The authors acknowledge Lichun Zhang for helping to establish the method and the Fluorescence Microscopy Service Unit, Carl von Ossietzky University of Oldenburg, for the use of the imaging facilities. This research was funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Germany&#39;s Excellence Strategy -EXC 2177/1.

<ol>
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The authors have no conflicts of interest to declare.

With the method outlined in this protocol, it is possible to immunolabel IHCs and synaptic structures in cochleae from young adult and aged gerbils, identify presumed functional synapses by co-localization of pre- and postsynaptic elements, allocate them to individual IHCs, and quantify their number, volume, and location.&#160;The antibodies used in this approach also labeled outer hair cells (OHCs; myoVIIa) and their presynaptic ribbons. Furthermore, a viable alternative for immunolabeling of both IHCs and OHCs is an an...

Age-related hearing loss is one of the world's most prevalent diseases that affects more than one-third of the world's population aged 65 years and older1. The underlying causes are still under debate and actively being investigated but may include the loss of the specialized synapses connecting inner hair cells (IHCs) with afferent auditory nerve fibers2. These ribbon synapses comprise a presynaptic structure that has vesicles filled with the neurotransmitter glutamate tethered to it, as well as postsynaptic &#945;-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) glutamate receptors3,4,5. In the gerbil, ~20 afferent auditory nerve fibers contact one IHC6,7,8. Fibers on the IHC facing the modiolus are opposed to large synaptic ribbons, while the fibers connecting on the pillar side of the IHC face small synaptic ribbons (i.e., in cats9, gerbils7, guinea pigs10, and mice3,11,12,13,14). Furthermore, in the gerbil, the size of the presynaptic ribbons and the postsynaptic glutamate patches are positively correlated7,14. Fibers that are opposed to large ribbons on the modiolar side of the IHC are small in caliber and have low spontaneous rates and high thresholds15. There is evidence that low spontaneous rate fibers are more vulnerable to noise exposure10 and ototoxic drugs16 than high-spontaneous low-threshold fibers, which are located on the pillar side of IHCs15. 
The loss of ribbon synapses is the earliest degenerative event in cochlear neural age-related hearing loss, while the loss of spiral ganglion cells and their afferent auditory nerve fibers lags behind17,18. Electrophysiological correlates include recordings of auditory brainstem responses17 and compound action potentials8; however, these do not reflect the subtleties of synapse loss, since low spontaneous rate fibers do not contribute to these measures16. More promising electrophysiological metrics are the mass potential-derived neural index19 and the peristimulus time response20. However, these are only reliable if the animal has no other cochlear pathologies, beyond auditory nerve fiber loss, that affect the activity of the remaining auditory nerve fibers8. Furthermore, behaviorally assessed thresholds in the gerbil were not correlated with synapse numbers21. Therefore, reliable quantification of surviving ribbon synapses and, thus, the number of functional auditory nerve fibers is only possible by direct examination of the cochlear tissue.
The Mongolian gerbil (Meriones unguiculatus) is a suitable animal model for studying age-related hearing loss. It has a short life span, has low-frequency hearing similar to humans, is easy to maintain, and shows similarities to human pathologies related to age-related hearing loss2,22,23,24. Gerbils are considered aged when they reach 36 months of age, which is near the end of their average life span22. Importantly, an age-related loss of ribbon synapses has been demonstrated in gerbils raised and aged in quiet environments8,21. 
Here, a protocol to immunolabel, dissect, and analyze cochleae from gerbils of different ages, from young adults to aged, is presented. Antibodies directed against components of the presynapse (CtBP2), postsynaptic glutamate receptor patches (GluA2), and IHCs (myoVIIa) are used. An autofluorescence quencher is applied that reduces the background in aged cochleae and leaves the fluorescence signal intact. Further, a description is given of how to dissect the cochlea to examine both the sensory epithelium and the stria vascularis. The cochlear length is measured to enable the selection of distinct cochlear locations that correspond to specific best frequencies25. Quantification of synapse numbers is carried out with the freely available software ImageJ26. Additional quantification of synapse volumes and locations within the individual HC is performed with software custom written in Matlab. This software is not made publicly available, as the authors lack the resources to provide professional documentation and support.

