Name: optogenetic stimulation of the auditory nerve
Uploaded: 2014-10-08T15:00:00
Description: Watch this Scientific Journal Video about Optogenetic Stimulation of the Auditory Nerve at JoVE.com

This work was supported by the German Federal Ministry of Education and Research (Bernstein Focus for Neurotechnology grant 01GQ0810, to T. Moser, and MED-EL Germany); the German Research Foundation through the Center for Nanoscale Microscopy and Molecular Physiology of the Brain (FZT 103, T. Moser) and through the SFB889, to N. Strenzke and T. Moser).

All experiments presented in this work were conducted with the ethical standards defined by the German law for the protection of experimental animals. The University of Goettingen board for animal welfare and the animal welfare office of the state of Lower Saxony approved the experiments.
1. Preparation of &#181;LED-stimulator
<ol>
	<li>For &#181;LEDs, first prepare the &#181;LED-stimulator. Use blue LEDs with 200 by 200 &#956;m active surface (&#181;LED, see Materials Table).</li>
	<li>Sold...

<ol>
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The described experiments demonstrate the optogenetic stimulation of the SGNs, and can, in principle, also be used to stimulate inner and/or outer hair cells, provided the expression of opsins. These experiments require much patience and care. As mentioned before, the most critical steps are a good cochleostomy/round window insertion as well as an appropriate position and orientation of the light source.
There are limitations with optogenetic stimulation when using ChR2. In our case oABR ampli...

According to the World Health Organization, 360 million people worldwide suffer from hearing loss. In deaf subjects, direct electrical stimulation of SGNs by CIs&#160;enable open speech comprehension in the majority of them1,2,4,5. Even though CIs have been implanted in more than 200,000 people, therefore being the most successful neuroprosthesis, sound encoding driven by the current cochlear implants is limited. CIs are based on electrical stimulation by a certain number of electrodes where each one activates a tonotopic region of the auditory nerve thus bypassing the dysfunctional sensory organ of Corti in the cochlea. Normal hearing listeners can discriminate more than 2,000 frequencies, however today&#39;s CIs use only up to 12-22 frequency channels4. This is due to widespread current flow from each stimulating electrode7,9, activating a large number of SGNs that represent many different sound frequencies8,15. This limitation can be improved using multipolar stimulation but at the expense of higher power consumption16,17. Their output dynamic range for sound intensity is also limited, typically below 6-20 dB4,18. For these reasons, improving frequency and intensity resolution are important objectives for increasing CI performance to ameliorate speech recognition in noisy environments, prosody comprehension and music perception.
A different option to stimulate the auditory nerve is optical stimulation. Light can be conveniently focused to target a small SGN population, promising better spatial confinement, increasing frequency resolution and also widening dynamic range, resulting in a better intensity resolution. Indeed, cochlear stimulation with infrared light has shown excellent frequency resolution in animal models10,11,19. One disadvantage of this kind of stimulation is that it requires higher energies than electrical stimulation10,11. Moreover, concerns about the ability of the method to directly stimulate auditory neurons have been raised12,20.
As an alternative to infrared stimulation, we employ optogenetics to render SGNs light sensitive. Optogenetics is a novel approach that combines genetic and optical techniques to non-invasively and specifically control cells with high temporal precision (reviews21-23). The currently most frequently used modality employs the expression of the microbial channelrhodopsin 2 (ChR2) gene of Chlamydomonas reinhardtii and variants thereof, encoding a light-gated cation channel24. ChR2 is a 7-transmembrane-helix protein that, when transduced into neurons and activated by blue light, acts as non-selective cation channel, thus depolarizing the cells24-27. ChR2 has been well characterized24,28-31 and many variants have been developed to modify action spectrum, gating and permeability properties32,33. The aim of our work is to establish cochlear optogenetics for the activation of the auditory pathway. We note that the optogenetic approach to stimulate the auditory nerve requires genetic manipulation of the spiral ganglion for the expression of channelrhodopsin. Working with mice and rats allows the use of available transgenic animals13,34,35, which provide expression of channelrhodopsin with little variability along the tonotopic axis and across animals36. Combining conditional alleles37 with appropriate Cre-lines provides for cell-specific expression. Gene transfer into the spiral ganglion of other animals requires the use of virus such as adeno-associated virus that is a standard approach in optogenetics38 and that we showed to work well in mice36. Genetic manipulation and expression of transgenes encoding alien proteins bear risks for adverse effects such as immune responses and/or proliferation, compromised condition or even death of genetically manipulated cells. For the purpose of this demonstration we use transgenic mice expressing ChR2 in spiral ganglion neurons under the Thy-1 promotor13 to optically stimulate the auditory pathway. We note that other channelrhodopsin variants can be used for the same purpose as we demonstrated using virus-mediated transfer of the variant CatCh14 into SGNs39.
While cochlear optogenetics requires genetic manipulation, it offers molecular tuning for optimized SGN stimulation and promises improved frequency and intensity resolution when compared to electrical stimulation. Optogenetic stimulation of the auditory pathway is highly relevant for hearing research. For example, it promises advances in studies of the activity-dependent refinement of tonotopy during development, in the analysis of the requirement for spectral integration in sound localization and of the extent of interaction between frequency-specific afferent projections in the central auditory system.

