Extreme Low Frequency Electromagnetic Field Stimulation Induces Metaplastic-Like Effects on LTP/ LTD

In modern societies, people are more likely to be exposed to technological devices that emit extreme low frequency (ELF, <; 300 Hz)-electromagnetic fields (EMFs). Although ELF-EMFs are successfully used as therapeutic agents in psychiatry treatment and rehabilitation practices, they are also considered to be environmental pollutants that pose a risk to human health. However, several studies have suggested that ELF-EMFs stimulation has the potential to ameliorate learning and memory processes in humans. Given that the underlying mechanisms of magnetic stimulation on the brain are not fully understood, this study aimed to investigate the effects of ELF-EMFs in learning and memory formation. Sprague-Dawley rats were used as a model system to evaluate learning and memory mechanisms based on the synaptic plasticity of the Schaffer-CA1 pathway in hippocampal slices using ELF-EMFs stimulation. Parameters were selected based on previous experiments (i.e., 15 hertz [Hz], 2 militesla [mT]), during, and after plasticity induction, basic frequencies of 1, 5, 20 and 100 Hz were applied and an on-line ELF-EMFs stimulation drive was used together, which previously defined as preceding, middle and post stimulation. Our results showed that the greatest effect on synaptic plasticity was observed when ELF-EMFs were paired with a plasticity induction protocol. Importantly, ELF-EMFs did not affect synapses that were weakly active or in synapses containing N-methyl-D-aspartate (NMDA) receptors that were blocked. This study highlights the metaplastic-like role of ELF-EMFs, acting as modulators of synaptic activity processes,as well as their regulation by NMDA receptor-dependent synaptic plasticity.