Study On Effects And Mechanism Of TDCPP On Nervous System In Rats

Objective:This study is aimed to investigate the effects and mechanism of tris(1,3-dichloropropyl)phosphate(TDCPP)which is one new kind of organophosphate flame retardants on nervous system in infant rats after a subacuteexposure.To determine whether this type of chemistry can induceoxidative stress in the cerebral cortex,hippocampus,and cerebellum,we observed the general toxicity and pathological changes of cerebral cortexand hippocampus of rats by Nissl staining and measured the contents of maleic dialdehyde(MDA)and the activity of total superoxide dismutase(T-SOD).To identify the mechanism of TDCPP on nervous system in the rodent,we determinedthe contents of Ach and the activity of AchE and ChAT in cerebral cortex,hippocampusand cerebellum.This work offers valuable insights on TDCPP,oxidative stress and neurotoxicity and providesthe basis for the further investigation.Methods:1.Thirty-two healthy infant SPF male and female SD rats were randomly divided into four groups with eight rats in each group according to weight respectively.Four groups included one control group and three TDCPP groups.Rats in control group were given soybean oil and the other three groups were given TDCPP at doses of 100mg/kg,200mg/kg and 400mg/kg through gavage,respectively,for 28 consecutive days.The behavior were observed and the body weight were measured every day during the experiment period.After 24 hours of the last exposure all of the rats were sacrificed.The liver,spleen,kidney,lung,brain,testis of male or ovary of female were collected and weighed to compute the organ coefficient.2.Six hemispheres of each group were selected to make paraffin sections.The pathological changes of cerebral cortex and hippocampus were observed by HE staining and Nissl staining.3.The oxidative indexes of cerebral cortex,hippocampus and cerebellum in each group were measured.The TBA method was used to measure the content of MDA and the hydroxylamine assay method was used to test the activity of T-SOD.4.The content of Ach and the activity of AchE and ChAT of cerebral cortex,hippocampus and cerebellum respectively in each group were also measured.Results:1.General toxicity: The body weights of the male were no significantly different between the control group and the experimental groups during the contamination.Compared to the control group,the coefficients of brain,spleen and lung were signficantly higher in the high-dose group of the male rats(P< 0.05).The coefficients of liver and kidney in three TDCPP groups were significangtly higher than control group(P<0.01).There was no difference in the coefficients of testis between the TDCPP groups and the control group(P> 0.05).In the female rats,conpared to the control group,the body weights of rats in the middle-dose group and the high-dose group were significant higher on the 7th day,but there was no difference at the end of experimental period(P> 0.05).The coefficients of liver and kidney in three TDCPP groups were significangtly higher than the control group(P<0.01).The coefficients of ovary in the middle-dose group and high-dose group were higher than that of the control group(P< 0.05).2.Pathological staining:(1)HE staining: In male rates,compared with the control group,the neurons shrunk and darker along with abnormal shape in the high-dose group in cerebral cortex and in the CA1 area of the hippocampus.No difference was observed in the CA3 area of hippocampus between the four groups.In female rats,neurons shrunk and became darker in cerebral cortex in the middle-dose group and high-dose group compared with the control group.In the CA1 area and the CA3 area of the hippocampus in the high-dose group,the number of neurons decreased along with wider wider cell spacing and lighter staining compared with the control group.(2)Nissl staining: In male rats,compared with the control group,the volume of neurons decreased evidently,the neurons changed into spindled shape or triangle,the outline of neurons became obscured and nuclei shrunk.In addition,neurons were darker in high-dose group in cerebral cortex.Compared with the control group,an array of neurons became disordered and cells were spaced wider in the CA1 area of the hippocampus in the middle-dose group and the high-dose group.The number of neurons decreased along with wider cell spacing and lighter staining in CA3 area of hippocampus in high-dose group.In female rats,nuclei were shrunkand neurons were darker in the high-dose group in cerebral cortex compared to the control group.In the CA1 area of the hippocampus,the array of neurons became disorderd along with lighter staining the middle-dose group and high-dose group compared to the control group.No difference was observed in the CA3 area of hippocampus between the four groups.3.The oxidative indexes: There was no difference in the content of MDA,the activity of T-SOD in the cerebral cortex,hippocampus and cerebellum between the control group and TDCPP groups in both the male and female rats.4.The content of Ach and the activity of AchE and ChAT:(1)In male rats,the content of Ach and the activity of AchE in cerebral cortex were no difference between the TDCPP groups and the control group(P> 0.05).In the hippocampus,the contents of Ach in middle-dose group and high-dose group were significantly higher than the control group(P< 0.05),but the activities of AchE and ChAT were no difference between the four groups(P> 0.05).In cerebellum,compared to the control group,the content of Ach and the activity of AchE were increased apparently in the middle-dose group and the high-dose group(P< 0.05),and the activity of ChAT in the high-dose group was significantly higher(P< 0.05).(2)In female rats,the content of Ach in middle-age was significantly higher in cerebral cortex compared to the control group(P< 0.05),and the activity of AchE in cerebral cortex was increased substantially in high-dose group and there was no difference in the activity of ChAT between the four groups.In the hippocampus,the content of Ach and the activity of AchE in middle-does group and high-does group were increased significantly compared to the control group(P< 0.05),and the activity of ChAT only increased in low-dose group(P< 0.05).In cerebellum,the content of Ach and the activity of AchE in middle-dose group and high-dose group were significantly higher than the control group(P< 0.05),and the activity of ChAT increased in the high-dose group(P< 0.05).Conclusion:After subacute exposure of TDCPP in SD rats by gavage,the coefficents of kidney and liver in male and female rats increased significantly in these three TDCPP groups,but the body weights were no difference at the end of study.From the results of Nissl staining,we observed that exposure to TDCPP could induce neurons of cerebral cortex and hippocampus changed in the numbers,array and morphology and even decreased the content of Nissl bodies in cytoplasm.In the study of the mechanism,exposure to TDCPP did not break the balance of oxidation-antioxidation system in cerebral cortex,hippocampus and cerebellum in both male and female rats.The neurotoxicity induced by TDCPP maybe related to the increased of the content of Ach,the activity of AchE and ChAT in hippocampus and cerebellum.In our study,there was no significant difference in neurotoxicity between the male and female rats.