Recording action potential propagation in single axons using multi-electrode arrays

Abstract

The small caliber of central nervous system (CNS) axons makes routine study of axonal physiology relatively difficult. However, while recording extracellular action potentials from neurons cultured on planer multi-electrode arrays (MEAs) we found activity among groups of electrodes consistent with action potential propagation in single neurons. Action potential propagation was evident as widespread, repetitive cooccurrence of extracellular action potentials (eAPs) among groups of electrodes. These eAPs occurred with invariant sequences and inter-electrode latencies that were consistent with reported measures of action potential propagation in unmyelinated axons. Within co-active electrode groups, the inter-electrode eAP latencies were temperature sensitive, as expected for action potential propagation. Our data are consistent with these signals primarily reflecting axonal action potential propagation, from axons with a high density of voltage-gated sodium channels. Repeated codetection of eAPs by multiple electrodes confirmed these eAPs are from individual neurons and averaging these eAPs revealed sub-threshold events at other electrodes.The sequence of electrodes at which eAPs co-occur uniquely identifies these neurons, allowing us to monitor spiking of single identified neurons within neuronal ensembles.We recorded dynamic changes in single axon physiology such as simultaneous increases and decreases in excitability in different portions of single axonal arbors over several hours. Over several weeks, we measured changes in inter-electrode propagation latencies and ongoing changes in excitability in different regions of single axonal arbors.We recorded action potential propagation signals in human induced pluripotent stem cell-derived neurons which could thus be used to study axonal physiology in human disease models.peer-reviewed) is the author/funder. All rights reserved. No reuse allowed without permission.The copyright holder for this preprint (which was not . http://dx.doi.org/10.1101/126425 doi: bioRxiv preprint first posted online Apr. 11, 2017; 3 Significance StatementStudying the physiology of central nervous system axons is limited by the technical challenges of recording from axons with pairs of patch or extracellular electrodes at two places along single axons. We studied action potential propagation in single axonal arbors with extracellular recording with multi-electrode arrays. These recordings were non-invasive and were done from several sites of small caliber axons and branches. Unlike conventional extracellular recording, we unambiguously identified and labelled the neuronal source of propagating action potentials. We manipulated and quantified action potential propagation and found a surprisingly high density of axonal voltage-gated sodium channels. Our experiments also demonstrate that the excitability of different portions of axonal arbors can be independently regulated on time scales from hours to weeks.

MEA Viewer: a High-performance Interactive Application for Visualizing Electrophysiological Data

“…Spikes detected on multiple electrodes but originating from single neurons are indicated by gray markers. Navigating the data in this way allows for unbiased assessment of spike detection and sorting performance of any data record, and enables the rapid visualization of redundant spike information, which can be underappreciated when analyzing MEA data (Tovar et al, 2017). The obvious utility of this visualization in MEA Viewer is that common spikedetection and sorting routines can be easily assessed in this view (Fig.…”

“…An additional unique feature of MEA Viewer is that it easily allows visualization of instances where the acquisition system captures action potential propagation in single neurons. Recent work with cultured neurons from mouse or human induced pluripotent stem cells ( iPSCs) demonstrates that signal propagation within individual neurons can be monitored by detection of nearcoincident spikes among MEA electrodes represent (Tovar et al 2017). Because they arise from single neurons, these signals can be aligned and averaged to reveal the extent of signal propagation within one cell within a neural network, immediately giving a display of the spatial extent of signal propagation.…”

“…MEA Viewer provides five main visualization interfaces: (i) the grid view displays the complete set of recorded extracellular signals, (ii) the signal comparison view allows users to select and display multiple recorded channels with superimposed spike data, (iii) an interactive raster view displays spike timestamp data for all recorded channels, (iv) the flashing spike view presents a spatialtemporal representation of the spiking behavior of the recorded channels and (v) the propagation signal view overlays aggregated spiking events, revealing an individual neuron's multielectrode propagation signal, as well as electrophysiological features typically masked by noise. We recently showed that MEAs can be used to monitor action potential propagation in single neurons (Tovar et al, 2017). Assigning spikes to a particular neuron is not typically possible with extracellular recording.…”

Use of a Neural Circuit Probe to Validate in silico Predictions of Inhibitory Connections

“…For each MEA recording, we first removed redundancy propagation signals [12] and then did spike sorting [13]. Extracellular signals were band pass filtered using a digital 2nd order Butterworth filter with cutoff frequencies of 0.2 and 4 kHz.…”

“…fit the GLM model (Fig 3a). Each unit corresponded to a spike train after spike sorting and removal of the redundancy inherent in propagation signals [12]. Then unit 10 was chosen as the in silico interventional target, i.e.…”