There was a time when if people talked of having a “gut feeling,” it was just a figurative saying. But evidence has been mounting to suggest that there might actually be more to it than could ever have been imagined, as scientists are learning how the microbes in our gut can seemingly influence what goes on in our brain. New research has expanded this even further, revealing that the bacteria influences not just the chemical dimension of the brain, but its physical makeup, too.
What they found in the study was that mice raised to have no gut bacteria showed an increase in gene expression in a certain region of their brain, known as the prefrontal cortex, when compared to other mice that had a normal community of bacteria in their gut, which is known as their microbiome. When the researchers then looked at which genes were influenced, they found that they were altering the level of insulation that wraps around the nerve fibers.
Known as the “myelin sheath,” this insulation is vital in the conduction of electrical impulses, sending the messages throughout the brain. The mice that lacked a microbiome produced thicker myelin sheaths, showing that there is seemingly a link between the physical characteristics of the brain and the microbiome in the gut. “It is likely that key signals from the gut to the brain provide a brake on myelination processes,” explains Professor John F. Cryan, who co-authored the study published in Translational Psychiatry. “Understanding these may open innovative gut microbiome-based strategies for tackling myelin-related disorders.”
The disorders Cryan refers to are those such as multiple sclerosis (MS). Those suffering from MS have a reduced amount of myelin surrounding their nerves, which heavily impacts their ability to send electrical impulses, disrupting the messages sent along them. This often results in difficulty with vision and movement, and in severe cases can lead to blindness and paralysis. By understanding how bacteria might be able to influence the development and maintenance of the myelin sheath, it could offer some form of treatment for those with conditions like MS.
It used to be thought that the information passed between the brain and the gut only went one way, with the brain giving the orders, but slowly, over the past decade, this idea has been chipped away at. Now there is a mountain of evidence to suggest that the connection between the two is far more of a two-way street, leading some to refer to the mass of nerves found in the gut as the body’s “second brain.” This has led some scientists to draw links between the bacteria found making a living in the gut, and certain mental disorders, from autism to schizophrenia, though obviously they are difficult to prove and can be highly controversial.
It does, however, raise the possibility that probiotics, or bacterial transplants, could be used to treat a whole spectrum of conditions. This might sound crazy, but there are examples where this has seemingly worked. For example, there is a case in which after a severe infection of Clostridium difficile, an otherwise healthy woman received a fecal transplant to repopulate her gut microbiome from her overweight daughter. In time, the recipient mother became obese. Doctors think that her weight might have been influenced by the bacteria that was given to her from her overweight daughter.