Abstract
Human brains were obtained at postmortem examination from 5 control male individuals aged from 56 to 78 years and with no history of Alzheimer's disease (Group I). Also from 7 patients aged between 59 to 80 years and with history of Alzheimer's disease (Group II). Tissues were obtained from the same area of the hippocampus in both groups within 24 hours postmortem and processed for electron microscopic study.
Two main types of synapses were encountered in the control Group I, symmetric and asymmetric synapses. The former had wide pre‐ and postsynaptic densities. The dendritic and axon terminals contained clear and dense‐cored vesicles in both types of synapses. There was no obvious difference between the width of the synaptic cleft of the two types of synapses. The mean surface density of the symmetric synapses of the control group was 990/mm2 and that of asymmetric synapses was 2164/mm2. The mean lengths of the synaptic opposition was 0.100 μm in the symmetric synapses and 0.121 μm in the asymmetric ones. In Group II with Alzheimer’ disease, vacuolations appeared within the dendrites and in the axon terminals. The myelinated nerve axons showed splitting of the lamellae of its myelin sheaths by intramyelinic vacuoles. The mean surface density of the symmetric synapses was 940/mm2 and that of asymmetric synapses was 1178/mm2. The mean length of the synaptic opposition was 0.271 μm in the symmetric synapses and 0.280 μm in the asymmetric ones.
It could be concluded that the hippocampus of individuals with Alzheimer's disease showed vacuolations at the synaptic junctions and in the myelin sheaths. The number of synapses decreased in these individual with a compensatory increase in the synaptic lengths.