If only it were that simple, people would have a better quality of life and the dairy industry would overtake Big Pharma in revenue. Yet, new research from investigators at the University of Virginia (UVA) School of Medicine has shown that symptoms of depression in mice can be reversed by feeding them Lactobacillus, a probiotic bacterial genus found in live cultures yogurt. Moreover, results from this new study describe a specific mechanism for how the bacteria affect mood, providing a direct link between 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,” explained senior study investigator Alban Gaultier, Ph.D., assistant professor of neuroscience at UVA School of Medicine. “It would be magical just to change your diet, to change the bacteria you take, and fix your health—and your mood.”
The findings from this study were published recently in Scientific Reports in an article entitled “Microbiota Alteration Is Associated with the Development of Stress-Induced Despair Behavior.”
Depression is one of the most common mental health conditions in the United States, with up to 7% of people experiencing a major depressive episode. “It’s a huge problem, and the treatments are not very good because they come with huge side effects,” Dr. Gaultier noted.
While many scientists have long held that the gut microbiome has a major influence on many body systems, including the brain, it has only been in recent years that many of the underlying molecular mechanisms have been explained. In that vein, Dr. Gaultier and his colleagues set out to see if they could find a concrete link between depression and gut health.
“When you’re stressed, you increase your chance of being depressed, and that’s been known for a long, long time,” Dr. Gaultier remarked. “So, the question that we wanted to ask is, does the microbiome participate in depression?”
The short answer seems to be yes. Dr. Gaultier and his team looked at the composition of the gut microbiome before and after mice were subjected to stress and found that the major change was the loss of Lactobacillus. With the loss of the bacterial genus came the onset of depression symptoms. Amazingly, feeding the mice Lactobacillus with their food returned them to almost normal. “A single strain of Lactobacillus is able to influence mood,” Dr. Gaultier remarked.
Importantly, the investigators wanted to determine the mechanism by which Lactobacillus influences depression. The researchers 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 increased—causing depression symptoms set in.
“This is the most consistent change we’ve seen across different experiments and different settings we call microbiome profiles,” stated lead study author Ioana Marin, a doctoral candidate in Dr. Gaultier’s laboratory. “This is a consistent change. We see Lactobacillus levels correlate directly with the behavior of these mice.”
While UVA researchers were excited by their findings, they urged caution about overinterpretation of the results, taking care 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. However, those symptoms are widely accepted as the best available model for looking at depression in creatures other than humans.
Yet, based on their findings, the investigators are looking to begin studying the effect in people as soon as possible. The researchers intend to examine the effects of Lactobacillus on depression in patients with multiple sclerosis, a group in which the disorder is common. Additionally, Dr. Gaultier and his team are continuing to better understand the role of kynurenine in depression onset and within the gut microbiota.
“There has been some work in humans and quite a bit in animal models talking about how this metabolite, kynurenine, can influence behavior,” Ms. Marin concluded. “It’s something produced with inflammation that we know is connected with depression. But the question remains: How? How does this molecule affect the brain? What are the processes? This is the road we want to take.”