Mice whose diets were supplemented with Lactobacillus rhamnosus—a bacterium commonly found in probiotic dietary supplements—experienced decreased stress and anxiety, according to a study published Monday (August 29) in Proceedings of the National Academy of Sciences.

In the past, researchers have investigated the effects of pathogenic bacteria, which are known to affect the brain by releasing toxins or stimulating the immune system. Now, researchers at University College Cork in Ireland and McMaster University in Canada found that in addition to its more well-known role in regulating bowel activity, the benign Lactobacillus rhamnosus can similarly affect the brain: when mice were fed a supplemented diet, they were calmer and produced less of the hormone corticosterone during stress tests that included exploring mazes or being forced to swim. The probiotics had an effect similar to that of antidepressant drugs in the mice, lead author John Cryan told Nature...

The researchers also found changes in gene activity that encode for GABA neurotransmitter receptors—receptors that are often targeted by anti-anxiety drugs. This resulted in more GABA receptors in some parts of the brain, and fewer in others—differences that corresponded to lower anxiety. When the connection between the brain and gut—the vagus nerve—was severed, these changes were not observed. The authors note that anxiety and bowel disorders are often found together in the same patient, suggesting a possible new avenue for treatment.

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