Treating depression like symptoms in mice with probiotics!

Researchers have reversed depression symptoms in mice by feeding them Lactobacillus, a probiotic bacteria found in live-cultures yogurt. Further, they have discovered a specific mechanism for how the bacteria affect mood, providing a direct link between the health of the gut microbiome and mental health.

“The big hope for this kind of research is that we won’t need to bother with complex drugs and side-effects when we can just play with the microbiome,” lead researcher said. “It would be magical just to change your diet, to change the bacteria you take, and fix your health – and your mood.”

“When you’re stressed, you increase your chance of being depressed, and that’s been known for a long, long time,” lead researcher said. “So the question that we wanted to ask is, does the microbiome participate in depression?”

The answer appears to be yes. Looking at the composition of the gut microbiome before and after mice were subjected to stress, the team found that the major change was the loss of Lactobacillus. With the loss of Lactobacillus came the onset of depression symptoms. Feeding the mice Lactobacillus with their food returned them to almost normal. “A single strain of Lactobacillus,” author observed, “is able to influence mood.”

The team then went on to determine the mechanism by which Lactobacillus influences depression. They found that the amount of Lactobacillus in the gut affects the level of a metabolite in the blood called kynurenine, which has been shown to drive depression. When Lactobacillus was diminished in the gut, the levels of kynurenine went up – and depression symptoms set in.

“This is the most consistent change we’ve seen across different experiments and different settings we call microbiome profiles,” explained the graduate student. “This is a consistent change. We see Lactobacillus levels correlate directly with the behavior of these mice.”

The lead author was careful to call the symptoms seen in mice as “depressive-like behavior” or “despair behavior,” as mice have no way to communicate that they are feeling depressed. But those symptoms are widely accepted as the best available model for looking at depression in creatures other than humans.

Based on the new findings, the lead author plans to begin studying the effect in people as soon as possible. He intends to examine the effects of Lactobacillus on depression in patients with multiple sclerosis, a group in which the disorder is common. Promisingly, the same biological substances and mechanisms Lactobacillus uses to affect mood in mice are also seen in humans, suggesting the effect may be the same.

In addition to looking at the effects in people, the researchers are continuing to explore the important role of kynurenine.

“There has been some work in humans and quite a bit in animal models talking about how this metabolite, kynurenine, can influence behavior,” author said. “It’s something produced with inflammation that we know is connected with depression. But the question still remains: How? How does this molecule affect the brain? What are the processes? This is the road we want to take.”

While there is no harm in people with depression eating yogurt – assuming they have no reasons to avoid dairy – people receiving treatment for depression should not stop taking their medications without consulting their physicians. More studies, the researchers noted, are needed.

The findings have been published online by the scientific journal Scientific Reports.