<table><tbody><tr><td>Albumin Fraction V biotin-free</td><td>Carl Roth</td><td>0163.2</td><td></td></tr><tr><td>anti-CtBP2 (IgG1 monoclonal mouse)</td><td>BD Biosciences, Eysins</td><td>612044</td><td></td></tr><tr><td>anti-GluA2 (IgG2a monoclonal mouse)</td><td>Millipore</td><td>MAB39</td><td></td></tr><tr><td>anti-mouse (IgG1)-AF 488</td><td>Molecular Probes Inc.</td><td>A21121</td><td></td></tr><tr><td>anti-MyosinVIIa (IgG polyclonal rabbit)</td><td>Proteus Biosciences</td><td>25e6790</td><td></td></tr><tr><td>Blade Holder &amp;amp; Breaker - Flat Jaws</td><td>Fine Science Tools</td><td>10052-11</td><td></td></tr><tr><td>Bonn Artery Scissors - Ball Tip</td><td>Fine Science Tools</td><td>14086-09</td><td></td></tr><tr><td>Coverslip thickness 1.5H, 24 x 60 mm</td><td>Carl Roth</td><td>LH26.1</td><td></td></tr><tr><td>Disposable Surgical Blade</td><td>Henry Schein</td><td>0473</td><td></td></tr><tr><td>donkey anti-rabbit (IgG)-AF647</td><td>Life Technologies-Molecular Probes</td><td>A-31573</td><td></td></tr><tr><td>Dumont #5 - Fine Forceps</td><td>Fine Science Tools</td><td>11254-20</td><td></td></tr><tr><td>Dumont #5SF Forceps</td><td>Fine Science Tools</td><td>11252-00</td><td></td></tr><tr><td>Ethanol, absolute 99.8%</td><td>Fisher Scientific</td><td>12468750</td><td></td></tr><tr><td>Ethylenediaminetetraacetic acid</td><td>Carl Roth</td><td>8040.2</td><td></td></tr><tr><td>Excel</td><td>Microsoft Corporation</td><td></td><td></td></tr><tr><td>Feather Double Edge Blade</td><td>PLANO</td><td>112-9</td><td></td></tr><tr><td>G19 Cannula</td><td>Henry Schein</td><td>9003633</td><td></td></tr><tr><td>goat anti-mouse (IgG2a)-AF568</td><td>Invitrogen</td><td>A-21134</td><td></td></tr><tr><td>Heparin</td><td>Ratiopharm</td><td>N68542.04</td><td></td></tr><tr><td>Huygens Essentials</td><td>Scientific Volume Imaging</td><td></td><td></td></tr><tr><td>ImageJ</td><td>Fiji</td><td></td><td></td></tr><tr><td>Immersol, Immersion oil 518F</td><td>Carl Zeiss</td><td>10539438</td><td></td></tr><tr><td>Intrafix Primeline Classic, 150 cm (mit Datamatrix Code auf der Sterilverpackung)</td><td>Braun</td><td>4062957E</td><td></td></tr><tr><td>ISM596D</td><td>Ismatec</td><td></td><td>peristaltic pump</td></tr><tr><td>KL 1600 LED</td><td>Schott</td><td>150.600</td><td>light source for stereomicroscope</td></tr><tr><td>Leica Application suite X</td><td>Leica Microsystem CMS GmbH</td><td></td><td></td></tr><tr><td>Leica TCS SP8 system</td><td>Leica Microsystem CMS GmbH</td><td></td><td></td></tr><tr><td>Matlab</td><td>The Mathworks Inc.</td><td></td><td></td></tr><tr><td>Mayo Scissors Tungston Carbide ToghCut</td><td>Fine Science Tools</td><td>14512-17</td><td></td></tr><tr><td>Mini-100 Orbital-Genie</td><td>Scientific Industries</td><td>SI-M100</td><td>for use in cold environment</td></tr><tr><td>Narcoren (pentobarbital)</td><td>Boehringer Ingelheim Vetmedica GmbH</td><td></td><td></td></tr><tr><td>Nikon Eclipse Ni-Ei</td><td>Nikon</td><td></td><td></td></tr><tr><td>NIS Elements</td><td>Nikon Europe B.V.</td><td></td><td></td></tr><tr><td>Paraformaldehyde</td><td>Carl Roth</td><td>0335.3</td><td></td></tr><tr><td>Petri dish without vents</td><td>Avantor VWR</td><td>390-1375</td><td></td></tr><tr><td>&lt;strong&gt;Phosphate-buffered saline:&lt;/strong&gt;</td><td></td><td></td><td></td></tr><tr><td>Disodium phosphate</td><td>AppliChem</td><td>A1046</td><td></td></tr><tr><td>Monopotassium phosphate</td><td>Carl Roth</td><td>3904.1</td><td></td></tr><tr><td>Potassium chloride</td><td>Carl Roth</td><td>6781.1</td><td></td></tr><tr><td>Sodium chloride</td><td>Sigma Aldrich</td><td>31434-M</td><td></td></tr><tr><td>Screw Cap Containers</td><td>Sarstedt</td><td>75.562.300</td><td></td></tr><tr><td>Sodium azide</td><td>Carl Roth</td><td>K305.1</td><td></td></tr><tr><td>Student Adson Forceps</td><td>Fine Science Tools</td><td>91106-12</td><td></td></tr><tr><td>Student Halsted-Mosquito Hemostat</td><td>Fine Science Tools</td><td>91308-12</td><td></td></tr><tr><td>Superfrost Adhesion Microscope Slides</td><td>Epredia</td><td>J1800AMNZ</td><td></td></tr><tr><td>Triton&amp;nbsp; X</td><td>Carl Roth</td><td>3051.2</td><td></td></tr><tr><td>TrueBlack Lipofuscin Autofluorescence Quencher</td><td>Biotium</td><td>23007</td><td></td></tr><tr><td>Vannas Spring Scissors, 3mm</td><td>Fine Science Tools</td><td>15000-00</td><td></td></tr><tr><td>Vectashield Antifade Mounting Medium</td><td>Vector Laboratories</td><td>H-1000</td><td></td></tr><tr><td>Vibrax VXR basic</td><td>IKA</td><td>0002819000</td><td></td></tr><tr><td>VX 7 Dish attachment for Vibrax VXR basic</td><td>IKA</td><td>953300</td><td></td></tr><tr><td>Wild TYP 355110 (Stereomicroscope)</td><td>Wild Heerbrugg</td><td></td><td>not available anymore</td></tr></tbody></table>

