Changes of Dendritic Spine Density and Morphology in the Superficial Layers of the Medial Entorhinal Cortex Induced by Extremely Low-Frequency Magnetic Field Exposure

Jiaxiang Xiong,Chao He,Gang Tan,Fang Chen,Zhian Hu,Zhengping Yu,Chao Li,Jingcheng Li,Lin Lu

doi:10.1371/journal.pone.0083561

Abstract

In the present study, we investigated the effects of chronic exposure (14 and 28 days) to a 0.5 mT 50 Hz extremely low-frequency magnetic field (ELM) on the dendritic spine density and shape in the superficial layers of the medial entorhinal cortex (MEC). We performed Golgi staining to reveal the dendritic spines of the principal neurons in rats. The results showed that ELM exposure induced a decrease in the spine density in the dendrites of stellate neurons and the basal dendrites of pyramidal neurons at both 14 days and 28 days, which was largely due to the loss of the thin and branched spines. The alteration in the density of mushroom and stubby spines post ELM exposure was cell-type specific. For the stellate neurons, ELM exposure slightly increased the density of stubby spines at 28 days, while it did not affect the density of mushroom spines at the same time. In the basal dendrites of pyramidal neurons, we observed a significant decrease in the mushroom spine density only at the later time point post ELM exposure, while the stubby spine density was reduced at 14 days and partially restored at 28 days post ELM exposure. ELM exposure-induced reduction in the spine density in the apical dendrites of pyramidal neurons was only observed at 28 days, reflecting the distinct vulnerability of spines in the apical and basal dendrites. Considering the changes in spine number and shape are involved in synaptic plasticity and the MEC is a part of neural network that is closely related to learning and memory, these findings may be helpful for explaining the ELM exposure-induced impairment in cognitive functions.

Highlights

The extremely low-frequency magnetic field (ELM) is produced by power lines used in transmission and distribution of electric power and by the numerous appliances (TV sets, PC monitors, mobile phones, etc.) used in houses and work places [1]
We showed that cranial ELM exposure altered the spine density and shape in the dendrites of stellate neurons and apical and basal dendrites of pyramidal neurons in the superficial layers of the medial entorhinal cortex (MEC)
There was a decrease in the spine density in the dendrites of stellate neurons and the basal dendrites of pyramidal neurons at both 14 days and 28 days post ELM exposure, which was predominantly attributed to the reduction of the thin spines

Summary

Introduction

The extremely low-frequency magnetic field (ELM) is produced by power lines used in transmission and distribution of electric power and by the numerous appliances (TV sets, PC monitors, mobile phones, etc.) used in houses and work places [1]. There is increasing evidence that exposure to ELM can influence learning and memory, some negative results have been reported [2,3]. Previous studies have shown that ELM exposure impaired acquisition and consolidation of spatial memory in rodents [4,5,6] and produced deficits in detour learning and one-trial passive avoidance learning in chicks [7,8]. It has been reported that exposure to ELM impaired the performance of humans in word recognition and visual discrimination tasks [9,10]. The entorhinal cortex (EC) is closely related to learning and memory and has long been viewed as the interface between cortical regions and hippocampus [11]. Dysfunction of the EC is associated with the development of Alzheimer’s disease and schizophrenia, both of which are characterized by impairments in learning and memory [17,18]

Methods

Results

Conclusion