Gut bugs build brain barrier

The blood brain barrier, which chemically ring-fences the nervous system from the rest of the body and is critical for the health of the brain, depends upon bacteria for its formation, a new study has shown. For the first time, this links the function, integrity and development of the nervous system with the bugs that colonise the intestines...

Working with laboratory mice, and writing in Science Translational Medicine, Sven Pettersson from the Karolinska Institute in Stockholm, Sweden, showed that mouse pups born to mothers uncolonised by any bacteria (these are so-called "germ-free mice" reared in sterile conditions) have a defective blood brain barrier.

Injected dye molecules, tracer substances or even antibodies, all of which would normally be excluded from the nervous system environment by the blood brain barrier, labelled up the brain tissue of the mice. But giving the animals a transplant of bowel bugs from normal, healthy mice led to a restoration of the barrier function, and the team were able to mimic the effect of the bugs' presence by supplementing the animals with a fatty acid called sodium butyrate, which is produced in large amounts by bowel bacteria.

The researchers speculate that through various signals, including production of fatty acid molecules, the presence of bugs in the gut - and even in a developing pup's mother's gut - signals the cells that form the blood brain barrier to activate.

At the moment the Karolinska team don't yet know how these effects are achieved, what the rest of the signals are, or what bacteria are the key players. It also needs to be confirmed whether the same process occurs in humans. If it does, the findings suggest that what a pregnant woman eats, and if she is exposed to antibiotics, may influence the development of her baby's blood brain barrier. This, in turn, could affect the development of the nervous system.

The discovery could also lead to a better understanding of the immune disease multiple sclerosis, a cardinal feature of which is a highly variable, relapsing and remitting course that affects different parts of the nervous system at different times. Perhaps the intestinal bacteria of MS patients are playing a role in manipulating the blood brain barrier, allowing the immune system to periodically gate-crash parts of the brain and spinal cord to trigger inflammation and disability.