# Does Nanosilver Have a Pronounced Toxic Effect on Humans?
## 3 Experimental Research Conducted by the Authors of the Review
### AgNPs Effect on the Brain and Behavior  
To study the effect of AgNPs on the brain and behavior, experiments were performed on mice exposed to AgNPs in adulthood [55]. The animals received a solution of AgNPs (size 25 nm; polyvinylpyrrolidone as coating agent) at a concentration of 25 \(\mathrm{\SIUnitSymbolMicro g}\)/mL for 2 or 4 months, while control individuals drank pure water. When consuming compound animal feedstuff, one mouse drank an average of 5.38 mL of liquid per day; consequently, the daily dose of AgNPs per mouse was 4.5 and 5 mg/kg of body weight for males and females, respectively. At the end of the experiment, the learning ability and spatial memory of the animals were assessed in the Morris water maze (MWM) [60]. In this standard behavioral test, an underwater platform on which the animal can climb to come out of the water is placed in a round white pool filled with water colored and turbid with milk powder. The task of the animal is to find this platform and memorize its location relative to the out-of-labyrinth landmarks [60] in order to use its spatial memory next time to find the platform quicker. The methodology for conducting tests is described in detail in [55]. To establish a correlation between possible cognitive impairments in the brain of animals exposed to NPs and the level of AgNPs accumulated in the brain, the silver content in the brain, as well as in other tissues and organs, was determined after the animals' slaughter using NAA [56]. NAA, due to the possibility of determining a wide number of elements in biological samples, allows assessing the content of silver and iron in organs and blood samples, estimating the passage of nanoparticles through the blood-brain barrier, and quantifying its accumulation in the neuronal tissues of the brain. The technique is described in detail in [55; 56]. According to the NAA results, the relative mass of silver in the brain of experimental animals was 319 \(\pm\) 155 ng after 2 months of nanoparticle intake and 870 \(\pm\) 200 ng after 4 months, which is significantly higher, almost an order of magnitude, than the silver content in the control group [55]. Notwithstanding the accumulation of silver in the brain, within groups of individuals with a preference for different behavioral strategies in the MWM (for details, see [61]), adult experimental animals learned to find the platform just as successfully as control ones. In experiments in which the period of AgNP intake passed after the initial testing, which made it possible to identify groups of individuals with a preference for different behavioral strategies in the test [55], all mice retained learned information about the test for 2 and 4 months. Thus, it was concluded that in adult animals, the long-term oral consumption of AgNPs did not impair the ability to form spatial memory, as well as the ability to store and apply information learned before exposure to AgNPs. Following this series of experiments, a study was carried out that simulated the effect of AgNPs on children born by women employed in the production industry or who were in close contact with AgNPs during pregnancy and lactation at home [57]. During the entire period of pregnancy and lactation (2 months in total), female mice were given to drink a solution of AgNPs (size 25 nm; polyvinylpyrrolidone as coating agent) with a concentration of 25 \(\upmu\)g/mL. Thus, their offspring were exposed to AgNPs during prenatal development and early postnatal development. When the pups reached the age of 2 months, their learning ability and spatial memory were assessed in the MWM, while the silver content in their brain and the mother's brain was determined by NAA. It was found that within groups of individuals with a preference for different behavioral strategies in the MWM, experimental mice did not learn to find the platform, while control individuals coped with the task successfully.