Name: neonatal murine cochlear explant technique as an in vitro screening tool in hearing research
Uploaded: 2017-06-08T15:00:00.000+00:00
Duration: 8 min 30 s
Description: Watch this Scientific Journal Video about Neonatal Murine Cochlear Explant Technique as an In Vitro Screening Tool in Hearing Research at JoVE.com

This work was supported by the National Institute of Deafness and Other Communication Disorders grants R01DC015824 (K.M.S.) and T32DC00038 (supporting S.D.), the Department of Defense grant W81XWH-15-1-0472 (K.M.S.), the Bertarelli Foundation (K.M.S.), the Nancy Sayles Day Foundation (K.M.S.), and the Lauer Tinnitus Research Center (K.M.S.). We thank Jessica E. Sagers, B.A. for insightful comments on the manuscript.

The study protocol was approved by the Institutional Animal Care and Use Committee (IACUC) of Massachusetts Eye and Ear. Experiments were carried out according to the Code of Ethics of the World Medical Association.
1. Preparing the Dissection
<ol>
	<li>Preparing the surgical table
	<ol>
		<li>Use 70% ethanol to disinfect the surgical table.</li>
		<li>Place two nonsterile prep pads next to the microscope.</li>
		<li>Prepare the instrument tray, including heat-sterilized operating scissors, a scalpel handle, a micro knife, and forceps (two each of #4 &#38; #55). Place the instrument tray and a 50 mm, clear-walled, glass-bottomed petri dish onto one non-sterile pad.</li>
		<li>Obtain a sterile #15 scalpel blade; a sealable plastic bag or container (to dispose of the carcasses in line with institutional guidelines); ice in a bucket; and cold, sterile Hank&#39;s Balanced Salt Solution (HBSS). Place these items onto the other nonsterile pad.</li>
		<li>Transfer the HBSS into a 50 mL plastic laboratory tube and put it on ice.</li>
	</ol>
	</li>
	<li>Preparing the culture
	<ol>
		<li>Prepare all materials in a laminar flow hood. For every four specimens, put four autoclaved 10 mm round glass cover slips in the four inlays of the 35 mm 4-well petri dish.</li>
		<li>For every 4 specimens, mix a total volume of 300 &#181;L consisting of the following in a microcentrifuge tube: 10 &#181;L of tissue adhesive, 285 &#181;L of NaHCO3, and 5 &#181;L of NaOH.</li>
		<li>Put 45 &#181;L of the resulting solution on every cover slip and leave it there for at least 20 min at RT; this solution can be left on the coverslip for several hours but cannot be left O/N.</li>
		<li>Place one or two 35 mm 4-well petri dish(es) inside a 10 cm Petri dish in order to create two barriers against contamination.</li>
		<li>Prepare culture medium containing 98% Dulbecco&#39;s Modified Eagle&#39;s Medium (DMEM), 1% N-2, and 1% ampicillin (65 &#181;L per well in a (micro)centrifuge tube). Warm the solution to 25 &#176;C prior to use.</li>
	</ol>
	</li>
</ol>
2. Murine Cochlear Explant Dissection
<ol>
	<li>Decapitation of the neonatal mouse
	<ol>
		<li>Obtain a 60 mm plastic petri dish and spray 70% ethanol in its lid so that the surface is wet.</li>
		<li>Pour cold HBSS from the plastic laboratory tube into the bottom part of the 60 mm plastic and the 50 mm clear-walled, glass-bottomed petri dish. Store the plastic laboratory tube and both petri dishes on ice to keep the tissue cold whenever it is not being dissected.</li>
		<li>Place a P3 -&#160;P5-aged neonatal mouse on ice in a cutoff finger of a latex glove and wait until the hypothermia induces loss of consciousness (approximately 1-3 min).</li>
		<li>Decapitate the mouse quickly with operating scissors and dispose of the body in the sealable plastic bag. Put the severed neonate head in the 70% ethanol in the lid of the 60 mm plastic petri dish.</li>
	</ol>
	</li>
	<li>Macroscopic dissection of the temporal bone
	<ol>
		<li>Remove the skin of the skull by making a superficial cut from the anterior to the posterior end (directly on top of the sagittal suture) using the scalpel blade.</li>
		<li>Cut both external auditory canals with the scalpel blade and fold the skin anteriorly to expose the whole cranium. 
		&#8203;NOTE: Although no dissection microscope is usually needed for this step, it can be used for improved visualization.</li>
		<li>Open the cranium along the sagittal suture using the #15 scalpel blade. Make sure to cut the cranium by gently moving the blade up and down from anterior to posterior to avoid compression of the cochleae. 
		&#8203;NOTE: The cranium should not be ossified at this age and should cut easily.</li>
		<li>Remove and discard the snout by making a vertical cut directly posterior to the orbits using the #15 scalpel blade. 
		&#8203;NOTE: The posterior part of the skull should still contain the brain and cochleae.</li>
		<li>Dispose of the forebrain, cerebellum, and brainstem through blunt dissection with #4 forceps.</li>
	</ol>
	</li>
	<li>Microscopic extraction of the cochleae
	<ol>
		<li>Adjust the microscope (6.5X&#160;magnification) and light source by placing forceps under the scope and optimizing the illumination and focus.</li>
		<li>Place the two halves of the cranium into the 60 mm plastic petri dish filled with cold HBSS.</li>
		<li>Completely expose the cochlea/e, identifiable as being adjacent to the surrounding stapedial artery (a tortuous artery within the temporal bone), and bluntly separate the organ from the temporal bone using #4 forceps.</li>
		<li>Transfer the cochlea into the 50 mm, clear-walled, glass-bottomed petri dish and position the dish under the microscope.</li>
		<li>Place the 60 mm plastic petri dish with the other half of the cranium on ice.</li>
		<li>Remove the cochlea from the vestibular system and carefully dissect the cochlear otic capsule (typically cartilaginous at this age) with #4 forceps. Use #55 forceps for all further steps.</li>
	</ol>
	</li>
	<li>Final steps of tissue processing
	<ol>
		<li>Continue with the processing of the inner ear tissue by carefully separating the spiral ligament adherent to the organ of Corti from the rest of the cochlea and the modiolus using the micro knife or two forceps.
		<ol>
			<li>Cut into the darker, translucent area at the crevice between the spiral ligament and the hair cell region and proceed to the subsequent removal of the spiral ligament by grasping it at the most basal aspect and gently unwinding it while moving apically.</li>
		</ol>
		</li>
		<li>Position the specimen to obtain a longitudinal, sagittal view of the cochlea and cut the cochlea into two to three sections using the micro knife, classifying these sections as the apical, (middle,)&#160;and basal turns. Remove the tissue superior and inferior to the actual layer of hair cells and neurites in order to achieve a cochlear explant piece that can lay horizontally on the petri dish. 
		&#8203;NOTE: An appropriate size for stable adhesion to the culture dish is approximately half of one cochlear turn.</li>
		<li>Remove the tectorial membrane, a very thin translucent layer immediately superior to the organ of Corti, by gently peeling it away with forceps.</li>
		<li>Remove Reissner&#39;s membrane, immediately superior to the SGNs, by touching it with forceps on both sides and peeling it away. 
		NOTE:&#160;Remove any laterally-located damaged hair cell areas by cutting them away with the micro knife.</li>
	</ol>
	</li>
</ol>
3. Transfer of Specimens to the Culture Plates
<ol>
	<li>Remove the 45 &#181;L of tissue adhesive solution from the four cover slips. Wash each cover slip with 50 &#181;L of sterile H2O. Aspirate the water.</li>
	<li>Pick up the 1 mL pipette. Wet the pipette tip with approximately 120 &#181;L of DMEM to prevent the specimen from adhering to the inside of the tip.</li>
