Neurochemical correlates of dementia severity in Alzheimer's disease: relative importance of the cholinergic deficits.

Cholinergic markers, neuropeptides, and amines and their metabolites were sampled from identical specimens across 10 neocortical regions in a large sample of Alzheimer's disease (AD) cases and controls. Levels of choline acetyltransferase, acetylcholinesterase, somatostatin, corticotropin-releasing factor, serotonin, and 5-hydroxyindoleacetic acid were significantly reduced in AD versus controls. After data reduction, the most descriptive neurochemical indices were used to examine the relationship of neurochemical measures and dementia severity within the AD sample, controlling for age effects. Dementia severity ratings were based on antemortem assessments (46.9% of AD sample) and postmortem chart review (53.1% of the AD sample). Choline acetyltransferase activity was highly correlated with clinical dementia ratings across the neocortex of the AD cases. Somatostatin and corticotropin-releasing factor levels were correlated with dementia severity only when control cases were included in the analyses. None of the amines, their metabolites, or the neuropeptides quantified related significantly to dementia severity in the AD cohort. These data (a) confirm the strong association of cholinergic deficits with functional impairment in AD and show that this association is independent of age and (b) suggest that of all the neurochemical species quantified, the cholinergic indices may be unique in their association with dementia severity.