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Could a dose of "good" bacteria chase away the blues? A study conducted in mice suggests that probiotics, beneficial microbes commonly found in yogurt and fermented foods, may some day aid in the treatment of mood disorders.

For the study, a team of Canadian and Irish researchers regularly fed one group of mice a broth spiked with a strain of bacteria called lactobacillus rhamnosus JB-1. Other mice were given a bacteria-free broth.

Normally timid creatures, the mice were put through a series of challenging experiments, such as being placed in a pool of water and forced to swim. The mice given the bacterial-enhanced diet seemed better able to cope with the stressful conditions. They showed far less anxiety and depression-like behaviour than the bacteria-deprived rodents.

Blood tests also revealed they had lower levels of the stress hormone corticosterone flowing through their veins. What's even more remarkable is that there was evidence of a change in certain neurochemical receptors in the brain, according to the findings published in the Proceedings of the National Academy of Sciences.

Researchers have long known that certain types of bacteria found in the gut are good for us. They aid in digestion and fight potentially harmful microbial invaders. But this study takes the concept of helpful bacteria to a new level.

"This is the first-ever demonstration that harmless bacteria, found naturally in the intestine, can influence mood and behaviour in a normal animal," said John Bienenstock, a co-author of the study and director of the McMaster Brain-Body Institute at St. Joseph's Healthcare in Hamilton.

Data gathered from the study suggest that the gut influences what happens in the brain through the vagus nerve that connects the two. When the nerve was severed, the bacteria-fed mice no longer exhibited a steely resolve against adversity.

The Canadian researchers, along with their Irish colleagues at University College Cork, eventually hope to conduct human trials. Much work needs to be done to prove that what helps mice can also benefit people.

And even if further research establishes that bacteria can provided a lift to those who are stressed or depressed, it's unlikely that you would get the same results from just any brand of yogurt.

Dr. Bienenstock noted the specific strain of lactobacillus used in the animal experiments is not currently found in commercial yogurts.

"Not all probiotics are the same," he said. "We tested bacteria that didn't work. So these effects are very likely to be strain specific." That suggests tests would have to be carried out on individual products to evaluate their mind-altering potential.

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