Synapse loss in the temporal lobe in Alzheimer's disease

The temporal lobe is a well-documented area showing neuropathological and neurochemical changes in Alzheimer's disease (AD). Autopsy tissue was obtained from the superior temporal (Brodmann area 22) and the middle temporal (Brodmann area 21) regions of the cortex from patients with AD (n = 10; postmortem time < 13 hr) and age-matched control subjects (n = 10; postmortem time < 13 hr). Ultrastructural examination of the tissue revealed a highly significant AD-related decline in synaptic numbers in lamina III and V in both the superior and the middle temporal gyrus. Both normal control and AD tissue samples demonstrated a significant negative correlation between the number of synapses and the synapse size, as indexed by the length of the postsynaptic density. This change in synaptic size appears to compensate for the loss of synaptic numbers when viewed in terms of total synaptic contact area. Although the AD tissue showed an average 30% decline in synaptic numbers, the total synaptic contact area remained largely unchanged in both regions of the cortex. There were no significant correlations with age, postmortem time, or number of plaques observed in these areas. The loss of synaptic contacts in AD does not appear to be isolated to a particular cortical region or lamina.