To study whether 50 Hz extremely low frequency electromagnetic field exposure affects adult hippocampal neurogenesis in vivo, and if so, to identify the molecular mechanisms underlying this action and its functional impact on synaptic plasticity.
ln a previous study (Piacentini et al. 2008), the authors demonstrated that exposure to extremely low frequency electromagnetic fields significantly enhances the neuronal differentiation of cortical neural stem cells in vitro and this effect is mediated by the upregulation of Cav1-calcium channel expression and activity.
71 mice were divided into an exposure group (n=38) and a sham exposure group (n=33): three exposed animals were used for RT-PCR and three for Western blot analysis on day four (on day four, because modulation of gene expression of transcription factors should precede the differentiation process). 14 exposed animals were used for immunofluorescence analysis on day seven (24 h after the final exposure session) and five mice on day 37 (30 days after exposure to study survival and integration of newly generated neurons). Additionally, 13 exposed animals were used for long-term potentiation experiments on day 37.
Exposure duration: continuous for 7 h/day on 4 days
Exposure duration: continuous for 1 h/day (n=3 mice), 3 h/day (n=3) or 7 h/day (n=13) on 7 days
Exposure duration: continuous for 7 h/day on 7 days
Extremely low frequency electromagnetic field exposure for seven days significantly enhanced neurogenesis in the dentate gyrus of adult mice, as shown by increased numbers of cells double-labeled (immune reactive) for BrdU and doublecortin (a marker for immature neurons).
Quantitative RT-PCR analysis of hippocampal extracts revealed significant exposure-induced increases in the gene expression of pro-neuronal genes (Mash1, NeuroD2, Hes1) and genes encoding Cav1.2 calcium channel alpha1C subunits. Increased protein expression of NeuroD1, NeuroD2 and Cav1 channels was also found by Western blot analysis.
Immunofluorescence experiments showed that 30 days after exposure roughly half of the newly generated immature neurons had survived and became mature dentate gyrus granule cells (as shown by their immune reactivity for both BrdU and NeuN, a marker for differentiated neurons) and were integrated into the granule cell layer of the dentate gyrus.
Electrophysiological experiments demonstrated that the new mature neurons influenced hippocampal synaptic plasticity, as reflected by increased long-term potentiation.
The data show that extremely low frequency electromagnetic field exposure can be an effective tool for increasing in vivo neurogenesis, and they could lead to the development of novel therapeutic approaches in regenerative medicine.