	<li>Transfer the specimens individually using the 1 mL pipette. Pipette a maximum of 70 &#181;L from the HBSS-filled, small, clear-walled, glass-bottomed petri dish and place the specimen along with the liquid on one of the 4 inlays (prepared with cover slips) in the 4-well petri dish.</li>
	<li>Check under the microscope (50X magnification) that the specimen is in the correct orientation. Ensure that the area of hair cells from which the tectorial membrane was removed faces upwards. Ensure that the basilar membrane, together with the trimmed, basal part of the modiolus, faces downwards and adheres to the coverslip.
	<ol>
		<li>If the specimen is oriented upside-down upon inspection, deposit the HBSS that remains in the pipette tip into the inlay and reposition the piece until it is correctly oriented. 
		NOTE: This will prevent hair cells from floating in culture medium without structural support from the coverslip, which could lead to degeneration.</li>
	</ol>
	</li>
	<li>Aspirate excess HBSS using the 1 mL pipette. Wait for 15 s.</li>
	<li>Pipette 60 &#181;L of the prepared warm culture medium (98% DMEM, 1% N-2, and 1% ampicillin) directly onto the specimen. Take care not to touch the specimen with the pipette. Replace the inner and outer petri dish covers and incubate O/N at 37 &#176;C.</li>
	<li>Put all of the stock solutions back in their proper places, dispose of carcasses and residual waste, decontaminate the surgical table according to institutional guidelines (e.g., using ethanol or hypochlorite), clean and autoclave the instruments, and discard the sharps in the appropriate container.</li>
</ol>
4. Adding Final Culture Media and Substances of Interest
NOTE: Cochlear explants will be ready for use 10-16 h later.
<ol>
	<li>Prepare a mixture of 97% DMEM, 1% fetal bovine serum (FBS), 1% N-2, and 1% ampicillin (65 &#181;L per well in a microcentrifuge tube; warm the solution to 25 &#176;C prior to use).</li>
	<li>Add other substances of interest to the solutions for the respective treatment groups. If fluorescent substances are added (e.g., green fluorescent protein (GFP)-expressing viruses; in a recent publication, a concentration of 1010 GC of Adeno-Associated Viruses (AAVs) was used for 48 h in 50 &#181;L)18, protect from light.</li>
	<li>Transfer the cochlear explant-containing petri dishes from the incubator and place them under the laminar flow hood.</li>
	<li>Aspirate the old culture medium (w/o FBS) with the pipette from the inlays.</li>
	<li>Add 60 &#181;L per well of the prepared warm culture (treatment) medium (97% DMEM, 1% FBS, 1% N-2, 1% ampicillin, and the substances of interest).</li>
	<li>Place the petri dish back into the incubator (37 &#176;C).</li>
	<li>View regularly under the microscope to identify signs of contamination, cellular migration, or detachment of the cochlear explant and perform staining after a maximum of 7 days.</li>
</ol>
5. Immunofluorescence - Day 1
<ol>
	<li>Prepare blocking solution (94% Phosphate-Buffered Saline (PBS), 5% normal goat or horse serum&#160;(NGS/NHS, depending on the secondary antibodies), and 1% non-ionic surfactant (see the Table of Materials)) and stock antibody solution (98.6% PBS, 1% NHS, and 0.4% non-ionic surfactant with the respective antibodies). 
	NOTE: Antibodies include rabbit anti-Myo7A at a concentration of 1:400+ (myosin 7A, for inner and outer hair cells) and mouse anti-TuJ1 1:200+ (&#946;-tubulin, for SGNs) OR mouse(IgG1) anti-CtBP2 1:200+ (c-terminal binding protein, for presynapse), mouse(IgG2a) anti-PSD95 1:50+ (postsynaptic density, for postsynapse), and chicken anti-NF-H 1:1000+ (neurofilament, for SGNs and nerve fibers). &#34;+&#34; means &#34;or higher.&#34;</li>
	<li>Aspirate the culture medium using a pipette. Take care not to touch the specimen.</li>
	<li>Under the laminar flow hood, rinse the cochlear explants twice with sterile PBS, placing the specimens on a shaker for 5 min after each wash.</li>
	<li>Fix the tissue in 4% paraformaldehyde (PFA - CAUTION) for 20 min on the shaker (under the hood). Aspirate the PFA.</li>
	<li>Apply 60 &#181;L of PBS to the cochlear explants and place the petri dish on a shaker for 5 min. Aspirate the PBS. Repeat 3x.</li>
	<li>Place the cochlear explants in prepared blocking solution (94% PBS, 5% NHS, and 1% non-ionic surfactant) for 30 min on shaker.</li>
	<li>Place the cochlear explants in a prepared stock antibody solution (98.6% PBS, 1% NHS, and 0.4% non-ionic surfactant) with the respective primary antibodies (vortex before use) O/N on a counter at RT. 
	NOTE:&#160;Wrap the petri dishes with damp paper towels enclosed in plastic wrap (or aluminum foil if the added solution contains fluorescent materials such as GFP-expressing viruses) to keep the dishes humid and to prevent evaporation of the antibody solution O/N.</li>
</ol>
6. Immunofluorescence - Day 2
<ol>
	<li>Prepare the 4&#39;,6-diamidino-2-phenylindole (DAPI) stain (300 nM) and use the stock antibody solution to obtain the correct secondary antibody mixtures, complementary to the primary antibodies in step 5.1. (e.g., goat anti-rabbit 488 1:200+ and goat anti-mouse 568 1:200+ OR goat anti-mouse (IgG1) 568 1:1000+, goat anti-mouse (IgG2a) 488 1:500+, and goat anti-chicken 647 1:200+ OR Phalloidin 568 1:200+ (for inner and outer hair cells)).</li>
	<li>Aspirate the primary antibody solution.</li>
	<li>Apply 60 &#181;L of PBS to the cochlear explants and place the petri dish on a shaker for 5 min. Aspirate the PBS. Repeat 3x.</li>
	<li>Place the cochlear explants in prepared stock antibody solution (98.6% PBS, 1% NHS, and 0.4% non-ionic surfactant) with the respective secondary antibodies (vortex before use) for 1.5 h on a counter and protect from light.</li>
	<li>Aspirate the secondary antibody solution and rinse the cochlear explants with a DAPI stain (placing on a shaker for 1 min and then aspirate).</li>
	<li>Apply 60 &#181;L of PBS to the cochlear explants and place the petri dish on a shaker for 5 min. Aspirate the PBS. Repeat 3x.</li>
	<li>Use forceps to remove coverslips with specimens from the 4-well plate, dip them into a recipient filled with distilled H2O, and dry the coverslips by vertically bringing them into contact with paper towels.</li>
	<li>Place a drop of antifade mounting medium onto the microscope slide and invert the coverslips to immerse the downward-facing tissue in the medium.</li>
	<li>Seal the coverslip using clear nail polish circumferentially covering the edge (without crushing the specimen under the glass). Leave the slides lying flat in a covered area away from light for 15 - 20 min until dry and then place them in a box or examine under the confocal microscope. 
	NOTE: Fluorescent staining is best preserved by storing the slides at 4 or -20 &#176;C.</li>
</ol>
7. Confocal Imaging
<ol>
	<li>Obtain an overview and zoomed-in pictures for the organ of Corti region, including neurites and SGNs. 
	NOTE: Standard settings for the imaging process: Format of 1,024 x 1,024 pixels, speed of 400 Hz, frame average of 3, 20% overall laser intensity, and usually 20X and 63X&#160;lens with oil immersion (potentially combined with 2X digital zoom). Channel settings for the DAPI, Myo7A, and TuJ1 staining protocol are outlined above: 405 5% DAPI, &#34;Smart Gain&#34; 766.8V, &#34;Smart Offset&#34; 0.0% - 488 15% fluorescein isothiocyanate (FITC), &#34;Smart Gain&#34; 622.2V, &#34;Smart Offset&#34; 0.0% - 561 13% tetramethylrhomadine isothiocyanate (TRITC), &#34;Smart Gain&#34; 562.4V, &#34;Smart Offset&#34; 0.0%.</li>
	<li>Merge the images in a z-stack using the software to obtain a z-axis projection.</li>
</ol>

