تاثير تماس مزمن با سطوح پايين سرب در دو مرحله تكاملي مختلف بر فرآيند يادگيري و حافظه در رات

The effect of chronic exposure to low level lead on learning and memory during two different developmental phases of Rat

Low-level lead exposure during brain development is known to affect functions of the central nervous system. The behavioral effects of lead have been studied extensively. Despite these efforts, the results are controversial so that the same behavioral test often produced conflicting results in different investigations. This study was carried out to assess the effects of exposure to chronic low level lead during two different phases of development: breast feeding (I) and after weaning (II) on learning and memory by active avoidance method. Wistar rats were exposed to the metal during breast feeding (I) and after weaning (lI) for 21 days, by replacing the drinking water of experimental groups by 0.05, 0.1, 0.2% lead acetate solution. Each test group had a corresponding control group receiving twice distilled water. Compared to the control groups, in phase I, a dose of 0.05% of lead acetate caused an increase in learning and memory, 0.2% produced an increase in memory and 0.1% caused a decrease in memory. ln phase 11 doses of 0.05% and 0.2% of lead acetate caused an increase in learning and memory. These data indicate that in chronic low-level lead poisoning, learning and memory are influenced by both the doses of the lead and the developmental phase. Different effects of lead exposure in children and adults, as well as inconsistencies between in vivo and in vitro studies, suggest that lead toxicity may have multiple mechanisms in the central nervous system.