Senile plaques in cortex of aged normal monkeys.

The density, type, and distributions of cortical senile plaques were determined in 6 aged rhesus monkeys. Plaque densities were highest in prefrontal and temporal cortices and lowest in occipital cortex. Neurite plaques contained many argentophilic neurites and little amyloid, mixed plaques had both neurites and amyloid, and amyloid plaques showed significant amounts of amyloid and fewer numbers of neurites. As total plaque density increased, there was a linear increase in the density of amyloid plaques, suggesting that plaques evolve from neurite, to mixed, to amyloid types.