immunolabeling and counting ribbon synapses in young adult and aged gerbil cochleae

The loss of ribbon synapses connecting inner hair cells and afferent auditory nerve fibers is assumed to be one cause of age-related hearing loss. The most common method for detecting the loss of ribbon synapses is immunolabeling because it allows for quantitative sampling from several tonotopic locations in an individual cochlea. However, the structures of interest are buried deep inside the bony cochlea. Gerbils are used as an animal model for age-related hearing loss. Here, routine protocols for fixation, immunolabeling gerbil cochlear whole mounts, confocal imaging, and quantifying ribbon synapse numbers and volumes are described. Furthermore, the particular challenges associated with obtaining good material from valuable aging individuals are highlighted. 
Gerbils are euthanized and either perfused cardiovascularly, or their tympanic bullae are carefully dissected out of the skull. The cochleae are opened at the apex and base and directly transferred to the fixative. Irrespective of the initial method, the cochleae are postfixed and subsequently decalcified. The tissue is then labeled with primary antibodies against pre- and postsynaptic structures and hair cells. Next, the cochleae are incubated with secondary fluorescence-tagged antibodies that are specific against their respective primary ones. The cochleae of aged gerbils are then treated with an autofluorescence quencher to reduce the typically substantial background fluorescence of older animals' tissues. 
Finally, cochleae are dissected into 6-11 segments. The entire cochlear length is reconstructed such that specific cochlear locations can be reliably determined between individuals. Confocal image stacks, acquired sequentially, help visualize hair cells and synapses at the chosen locations. The confocal stacks are deconvolved, and the synapses are either counted manually using ImageJ, or more extensive quantification of synaptic structures is carried out with image analysis procedures custom-written in Matlab.

Cochleae were either harvested after cardiovascular perfusion with fixative of the whole animal or rapidly dissected after euthanizing the animal and immersion-fixed. With the latter method, the IHCs stayed in place during dissection, whereas, in cases of unsuccessful perfusion and thus insufficiently fixed tissue, the sensory epithelium was often destroyed. Note that the authors encountered cases where fixation of the cochleae after transcardial perfusion was insufficient while fixation of the brain was still adequate. ...

Watch this Scientific Journal Video about Immunolabeling and Counting Ribbon Synapses in Young Adult and Aged Gerbil Cochleae at JoVE.com

Immunolabeling and Counting Ribbon Synapses in Young Adult and Aged Gerbil Cochleae

A protocol for processing young adult and aged gerbil cochleae by immunolabeling the afferent synaptic structures and hair cells, quenching autofluorescence in aged tissue, dissecting and estimating the length of the cochleae, and quantifying the synapses in image stacks obtained with confocal imaging is presented.

