recorded those differences in detail . After sequencing the mixed-together genomes of fecal bacteria from 724 people — a group with Parkinson ’ s and another without — the authors saw a number of distinct changes in the guts of people who suffered from the disease .
The Parkinson ’ s group had dramatically lower amounts of certain species of Prevotella , a type of bacterium that helps the body break down plantbased fiber ( changes like this in gut flora could explain why people with Parkinson ’ s disease often experience constipation ). At the same time , the study found , two harmful species of Enterobacteriaceae , a family of microbes that includes Salmonella , E . coli and other bugs , proliferated . Those bacteria may be involved in a chain of biochemical events that eventually kill brain cells in Parkinson ’ s patients , says Tim Sampson , a biologist at Emory University School of Medicine and coauthor of the study .
At first glance , the relationship between bacteria and brain disease isn ’ t exactly obvious . How can a change in gut microbes kick off a devastating neurodegenerative disorder ? The relationship between the two may seem counterintuitive — but Sampson says it comes down to the subtle ways that the brain and the gut are connected . the gut and respond accordingly . This circuitry controls muscle movement , local blood flow , secretion of mucus and other essential digestive functions .
Since the cells of the enteric nervous system are embedded in the gut wall , many of them come into close contact with the lumen — the cavity of the gut that contains the microbiome — where they can interact directly with biochemicals created by bacteria . Some of these are sticky proteins called curli ( pronounced CURLeye ) that may be implicated in Parkinson ’ s .
Under normal circumstances , curli proteins let Enterobacteria build biofilms , the gooey mats that protect the microbes and help them stay put in the gut . Yet if a curli molecule touches a common protein created by nerve cells — called alphasynuclein — that protein begins
to misfold and form a dangerous mass called an aggregate . Once created , these aggregates can spread widely though the nervous system , leapfrog from cell to cell and eventually enter the brain through the vagus nerve , the main pathway that carries signals between the brain and the gut . It ’ s thought that in some cases of Parkinson ’ s in humans , changes in the gut microbiome may activate that process , says Emeran Mayer , a gastroenterologist and neuroscientist at UCLA and coauthor of a recent overview of the gut-brain connection in the Annual Review of Medicine .
Suspicion that the vagus plays a key role in neurodegenerative disease has been growing in recent years . A 2017 study in the journal Neurology , Mayer notes , showed that “ If you cut the vagus nerve , it decreases the risk for Parkinson ’ s disease . That ’ s a pretty strong indication that
In the walls of the intestines , a network of neurons called the enteric nervous system lets the body sense what ’ s going on in
Species of bacteria from a group known as Prevotella ( shown here in a 3-D illustration ) are dramatically lower in the fecal matter of Parkinson ’ s patients , research has found .
CREDIT : KATERYNA KON / SHUTTERSTOCK
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