Armaghane Danesh Bimonthly Journal (Dec 2019)
The Effect of Chronic Exposure to Low-Level Lead on Learning in the Active Rat Avoidant Conditional Approach
Abstract
Background & aim: Lead is an environmental contaminant and capable of making major changes to the structure and function of the human brain, especially children. Chronic exposure to low levels of lead affects and causes changes in the function of the central nervous system. Therefore, the aim of this study was to determine the effects of chronic exposure to low levels of Pb on learning in the active rat avoidant conditional approach. Methods: In the present experimental study which was conducted in 2018, 24 adult male mice were randomly divided into four equal groups for analysis. The drinking water of the test groups was contaminated with one concentration of 0.1, 0.33 or 1 g / L of lead acetate for 28 days. The experiments were carried out in a semi-dark place. On day 29 for adaptation, each animal was housed separately for 10 minutes without any stimulus in the shuttle box and was free to move. On days 30, 33, and 36, the experiments were performed 40 times (ie, 120 times in total) in each rat for 80 seconds as followed: a 60-second light escape (conditioned stimulus), a 5-second light pause, an active avoidance period consisting of 10 seconds of sound (unconditioned stimulus) with light, and then a warning period of 5 seconds without light and sound. The variable considered was the number of times of the 40 tests that the animal took refuge in the safe cell during each of the above three stages. Data were analyzed using Tukey test. Results: The results indicated that in the warning period, concentration of 0.1 g / L of lead acetate in drinking water considerably weakened learning and showed a significant decrease compared to the control group (p <0.05). In the active avoidance period, on the other hand, the animals receiving the highest doses of lead acetate (1 g / l) showed a significant increase in their learning compared to the control group (p <0.05), but in the escape period, concentrations of 0.1, 0.33 and 1 g / L of lead acetate made no significant change in learning rate compared to the control group. Conclusion: According to the findings, lead contamination has an effect on learning in the mouse model. However, this effect mainly leads to impaired learning and the type of animal response varies depending on the period and dose used.
