| BackgroundCadmium can cause developmental neurotoxicity and intestinal flora disorder.Due to its extremely long biological half-life and low excretion rate,study of low-dose cadmium pollution is of great significance for the growth and development of offspring.Brain derived neurotrophic factor(BDNF)and the serotonin system are involved in the regulation of neurodevelopment and intestinal function.However,the effects of cadmium on neurotoxicity and flora during development and the mechanism of BDNF and serotonin system are still unclear.In this study,we exposed the larval zebrafish to ecologically relevant concentrations of cadmium to explore whether they could induce microbiota dysbiosis and have the impact on brain function and behaviour.Moreover,we investigate the expression levels of the bdnf gene and the serotonergic genes in zebrafish.And these genes may participate in the regulation of Cd-dependent neurotoxicity.Methods1.To evaluate the effects of ecologically relevant concentrations of cadmium malformation,mortality,spontaneous movement,heartbeat,and hatching rate were measured;2.The change of the spontaneous movement behavior of the zebrafish larvae were detected by using the ViewPoint Zebrabox video-track tracking system;3.ICP-MS was performed to measure the concentration of Cd in zebrafish larvae;4.The composition of the microbiome of zebrafish larvae was analyzed by 16s DNA sequencing analysis;5.The mRNA expression of bdnf and genes involved in serotonin(tph2,tphlb,slc6a4a and mao)were assessed by quantitative PCR;6.To analyze the effect of Lactobacillus rhamnosus GG(LGG)on locomotor and the mRNA expression of bdnf and genes involved in serotonin.Results1.Exposure to Cd resulted in increases in malformation rates respectively(P<0.05),at the concentrations of 1.25?g/L,2.5?g/L and 5?g/L.Mortality increased with increasing concentrations of Cd,with a significant increase in mortality in the 5?g/L Cd-treated group.The hatching rate of treatment groups had no difference compare with the control group.And spontaneous movement had no difference during these groups too.Heart beat decreased with increasing concentrations of Cd,and had a significant difference in the 5?g/LCd-treated group(P<0.05);2.Exposure to Cd reduced the average distance of movement and number of activities in larvae compared with the control group,dose-dependently.Particularly there were statistical differences between the 5?g/L Cd exposure group and the control group(P<0.05);3.The larvae of the three Cd-treated groups showed a significant obvious increase in the bioaccumulation of metal compared with the control group.And the average concentrations of the Cd increased in a dose-dependent manner;4.Analysis of the intestine samples revealed that the proportion of Firmicutes was decreased and that of Proteobacteria was increased with dose-response effect;5.At the genus level,there were 12 kinds of microbiota which are involved in the regulation of neurodegenerative diseases proved by previous studies,changed in Cd-treated group compared with control group;6.The Cd exposure group(5?g/L)showed a significant increase of bdnf?tph2?tphlb and a significant decrease of slc6a4a?mao expression compared with the control group;7.Lactobacillus rhamnosus GG has a protection effect on Cd-dependent neurotoxicity,which included locomotor and some genes expression.Conclusion1.Ecologically Relevant Concentrations of cadmium exposure causes developmental neurotoxicity in zebrafish;Cd exposure changed bacterial relative abundance in larval zebrafish.At the genus level,there were 12 kinds of microbiota changed in Cd-treated group compared with control group.And top 7 of them have been found involved in the regulation of neurodegenerative diseases proved by previous studies;2.These data suggest BDNF signalling and serotonergic system may participate in gut-to-brain communication with Cd exposure.LGG can protect the developmental neurotoxicity induced by cadmium exposure. |
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