In research presented recently at the International Stroke Conference, scientists from the West Virginia University School of Medicine revealed distinct changes can be observed in an animal's microbiome after suffering from an induced stroke. These alterations were found to persist for several weeks following the stroke, adding new evidence to the compelling gut-brain connection.

The main focus of this new study was to examine the longer term effects of a stroke on the microbiome. Prior research from the same team revealed a stroke does have an immediate effect on the microbiome, but how long these effects last for was not known. Using animal models the researchers conducted microbiome examinations three days, two weeks and four weeks following an induced stroke.

Several key bacterial shifts were prominently identified in the days following the stroke. A notable decrease was seen in Bifidobacteriaceae, a common bacteria found in probiotics, up to four weeks past the stroke, while increases were seen in Helicobacteraceae across the same observational period.

Another big post-stroke change was seen in the ratio of Firmicutes-to-Bacteriodetes. An imbalance in the ratio between these two bacteria has been implicated in a variety of metabolic disorders, including diabetes and obesity. Two weeks after the stroke this ratio was six times higher than the control group. At the four-week point post-stroke the ratio had fallen, but was still three times higher than normal.

What this all means is still up for debate, with no specific implications suggested by the researchers. From a broader, hypothetical perspective the scientists do suggest the longer term changes could certainly be affecting the brain's ability to recover from the initial stroke.

"Big picture: seeing a persistent, chronic change 28 days after stroke that is associated with this increase in some of the negative bacteria means that this could have negative effects on brain function and behavior," says Candice Brown, one of the researchers working on the project. "Ultimately, this could slow or prevent post-stroke recovery."

Another intriguing change in the gut seemingly brought on by the stroke were notable abnormalities in intestinal tissue. Normally in healthy animal models this tissue appears structured in orderly ways, almost like branches of coral. However, close examination up to four weeks post-stroke revealed the villi, structures that project off the intestinal wall, were scrambled and visibly quite different from the healthy models.

"There's disorganization here," explains Allison Brichacek, another researcher working on the project. "There's also less space between the villi to allow nutrients to move around."

It is certainly early days for this research, and it's unclear exactly what this all means for future stroke treatments. What it does affirm is the strange and complex bi-directional relationship that seems to exist between the brain and the gut. We know that this is a two-way street, with the gut influencing the brain as much as the brain influences the gut.

A study from 2017 revealed how traumatic brain injury can influence direct changes in an animal's colon, and conversely, the effects of that traumatic brain injury can be worsened by the presence of certain negative gut bacteria. Another compelling study from 2017 suggested magnetic simulation to specific areas in the brain can affect the composition of a person's gut microbiome.

This new research is yet to be published in a peer-reviewed journal, or verified in human models, but if it is confirmed it adds another exciting piece of evidence to the bi-directional relationship between the gut and the brain. The new research doesn't imply that a stroke is fundamentally caused by an imbalance in the microbiome, but it is hypothesized that stroke recovery could be improved by looking at ways to restore gut health to normalcy following an acute stroke.

"If it ends up being that the gut has an influence on the repair of the brain, maybe our stroke treatments shouldn't just be focused on what we can do for the brain," says Brichacek. "Maybe we need to think about what can we do for the gut."

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