High Anxiety

It’s becoming common knowledge that the human microbiome has a significant effect on our lives. The collection of microorganisms living on our skin and in our gut aid in everything from immune defense to digestion and, as recent studies show, even our psychological well-being.

Giada De Palma of McMaster University in Ontario dove into the effects of gut bacteria on stress in mice, a common proxy for humans in lab experiments. She and her colleagues started by separating young mice from their mothers (traumatic even for the smallest mammals). Some of the mice were completely microbe-free, while others lacked certain key strains of bacteria in their tiny mouse tummies. Then the researchers watched for stressed-out behavior. No, not binge watching Netflix and eating Ben and Jerry’s: the scientists used standard measures like the tail-suspension test and comparing the time spent in light or dark areas of their enclosure to simulate stressful environments. In addition, the team measured neurotransmitter levels that correspond to mouse stress.

In general, the mice without gut bacteria showed fewer stress-like symptoms than those that were just missing a few strains. Introducing bacteria back into these mice made some anxious behaviors return, although to a lesser extent than the control mice who weren’t altered. It would seem evident that the mouse microbiome is important to developing a healthy anxiety response, but the researchers aren’t so sure. Some of their experiments suggested the opposite, and referenced conflicting research published in the last two years. De Palma and her co-authors think that the type of stress test may be a factor, and emphasize the need for “well-controlled conditions” and a “strictly sterile environment.”

Either way it is clear that the mouse microbiome has significant effects on how the animals experience anxiety. Don’t take it as a cure for stress-eating, though: you probably need those same bacteria to down your pint of cookies ’n cream.

Image: Мышь 2, George Shuklin/Wikimedia