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	<tbody>
		<tr>
			<td>Urethane</td>
			<td>Sigma Aldrich</td>
			<td>U2500-100G</td>
			<td>Anesthetic</td>
		</tr>
		<tr>
			<td>Xylazine HCl</td>
			<td>RXV</td>
			<td></td>
			<td>Sedative and analgesic</td>
		</tr>
		<tr>
			<td>Buprenorphine</td>
			<td>Reckitt Benckiser</td>
			<td></td>
			<td>Analgesic</td>
		</tr>
		<tr>
			<td>Dumont #5 Forceps</td>
			<td>Fine Science Tools</td>
			<td>11251-10</td>
			<td>It is used to hold hard tissue, e.g. bone or materials. Never use them to hold soft delicated tissue&#160;</td>
		</tr>
		<tr>
			<td>Dumont #5 - Fine Forceps</td>
			<td>Fine Science Tools</td>
			<td>11254-20</td>
			<td>Only to be used to hold soft tissue</td>
		</tr>
		<tr>
			<td>Fine Scissors - Sharp</td>
			<td>Fine Science Tools</td>
			<td>14060-09</td>
			<td>To open the skin and help with the muscle dissection</td>
		</tr>
		<tr>
			<td>Lempert Rongeurs&#160;</td>
			<td>Fine Science Tools</td>
			<td>16004-16</td>
			<td>They are very useful to easily remove the bone from the bulla</td>
		</tr>
		<tr>
			<td>473-nm laser&#160;</td>
			<td>Changchun New Industries</td>
			<td>MLL-III473</td>
			<td>100 mW solid state 473 nm laser</td>
		</tr>
		<tr>
			<td>Laser driver&#160;</td>
			<td>Changchun New Industries</td>
			<td>DPSSL MLL 100 mW</td>
			<td>TTL operated laser driver</td>
		</tr>
		<tr>
			<td>250 &#181;m optical fiber</td>
			<td>Any comercial ; e.g. Thorlabs</td>
			<td>M42L05</td>
			<td></td>
		</tr>
		<tr>
			<td>Acousto-optical modulator</td>
			<td>Crystal Technology, Inc.</td>
			<td>PCAOM VIS</td>
			<td>Control the amount of light coupled into the fiber from the laser</td>
		</tr>
		<tr>
			<td>Controller for Acousto-optical modulator</td>
			<td>Crystal Technology, Inc.</td>
			<td>160T1-8SAR-24-0.8</td>
			<td>Control the acousto-optic modulator</td>
		</tr>
		<tr>
			<td>Solo2 laser power &#38; energy meter</td>
			<td>Gentec-EO</td>
			<td></td>
			<td>Used to measure light intensity of the LED and the fiber coupled laser</td>
		</tr>
		<tr>
			<td>Blue &#181;LED</td>
			<td>Cree</td>
			<td>C470UT200</td>
			<td>It is necessary to build several &#956;LED devices because easily get damaged or the isolation is not good enough</td>
		</tr>
		<tr>
			<td>TDT System&#160;</td>
			<td>Tucker-Davis Technologies</td>
			<td>RZ6-A-P1</td>
			<td>It can be used any system for stimulus generation&#160; presentation and data acquisition</td>
		</tr>
		<tr>
			<td>Single-shank, 16-channel silicon probe</td>
			<td>Neuronexus</td>
			<td>a1x16-5mm-100-177-CM16LP&#160;</td>
			<td>These are fragile devises, must be handled carefully and cleaned after use</td>
		</tr>
		<tr>
			<td>Omnidrill</td>
			<td>World Precision Instruments</td>
			<td>503598</td>
			<td>Perform craniotomy for IC recordings and reference screw implantation</td>
		</tr>
		<tr>
			<td>Micro Drill Steel Burrs</td>
			<td>any commercial; e.g. Fine Science Tools</td>
			<td>19007-07</td>
			<td></td>
		</tr>
		<tr>
			<td>Self tapping bone screw</td>
			<td>any commercial; e.g. Fine Science Tools</td>
			<td>19010-10</td>
			<td>Reference screw</td>
		</tr>
		<tr>
			<td>Micromanipulator</td>
			<td>any commercial; e.g. Luigs+NeumannInVivo Unit Junior 4 axis</td>
			<td></td>
			<td>Positioning of recording probe</td>
		</tr>
	</tbody>
</table>

