Effects Of Chronic Exposure To Arsenic On D-aspartic Acid Levels In The Mice Brains And An Exploration Of The Mechanism Of Neurobehavioral Changes In The Mice

Objective:To observe the effects of chronic arsenic exposure on the central nervous system,including learning and memory,D-aspartic acid levels and microglials in mice.To explore the possible mechanism of central nervous system impariment and neurobehavioral changes when chronic arsenic exposure.Methods:Forty-two healthy three-week-old C57BL/6J male mice were randomly divided into seven groups,with six mice in each group:?1?control group;?2?low dose group;?3?medium dose group;?4?high dose group;?5?control group-;?6?high dose group-;?7?high dose group+.?1??2??3??4?group of mice were exposed to arsenic for 24 weeks by free drinking water,?5??6??7?group of mice were exposed to arsenic for 36weeks by free drinking water.General observation was made during feeding and mice were weighted every 3 weeks.Morris water maze was conducted to assess the mice learning and memory.Nissl staining histological study was done to observe the Nissl bodies and the neurons.The changes of neuron,synapse and glial cell were observed by transmission electron microscope.The distribution of D-aspartic acid in the brain of mice was observed by immunohistochemistry.in vitro method,BV-2 microglia exposed to arsenic,were set up to explore the possible mechanism of arsenic effect on microglia.Results:?1?During arsenic exposure period,mice in the arsenic exposed groups were irritable,but no death.At 24 and 36 weeks,compared with their respective control groups,there were no significant differences in body weight and brain organ coefficient of the exposed groups?P>0.05?.?2?After 24 weeks arsenic exposure,compared with the control group,the escape latency in the medium and high dose groups incresed,and the differences were statistically significant?P<0.05?.The number of crossing the platform of the high dose groups decreased compared with the control group,and the differences were statistically significant?P<0.05?.Compared with the control group,the target quadrant residence time and the target quadrant residence time%in the high dose group decreased,and the differences were statistically significant?P<0.05?.After 36 weeks arsenic exposure,compared with the control group-,the escape latency of mice in the exposed groups increased,and the differences were statistically significant?P<0.05?.There were no significant differences in the number of crossing the platform,the target quadrant residence time and residence time%among groups?P>0.05?.?3?Compared with the respective control groups,smaller,sparse disorderly arranged neurons with reduced Nissl bodies and vacuol-like changes were observed in the cerebral cortex and hippocampus of the exposed group after 24 and 36 weeks arsenic exposure.?4?After 24 weeks arsenic exposure,compared with the control group,shrunken and deformed neurons,swollen and vacuolated mitochondrias,reduced endoplasmic reticulums,thin PSD,and shrunken and deformed glial cell with dispersed nuclei were observed in the cerebral cortex and hippocampus of the exposed groups.Demyelination was observed in the cerebral cortex of the high dose group.After 36 weeks arsenic exposure,compared with the control group-,shrunken and deformed neurons,swollen and vacuolated mitochondria,shrinkaged and deformationed glial cells with dispersed nuclei,and demyelination were observed in the cerebral cortex and hippocampus of the exposed groups.In addition,PSD thickness decreased in the high dose group-,while PSD thickness increased in the high dose group+.?5?Compared with the respective control groups,the levels of D-aspartic acid increased in the cerebral cortex of mice the exposed group after 24 and 36 weeks arsenic exposure,while the levels of D-aspartic acid decreased in the hippocampus.?6?Compared with the control group,BV-2 microglia were activated in the treatment groups,and the survival rate of cells decreased.Except0.01 mol/L NaAsO₂ group,the differences of the survival rate of cells in the treatment groups were statistically significant?P<0.05?.Compared with the control group,the apoptosis rate of the treated groups were significantly increased,and the differences were statistically significant?P<0.05?.Compared with the NaAsO₂ group,the activation status of BV-2microglia in the NaAsO₂+minocycline group was inhibited to some extent.The secretion of IL-1?,IL-6 and TNF-?in the supernatant of NaAsO₂+minocycline group decreased,and the secretion of INF-?increased,which were statistically differences compared with the NaAsO₂ group?P<0.05?.Compared with NaAsO₂ group,the expression of COX-2 mRNA in the NaAsO₂+minocycline group was down-regulated,and the difference was statistically significant?P<0.05?.After the light band was analyzed,the expression of COX-2 protein significantly decreased in the NaAsO₂+minocycline group compared with the NaAsO₂ group,and the difference was statistically significant?P<0.05?.Conclusion:Chronic arsenic exposure could bring irreversible damage to the central nervous system,impairing spatial learning and memory of mice.Chronic arsenic exposure affected the D-aspartic acid levels in brain of mice.Arsenic could activate BV-2 microglial cells.Minocycline could inhibit arsenic-induced BV-2 microglial cells activation by downregulating COX-2.