Ji Dong

Relationship between Cognition Function and Hippocampus Structure after Long-term Microwave Exposure

OBJECTIVE To analyze the effects of long-term microwave exposure on hippocampal structure and function in the rat. METHODS Experiments were performed on 184 male Wistar rats (three exposure groups and a sham group). Microwaves were applied daily for 6 min over 1 month at average power densities of 2.5, 5, and 10 mW/cm2. Learning and memory abilities were assessed by Morris water maze. High performance liquid chromatography was used to detect neurotransmitter concentrations in the hippocampus. Hippocampal structures were observed by histopathological analysis. RESULTS Following long-term microwave exposure there was a significant decrease in learning and memory activity in the 7 d, 14 d, and 1 m in all three microwave exposure groups. Neurotransmitter concentrations of four amino acids (glutamate, aspartic acid, glycine, and gamma-aminobutyric acid) in hippocampus were increased in the 2.5 and 5 mW/cm2 groups and decreased in the 10 mW/cm2 group. There was evidence of neuronal degeneration and enlarged perivascular spaces in the hippocampus in the microwave exposure groups. Further, mitochondria became swollen and cristae were disordered. The rough endoplasmic reticulum exhibited sacculated distension and there was a decrease in the quantity of synaptic vesicles. CONCLUSION These data suggest that the hippocampus can be injured by long-term microwave exposure, which might result in impairment of cognitive function due to neurotransmitter disruption.

Impairment of long-term potentiation induction is essential for the disruption of spatial memory after microwave exposure

Abstract Purpose: To assess the impact of microwave exposure on learning and memory and to explore the underlying mechanisms. Materials and methods: 100 Wistar rats were exposed to a 2.856 GHz pulsed microwave field at average power densities of 0 mW/cm2, 5 mW/cm2, 10 mW/cm2 and 50 mW/cm2 for 6 min. The spatial memory was assessed by the Morris Water Maze (MWM) task. An in vivo study was conducted soon after microwave exposure to evaluate the changes of population spike (PS) amplitudes of long-term potentiation (LTP) in the medial perforant path (MPP)-dentate gyrus (DG) pathway. The structure of the hippocampus was observed by the light microscopy and the transmission electron microscopy (TEM) at 7 d after microwave exposure. Results: Our results showed that the rats exposed in 10 mW/cm2 and 50 mW/cm2 microwave displayed significant deficits in spatial learning and memory at 6 h, 1 d and 3 d after exposure. Decreased PS amplitudes were also found after 10 mW/cm2 and 50 mW/cm2 microwave exposure. In addition, varying degrees of degeneration of hippocampal neurons, decreased synaptic vesicles and blurred synaptic clefts were observed in the rats exposed in 10 mW/cm2 and 50 mW/cm2 microwave. Compared with the sham group, the rats exposed in 5 mW/cm2 microwave showed no difference in the above experiments. Conclusions: This study suggested that impairment of LTP induction and the damages of hippocampal structure, especially changes of synapses, might contribute to cognitive impairment after microwave exposure.

Alterations of cognitive function and 5-HT system in rats after long term microwave exposure

The increased use of microwaves raises concerns about its impact on health including cognitive function in which neurotransmitter system plays an important role. In this study, we focused on the serotonin system and evaluated the long term effects of chronic microwave radiation on cognition and correlated items. Wistar rats were exposed or sham exposed to 2.856GHz microwaves with the average power density of 5, 10, 20 or 30mW/cm(2) respectively for 6min three times a week up to 6weeks. At different time points after the last exposure, spatial learning and memory function, morphology structure of the hippocampus, electroencephalogram (EEG) and neurotransmitter content (amino acid and monoamine) of rats were tested. Above results raised our interest in serotonin system. Tryptophan hydroxylase 1 (TPH1) and monoamine oxidase (MAO), two important rate-limiting enzymes in serotonin synthesis and metabolic process respectively, were detected. Expressions of serotonin receptors including 5-HT1A, 2A, 2C receptors were measured. We demonstrated that chronic exposure to microwave (2.856GHz, with the average power density of 5, 10, 20 and 30mW/cm(2)) could induce dose-dependent deficit of spatial learning and memory in rats accompanied with inhibition of brain electrical activity, the degeneration of hippocampus neurons, and the disturbance of neurotransmitters, among which the increase of 5-HT occurred as the main long-term change that the decrease of its metabolism partly contributed to. Besides, the variations of 5-HT1AR and 5-HT2CR expressions were also indicated. The results suggested that in the long-term way, chronic microwave exposure could induce cognitive deficit and 5-HT system may be involved in it.

