Effects Of 5.8 GHz Microwave On Learning And Memory Ability Of Rats

BackgroundMicrowave refers to the electromagnetic wave with frequency range from 300 MHz～300 GHz,which is mainly generated by wireless communication devices,radar equipment and etc.Among which,the 5.8 GHz microwave was less used as public radio band in the past years.It was reported that 5.8 GHz would be expected to replace the current 2.4 GHz wireless technology in the near future due to its high bandwidth and strong anti-interference.Recently,5.8 GHz spectrum has been authorized to be the common spectrum of point-to-point or point-to-multi-point spread spectrum communication system,high-speed wireless local area network,broadband wireless access system,bluetooth technology system and vehicle wireless automatic identification system in China.Lot of studies have shown that the brain is sensitive to electromagnetic radiation Under certain conditions,electromagnetic radiation could induce neurological behavior changes in human and animals.The biological effects of 5.8 GHz microwave are rarely studied at present.Particularly,the effects of 5.8 GHz microwave on neurological behavior such as learning and memory ability have not been reported yet.Therefore,we investigated the effects of exposure to 5.8 GHz microwave on learning and memory ability along with the hippocampal synaptic plasticity of rats in this study.ObjectiveTo investigate the effects of 5.8 GHz microwave on the learning and memory ability along with the hippocampal synaptic plasticity of rats,so as to provide theoretical and experimental evidence for scientific evaluation of potential hazards of 5.8 GHz microwave on central nervous system and for the establishment and revision of relevant health standards.Part Ⅰ:Effects of Exposure to 5.8 GHz Microwave(1 h/d,15 d or 30 d)on Learning and Memory Ability of RatsMaterials and Methods1.Irradiation source:5.8 GHz microwave radiation system consisted of signal generator,amplifier and antenna.2.Animal groups and microwave exposure:80 healthy adult male Sprague-Dawley rats with body weight(180 ± 3)g were randomly divided into Microwave exposure group(Microwave,n=40)and Sham exposure group(Sham,n=40).The animals were exposed or sham exposed to microwave 1 h/d for 15 d or 30 d with the power density(PD)of 74.25 W/m2.The specific absorption rate(SAR)value of whole body and head was 1.15 W/kg and 2.33 W/kg,respectively.The animals in the Sham group were treated in the same way as those in the Microwave group,except for the control system switched off.3.Detection methods:1)The general condition of the animals(rectal temperature,body weight,haematology,serum biochemical markers)were examined.2)The learning and memory ability of rats was evaluated by Morris water maze(MWM)and Novel object recognition(NOR).3)To estimate the damage of hippocampal neurons,the hippocampal morphology,the level of brain injury factors in serum and the level of inflammatory factors in hippocampus was investigated.4)To evaluate the hippocampal synaptic plasticity,the density of dendritic spines,the content of neurotransmitters and the protein level of Postsynaptic density protein 95(PSD95)and Synaptophysin in hippocampus were exploredResults1.Effects of exposure to 5.8 GHz microwave(1 h/d,15 d or 30 d)on the general condition of rats1.1 The results of temperature measurement and body weight monitoring showed that the change of rectal temperature in each group was no more than 1℃ before and after microwave exposure or sham exposure for 1 h,which suggested that exposure to 5.8 GHz microwave under current condition could not induce thermal effect.During the whole experiment,the body weight of rats continuously increased with the extension of time There was no significant difference in body weight between Microwave group and Sham group(P>0.05)1.2 The results of the blood routine examination and the liver and kidney function examination showed that the blood routine indexes(the number of red blood cells,platelets and white blood cells,the content of haemoglobin,the percentage of lymphocyte and neutrophil),the liver and kidney function indexes(the content of alanine transaminase,aspartate transaminase and serum creatinine)did not significantly change in Microwave 15 d group or Microwave 30 d group,compared with Sham group(P>0.05)The above results suggested that exposure to 5.8 GHz microwave(1 h/d,15 d or 30 d)had no obvious effect on the general health of rats2.Effects of exposure to 5.8 GHz microwave(1 h/d,15 d or 30 d)on the learning and memory ability of rats2.1.The results of MWM showed that,there was no significant difference in the escape latency,the frequency of crossing the plateau,the percentage of time spent in the target quadrant and the latency of the first arrival to the plateau in Microwave 15 d group or Microwave 30 d group,compared with Sham group(P>0.05),which suggested that exposure to 5.8 GHz microwave under current condition had no obvious effect on the spatial learning and memory ability of rats2.2 The results of NOR showed that,there was no significant difference in the exploration time for novel and familiar objects,the percentage of exploring time for novel objects and the discrimination index in Microwave 15 d group or Microwave 30 d group,compared with Sham group(P>0.05),which suggested that exposure to 5.8 GHz microwave under current condition had no obvious