We have written before about the importance of the microbiome in enforcing gut impermeability. Evidence is mounting that bacteria are crucial for preventing ‘leaky’, or permeable guts. Leaky guts allow molecules to pass through them, which can cause many problems, especially for the immune system. The blood brain barrier (BBB) is equally important, as it prevents toxins and molecules from entering the brain from the blood vessels. Now, researchers have discovered the microbiome may have an equally important function towards BBB impermeability. An article was published last week in the journal Science Translational Medicine that has shown the first link between gut bacteria and the BBB.

Researchers raised 2 groups of mice: a control group that was normally reared and had a natural gut microbiome, and a germ-free group of mice that had no gut bacteria at all. They then tested these mice’s BBB permeability using various techniques. The normal mice had a normal, impermeable BBB, while the germ-free mice had very permeable BBBs. This permeability persisted, unchecked, through adulthood in the germ free mice. However, when the researchers transplanted the microbiomes of normal mice into the guts of the germ-free mice, their BBBs very rapidly ‘tightened’ and became normal.

Gut permeability regulation by bacteria has been related to the presence of short-chained fatty acids (SCFAs), which gut bacteria produce. The scientists wondered if these SCFAs may also have a role in regulating BBB permeability. They fed some of the germ-free mice with SCFAs and their BBB permeability decreased and resembled the BBB of normal mice.

This study demonstrates a new, until now, unknown function of the microbiome: it is critical to creating an impermeable BBB. The impermeability of the BBB is essential for neuron growth and overall brain function, so this study is another in a long line that shows a healthy gut leads to a healthy brain.