Real-time detection of stimulus response in cultured neurons by high-intensity intermediate-frequency magnetic field exposure

Abstract

Threshold values of neuronal stimulation and modulation associated with exposure to time-varying electromagnetic fields contribute to establishing human protection guidelines and standards. However, biological evidence of threshold values in the intermediate-frequency range is limited. Additionally, although it is known that dendrites, a type of unmyelinated neuronal fibre, play an important role in information processing in the central nervous system, the stimulus threshold in dendrites has not been sufficiently investigated. We evaluated the excitation site-specific stimulus response of rat brain-derived cultured neurons by using a 20 kHz high-intensity intermediate-frequency magnetic field (hIF-MF) exposure system, a non-conductive fibre-optic imaging (NCFI) system, combined with a micro-patterning technique. Our hIF-MF exposure and NCFI system permitted real-time detection of the intracellular calcium ([Ca2+]i) spikes in neuronal cell bodies or unmyelinated neuronal fibres during exposure to a 20 kHz, 70 mT (peak), burst-type sinusoidal wave hIF-MF. Dosimetry of the induced electric fields intensities in the extracellular solution indicated that about 50% of unmyelinated neuronal fibres respond at about 147 V m-1. In contrast, the threshold of the [Ca2+]i spikes in neuronal cell bodies were lower than that in unmyelinated neuronal fibres. Our results provide a basis for understanding site-specific differences in the responses of cultured neurons to hIF-MFs.

Fabrication of a Miniature Figure-of-Eight Coil for Micromagnetic Stimulation on Neuronal Tissue

“…A fluorescence imaging system combined with a fluorescence microscope (Eclipse Ti, Nikon, Tokyo, Japan), cooled charge-coupled device camera (Im-agEM, Hamamatsu, Shizuoka, Japan), and the associated software (Aquacosmos 2.6, Hamamatsu) were used to detect the intracellular calcium dynamics. The response stimulated by MF exposure was evaluated by using previously published methods [9]. For MF exposure of cultured human neuronal networks, the mFo8 coils were positioned in the vicinity of the cells by using a micromanipulator (MC-35 A, Narishige, Tokyo, Japan), and micropositioning was performed under fluorescence microscopy.…”

Non-conductive fiber optic imaging system for real-time detection of stimulus responses under high-intensity and low-frequency magnetic field exposure

“…In addition, the biological threshold in the 10-100 kHz intermediate frequency range used by induction heating (IH) or wireless power transfer (WPT) technologies is not well understood. To address these issues, we have previously developed a non-conductive fiber optic imaging system for real-time detection of neuronal activity at the cellular level in high-intensity, timevarying EMF exposure environments [2][3][4]. In this talk, we will present the proposed experimental system to elucidate low-frequency stimulus thresholds and neuronal modulation mechanisms using in vitro approaches.…”

Firing patterns and bifurcation analysis of neurons under electromagnetic induction

“…Interestingly, Barry et al have found the magnetic field, indicating that the magnetic field exists generated by action potential [1]. The exogenous magnetic field has obvious influence on the electrical activity of neurons [20] [21]. Therefore, it is a direction to study theoretically the dynamic behavior of neurons under electromagnetic induction.…”