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

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.

Human exposure to power frequency magnetic fields up to 7.6 mT: An integrated EEG/fMRI study

“…One possible biological substrate for this effect is the modulation of "synaptic plasticity," which is one plausible candidate for explaining the persistence of effects after exposure, and also that effects take place after some time [Modolo et al, 2013a,b]. This possibility is supported by recent experimental results on synaptic plasticity mechanisms in rats exposed to 50 Hz MF [Xiong et al, 2013]. To summarize, our results do not provide support for acute effects on brain electrical activity and functional activation due to 60 Hz sinusoidal MF exposure up to 7.6 mT (i.e., about 76,000 times higher than typical daily exposure of public to power-line frequency MF).…”

“…Reported effects of ELF MF on brain activity often indicate that human EEG is prone to modulation in the occipital lobe in the alpha band [Cook et al, , ; Ghione et al, ]. Importantly, the duration of exposure is a critical factor to take into account to address the problem of biological mechanisms involved in the experimentally recorded effect: in the case of biological effects reported after the cessation of prolonged exposure (>30 min), it has been suggested that changes in synaptic plasticity could be involved [Modolo et al, ,] with some recent experimental support for this hypothesis [Xiong et al, ]. In the case of acute exposure, changes in synaptic plasticity are unlikely since such effects take time to develop.…”

Neuritin reverses deficits in murine novel object associative recognition memory caused by exposure to extremely low-frequency (50 Hz) electromagnetic fields

“…Recent work by Xiong et al . (2013) demonstrated that ELF MFs exposure can decrease dendritic spine densities 5 . We thus used Golgi staining to investigate the effect of ELF MFs exposure on dendritic spine densities in hippocampal CA1 pyramidal cells.…”

“…A recent study by Xiong et al . (2013) indicated that exposing rats to ELF MFs for 14 or 28 days induced a decrease in spine density in the superficial layers of the medial entorhinal cortex 5 . Since the structure and density of dendritic spines are crucial determinants of neuronal input-output transformations and resulting synaptic plasticity, these data imply that ELF MFs exposure might induce impairment in cognitive functions via reduction of spine number.…”

Exposure to 50 Hz magnetic field modulates GABAA currents in cerebellar granule neurons through an EP receptor‐mediated PKC pathway

“…(2014) indicated that long‐term exposure to ELF‐MF significantly increased anxiety without affecting locomotion, and there was a significant elevation of both GABA and glutamate levels in the hippocampus and hypothalamus of mice exposed . Furthermore, ELF‐MF exposure can change dendritic spine density and morphology in the entorhinal cortical neurons, and had caused a long‐lasting increase in the excitatory state of the neurons in the cortex and hippocampus . Although the effect of ELF‐MFs on the activity of neuronal excitability controlling channels including Ca 2+ ‐active potassium channels and Na + channels have previous investigated, very few studies have investigated the effects of ELF‐MF on ligand‐gated channels, particularly γ‐aminobutyric acid (GABA) type A receptors (GABA A Rs).…”