SMF-induced Brain Injury And The Underlying Mechanisms With DAT As The Target

Magnetic field(MF)is widely used in transportation,medical apparatus,military,mobile communication,etc.,at the same time,its health hazards are becoming more and more concerned.The frequency of medium strong static magnetic field(SMF)is 0,while its strength is in the range of 1 mT~1 T.The magnetic field may have damaging effects on the nervous,blood,endocrine,immune and reproductive system,among which the nervous system is one of the most sensitive systems.At present,the research on the biological effects of magnetic field is mainly focused on that of the extremely low frequency magnetic field.The brain damage induced by medium strong SMF is rarely reported,besides that,the underlying mechanism of SMF biological effects is still elucidated.Therefore,it is of important theoretical value and practical significance to study the effects of medium strong SMF on brain and the underlying mechanisms.Epidemiological investigation showed that magnetic exposure could cause anxiety,depression and mood changes.The dopaminergic system plays an important role in mood control.Studies have shown that the ventral tegmental area-edge lobe loop of the dopamine neural pathway is mainly involved in the regulation of reward,emotion and memory.DAT belongs to Na~+/Cl~-co-transporter family protein,which has the function of reuptake of dopamine in synaptic clearance.It is speculated that magnetic field can change the function of DAT by affecting the motion of Na~+.In this study,the effects on brain of the medium strong SMF was investigated by the detection of rat behavior,electroencephalogram,brain glucose metabolism and brain tissue pathological changes during the course of medium strong SMF exposure.DAT served as the target to clarify the mechanisms of brain damage induced by SMF,The changes of dopaminergic system was investigated by in vivo and in vitro experiments,meanwhile,the influence of MF on the key enzyme in glucose metabolism containing magnetic atoms was also detected,so to find out the underlying mechanism of MF-induced brain damage.Materials and methods1.Methods to investigate the MF-induced brain damageTotal 97 SPF Wistar male rats were randomly divided into control group(C),low-intensity group(50mT,L),medium-intensity group(100mT,M),and the high-intensity group(200mT,H).The ethology,glucose metabolism in the brain region,electroencephalogram and hippocampal,striatum pathological changes of rats were detected by Sucrose preference test,open field test,PET,brain electrophysiology,pathological observation before exposure,on 1st,5th,10th,15th and 30th day of SMF exposure or on 7th and 15th day after SMF exposure.2.Methods to study the mechanism of MF-induced brain injury with DAT as the targetDA,DR2,DAT,HK1 and PFK1 in brain were detected by ELISA,western blot and immunohistochemistry.MN9D cells were selected to be exposed by the SMF of 200mT for 15,30 or 60 minutes,the cell proliferation activity,DA,DAT,DR2,HK1 and PFK1were detected by MTT,ELISA and western blot at 30,60min,6,12,24 and 48h after exposure respectively.Results1.Medium strong SMF exposure could cause behavioral,physiological and pathological changes in rats1.1 Medium strong SMF exposure reduced self-distribution and exploration of rats On 10th day of 200mT MF exposure,the total distance of movement,central distance,peripheral distance and the number of standing on the wall of the rats in group H significantly decreased.1.2 Medium strong SMF exposure caused depressive symptoms in rats On the 30th day of 200mT MF exposure,the sugar-water preference index of rats in group H significantly decreased.But there was no significant difference in the sugar-water preference index between groups H and C on 7d after the termination of exposure.1.3 Medium strong SMF exposure changed glucose metabolism of rats'brain Glucose metabolism increased in each brain area of rats in H group exposed for 1h.On the 5th day of exposure,the glucose metabolism in each brain area weakened,and glucose metabolism in the parietal lobe,hippocampus and striatum area significantly decreased.The changes of glucose metabolism in brain of rats in groups M and L also showed a trend of increasing first,then decreasing and increasing again at last,but there was no statistical difference.1.4 Medium strong SMF exposure could induce electroencephalogram abnormity in rats The electroencephalogram of rats had increased electroencephalogram?-wave in three exposed groups on the 5th day of exposure,while the changes of groups M and H were more significant.The relative power values of?-wave and?-wave power of groups M and H significantly decreased on the 15th day of exposure.The relative power value of the delta-wave power of group H increased significantly on the 10th and 15th day of exposure.The center-of-gravity frequency F decreased in all exposure groups.1.5 Medium strong SMF exposure induced hippocampus and striatum pathological changes in rats Neurons in the exposed hippocampus and striatum showed varying degrees of nucleus pyknosis,cell edema,mildly widened perivascular space on the 15th day of exposure.These changes were intensity-dependent.2.The medium strong SMF exposure caused abnormalities in the dopaminergic system and glucose metabolism2.1 Medium strong SMF exposure changed DA contents in brain tissue and MN9D cells Brain DA in rats:brain DA of rats in H group increased significantly on the 10th day of exposure,while there was a significant increase of brain DA in the M and H groups on the 15th day of exposure.Intra cellular DA:the intra cellular DA of 15min group increased significantly,while that of the 60min group decreased significantly at30min after the termination of SMF exposure.The intra cellular DA of 60min group significantly decreased at 60min after the termination of SMF exposure.Extracellular DA:the extracellular DA of 15min group was significantly lower,and that of the 60min group was significantly higher at 30min and 60min after the termination of exposure,compared with that of the C group.2.2 Medium strong SMF exposure changed the expression of DAT and DR2 in brain and MN9D cells(1)Western blot results showed DAT in brain tissue of groups M and H increased significantly on the 15th day of exposure.DR2 in brain tissue of group H decreased significantly on the 5th day of exposure,while that of groups M and H reduced significantly on the 10th day of exposure.Then on the 15th day of exposure brain DR2 of rats in three exposure groups all significantly decreased.(2)Immunochemistry results showed DAT in striatum of group H increased significantly on the 5th,10th and 15th day of exposure.DR2 in striatum of groups M and H reduced significantly on the 10th day of exposure,while DR2 of all exposure groups decreased significantly on the 15th day of exposure.On the 10th day of exposure,DAT in hippocampus of group M and H increased significantly,while DAT of all exposure groups increased significantly on the 15th day of exposure.DR2 in hippocampus of all exposure groups decreased significantly on the 15th day of exposure.(3)DAT in MN9D cells of 15min group and 60min group exposed by 200mT SMF increased significantly at 60min after the termination of exposure.2.3 Medium strong SMF exposure reduced HK1 and PFK1 in brain and MN9D cells(1)On the 5th and 10th day of exposure,HK1 in brain tissue of group H decreased significantly,while HK1 in each exposure group reduced significantly on the 15th day of exposure.PFK1 in brain of group M and H reduced significantly on the 5th and 10th day of exposure,while PFK1 of three exposure groups decreased significantly on the15th day of exposure.(2)HK1 and PFK1 in exposed MN9D cells of 30min and 60min groups decreased significantly at 30 and 60min after termination of exposure.Conclusion1.Medium strong SMF exposure could induce brain damage in rats.Rats exposed by SMF developed anxiety and depression,glucose metabolism abnormalities,decreased EEG excitability and pathological changes in hippocampus and striatum.The above changes were intensity and time dependent.Changes of glucose metabolism first appeared,followed by abnormal EEG,then pathological and behavioral changes were observed.2.Medium strong SMF exposure could change DA content in brain and dopaminergic neurons by influence the expression of DAT and DR2.The DA system dysfunction is one of the mechanisms of depression caused by SMF exposure.In addition,medium strong SMF exposure could change glucose metabolism in brain by inhibition of HK1 and PFK1,which is one of the mechanisms of SMF-induced brain injury.