Synaptic density in the inner molecular layer of the hippocampal dentate gyrus in Alzheimer disease

We examined the inner molecular layer (IML) of the hippocampal dentate gyru s for possible changes in synaptic density. Material was obtained from 9 in dividuals with Alzheimer disease (AD) and compared to samples obtained from 10 age-matched, postmortem-matched neurologically normal controls, employi ng standard ultrastructural techniques. Statistical analyses demonstrated a significant decline in synaptic numbers between controls and AD subjects. This decline was accompanied by a significant increase in apposition length and resulted in a significant correlation with the synaptic density. As th e number of synapses declined, the apposition length increased. Assessment was also made of the granule cells density and the analyses showed a signif icant decline in the synapse to granule cell ratio in the AD group. This de cline in the density of synaptic contacts in the IML reflects a more widesp read decline in plasticity in AD and may be related to the memory problems associated with the disease.