Senile plaques, amyloid beta-protein, and acetylcholinesterase fibres: laminar distributions in Alzheimer's disease striate cortex.

The laminar distributions of senile plaques and amyloid beta-protein (A beta P) within the striate cortex of patients with Alzheimer's disease (AD) were studied with enhanced Bielschowsky (roughly equivalent to the Campbell technique) and immunohistochemical methods. The laminar distribution of acetylcholinesterase (AChE) fibres within the striate cortex of both AD patients and control patients was studied with an enzyme histochemical method. Quantification of Bielschowsky-stained plaque numbers along intersect lines drawn parallel to laminar boundaries revealed a significant aggregation of plaques at the interface of layers IVc and V. Lines drawn through layer VI intersected significantly fewer plaques than lines through other laminae. Immunoperoxidase staining for A beta P revealed a similar distribution of senile plaques, and addition, prominent, diffuse deposits of A beta P within layers I and IVc. AChE fibres were markedly depleted in the striate cortex of AD cases. In control cases, AChE fibres were, like A beta P immunoreactivity, concentrated within layer I and IVc. The results indicate that enhanced silver methods may not reveal the complete distribution of A beta P. The codistribution of A beta P-immunoreactive diffuse amyloid deposits and AChE fibres to the same cortical laminae is consistent with the possibility that these deposits may be formed from degenerating cholinergic elements. The formation of a line of senile plaques at the interface of two cortical laminae within the striate cortex, in an anatomically analogous situation to a similar line of plaques within the dentate gyrus, suggests that formation of well-defined plaques may be accelerated by the interaction of specific neuronal systems.