Amyloid deposition in the nucleus basalis of Meynert complex: a topographic marker for degenerating cell clusters in Alzheimer's disease.

The deficiency of the cholinergic cortical projection system arising in the different basal forebrain structures collectively referred to as nucleus basalis of Meynert complex is a constant finding in Alzheimer's disease, a disorder which is neuropathologically characterised by the appearance of three intracerebral formes of twisted β-pleated sheet (amyloid) fibrils, neurofibrillary tangles, amyloid-containing neuritic plaques and congophilic amyloid angiopathy. In the present study the quantitative relationship between these hallmarks of the disease, amyloid deposition and neuronal loss in the cholinergic basal forebrain system, was investigated in ten cases of Alzheimer's disease. Besides a constant involvement of the cerebral cortex and hippocampus, all cases of Alzheimer's disease show a large amount of amyloid in the medial septal nucleus, in the diagonal band nucleus and in the substantia innominata which is correlated with neuronal loss in these areas. These amyloid deposits in the basal forebrain are due to congophilic angiopathy associated with plaques and neurofibrillary tangles. The distribution of amyloid deposition in the basal forebrain is restricted entirely to those neuronal clusters which represent the origin of cholinergic innervation of the cerebral cortex and hippocampus. Immediately adjacent structures are not affected. These findings suggest a pathogenetic role of amyloid deposition in the mechanism of degeneration of the cholingeric basal forebrain system.