Abstract
Autonomic nerves convey essential neural signals that regulate vital body functions. Recording clearly distinctive physiological neural signals from autonomic nerves will help develop new treatments for restoring regulatory functions. However, this is very challenging due to the small nature of autonomic nerves and the low-amplitude signals from their small axons. We developed a multi-channel, high-density, intraneural carbon fiber microelectrode array (CFMA) with ultra-small electrodes (8–9 µm in diameter, 150–250 µm in length) for recording physiological action potentials from small autonomic nerves. In this study, we inserted CFMA with up to 16 recording carbon fibers in the cervical vagus nerve of 22 isoflurane-anesthetized rats. We recorded action potentials with peak-to-peak amplitudes of 15.1–91.7 µV and signal-to-noise ratios of 2.0–8.3 on multiple carbon fibers per experiment, determined conduction velocities of some vagal signals in the afferent (0.7–4.4 m/s) and efferent (0.7–8.8 m/s) directions, and monitored firing rate changes in breathing and blood glucose modulated conditions. Overall, these experiments demonstrated that CFMA is a novel interface for in-vivo intraneural action potential recordings. This work is considerable progress towards the comprehensive understanding of physiological neural signaling in vital regulatory functions controlled by autonomic nerves.
Highlights
Autonomic nerves convey essential neural signals that regulate vital body functions
Fibers within each of the two rows had a pitch of 132 μm, and the two rows were separated by 50 μm (Fig. 1a)
Three of the carbon fiber microelectrode array (CFMA) were used in more than one experiment (4–8 experiments per CFMA), which initially had a total of 48 functional carbon fibers (16 carbon fibers per CFMA) with an average impedance of 52.8 ± 36.8 kΩ after insertion in the first experiment
Summary
Autonomic nerves convey essential neural signals that regulate vital body functions. Recording clearly distinctive physiological neural signals from autonomic nerves will help develop new treatments for restoring regulatory functions. The vagus nerve at the cervical level is partially composed of myelinated Aδ and B fibers[9,10], but the great majority of axons (over 80%) are unmyelinated C-fibers[2,11,12] These fibers predominantly convey afferent (sensory) signals from the innervated organs to the central nervous s ystem[13]. Another research group inserted 4-channel carbon fiber arrays (electrode diameter ≤ 15 μm, pitch of 150 μm) in tracheosyringeal nerves of zebra finch birds, which are 125 μm in diameter and mostly composed of myelinated fibers (99%)[30] They obtained spontaneous recordings but primarily demonstrated electrical stimulation-evoked compound neural responses. A need remains for an intraneural electrode array that can record physiological single-neuron activity at multiple sampling locations within small autonomic nerves
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