Antibiotics strong enough to kill off gut bacteria can also stop the growth of new brains cells in the hippocampus, a section of the brain associated with with memory, reports a study in mice published in Cell Reports on May 19. Researchers also uncovered a clue to why - a type of white blood cell seems to act as a communicator between the brain, the immune system and the gut.
Wolf first saw clues that the immune system could influence the health and growth of brain cells through research into T cells nearly 10 years ago. But there were few studies that found a link from the brain to the immune system and back to the gut.
In the study, the researchers gave a group of mice enough antibiotics for them to become nearly free of intestinal microbes, Compared to untreated mice, the mice who lost their healthy gut bacteria performed worse in memory tests and showed a loss of neurogenesis (new brain cells) in a section of their hippocampus that typically produces new brain cells throughout an individual's lifetime. At the same time that the mice experienced memory and neurogenesis loss, the research team detected a lower level of white blood cells (specifically monocytes), marked with Ly6Chi in the brain, blood and bone marrow. So researchers tested whether it was indeed the Ly6Chi monocytes behind the changes in neurogenesis and memory.
In another experiment, the team compared untreated mice to mice that had healthy gut bacteria levels but low levels of Ly6Chi either due to genetics or due to treatment with antibodies that target Ly6Chi cells. In both cases, mice with low Ly6Chi levels in mice treated with antibiotics, then memory and neurogenesis deficits as mice in the other experiment who had lost gut bacteria.Furthermore, if the researchers replaced the Ly6Chi levels in mice treated with antibiotics, them memory and neurogenesis improved.
Luckily, the adverse side effects of the antibiotics could be reversed. Mice who received probiotics or who exercised on a wheel after receiving antibiotics regained memory and neurogenesis.
Luckily, the adverse side effects of the antibiotics could be reversed. Mice who received probiotics or who exercised on a wheel after receiving antibiotics regained memory and neurogenesis.
But one result in the experiment raised more questions about the gut's bacteria and the link between Ly6Chi and the brain. While probiotics helped the mice regain memory, fecal transplants to restore a healthy gut bacteria did not have an effect.
In future, researchers also hope to see more clinical trails investigating whether probiotic treatments will improve symptoms in patients with neurodegenerative and psychiatric disorder.
Luckily, the adverse side effects of the antibiotics could be reversed. Mice who received probiotics or who exercised on a wheel after receiving antibiotics regained memory and neurogenesis.
Luckily, the adverse side effects of the antibiotics could be reversed. Mice who received probiotics or who exercised on a wheel after receiving antibiotics regained memory and neurogenesis.
But one result in the experiment raised more questions about the gut's bacteria and the link between Ly6Chi and the brain. While probiotics helped the mice regain memory, fecal transplants to restore a healthy gut bacteria did not have an effect.
In future, researchers also hope to see more clinical trails investigating whether probiotic treatments will improve symptoms in patients with neurodegenerative and psychiatric disorder.
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