Impaired recognition memory and emotional reactivity associated with loss of cortical integrity in rats after chronic exposure to aluminum

Although the neurotoxic effects of aluminum (Al) have been extensively investigated, with a particular emphasis on the contribution of this metal to several neurodegenerative conditions such as Alzheimer’s disease, there are few studies on behavioral impairments associated with Al exposure. This lack of data is even more provocative since recent researches have shown that Al induces significant cerebrovascular alterations in cortical architectures. We have investigated possible behavioral impairments of spatial recognition memory and emotional reactivity on rats that were chronically exposed to Al. Concurently, we have studied cytoarchitectural integrity of isocortex, hippocampus and entorhinal cortex, and striatopallidal structures on brain sections stained with the Bielchowsky silver stain method. Our results indicated spatial recognition memory deficits that were significantly represented on spontaneous alternation task performances, but less obvious on Morris water maze task performances of experimental animals, suggesting differences in the sensitivity of these two spatial memory paradigms. We also observed emotional reactivity patterns of modifications on male and female rats exposed to Al. This sexsegregated difference was not completely surprising since estrogens could have neuroprotective effects on adult female rats exposed to Al, although this specific hormonal modulation remains to be tested. These behavioral modifications were associated with massive cellular depletion in frontal isocortex, hippocampus and entorhinal cortex, but relatively spared striatopallidal structures. We concluded that Al primarily induces the structural alteration and functional isolation of the hippocampus, correlated with behavioral deficits on hippocampal-dependent tasks.