Optogenetic stimulation of the auditory pathway
Victor H. Hernandez, … , Nicola Strenzke, Tobias Moser
Victor H. Hernandez, … , Nicola Strenzke, Tobias Moser
Published February 10, 2014
Citation Information: J Clin Invest. 2014;124(3):1114-1129. https://doi.org/10.1172/JCI69050.
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Optogenetic stimulation of the auditory pathway

Abstract

Auditory prostheses can partially restore speech comprehension when hearing fails. Sound coding with current prostheses is based on electrical stimulation of auditory neurons and has limited frequency resolution due to broad current spread within the cochlea. In contrast, optical stimulation can be spatially confined, which may improve frequency resolution. Here, we used animal models to characterize optogenetic stimulation, which is the optical stimulation of neurons genetically engineered to express the light-gated ion channel channelrhodopsin-2 (ChR2). Optogenetic stimulation of spiral ganglion neurons (SGNs) activated the auditory pathway, as demonstrated by recordings of single neuron and neuronal population responses. Furthermore, optogenetic stimulation of SGNs restored auditory activity in deaf mice. Approximation of the spatial spread of cochlear excitation by recording local field potentials (LFPs) in the inferior colliculus in response to suprathreshold optical, acoustic, and electrical stimuli indicated that optogenetic stimulation achieves better frequency resolution than monopolar electrical stimulation. Virus-mediated expression of a ChR2 variant with greater light sensitivity in SGNs reduced the amount of light required for responses and allowed neuronal spiking following stimulation up to 60 Hz. Our study demonstrates a strategy for optogenetic stimulation of the auditory pathway in rodents and lays the groundwork for future applications of cochlear optogenetics in auditory research and prosthetics.

Authors

Victor H. Hernandez, Anna Gehrt, Kirsten Reuter, Zhizi Jing, Marcus Jeschke, Alejandro Mendoza Schulz, Gerhard Hoch, Matthias Bartels, Gerhard Vogt, Carolyn W. Garnham, Hiromu Yawo, Yugo Fukazawa, George J. Augustine, Ernst Bamberg, Sebastian Kügler, Tim Salditt, Livia de Hoz, Nicola Strenzke, Tobias Moser

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Figure 1

Optical activation of the auditory pathway in ChR2 transgenic mice.

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Optical activation of the auditory pathway in ChR2 transgenic mice. (A...
(A) ChR2-YFP expression in SGNs in a section of an entire mouse cochlea following GFP immunolabeling and phalloidin-AF-568 labeling of actin. Scale bar: 500 μm. Inset: SGNs costained for NF200 and GFP, arrow points to a GFP-positive SGN with typical bipolar morphology. Scale bar: 20 μm. (B) ChR2-YFP is expressed in peripheral neurites of SGNs projecting to IHCs (radial fibers); immunolabeling for GFP and parvalbumin (outer hair cells and inner hair cells not included in this projection of confocal sections). Scale bar: 20 μm. (C) typical surgical situs used for optical stimulation; retroauricular approach through the middle ear to the cochlea; cochleostomy and landmarks. Scale bar: 1 mm. (D) μLED probe. Using a micromanipulator, a glass capillary was used to position the μLED onto the cochleostomy. Scale bar: 1 mm. Inset shows en face view of the illuminated 200-μm LED emitting surface. (E) aABRs before (black) and after (red) cochleostomy. Left panel: grand average of responses to 1,000 clicks at 80 dB SPL (peak equivalent), applied at 10 Hz. Right panel: aABR threshold for clicks and 12-kHz tone bursts (n = 11 for both panels; *P < 0.001, paired Student’s t test). (F) Representative oABRs in response to rectangular 5-ms power LED stimulation at 4 mW/mm2 and 1 Hz (average of 56 trials). (G) Representative eABRs in response to stimulation with 900-μA currents at 20 Hz via glass-insulated tungsten electrodes (one placed inside and one outside the cochlea; average of 200 trials).