effect on the scene memory ability of rats3.Effects of exposure to 5.8 GHz microwave(1 h/d,15 d or 30 d)on the hippocampal neurons of rats3.1 The results of HE stain showed that,the hippocampal morphology of rats in Microwave 15 d group or Microwave 30 d group did not change obviously,compared with Sham group.The results of Nissl stain showed that,there was no significant difference in the number of neurons in CA1 area and DG area of hippocampus in Microwave 15 d group or Microwave 30 d group,compared with Sham group(P>0.05)These results suggested that exposure to 5.8 GHz microwave under current condition had no obvious effect on the hippocampal morphology of rats3.2 The results of ELISA showed that,there was no significant difference in the content of brain injury factors including Neuron specific enolase(NSE)and s100 calcium binding protein B(S100B)in serum of rats in Microwave 15 d group or Microwave 30 d group,compared with Sham group(P>0.05),as well as the content of inflammatory or anti-inflammatory factors such as Tumor necrosis factor-α(TNF-α),Interleukin-1β(IL-1β),Interleukin-10(IL-10)and Transforming growth factor-β1(TGF-βl)in hippocampus of rats(P>0.05),which suggested that exposure to 5.8 GHz microwave under current condition had no obvious effect on hippocampal neurons of rats4.Effects of exposure to 5.8 GHz microwave(1 h/d,15 d or 30 d)on the hippocampal synaptic plasticity of rats4.1 Golgi stain showed that,compared with Sham group,the density of apical and basal dendritic spines in CA1 area of rats in Microwave 15 d group or Microwave 30 d group did not significantly change(P>0.05),which suggested that exposure to 5.8 GHz microwave under current condition had no obvious effect on dendrite spine density in CA1 area of hippocampus.4.2 The results of liquid chromatography-mass spectrometry(LC-MS)showed that,there was no significant change in the content of multiple hippocampal neurotransmitters in Microwave 15 d group or Microwave 30 d group,compared with Sham group(P>0.05),which suggested that exposure to 5.8 GHz microwave under current condition had no obvious effect on the content of hippocampal neurotransmitters of rats.4.3 The results of western blot(WB)showed that the protein level of PSD95 and Synaptophysin in hippocampus was not significantly changed in Microwave 15 d group or Microwave 30 d group,compared with Sham group(P>0.05),which suggested that exposure to 5.8 GHz microwave under current condition had no obvious effect on synaptic protein in hippocampus of rats.The above results suggested that exposure to 5.8 GHz microwave(1 h/d,15 d or 30 d)had no obvious effect on the learning and memory ability along with the hippocampal synaptic plasticity of rats.Part Ⅱ:Effects of Exposure to 5.8 GHz Microwave(2 h/d or 4 h/d,15 d)on Learning and Memory Ability of RatsMaterials and Methods1.Irradiation source:Same as Part I2.Animal groups and microwave exposure:75 healthy adult male Sprague-Dawley rats with body weight(258 ± 5)g were randomly divided into Sham exposure group(Sham,n=25),Microwave exposure for 2 h(Microwave 2 h,n=25)group and for 4 h(Microwave 4 h,n=25)group.Both Microwave groups were continuously exposed for 15 d,with PD of 74.25 W/m2,whole-body SAR of 1.15 W/kg and head SAR 2.33 W/kg.The animals in the Sham group were treated in the same way as those in the Microwave groups,except for the control system switched off.3.Detection methods:1)The general condition of the animals(body weight,haematology,serum biochemical markers)were examined.2)MWM,NOR and Fear conditioning test(FCT)were used to evaluate the ability of spatial and non-spatial memory of rats.3)To estimate the damage of hippocampal neurons,the hippocampal morphology,the content of brain injury factors in serum,the inflammatory factors in hippocampus,the membrane potential and ultrastructure of mitochondrion were explored 4)To assess the hippocampal synaptic plasticity,the density of dendritic spines,the synaptic ultrastructure,the content of hippocampal neurotransmitters and the level of synaptic plasticity related protein were investigatedResults1.Effects of exposure to 5.8 GHz microwave(2 h/d or 4 h/d,15 d)on the general condition of rats1.1 The results of body weight monitoring showed that,during the whole experiment,the rats in each group were generally in good condition,the body weight of rats continuously increased with the extension of time.There was no significant difference in the body weight between Microwave group and Sham group(P>0.05)1.2 The results of the blood routine examination and the liver and kidney function examination showed that,after exposure for 15 d,the blood routine indexes and the liver and kidney function indexes did not significantly change in Microwave 2 h group or Microwave 4 h group,compared with Sham group(P>0.05)The above results suggested that exposure to 5.8 GHz microwave(2 h/d or 4 h/d,15 d)had no obvious effect on the general health of rats2.Effects of exposure to 5.8 GHz microwave(2 h/d or 4 h/d,15 d)on the learning and memory ability of rats2.1.The results of MWM showed that,after exposure for 15 d,there was no significant difference in the performance of three groups in the training trial,as well as in the probe trial(P>0.05),which suggested that exposure to 5.8 GHz microwave under current condition had no obvious effect on the spatial learning and memory ability of rats2.2 The results of