In Vitro Study of Neurochemical Changes Following Low-Intensity Magnetic Stimulation

Given its ability to modulate neuronal excitability, low-intensity magnetic stimulation (LIMS) has therapeutic potential in the treatment of neurological disorders. However, the underlying of LIMS effects remain poorly understood because LIMS does not directly generate action potentials. We aimed to elucidate these mechanisms by studying and systematically comparing the neurochemical changes induced in vitro by LIMS. To this end, we developed a simple in vitro magnetic stimulation device that allowed delivery of a range of stimulation parameters in order to generate sufficient field intensity for the subthreshold. In characterizing our custom-built system, we conducted computational simulations to determine the electromagnetic field exposure to a cell culture dish. Subsequently, using the custom-built LIMS system, we applied three different stimulation protocols to differentiated neuroblastoma cells for 30 min and then assessed the resultant neurochemical changes. We found that high-frequency (HF: 10 Hz) stimulation increased levels of the excitatory neurotransmitter, glutamate, while low-frequency (LF: 1 Hz) stimulation increased levels of the inhibitory neurotransmitter, GABA. These results suggest that LIMS effects are frequency-dependent: suppression of neuroexcitability occurs at LF and facilitation occurs at HF. Furthermore, we observed pattern-dependent changes when comparing repetitive high-frequency (rHF) and intermittent high-frequency (iHF) stimulations: iHF took more time to induce neurochemical change than rHF. In addition, we found that calcium changes were closely associated with glutamate changes in response to different stimulation parameters. Our experimental findings indicate that LIMS induces the release of neurotransmitters and affects neuronal excitability at magnetic field intensities far lower than suprathreshold, and that this in turn induces action potentials. Therefore, this study provides a cellular framework for understanding how low-intensity magnetic stimulation could affect clinical outcomes.