Ultrastructural Alterations in Granular Neurons of the Dentate Fascia Caused by Intrahippocampal Injection of Beta-Amyloid 1-42.

The deposition of beta-amyloid (Aβ) in the brain is detected in Alzheimer's disease and during ageing. Until now, ultrastructural studies of changes caused by Aβ in the dentate gyrus are very scarce. The effects of Aβ 1-42 injection into the CA1 field of rat hippocampus were studied by electron microscopy. In 2 weeks after injection of aggregated Aβ in low concentrations, destructive changes were seen in the structure of dentate gyrus cells, which consisted in a decrease in the number of dentate gyrus neurons and axo-dendritic synapses. These changes were accompanied by enlargement of the endoplasmic reticulum cisterns and widening of the active zones of synapses. Thus, injection of aggregated Aβ 1-42 into the hippocampus led to irreversible (a decrease in the number of neurons and axo-dendritic synapses, agglutination of synthetic vesicles) and adaptive changes (an increase in the sizes of endoplasmic reticulum cisterns and active zones of synapses) in dentate gyrus neurons aimed at the maintenance of functional activity of the nervous system.