Name: a revised surgical approach to induce endolymphatic hydrops in the guinea pig
Uploaded: 2020-06-04T13:30:00
Description: Watch this Scientific Journal Video about A Revised Surgical Approach to Induce Endolymphatic Hydrops in the Guinea Pig at JoVE.com

We thank Shannon M. Lefler for assistance with figures and the Table of Materials. Research reported in this publication was supported by the National Institute of Deafness and Other Communication Disorders within the National Institutes of Health, through the &#34;Development of Clinician/Researchers in Academic ENT&#34; training grant, award number T32DC000022 (C.V.V.) and by R01 DC014997 (J.T.L). The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.

All procedures listed immediately below in the Protocol section were conducted as described in protocols approved by the Washington University in St. Louis Institutional Animal Care and Use Committee.
1. Anesthetic Induction and Monitoring of Vital Signs
NOTE: This study used pigmented NIH-strain guinea pigs obtained from an in-house breeding colony.
<ol>
	<li>Use guinea pigs of either sex, weighing at least 350 g.</li>
	<li>Place the guinea pig i...

<ol>
	<li>Kimura, R. S., Schuknecht, H. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Membranous+Hydrops+in+the+Inner+Ear+of+the+Guinea+Pig+after+Obliteration+of+the+Endolymphatic+Sac.">Membranous Hydrops in the Inner Ear of the Guinea Pig after Obliteration of the Endolymphatic Sac.</a> Pract oto-rhino-laryng. 27, 343-354 (1965).</li><li>Salt, A. N., DeMott, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Time+course+of+endolymph+volume+increase+in+experimental+hydrops+measured+in+vivo+with+an+ionic+volume+marker.">Time course of endolymph volume increase in experimental hydrops measured in vivo with an ionic volume marker.</a> Hearing Research. 74 (1-2), 165-172 (1994).</li><li>Walsted, A., Garbarsch, C., Michaels, L. <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+craniotomy+and+cerebrospinal+fluid+loss+on+the+inner+ear.+An+experimental+study.">Effect of craniotomy and cerebrospinal fluid loss on the inner ear. An experimental study.</a> Acta Oto-Laryngologica. 114 (6), 626-631 (1994).</li><li>Andrews, J. C., Bohmer, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+surgical+approach+to+the+endolymphatic+sac+and+the+cochlear+aqueduct+in+the+guinea+pig.">The surgical approach to the endolymphatic sac and the cochlear aqueduct in the guinea pig.</a> American Journal of Otolaryngology. 10 (1), 61-66 (1989).</li><li>Lee, J. R., Wright, C. G., Meyerhoff, W. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Modified+occipital+approach+to+the+endolymphatic+sac+and+cochlear+aqueduct+of+the+guinea+pig.">Modified occipital approach to the endolymphatic sac and cochlear aqueduct of the guinea pig.</a> American Journal of Otolaryngology. 14 (2), 165-169 (1993).</li><li>Megerian, C. A., 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=Surgical+induction+of+endolymphatic+hydrops+by+obliteration+of+the+endolymphatic+duct.">Surgical induction of endolymphatic hydrops by obliteration of the endolymphatic duct.</a> Journal of Visualized Experiments. (35), (2010).</li><li>Lichtenhan, J. T., Cooper, N. P., Guinan, J. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+new+auditory+threshold+estimation+technique+for+low+frequencies:+proof+of+concept.">A new auditory threshold estimation technique for low frequencies: proof of concept.</a> Ear and Hearing. 34 (1), 42-51 (2013).</li><li>Lichtenhan, J. T., Hartsock, J., Dornhoffer, J. R., Donovan, K. M., Salt, A. N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Drug+delivery+into+the+cochlear+apex:+Improved+control+to+sequentially+affect+finely+spaced+regions+along+the+entire+length+of+the+cochlear+spiral.">Drug delivery into the cochlear apex: Improved control to sequentially affect finely spaced regions along the entire length of the cochlear spiral.</a> Journal of Neuroscience Methods. 273, 201-209 (2016).</li><li>Lichtenhan, J. T., Hartsock, J. J., Gill, R. M., Guinan, J. J., Salt, A. N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+auditory+nerve+overlapped+waveform+(ANOW)+originates+in+the+cochlear+apex.">The auditory nerve overlapped waveform (ANOW) originates in the cochlear apex.</a> Journal of the Association for Research in Otolaryngology. 15 (3), 395-411 (2014).</li><li>Lichtenhan, J. T., Hirose, K., Buchman, C. A., Duncan, R. K., Salt, A. N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Direct+administration+of+2-Hydroxypropyl-Beta-Cyclodextrin+into+guinea+pig+cochleae:+Effects+on+physiological+and+histological+measurements.">Direct administration of 2-Hydroxypropyl-Beta-Cyclodextrin into guinea pig cochleae: Effects on physiological and histological measurements.</a> PloS One. 12 (4), e0175236 (2017).</li><li>Schneider, C. A., Rasband, W. S., Eliceiri, K. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=NIH+Image+to+ImageJ:+25+years+of+image+analysis.">NIH Image to ImageJ: 25 years of image analysis.</a> Nature Methods. 9 (7), 671-675 (2012).</li></ol>

The presented extradural method had a success rate of 86% in achieving histologically confirmed endolymphatic hydrops and low-frequency hearing loss. The method reliably achieved histological evidence of endolymphatic hydrops by post-operative day 30, consistent with prior studies that used an intradural approach2. The significance of the method with respect to existing methods is that a CSF leak is not required, thus removing a potential confounding variable that has been suggested to result in a...

