Alzheimer's disease: β-amyloid precursor protein expression in the nucleus basalis of Meynert

The nucleus basalis of Meynert (nbM) was examined using immunocytochemistry for β-amyloid precursor protein (βAPP) expression in Alzheimer's disease (AD). In mild AD cases, light labeling of the cell body and proximal processes was observed, and small intracellular structures were labeled rarely. In the more severe cases, intense cytoplasmic βAPP labeling was seen, often along with small βAPP-positive structures. Double-labeling experiments demonstrated that in the more severe cases these small structures were also decorated by a neurofibrillary tangle (NFT) antiserum. Other neurons in the severe cases showed incorporation of βAPP into large inclusions, which were also labeled with the NFT antiserum. However, some large inclusions in the severe cases were labeled by the NFT antiserum but contained no βAPP. Extraneuronal NFTs did not show βAPP labeling and did not react with an antibody to the β-amyloid peptide. These results suggest that increased expression of βAPP coincides with intracellular NFT formation in the nbM; but that the formation of extraneuronal NFTs results in a loss of βAPP immunoreactivity.