<ol>
	<li>Geleoc, G. S., Holt, J. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Sound+strategies+for+hearing+restoration).">Sound strategies for hearing restoration).</a> Science. 344 (6184), 1241062 (2014).</li><li>Kujawa, S. G., Liberman, M. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Acceleration+of+age-related+hearing+loss+by+early+noise+exposure:+evidence+of+a+misspent+youth.">Acceleration of age-related hearing loss by early noise exposure: evidence of a misspent youth.</a> J Neurosci. 26 (7), 2115-2123 (2006).</li><li>Kujawa, S. G., Liberman, M. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Adding+insult+to+injury:+cochlear+nerve+degeneration+after+&amp;#34;temporary&amp;#34;+noise-induced+hearing+loss.">Adding insult to injury: cochlear nerve degeneration after &amp;#34;temporary&amp;#34; noise-induced hearing loss.</a> J Neurosci. 29 (45), 14077-14085 (2009).</li><li>Makary, C. A., Shin, J., Kujawa, S. G., Liberman, M. C., Merchant, S. N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Age-related+primary+cochlear+neuronal+degeneration+in+human+temporal+bones.">Age-related primary cochlear neuronal degeneration in human temporal bones.</a> J Assoc Res Otolaryngol. 12 (6), 711-717 (2011).</li><li>Jensen, J. B., Lysaght, A. C., Liberman, M. C., Qvortrup, K., Stankovic, K. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Immediate+and+delayed+cochlear+neuropathy+after+noise+exposure+in+pubescent+mice.">Immediate and delayed cochlear neuropathy after noise exposure in pubescent mice.</a> PLoS One. 10 (5), (2015).</li><li>Landegger, L. D., Psaltis, D., Stankovic, K. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Human+audiometric+thresholds+do+not+predict+specific+cellular+damage+in+the+inner+ear.">Human audiometric thresholds do not predict specific cellular damage in the inner ear.</a> Hear Res. , 83-93 (2016).</li><li>Wang, H. C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Spontaneous+Activity+of+Cochlear+Hair+Cells+Triggered+by+Fluid+Secretion+Mechanism+in+Adjacent+Support+Cells.">Spontaneous Activity of Cochlear Hair Cells Triggered by Fluid Secretion Mechanism in Adjacent Support Cells.</a> Cell. 163 (6), 1348-1359 (2015).</li><li>Barclay, M., Ryan, A. F., Housley, G. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Type+I+vs+type+II+spiral+ganglion+neurons+exhibit+differential+survival+and+neuritogenesis+during+cochlear+development.">Type I vs type II spiral ganglion neurons exhibit differential survival and neuritogenesis during cochlear development.</a> Neural Dev. 6, (2011).</li><li>Dinh, C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Short+interfering+RNA+against+Bax+attenuates+TNFalpha-induced+ototoxicity+in+rat+organ+of+Corti+explants.">Short interfering RNA against Bax attenuates TNFalpha-induced ototoxicity in rat organ of Corti explants.</a> Otolaryngol Head Neck Surg. 148 (5), 834-840 (2013).</li><li>Mazurek, B., Yu, Y., Haupt, H., Szczepek, A. J., Olze, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Salicylate+modulates+Hsp70+expression+in+the+explanted+organ+of+Corti.">Salicylate modulates Hsp70 expression in the explanted organ of Corti.</a> Neurosci Lett. 501 (2), 67-71 (2011).</li><li>Kao, S. Y., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Loss+of+osteoprotegerin+expression+in+the+inner+ear+causes+degeneration+of+the+cochlear+nerve+and+sensorineural+hearing+loss.">Loss of osteoprotegerin expression in the inner ear causes degeneration of the cochlear nerve and sensorineural hearing loss.</a> Neurobiol Dis. 56, 25-33 (2013).</li><li>Jan, T. A., Chai, R., Sayyid, Z. N., Cheng, A. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Isolating+LacZ-expressing+cells+from+mouse+inner+ear+tissues+using+flow+cytometry.">Isolating LacZ-expressing cells from mouse inner ear tissues using flow cytometry.</a> J Vis Exp. (58), e3432 (2011).</li><li>Haque, K. D., Pandey, A. K., Kelley, M. W., Puligilla, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Culture+of+embryonic+mouse+cochlear+explants+and+gene+transfer+by+electroporation.">Culture of embryonic mouse cochlear explants and gene transfer by electroporation.</a> J Vis Exp. (95), e52260 (2015).</li><li>Parker, M., Brugeaud, A., Edge, A. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Primary+culture+and+plasmid+electroporation+of+the+murine+organ+of+Corti.">Primary culture and plasmid electroporation of the murine organ of Corti.</a> J Vis Exp. (36), (2010).</li><li>Mulvaney, J. F., Dabdoub, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Long-term+time+lapse+imaging+of+mouse+cochlear+explants.">Long-term time lapse imaging of mouse cochlear explants.</a> J Vis Exp. (93), e52101 (2014).</li><li>Wang, Q., Green, S. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Functional+role+of+neurotrophin-3+in+synapse+regeneration+by+spiral+ganglion+neurons+on+inner+hair+cells+after+excitotoxic+trauma+in+vitro.">Functional role of neurotrophin-3 in synapse regeneration by spiral ganglion neurons on inner hair cells after excitotoxic trauma in vitro.</a> J Neurosci. 31 (21), 7938-7949 (2011).</li><li>Landegger, L. D., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+synthetic+AAV+vector+enables+safe+and+efficient+gene+transfer+to+the+mammalian+inner+ear.">A synthetic AAV vector enables safe and efficient gene transfer to the mammalian inner ear.</a> Nat Biotechnol. 35 (3), 280-284 (2017).</li><li>Dilwali, S., Landegger, L. D., Soares, V. Y., Deschler, D. G., Stankovic, K. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Secreted+Factors+from+Human+Vestibular+Schwannomas+Can+Cause+Cochlear+Damage.">Secreted Factors from Human Vestibular Schwannomas Can Cause Cochlear Damage.</a> Sci Rep. 5, 18599 (2015).</li><li>Soares, V. Y., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Extracellular+vesicles+derived+from+human+vestibular+schwannomas+associated+with+poor+hearing+damage+cochlear+cells.">Extracellular vesicles derived from human vestibular schwannomas associated with poor hearing damage cochlear cells.</a> Neuro Oncol. , (2016).</li><li>Tong, M., Brugeaud, A., Edge, A. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Regenerated+synapses+between+postnatal+hair+cells+and+auditory+neurons.">Regenerated synapses between postnatal hair cells and auditory neurons.</a> J Assoc Res Otolaryngol. 14 (3), 321-329 (2013).</li><li>Yuan, Y., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ouabain-induced+cochlear+nerve+degeneration:+synaptic+loss+and+plasticity+in+a+mouse+model+of+auditory+neuropathy.">Ouabain-induced cochlear nerve degeneration: synaptic loss and plasticity in a mouse model of auditory neuropathy.</a> J Assoc Res Otolaryngol. 15 (1), 31-43 (2014).</li><li>Fernandez, K. A., Jeffers, P. W., Lall, K., Liberman, M. C., Kujawa, S. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Aging+after+noise+exposure:+acceleration+of+cochlear+synaptopathy+in+&amp;#34;recovered&amp;#34;+ears.">Aging after noise exposure: acceleration of cochlear synaptopathy in &amp;#34;recovered&amp;#34; ears.</a> J Neurosci. 35 (19), 7509-7520 (2015).</li><li>Barclay, M., Constable, R., James, N. R., Thorne, P. R., Montgomery, J. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Reduced+sensory+stimulation+alters+the+molecular+make-up+of+glutamatergic+hair+cell+synapses+in+the+developing+cochlea.">Reduced sensory stimulation alters the molecular make-up of glutamatergic hair cell synapses in the developing cochlea.</a> Neuroscience. , 50-62 (2016).</li><li>Zinn, E., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=In+Silico+Reconstruction+of+the+Viral+Evolutionary+Lineage+Yields+a+Potent+Gene+Therapy+Vector.">In Silico Reconstruction of the Viral Evolutionary Lineage Yields a Potent Gene Therapy Vector.</a> Cell Rep. 12 (6), 1056-1068 (2015).</li><li>Wu, Z., Yang, H., Colosi, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effect+of+genome+size+on+AAV+vector+packaging.">Effect of genome size on AAV vector packaging.</a> Mol Ther. 18 (1), 80-86 (2010).</li><li>Shu, Y., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Identification+of+Adeno-Associated+Viral+Vectors+That+Target+Neonatal+and+Adult+Mammalian+Inner+Ear+Cell+Subtypes.">Identification of Adeno-Associated Viral Vectors That Target Neonatal and Adult Mammalian Inner Ear Cell Subtypes.</a> Hum Gene Ther. , (2016).</li><li>Kao, S. Y., Soares, V. Y., Kristiansen, A. G., Stankovic, K. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Activation+of+TRAIL-DR5+pathway+promotes+sensorineural+degeneration+in+the+inner+ear.">Activation of TRAIL-DR5 pathway promotes sensorineural degeneration in the inner ear.</a> Aging Cell. 15 (2), 301-308 (2016).</li></ol>