The loss of ribbon synapses connecting inner hair cells and afferent auditory nerve fibers is assumed to be one cause of age-related hearing loss. The ...

immunolabeling-counting-ribbon-synapses-young-adult-aged-gerbil

Universidad de Cartagena UDEC

Research

JoVE Journal

Neuroscience

2.4K Views.  Carl von Ossietzky University Oldenburg. A protocol for processing young adult and aged gerbil cochleae by immunolabeling the afferent synaptic structures and hair cells, quenching autofluorescence in aged tissue, dissecting and estimating the length of the cochleae, and quantifying the synapses in image stacks obtained with confocal imaging is presented.

Video: Immunolabeling and Counting Ribbon Synapses in Young Adult and Aged Gerbil Cochleae

DiOLISTIC Labeling of Neurons from Rodent and Non-human Primate Brain Slices

DiOLISTIC staining uses the gene gun to introduce fluorescent dyes, such as DiI, into neurons of brain slices (Gan et al., 2009; O'Brien and Lummis, 2007; Gan et al., 2000). Here we provide a detailed description of each step required together with exemplary images of good and bad outcomes that will help when setting up the technique. In our experience, a few steps proved critical for the successful application of DiOLISTICS. These considerations include the quality of the DiI-coated bullets, the extent of fixative exposure, and the concentration of detergent used in the incubation solutions. Tips and solutions for common problems are provided. This is a versatile labeling technique that can be applied to multiple animal species at a wide range of ages. Unlike other fluorescent labeling techniques that are limited to preparations from young animals or restricted to mice because they rely on the expression of a fluorescent transgene, DiOLISTIC labeling can be applied to animals of all ages, species and genotypes and it can be used in combination with immunostaining to identify a specific subpopulation of cells. Here we demonstrate the use of DiOLISTICS to label neurons in brain slices from adult mice and adult non-human primates with the purpose of quantifying dendrite branching and dendritic spine morphology.

We demonstrate the use of the gene gun to introduce fluorescent dyes, such as DiI, into neurons in brain slices from rodents and non-human primates of different ages. In this particular case, we use adult mice (3-6 months old) and adult cynomologus monkeys (9-15 years old). This technique, originally described by the laboratory of Dr. Lichtman (Gan et al., 2000), is well suited for the study of dendritic branching and dendritic spine morphology and can be combined with traditional immunostaining, if detergents are kept at a low concentration.

DiOLISTIC staining uses the gene gun to introduce fluorescent dyes, such as DiI, into neurons of brain slices (Gan et al., 2009; O'Brien and Lummis, 2007; ...

Quantifying Synapses: an Immunocytochemistry-based Assay to Quantify Synapse Number

One of the most important goals in neuroscience is to understand the molecular cues that instruct early stages of synapse formation. As such it has become imperative to develop objective approaches to quantify changes in synaptic connectivity. Starting from sample fixation, this protocol details how to quantify synapse number both in dissociated neuronal culture and in brain sections using immunocytochemistry. Using compartment-specific antibodies, we label presynaptic terminals as well as sites of postsynaptic specialization. We define synapses as points of colocalization between the signals generated by these markers. The number of these colocalizations is quantified using a plug in Puncta Analyzer (written by Bary Wark, available upon request, c.eroglu@cellbio.duke.edu) under the ImageJ analysis software platform. The synapse assay described in this protocol can be applied to any neural tissue or culture preparation for which you have selective pre- and postsynaptic markers. This synapse assay is a valuable tool that can be widely utilized in the study of synaptic development.

This protocol details how to quantify synapse number both in dissociated neuronal culture and in brain sections using immunocytochemistry. Using compartment-specific antibodies, we label presynaptic terminals as well as sites of postsynaptic specialization. We define synapses as points of colocalization between the signals generated by these markers.

One of the most important goals in neuroscience is to understand the molecular cues that instruct early stages of synapse formation. As such it has become ...

