to   
   make me think some of the findings from animal studies can be extrapolated to   
   humans."    
      
   Dr. Mayer and his team were the first to establish a concrete connection   
   between gut bacteria and brain function in humans. Their study, published last   
   year, was funded in part by Danone Research, a division of multinational food   
   company Danone.    
      
   The researchers gave 12 healthy women fermented milk containing a probiotic   
   supplement made up of five different strains of bacteria thought to have a   
   positive effect on the intestines. The women drank the milk two times a day   
   over the course of four    
   weeks. Another group of 11 women drank milk without probiotics.    
      
   Mayer scanned both groups' brains before and after treatment, while showing   
   them photos of people with emotional facial expressions such as anger or fear.    
      
   The women who drank probiotics showed a reduced brain response to the faces,   
   compared with the women who weren't given probiotics.    
      
   "So what does that mean?" asks Dr. Mayer. "You could say the group with   
   probiotics perceived negative emotions as less threatening. They had a   
   decreased brain response to stress."    
      
   While the probiotics group did not report changes in their emotional state   
   after treatment, they didn't suffer from stress or anxiety to being with.    
      
   Dr. Mayer and his team plan to follow up with studies testing the impact of   
   probiotics on those with high anxiety. In a separate study, they are looking   
   into the potential effect of fecal transplants in children with autism.    
      
   Bacteria-autism connection    
      
   Elaine Hsiao, a neurobiologist at the California Institute of Technology, is   
   also delving into bacteria's influence on autistic behaviour. Hsiao and her   
   team published a study last year about autistic mice that supports the theory   
   that changes in gut    
   bacteria can affect certain autistic behaviours.    
      
   As is the case with humans, autistic mice have abnormal levels of bacteria in   
   their guts. But after feeding them applesauce laced with the gut bacterium   
   Bacteroides fragilis for three weeks, Hsiao found the levels of several   
   species of bacteria in the    
   mice's guts returned to normal. More importantly, some of the animals'   
   autistic behaviours changed.    
      
   Before the treatment, Hsiao's team gave the mice three behavioural tests.    
      
   In one test, mice were placed in a box attached to two other boxes. One   
   contained another mouse; the other a toy. Mice could choose to play with the   
   toy or the mouse. Mice without autism showed normal social behaviour by   
   playing with the mouse. Autistic    
   mice, by contrast, preferred the toy.    
      
   A second test measured communication. Mice "speak" in the ultrasonic range,   
   which humans can't hear. Hsiao recorded their calls using a special microphone   
   that can pick up ultrasonic frequencies.    
      
   "The autistic ones produced fewer calls and the calls were shorter," she says.   
   In other words, they communicated less than normal mice.    
      
   Finally, she placed mice in a bin containing wood shavings and a few marbles.   
   In the wild, mice normally bury things. Hsiao's autistic mice did indeed bury   
   the marbles, but they then dug them up and reburied them -- over and over.    
      
   After eating the applesauce with B. fragilis, the autistic mice stopped   
   compulsively burying marbles. They also communicated like normal mice. What   
   didn't change, however, was their preference for toys over other mice.    
      
   Changing brain chemistry?    
      
   Exactly how bacteria alter mood and behaviour -- in mice or humans -- remains   
   unknown. One theory has to do with bacterial waste called metabolites.   
   Bacteria feed on nutrients we ingest with our food, and like people, bacteria   
   don't use everything they    
   eat. Whatever doesn't fuel their growth and reproduction, the bacteria expel   
   as waste.    
      
      
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    * Origin: you cannot sedate... all the things you hate (1:229/2)