Parkinson's Disease and the Gut-Brain Axis

Parkinson’s disease is a brain disease known for producing problems with muscle movement. These problems can include shaking tremors, stiffness in muscles, and difficulty with balance and walking. The direct cause of these problems is because of a decrease in the production of dopamine. Dopamine is a chemical in the brain used to communicate information between nerves. It is also used to direct motor function. The motor coordination part of the brain, the basal ganglia, requires dopamine to function. Without dopamine, the basal ganglia can’t coordinate your muscles well. This means you can't coordinate smooth, balanced, and nuanced movements. The stereotypical shaking in Parkinson’s patients is the result. It’s akin to what would happen if the traffic lights in a city weren’t receiving enough power. Cars would still get through town, but traffic would be slow, backed up, jerky, and would only get worse.

Parkinson’s is a progressive disease, meaning that it gets worse over time. Because of this, it affects older individuals. It affects about 1% of those 65 and older, and 3% of adults over 80. Additionally, it is expected that the number of people with Parkinson’s Disease may increase by up to 30% by 2030. Though it can affect any older individual, it is more common in men. There are genetic and environmental factors that can increase the chance of getting Parkinson’s. These include being of European or South American descent, smoking, and exposure to pesticides. Surprisingly, there is also a link between Parkinson’s and your gut!

Your gut has a direct link to the brain, through the Gut-Brain-Axis via a special nerve called the Vagus Nerve. The Vagus Nerve travels from the brain and some important parts of the digestive system (stomach, large, and small intestine). This nerve communicates a lot of information. It is partially responsible for mood, hunger, and energy, and helps coordinate immune responses. Though the brain is the thinking center of the body, it needs input from the body to make decisions. Interestingly, 90% of Vagus Nerve information flows from the gut to the brain! Disruptions in the gut can therefore have massive effects on how your brain functions.  This appears to be true with Parkinson’s Disease. Research shows that misfolded proteins called alpha-synuclein may be able to travel through the Vagus Nerve. This may damage the part of the brain responsible for muscle control, called the Basal Ganglia.

Research has actually found that disruptions of the gut can affect every system the Vagus Nerve touches. This might be one of the causes for some of Parkinson’s other effects, including non-motor disruptions.  These can include Rapid eye movement Behavior Disorder (RBD), mood disorders, cognitive problems like attention and learning, and even hallucinations.

So far, there aren’t any therapies that can reverse the effects of Parkinson’s Disease. Doctors prescribe l-DOPA to replicate dopamine production in the brain. This helps the Basal Ganglia coordinate movement to reduce the symptoms of Parkinson’s. Unfortunately, we can't yet reverse the progressive nature of the disease. Luckily, clinical trials are aiming to discover disease-modifying treatments!

References:

Breit, S., Kupferberg, A., Rogler, G., & Hasler, G. (2018). Vagus nerve as modulator of the brain–gut axis in psychiatric and inflammatory disorders. Frontiers in psychiatry, 44.

Kandel, E. R., Schwartz, J. H., Jessell, T. M., Siegelbaum, S., Hudspeth, A. J., & Mack, S. (Eds.). (2000). Principles of neural science (Vol. 4, pp. 1227-1246). New York: McGraw-hill.

Kouli, A., Torsney, K. M., & Kuan, W. L. (2018). Parkinson’s disease: etiology, neuropathology, and pathogenesis. Exon Publications, 3-26.

Lanciego, J. L., Luquin, N., & Obeso, J. A. (2012). Functional neuroanatomy of the basal ganglia. Cold Spring Harbor perspectives in medicine, 2(12), a009621.

NIH, National Institute on Aging. (2017). Parkinson’s Disease. https://www.nia.nih.gov/health/parkinsons-disease

Schwarz, P. B., & Peever, J. H. (2011). Dopamine triggers skeletal muscle tone by activating D1-like receptors on somatic motoneurons. Journal of neurophysiology, 106(3), 1299-1309.

Shaik, L., Kashyap, R., Thotamgari, S. R., Singh, R., & Khanna, S. (2020). Gut-brain axis and its neuro-psychiatric effects: A narrative review. Cureus, 12(10).