Optical read-out and modulation of peripheral nerve activity

Abstract

Numerous clinical and research applications necessitate the ability to interface with peripheral nerve fibers to read and control relevant neural pathways. Visceral organ modulation and rehabilitative prosthesis are two areas which could benefit greatly from improved neural interfacing approaches. Therapeutic neural interfacing, or 'bioelectronic medicine', has potential to affect a broad range of disorders given that all the major organs of the viscera are neurally innervated. However, a better understanding of the neural pathways that underlie function and a means to precisely interface with these fibers are required. Existing peripheral nerve interfaces, consisting primarily of electrode-based designs, are unsuited for highly specific (individual axon) communication and/or are invasive to the tissue. Our laboratory has explored an optogenetic approach by which optically sensitive reporters and actuators are targeted to specific cell (axon) types. The nature of such an approach is laid out in this short perspective, along with associated technologies and challenges.

Keywords: GCaMP; adeno-associated virus; bioelectronic medicine; optogenetics; peripheral nerve interface; prosthesis control.

Figure 1

Imaging of neural activity with calcium sensitive fluorescent sensors. (A) Field of mouse tibial nerve axons loaded with the synthetic calcium indicator Calcium Green-1 Dextran. At least six nodes of Ranvier yield a calcium-coupled fluorescence change in response to a 1 s train of action potentials (100 Hz). Signal amplitudes among the six nodes range from 11–24%. Black bar indicates action potential stimulus. Inset scale bars: 1 second and 5% signal change. (B) Frequency-modulated calcium fluorescence traces from a peripheral nerve axon node of Ranvier with bars indicating mean steady-state amplitude. (Data from panels A & B are from Fontaine et al., 2017.) (C) Image of the genetically expressed calcium indicator GCaMP6f transduced in axons of the peripheral nerve by intramuscular injection of an adeno-associated viral (AAV) vector.