Abnormality of synaptic vesicular associated proteins in cerebral cortex and hippocampus after microwave exposure

Studies were performed to determine the effects of microwave on synaptic vesicles and the expression of synaptic vesicular associated proteins including synapsin I, VAMP‐2, syntaxin, and synaptophysin. 25 Wistar rats were exposed to microwave which the average power density was 30 mW/cm2, and whole body average specific absorption rate was 14.1 W/kg for 5 min. Synaptosome preparations in the cerebral cortex and hippocampus were obtained by isotonic Percoll/sucrose discontinuous gradients at 6 h, 1, 3, and 7 days after radiation. The expression of synaptic vesicular associated proteins was measured using Western blots and image analysis. The interaction between VAMP‐2 and syntaxin was examined by coimmunoprecipitation analysis. Synapsin I in the cerebral cortex were decreased at 3 days (P < 0.01) after radiation and in the hippocampus increased at 1 day (P < 0.01), decreased at 3 days (P < 0.01), increased again at 7 days (P < 0.01) after exposure, compared with the sham‐treated controls. Synaptophysin were increased in 1–7 days (P < 0.01) after exposure in the cerebral cortex and hippocampus. VAMP‐2 were decreased at 1 and 3 days (P < 0.01) and syntaxin were decreased in 6 h to 3 days (P < 0.01) after radiation in the cerebral cortex and hippocampus. The interactions between VAMP‐2 and syntaxin were decreased at 3–7 days (P < 0.01) after radiation in the cerebral cortex and hippocampus, compared with the sham‐treated controls. These results suggest that 30 mW/cm2 (SAR 14.1 W/kg) microwave radiation can result in the perturbation of the synaptic vesicles associated proteins: synapsin I, synaptophysin, VAMP‐2, and syntaxin. The perturbation could induce the deposit of synaptic vesicle, which might be relative to the dysfunction of the synaptic transmission, even the cognition deficit. Synapse 63:1010–1016, 2009.

Microwave Exposure Impairs Synaptic Plasticity in the Rat Hippocampus and PC12 Cells through Over-activation of the NMDA Receptor Signaling Pathway *

OBJECTIVE The aim of this study is to investigate whether microwave exposure would affect the N-methyl-D-aspartate receptor (NMDAR) signaling pathway to establish whether this plays a role in synaptic plasticity impairment. METHODS 48 male Wistar rats were exposed to 30 mW/cm2 microwave for 10 min every other day for three times. Hippocampal structure was observed through H&E staining and transmission electron microscope. PC12 cells were exposed to 30 mW/cm2 microwave for 5 min and the synapse morphology was visualized with scanning electron microscope and atomic force microscope. The release of amino acid neurotransmitters and calcium influx were detected. The expressions of several key NMDAR signaling molecules were evaluated. RESULTS Microwave exposure caused injury in rat hippocampal structure and PC12 cells, especially the structure and quantity of synapses. The ratio of glutamic acid and gamma-aminobutyric acid neurotransmitters was increased and the intracellular calcium level was elevated in PC12 cells. A significant change in NMDAR subunits (NR1, NR2A, and NR2B) and related signaling molecules (Ca2+/calmodulin-dependent kinase II gamma and phosphorylated cAMP-response element binding protein) were examined. CONCLUSION 30 mW/cm2 microwave exposure resulted in alterations of synaptic structure, amino acid neurotransmitter release and calcium influx. NMDAR signaling molecules were closely associated with impaired synaptic plasticity.

