Exposure to RF-EMF Alters Postsynaptic Structure and Hinders Neurite Outgrowth in Developing Hippocampal Neurons of Early Postnatal Mice.

Ju Hwan Kim,Yeong Ran Hwang,Hyung-Gun Kim,Hee Jung Kim,Hye Ran Park,Kyung Hwun Chung,Hak Rim Kim

doi:10.3390/ijms22105340

Abstract

Exposure to radiofrequency electromagnetic fields (RF-EMFs) has increased rapidly in children, but information on the effects of RF-EMF exposure to the central nervous system in children is limited. In this study, pups and dams were exposed to whole-body RF-EMF at 4.0 W/kg specific absorption rate (SAR) for 5 h per day for 4 weeks (from postnatal day (P) 1 to P28). The effects of RF-EMF exposure on neurons were evaluated by using both pups’ hippocampus and primary cultured hippocampal neurons. The total number of dendritic spines showed statistically significant decreases in the dentate gyrus (DG) but was not altered in the cornu ammonis (CA1) in hippocampal neurons. In particular, the number of mushroom-type dendritic spines showed statistically significant decreases in the CA1 and DG. The expression of glutamate receptors was decreased in mushroom-type dendritic spines in the CA1 and DG of hippocampal neurons following RF-EMF exposure. The expression of brain-derived neurotrophic factor (BDNF) in the CA1 and DG was significantly lower statistically in RF-EMF-exposed mice. The number of post-synaptic density protein 95 (PSD95) puncta gradually increased over time but was significantly decreased statistically at days in vitro (DIV) 5, 7, and 9 following RF-EMF exposure. Decreased BDNF expression was restricted to the soma and was not observed in neurites of hippocampal neurons following RF-EMF exposure. The length of neurite outgrowth and number of branches showed statistically significant decreases, but no changes in the soma size of hippocampal neurons were observed. Further, the memory index showed statistically significant decreases in RF-EMF-exposed mice, suggesting that decreased synaptic density following RF-EMF exposure at early developmental stages may affect memory function. Collectively, these data suggest that hindered neuronal outgrowth following RF-EMF exposure may decrease overall synaptic density during early neurite development of hippocampal neurons.

Highlights

Dendritic spines (DSs) of neurites in the hippocampus were analyzed using hippocampal sections isolated from mice exposed to 1850 MHz radiofrequency electromagnetic fields (RF-EMFs) at a specific absorption rate (SAR) value of 4.0 W/kg for 5 h per day for 4 weeks to examine the effects of RF-EMF exposure on neurodevelopment and synapse formation
Given the decrease in synaptic density in RF-EMF-exposed mice, we further examined the expression levels of glutamate receptors (NMDA and amino-3-hydroxy5methyl-4-isoxazolepropionic acid (AMPA) receptors), which are involved in synapse formation, in primary cultured hippocampal neurons on days in vitro (DIV) 9
brain-derived neurotrophic factor (BDNF) Expression Is Decreased at the Soma but Not Neurites of Hippocampal Neurons

Summary

Introduction

As mobile phone use typically requires close contact with the head, possible effects on the brain are of particular concern [1]. There is accumulating evidence regarding the biological effects of RF-EMF exposure on the central nervous system (CNS), such as changes in intracellular calcium homeostasis, neuronal damage, and perturbations in neurotransmitter systems [2,3,4]. Exposure to RF-EMF has increased rapidly in children. Mobile phone use has become the major determinant of RF-EMF exposure [5]. RF-EMF exposure may have a greater impact on children during the developmental stages of the nervous system. We recently demonstrated that exposure to 1850 MHz RF-EMF in early postnatal mice resulted in morphological changes in synapses in the auditory brainstem in the absence of functional abnormalities [8]

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