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.
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.
| Exposure | Parameters |
|---|---|
|
Exposure 1:
50 Hz
Exposure duration:
4 h/day for 14 or 28 days
|
|
| Frequency | 50 Hz |
|---|---|
| Type | |
| Waveform | |
| Exposure duration | 4 h/day for 14 or 28 days |
| Measurand | Value | Type | Method | Mass | Remarks |
|---|---|---|---|---|---|
| magnetic flux density | 0.5 mT | mean | measured | - | in the center of the coils |
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.
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