The presence of microvascular changes has been documented both in brain aging and Alzheimer disease (AD), although the relationship between the morphometry of brain capillaries and cognitive impairment is still unknown. We performed an analysis of capillary morphometric parameters and AD-related pathology in 19 elderly individuals with variable degrees of cognitive decline. Cognitive status was assessed prospectively using the Clinical Dementia Rating (CDR) scale. Total capillary lengths and numbers as well as mean length-weighted diameter, total neurofibrillary tangle (NFT) and neuron numbers, and amyloid volume were estimated in entorhinal cortex and the CA1 field. Total capillary numbers and mean diameters explained almost 40% of the neuron number variability in both the CA1 and entorhinal cortex. Total capillary length and numbers in the CA1 and entorhinal cortex did not predict cognitive status. Mean capillary diameters in the CA1 and entorhinal cortex were significantly related to CDR scores, explaining 18.5% and 31.1% of the cognitive variability, respectively. This relationship persisted after controlling for NFT and neuron numbers in multivariate regression models. Consistent with the growing interest about microvascular pathology in brain aging, the present data indicate that changes in capillary morphometric parameters may represent independent predictors of AD-related neuronal depletion and cognitive decline.
The neocortex of primates contains several distinct neuron subtypes. Among these, Betz cells of primary motor cortex and Meynert cells of primary visual cortex are of particular interest for their potential role in specialized sensorimotor adaptations of primates. Betz cells are involved in setting muscle tone prior to fine motor output and Meynert cells participate in the processing of visual motion. We measured the soma volumes of Betz cells, Meynert cells, and adjacent infragranular pyramidal neurons in 23 species of primate and two species of non-primate mammal (Tupaia glis and Pteropus poliocephalus) using unbiased stereological techniques to examine their allometric scaling relationships and socioecological correlations. Results show that Betz somata become proportionally larger with increases in body weight, brain weight, and encephalization whereas Meynert somata remain a constant proportion larger than other visual pyramidal cells. Phylogenetic variance in the volumetric scaling of these neuronal subtypes might be related to species-specific adaptations. Enlargement of Meynert cells in terrestrial anthropoids living in open habitats, for example, might serve as an anatomical substrate for predator detection. Modification of the connectional and physiological properties of these neurons could constitute an important evolutionary mode for species-specific adaptation.
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