Parkinson’s and the gut

Parkinson’s is often preceded by problems in the gut, and alterations in the nervous system surrounding the gut accompany the condition. In addition, the gut microbiome is emerging as an important regulator of neurodegenerative disease, and accumulating evidence has linked gut microbes to Parkinson’s symptoms and biology.

There is also emerging evidence that our immune system has significant function beyond simply fighting infection; that immune cells in the gut are programmed to relocate within the body homing in on the brain for example, to support the central nervous system (CNS). Scientists also believe that the gut microbiome might influence the brain through the neuronal circuitry that links the gut to the brain via the vagus nerve; this nerve appears to act as a physical link between our organs and the CNS.

Evidence for the vagus nerve connection stems from research of the protein alpha-synuclein in Parkinson’s; when misfolded aggregates of alpha-synuclein have been injected into the gut in laboratory models of Parkinson’s, they travel through the vagal nerve up to the brain.

This gut-brain connection could also be down to chemical messages carried via small molecules called metabolites that re made by the gut microbiome to break down food, drugs, and other natural and man-made compounds. Research has shown that some metabolites made by gut microbes, including psychoactive metabolites, can transit from the gut across the blood-brain barrier and into the brain, where they can potentially impact mood and behaviour and regulate immune cells in the brain.

Researchers have also found that this gut-brain connection isn’t only a one-way journey. Changes that happen within the CNS can also be relayed to the immune system and the gut. Studies have shown that the activation of specific neurons in the brain in response to inflammation in the gut, trigger an immune response in the gut itself; supporting the evidence of a two-way gut-brain connection.

People with Parkinson’s also exhibit differences in their microbiomes to those people without the condition, but researchers don’t yet understand why this happens. An intriguing observation about Parkinson’s is that early symptoms can include dysfunction of the gut, usually resulting in constipation, and this precedes the onset of Parkinson’s sometimes by decades.