Quantitative assessment of synaptic density in the entorhinal cortex in Alzheimer's disease.

We quantified the synaptic density in the entorhinal cortex (Brodmann area 28) in autopsy material from 10 individuals with Alzheimer's disease and compared them to 11 age-matched, postmortem-matched control subjects without dementia, using standard electron microscopy. The statistical data showed no change in synaptic density between control and Alzheimer subjects, in either lamina III or V of the cortex. There were no correlations between synaptic density and synaptic apposition length or density of senile plaques. The entorhinal cortex stands in marked contrast to other cortical areas that show a significant decline in synaptic numbers with Alzheimer's disease. This preservation of synaptic numbers may be related to a plasticity response that is greater in the entorhinal area than in other areas of the cortex.