The authors have nothing to disclose.

Researchers must perfect the dissection technique before carrying out experiments involving cochlear explants. Hair cells are commonly damaged during dissections performed early on in the learning curve, and a particularly problematic moment for their integrity is the removal of the tectorial membrane, which requires steady hands, proper tools, and experience. To save time and resources, a visual control should be performed under the dissection microscope and potentially damaged areas should be noted. Instead of using ex...

Sensorineural Hearing Loss (SNHL) reflects damage to the inner ear or ascending auditory pathway. While hearing loss is the most common sensory deficit in humans1, curative therapies do not yet exist2. Although cochlear or auditory brainstem implants can restore some degree of hearing to patients with severe to profound SNHL, the hearing provided by these devices is still very different from &#34;natural&#34; hearing, especially during attempts to understand speech in noise or to listen to music.
While hair cell degeneration has long been considered the primary consequence of traumatic auditory events (e.g., exposure to loud noise), there is growing evidence that the synapses transmitting information from hair cells to the auditory nerve are at least as vulnerable to acoustic trauma3,4,5,6. Since human audiometric thresholds, the current gold standard for the evaluation of hearing function, do not predict specific cellular damage in the inner ear, more refined tools are needed to detect cellular degeneration as soon as possible and to initiate adequate treatment7.
Promising pharmaceutical treatments for hearing loss are often tested on homogenous cell cultures in vitro, but such systems do not accurately model the cochlear microenvironment. Cochlear cells are known to secrete trophic factors that influence other cell types within the cochlea8,9, a crucial in vivo process that is lost when the organ of Corti10,11 or Spiral Ganglion Neurons (SGNs)12 are cultured in isolation or when molecular markers are analyzed13. However, in vivo studies that may be necessary for the validation of in vitro data to establish new, personalized treatments for hearing loss in the pursuit of &#34;precision medicine&#34; require significant resources and time. This is especially relevant when considering how much effort is required to perfect and perform middle ear or round window membrane injections with hearing tests and the subsequent dissection of cochlear whole-mounts. The efficient screening of promising compounds in organotypic ex vivo cultures known as cochlear explants provides an economic and reliable alternative14,15,16,17.
This article details a protocol by which to generate, maintain, and evaluate treated cochlear explants. Specific applications for this model are emphasized, including its use in the screening of potentially therapeutic compounds and the comparative evaluation of viral vectors for gene therapy. An ex vivo explant approach allows researchers to visualize the effects of a given treatment on different cell populations in situ, facilitating the identification of cell type-specific mechanisms and the subsequent refinement of targeted therapeutics.
Overall, this technique provides a model to study the cochlea ex vivo while preserving vital cross-talk between the vastly different cell types that coexist within the cochlea.

