Perhaps with disruption of the BBB, the area of the substantia nigra is most susceptible to damage from toxins, infectious agents etc, partially owing to the fact that the lowest density of glutathione peroxidase postitive glial cells is found in the substantia nigra, rendering this dopaminergic cell group less protected and more susceptible to oxidative stress and thus vulnerable to Parkinson’s disease...just thinking while typing.....another coincidential fact just occurred to me and just as quickly left (must learn to type faster than I forget??)