Neurofibrillary degeneration induced by systemic aluminum.

Neurofibrillary degeneration was induced in brain of rabbits by repeated, subcutaneous administration of soluble aluminum salts. Atomic absorption spectroscopy showed brain aluminum levels to increase from 1.1+/0.3mug/g (dry weight) in uninjected animals to concentrations ranging from 2.5 to 47.9 mug/g (dry weight). The Bielschowski silver stain revealed intracellular, argentophilic deposits, which were birefringent when stained with Congo red and viewed in polarized light. The histochemical stain morin revealed aluminum to be concentrated on nuclear chromatin. Analysis by electron microscopy showed the intra-neuronal deposits to be composed of accumulations of 100 A diameter filaments. These observations indicate that systemic aluminum crosses an apparently intact blood-brain barrier and induces neurofibrillary degeneration identical to that following direct brain injection.