Endolymphatic hydrops is an enlargement of scala media. The presence of endolymphatic hydrops can be measured using the cross-sectional area of scala media. It is thought that clinical endolymphatic hydrops can be associated with low-frequency sensorineural hearing loss, such as that seen in Meniere&#39;s disease.&#160;But the origin(s) of the hearing loss remain unclear. To adequately study the origins of low-frequency hearing loss associated with endolymphatic hydrops, a reliable model is needed.
In 1965, Kimura and Schuknecht described how to induce endolymphatic hydrops in the guinea pig using an intradural approach1. Their technique involved using a posterior cranial fossa approach to access the operculum and subarcuate fossa. The steps involved incising dura, retracting the cerebellum with a Ringer&#39;s solution soaked cotton pad, and drilling across the endolymphatic duct and the intermediate portion of the endolymphatic sac. Bone wax was then placed into the operculum to separate the endolymphatic duct from the distal endolymphatic sac. The craniotomy defect was closed by placing absorbable gelatin powder (e.g., Gelfoam) and reapproximating the overlying muscles. Histologic evidence of endolymphatic hydrops was consistently found at post-operative days 1, 3, 7, 14, 21, and 30, demonstrating that the intradural approach was a reliable method&#160;to induce histologically-confirmed endolymphatic hydrops. Using the same intradural approach as Kimura and Schuknecht, but with different time points, Salt and DeMott confirmed that scala media in the second turn of the cochlea was significantly enlarged at day 4 and beyond2. While the actual morbidity of inducing a cerebrospinal fluid (CSF) leak using Kimura and Schuknecht&#39;s intradural approach was not reported in the original study, the presence of a CSF leak could increase the risk of meningitis. It has been suggested that loss of CSF could lead to an outflow of perilymph, resulting in a simultaneous temporary expansion of the endolymphatic volume in the guinea pig3. An extradural approach to inducing endolymphatic&#160;hydrops would be a safer option.
In 1989, Andrews and Bohmer described two extradural surgical approaches to reach the endolymphatic sac and duct, via either a middle cranial fossa approach or posterior cranial fossa approach, to obliterate the endolymphatic sac4. They described removing the operculum with a diamond drill, and then either drilling off the intermediate portion of the endolymphatic sac or using a fine pick to disrupt the endolymphatic sac and duct. In 1993, Lee, Wright, and Meyerhoff described a similar approach, which included drilling through the endolymphatic sac and duct, but differed in that they also simultaneously obstructed the cochlear aqueduct5. They demonstrated the presence of endolymphatic hydrops, as assessed via histology, at four weeks after obliterating the endolymphatic sac and obstructing the cochlear aqueduct. Megerian et al. was the first to publish a video article demonstrating an extradural obliteration of the endolymphatic sac and duct that involved drilling directly on the medial portion of the operculum to enter into the endolymphatic sac and duct6. They demonstrated histologic evidence of endolymphatic hydrops in a guinea pig sacrificed at 28 weeks after surgery, as well as hearing loss in the 16 kHz region6. Whether it was possible to induce histologically confirmed endolymphatic hydrops and low-frequency hearing loss at an early time point using extradural approaches was unknown.
The overall goal of this report is to demonstrate an extradural approach to induce experimental endolymphatic hydrops at 30 days post-operatively by obliterating the endolymphatic sac and injuring the endolymphatic duct with a fine pick. The rationale behind the use of this technique is the advantage of avoiding the need to drill on the petrous temporal bone, thereby removing the risk of accidentally injuring the dura and causing a CSF leak, mitigating the possibility of injuring the posterior semicircular canal, and reducing the risk of injury to the sigmoid sinus.

