PGP and Alzheimer disease: The findings of this study, however, indicate that regional variations in P-gp expression within the brain, and particularly higher levels within the brainstem, may protect against the development of beta amyloid accumulation and senile plaque pathogenesis, and as well, within the superior temporal cortex and perhaps other areas of neocortex, there may be a mechanistic relationship between alterations in P-gp expression as a function of AD disease progression and a progressive accumulation of beta amyloid senile plaque burden.