Neurotoxic Effects Of Silver Nanoparticles On Brain Of Zebrafish(Danio Rerio)

Silver nanoparticles(Ag NPs)have been widely used in many fields because of its unique antibacterial properties.With the increase of application of Ag NPs,its ecological and health risks have attracted wide attention from all walks of life.It had been proved that Ag NPs can affect the skin,respiratory system,digestive system,nervous system,blood system,reproductive development and other systems.However,there are few reports about the effects of Ag NPs on the biological nervous system,and the neurotoxic effects and mechanisms of Ag NPs need to be further studied.According to the relevant references and the 96 h LC50(283.13 ?g/L)of Ag NPs on zebrafish(Danio rerio),the fishes were exposed to Ag NPs(0,50 and 100 ?g/L)for 30 days.First of all,the content of Ag~+ and the histological changes in the brain of zebrafish exposed to different concentrations of Ag NPs were tested using ICP-MS and light microscopy.Then,the activities of antioxidant enzymes(T-SOD and CAT)and the m RNA expression levels of inflammatory factor-related genes(il-1?,il-8,il-6 and tnf-?)were detected in order to expolre the neurotoxic effects of Ag NPs.Finally,the content of GABA and the m RNA expression levels of gabra1,gat1,abat,gad1 and c-fos in the brain of zebrafish exposed to Ag NPs were analyzed to study the neurotoxic mechanism of Ag NPs mediated by the GABA metabolic pathway.The results are as follows:1.After Ag NPs exposure for 30 days,the content of Ag~+ was significantly enhanced by 50 and 100 ?g/L Ag NPs exposure(p<0.01)and the molecular layer,purkinje cell layer and granular layer of zebrafish cerebellum were not obvious,and the purkinje cell layer almost disappeared.Compared with the control group,the number of cells in the granular layer was decreased by Ag NPs exposure,and the arrangement was loose.Some of the granular cells were hematose,disintegrated,or disappeared,and leukocyte infiltration was observed in some parts of the cells.The nucleus ofthe molecular layer were moved to one side,and the number of cells was decreased.With the increase of Ag NPs concentration,the brain damage of zebrafish was more obvious.2.The activities of T-SOD and CAT in the brain of zebrafish were determined.Results showed that the T-SOD activity was inhibited notably by 50 ?g/L Ag NPs exposure(p<0.01)and the CAT activity was also inhibited remarkably by 50 ?g/L and 100 ?g/L Ag NPs exposure(p<0.01).At the same time,the m RNA expression of il-1? and il-8 in the brain was significantly enhanced by 50 ?g/L and 100 ?g/L Ag NPs exposure(p<0.05).The m RNA expression of il-6 and tnf-? was induced by 100 ?g/L Ag NPs exposure(p<0.01).3.After Ag NPs exposure for 30 days,the content of GABA was decreased remarkably by 50 ?g/L Ag NPs exposure(p<0.01).The m RNA expression of GABA metabolic pathway-related genes(gabra1,gat1,abat and gad1b)in the brain of zebrafish were changed by Ag NPs exposure.The m RNA expression of gabra1,abat and gad1 were notably up-regulated in all the Ag NPs treatment groups(p<0.05).The transcriptional level of gat1 was significantly up-regulated in 100 ?g/L Ag NPs exposure(p<0.01).In addition,the transcriptional express of c-fos was significantly enhanced by100 ?g/L Ag NPs exposure(p<0.05).Based on the findings of this study,the following conclusions can be drawn:1.Ag NPs could accumulate in the brain of zebrafish.With the increase of Ag NPs concentration,the content of Ag~+ was significantly enhanced(p<0.01).The histological changes in the brain of zebrafish were induced by Ag NPs exposure.2.Ag NPs exposure disturbed the antioxidant enzyme system and regulated the m RNA expression of inflammatory factor-related genes in zebrafish brain,which lead to oxidative damage and inflammation.3.Ag NPs exposure might decrease the content of GABA by accelerating the transport and metabolism of GABA in zebrafish brain,which led to neurotoxic effects.