Doctors who take care of people with Parkinson’s have long known that the brain changes associated with the disease also come with a number of physical changes, especially in the digestive system. Patients often complain of constipation or bloating, difficulty swallowing and indigestion. Often these symptoms start years before the loss of motor control, the hallmark of the disease.
In a new paper published in the journal Cell, researchers led by Sarkis Mazmanian of the California Institute of Technology may have an explanation for that connection. Working with mouse models of the brain disorder, they found that changes in gut microbes may play a role in triggering Parkinson’s. When he and his team transplanted fecal samples from people with Parkinson’s into the mice—which were raised in a germ-free setting and therefore not exposed to other bacteria or viruses—the animals’ Parkinson’s symptoms worsened. The same did not happen when the mice received samples from people without the disease.
“What we extrapolate from that is that there is a microbial profile that is different in Parkinson’s,” says Mazmanian. “Perhaps those changes are contributing to disease; we’re a long way from proving that’s the case in humans, but at least in mouse models that’s what the data suggest.”
Mazmanian has a list of about a dozen species of microbes that might be important in the disease; some are missing in the Parkinson’s patients, which may mean that they provide some protection against the neurodegenerative condition. Mazmanian has created a company, Axial Biotherapeutics, to research these species further as possible microbial treatments for brain diseases.
That the state of the gut can affect the brain may at first sound unlikely, but Mazmanian points out that up to 70% of the neurons outside of the brain exist in the intestines. This network of nerves is connected to the brain via the vagus nerve, which connects everything from the chest, lungs and abdomen to the neck and larynx. Finding a possible bridge that links the gut and the brain in the form of microbes may, with more research, lead to new treatments for Parkinson’s.