Figure 2.

Contribution of the gut microbiota in Parkinson's disease progression. (A) The healthy bi-directional communication between the brain and the gut, highlighting the involvement of the vagus nerve. (B) The brain-gut axis and non-motor symptoms of Parkinson's disease (PD) including both central and gastrointestinal dysfunction. (C) Environmental factors such as the gut microbiota, might begin a pathological process within enteric nerve cell plexus, causing mucosal inflammation and oxidative stress, thereby initiating alpha-synuclein (α-syn) accumulation. The vagal nerve might provide a footpath for the spread of α-Syn from the Enteric Nervous System to the brain through the brainstem, Substancia nigra, basal forebrain and finally the cortical areas where is activated the neurodegeneration and neuroinflammation process described in PD.