Objective: Neuroimaging and other biomarker assays suggest that the pathological processes of Alzheimer’s disease (AD) initiate years prior to clinical dementia onset. However some 30%-50% of older individuals that harbor AD pathology do not become symptomatic in their lifetime. It is hypothesized that such individuals exhibit cognitive resilience that protects against AD dementia. We hypothesized that in cases with AD pathology structural changes in dendritic spines would distinguish individuals that had or did not have clinical dementia.
Methods: We compared dendritic spines within layers II and III pyramidal neuron dendrites in Brodmann Area 46 dorsolateral prefrontal cortex using the Golgi-Cox technique in 12 age-matched pathology-free controls, 8 controls with AD pathology (CAD), and 21 AD cases. We used highly optimized methods to trace impregnated dendrites from brightfield microscopy images which enabled accurate three-dimensional digital reconstruction of dendritic structure for morphologic analyses.
Results: Spine density was similar among control and CAD cases but reduced significantly in AD. Thin and mushroom spines were reduced significantly in AD compared to CAD brains, whereas stubby spine density was decreased significantly in CAD and AD compared to controls. Increased spine extent distinguished CAD cases from controls and AD. Linear regression analysis of all cases indicated that spine density was not associated with neuritic plaque score but did display negative correlation with Braak staging.
Interpretation: These observations provide cellular evidence to support the hypothesis that dendritic spine plasticity is a mechanism of cognitive resilience that protects older individuals with AD pathology from developing dementia. This article is protected by copyright. All rights reserved.