Multiple sclerosis is an autoimmune disorder characterized by damage to myelin, the insulating sheath around the axons of nerve cells that allows for faster electrical impulse conduction.  Myelination is critical for everyday brain function.  Damaged myelin results in altered synaptic transmission and clinical symptoms.

Previous research from the group reported a thinning of myelin and a reduction of myelinated fibers in preclinical models of depression, thereby providing a biological insight for the high rate of depression in MS patients.

The current study identifies bacteria-derived gut metabolites that can affect myelin content in the brains of mice and induce depression-like symptoms.
 
Researchers transferred fecal bacteria including members of the Clostridiales, Lachnospiraceae and Ruminococcaceae  from the gut of depressed mice to genetically distinct mice exhibiting non-depressed behavior.  The study showed that the transfer of microbiota was sufficient to induce social withdrawal behaviors and change the expression of myelin genes and myelin content in the brains of the recipient mice.

“Our findings will help in the understanding of microbiota in modulating multiple sclerosis,” says the author.  “The study provides a proof of principle that gut metabolites have the ability to affect myelin content irrespective of the genetic makeup of mice.  We are hopeful these metabolites can be targeted for potential future therapies.”
 
In an effort to define the mechanism of gut-brain communication, researchers identified bacterial communities associated with increased levels of cresol, a substance that has the ability to pass the blood-brain barrier.  When the precursors of myelin-forming cells were cultured in a dish and exposed to cresol, they lost their ability to form myelin, thereby suggesting that a gut-derived metabolite impacted myelin formation in the brain.
 
Further study is needed to translate these findings to humans and to identify bacterial populations with the potential to boost myelin production.
 
http://www.mountsinai.org/about-us/newsroom/press-releases/transfer-of-gut-bacteria-affects-brain-function-and-nerve-fiber-insulation