A behavioral and ultrastructural dissection of the interference of aluminum with aging

The persistence of neuroscientists in exploring aluminium's (Al) possible contribution to the pathogenesis of Alzheimer's disease (AD) has resulted in a wealth of researches detailing the biological toxicity of this metal. However, to date, there have been few accounts of the interference of Al with aging and its relevance to the pathogenesis of AD. We investigated the behavioral and the ultrastructural signatures of Al in the hippocampus on young and aging rats which were exposed for three months to aluminium gluconate. The aging animals displayed decreased scores of activity and emotionality, and the Al-exposed aging males had altered emotional reactivity behaviors. The electron-microscopic analysis indicated that Al promoted in the aging hippocampus a variety of cellular and ultrastructural degenerative signs, such as granulo-vacuolar degenerations, deposition of lipofuscin and amyloid in the cytoplasm of neurons and astrocytes, and in extracellular compartments, Hirano bodies, demyelination and the atrophy of the mitochondria. Moreover, the quantitation of myelin sheath width and the diameter of mitochondria measured on randomly selected samples confirmed that myelin and mitochondria are primary targets of Al's toxicity. Demyelination and mitochondrial atrophy seemed more advanced in the hippocampus of Al-exposed aging males, supporting the effect of sex suggested by the behavioral results. These findings and other collateral results also reported here are discussed in the context of a possible involvement of Al in AD, mediated by aging and catalyzed by hepatic morphopathology.