Electrical Characterisation of Aδ-Fibres Based on Human in vivo Electrostimulation Threshold.

Shota Tanaka,Akimasa Hirata,Shoogo Ueno,Jose Gomez-Tames,Koji Inui,Toshiaki Wasaka

doi:10.3389/fnins.2020.588056

Abstract

Electrical stimulation of small fibres is gaining attention in the diagnosis of peripheral neuropathies, such as diabetes mellitus, and pain research. However, it is still challenging to characterise the electrical characteristics of axons in small fibres (Aδ and C fibres). In particular, in vitro measurement for human Aδ-fibre is difficult due to the presence of myelin and ethical reason. In this study, we investigate the in vivo electrical characteristics of the human Aδ-fibre to derive strength–duration (S–D) curves from the measurement. The Aδ-fibres are stimulated using coaxial planar electrodes with intraepidermal needle tip. For human volunteer experiments, the S–D curve of Aδ-fibre is obtained in terms of injected electrical current. With the computational analysis, the standard deviation of the S–D curve is mostly attributed to the thickness of the stratum corneum and depth of the needle tip, in addition to the fibre thickness. Then, we derive electrical parameters of the axon in the Aδ-fibre based on a conventional fibre model. The parameters derived here would be important in exploring the optimal stimulation condition of Aδ-fibres.

Highlights

Different receptors and peripheral nerve fibres convey somatosensory information to the central nervous system
We evaluated the coefficient of variation (CoV) of measured rheobases and its normalised values (Table 1)
The CoV is the standard deviation divided by the average value

Summary

Introduction

Different receptors and peripheral nerve fibres convey somatosensory information to the central nervous system. Selective stimulation of nerve fibres is essential in observing the activation of a somatosensory submodality system. The rationale for this is based on different conduction velocities of fibres with different thicknesses (Vallbo et al, 1979). Terminals of afferent Aδ- and C-fibres are located in the epidermis. Mechanoreceptors are located in the upper layer of the dermis. Recent studies used selective stimulation of small fibres in patients suffering from peripheral neuropathies, such as diabetes mellitus (Kukidome et al, 2015; Omori et al, 2017; Suzuki et al, 2020)

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Results

Conclusion