Here is another paper being published early in 2008 on the BBB in PD. I have been in touch with one of the authors, some 9 months ago, and gave the information in my thread, "BBB updated". The interesting point is if we can manipulate the BBB to a porosity of a healthy personm we could open the door to stopping PD, AD, MS, ALS and others in one.
Lancet Neurol 2008; 7: 84–96
Strategies to advance translational research into brain
barriers.
Edward Neuwelt, N Joan Abbott, Lauren Abrey, William A Banks, Brian Blakley, Thomas Davis, Britta Engelhardt, Paula Grammas,
Maiken Nedergaard, John Nutt, William Pardridge, Gary A Rosenberg, Quentin Smith, Lester R Drewes

"In the clinical arena of neurodegenerative disorders,
the BBB is traditionally seen as irrelevant or simply as a
barrier to treatment. In reality, the brain barriers have
important roles in the pathology and progression of a
broad spectrum of CNS disorders, including Alzheimer’s
disease, Parkinson’s disease, amyotrophic lateral
sclerosis, and multiple sclerosis. From a clinical and
basic science perspective, the brain barriers are vital for
CNS homoeostasis and the preservation of neuronal
integrity. The alterations to the cerebral microcirculation
and BBB in neurodegenerative diseases need to be
investigated, and the CNS microvasculature might be a
new target for therapeutic development."

Discussion with another researcher gave me an answer I have been seeking for some time, so another question and answer can be added to the list in my BBB update thread. The BBB is involved in AD as well as PD, but what decides which disease you get? If the BBB was defective uniformly, you might expect we would get both diseases. I speculated AD might require say, a higher permeability than PD, OK, but that would mean you get PD then get AD. That didn't add up. However, I now learn that the BBB is in sections, protecting various areas, So presumably you could be born with the pD section defective, or could damage it environmentally, eg pesticides, and just get PD not AD. Or in rare cases you could damage both ares and get both diseases. It is increasingly looking as though Rick is right when he suggests inflammation precedes the BBB damage.

Ron