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			<td>12 mL syringe</td>
			<td>Henke-Sass Wolf</td>
			<td>5100-X00V0</td>
			<td></td>
		</tr>
		<tr>
			<td>1 mL and 3 mL syringe</td>
			<td>BD Precision(Ordered from Fischer Sci)</td>
			<td>14-826-87 15859152</td>
			<td></td>
		</tr>
		<tr>
			<td>27.5 butterfly gauge needle</td>
			<td>Terumo Surflo Winged Infusion Set, Terumo Corporation, Japan) (Ordered from McKesson)</td>
			<td>448407</td>
			<td></td>
		</tr>
		<tr>
			<td>4-0 suture</td>
			<td>McKesson</td>
			<td>1034507</td>
			<td></td>
		</tr>
		<tr>
			<td>4x4 gauze sponges</td>
			<td>Dukal (Ordered form McKesson)</td>
			<td>374454</td>
			<td></td>
		</tr>
		<tr>
			<td>60mL syringe</td>
			<td>Fisher Sci</td>
			<td>22-031-375</td>
			<td></td>
		</tr>
		<tr>
			<td>Anspach otologic drill</td>
			<td>Anspach</td>
			<td>SC2100</td>
			<td></td>
		</tr>
		<tr>
			<td>atipamezole</td>
			<td>Zoetis</td>
			<td>107204-6</td>
			<td></td>
		</tr>
		<tr>
			<td>autoclave</td>
			<td>Fisher sci</td>
			<td><a href="https://www.fishersci.com/shop/products/fisher-scientific-isotemp-general-purpose-heating-drying-ovens/151030508">15-103-0508</a></td>
			<td></td>
		</tr>
		<tr>
			<td>autoclave bags</td>
			<td>McKesson</td>
			<td>524881</td>
			<td></td>
		</tr>
		<tr>
			<td>bayonet separator</td>
			<td>Olympus</td>
			<td>AL 130564</td>
			<td></td>
		</tr>
		<tr>
			<td>bupivicaine</td>
			<td>auro Medics Pharma</td>
			<td>555150-169-10</td>
			<td></td>
		</tr>
		<tr>
			<td>clear sterile drape</td>
			<td>3M</td>
			<td>1020</td>
			<td></td>
		</tr>
		<tr>
			<td>cotton balls</td>
			<td>Fisherbrand (ordered from Fisher Sci)</td>
			<td>22-456-885</td>
			<td></td>
		</tr>
		<tr>
			<td>cotton swabs</td>
			<td>McKesson</td>
			<td>508716</td>
			<td></td>
		</tr>
		<tr>
			<td>diamond burrs #3, #2, #1, and #0.5 mm</td>
			<td>Anspach</td>
			<td>QD8-3SD; QD8-2SD; QD8-1SD; QD8-05SD</td>
			<td></td>
		</tr>
		<tr>
			<td>diaper pad</td>
			<td>McKesson</td>
			<td>945330</td>
			<td></td>
		</tr>
		<tr>
			<td>disposable 15 blade</td>
			<td>Swann-Morton</td>
			<td>0305</td>
			<td></td>
		</tr>
		<tr>
			<td>enrofloxacin</td>
			<td>Hospira</td>
			<td>0409-4888-01</td>
			<td></td>
		</tr>
		<tr>
			<td>epinephrine</td>
			<td>McKesson</td>
			<td><a href="https://www.findacode.com/code.php?set=NDC&amp;c=63739-0456">63739-0456</a></td>
			<td></td>
		</tr>
		<tr>
			<td>eye ointment</td>
			<td>Dechra Vet Products</td>
			<td>17033-211-38</td>
			<td></td>
		</tr>
		<tr>
			<td>Freer elevator</td>
			<td>Grace Medical</td>
			<td>215100FX</td>
			<td></td>
		</tr>
		<tr>
			<td>gelfoam</td>
			<td>Pfizer (Ordered from McKesson)</td>
			<td>82830</td>
			<td></td>
		</tr>
		<tr>
			<td>hair trimmers</td>
			<td>Oster Power Pro Cordless (ordered from Amazon)</td>
			<td>078400-020-000</td>
			<td></td>
		</tr>
		<tr>
			<td>iodine scrub</td>
			<td>Purdue Pharma (ordered from mcKesson)</td>
			<td>521243</td>
			<td></td>
		</tr>
		<tr>
			<td>iris scissors</td>
			<td>Olympus</td>
			<td>CL-542114</td>
			<td></td>
		</tr>
		<tr>
			<td>ketamine</td>
			<td>Henry Schein Animal Health</td>
			<td>55853</td>
			<td></td>
		</tr>
		<tr>
			<td>lactated ringers</td>
			<td>B. Braun Medical (ordered from McKesson)</td>
			<td>186662</td>
			<td></td>
		</tr>
		<tr>
			<td>lancet knife by Rosen</td>
			<td>Grace Medical</td>
			<td>151100FX</td>
			<td>referred to as curette in the text</td>
		</tr>
		<tr>
			<td>lubricant</td>
			<td>Milex (ordered from Cooper Surgical)</td>
			<td>MX5030</td>
			<td></td>
		</tr>
		<tr>
			<td>masking tape</td>
			<td>3M (ordered from fisher sci</td>
			<td>19047259</td>
			<td></td>
		</tr>
		<tr>
			<td>metal rectangle basin</td>
			<td>Amazon</td>
			<td>B07NQDBC6T</td>
			<td></td>
		</tr>
		<tr>
			<td>needle holder</td>
			<td>Olympus</td>
			<td>CR 213015-ENT</td>
			<td></td>
		</tr>
		<tr>
			<td>needles: 27 gage, 18 gauge</td>
			<td>BD Precision(Ordered from Fischer Sci)</td>
			<td><a href="https://www.fishersci.com/shop/products/bd-general-use-precisionglide-hypodermic-needles-20/1482648">14-826-48 14-826-5D</a></td>
			<td></td>
		</tr>
		<tr>
			<td>neonatal warming isollete</td>
			<td>Air Borne Life Support Systems</td>
			<td>731-1800</td>
			<td></td>
		</tr>
		<tr>
			<td>operating microscope</td>
			<td>Carl Zeiss</td>
			<td>OPMI pico</td>
			<td></td>
		</tr>
		<tr>
			<td>oxygen tank</td>
			<td>AirGas</td>
			<td>OX USP200</td>
			<td></td>
		</tr>
		<tr>
			<td>pulse ox</td>
			<td>CapnoTrue (Ordered from Medacx)</td>
			<td>M-3090112001</td>
			<td></td>
		</tr>
		<tr>
			<td>rectal probe with heating blanket</td>
			<td>Harvard Apparatus</td>
			<td>probe: PY2 50-7217 Heating Blanket: PY2 50-7214</td>
			<td></td>
		</tr>
		<tr>
			<td>red body holder</td>
			<td>Lichtenhan Lab</td>
			<td>N/A</td>
			<td>In-house product</td>
		</tr>
		<tr>
			<td>right angle</td>
			<td>Olympus</td>
			<td>BV-230337</td>
			<td></td>
		</tr>
		<tr>
			<td>rosen needle</td>
			<td>Olympus</td>
			<td>AM-130566</td>
			<td>customized, it is the instrument I use to tear the sac</td>
		</tr>
		<tr>
			<td>rubber tubing for O2 administration</td>
			<td>Fisher Sci</td>
			<td>14-171-104</td>
			<td></td>
		</tr>
		<tr>
			<td>saran wrap</td>
			<td>Fisher Sci</td>
			<td>NC9617977</td>
			<td></td>
		</tr>
		<tr>
			<td>stereotactic head holder</td>
			<td>WUSTL Instrument Machine Shop</td>
			<td>N/A</td>
			<td>In-house product</td>
		</tr>
		<tr>
			<td>sterile drapes</td>
			<td>Cardinal Health</td>
			<td>7553</td>
			<td></td>
		</tr>
		<tr>
			<td>suction tube by Baron</td>
			<td>Grace Medical</td>
			<td>034903FX 034905FX</td>
			<td>#3 and #5 Suction</td>
		</tr>
		<tr>
			<td>tissue forceps adson brown</td>
			<td>Grace Medical</td>
			<td>325112FX</td>
			<td></td>
		</tr>
		<tr>
			<td>Weitlander retractor</td>
			<td>Olympus Grace Medical</td>
			<td>BL200011 100313FX</td>
			<td></td>
		</tr>
		<tr>
			<td>xylazine</td>
			<td>Akorn</td>
			<td>59399-110-20</td>
			<td></td>
		</tr>
	</tbody>
</table>