MicroRNAs: Novel Mechanism Involved in the Pathogenesis of Microwave Exposure on Rats’ Hippocampus

Microwave-induced adverse health outcomes have been gaining much attention in recent years. The hippocampus is sensitive and vulnerable to microwave exposure. Studies from our group and others showed that microwave-induced structural and functional injury of hippocampus, accompanied with alteration of gene and protein expression. It has been demonstrated that microRNAs (miRNAs) were involved in the physiological and pathological processes of brain. In this study, the miRNAs expression profiles of microwave-exposed hippocampus were detected by microarray analysis and verified by real-time polymerase chain reaction (PCR). At 7 days after 30 mW/cm2 microwave exposure, the expression of 12 miRNAs increased, while other 70 miRNAs decreased in rats’ hippocampus. However, most of miRNAs restored to normal levels at 14 days after exposure, only two upregulated miRNAs and 14 downregulated miRNAs were detected. Gene transcription, neuroprotection and receptors function related target genes were predicated by miRDB, miRbase and miRanda. Moreover, these differentially expressed miRNAs were involved in brain-related signaling pathways, such as synaptic vesicle cycle, long-term depression, calcium signaling and neurotrophin signaling pathways. In conclusion, we successfully characterized the miRNA profiles in microwave-exposed hippocampus, and that will be helpful to clarify the molecular mechanism and provide potential therapeutic targets.

The relationship between NMDA receptors and microwave-induced learning and memory impairment: a long-term observation on Wistar rats.

Abstract Purpose: To investigate whether high power microwave could cause continuous disorders to learning and memory in Wistar rats and to explore the underlying mechanisms. Materials and methods: Eighty Wistar rats were exposed to a 2.856 GHz pulsed microwave source at a power density of 0 mW/cm2 and 50 mW/cm2 microwave for 6 min. The spatial memory ability, the structure of the hippocampus, contents of amino acids neurotransmitters in hippocampus and the expression of N-methyl-D-aspartic acid receptors (NMDAR) subunit 1, 2A and 2B (NR1, NR2A and NR2B) were detected at 1, 3, 6, 9, 12 and 18 months after microwave exposure. Results: Our results showed that the microwave-exposed rats showed consistent deficiencies in spatial learning and memory. The level of amino acid neurotransmitters also decreased after microwave radiation. The ratio of glutamate (Glu) and gammaaminobutyric acid (GABA) significantly decreased at 6 months. Besides, the hippocampus showed varying degrees of degeneration of neurons, increased postsynaptic density and blurred synaptic clefts in the exposure group. The NR1 and NR2B expression showed a significant decrease, especially the NR2B expression. Conclusions: This study indicated that the content of amino acids neurotransmitters, the expression of NMDAR subunits and the variation of hippocampal structure might contribute to the long-term cognitive impairment after microwave exposure.

Reduction of phosphorylated synapsin I (ser-553) leads to spatial memory impairment by attenuating GABA release after microwave exposure in Wistar rats.

Background Abnormal release of neurotransmitters after microwave exposure can cause learning and memory deficits. This study investigated the mechanism of this effect by exploring the potential role of phosphorylated synapsin I (p-Syn I). Methods Wistar rats, rat hippocampal synaptosomes, and differentiated (neuronal) PC12 cells were exposed to microwave radiation for 5 min at a mean power density of 30 mW/cm2. Sham group rats, synaptosomes, and cells were otherwise identically treated and acted as controls for all of the following post-exposure analyses. Spatial learning and memory in rats was assessed using the Morris Water Maze (MWM) navigation task. The protein expression and presynaptic distribution of p-Syn I and neurotransmitter transporters were examined via western blotting and immunoelectron microscopy, respectively. Levels amino acid neurotransmitter release from rat hippocampal synaptosomes and PC12 cells were measured using high performance liquid chromatograph (HPLC) at 6 hours after exposure, with or without synapsin I silencing via shRNA transfection. Results In the rat experiments, there was a decrease in spatial memory performance after microwave exposure. The expression of p-Syn I (ser-553) was decreased at 3 days post-exposure and elevated at later time points. Vesicular GABA transporter (VGAT) was significantly elevated after exposure. The GABA release from synaptosomes was attenuated and p-Syn I (ser-553) and VGAT were both enriched in small clear synaptic vesicles, which abnormally assembled in the presynaptic terminal after exposure. In the PC12 cell experiments, the expression of p-Syn I (ser-553) and GABA release were both attenuated at 6 hours after exposure. Both microwave exposure and p-Syn I silencing reduced GABA release and maximal reduction was found for the combination of the two, indicating a synergetic effect. Conclusion p-Syn I (ser-553) was found to play a key role in the impaired GABA release and cognitive dysfunction that was induced by microwave exposure.

