Comparative study between radiofrequency-induced and muscimol-induced inhibition of cultured networks of cortical neuron

Abstract

Previous studies have shown that spontaneously active cultured networks of cortical neuron grown planar microelectrode arrays are sensitive to radiofrequency (RF) fields and exhibit an inhibitory response more pronounced as the exposure time and power increase. To better understand the mechanism behind the observed effects, we aimed at identifying similarities and differences between the inhibitory effect of RF fields (continuous wave, 1800 MHz) to the γ-aminobutyric acid type A (GABAA) receptor agonist muscimol (MU). Inhibition of the network bursting activity in response to RF exposure became apparent at an SAR level of 28.6 W/kg and co-occurred with an elevation of the culture medium temperature of ~1°C. Exposure to RF fields preferentially inhibits bursting over spiking activity and exerts fewer constraints on neural network bursting synchrony, differentiating it from a pharmacological inhibition with MU. Network rebound excitation, a phenomenon relying on the intrinsic properties of cortical neurons, was observed following the removal of tonic hyperpolarization after washout of MU but not in response to cessation of RF exposure. This implies that hyperpolarization is not the main driving force mediating the inhibitory effects of RF fields. At the level of single neurons, network inhibition induced by MU and RF fields occurred with reduced action potential (AP) half-width. As changes in AP waveform strongly influence efficacy of synaptic transmission, the narrowing effect on AP seen under RF exposure might contribute to reducing network bursting activity. By pointing only to a partial overlap between the inhibitory hallmarks of these two forms of inhibition, our data suggest that the inhibitory mechanisms of the action of RF fields differ from the ones mediated by the activation of GABAA receptors.

In vitro exposure of neuronal networks to the 5G-3.5 GHz signal

“…These findings suggest that the carrier frequency does not influence the amplitude of the effect in the 1.8–3.5 GHz range. Furthermore, the present findings at 1.8 GHz are in agreement with our previous published work ( 10 ), which showed a comparable decrease of ~35% of the MBR under CW exposure at the same SAR level, while the culture medium was then continuously and slowly perfused. This indicates that the circulation of thermostated culture medium during the 75 min experiment is not necessary to induce this effect.…”

“…We next assessed how exposure to 3.5 GHz signals (CW and 5G) at a SAR value of 28 W/kg impacted the electrical activity of the neurons. While this SAR value is well above the guidelines, it corresponds to the level used in our previous exposure experiment at 1.8 GHz ( 10 ). Figure 5 shows representative examples of the recorded S2, E, and P1 phases and corresponding raster plots during exposure to 5G signals at 28 W/kg.…”

“…We performed electrophysiological recordings of neuronal networks using MEAs as described previously ( 10 ). The active area of each MEA was coated with 0.1 mg/mL poly-L-lysine (PLL) (Sigma-Aldrich) and 0.05 mg/mL laminin (Sigma-Aldrich) for improved adherence.…”

“…We also assessed the effects of high-level signals (SAR of 28 W/kg) as we previously observed an inhibitory effect of CW 1.8 GHz-RF exposure at 28 W/kg ( 10 ). In this previous study, the experimental conditions differed on one point: the culture medium was continuously perfused.…”

“…Beyond these adjustments, our experiments provided strong evidence of decreased electrical activity of cortical neuronal cultures during RF exposure. In a further effort to identify the inhibitory mechanisms triggered by RF exposure on cortical neurons, we next have shown that they differ from the ones mediated by the activation of GABA A receptors ( 10 ).…”