Cerebral cortex and hippocampus respond differently after post-natal exposure to uranium

Abstract

The central nervous system (CNS) is known to be sensitive to pollutants during its development. Uranium (U) is a heavy metal that occurs naturally in the environment as a component of the earth's crust, and populations may therefore be chronically exposed to U through drinking water and food. Previous studies have shown that the CNS is a target of U in rats exposed in adulthood. We assessed the effects of U on behavior and cholinergic system of rats exposed from birth for 10 weeks at 10 mg.L⁻¹ or 40 mg.L⁻¹. For behavioral analysis, the sleep/wake cycle (recorded by telemetry), the object recognition memory and the spatial working memory (Y-maze) were evaluated. Acetylcholine (ACh) and acetylcholinesterase (AChE) levels were evaluated in the entorhinal cortex and hippocampus. At 40 mg.L⁻¹, U exposure impaired object recognition memory (-20%), but neither spatial working memory nor the sleep/wake cycle was impaired. A significant decrease was observed in both the ACh concentration (-14%) and AChE activity (-14%) in the entorhinal cortex, but not in the hippocampus. Any significant effect on behaviour and cholinergic system was observed at 10 mg U.L⁻¹. These results demonstrate that early exposure to U during postnatal life induces a structure cerebral-dependant cholinergic response and modifies such memory process in rats. This exposure to U early in life could have potential delayed effects in adulthood.