<table><tbody><tr><td>Ampicillin, Sodium Salt</td><td>Invitrogen</td><td>11593-027</td><td></td></tr><tr><td>anti-CtBP2 antibody, mouse(IgG1)</td><td>BD Transduction Laboratories</td><td>612044</td><td></td></tr><tr><td>anti-Myo7A antibody, rabbit</td><td>Proteus Biosciences</td><td>25-6790</td><td></td></tr><tr><td>anti-NF-H antibody, chicken</td><td>EMD Millipore</td><td>AB5539</td><td></td></tr><tr><td>anti-PSD95 antibody, mouse(IgG2a)</td><td>Antibodies Inc.</td><td>75-028</td><td></td></tr><tr><td>anti-TuJ1 antibody, mouse</td><td>BioLegend</td><td>801202</td><td></td></tr><tr><td>Cell-Tak Cell and Tissue Adhesive, 5 mg</td><td>Corning</td><td>354241</td><td></td></tr><tr><td>CELLSTAR 15 mL Centrifuge Tubes, Conical bottom, Graduation, Sterile</td><td>Greiner Bio-One</td><td>188161</td><td></td></tr><tr><td>CELLSTAR Cell Culture Dish, 100 x 20 mm</td><td>Greiner Bio-One</td><td>664160</td><td></td></tr><tr><td>CELLSTAR Cell Culture Dish, 35 x 10 mm, 4 inner rings</td><td>Greiner Bio-One</td><td>627170</td><td></td></tr><tr><td>CELLSTAR Cell Culture Dish, 60 x 15 mm</td><td>Greiner Bio-One</td><td>628160</td><td></td></tr><tr><td>CELLSTAR 50 mL Centrifuge Tubes, Conical bottom, Graduation, Sterile</td><td>Greiner Bio-One</td><td>227261</td><td></td></tr><tr><td>Clear Nail Polish</td><td>Electron Microscopy Sciences</td><td>72180</td><td></td></tr><tr><td>Clear Wall Glass Bottom Dishes (Glass 40mm), PELCO&amp;reg;, Sleeve/20, 50 x 7 mm</td><td>Ted Pella Inc.</td><td>14027-20</td><td></td></tr><tr><td>Coverslips, Round, Glass, 10 mm diameter, Thickness #1, 0.13 - 0.16mm</td><td>Ted Pella Inc.</td><td>260368</td><td></td></tr><tr><td>DAPI (4&#039;,6-Diamidino-2-Phenylindole, Dihydrochloride)</td><td>Thermo Fisher Scientific</td><td>D1306</td><td></td></tr><tr><td>Distilled water, 500 mL</td><td>Thermo Fisher Scientific</td><td>15230-162&amp;nbsp;</td><td></td></tr><tr><td>Dulbecco&#039;s Modified Eagle&#039;s Medium (DMEM), high glucose, pyruvate, no glutamine, 500 mL</td><td>Thermo Fisher Scientific</td><td>10313-039</td><td></td></tr><tr><td>Dumont #4 Forceps</td><td>Fine Science Tools</td><td>11241-30</td><td></td></tr><tr><td>Dumont #55 Forceps (Dumostar)</td><td>Fine Science Tools</td><td>11295-51</td><td></td></tr><tr><td>Ethyl alcohol (EtOH), Pure, 200 proof, anhydrous, &amp;ge;99.5%</td><td>Sigma-Aldrich</td><td>459836-1L</td><td></td></tr><tr><td>Fetal Bovine Serum (FBS), qualified, USDA-approved regions, 500 mL</td><td>Thermo Fisher Scientific</td><td>10437-028&amp;nbsp;</td><td>Aliquot in 50 mL tubes and store in -20&amp;deg;C freezer</td></tr><tr><td>goat anti-chicken-647 secondary antibody</td><td>Thermo Fisher Scientific</td><td>A-21469</td><td></td></tr><tr><td>goat anti-mouse(IgG)-568 secondary antibody</td><td>Thermo Fisher Scientific</td><td>A-11004</td><td></td></tr><tr><td>goat anti-mouse(IgG1)-568 secondary antibody</td><td>Thermo Fisher Scientific</td><td>A-21124</td><td></td></tr><tr><td>goat anti-mouse(IgG2a)-488 secondary antibody</td><td>Thermo Fisher Scientific</td><td>A-21131</td><td></td></tr><tr><td>goat anti-rabbit-488 secondary antibody</td><td>Thermo Fisher Scientific</td><td>R37116</td><td></td></tr><tr><td>H&lt;sub&gt;2&lt;/sub&gt;O, sterile, EmbryoMax Ultra Pure Water, 500 mL</td><td>EMD Millipore</td><td>TMS-006-B</td><td></td></tr><tr><td>Hank&#039;s Balanced Salt Solution (HBSS), calcium, magnesium, no phenol red, 500 mL</td><td>Thermo Fisher Scientific</td><td>14025-092</td><td></td></tr><tr><td>Instrument Tray with Lid Stainless Steel</td><td>Mountainside Medical</td><td>TechMed4255</td><td></td></tr><tr><td>Micro (dissecting) knife &amp;ndash; angled 30&amp;deg;</td><td>Fine Science Tools</td><td>10056-12</td><td></td></tr><tr><td>Microscope slides, VistaVision, color-coded, 75 x 25 mm (3 x 1&quot;), 1 mm thick, white, pack of 72</td><td>VWR</td><td>16004-382</td><td></td></tr><tr><td>N-2 Supplement (100X), 5 mL</td><td>Thermo Fisher Scientific</td><td>17502-048</td><td></td></tr><tr><td>NaHCO&lt;sub&gt;3&lt;/sub&gt;, Sodium Bicarbonate 7.5% solution, 100 mL</td><td>Thermo Fisher Scientific</td><td>25080-094</td><td></td></tr><tr><td>NaOH, sodium hydroxide solution, 1 L</td><td>Thermo Fisher Scientific</td><td>SS266-1</td><td></td></tr><tr><td>Normal Horse Serum (NHS)</td><td>Invitrogen</td><td>16050130</td><td></td></tr><tr><td>Operating scissors</td><td>Roboz Surgical Instruments Co.</td><td>RS-6806</td><td></td></tr><tr><td>Paraformaldehyde (PFA), Reagent Grade, Crystalline</td><td>Sigma-Aldrich</td><td>P6148</td><td>Prior to use: Establish Standard Operating Procedures based on protocols available online</td></tr><tr><td>PBS, pH 7.4, 500 mL</td><td>Thermo Fisher Scientific</td><td>10010-023&amp;nbsp;</td><td>Autoclave prior to use</td></tr><tr><td>Phalloidin, Alexa Fluor 568&amp;nbsp;</td><td>Thermo Fisher Scientific</td><td>A12380</td><td></td></tr><tr><td>Prep Pad, Non Sterile&amp;nbsp;</td><td>Medline</td><td>05136CS</td><td></td></tr><tr><td>Safe-Lock Microcentrifuge Tubes, Polypropylene, 0.5 mL</td><td>Eppendorf</td><td>022363719</td><td>Autoclave prior to use</td></tr><tr><td>Safe-Lock Microcentrifuge Tubes, Polypropylene, 1.5 mL</td><td>Eppendorf</td><td>022363204</td><td>Autoclave prior to use</td></tr><tr><td>Scalpel Blades - #15</td><td>Fine Science Tools</td><td>10015-00</td><td></td></tr><tr><td>Scalpel Handle - #4</td><td>Fine Science Tools</td><td>10004-13</td><td></td></tr><tr><td>Stemi 2000-C Stereo Microscope</td><td>Zeiss&amp;nbsp;</td><td>000000-1106-133</td><td></td></tr><tr><td>TCS SP5 confocal microscope</td><td>Leica</td><td>N/A</td><td></td></tr><tr><td>Triton-X (non-ionic surfactant)</td><td>Integra</td><td>T756.30.30</td><td></td></tr><tr><td>VectaShield antifade mounting medium for fluorescence</td><td>Vector Laboratories, Inc.</td><td>H-1000</td><td></td></tr><tr><td>Zipper Bag, Reclosable, 4 x 6&#039;&#039; - 2 mm thick</td><td>Zipline</td><td>0609132541599</td><td></td></tr></tbody></table>

neonatal murine cochlear explant technique as an in vitro screening tool in hearing research

While there have been remarkable advances in hearing research over the past few decades, there is still no cure for Sensorineural Hearing Loss (SNHL), a condition that typically involves damage to or loss of the delicate mechanosensory structures of the inner ear. Sophisticated in vitro and ex vivo assays have emerged in recent years, enabling the screening of an increasing number of potentially therapeutic compounds while minimizing resources and accelerating efforts to develop cures for SNHL. Though homogenous cultures of certain cell types continue to play an important role in current research, many scientists now rely on more complex organotypic cultures of murine inner ears, also known as cochlear explants. The preservation of organized cellular structures within the inner ear facilitates the in situ evaluation of various components of the cochlear infrastructure, including inner and outer hair cells, spiral ganglion neurons, neurites, and supporting cells. Here we present the preparation, culture, treatment, and immunostaining of neonatal murine cochlear explants. The careful preparation of these explants facilitates the identification of mechanisms that contribute to SNHL and constitutes a valuable tool for the hearing research community.

