A recent report
http://www.ncbi.nlm.nih.gov/entrez/q..._uids=17503739
states,

"Though the BBB is thought to be intact during neurodegenerative diseases such as Alzheimer's (AD) and Parkinson's disease (PD), recent evidence argues otherwise."
The report goes on to say,
" Dysfunction of the BBB may be involved in disease progression,..........
Developing a better appreciation of BBB dysfunction in AD and PD may not only provide novel strategies in treatment, but will prove an interesting milestone in understanding neurodegenerative disease etiology and progression."

I have found many other references that indicate PD is associted with a defective BBB, but my PC is giving problems, and won't allow me to save them. Try doing a search on defective or leaky BBB and PD.
There is all the evidence I previously posted, Prof Leender's work showing PWP all have a defective BBB, all the most popular beneficial supplements such as curcumin, alpha lipoic acid etc all tighten down the BBB, whilst stress, known toxic compounds, old age, etc all open the BBB
It would be very interesting to try and find a way to reduce the permeability of our BBB to that of a normal person.
Ron