Low-intensity repetitive magnetic stimulation lowers action potential threshold and increases spike firing in layer 5 pyramidal neurons in vitro

Abstract

Abstract-Repetitive transcranial magnetic stimulation (rTMS) has become a popular method of modulating neural plasticity in humans. Clinically, rTMS is delivered at high intensities to modulate neuronal excitability. While the high-intensity magnetic field can be targeted to stimulate specific cortical regions, areas adjacent to the targeted area receive stimulation at a lower intensity and may contribute to the overall plasticity induced by rTMS. We have previously shown that low-intensity rTMS induces molecular and structural plasticity in vivo, but the effects on membrane properties and neural excitability have not been investigated. Here we investigated the acute effect of low-intensity repetitive magnetic stimulation (LI-rMS) on neuronal excitability and potential changes on the passive and active electrophysiological properties of layer 5 pyramidal neurons in vitro. Whole-cell current clamp recordings were made at baseline prior to subthreshold LI-rMS (600 pulses of iTBS, n = 9 cells from 7 animals) or sham (n = 10 cells from 9 animals), immediately after stimulation, as well as 10 and 20 min post-stimulation. Our results show that LI-rMS does not alter passive membrane properties (resting membrane potential and input resistance) but hyperpolarises action potential threshold and increases evoked spike-firing frequency. Increases in spike firing frequency were present throughout the 20 min poststimulation whereas action potential (AP) threshold hyperpolarization was present immediately after stimulation and at 20 min post-stimulation. These results provide evidence that LI-rMS alters neuronal excitability of excitatory neurons. We suggest that regions outside the targeted region of high-intensity rTMS are susceptible to neuromodulation and may contribute to rTMS-induced plasticity. Ó

The effects of repetitive transcranial magnetic stimulation in an animal model of tinnitus

“…Lastly, another difference between our study and human studies is that the LI-rTMS used in our study is different from the high intensity rTMS applied in humans because it does not induce action potentials and therefore is unlikely to induce classical forms of synaptic plasticity such as LTD. Rather LI-rTMS induces changes in intracellular calcium levels and regulates gene expression64, which underpin short and long lasting changes in excitability6566 and structural reorganisation16. Such long-lasting changes are in line with our findings that the effects of LI-rTMS on behaviour could still be detected at three days after the final LI-rTMS session.…”

Releasing the Cortical Brake by Non-Invasive Electromagnetic Stimulation? rTMS Induces LTD of GABAergic Neurotransmission

“…Apparently, rTMS represents a promising tool in this context. While rTMS-induced changes in intrinsic cellular properties (Tang et al, 2016) and other mechanisms need to be considered, e.g., modulation of gene expression, mRNA-sorting and local protein synthesis, morphological changes, glial and vascular effects, we are confident that the emerging concept of rTMS-induced local disinhibition may provide an interesting framework for future studies.…”

Low‐intensity transcranial magnetic stimulation promotes the survival and maturation of newborn oligodendrocytes in the adult mouse brain

“… Figure S1 Administration of LI‐rTMS to mice using a specialised rodent coil (A) Photograph of the 8 mm circular rodent coil used to deliver LI‐rTMS to mice in this study (Tang et al, ). (B) Schematic showing the method of restraint (plastic body contour shape restraint bag; pink), placement of the coil (red circle) and approximate region where the greatest current is generated (red circle).…”