Postsynaptic Recordings at Afferent Dendrites Contacting Cochlear Inner Hair Cells: Monitoring Multivesicular Release at a Ribbon Synapse

The afferent synapse between the inner hair cell (IHC) and the auditory nerve fiber provides an electrophysiologically accessible site for recording the postsynaptic activity of a single ribbon synapse 1-4. Ribbon synapses of sensory cells release neurotransmitter continuously, the rate of which is modulated in response to graded changes in IHC membrane potential 5. Ribbon synapses have been shown to operate by multivesicular release, where multiple vesicles can be released simultaneously to evoke excitatory postsynaptic currents (EPSCs) of varying amplitudes 1, 4, 6-11. Neither the role of the presynaptic ribbon, nor the mechanism underlying multivesicular release is currently well understood.
The IHC is innervated by 10-20 auditory nerve fibers, and every fiber contacts the IHC with a unmyelinated single ending to form a single ribbon synapse. The small size of the afferent boutons contacting IHCs (approximately 1 &mu;m in diameter) enables recordings with exceptional temporal resolution to be made. Furthermore, the technique can be adapted to record from both pre- and postsynaptic cells simultaneously, allowing the transfer function at the synapse to be studied directly 2. This method therefore provides a means by which fundamental aspects of neurotransmission can be studied, from multivesicular release to the elusive function of the ribbon in sensory cells.

Whole-cell patch-clamp recordings from auditory nerve fiber dendrites at the inner hair cell ribbon synapse in the mammalian cochlea.

The afferent synapse between the inner hair cell (IHC) and the auditory nerve fiber provides an electrophysiologically accessible site for recording the ...

Post-embedding Immunogold Labeling of Synaptic Proteins in Hippocampal Slice Cultures

Immunoelectron microscopy is a powerful tool to study biological molecules at the subcellular level. Antibodies coupled to electron-dense markers such as colloidal gold can reveal the localization and distribution of specific antigens in various tissues1. The two most widely used techniques are pre-embedding and post-embedding techniques. In pre-embedding immunogold-electron microscopy (EM) techniques, the tissue must be permeabilized to allow antibody penetration before it is embedded. These techniques are ideal for preserving structures but poor penetration of the antibody (often only the first few micrometers) is a considerable drawback2. The post-embedding labeling methods can avoid this problem because labeling takes place on sections of fixed tissues where antigens are more easily accessible. Over the years, a number of modifications have improved the post-embedding methods to enhance immunoreactivity and to preserve ultrastructure3-5.
Tissue fixation is a crucial part of EM studies. Fixatives chemically crosslink the macromolecules to lock the tissue structures in place. The choice of fixative affects not only structural preservation but also antigenicity and contrast. Osmium tetroxide (OsO4), formaldehyde, and glutaraldehyde have been the standard fixatives for decades, including for central nervous system (CNS) tissues that are especially prone to structural damage during chemical and physical processing. Unfortunately, OsO4 is highly reactive and has been shown to mask antigens6, resulting in poor and insufficient labeling. Alternative approaches to avoid chemical fixation include freezing the tissues. But these techniques are difficult to perform and require expensive instrumentation. To address some of these problems and to improve CNS tissue labeling, Phend et al. replaced OsO4 with uranyl acetate (UA) and tannic acid (TA), and successfully introduced additional modifications to improve the sensitivity of antigen detection and structural preservation in brain and spinal cord tissues7. We have adopted this osmium-free post-embedding method to rat brain tissue and optimized the immunogold labeling technique to detect and study synaptic proteins.
We present here a method to determine the ultrastructural localization of synaptic proteins in rat hippocampal CA1 pyramidal neurons. We use organotypic hippocampal cultured slices. These slices maintain the trisynaptic circuitry of the hippocampus, and thus are especially useful for studying synaptic plasticity, a mechanism widely thought to underlie learning and memory. Organotypic hippocampal slices from postnatal day 5 and 6 mouse/rat pups can be prepared as described previously8, and are especially useful to acutely knockdown or overexpress exogenous proteins. We have previously used this protocol to characterize neurogranin (Ng), a neuron-specific protein with a critical role in regulating synaptic function8,9 . We have also used it to characterize the ultrastructural localization of calmodulin (CaM) and Ca2+/CaM-dependent protein kinase II (CaMKII)10. As illustrated in the results, this protocol allows good ultrastructural preservation of dendritic spines and efficient labeling of Ng to help characterize its distribution in the spine8. Furthermore, the procedure described here can have wide applicability in studying many other proteins involved in neuronal functions.

