The distribution of neuritic plaques and acetylcholinesterase staining in the amygdala in Alzheimer's disease.

The relationship between neuritic plaque formation in Alzheimer's disease and cholinergic innervation of brain regions is unclear. Many neuritic plaques are found in the amygdala, which also receives dense cholinergic innervation from the ventral forebrain, predominantly to the basolateral complex. To determine whether the regional distribution of neuritic plaques is related to the pattern of cholinergic innervation, we studied serial sections through the amygdala of four patients with Alzheimer's disease and four neurologically normal patients. We compared acetylcholinesterase reactivity, neuritic plaques stained with thioflavine S, and cytoarchitectural features in adjacent sections. Neuritic plaque counts were high in most amygdaloid nuclei but were significantly lower in the most acetylcholinesterase-positive region, the lateral portion of the basal nucleus of the amygdala. Acetylcholinesterase reactivity was reduced in the Alzheimer's cases, but the basal nucleus was easily recognized by the characteristic large neurons. The morphology of neuritic plaques also differed in the various regions. These results show that neuritic plaques occur to varying degrees in all nuclei of the amygdala, but are significantly less frequent in the region that receives the most prominent innervation from the cholinergic ventral forebrain.