Transfer of gut bacteria affects brain function and nerve fiber insulation

So maybe you want a fecal transplant from a happy person to treat your depression. I'm assuming that this would work the same way in reverse as this research shows.
http://www.mdlinx.com/internal-medicine/medical-news-article/2016/04/22/6639469/?news_id=2386&

The Mount Sinai Hospital, 04/22/2016

Specific combinations of gut bacteria produce substances that affect myelin content and cause social avoidance behaviors in mice, according to a study conducted at the Icahn School of Medicine at Mount Sinai and published in the journal eLife. This research suggests that targeting intestinal bacteria, or their metabolites, could be one way to treat debilitating psychiatric disorders and demyelinating diseases, like multiple sclerosis. This current study led by Patrizia Casaccia, MD, PhD, Professor of Neuroscience, Genetics and Genomics, and Neurology, and Chief of the Center of Excellence for Myelin Repair, and post–doctoral fellow Mar Gacias, PhD, identifies bacteria–derived gut metabolites that can affect myelin content in the brains of mice and induce depression–like symptoms. Researchers transferred fecal bacteria 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. 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.