a revised surgical approach to induce endolymphatic hydrops in the guinea pig

Endolymphatic hydrops is an enlargement of scala media that is most often associated with Meniere&#39;s disease, though the pathophysiologic mechanism(s) remain unclear. In order to adequately study the attributes of endolymphatic hydrops, such as the origins of low-frequency hearing loss, a reliable model is needed. The guinea pig is a&#160;good model because it hears in the low-frequency regions that are putatively affected by endolymphatic hydrops. Previous research has demonstrated that endolymphatic hydrops can be induced surgically via intradural or extradural approaches that involve drilling on the endolymphatic duct and sac. However, whether it was possible to create an endolymphatic hydrops model using an extradural approach that avoided dangerous drilling on the endolymphatic duct and sac was unknown. The objective of this study was to demonstrate a revised extradural approach to induce experimental endolymphatic hydrops at 30 days post-operatively by obliterating the endolymphatic sac and injuring the endolymphatic duct with a fine pick. The sample size consisted of seven guinea pigs. Functional measurements of hearing were made and temporal bones were subsequently harvested for histologic analysis. The approach had a success rate of 86% in achieving endolymphatic hydrops. The risk of cerebrospinal fluid leak was minimal. No perioperative deaths or injuries to the posterior semicircular canal occurred in the sample. The presented method demonstrates a safe and reliable way to induce endolymphatic hydrops at a relatively quick time point of 30 days. The clinical implications are that the presented method provides a reliable model to further explore the origins of low-frequency hearing loss that can be associated endolymphatic hydrops.

The presented method used an extradural approach to obliterate the endolymphatic sac and injure the endolymphatic duct with a fine pick in seven guinea pigs consisting of two males and five females. The average duration of surgery was 2 hours from incision to closure. The total drill time ranged from 5-10 minutes. Up to&#160;4 hours was needed for the guinea pig to fully emerge from anesthesia. There were no intra-operative or post-operative deaths in the sample. There were no injuries to...

Watch this Scientific Journal Video about A Revised Surgical Approach to Induce Endolymphatic Hydrops in the Guinea Pig at JoVE.com

A Revised Surgical Approach to Induce Endolymphatic Hydrops in the Guinea Pig

This article demonstrates an extradural approach to obliterate the guinea pig endolymphatic sac and injure the endolymphatic duct with a fine pick in order to induce experimental endolymphatic hydrops.

Endolymphatic hydrops is an enlargement of scala media that is most often associated with Meniere&#39;s disease, though the pathophysiologic mechanism(s) ...

