Probiotics Calm Mice (via the vagus nerve)

[Ignis]

The latest evidence for this “gut-brain axis” comes from Javier Bravo at University College Cork. He fed mice with a probiotic bacterium called Lactobacillus rhamnosus, often found in yoghurts and dairy products. The bacterial menu changed the levels of signalling chemicals in the rodents’ brains, and reduced behaviours associated with stress, anxiety and depression.

Probiotic bacteria – those that benefit their host – are the subject of sweeping, hand-waving health claims. But beneath the breathless marketing hype, there is some intriguing underlying science. For example, some trials have found that probiotics can help to alleviate the mood symptoms that accompany irritable bowel or chronic fatigue syndrome. To that end, Bravo wanted to see if L.rhamnosus could influence the brains of normal, healthy animals.

Bravo found that his mice, after regularly eating Lactobacillus, were more likely to spend time in the exposed parts of a maze (a common test for anxiety symptoms) than those who ate bacteria-free meals. They were also less likely to drift motionlessly when plopped into water (a common test for depressive symptoms). And during stressful situations, they built up lower levels of stress hormones.

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It may seem odd that bacteria in an animal’s gut can control what happens in its brain, on the other side of the body. But the two organs have a direct line between them – the long, branching vagus nerve, which transmits information from the gut and other visceral organs to the brain. When Bravo severed the vagus nerve in his mice, Lactobacillus lost all of its influence. It changed neither the rodents’ behaviour nor their GABA receptor levels.

-- story @ Discover Magazine