A couple of recent papers related to the gut-brain axis
 

"The gut-brain axis in Parkinson's disease: Possibilities for food-based therapies", Perez-Pardo et al., Eur J Pharmacol 2017 May 23, doi: 10.1016/j.ejphar.2017.05.042.

The gut-brain axis in Parkinson's disease: Possibilities for food-based therapies. - PubMed - NCBI

(this is an open-access document)

"Structural changes of gut microbiota in Parkinson's disease and its correlation with clinical features", Li et al., Sci China Life Sci 2017 May 20, doi: 10.1007/s11427-016-9001-4.

Structural changes of gut microbiota in Parkinson's disease and its correlation with clinical features. - PubMed - NCBI

​(abstract only, the rest is behind the paywall)

Hat tip to aspergerian at HU for the links.