Qian, Xh., Liu, Xl., Chen, G. et al. Injection of amyloid-β to lateral ventricle induces gut microbiota dysbiosis in association with inhibition of cholinergic anti-inflammatory pathways in Alzheimer’s disease. J Neuroinflammation 19, 236 (2022). https://doi.org/10.1186/s12974-022-02599-4

Paper explains a possible two-way action in the function of amyloid (tau) in being both the cause of dementia and the effect on gut microbiome in dementia.

It is very likely the same criteria apply to Parkinson’s although the progression of early Parkinson’s symptoms tends to make the gut to brain path more likely. Acceptance of this progression is very limited amongst grant givers  so this paper may be a sop to them and a way of breaking the deadlock on research.