Researchers at Aarhus University and Aarhus University Hospital in Denmark recently reported new evidence that Parkinson’s disease development may actually start in the gut. The study entitled “Vagotomy and subsequent risk of Parkinson’s disease” was published in the journal Annals of Neurology.
Parkinson’s disease is a progressive neurodegenerative disorder that develops gradually, with patients usually experiencing the first symptoms around the age of 60 or older. As the disease progresses, the symptoms worsen from a barely noticeable tremor in the hands to serious difficulties in speaking, locomotion, coordination and balance. The disease is caused by the premature death of dopaminergic neurons. There is currently no cure for Parkinson’s, and it is estimated that one in every 1,000 individuals worldwide suffer from the disease.
It has been previously suggested that Parkinson’s disease is linked to the vagus nerve, one of the 12 cranial nerves that extends from the brainstem to the abdomen passing multiple organs including the heart, esophagus and lungs. The vagus nerve controls unconscious body procedures like a constant heart rate and food digestion.
In this study, researchers conducted the first and largest epidemiological analysis assessing the possible relationship between the vagus nerve and Parkinson’s disease development in humans.
The team analyzed patients in Denmark who were submitted during 1977 to 1995 to vagotomy, a surgical procedure to remove part or resect the vagus nerve. “We have conducted a registry study of almost 15,000 patients who have had the vagus nerve in their stomach severed. Between approximately 1970-1995 this procedure was a very common method of ulcer treatment. If it really is correct that Parkinson’s starts in the gut and spreads through the vagus nerve, then these vagotomy patients should naturally be protected against developing Parkinson’s disease,” explained the study’s lead author Dr. Elisabeth Svensson in a news release.
The researchers found that their hypothesis was correct. Patients who underwent truncal vagotomy (denervation of the pylorus, liver, pancreas, and small and large bowel) had a decreased risk of developing Parkinson’s disease in comparison to the normal general population and patients who were submitted to super-selective vagotomy (denervation of branches supplying only the lower esophagus and stomach). The risk for Parkinson’s disease was similar between the general population and patients who underwent super-selective vagotomy. These results strongly support the idea that Parkinson’s disease begins in the gastrointestinal tract and spreads to the brain through the vagus nerve.
“Our study shows that patients who have had the entire vagus nerve severed were protected against Parkinson’s disease. Their risk was halved after 20 years. However, patients who had only had a small part of the vagus nerve severed where not protected. This also fits the hypothesis that the disease process is strongly dependent on a fully or partially intact vagus nerve to be able to reach and affect the brain,” noted Dr. Svensson.
The team concluded that full truncal vagotomy is associated with a decreased risk for subsequent Parkinson’s disease, suggesting that the vagal nerve plays a crucial role in disease pathogenesis. Researchers hypothesize that Parkinson’s may be caused by an enteric neurotropic pathogen that enters the brain through the vagal nerve.
Interestingly, many Parkinson’s patients suffered from gastrointestinal manifestations before the disease was diagnosed. “Patients with Parkinson’s disease are often constipated many years before they receive the diagnosis, which may be an early marker of the link between neurologic and gastroenterologic pathology related to the vagus nerve” said Dr. Svensson.
The team hopes to identify risk factors for Parkinson’s disease that can help its prevention. “Now that we have found an association between the vagus nerve and the development of Parkinson’s disease, it is important to carry out research into the factors that may trigger this neurological degeneration, so that we can prevent the development of the disease. To be able to do this will naturally be a major breakthrough,” concluded Dr. Svensson.
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