While many protocols focus on organ of Corti explants, this technique attempts to preserve the anatomy of the entire cochlear turn, including the SGNs. This gives researchers the opportunity to analyze the effects of a given treatment on neurites and somata of SGNs in addition to the organ of Corti. Performing a dissection that preserves part of the modiolus, as described here, is more technically challenging than explanting the organ of Corti alone. However, the neurite and SGN area is i...

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Neonatal Murine Cochlear Explant Technique as an In Vitro Screening Tool in Hearing Research

The goal of this protocol is to demonstrate the preparation, culture, treatment, and immunostaining of neonatal murine cochlear explants. The technique can be utilized as an in vitro screening tool in hearing research.

Neonatal Murine Cochlear Explant Technique as an In Vitro Screening Tool in Hearing Research

While there have been remarkable advances in hearing research over the past few decades, there is still no cure for Sensorineural Hearing Loss (SNHL), a ...

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17.5K Views.  Massachusetts Eye and Ear. The goal of this protocol is to demonstrate the preparation, culture, treatment, and immunostaining of neonatal murine cochlear explants. The technique can be utilized as an in vitro screening tool in hearing research.

Video: Neonatal Murine Cochlear Explant Technique as an In Vitro Screening Tool in Hearing Research

Culture of Embryonic Mouse Cochlear Explants and Gene Transfer by Electroporation

Auditory hair cells located within the mouse organ of Corti detect and transmit sound information to the central nervous system. The mechanosensory hair cells are aligned in one row of inner hair cells and three rows of outer hair cells that extend along the basal to apical axis of the cochlea. The explant culture technique described here provides an efficient method to isolate and maintain cochlear explants from the embryonic mouse inner ear. Also, the morphology and molecular characteristics of sensory hair cells and nonsensory supporting cells within the cochlear explant cultures resemble those observed in vivo and can be studied within its intrinsic cellular environment. The cochlear explants can serve as important experimental tools for the identification and characterization of molecular and genetic pathways that are involved in cellular specification and patterning. Although transgenic mouse models provide an effective approach for gene expression studies, a considerable number of mouse mutants die during embryonic development thereby hindering the analysis and interpretation of developmental phenotypes. The organ of Corti from mutant mice that die before birth can be cultured so that their in vitro development and responses to different factors can be analyzed. Additionally, we describe a technique for electroporating embryonic cochlear explants ex vivo which can be used to downregulate or overexpress specific gene(s) and analyze their potential endogenous function and test whether specific gene product is necessary or sufficient in a given context to influence mammalian cochlear development1-8.

We present a method that describes isolation and culture of cochlear explants from embryonic mouse inner ear. We also demonstrate a method for gene transfer into cochlear explants via square-wave electroporation. The in vitro explant culture coupled with gene transfer technique enables researchers to study the effects of altering gene expression during development.

Auditory hair cells located within the mouse organ of Corti detect and transmit sound information to the central nervous system. The mechanosensory hair ...

Developmental Biology

Making Sense of Listening: The IMAP Test Battery

The ability to hear is only the first step towards making sense of the range of information contained in an auditory signal. Of equal importance are the abilities to extract and use the information encoded in the auditory signal. We refer to these as listening skills (or auditory processing AP). Deficits in these skills are associated with delayed language and literacy development, though the nature of the relevant deficits and their causal connection with these delays is hotly debated.
When a child is referred to a health professional with normal hearing and unexplained difficulties in listening, or associated delays in language or literacy development, they should ideally be assessed with a combination of psychoacoustic (AP) tests, suitable for children and for use in a clinic, together with cognitive tests to measure attention, working memory, IQ, and language skills. Such a detailed examination needs to be relatively short and within the technical capability of any suitably qualified professional. Current tests for the presence of AP deficits tend to be poorly constructed and inadequately validated within the normal population. They have little or no reference to the presenting symptoms of the child, and typically include a linguistic component. Poor performance may thus reflect problems with language rather than with AP. To assist in the assessment of children with listening difficulties, pediatric audiologists need a single, standardized child-appropriate test battery based on the use of language-free stimuli.
We present the IMAP test battery which was developed at the MRC Institute of Hearing Research to supplement tests currently used to investigate cases of suspected AP deficits. IMAP assesses a range of relevant auditory and cognitive skills and takes about one hour to complete. It has been standardized in 1500 normally-hearing children from across the UK, aged 6-11 years. Since its development, it has been successfully used in a number of large scale studies both in the UK and the USA. IMAP provides measures for separating out sensory from cognitive contributions to hearing. It further limits confounds due to procedural effects by presenting tests in a child-friendly game-format. Stimulus-generation, management of test protocols and control of test presentation is mediated by the IHR-STAR software platform. This provides a standardized methodology for a range of applications and ensures replicable procedures across testers. IHR-STAR provides a flexible, user-programmable environment that currently has additional applications for hearing screening, mapping cochlear implant electrodes, and academic research or teaching.

A test battery (IMAP) for performing an in-depth assessment of auditory and cognitive abilities contributing to listening skills is described. It is quick to administer, child-friendly and free from linguistic confounds. Stimulus generation and protocol management are controlled via a software platform (IHR-STAR) to ensure replicable procedures.

The ability to hear is only the first step towards making sense of the range of information contained in an auditory signal. Of equal importance are the ...