Using this procedure, endolymphatic hydrops can be induced relatively quickly in guinea pigs with an adequate success rate. The main advantage of this technique is that endolymphatic hydrops can be induced with minimal risk for CSF leak or injury to the posterior semicircular canal. After confirming a lack of response to pedal reflex, inject a 12 milliliter subcutaneous fluid bolus of lactated Ringer's solution into the back of the anesthetized guinea pig and place the guinea pig in the supine position on a warming pad.Place a 27.5 gauge butterfly needle intraperitoneally confirming a correct placement by the presence of air only within the needle tip and place the guinea pig in the prone position. Secure the head in a stereotactic holder and secure a pulse oximeter onto an unpigmented foot. Use a rectal probe and a warming blanket to maintain the body temperature at 38 degrees Celsius and apply ointment to the animal's eyes.Place a piece of masking tape over the back to provide adequate tension along the skin overlying the occiput and fix the ends of the tape to the stereotactic holder. Then liberally prep the skin overlying the occiput and posterior neck with three consecutive iodine scrubs and 70%alcohol and place a sterile drape over the animal. Begin the surgical procedure by using a number 15 blade to make a small midline incision along the posterior occiput extending down to the posterior neck.Once under the skin, use iris scissors to detach the right posterior cervical muscles from the occipital bone, controlling any bleeding with pressure from a sterile cotton ball. Using a dissecting microscope and a combination of a number three, two, and one millimeter diamond burrs with a 5-0 suction and sterile irrigation, perform a craniectomy that is bounded as far as the external occipital crest laterally, lambdoidal ridge superiorly, the occipitomastoid suture line medially, and the dorsal margin of the foramen magnum inferiorly. And use a 0.5 millimeter diamond burr to skeletonize the sigmoid sinus.Gently place a small piece of saline moistened cotton under the bone while separating the occipital bone from the dura. Carefully remove the bone overlying the sinus and use a cotton ball to gently retract the sigmoid sinus medially. Carefully retract the sigmoid sinus and identify the operculum as a slit-like structure located within the petrous temporal bone.The extraosseous portion of the endolymphatic sac can be visualized as a clear sac-like connection between the operculum and the dura overlying the sigmoid sinus. Apply gentle medial retraction to the sigmoid sinus to clearly visualize the extraosseous portion of the endolymphatic sac and increase the tension between the extraosseous and intraosseous portions of the sac. Using a fine angled pick, gently expunge the intermediate portion of the endolymphatic sac and broadly scrape a fine pick inside the operculum along the inside of the bone.It's critical to the success of this procedure that no visible connection between the dura and the operculum remain. Use a small curette to scrape along the temporal bone to obtain bone chips and generously pack the operculum with the bone chips. Seal the operculum with bone wax taking care that there is no excess wax dislodged into the skull and use bone wax to cover the craniectomy defect.Then approximate the posterior cervical muscles with 4-0 braided absorbable sutures in an interrupted fashion and perform a two-layer closure by approximating the deep layer with simple interrupted sutures and the epidermal layer using a subcuticular closure with a 4-0 braided absorbable suture. In this representative experiment, histologic analysis of the temporal bones revealed endolymphatic hydrops throughout the right cochlea compared to the left cochlea in six out of seven guinea pigs. Quantification of the cross-sectional area of the scala media across each turn indicated that the cross-sectional area was generally larger in the ears of animals that survived 30 days after obliteration of the endolymphatic sac compared to that observed in control animals.Auditory nerve overlapped waveform thresholds were increased in animals with endolymphatic hydrops demonstrating the presence of low-frequency hearing loss while most high-frequency cochlear compound action potential thresholds between eight and 20 kilohertz were within the normal range. If the area between the dura and the operculum is dry after expunging the sac, try placing additional retraction on the sigmoid sinus to make sure there's no visible connection between it and the operculum. Following this procedure, additional studies on cochlear anatomy and physiology can be performed to address important research questions about endolymphatic hydrops.

a-revised-surgical-approach-to-induce-endolymphatic-hydrops-guinea

Research

JoVE Journal

Neuroscience

A Rapid Approach to High-Resolution Fluorescence Imaging in Semi-Thick Brain Slices

A fundamental goal to both basic and clinical neuroscience is to better understand the identities, molecular makeup, and patterns of connectivity that are characteristic to neurons in both normal and diseased brain. Towards this, a great deal of effort has been placed on building high-resolution neuroanatomical maps1-3. With the expansion of molecular genetics and advances in light microscopy has come the ability to query not only neuronal morphologies, but also the molecular and cellular makeup of individual neurons and their associated networks4. Major advances in the ability to mark and manipulate neurons through transgenic and gene targeting technologies in the rodent now allow investigators to 'program' neuronal subsets at will5-6. Arguably, one of the most influential contributions to contemporary neuroscience has been the discovery and cloning of genes encoding fluorescent proteins (FPs) in marine invertebrates7-8, alongside their subsequent engineering to yield an ever-expanding toolbox of vital reporters9. Exploiting cell type-specific promoter activity to drive targeted FP expression in discrete neuronal populations now affords neuroanatomical investigation with genetic precision.
Engineering FP expression in neurons has vastly improved our understanding of brain structure and function. However, imaging individual neurons and their associated networks in deep brain tissues, or in three dimensions, has remained a challenge. Due to high lipid content, nervous tissue is rather opaque and exhibits auto fluorescence. These inherent biophysical properties make it difficult to visualize and image fluorescently labelled neurons at high resolution using standard epifluorescent or confocal microscopy beyond depths of tens of microns. To circumvent this challenge investigators often employ serial thin-section imaging and reconstruction methods10, or 2-photon laser scanning microscopy11. Current drawbacks to these approaches are the associated labor-intensive tissue preparation, or cost-prohibitive instrumentation respectively.
Here, we present a relatively rapid and simple method to visualize fluorescently labelled cells in fixed semi-thick mouse brain slices by optical clearing and imaging. In the attached protocol we describe the methods of: 1) fixing brain tissue in situ via intracardial perfusion, 2) dissection and removal of whole brain, 3) stationary brain embedding in agarose, 4) precision semi-thick slice preparation using new vibratome instrumentation, 5) clearing brain tissue through a glycerol gradient, and 6) mounting on glass slides for light microscopy and z-stack reconstruction (Figure 1).
For preparing brain slices we implemented a relatively new piece of instrumentation called the 'Compresstome' VF-200 (http://www.precisionary.com/products_vf200.html). This instrument is a semi-automated microtome equipped with a motorized advance and blade vibration system with features similar in function to other vibratomes. Unlike other vibratomes, the tissue to be sliced is mounted in an agarose plug within a stainless steel cylinder. The tissue is extruded at desired thicknesses from the cylinder, and cut by the forward advancing vibrating blade. The agarose plug/cylinder system allows for reproducible tissue mounting, alignment, and precision cutting. In our hands, the 'Compresstome' yields high quality tissue slices for electrophysiology, immunohistochemistry, and direct fixed-tissue mounting and imaging. Combined with optical clearing, here we demonstrate the preparation of semi-thick fixed brain slices for high-resolution fluorescent imaging.

