Gut microbes may impact on brain development and function

gutbrainbarrierAn increasing amount of research has come out in recent years illustrating the crucial relevance of healthy gut bacteria. Now a new study from the Karolinska Institutet has revealed that our gut-residing microbes can influence the integrity of the blood-brain barrier. The blood brain barrier acts by protecting the brain from harmful substances in the blood.

The scientists demonstrated that the transport of molecules across the blood-brain barrier can be regulated by gut microbes. Mice models were used and the first group was raised in an environment where they were exposed to normal bacteria, and the second (called germ-free mice) was kept in a sterile environment without any bacteria.

The germ free mice demonstrated an increased leakiness of the blood-brain barrier maintained into adulthood. The permeability of the blood brain barrier was circumvented when the mice were exposed to transplantation of normal gut microbes.

“We showed that the presence of the maternal gut microbiota during late pregnancy blocked the passage of labeled antibodies from the circulation into the brain parenchyma of the growing fetus,” said first author Dr. Viorica Braniste at the Department of Microbiology, Tumor and Cell Biology at Karolinska Institutet. “In contrast, in age-matched fetuses from germ-free mothers, these labeled antibodies easily crossed the blood-brain barrier and was detected within the brain parenchyma.”– which therefore play an important role in the protection of the brain.

“These findings further underscore the importance of the maternal microbes during early life and that our bacteria are an integrated component of our body physiology,” says Professor Sven Pettersson, the principal investigator at the Department of Microbiology, Tumor and Cell Biology. “Given that the microbiome composition and diversity change over time, it is tempting to speculate that the blood-brain barrier integrity also may fluctuate depending on the microbiome. This knowledge may be used to develop new ways for opening the blood-brain-barrier to increase the efficacy of the brain cancer drugs and for the design of treatment regimes that strengthens the integrity of the blood-brain barrier.”

The research findings may also explain why some children with autism spectrum disorder symptoms have their symptoms reversed upon the introduction of a probiotic diet that re-balances their gut bacteria.


V. Braniste, M. Al-Asmakh, C. Kowal, F. Anuar, A. Abbaspour, M. Toth, A. Korecka, N. Bakocevic, N. L. Guan, P. Kundu, B. Gulyas, C. Halldin, K. Hultenby, H. Nilsson, H. Hebert, B. T. Volpe, B. Diamond, S. Pettersson. The gut microbiota influences blood-brain barrier permeability in mice. Science Translational Medicine, 2014; 6 (263): 263ra158 DOI: 10.1126/scitranslmed.3009759

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