Assessing the utility of Magneto to control neuronal excitability in the somatosensory cortex

Abstract

Magnetic neuromodulation has outstanding promise for the development of novel neural interfaces without direct physical intervention with the brain. Here we tested the utility of Magneto in the adult somatosensory cortex by performing whole-cell intracellular recordings in vitro and extracellular recordings in freely moving mice. Results show that magnetic stimulation does not alter subthreshold membrane excitability or contribute to the generation of action potentials in virally transduced neurons expressing Magneto.Recently introduced Magneto (Wheeler et al., 2016) might provide the highly sought after neuromagnetic actuation in a cell-targeted manner. Some of the excitement about Magneto originates from its design which is comprised of a calcium-permeable non-selective cation channel (Transient receptor potential cation channel subfamily V member 4, TRPV4) fused to the paramagnetic protein ferritin (Wheeler et al., 2016) . This single-construct approach provides a simplified mean for magnetic intervention with neuronal activity.Here, we used lentiviral delivery of Magneto linked to mCherry (Magneto2.0-P2A-mCherry), expressed under the control of ubiquitin promoter for >2 weeks (Fig. 1a) before observing and interfering with neural activity (see Methods online), and after confirming successful cleavage of Magneto from mCherry (Suppl.Fig. 2a-3) and the subcellular analysis of the expressed protein localization (Suppl.Fig. 2b) in a neuronal cell line . Chronic extracellular recordings in freely moving mice (Allen et al., 2003; Celikel et al., 2004; Clem et al., 2008) with 15 tetrodes enabled high-density sampling of neural activity in the vicinity of transduced cells, and yielded well-isolated (Suppl.Fig. 4) , stable units (Fig. 1b) . Comparison of firing rates within cells across magnetic stimulus conditions (off vs on) showed that magnetic stimulation does not alter the rate of action potentials (APs; Fig. 1c ); neither does it modulate the inter-spike interval within cells, nor spike-timing across single units recorded from the same tetrode (Suppl.Fig. 5,6) . The lack of spiking was not because neurons could not 1

Uncovering a possible role of reactive oxygen species in magnetogenetics

“…While several groups have reproduced the key observation that a sufficiently strong magnetic field can gate TRPV1 [15][16][17] and TRPV4 18,42 , some theoretical calculations have questioned whether ferritin's magnetic properties are sufficient to actuate the channels by either localized heating or mechanical force 24 , as has been proposed. Additionally, follow-up studies of the TRPV4-ferritin platform by Wang et al 43 , Xu et al 44 , and Kole et al 45 , all using electrophysiological readouts, have been unsuccessful in recapitulating the results by Wheeler et al 18 , leading others to suggest alternative physical mechanisms that may account for the growing body of empiric data 42,46,47 . However, none of these studies proposed a possible chemical mechanism, a possibility that was tested here using chemical inhibitors or quenchers of reactive oxygen species generation.…”

Lipid Oxidation Induced by RF Waves and Mediated by Ferritin Iron Causes Activation of Ferritin-Tagged Ion Channels

“…Other recent studies utilized genetically encoded TRP channels tagged with ferritins, actuated by magnetic fields. It is necessary to make a distinction between approaches using static (Stanley et al, 2016;Wheeler et al, 2016) and RF (Hutson et al, 2017;Stanley et al, 2016) fields as the underlying mechanisms, which are likely different, and especially when the efficacy of these technologies is still being investigated (Kole et al, 2019;Wang et al, 2019;Xu et al, 2019). The focus of the present study was to gain insight into the molecular basis of the RF-induced activation of FeRIC channels.…”

“…There have been several independent reports of experimental evidence of magnetic control of transient receptor potential channels, TRPV1 and TRPV4, that are tagged with magnetic nanoparticles using either static (Stanley et al, 2015(Stanley et al, , 2016Wheeler et al, 2016) or radiofrequency (RF) waves (Chen et al, 2015;Huang et al, 2010;Hutson et al, 2017;Munshi et al, 2017;Stanley et al, 2012Stanley et al, , 2015Stanley et al, , 2016. While the mechanisms of both static and RF-induced channel activation remain unclear and controversial (Barbic, 2019;Duret et al, 2019;Kole et al, 2019;Meister, 2016;Wang et al, 2019;Wheeler et al, 2016Wheeler et al, , 2019Xu et al, 2019), the present study uses only RF waves.…”

Cortical representation of touchin silico

“…The slices from the barrel cortex were described before (Kole et al, 2020; Kole and Celikel, 2019) with minor modifications. In short, juvenile mice from either sex were perfused using 4% paraformaldehyde before tangential sections were prepared.…”