Here we describe a rapid and simple method to image fluorescently labeled cells in semi-thick brain slices. By fixing, slicing, and optically clearing brain tissue we describe how standard epifluorescent or confocal imaging can be used to visualize individual cells and neuronal networks within intact nervous tissue.

A fundamental goal to both basic and clinical neuroscience is to better understand the identities, molecular makeup, and patterns of connectivity that are ...

Using a Comparative Species Approach to Investigate the Neurobiology of Paternal Responses

A goal of behavioral neuroscience is to identify underlying neurobiological factors that regulate specific behaviors. Using animal models to accomplish this goal, many methodological strategies require invasive techniques to manipulate the intensity of the behavior of interest (e.g., lesion methods, pharmacological manipulations, microdialysis techniques, genetically-engineered animal models). The utilization of a comparative species approach allows researchers to take advantage of naturally occurring differences in response strategies existing in closely related species. In our lab, we use two species of the Peromyscus genus that differ in paternal responses. The male California deer mouse (Peromyscus californicus) exhibits the same parental responses as the female whereas its cousin, the common deer mouse (Peromyscus maniculatus) exhibits virtually no nurturing/parental responses in the presence of pups. Of specific interest in this article is an exploration of the neurobiological factors associated with the affiliative social responses exhibited by the paternal California deer mouse. Because the behavioral neuroscience approach is multifaceted, the following key components of the study will be briefly addressed: the identification of appropriate species for this type of research; data collection for behavioral analysis; preparation and sectioning of the brains; basic steps involved in immunocytochemistry for the quantification of vasopressin-immunoreactivity; the use of neuroimaging software to quantify the brain tissue; the use of a microsequencing video analysis to score behavior and, finally, the appropriate statistical analyses to provide the most informed interpretations of the research findings.

The comparative species approach allows behavioral neuroscientists to explore various neurobiological factors associated with specific behaviors viewed as characteristic of a specific animal model. Taking advantage of naturally occurring differences in behavior between closely related species, this technique doesn&#x2019;t require invasive techniques to manipulate the expression of the behavior.

A goal of behavioral neuroscience is to identify underlying neurobiological factors that regulate specific behaviors.  Using animal models to accomplish ...

A New Approach that Eliminates Handling for Studying Aggression and the "Loser" Effect in Drosophila melanogaster

Aggressive behavior in Drosophila melanogaster is composed of the sequential expression of stereotypical behavioral patterns (for analysis see 1). This complex behavior is influenced by genetic, hormonal and environmental factors. As in many organisms, previous fighting experience influences the fighting strategy of flies and the outcome of later contests: losing a fight increases the probability of losing later contests, revealing &#34;loser&#34; effects that likely involve learning and memory 2-4. The learning and memory that accompanies expression of complex social behaviors like aggression, is sensitive to pre-test handling of animals 5,6. Many experimental procedures are used in different laboratories to study aggression 7-9, however, no routinely used protocol that excludes handling of flies is currently available. Here, we report a new behavioral apparatus that eliminates handling of flies, using instead their innate negative geotactic responses to move animals into or out of fighting chambers. In this protocol, small circular fight arenas containing a food cup are divided into two equal halves by a removable plastic slider prior to introduction of flies. Flies enter chambers from their home isolation vials via sliding chamber doors and geotaxis. Upon removal of plastic sliders, flies are free to interact. After specified time periods, flies are separated again by sliders for subsequent experimentation. All of this is done easily without handling of individual flies. This apparatus offers a novel approach to study aggression and the associated learning and memory, including the formation of &#34;loser&#34; effects in fly fights. In addition, this new general-purpose behavioral apparatus can be employed to study other social behaviors of flies and should, in general, be of interest for investigating experience-related changes in fundamental behavioral processes.

A New Approach that Eliminates Handling for Studying Aggression and the &quot;Loser&quot; Effect in Drosophila melanogaster

During fruit fly fights, the behavioral patterns observed, fight dynamics, and associated learning and memory are influenced by experimental conditions. The protocol presented here describes a novel procedure that entirely eliminates handling of flies during experiments. This improves fight dynamics and allows formation of strong &#34;loser&#34; effects.

Aggressive behavior in Drosophila melanogaster is composed of the sequential expression of stereotypical behavioral patterns (for analysis see 1). This ...

A Simple Approach to Induce Experimental Autoimmune Neuritis in C57BL/6 Mice for Functional and Neuropathological Assessments

Experimental autoimmune neuritis (EAN) is a well-appreciated experimental model of autoimmune peripheral demyelinating diseases. EAN disease is induced by immunizing mice with neurogenic peptides to direct an inflammatory attack toward components of the peripheral nervous system (PNS). Recent advances have enabled the induction of EAN in the relatively resistant C57BL/6 mouse line using myelin protein zero (P0)106-125 or P0180-199 peptides delivered in adjuvant combined with the injection of pertussis toxin. The ability to induce EAN in the C57BL/6 strain allows for the use of the numerous genetic tools that exist on this mouse background, and thus allows the sophisticated study of disease pathogenesis and interrogation of the mechanistic action of novel therapeutics in combination with transgenic approaches. In this study, we demonstrate a simple approach to successfully induce EAN using the P0180-199 peptide in C57BL/6 mice. We also outline a protocol for the assessment of functional deficits that occur in this model, accompanied by an array of neuropathological features. Thus, this model is a powerful experimental model to study the pathogenesis of human peripheral demyelinating neuropathies, and to determine the efficacy of potential therapies that aim to promote myelin repair and protect against nerve damage in autoimmune neuritis.