A Strategy to Identify de Novo Mutations in Common Disorders such as Autism and Schizophrenia

There are several lines of evidence supporting the role of de novo mutations as a mechanism for common disorders, such as autism and schizophrenia. First, the de novo mutation rate in humans is relatively high, so new mutations are generated at a high frequency in the population. However, de novo mutations have not been reported in most common diseases. Mutations in genes leading to severe diseases where there is a strong negative selection against the phenotype, such as lethality in embryonic stages or reduced reproductive fitness, will not be transmitted to multiple family members, and therefore will not be detected by linkage gene mapping or association studies. The observation of very high concordance in monozygotic twins and very low concordance in dizygotic twins also strongly supports the hypothesis that a significant fraction of cases may result from new mutations. Such is the case for diseases such as autism and schizophrenia. Second, despite reduced reproductive fitness1 and extremely variable environmental factors, the incidence of some diseases is maintained worldwide at a relatively high and constant rate. This is the case for autism and schizophrenia, with an incidence of approximately 1% worldwide. Mutational load can be thought of as a balance between selection for or against a deleterious mutation and its production by de novo mutation. Lower rates of reproduction constitute a negative selection factor that should reduce the number of mutant alleles in the population, ultimately leading to decreased disease prevalence. These selective pressures tend to be of different intensity in different environments. Nonetheless, these severe mental disorders have been maintained at a constant relatively high prevalence in the worldwide population across a wide range of cultures and countries despite a strong negative selection against them2. This is not what one would predict in diseases with reduced reproductive fitness, unless there was a high new mutation rate. Finally, the effects of paternal age: there is a significantly increased risk of the disease with increasing paternal age, which could result from the age related increase in paternal de novo mutations. This is the case for autism and schizophrenia3. The male-to-female ratio of mutation rate is estimated at about 4&#x2013;6:1, presumably due to a higher number of germ-cell divisions with age in males. Therefore, one would predict that de novo mutations would more frequently come from males, particularly older males4. A high rate of new mutations may in part explain why genetic studies have so far failed to identify many genes predisposing to complexes diseases genes, such as autism and schizophrenia, and why diseases have been identified for a mere 3% of genes in the human genome. Identification for de novo mutations as a cause of a disease requires a targeted molecular approach, which includes studying parents and affected subjects. The process for determining if the genetic basis of a disease may result in part from de novo mutations and the molecular approach to establish this link will be illustrated, using autism and schizophrenia as examples.

Molecular genetic strategy for finding de novo mutations causing common disorders such as autism and schizophrenia.

There are several lines of evidence supporting the role of de novo mutations as a mechanism for common disorders, such as autism and schizophrenia. First, ...

Primary Culture and Plasmid Electroporation of the Murine Organ of Corti. 

In all mammals, the sensory epithelium for audition is located along the spiraling organ of Corti that resides within the conch shaped cochlea of the inner ear (fig 1). Hair cells in the developing cochlea, which are the mechanosensory cells of the auditory system, are aligned in one row of inner hair cells and three (in the base and mid-turns) to four (in the apical turn) rows of outer hair cells that span the length of the organ of Corti. Hair cells transduce sound-induced mechanical vibrations of the basilar membrane into neural impulses that the brain can interpret. Most cases of sensorineural hearing loss are caused by death or dysfunction of cochlear hair cells.
An increasingly essential tool in auditory research is the isolation and in vitro culture of the organ explant 1,2,9. Once isolated, the explants may be utilized in several ways to provide information regarding normative, anomalous, or therapeutic physiology. Gene expression, stereocilia motility, cell and molecular biology, as well as biological approaches for hair cell regeneration are examples of experimental applications of organ of Corti explants.
This protocol describes a method for the isolation and culture of the organ of Corti from neonatal mice. The accompanying video includes stepwise directions for the isolation of the temporal bone from mouse pups, and subsequent isolation of the cochlea, spiral ligament, and organ of Corti. Once isolated, the sensory epithelium can be plated and cultured in vitro in its entirety, or as a further dissected micro-isolate that lacks the spiral limbus and spiral ganglion neurons. Using this method, primary explants can be maintained for 7-10 days. As an example of the utility of this procedure, organ of Corti explants will be electroporated with an exogenous DsRed reporter gene. This method provides an improvement over other published methods because it provides reproducible, unambiguous, and stepwise directions for the isolation, microdissection, and primary culture of the organ of Corti.

Primary Culture and Plasmid Electroporation of the Murine Organ of Corti.

This procedure describes a method for the isolation and culture of the murine organ of Corti with or without the spiral limbus and spiral ganglion neurons. We also demonstrate a method for the expression of an exogenous reporter gene in the organ of Corti explant by electroporation.

In all mammals, the sensory epithelium for audition is located along the spiraling organ of Corti that resides within the conch shaped cochlea of the ...

Long-term Time Lapse Imaging of Mouse Cochlear Explants

Here we present a method for long-term time-lapse imaging of live embryonic mouse cochlear explants. The developmental program responsible for building the highly ordered, complex structure of the mammalian cochlea proceeds for around ten days. In order to study changes in gene expression over this period and their response to pharmaceutical or genetic manipulation, long-term imaging is necessary. Previously, live imaging has typically been limited by the viability of explanted tissue in a humidified chamber atop a standard microscope. Difficulty in maintaining optimal conditions for culture growth with regard to humidity and temperature has placed limits on the length of imaging experiments. A microscope integrated into a modified tissue culture incubator provides an excellent environment for long term-live imaging. In this method we demonstrate how to establish embryonic mouse cochlear explants and how to use an incubator microscope to conduct time lapse imaging using both bright field and fluorescent microscopy to examine the behavior of a typical embryonic day (E) 13 cochlear explant and Sox2, a marker of the prosensory cells of the cochlea, over 5 days.

Live imaging of the embryonic mammalian cochlea is challenging because the developmental processes at hand operate on a temporal gradient over ten days. Here we present a method for culturing and then imaging embryonic cochlear explant tissue taken from a fluorescent reporter mouse over five days.

Here we present a method for long-term time-lapse imaging of live embryonic mouse cochlear explants. The developmental program responsible for building ...

Neuroscience

The Mouse Round-window Approach for Ototoxic Agent Delivery: A Rapid and Reliable Technique for Inducing Cochlear Cell Degeneration

Investigators have utilized a wide array of animal models and investigative techniques to study the mammalian auditory system. Much of the basic research involving the cochlea and its associated neural pathways entails exposure of model cochleae to a variety of ototoxic agents. This allows investigators to study the effects of targeted damage to cochlear structures, and in some cases, the self-repair or regeneration of those structures. Various techniques exist for delivery of ototoxic agents to the cochlea. When selecting a particular technique, investigators must consider a number of factors, including the induction of inadvertent systemic toxicity, the amount of cochlear damage produced by the surgical procedure itself, the type of lesion desired, animal survivability, and reproducibility/reliability of results. Currently established techniques include parenteral injection, intra-peritoneal injection, trans-tympanic injection, endolymphatic sac injection, and cochleostomy with perilymphatic perfusion. Each of these methods has been successfully utilized and is well described in the literature; yet, each has various shortcomings. Here, we present a technique for topical application of ototoxic agents directly to the round window niche. This technique is non-invasive to inner ear structures, produces rapid onset of reliably targeted lesions, avoids systemic toxicity, and allows for an intra-animal control (the contra-lateral ear). Results stemming from this approach have helped deeper understanding of auditory pathophysiology, cochlear cell degeneration, and regenerative capacity in response to an acute injury. Future investigations may use this method to conduct interventional studies involving gene therapy and stem cell transplantation to combat hearing loss.

Various methods exist for introducing ototoxic agents to the cochleae of animal models. Presented is a surgical protocol for delivery of ototoxic agents to the round window niche. The procedure is reliable, creates targeted intra-cochlear lesions, and avoids mechanical damage to the microarchitecture. Examination of cochlear self-repair/regeneration is possible.

Investigators have utilized a wide array of animal models and investigative techniques to study the mammalian auditory system. Much of the basic research ...