optogenetic stimulation of the auditory nerve

Direct electrical stimulation of spiral ganglion neurons (SGNs) by cochlear implants (CIs) enables open speech comprehension in the majority of implanted deaf subjects1-6. Nonetheless, sound coding with current CIs has poor frequency and intensity resolution due to broad current spread from each electrode contact activating a large number of SGNs along the tonotopic axis of the cochlea7-9. Optical stimulation is proposed as an alternative to electrical stimulation that promises spatially more confined activation of SGNs and, hence, higher frequency resolution of coding. In recent years, direct infrared illumination of&#160;the cochlea has been used to evoke responses in the auditory nerve10. Nevertheless it requires higher energies than electrical stimulation10,11 and uncertainty remains as to the underlying mechanism12. Here we describe a method based on optogenetics to stimulate SGNs with low intensity blue light, using transgenic mice with neuronal expression of channelrhodopsin 2 (ChR2)13 or virus-mediated expression of the ChR2-variant CatCh14. We used micro-light emitting diodes (&#181;LEDs) and fiber-coupled lasers to stimulate ChR2-expressing SGNs through a small artificial opening (cochleostomy) or the round window. We assayed the responses by scalp recordings of light-evoked potentials (optogenetic auditory brainstem response: oABR) or by microelectrode recordings from the auditory pathway and compared them with acoustic and electrical stimulation.

An optimal cochleostomy is critical and increases the probability of a successful experiment. This means the window is regular, small, and there is no injury of the internal cochlear structures. For example, bleeding indicates damage of the stria vascularis. A good example is presented in Figure 1B.
Using ChR2-transgenic mice, ChR2 is expressed in the SGNs within the cochlea (Figure 1C). Blue light illumination, either by &#181;LED or laser, e...

Watch this Scientific Journal Video about Optogenetic Stimulation of the Auditory Nerve at JoVE.com

Optogenetic Stimulation of the Auditory Nerve

Cochlear implants (CIs) enable hearing by direct electrical stimulation of the auditory nerve. However, poor frequency and intensity resolution limits the quality of hearing with CIs. Here we describe optogenetic stimulation of the auditory nerve in mice as an alternative strategy for auditory research and developing future CIs.

Direct electrical stimulation of spiral ganglion neurons (SGNs) by cochlear implants (CIs) enables open speech comprehension in the majority of implanted ...

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Selective Viral Transduction of Adult-born Olfactory Neurons for Chronic in vivo Optogenetic Stimulation

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Fiber-optic Implantation for Chronic Optogenetic Stimulation of Brain Tissue

Elucidating patterns of neuronal connectivity has been a challenge for both clinical and basic neuroscience. Electrophysiology has been the gold standard ...

Optogenetic Stimulation of Escape Behavior in Drosophila melanogaster

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Selective Tracing of Auditory Fibers in the Avian Embryonic Vestibulocochlear Nerve

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In vivo Optogenetic Stimulation of the Rodent Central Nervous System

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Direct Visualization of the Murine Dorsal Cochlear Nucleus for Optogenetic Stimulation of the Auditory Pathway

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Assessment of Neuromuscular Function Using Percutaneous Electrical Nerve Stimulation

Percutaneous electrical nerve stimulation is a non-invasive method commonly used to evaluate neuromuscular function from brain to muscle (supra-spinal, ...