Study type: Medical/biological study (experimental study)

The extremely low-frequency magnetic field exposure differently affects the AMPAR and NMDAR subunit expressions in the hippocampus, entorhinal cortex and prefrontal cortex without effects on the rat spatial learning and memory. med./bio.

Published in: Environ Res 2014; 134: 74-80

Aim of study (acc. to author)

To examine the effects of chronic exposure to extremely low frequency magnetic fields on the subunit protein expression of two synaptic receptors in the brain and on spatial learning and memory in rats.

Background/further details

The N-methyl-D-aspartate receptor (NMDA receptor) and the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPA receptor) are glutamate receptors which mediate the fast excitatory neurotransmission in the brain. These receptors play an important role in synaptic plasticity and learning.
60 rats were randomly assigned to one of four groups: 1.) sham exposure for 14 days, 2.) exposure for 14 days, 3.) sham exposure for 28 days and 4.) exposure for 28 days. After the exposure, some animals (5 rats from group 1 and 2, respectively; 6 rats from group 3 and 4, respectively) were immediately used for protein expression analysis, while the others (10 rats from group 1 and 2, respectively; 9 rats from group 3 and 4, respectively) were tested in the Morris water maze.

Endpoint

Exposure

Exposure Parameters
Exposure 1: 50 Hz
Exposure duration: 4 h/day for 14 or 28 days

Exposure 1

Main characteristics
Frequency 50 Hz
Type
Waveform
Exposure duration 4 h/day for 14 or 28 days
Exposure setup
Exposure source
Setup round coil electromagnet with a 1000 turned copper wire constructed on a glass fibre cylinder, the centre of each cage was 15 cm vertical below the poles
Parameters
Measurand Value Type Method Mass Remarks
magnetic flux density 0.5 mT mean measured - in the center of the coils

Reference articles

  • Xiong J et al. (2013): Changes of dendritic spine density and morphology in the superficial layers of the medial entorhinal cortex induced by extremely low-frequency magnetic field exposure.

Exposed system:

Methods Endpoint/measurement parameters/methodology

Investigated system:
Investigated organ system:
Time of investigation:
  • after exposure

Main outcome of study (acc. to author)

The magnetic field exposure changed the expression levels of the NMDA receptor and AMPA receptor subunits differently.
Regarding the subunit protein expression of the NMDA receptor, significant increases in the hippocampus were observed after exposure (increased levels of GluN2A and GluN2B after 14 days, increased levels of GluN2B after 28 days) compared to the sham exposure. Additionally in the entorhinal cortex of exposed rats, the NMDA receptor subunit expression was significantly changed (increased levels of GluN1 and GluN2A after 14 days, decreased level of GluN2A after 28 days, increased level of GluN2B after 28 days) in comparison to the sham exposure while in the prefrontal cortex, significant increases were observed (increased levels of GluN1 and GluN2A after 14 days, increased level of GluN1 after 28 days).
Regarding the subunit protein expression of the AMPA receptor, no significant alterations in the hippocampus of exposed rats were observed when compared to the sham exposed rats, while significant decreases were found in the entorhinal cortex (decreased level of GluA2 after 28 days) and in the prefrontal cortex (decreased level of GluA3 after 14 days).
No significant differences occurred regarding spatial learning and memory in the Morris Water maze between the exposed and the sham exposed rats.
The authors conclude that exposure to extremely low frequency magnetic fields could have an influence on the subunit protein expression of synaptic glutamate receptors but does not change the spatial memory and learning abilities of rats.

Study character:

Study funded by

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