This report outlines a simple approach to successfully induce experimental autoimmune neuritis (EAN) using the myelin protein zero (P0)180-199 peptide in combination with Freund&#39;s complete adjuvant and pertussis toxin. We present a sophisticated paradigm capable of accurately assessing the extent of functional deficits and neuropathology that occur in this EAN.

Experimental autoimmune neuritis (EAN) is a well-appreciated experimental model of autoimmune peripheral demyelinating diseases. EAN disease is induced by ...

An Alternative Approach to Study Primary Events in Neurodegeneration Using Ex Vivo Rat Brain Slices

Despite&#160;numerous studies that attempt to develop reliable animal models&#160;which reflecting the primary processes underlying neurodegeneration, very few have been widely accepted. Here, we propose&#160;a new procedure&#160;adapted from the well-known ex vivo brain slice technique, which offers a closer in vivo-like scenario than in vitro preparations, for investigating the early events triggering cell degeneration, as observed in Alzheimer&#39;s disease (AD). This variation consists of simple and easily reproducible steps, which enable preservation of the anatomical cytoarchitecture of the selected brain region and its local functionality in a physiological milieu. Different anatomical areas can be obtained from the same brain, providing the opportunity to perform multiple experiments with the treatments in question in a site-, dose-, and time-dependent manner. Potential limitations&#160;which could affect the outcomes related to this methodology are related to the conservation of the tissue, i.e., the maintenance of its anatomical integrity during the slicing and incubation steps and the section thickness, which can influence the biochemical and immunohistochemical analysis. This approach can be employed for different purposes, such as exploring molecular mechanisms involved in physiological or pathological conditions, drug screening, or dose-response assays. Finally, this protocol could also reduce the number of animals employed in behavioral studies. The application reported here has been recently described and tested for the first time on ex vivo rat brain slices containing the basal forebrain (BF), which is one of the cerebral regions primarily affected in AD. Specifically, it has been demonstrated that the administration of a toxic peptide derived from the C-terminus of acetylcholinesterase (AChE) could prompt an AD-like profile, triggering, along the antero-posterior axis of the BF, a differential expression of proteins altered in AD, such as the alpha7 nicotinic receptor (&#945;7-nAChR), phosphorylated Tau (p-Tau), and amyloid beta (A&#946;).

An Alternative Approach to Study Primary Events in Neurodegeneration Using Ex Vivo Rat Brain Slices

We present a method which can&#160;provide further insights into the early events underlying neurodegeneration and based on the established ex-vivo brain technique, combining the advantages of in vivo and in vitro experiments. Moreover, it represents a unique opportunity for direct comparison of treated and untreated group in the same anatomical plane.

Despite&#160;numerous studies that attempt to develop reliable animal models&#160;which reflecting the primary processes underlying neurodegeneration, ...

A Benchtop Approach to the Location Specific Blood Brain Barrier Opening using Focused Ultrasound in a Rat Model

Stereotaxic surgery is the gold standard for localized drug and gene delivery to the rodent brain. This technique has many advantages over systemic delivery including precise localization to a target brain region and reduction of off target side effects. However, stereotaxic surgery is highly invasive which limits its translational efficacy, requires long recovery times, and provides challenges when targeting multiple brain regions. Focused ultrasound (FUS) can be used in combination with circulating microbubbles to transiently open the blood brain barrier (BBB) in millimeter sized regions. This allows intracranial localization of systemically delivered agents that cannot normally cross the BBB. This technique provides a noninvasive alternative to stereotaxic surgery. However, to date this technique has yet to be widely adopted in neuroscience laboratories due to the limited access to equipment and standardized methods. The overall goal of this protocol is to provide a benchtop approach to FUS BBB opening (BBBO) that is affordable and reproducible and can therefore be easily adopted by any laboratory.

Focused ultrasound with microbubble agents can open the blood brain barrier focally and transiently. This technique has been used to deliver a wide range of agents across the blood brain barrier. This article provides a detailed protocol for the localized delivery to the rodent brain with or without MRI guidance.

Stereotaxic surgery is the gold standard for localized drug and gene delivery to the rodent brain. This technique has many advantages over systemic ...

Combining Behavior and EEG to Study the Effects of Mindfulness Meditation on Episodic Memory

Although there has been recent interest in how mindfulness meditation can affect episodic memory as well as brain structure and function, no study has examined the behavioral and neural effects of mindfulness meditation on episodic memory. Here we present a protocol that combines mindfulness meditation training, an episodic memory task, and EEG to examine how mindfulness meditation changes behavioral performance and the neural correlates of episodic memory. Subjects in a mindfulness meditation experimental group were compared to a waitlist control group. Subjects in the mindfulness meditation experimental group spent four weeks training and practicing mindfulness meditation. Mindfulness was measured before and after training using the Five Facet Mindfulness Questionnaire (FFMQ). Episodic memory was measured before and after training using a source recognition task. During the retrieval phase of the source recognition task, EEG was recorded. The results showed that mindfulness, source recognition behavioral performance, and EEG theta power in right frontal and left parietal channels increased following mindfulness meditation training. In addition, increases in mindfulness correlated with increases in theta power in right frontal channels. Therefore, results obtained from combining mindfulness meditation training, an episodic memory task, and EEG reveal the behavioral and neural effects of mindfulness meditation on episodic memory.

