Abstract
We studied the effects of chronic intoxication with the heavy metals lead (Pb2+) and zinc (Zn2+) on memory formation in mice. Animals were intoxicated through drinking water during the pre- and postnatal periods and then tested in the step-through inhibitory avoidance memory task. Chronic postnatal intoxication with Pb2+ did not change the step-through latency values recorded during the 4 weeks of the test (ANOVA, P>0.05). In contrast, mice intoxicated during the prenatal period showed significantly reduced latency values when compared to the control group (day 1: q = 4.62, P<0.05; day 7: q = 4.42, P<0.05; day 14: q = 5.65, P<0.05; day 21: q = 3.96, P<0.05, and day 28: q = 6.09, P<0.05). Although chronic postnatal intoxication with Zn2+ did not alter a memory retention test performed 24 h after training, we noticed a gradual decrease in latency at subsequent 4-week intervals (F = 3.07, P<0.05), an effect that was not observed in the control or in the Pb2+-treated groups. These results suggest an impairment of memory formation by Pb2+ when the animals are exposed during the critical period of neurogenesis, while Zn2+ appears to facilitate learning extinction.
Highlights
Forty-nine male and female Swiss mice (20-30 g) from our own colony were used
Given the evidence for the differential actions of Pb2+ and Zn2+ on neuronal development and their concentrations in a brain area critical to memory formation, we evaluated the effects of chronic intoxication with these heavy metals during pre- and postnatal stages of development on performance in the step-through inhibitory avoidance task
The inhibitory avoidance model was used to study the effects of lead and zinc on memory formation [12]
Summary
Forty-nine male and female Swiss mice (20-30 g) from our own colony were used. The animals were distributed into 4 experimental groups and maintained at constant temperature (24.8 ± 0.2oC), with free access to food and water. Given the evidence for the differential actions of Pb2+ and Zn2+ on neuronal development and their concentrations in a brain area critical to memory formation, we evaluated the effects of chronic intoxication with these heavy metals during pre- and postnatal stages of development on performance in the step-through inhibitory avoidance task. A group of 13 mice were exposed to lead acetate at the same concentration for 60 days beginning during the second month of life (postnatal lead group, PostPb).
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