Monday, January 05, 2015

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

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


Li H1Peng R1Wang C1Qiao S1Yong-Zou1Gao Y1Xu X1Wang S1Dong J1Zuo H1Li-Zhao1Zhou H2Wang L3Hu X4. Alterations of cognitive function and 5-HT system in rats after long term microwave exposure. Physiol Behav. 2014 Dec 24. pii: S0031-9384(14)00663-5. doi: 10.1016/j.physbeh.2014.12.039. [Epub ahead of print].

Abstract

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 serotonergic 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/cm2 respectively for 6 minutes three times a week up to 6 weeks. 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/cm2) 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.
Highlights
• Long term microwave exposure induced dose-dependent cognitive function deficit.
• Among neurotransmitters, the increase of 5-HT was the main remote effect.
• 5-HT system may be involved in microwave-induced cognitive deficit.
In summary, our observations indicated that long-term exposure to microwave (2.856 GHz, with the average power density of 5, 10, 20 and 30 mW/cm2) could induce dose-dependent deficit of spatial learning and memory accompanied with the inhibition of brain electrical activity, the degeneration of hippocampus neurons, and disturbances of neurotransmitters. Further experiments elucidated that elevated level of metabolism partly contributed to the increase of 5-HT after microwave exposure. Besides aberrant 5-HT1AR and 5-HT2CR expressions were also indications of 5-HT system modulation. We assumed that 5-HT system may be involved in microwave exposure-induced cognitive deficit and further studies are needed to confirm that.
-- 
Joel M. Moskowitz, Ph.D., Director
Center for Family and Community Health
School of Public Health
University of California, Berkeley

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