A behavioral and histological study of the effects of long-term exposure of adult rats to aluminum.

Aluminum (Al) has been etiologically and epidemiologically related to several neurologic conditions, including Alzheimer's disease (AD). The effects of Al long-term exposure were investigated to describe the associated behavioral and brain modifications. Adult rats were intraperitoneally injected three times a week for 6 months with ecological doses of Al gluconate (0.85 mg/kg). The Al overload was confirmed by the significantly increased level of Al in serum. We assessed fear conditioning, spatial memory and emotional reactivity by shuttle-box task, Morris water maze, and open-field, respectively. The performance of the experimental animals at the shuttle-box task was significantly lower (p <.01) compared to that of control. The experimental animals had impaired spatial memory, with lower and more fluctuant performance at Morris water maze. The noxious-driven behavior of the experimental animals was also altered, with significantly lower activity scores (p <.05), and high emotionality scores (p <.01) at the open-field. We recovered and processed the brain for aluminum and amyloid deposits. The brains of experimental animals, studied by optical microscopy, displayed a massive cellular depletion in the hippocampal formation, particularly, the CAl field, and also in the temporal and parietal cortex. We observed numerous ghost-like neurons with cytoplasmic and nuclear vacuolations, and with Al deposits. The hippocampus contained extracellular accumulations of Al and amyloid surrounded by nuclei of degenerating cells, which we interpreted as neuritic plaques. The cerebrovasculature was distorted, with a significant thickening of the wall of capillaries, associated with amyloid deposits. These behavioral and neuropathological modifications associated with long-term exposure to Al are reminiscent of those observed in AD.