To investigate the effect of a 50 Hz magnetic field on olfactory memory and hippocampal neurogenesis in mice as well as the role of the Wnt/β-catenin signal pathway.
In the adult mammalian brain, neurogenesis occurs in the subventricular zone (between striatum and lateral ventricles) and the dentate gyrus of the hippocampus. The Wnt/β-catenin pathway plays a pivotal role in the regulation of cell proliferation, differentiation, genetic stability, migration, and apoptosis and seems also to be important for neurogenesis.
For in vivo tests, mice were randomly divided into two groups: A sham exposure group and a magnetic field exposed group. Several behavioral tests and neuronal examinations were performed with 7-10 animals per group, respectively. Partially the mice were injected with the Wnt inhibitor Dkk-1. The expression of neuronal genes was examined in 3 animals per group, respectively.
To further examine the molecular mechanisms, in vitro tests with neural stem cells were performed.
| Exposure | Parameters |
|---|---|
|
Exposure 1:
50 Hz
Exposure duration:
3.5 hours/day for 12 days
|
|
|
Exposure 2:
50 Hz
Exposure duration:
3.5 hours/day for 4 days
|
|
|
Exposure 3:
50 Hz
Exposure duration:
3, 6, or 24 hours
in vitro experiments
|
|
| Frequency | 50 Hz |
|---|---|
| Type | |
| Exposure duration | 3.5 hours/day for 12 days |
| Additional info | in vivo behavioral and immunofluorescence experiments |
| Exposure source | |
|---|---|
| Chamber | plastic housing cages containing mice were placed inside the solenoid |
| Setup | magnetic field was generated by a solenoid surrounding a plexiglas cylinder (diameter 20 cm; length 42 cm) |
| Sham exposure | A sham exposure was conducted. |
| Additional info | mice of the control group were also put in the solenoid for sham exposure, but the power generator was switched off |
| Measurand | Value | Type | Method | Mass | Remarks |
|---|---|---|---|---|---|
| magnetic flux density | 1 mT | - | - | - | - |
| Frequency | 50 Hz |
|---|---|
| Type | |
| Exposure duration | 3.5 hours/day for 4 days |
| Additional info | in vivo gene expression experiments, western blot and immunofluorescence of β-catenin |
| Exposure source |
|
|---|---|
| Sham exposure | A sham exposure was conducted. |
| Measurand | Value | Type | Method | Mass | Remarks |
|---|---|---|---|---|---|
| magnetic flux density | 1 mT | - | - | - | - |
| Frequency | 50 Hz |
|---|---|
| Type | |
| Exposure duration | 3, 6, or 24 hours |
| Additional info | in vitro experiments |
| Measurand | Value | Type | Method | Mass | Remarks |
|---|---|---|---|---|---|
| magnetic flux density | 1 mT | - | - | - | - |
Magnetic field exposed mice showed a significantly enhanced odor discrimination and olfactory memory compared to sham exposed mice as well as a significantly increased neurogenesis in the subventricular zone. This was accompanied by significantly increased mRNA levels of Wnt3, Hes1, and Mash1 in the subventricular zone of exposed mice as well as in neuronal stem cells of the subventricular zone (in vitro) when compared with the corresponding control group, while in the hippocampus of exposed mice only Hes1 and Mash1 were significantly up-regulated. The level of β-catenin (downstream target of Wnt3) was significantly increased in the nuclei of exposed neural stem cells (in vitro) compared to sham exposed cells. The Wnt inhibitor Dkk-1 abolished the magnetic field induced increases in neurogenesis (in vivo), olfactory memory (in vivo) and up-regulation of Wnt3, Hes1, and Mash1 (in vitro). Additionally, Dkk-1 significantly decreased the level of β-catenin in the nucleus of cells in the subventricular zone compared to those without Dkk-1, while no effect was seen in the hippocampus.
The authors conclude that 50 Hz magnetic fields could improve the olfactory memory of mice via the Wnt/β-catenin signal pathway in the subventricular zone.
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