Effects of Chronic Contact with Low Levels of Lead Acetate on Learning in Active Mice Avoidance Conditional Approach

Introduction: Lead (Pb) is a major pollutant in the environment, which, upon long exposure, can impose a broad range of abnormalities in the structure and function of the brain, especially in the infant. Despite the efforts made in the behavioral effects of lead on the results, there are contradictions and conflicts. In this study, we assessed the effect of chronic exposure to low levels of lead acetate (LA) on active avoidance in the mouse as a laboratory animal model. Materials & Methods: In this study, 24 adult male mice were divided into 4 groups of 6 each. Drinking water of the animals was polluted with either 0 (control), 0.1, 0.33 or 1 g/L of LA for 28 days. All experiments were done in a semi-dark place. On day 29, all animals were placed separately in the shuttle box device without any stimulation for 10 min in order to adopt to test situation. Tests were done on days 30, 33 and 36, 40 times per animal each time (120 in total) consisting of the following phases: Light for 60 sec (Escape Period = EP), then 5 sec no light, then 10 sec sound stimulus (Active Avoidance Period = AAP), then 5 sec no light – no sound (Alarming Period = AP). The number of times out of 40 that animal leaves the test compartment to the safe one was recorded during the mentioned 3 periods. The collected data were analyzed using SPSS software and Tukey test. Results: The results showed that, during the alert period, concentration of 0.1 (g / L) of lead acetate in drinking water significantly impaired learning, Compared to the control group, it showed a significant decrease (P <0.05). On the other hand, during the active avoidance period, the animals receiving the highest dose of lead acetate (1 g / L) showed a significant increase in their learning compared to the control group (P <0.05). But during the escape period, concentrations of 0.1, 0.33 and 1 (g / L) of lead acetate did not change significantly in the level of learning compared to the control group.