In vitro multichannel single-unit recordings of action potentials from the mouse sciatic nerve

Abstract

Electrode arrays interfacing with peripheral nerves are essential for neuromodulation devices targeting peripheral organs to relieve symptoms. To modulate (i.e., single-unit recording and stimulating) individual peripheral nerve axons remains a technical challenge. Here, we report an in vitro setup to allow simultaneous single-unit recordings from multiple mouse sciatic nerve axons. The sciatic nerve (~30 mm) was harvested and transferred to a tissue chamber, the ~5mm distal end pulled into an adjacent recording chamber filled with paraffin oil. A custom-built multi-wire electrode array was used to interface with split fine nerve filaments. Single-unit action potentials were evoked by electrical stimulation and recorded from 186 axons, of which 49.5% were classed A-type with conduction velocities (CV) greater than 1 m/s and 50.5% were C-type (CV < 1 m/s). The single-unit recordings had no apparent bias towards A- or C-type axons, were robust and repeatable for over 60 minutes, and thus an ideal opportunity to assess different neuromodulation strategies targeting peripheral nerves. For instance, ultrasonic modulation of action potential transmission was assessed using the setup, indicating increased nerve conduction velocity following ultrasound stimulus. This setup can also be used to objectively assess the design of next-generation electrode arrays interfacing with peripheral nerves.

Optimal Multichannel Artifact Prediction and Removal for Neural Stimulation and Brain Machine Interfaces

“…Extracellular recordings from multiple teased nerve filaments were conducted by a custom-built 5-channel electrode array consisting of micro-wires deployed parallel to each other with ∼150 μm clearance as described previously ( Chen et al, 2017 ; Ilham et al, 2018 ). Recordings were digitized at 25 kHz, band-pass filtered (300−3000 Hz) and stored on a PC using an integrated neural recording and stimulating system (IZ2H stimulator, PZ5-32 neurodigitizer and RZ5D processor, TDT, Alchua, Florida, United States).…”

“…All procedures were approved by the University of Connecticut Institutional Animal Care and Use Committee. Sciatic nerves of male C57BL/6 mice (6-8 weeks, Taconic, Germantown, NJ, United States) were harvested for extracellular recordings from teased nerve filaments as detailed previously (Chen et al, 2017;Ilham et al, 2018). Mice were anesthetized by isoflurane inhalation, euthanized by exsanguination from perforating the right atrium, and perfused through the left ventricle with oxygenated Krebs solution (in mM: 117.9 NaCl, 4.7 KCl, 25 NaHCO 3 , 1.3 NaH 2 PO 4 , 1.2 MgSO 4 , 2.5 CaCl 2 , and 11.1 D-glucose).…”

A Review on Ultrasonic Neuromodulation of the Peripheral Nervous System: Enhanced or Suppressed Activities?

“…Nerve axons in the PNS are generally protected by soft connective tissue stacked in multiple layers, in contrast to the neurons and processes in the CNS, protected by bony structures like the skull or the vertebrae. These tightly wrapped tissue layers in the PNS, functioning as electrical insulators, pose a great challenge in recording electrophysiological activities from individual nerve axons, i.e., single-unit recordings [48]; recordings from individual neurons or axons in the CNS are straightforward when the electrodes are placed inside the skull or vertebrae. Consequently, the major metrics to assess the neuromodulatory effects on the PNS are either CAP, as a summation of action potentials from a bulk nerve bundle [47,[49][50][51][52], or evoked muscle forces, as an indicator of motor nerve functions [42,53,54].…”

“…However, the characteristics of a CAP (peak amplitude, temporal location, and spread) depend on the temporal summation of a population of action potentials from axons with various spatial locations, morphologies, and insulation environment. The CAP characteristics can also be affected by changes in recording conditions, e.g., relative position of the electrode sites and axons, change of access impedance of recording electrodes due to altered moisture conditions, and multiple/chronic use of electrodes [48]. Thus, neither the changes in CAP amplitude nor the assumed changes in conduction delay (Figure 2A) can appropriately be representative of the effects of US neuromodulation.…”

A microfabricated nerve-on-a-chip platform for rapid assessment of neural conduction in explanted peripheral nerve fibers

“…Alternatively, penetrating or suction electrodes may be used 27 , 28 . The resulting SNR typically allow the detection of multiple SFPA composing CAP 21 and conduction velocity computation but these experimental techniques are cumbersome and time consuming.…”