Cochlear Surface Preparation in the Adult Mouse

Auditory processing in the cochlea depends on the integrity of the mechanosensory hair cells. Over a lifetime, hearing loss can be acquired from numerous etiologies such as exposure to excessive noise, the use of ototoxic medications, bacterial or viral ear infections, head injuries, and the aging process. Loss of sensory hair cells is a common pathological feature of the varieties of acquired hearing loss. Additionally, the inner hair cell synapse can be damaged by mild insults. Therefore, surface preparations of cochlear epithelia, in combination with immunolabeling techniques and confocal imagery, are a very useful tool for the investigation of cochlear pathologies, including losses of ribbon synapses and sensory hair cells, changes in protein levels in hair cells and supporting cells, hair cell regeneration, and determination of report gene expression (i.e., GFP) for verification of successful transduction and identification of transduced cell types. The cochlea, a bony spiral-shaped structure in the inner ear, holds the auditory sensory end organ, the organ of Corti (OC). Sensory hair cells and surrounding supporting cells in the OC are contained in the cochlear duct and rest on the basilar membrane, organized in a tonotopic fashion with high-frequency detection occurring in the base and low-frequency in the apex. With the availability of molecular and genetic information and the ability to manipulate genes by knockout and knock-in techniques, mice have been widely used in biological research, including in hearing science. However, the adult mouse cochlea is miniscule, and the cochlear epithelium is encapsulated in a bony labyrinth, making microdissection difficult. Although dissection techniques have been developed and used in many laboratories, this modified microdissection method using cell and tissue adhesive is easier and more convenient. It can be used in all types of adult mouse cochleae following decalcification.

This article presents a modified cochlear surface preparation method that requires decalcification and use of a cell and tissue adhesive to adhere the pieces of cochlear epithelia to 10 mm round cover slips for immunohistochemistry in adult mouse cochleae.

Auditory processing in the cochlea depends on the integrity of the mechanosensory hair cells. Over a lifetime, hearing loss can be acquired from numerous ...

In vitro Time-lapse Live-Cell Imaging to Explore Cell Migration toward the Organ of Corti

To study the effects of mesenchymal stem cells (MSCs) on cell regeneration and treatment, this method tracks MSC migration and morphological changes after co-culture with cochlear epithelium. The organ of Corti was immobilized on a plastic coverslip by pressing a portion of the Reissner's membrane generated during the dissection. MSCs confined by a glass cylinder migrated toward cochlear epithelium when the cylinder was removed. Their predominant localization was observed in the modiolus of the organ of Corti, aligned in a direction similarly to that of the nerve fibers. However, some MSCs were localized in the limbus area and showed a horizontally elongated shape. In addition, migration into the hair cell area was increased, and the morphology of the MSCs changed to various forms after kanamycin treatment. In conclusion, the results of this study indicate that the coculture of MSCs with cochlear epithelium will be useful for the development of therapeutics via cell transplantation and for studies of cell regeneration that can examine various conditions and factors.

In this study, we present a real-time imaging method using confocal microscopy to observe cells moving toward damaged tissue by ex vivo incubation with the cochlear epithelium containing the organ of Corti.

To study the effects of mesenchymal stem cells (MSCs) on cell regeneration and treatment, this method tracks MSC migration and morphological changes after ...

Whole Neonatal Cochlear Explants as an In vitro Model

Untreated hearing loss imposes significant costs on the global healthcare system and impairs individuals' quality of life. Sensorineural hearing loss is characterized by the cumulative and irreversible loss of sensory hair cells and auditory nerves in the cochlea. Entire and vital cochlear explants are one of the fundamental tools in hearing research to detect hair cell loss and to characterize the molecular mechanisms of the inner ear cells. Many years ago, a protocol for neonatal cochlear isolation was developed, and although it has been modified over time, it still holds potential for improvement. 
This paper presents an optimized protocol for isolating and culturing whole neonatal cochlear explants in multi-well culture chambers that enables the study of hair cells and spiral ganglion neuron cells along the entire length of the cochlea. The protocol was tested using cochlear explants from mice and rats. Healthy cochlear explants were obtained to study the interaction between hair cells, spiral ganglion neuron cells, and the surrounding supporting cells. 
One of the main advantages of this method is that it simplifies the organ culture steps without compromising the quality of the explants. All three turns of the organ of Corti are attached to the bottom of the chamber, which facilitates in vitro experiments and the comprehensive analysis of the explants. We provide some examples of cochlear images from different experiments with live and fixed explants, demonstrating that the explants retain their structure despite exposure to ototoxic drugs. This optimized protocol can be widely used for the integrative analysis of the mammalian cochlea.

Whole Neonatal Cochlear Explants as an In vitro Model

The current protocol updates previous protocols and incorporates relatively straightforward approaches for culturing high-quality cochlear explants. This provides reliable data acquisition and high-resolution imaging in live and fixed cells. This protocol supports the ongoing trend of studying inner ear cells.

Untreated hearing loss imposes significant costs on the global healthcare system and impairs individuals' quality of life. Sensorineural hearing loss is ...

Efficient In Vitro Cultivation of Mouse Cochlear Hair Cells

Isolation and Culture of Primary Cochlear Hair Cells from Neonatal Mice

Cochlear hair cells are the sensory receptors of the auditory system. These cells are located in the organ of Corti, the sensory organ responsible for hearing, within the osseous labyrinth of the inner ear. Cochlear hair cells consist of two anatomically and functionally distinct types: outer and inner hair cells. Damage to either of them results in hearing loss. Notably, as inner hair cells cannot regenerate, and damage to them is permanent. Hence, in vitro cultivation of primary hair cells is indispensable for investigating the protective or regenerative effects of cochlear hair cells. This study aimed to discover a method for isolating and cultivating mouse hair cells. 
After manual removal of the cochlear lateral wall, the auditory epithelium was meticulously dissected from the cochlear modiolus under a microscope, incubated in a mixture consisting of 0.25% trypsin-EDTA for 10 min at 37 &#176;C, and gently suspended in culture medium using a 200 &#181;L pipette tip. The cell suspension was passed through a cell filter, the filtrate was centrifuged, and cells were cultured in 24-well plates. Hair cells were identified based on their capacity to express a mechanotransduction complex, myosin-VIIa, which is involved in motor tensions, and via selective labeling of F-actin using phalloidin. Cells reached &gt;90% confluence after 4 d in culture. This method can enhance our understanding of the biological characteristics of in vitro cultured hair cells and demonstrate the efficiency of cochlear hair cell cultures, establishing a solid methodological foundation for further auditory research.

Author Spotlight: Advancements in Cultivating Mouse Hair Cells for Auditory Research 

Herein, we present a detailed protocol for isolating and culturing primary cochlear hair cells from mice. Initially, the organ of Corti was dissected from neonatal (aged 3-5 days) murine cochleae under a microscope. Subsequently, cells were enzymatically digested into a single-cell suspension and identified using immunofluorescence after several days in culture.

Cochlear hair cells are the sensory receptors of the auditory system. These cells are located in the organ of Corti, the sensory organ responsible for ...

Neonatal Murine Cochlear Explant Technique as an In Vitro Screening Tool in Hearing Research

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Cochlear Surface Preparation in the Adult Mouse

In vitro Time-lapse Live-Cell Imaging to Explore Cell Migration toward the Organ of Corti

Whole Neonatal Cochlear Explants as an In vitro Model

Isolation and Culture of Primary Cochlear Hair Cells from Neonatal Mice