To investigate the long-term effects of an exposure to extremely low frequency magnetic field on the synaptic functions in the developing rat brain.
Rats were exposed or sham exposed for 7 days: either in utero during the second week of pregnancy (sham exposure and exposure, each n=5)) or postnatal with the beginning of the third day after birth (n=6 sham exposure, n=6 exposure).
Rats were sacrificed in the age of two month and brain slices were examined. Altogether 32 neocortical and 31 hippocampal slices were tested (5-9 per group).
| Exposure | Parameters |
|---|---|
|
Exposure 1:
50 Hz
Exposure duration:
continuous for 7 days during the second week of pregnancy
|
|
|
Exposure 2:
50 Hz
Exposure duration:
continuous for 7 days beginning with the third day after birth
|
|
| Frequency | 50 Hz |
|---|---|
| Type | |
| Waveform | |
| Exposure duration | continuous for 7 days during the second week of pregnancy |
| Exposure source | |
|---|---|
| Setup | Helmholtz coil apparatus consisting of two solenoids with a radius of 21 cm each, 21 cm apart; homogenous vertical field in the space between the coils; coils constructed of 240 turns of glaze-insulated copper wire (d=1.4 mm); rats placed in 35 cm x 35 cm x 17 cm opaque plastic boxes in the center of the coils, temperature in boxes 24 ± 0.5°C |
| Sham exposure | A sham exposure was conducted. |
| Measurand | Value | Type | Method | Mass | Remarks |
|---|---|---|---|---|---|
| magnetic flux density | 0.5 mT | - | measured | - | ± 25 µT |
| Frequency | 50 Hz |
|---|---|
| Type | |
| Waveform | |
| Exposure duration | continuous for 7 days beginning with the third day after birth |
| Exposure source |
|
|---|
| Measurand | Value | Type | Method | Mass | Remarks |
|---|---|---|---|---|---|
| magnetic flux density | 3 mT | - | measured | - | - |
Exposure during the pregnancy and exposure in the early postnatal age led to a significantly increased amplitude of evoked potentials in the hippocampal slices compared to the corresponding sham exposure group. Neocortical slices responded mostly to postnatal exposure. There, the amplitude of the excitatory postsynaptic potentials was significantly increased when compared to the sham exposure.
In neocortical sclices from sham exposed rats, typically paired-pulse depression appeared. However, an exposure during the pregnancy significantly inhibited the paired-pulse depression and significantly decreased the efficacy of long-term potentiation induction. No exposure effect on the paired-pulse depression and on the efficacy of the long-term potentiation induction was observed in hippocampal slices (exposed during pregnancy and postnatal) or in postnatal exposed rats in neocortical slices.
The authors conclude that exposure to extremely low frequency magnetic fields has an effect on basic synaptic functions and synaptic plasticity in the developing rat brain.
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