Alzheimer's disease-related synapse loss in the cingulate cortex.

Synapse loss is considered a profound neuropathology associated with Alzheimer's disease (AD). This AD-related change in connectivity can be demonstrated in many regions of the neocortex. The posterior cingulate cortex has been identified as an area involved early in the disease process but has not been well studied. The anterior cingulate cortex, which is morphologically distinct from the posterior cingulate, is also involved in AD. The present study employed ultrastructural techniques to assess synaptic numbers in these two regions of association cortex. Both cingulate areas demonstrated a significant loss in lamina III in AD, while only the posterior cingulate manifested a loss in lamina V. The failure to find a significant change in lamina V of the anterior cingulate may be related to its connectivity with the motor system. The heterogeneity of synaptic change in this cortical region may reflect important information concerning corticocortico connectivity changes in AD.