Why might gut bugs be linked to mood?

THAT'S THE WHY:IT MIGHT not be the most appetising of thoughts, but your gut typically harbours trillions of bacteria. Just what is in there and what they all do is the subject of intense scientific scrutiny these days. And a group at University College Cork has been particularly looking at potential links between the microbes hanging out in the gut and mood, in mice at least.

One study they did, published last year in the Proceedings of the National Academy of Sciences, found that when they fed mice with a strain of Lactobacillus rhamnosus bacteria, the behaviour of the mice suggested they were less anxious than the mice that didn’t eat the probiotic. The Lactobacillus-munching mice had different brain chemistry relating to stress too.

More recently, the UCC researchers published a paper in Molecular Psychiatry describing how, again in mice, the absence of bacteria during early life affected concentrations of a neurotransmitter called serotonin in the brain in adulthood. Serotonin is thought to play a role in regulating mood.

“We are increasingly realigning how important gut bacteria are to all aspects of health and disease and even behaviour,” says researcher Prof John Cryan from the Alimentary Pharmabiotic Centre.

“These data highlight that the make-up of gut bacteria in early life can have a major governing factor over brain function in later life.”

It’s a bit of a leap from mice to humans, and long-term studies in humans are now required to fully validate the findings, but Prof Cryan expresses confidence that the effects will translate to human behaviour.