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 array 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 dissimilarities between the inhibitory effect of RF fields (continuous wave, 1800 MHz) to the γ-Aminobutyric acid type A (GABA A) receptor agonist muscimol (MU). Inhibition of 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 degree Celsius. Differently to a pharmacological inhibition with MU, exposure to RF fields preferentially inhibits bursting over spiking activity and exerts less constrains on neural network bursting synchrony. Network rebound excitation, a phenomenon relying on intrinsic properties of cortical neurons, was observed consecutively to the removal of tonic hyperpolarization after washout of MU but not in response to cessation of RF exposure which 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 change in AP waveform tightly influence efficiency of synaptic transmission, the narrowing effect on AP seen under RF exposure might contribute to reduce 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 action of RF fields differ from the ones mediated by the activation of GABA A receptor. The rapid onset of the inhibitory effect of RF fields and its reversibility strikingly similar to MU are in favour of a mechanism interacting with fast operating targets at the membrane such as ion channels.