Changes in the brain in aging and Alzheimer's disease assessed by neuronal counts.

Changes in the magnitude of neuronal loss, which represent the end point of neuronal degeneration, are controversial and of limited utility as a measure of functional decline in aging and Alzheimer's disease (AD). Changes in the size of neurons and organelles, in the distributions of dendritic and synaptic fields, and in the relationships between neurons and the transmitter substances they produce, may be more useful in that they estimate changes in neuronal function prior to neuronal loss. The quantitative assessment of metabolic change in individual neurons by measuring histochemical reactivity, or more directly measuring enzyme activity or the amounts of its products might more reliably reflect degenerative changes associated with aging or AD, prior to the loss of neurons.