Thermal effect induced by low-frequency magnetic field on physiological characteristics in hippocampal CA1 region of rat

Abstract

The aim of the present study is to analyze the influences of low-frequency magnetic stimulation on spontaneous excitatory postsynaptic currents (sEPSC) and action potentials (AP) of rat hippocampal CA1pyramidal neurons. Although this is a very common subject of neuroscience and electrophysiology, the thermal effects of the applied magnetic fields were always neglected in most previous studies, which might lead to improper conclusions. Therefore, we preformed a series of experiments to investigate the possible influences of these thermal effects. According to our previous simulation results, the temperature will not be higher than 4 °C even with the heating of a very high intensity applied magnetic field. So we do a series of whole-cell clamp experiments under 25 °C, 30 °C, 35 °C, and 40 °C, respectively. Using whole-cell patch-clamp technique, sEPSC and AP measurements were acquired for flux densities of 0 (thermal effect only), 7, 14, and 23 mT at temperatures of 25 °C, 30 °C, 35 °C, and 40 °C. The results show that the amplitudes of sEPSC and AP would both decrease with the temperature regardless of the intensity of the magnetic field. As is known, the sEPSC and AP will both affect the functions of neuron network, so we could reach to the conclusion that the temperature increase originating from the thermal heating effects of the applied magnetic field will also have influences on the functions of neurons or synapses. Furthermore, according the results, the thermal sensitivity of sEPSC and AP might be an inherent characteristic of neurons, and was not affected by the strength of the electromagnetic field.