Properties of CA3 Dendritic Excrescences in Alzheimer's Disease

What is it about?

CA3 pyramidal neurons and hilar mossy neurons possess large and branched dendritic spines, named thorny excrescences. Studies on experimental animals have shown great morphologic adaptation of the excrescences and the whole dendritic tree of CA3 pyramidal neurons in changes of environmental conditions. However, the available data about the excrescences in human brain is short and insufficient about their properties in Alzheimer’s disease. In the present study, these dendritic structures were studied and compared in CA3 area of hippocampus in patients suffered from Alzheimer’s disease, age matched controls and young individuals. Golgi impregnated material under light microscopy was used for the description of the structural characteristics of the excrescences. Morphometric estimation of their density on the apical and basilar dendritic tree and their average length revealed reduced density and significantly increased size in Alzheimer’s disease patients. The mean density of the excrescences on the apical dendritic tree of the patients compared to age matched controls is reduced 32.8% (p<0.001), while the mean number of long excrescences (longer than 5μm) is increased 32.6% (p<0.05). On the basilar dendritic tree, the reduction in density is 26.3% (p<0.05) and the increase in the number of long excrescences is 23.3% (p>0.05). These enlarged thorny excrescences can be even longer than 10μm, appearing as “giant spines”. The increased size of the excrescences is considered as a remodeling procedure (compensative mechanism) of the CA3 pyramidal neurons for the balancing of the reduction in the spinal density.

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Why is it important?

The properties of the excrescences described here are in favor of a great adaptation of these structures in different conditions and resistance to the progressive degeneration of Alzheimer’s disease. This hypothesis can further be tested by electron microscopy; however, the functional significance of these enlarged excrescences cannot be estimated, since there is still no consent about the impact of post-mortem morphological findings into patients’ cognitive performance [52-54]. Similar compensatory mechanisms in CA3 area have been previously described in rat brain under chronic restraint stress and learning, concerning rewiring of the whole dendritic tree and the excrescences

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