Repetitive transcranial magnetic stimulation enhances the neuronal excitability of mice by regulating dynamic characteristics of Granule cells’ Ion channels

This study aims to explore the effects of acute high-frequency repetitive transcranial magnetic stimulation (hf-rTMS) on neuronal excitability of granule cells in the hippocampal dentate gyrus, as well as the underlying intrinsic mediating mechanisms by which rTMS regulates neuronal excitability. First, high-frequency single TMS was used to measure the motor threshold (MT) of mice. Then, rTMS with different intensities of 0 MT (control), 0.8 MT, and 1.2 MT were applied to acute mice brain slices. Next, patch-clamp technique was used to record the resting membrane potential and evoked nerve discharge of granule cells, as well as the voltage-gated sodium current (I_Na) of voltage-gated sodium channels (VGSCs), transient outward potassium current (I_A) and delayed rectifier potassium current (I_K) of voltage-gated potassium channels (Kv). Results showed that acute hf-rTMS in both 0.8 MT and 1.2 MT groups significantly activated I_Na and inhibited I_A and I_K compared with control group, due to the changes of dynamic characteristics of VGSCs and Kv. Acute hf-rTMS in both 0.8 MT and 1.2 MT groups significantly increased membrane potential and nerve discharge frequency. Therefore, changing dynamic characteristics of VGSCs and Kv, activating I_Na and inhibiting I_A and I_K might be one of the intrinsic mediating mechanisms by which rTMS enhanced the neuronal excitability of granular cells, and this regulatory effect increased with the increase of stimulus intensity.