The localization and distribution of proteins provide important information for understanding their cellular functions. The superior spatial resolution of electron microscopy (EM) can be used to determine the subcellular localization of a given antigen following immunohistochemistry. For tissues of the central nervous system (CNS), preserving structural integrity while maintaining antigenicity has been especially difficult in EM studies. Here, we adopt a procedure that has been used to preserve structures and antigens in the CNS to study and characterize synaptic proteins in rat hippocampal CA1 pyramidal neurons.

Immunoelectron microscopy is a powerful tool to study biological molecules at the subcellular level. Antibodies coupled to electron-dense markers such as ...

Immunohistochemistry and Multiple Labeling with Antibodies from the Same Host Species to Study Adult Hippocampal Neurogenesis

Adult neurogenesis is a highly regulated, multi-stage process in which new neurons are generated from an activated neural stem cell via increasingly committed intermediate progenitor subtypes. Each of these subtypes expresses a set of specific molecular markers that, together with specific morphological criteria, can be used for their identification. Typically, immunofluorescent techniques are applied involving subtype-specific antibodies in combination with exo- or endogenous proliferation markers. We herein describe immunolabeling methods for the detection and quantification of all stages of adult hippocampal neurogenesis. These comprise the application of thymidine analogs, transcardial perfusion, tissue processing, heat-induced epitope retrieval, ABC immunohistochemistry, multiple indirect immunofluorescence, confocal microscopy and cell quantification. Furthermore we present&#160;a sequential multiple immunofluorescence protocol which circumvents problems usually arising from the need of using primary antibodies raised in the same host species. It allows an accurate identification of all hippocampal progenitor subtypes together with a proliferation marker within a single section. These techniques are a powerful tool to study the regulation of different progenitor subtypes in parallel, their involvement in brain pathologies and their role in specific brain functions.

This video article illustrates a comprehensive protocol to detect and quantify all stages of adult hippocampal neurogenesis within the same tissue section. We elaborated a method to overcome the limitations of indirect multiple immunofluorescence that arise when suitable antibodies from different host species are unavailable.

Adult neurogenesis is a highly regulated, multi-stage process in which new neurons are generated from an activated neural stem cell via increasingly ...

Whole Mount Dissection and Immunofluorescence of the Adult Mouse Cochlea

The organ of Corti, housed in the cochlea of the inner ear, contains mechanosensory hair cells and surrounding supporting cells which are organized in a spiral shape and have a tonotopic gradient for sound detection. The mouse cochlea is approximately 6 mm long and often divided into three turns (apex, middle, and base) for analysis. To investigate cell loss, cell division, or mosaic gene expression, the whole mount or surface preparation of the cochlea is useful. This dissection method allows visualization of all cells within the organ of Corti when combined with immunostaining and confocal microscopy to image cells at different planes in the z-axis. Multiple optical cross-sections can also be obtained from these z-stack images. In addition, the whole mount dissection method can be used for scanning electron microscopy, although a different fixation method is needed. Here, we present a method to isolate the organ of Corti as three intact cochlear turns (apex, middle, and base). This method can be used for mice ranging from one week of age through adulthood and differs from the technique used for neonatal samples where calcification of the cochlea is incomplete. A slightly modified version can be used for dissection of the rat cochlea. We also demonstrate a procedure for immunostaining with fluorescently tagged antibodies.

We present a method to isolate the adult organ of Corti as three intact cochlear turns (apex, middle, and base). We also demonstrate a procedure for immunostaining with fluorescently tagged antibodies. Together these techniques allow the study of hair cells, supporting cells, and other cell types found in the cochlea.

The organ of Corti, housed in the cochlea of the inner ear, contains mechanosensory hair cells and surrounding supporting cells which are organized in a ...

Cryosectioning and Immunostaining Mouse Inner Ear Tissue: From Embryonic to Adult Stages

This protocol details general histology methods for preparing inner ear samples from embryonic, neonatal, and adult mice. The purpose of this protocol is to provide a straightforward and standardized method for inner ear tissue processing for researchers, possibly new to the field, interested in working with the mouse cochlea. Included here are protocols for dissection, fixation, embedding, cryosectioning, and immunostaining. Section immunostaining is one of the best methods for examining individual cells within the context of the entire cochlea.
Key steps include dissecting the inner ear away from the skull, fixing the tissue using 4% paraformaldehyde, embedding with Optimal Cutting Temperature compound, cryosectioning, and immunostaining with antibodies targeting specific proteins expressed by the cochlea.
Included in our methods are special considerations made for the cochlea given its 
shape and structure.&#160;Reasonably good focus and dissection skills are needed, as tissue damage can affect the quality of immunostaining and consistency among samples. However, with the procedures we outline, most users can be trained in a few weeks to make beautiful preparations. Overall, this protocol offers a valuable way to promote research to understand auditory development, function, and disease in mouse models.

