Infrared inhibition impacts on locally initiated and propagating action potentials and the downstream synaptic transmission.

Jen-Wei Lin,Michelle Y Sander,Xuedong Zhu

doi:10.1117/1.nph.7.4.045003

Abstract

.Significance: Systematic studies of the physiological outputs induced by infrared (IR)-mediated inhibition of motor nerves can provide guidance for therapeutic applications and offer critical insights into IR light modulation of complex neural networks.Aim: We explore the IR-mediated inhibition of action potentials (APs) that either propagate along single axons or are initiated locally and their downstream synaptic transmission responses.Approach: APs were evoked locally by two-electrode current clamp or at a distance for propagating APs. The neuromuscular transmission was recorded with intracellular electrodes in muscle cells or macro-patch pipettes on terminal bouton clusters.Results: IR light pulses completely and reversibly terminate the locally initiated APs firing at low frequencies, which leads to blocking of the synaptic transmission. However, IR light pulses only suppress but do not block the amplitude and duration of propagating APs nor locally initiated APs firing at high frequencies. Such suppressed APs do not influence the postsynaptic responses at a distance. While the suppression of AP amplitude and duration is similar for propagating and locally evoked APs, only the former exhibits a 7% to 21% increase in the maximum time derivative of the AP rising phase.Conclusions: The suppressed APs of motor axons can resume their waveforms after passing the localized IR light illumination site, leaving the muscular and synaptic responses unchanged. IR-mediated modulation on propagating and locally evoked APs should be considered as two separate models for axonal and somatic modulations.

Highlights

Excitatory axons were used in APprop and macro-patch recordings to take the advantage of higher signal-to-noise ratios of excitatory postsynaptic potentials (EPSPs) and excitatory postsynaptic currents (EPSCs)
We first compared the IR-mediated inhibition of the APTECC and the APprop
A detailed comparison of the APTECC recorded at the end of the IR light pulse showed that the inhibition of the APTECC amplitude and duration was more pronounced for higher power of the IR light illumination [Figs. 1(i) and 1(j)]

Summary

Introduction

Infrared (IR) light has emerged as a new modality that can reliably modulate both neural and muscular activities with the advantages of being contact-free, spatially selective, and MRI compatible.[1,2,3] IR-mediated modulation of excitable tissues has been demonstrated in a wide NeurophotonicsDownloaded From: https://www.spiedigitallibrary.org/journals/Neurophotonics on 18 Jan 2022 Terms of Use: https://www.spiedigitallibrary.org/terms-of-useOct–Dec 2020 Vol 7(4)Zhu, Lin and Sander: Infrared inhibition impacts on locally initiated and propagating. . .range of promising clinical applications, such as cochlear prostheses,[4,5] brain stimulation and mapping,[6,7,8,9] cardiac pacing,[10] and neural monitoring during surgery.[11,12] The main biological processes induced by pulsed IR light are attributed to the spatiotemporal thermal transients generated by water and tissue absorption,[13] which in turn can alter the membrane capacitance,[14,15,16,17] membrane resistance,[18,19] ion channel activities,[19,20,21,22,23,24,25] and intracellular calcium dynamics.[6,26,27,28,29,30] The temperature-sensitive transient receptor potential channels have received particular attention due to their intrinsic temperature sentisitivity.[25,27,28,30,31] The presence of multiple IR-interacting targets in neural tissues suggests the need for an integrated approach to understand IR-mediated modulation. Infrared (IR) light has emerged as a new modality that can reliably modulate both neural and muscular activities with the advantages of being contact-free, spatially selective, and MRI compatible.[1,2,3] IR-mediated modulation of excitable tissues has been demonstrated in a wide Neurophotonics. Gaining insights into how a neuron as a functional whole is modulated by IR light irradiation is the first step toward a more thorough understanding of IR-mediated modulation of a complex network

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