Effect Of Hexavalent Chromium On Apoptosis Of Hippocampal Neurons And Learning-memory Function Injury In Developing Rats

ObjectiveTo explore the effect of hexavalent chromium exposure on apoptosis of hippocampal CA1 region neurons and learning-memory function injury in developing rats and its mechanisms.MethodsTwelve healthy SPF grade pregnant SD rats were selected on study.After offspring rats were born,pregnant rats were randomly divided into 4 groups;the control group(distilled water),the potassium dichromate solution exposure groups with different doses of 0.8mg/kg,4mg/kg and 20mg/kg body weight.Exposure since birth 1d,the offspring rats were exposed to breast milk at lactation stage,the feeding stage(after 21d)was treated by oral gavage.The offspring rats were given by the same volume gavage solvent,once a day,weighed 1 times every three days,and the dosage was adjusted according to the body weight.The treatments were conducted for six mouths.During the exposure period,the situation in offspring rats such as diet,daily water intake,coat color,feces,behavior,body weight change,etc,were observed.Male offspring rats were selected for experiment,after removing individual dead rats,a total of 40.The control group was 11,and the low,middle and high dose group were 10,10 and 9,respectively.Weighing 12 hours ago before drawing materials,and fasting can not help but water.The content of hexavalent chromium in blood was detected by atomic absorption spectrophotometer.Morris water maze test was used to evaluate the learning-memory ability.HE staining was used to observe the morphologic changes of hippocampal CA1 region neurons,the degree of apoptosis in the hippocampus CA1 region neurons by TUNEL staining,and the expression of Caspase-3 was determined by Immunohistochemical assay.The contents of TNF-α and IL-1β in brain tissue were detected by ELISA assay(enzyme-linked immunosorbent assay).Using Excel 2016 to establish a database,the data were analyzed by SPSS 22 software,the measurement data was represented by x ±s.The percentage of search effective strategies in Morris water maze positioning navigation experiment were compared with repeated measurement analysis of variance,other multiple groups of the mean comparison using single factor analysis of variance(One-Way ANOVA)and pairwise comparison.The LSD method was used for the homogeneity of variance,and Dunnett’s T3 test was used for the variance.The comparison of the number of different groups and different time points was analyzed by the variance of repeated measurements.P<0.05 was considered statistically significant.ResultsDuring the experiment period,the rats in the control group had white hair,rapid reaction,and normal growth of diet and body weight;while with the increase of the exposure days,the color of the rats became darker and darker,the appetite decreased,the reaction was unresponsive,and the body weight increased slowly compared with the control group.The learning and memory abilities of rats of the potassium dichromate exposure groups were lower than those of the control group(P<0.05);the content of Cr6+ in blood of the potassium dichromate exposure groups were higher than those in the control group(P<0.05);HE staining showed that with the increase of exposure dose,the neurons in the hippocampal CA1 region of different exposure groups showed different degrees of intercellular space broadening,cell arrangement sparse and disorder,partial cell volume reduced and other pathological changes;TUNEL cell apoptosis assay showed that the control group had rare positive cells,and the rate of apoptosis was low(3.33±0.98)%,The apoptosis rate of potassium dichromate group increased gradually with the increase of exposure dose,which were(9.34±2.42)%,(18.03±1.40)% and(23.91±3.21)%,respectively;Immunohistochemical staining showed that with the increase of potassium dichromate concentration,the number of activated Caspase-3 positive cells increased significantly;and the contents of TNF-α and IL-1β in brain tissue of potassium dichromate exposure groups were all higher than those in control group(P<0.05).ConclusionLong-term hexavalent chromium exposure can damage the recognition function of rats in developing period and decrease the learning-memory ability.Its mechanism of action is related to the increase of inflammatory factors caused by hexavalent chromium and resulted in the neurons apoptosis in the hippocampus CA1 region.