To investigate the influence of exposure to extremely low frequency magnetic fields on the survival of hippocampal newly developed cells of mice.
In a previous study, the authors demonstrated that exposure to extremely low frequency magnetic fields stimulates the hippocampal neurogenesis in adult mice (Cuccurazzu et al., 2010). To extend the previous study, 2 further experiments were performed: An in vivo and an in vitro experiment.
For the in vivo experiment, 54 juvenile mice were divided into an exposure and a sham exposure group. Different examinations were performed.
1.) For immunohistochemical analysis, 10 mice from each group received daily injections of 100 mg/kg bromodeoxyuridine (BrdU) for 3 consecutive days. 9 days after the last injection, mice were exposed or sham exposed on six days. Half of the mice were killed 3 days after the last exposure or sham exposure session and the other half after 9 days (each group n=5).
2.) For the Western blot analysis, animals were killed 3 days after the last exposure (n=4) or sham exposure (n=4) session.
3.) Apoptosis in the dentate gyrus was examined 3 days after the last exposure (n=3) or sham exposure (n=3) session.
4.) A set of 20 mice (exposure group n=10; sham exposure group n=10) was used for cognitive and memory test. The novel recognition test was performed during the 4th, 5th and 6th day, while the Morris water maze was performed from the 9th to the 13th day after the exposure or sham exposure session.
For the in vitro experiment, cultured hippocampal neural stem cells were cultivated in an incubator while exposed or sham exposed. Apoptosis and protein expression of microtubule-associated protein 2 (MAP2; protein which is involved in microtubule assembly, an essential step in neurogenesis) was tested in the presence or absence of the pro-apoptotic beta-amyloid protein.
| Exposure | Parameters |
|---|---|
|
Exposure 1:
50 Hz
Exposure duration:
3.5 hours/per day for 6 days
in vivo experiment
|
|
|
Exposure 2:
50 Hz
Exposure duration:
continuous for 3 days
in vitro experiment
|
|
| Frequency | 50 Hz |
|---|---|
| Type | |
| Exposure duration | 3.5 hours/per day for 6 days |
| Additional info | in vivo experiment |
| Exposure source | |
|---|---|
| Setup | solenoid was positioned around a Plexiglas cylinder (diameter 20 cm, length 42 cm), in which the plastic cage (33 x 15 x 13 cm) was placed, 3 to 4 freely moving mice per cage |
| Sham exposure | A sham exposure was conducted. |
| Measurand | Value | Type | Method | Mass | Remarks |
|---|---|---|---|---|---|
| magnetic flux density | 1 mT | - | - | - | - |
| Frequency | 50 Hz |
|---|---|
| Type | |
| Exposure duration | continuous for 3 days |
| Additional info | in vitro experiment |
| Exposure source | |
|---|---|
| Setup | solenoid was positioned inside a CO2 incubator, surfaces of culture plates were parallel to the force lines of the magnetic field, temperature was (due to used incubator) 37.0°C or 37.4°C, maximum temperature increase in the cultures during exposure was 0.4 ± 0.1°C |
| Sham exposure | A sham exposure was conducted. |
| Measurand | Value | Type | Method | Mass | Remarks |
|---|---|---|---|---|---|
| magnetic flux density | 1 mT | - | - | - | - |
In exposed mice, the cell proliferation was significantly increased in comparison to the sham exposed group (increased number of BrdU and doublecortin-positive cells). This enhanced cell proliferation in the exposure group was accompanied by an increased mature stage of the cells (significantly increased protein expression of the neural marker NeuN) and a significantly decreased apoptosis rate in comparison to the sham exposure group. Also in the cell cultures, the cell survival was significantly increased and the apoptosis was significantly decreased after exposure in comparison to the sham exposure. Both in the exposed cell cultures and in the hippocampus of exposed mice, the protein expression of the pro-apoptotic protein Bax was significantly decreased while the anti-apoptotic protein Bcl-2 was significantly increased compared to the sham exposed groups. In exposed cell cultures treated with beta-amyloid protein, the protein expression of microtubule-associated protein 2 was significantly higher than in sham exposed ones treated with beta-amyloid protein.
Exposed mice showed significantly improved memory and learning abilities compared to sham exposed mice.
The authors conclude that exposure to extremely low frequency magnetic fields promotes the survival of hippocampal newly developed cells in mice.
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