NOR showed that,after exposure for 15 d,there was no significant difference in the preference of novel object in Microwave 2 h group or Microwave 4 h group,compared with Sham group(P>0.05),which suggested that exposure to 5.8 GHz microwave under current condition had no obvious effect on the scene memory ability of rats2.3 The results of FCT showed that,compared with Sham group,Microwave 2 h group or Microwave 4 h group had no significant difference in the percentage of rigidity time after exposure for 15 d(P>0.05),which suggested that exposure to 5.8 GHz microwave under current condition had no obvious effect on the emotional memory ability of rats3.Effects of exposure to 5.8 GHz microwave(2 h/d or 4 h/d,15 d)on the hippocampal neurons of rats3.1 The results of HE stain showed that,after exposure for 15 d,the hippocampal morphology of rats in Microwave 2 h group or Microwave 4 h group did not change obviously,compared with Sham group.The results of Nissl stain showed that,there was no significant difference in the number of neurons in CA1 area and DG area in Microwave 2 h group or Microwave 4 h group,compared with Sham group(P>0.05).These results suggested that exposure to 5.8 GHz microwave under current condition had no obvious effect on the hippocampal morphology3.2 The results of ELISA showed that,after exposure for 15 d,there was no significant difference in the level of brain injury factors(NSE and S100B)in serum and the level of inflammatory factors(TNF-α,IL-1β,IL-10,TGF-β1)in hippocampus of rats in Microwave 2 h group or Microwave 4 h group,compared with Sham group(P>0.05),which suggested that exposure to 5.8 GHz microwave under current condition had no obvious effect on hippocampal neurons of rats3.3 The results of JC-1 assay showed that,after exposure for 15 d,Microwave 2 h group or Microwave 4 h group had no significant difference in the content of mitochondrial JC-1 monomer,compared with Sham group(P>0.05),which suggested that exposure to 5.8 GHz microwave under current condition had no obvious effect on mitochondrial function in hippocampal neurons of rats3.4 The results of transmission electron microscopy showed that,after exposure for 15 d,no obvious mitochondrial swelling was observed in each group.The mitochondrial ridges of the hippocampal neurons in each group were clear,the mitochondrial membrane was intact,which suggested that exposure to 5.8 GHz microwave under current condition had no obvious effect on the mitochondrial ultrastructure of hippocampal neurons of rats4.Effects of exposure to 5.8 GHz microwave(2 h/d or 4 h/d,15 d)on the hippocampal synaptic plasticity4.1 Golgi stain showed that,compared with Sham group,the density of apical and basal dendritic spines in CA1 area of hippocampus in Microwave 2 h group or Microwave 4 h group was not significantly changed after exposure for 15 d(P>0.05),which suggested that exposure to 5.8 GHz microwave under current condition had no obvious effect on dendrite spine density in CA1 area of hippocampus4.2 The results of transmission electron microscopy showed that,after exposure for 15 d,no obvious synaptic disintegration was observed in each group.The pre-and post-synaptic membranes were clear and intact,the synaptic vesicles were uniformly sized and clustered in the presynaptic terminal.The size of synapses,number of synaptic vesicles,width of synaptic cleft and area of postsynaptic dense in Microwave 2 h group or Microwave 4 h group were not significantly changed,compared with those in Sham group(P>0.05),which suggested that exposure to 5.8 GHz microwave under current condition had no obvious effect on the synaptic ultrastructure in hippocampus of rats4.3 The results of LC-MS showed that,after exposure for 15 d,there was no significant change in the content of multiple hippocampal neurotransmitters in Microwave 2 h group or Microwave 4 h group,compared with Sham group(P>0.05),which suggested that exposed to 5.8 GHz microwave under current condition had no obvious effect on the content of hippocampal neurotransmitters of rats4.4 The results of WB showed that after exposure for 15 d,the protein level of PSD95,Synaptophysin and cAMP-response element binding protein(CREB)in hippocampus were not significantly changed in Microwave 2 h group or Microwave 4 h group,compared with Sham group(P>0.05),which suggested that exposed to 5.8 GHz microwave under current condition had no obvious effect on the expression of synaptic plasticity related protein in hippocampus of ratsThe above results indicated that exposure to 5.8 GHz microwave(2 h/d or 4 h/d,15 d)had no obvious effect on the learning and memory ability along with the hippocampal synaptic plasticity of ratsConclusions1.Under this experimental condition,exposure to 5.8 GHz microwave(1 h/d,15 d or 30 d)had no obvious effect on general condition,learning and memory ability and hippocampal synaptic plasticity of rats2.Under this experimental condition,exposure to 5.8 GHz microwave(2 h/d or 4 h/d,15 d)had no obvious effect on general condition,learning and memory ability and hippocampal synaptic plasticity of ratsThe above results provide theoretical and experimental evidence for scientific evaluation of potential health hazards of 5.8 GHz microwave and for the establishment and revision of relevant health standards.The results also provide biosecurity evidence for the popularization of 5.8 GHz wireless technology.