Hi Thelma,
I had forgotten about the research using mannitol (which is a sugar), to temporarilly open the pores of the BBB. This is used as a method of drug delivery for drugs which normally will not get through the barrier. I think you have to distinguish between a short temporary opening of the BBB, and the permanently open BBB we Parkies suffer from. We have probably had a defective BBB since childhood, with continuing toxin entry into the brain, until 80% of the dopamine neurons are either dead or dormant, and we then show symptoms of PD.
Ron