Parkinson’s and the Gastrointestinal Tract

Ana Roibu

Parkinson’s disease, named after the English doctor James Parkinson, is a chronic and progressive degenerative disorder of the central nervous system. It mainly affects the motor system. The cause is still not clear, although a mixture of both genetic and environmental factors are known to be involved. Apoptosis of neurons in the substantia nigra, a region in the brain responsible for movement and reward, has been shown in all patients suffering from this disease. Research has shown that the symptoms, which include tremors, shaking, bradykinesia, and instability, are the result of the loss of brain cells that produce dopamine. Therefore, the most commonly used treatment far is with L-dopa, the precursor of dopamine, which, unlike dopamine itself, can cross the blood-brain barrier. Unfortunately, this is not a cure and it is just a way to relieve some of the symptoms.

Recent studies from the University of Alabama at Birmingham have discovered even more evidence that each individual’s gut microbiota ties with the changes associated with developing Parkinsons’s. It has been known that a certain balance is necessary for the well-being of the organism, but “alterations in the composition of gut microbiota have been linked to a range of disorders,” as mentioned by the head of the lab, Haydeh Payami. The study used 197 patients suffering from Parkinson’s and 130 controls from three regions of the United States (Atlanta, Seattle and New York). After studying each individual’s microbiome make-up, they found that some strains of bacteria were present in a greater number of the patients than in the healthy individuals, while other species were reduced. In the patients, there was also a clear difference in their microbiome depending on the medication used as part of their treatment. Additionally, there was an unpredicted difference in microbiome imbalance as a function of their geographic location, which could be the cause of dietary differences in the environment and the lifestyle specific to the three different regions.

It is hypothesized that Parkinson’s might actually start in the gastrointestinal tract and then spread to the brain via the vagus nerve, the longest cranial nerve and a crucial part of the parasympathetic nervous system, causing interference in the gastrointestinal tract. This would explain the other symptoms stated by the patients, which the researchers often found strange and unexplainable. Looking back, they found that patients who develop Parkinson’s often report digestive problems such as constipation up to 10 years prior to the development of tremors and bradykinesia. Studies in mice models have shown that the “toxic fibres that build up around the nerve cells of Parkinson’s patients can influence the nerves in the brain in a matter of weeks,” as found at the California Institute of Technology.

The spread of toxic fibres, made out of alpha-synuclein, is abnormal in Parkinson’s– the alpha-synuclein molecules bind together and lead to the formation of fibres which are damaging the nerves in the central nervous system. Researchers were speculating over ten years ago that those who had these fibres in their nervous system also had them in their gastrointestinal tract. Nowadays, researchers are more certain that the gastrointestinal microbiota releases chemicals which overexcites parts of the brain and leads to damage and diseases such as Parkinson’s. Clearly, more research needs to be done, but this is a breakthrough for the way the disease will be treated.

Edited by: Daryn Dever, Karen Yung, and Shreya Singireddy