This protocol, intended for novice users of mouse inner ear tissue, comprehensively details steps for processing mouse inner ears at different developmental stages for section immunostaining.

This protocol details general histology methods for preparing inner ear samples from embryonic, neonatal, and adult mice. The purpose of this protocol is ...

Developmental Biology

Morphological and Functional Evaluation of Ribbon Synapses at Specific Frequency Regions of the Mouse Cochlea

Cochlear inner hair cells (IHCs) transmit acoustic signals to spiral ganglion neurons (SGNs) through ribbon synapses. Several experimental studies have indicated that hair cell synapses may be the initial targets in sensorineural hearing loss (SNHL). Such studies have proposed the concept of cochlear &#34;synaptopathy&#34;, which refers to alterations in ribbon synapse number, structure, or function that result in abnormal synaptic transmission between IHCs and SGNs. While cochlear synaptopathy is irreversible, it does not affect the hearing threshold. In noise-induced experimental models, restricted damage to IHC synapses in select frequency regions is employed to identify the environmental factors that specifically cause synaptopathy, as well as the physiological consequences of disturbing this inner ear circuit. Here, we present a protocol for analyzing cochlear synaptic morphology and function at a specific frequency region in adult mice. In this protocol, cochlear localization of specific frequency regions is performed using place-frequency maps in conjunction with cochleogram data, following which the morphological characteristics of ribbon synapses are evaluated via synaptic immunostaining. The functional status of ribbon synapses is then determined based on the amplitudes of auditory brainstem response (ABR) wave I. The present report demonstrates that this approach can be used to deepen our understanding of the pathogenesis and mechanisms of synaptic dysfunction in the cochlea, which may aid in the development of novel therapeutic interventions.

This manuscript describes an experimental protocol for evaluating the morphological characteristics and functional status of ribbon synapses in normal mice. The present model is also suitable for noise-induced and age-related cochlear synaptopathy-restricted models. The correlative results of previous mouse studies are also discussed.

Cochlear inner hair cells (IHCs) transmit acoustic signals to spiral ganglion neurons (SGNs) through ribbon synapses. Several experimental studies have ...

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 ...

Imaging the Aging Cochlea with Light-Sheet Fluorescence Microscopy

Deafness is the most common sensory impairment, affecting approximately 5% or 430 million people worldwide as per the World Health Organization1. Aging or presbycusis is a primary cause of sensorineural hearing loss and is characterized by damage to hair cells, spiral ganglion neurons (SGNs), and the stria vascularis. These structures reside within the cochlea, which has a complex, spiral-shaped anatomy of membranous tissues suspended in fluid and surrounded by bone. These properties make it technically difficult to investigate and quantify histopathological changes. To address this need, we developed a light-sheet microscope (TSLIM) that can image and digitize the whole cochlea to facilitate the study of structure-function relationships in the inner ear. Well-aligned serial sections of the whole cochlea result in a stack of images for three-dimensional (3D) volume rendering and segmentation of individual structures for 3D visualization and quantitative analysis (i.e., length, width, surface, volume, and number). Cochleae require minimal processing steps (fixation, decalcification, dehydration, staining, and optical clearing), all of which are compatible with subsequent high-resolution imaging by scanning and transmission electron microscopy. Since all the tissues are present in the stacks, each structure can be assessed individually or relative to other structures. In addition, since imaging uses fluorescent probes, immunohistochemistry and ligand binding can be used to identify specific structures and their 3D volume or distribution within the cochlea. Here we used TSLIM to examine cochleae from aged mice to quantify the loss of hair cells and spiral ganglion neurons. In addition, advanced analyses (e.g., cluster analysis) were used to visualize local reductions of spiral ganglion neurons in Rosenthal&#39;s canal along its 3D volume. These approaches demonstrate TSLIM microscopy&#39;s ability to quantify structure-function relationships within and between cochleae.

A light-sheet microscope was developed to image and digitize whole cochlea.

Deafness is the most common sensory impairment, affecting approximately 5% or 430 million people worldwide as per the World Health Organization1. Aging or ...