Silver nanoparticles alter learning and memory formation in an aquatic organism, Lymnaea stagnalis

- A higher concentration (10 μg/L) enhances memory formation.
- The highest concentration (50 μg/L) blocks memory formation.
- Chronic and acute exposures were no different.
- AgNO3 concentrations (1, 5 and 10 μg/L respectively) have similar effects.
- Memory recall is context specific, thus snails trained in AgNPs do not exhibit memory when tested in AgNO3 and vice-versa.

We tested the effect of silver nanoparticles (AgNPs) on the ability of the pond snail, Lymnaea stagnalis, to learn and form long-term memory (LTM) following operant conditioning of aerial respiration. We hypothesized that the AgNPs would act as a stressor and prevent learning and LTM formation. We tested snails exposed for either 72 h or only during training and testing for memory (i.e. 0.5 h) and found no difference between those treatments. We found that at a low concentration of AgNPs (5 μg/L) neither learning and nor memory formation were altered. When we increased the concentration of AgNPs (10 μg/L) we found that memory formation was enhanced. Finally, at a higher concentration (50 μg/L) memory formation was blocked. To determine if the disassociation of Ag+ from the AgNPs caused the effects on memory we performed similar experiments with AgNO3 and found similar concentration-dependent results. Finally, we found that snails perceive the AgNPs differently from Ag+ as there was context specific memory. That is, snails trained in AgNPs did not show memory when tested in Ag+ and vice-versa. We believe that changes in memory formation may be a more sensitive determination of AgNPs on aquatic organisms than the determination of a LC50.

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