In mice, a special kind of immune cells help gut bacteria 'talk' to the brain, according to a new study published in Cell Reports. This finding could help manage the symptoms of mental disorders.
Researchers from the Max Delbrück Center for Molecular Medicine in the Helmholtz Association administered a strong dose of antibiotics to mice in order to switch off their microbiome. These mice formed fewer nerve cells in their hippocampus compared to the control group, resulting in impaired neurogenesis. "We injected BrdU, which incorporated into proliferating cells during the S phase of mitosis. After 4 weeks we sacrificed the mice and dissected the brains. We stained with antibodies against BrdU to label the cells that proliferated over the last 4 weeks of the mouse's life. We also labeled them with two markers for juvenile and adult neurons to measure neurogenesis, which is the the generation of new neurons in the hippocampus, an area of the brain needed for memory consolidation and pattern recognition," Dr. Susanne Wolfe from the MDC research group told ALN exclusively.
Interestingly, mice without active gut bacteria also showed a lowered population of a specific immune cell, the Ly6Chi monocytes. This led the researchers to wonder if the monocytes functioned as an intermediary between the microbiome and the brain. "We were interested to find a communication route between gut and brain. The cells of the immune system was a good candidate to look at since they can travel fast throughout the whole body. Amongst several subsets of immune cells, we found the Ly6Chi cells in the brain to be regulated in the same pattern like neurogenesis: down in abx treated mice, not recovered in fecal transplanted mice, fully restored in numbers after running and probiotics," Wolfe added. "When we took healthy mice and depleted the Ly6Chi cells by antibody treatment, we saw a decline in neurogenesis. Also when we used a knock out for the cell subset, neurogenesis was impaired. Finally, when we gave Ly6Chi cells back to Abx mice, we could restore neurogenesis."
This research suggests that the microbiome may play a role in mental disorders. "Given that every research done in mice has the disadvantage that is was done in mice and not in humans, we believe that we provide some evidence that probiotics apart from exercise could be a good treatment for humans suffering from gut imbalance and from impaired neurogenesis, which might be accompanied by impaired memory and learning. Its not going to be a miracle supplement, but it might help to support a healthy lifestyle," Wolfe concluded.