Ultracytochemical Studies of the Effects of Aluminum on the Blood-brain Barrier of Mice

We studied the effect of chronic exposure (6 weeks and 6 months) of mice to drinking (tap) water containing 1.76% (0.06 M) aluminum lactate on some cytochemical properties of the blood-brain barrier (BBB). The plasmalemma-bound enzymatic activities of alkaline phosphatase (AP) and Ca(2+)-activated adenosine triphosphatase (Ca(2+)-ATPase) were studied at the ultrastructural level. Anionic sites were localized with cationized ferritin in a pre-embedding procedure and with cationic colloidal gold in a post-embedding procedure applied to brain samples embedded in Lowicryl K4M. Intravenously injected Evans blue and horseradish peroxidase (HRP) were used for evaluation of the functional state of the BBB. The results indicate that chronic exposure to aluminum does not noticeably affect barrier function of the endothelium of cerebral cortex blood microvessels. Focal leakage of larger than capillary microvessels (presumably arterioles and venules) was observed only in a few areas, such as the basal ganglia and amygdaloid nuclei. The localization of both enzymatic activities (AP and Ca(2+)-ATPase) in microvessels remained essentially unchanged. The localization of anionic sites was also unchanged except on the luminal surface of the endothelium of a few blood microvessels located in areas of the brain where leakage of the injected HRP was noted. In these vessels the injected HRP was often attached to the luminal surface of the endothelial cells, suggesting its increased stickiness. These data, compared with our previous observations on brain microvascular endothelial cells growing in vitro, indicate that cytotoxicity of aluminum is evidently less pronounced in the living organism, presumably due to action of detoxicating and regulatory mechanisms.