Here we present a protocol for combining mindfulness meditation training, an episodic memory task, and EEG to understand the behavioral and neural effects of mindfulness meditation on episodic memory.

Although there has been recent interest in how mindfulness meditation can affect episodic memory as well as brain structure and function, no study has ...

Extraction and Dissection of the Domesticated Pig Brain

Use of the pig as a preclinical and translatable animal model has been well-documented and accepted by research fields investigating cardiovascular systems, gastrointestinal systems, and nutrition, and the pig is increasingly being used as a large animal model in neuroscience. Furthermore, the pig is an accepted model to study neurodevelopment as it displays brain growth and development patterns similar to what occurs in humans. As a less common animal model in neuroscience, surgical and dissection procedures on pigs may not be as familiar or well-practiced among researchers. Therefore, a standardized visual protocol detailing consistent extraction and dissection methods may prove valuable for researchers working with the pig. The following video showcases a technique to remove the pig brain while keeping the cortex and brainstem intact and reviews methods to dissect several commonly investigated brain regions including the brainstem, cerebellum, midbrain, hippocampus, striatum, thalamus, and medial prefrontal cortex. The purpose of this video is to provide researchers with the tools and knowledge necessary to consistently perform a brain extraction and dissection on the four-week-old pig.

This protocol details the technique for removal of the pig brain in its entirety and dissection of several brain regions commonly studied in neuroscience.

Use of the pig as a preclinical and translatable animal model has been well-documented and accepted by research fields investigating cardiovascular ...

Pre-Chiasmatic, Single Injection of Autologous Blood to Induce Experimental Subarachnoid Hemorrhage in a Rat Model

Despite advances in treatment over the last decades, subarachnoid hemorrhage (SAH) continues to carry a high burden of morbidity and mortality, largely afflicting a fairly young population. Several animal models of SAH have been developed to investigate the pathophysiological mechanisms behind SAH and to test pharmacological interventions. The pre-chiasmatic, single injection model in the rat presented in this article is an experimental model of SAH with a predetermined blood volume. Briefly, the animal is anesthetized, intubated, and kept under mechanical ventilation. Temperature is regulated with a heating pad. A catheter is placed in the tail artery, enabling continuous blood pressure measurement as well as blood sampling. The atlantooccipital membrane is incised and a catheter for pressure recording is placed in the cisterna magna to enable intracerebral pressure measurement. This catheter can also be used for intrathecal therapeutic interventions. The rat is placed in a stereotaxic frame, a burr hole is drilled anteriorly to the bregma, and a catheter is inserted through the burr hole and placed just anterior to the optic chiasm. Autologous blood (0.3 mL) is withdrawn from the tail catheter and manually injected. This results in a rise of intracerebral pressure and a decrease of cerebral blood flow. The animal is kept sedated for 30 min and given subcutaneous saline and analgesics. The animal is extubated and returned to its cage. The pre-chiasmatic model has a high reproducibility rate and limited variation between animals due to the pre-determined blood volume. It mimics SAH in humans making it a relevant model for SAH research.

Subarachnoid hemorrhage continues to carry a high burden of mortality and morbidity in man. To facilitate further research into the condition and its pathophysiology, a pre-chiasmatic, single injection model is presented.

Despite advances in treatment over the last decades, subarachnoid hemorrhage (SAH) continues to carry a high burden of morbidity and mortality, largely ...

Stereotaxic Surgical Approach to Microinject the Caudal Brainstem and Upper Cervical Spinal Cord via the Cisterna Magna in Mice

Stereotaxic surgery to target brain sites in mice is commonly guided by skull landmarks. Access is then obtained via burr holes drilled through the skull. This standard approach can be challenging for targets in the caudal brainstem and upper cervical cord due to specific anatomical challenges as these sites are remote from skull landmarks, leading to imprecision. Here we outline an alternative stereotaxic approach via the cisterna magna that has been used to target discrete regions of interest in the caudal brainstem and upper cervical cord. The cisterna magna extends from the occipital bone to the atlas (i.e., the second vertebral bone), is filled with cerebrospinal fluid, and is covered by dura mater. This approach provides a reproducible route of access to select central nervous system (CNS) structures that are otherwise hard to reach due to anatomical barriers. Furthermore, it allows for direct visualization of brainstem landmarks in close proximity to the target sites, increasing accuracy when delivering small injection volumes to restricted regions of interest in the caudal brainstem and upper cervical cord. Finally, this approach provides an opportunity to avoid the cerebellum, which can be important for motor and sensorimotor studies.

Stereotaxic Surgical Approach to Microinject the Caudal Brainstem and Upper Cervical Spinal Cord via the Cisterna Magna in Mice

Stereotaxic surgery to target brain sites in mice commonly involves access through the skull bones and is guided by skull landmarks. Here we outline an alternative stereotaxic approach to target the caudal brainstem and upper cervical spinal cord via the cisterna magna that relies on direct visualization of brainstem landmarks.

Stereotaxic surgery to target brain sites in mice is commonly guided by skull landmarks. Access is then obtained via burr holes drilled through the skull. ...