The compound Chinese medicine "Kang Fu Ling" protects against high power microwave-induced myocardial injury.

Background The prevention and treatment of Microwave-caused cardiovascular injury remains elusive. This study investigated the cardiovascular protective effects of compound Chinese medicine “Kang Fu Ling” (KFL) against high power microwave (HPM)-induced myocardial injury and the role of the mitochondrial permeability transition pore (mPTP) opening in KFL protection. Methods Male Wistar rats (100) were divided into 5 equal groups: no treatment, radiation only, or radiation followed by treatment with KFL at 0.75, 1.5, or 3 g/kg/day. Electrocardiography was used to Electrophysiological examination. Histological and ultrastructural changes in heart tissue and isolated mitochondria were observed by light microscope and electron microscopy. mPTP opening and mitochondrial membrane potential were detected by confocal laser scanning microscopy and fluorescence analysis. Connexin-43 (Cx-43) and endothelial nitric oxide synthase (eNOS) were detected by immunohistochemistry. The expression of voltage-dependent anion channel (VDAC) was detected by western blotting. Results At 7 days after radiation, rats without KFL treatment showed a significantly lower heart rate (P<0.01) than untreated controls and a J point shift. Myocyte swelling and rearrangement were evident. Mitochondria exhibited rupture, and decreased fluorescence intensity, suggesting opening of mPTP and a consequent reduction in mitochondrial membrane potential. After treatment with 1.5 g/kg/day KFL for 7 d, the heart rate increased significantly (P<0.01), and the J point shift was reduced flavorfully (P<0.05) compared to untreated, irradiated rats; myocytes and mitochondria were of normal morphology. The fluorescence intensities of dye-treated mitochondria were also increased, suggesting inhibition of mPTP opening and preservation of the mitochondrial membrane potential. The microwave-induced decrease of Cx-43 and VDAC protein expression was significantly reversed. Conclusion Microwave radiation can cause electrophysiological, histological and ultrastructural changes in the heart. KFL at 1.5 g/kg/day had the greatest protective effect on these cardiovascular events. mPTP plays an important role in the protective effects of KFL against microwave-radiation-induced myocardial injury.

Microwave radiation leading to shrinkage of dendritic spines in hippocampal neurons mediated by SNK-SPAR pathway

The popularization of microwave raised concerns about its influence on health including cognitive function which is associated greatly with dendritic spines plasticity. SNK-SPAR is a molecular pathway for neuronal homeostatic plasticity during chronically elevated activity. In this study, Wistar rats were exposed to microwaves (30 mW/cm2 for 6 min, 3 times/week for 6 weeks). Spatial learning and memory function, distribution of dendritic spines, ultrastructure of the neurons and their dendritic spines in hippocampus as well as the related critical molecules of SNK-SPAR pathway were examined at different time points after microwave exposure. There was deficiency in spatial learning and memory in rats, loss of spines in granule cells and shrinkage of mature spines in pyramidal cells, accompanied with alteration of ultrastructure of hippocampus neurons. After exposure to 30 mW/cm2 microwave radiation, the up-regulated SNK induced decrease of SPAR and PSD-95, which was thought to cause the changes mentioned above. In conclusion, the microwave radiation led to shrinkage and even loss of dendritic spines in hippocampus by SNK-SPAR pathway, resulting in the cognitive impairments.