Cryoembedding and sectioning of cochleas for immunocytochemistry and in situ hybridization

A guide to preclinical evaluation of hydrogel-based devices for treatment of cartilage lesions

The drive to develop cartilage implants for the treatment of major defects in the musculoskeletal system has resulted in a major research thrust towards developing biomaterial devices for cartilage repair. Investigational devices for the restoration of articular cartilage are considered as significant risk materials by regulatory bodies and therefore proof of efficacy and safety prior to clinical testing represents a critical phase of the multidisciplinary effort to bridge the gap between bench and bedside. To date, review articles have thoroughly covered different scientific facets of cartilage engineering paradigm, but surprisingly, little attention has been given to the preclinical considerations revolving around the validation of a biomaterial implant. Considering hydrogel-based cartilage products as an example, the present review endeavors to provide a summary of the critical prerequisites that such devices should meet for cartilage repair, for successful implantation and subsequent preclinical validation prior to clinical trials. Considerations pertaining to the choice of appropriate animal model, characterization techniques for the quantitative and qualitative outcome measures, as well as concerns with respect to GLP practices are also extensively discussed. This article is not meant to provide a systematic review, but rather to introduce a device validation-based roadmap to the academic investigator, in anticipation of future healthcare commercialization. STATEMENT OF SIGNIFICANCE: There are significant challenges around translation of in vitro cartilage repair strategies to approved therapies. New biomaterial-based devices must undergo exhaustive investigations to ensure their safety and efficacy prior to clinical trials. These considerations are required to be applied from early developmental stages. Although there are numerous research works on cartilage devices and their in vivo evaluations, little attention has been given into the preclinical pathway and the corresponding approval processes. With a focus on hydrogel devices to concretely illustrate the preclinical path, this review paper intends to highlight the various considerations regarding the preclinical validation of hydrogel devices for cartilage repair, from regulatory considerations, to implantation strategies, device performance aspects and characterizations.

An enhanced antioxidant strategy of astaxanthin encapsulated in ROS-responsive nanoparticles for combating cisplatin-induced ototoxicity

Background

Excessive accumulation of reactive oxygen species (ROS) has been documented as the crucial cellular mechanism of cisplatin-induced ototoxicity. However, numerous antioxidants have failed in clinical studies partly due to inefficient drug delivery to the cochlea. A drug delivery system is an attractive strategy to overcome this drawback.

Methods and results

In the present study, we proposed the combination of antioxidant astaxanthin (ATX) and ROS-responsive/consuming nanoparticles (PPS-NP) to combat cisplatin-induced ototoxicity. ATX-PPS-NP were constructed by the self-assembly of an amphiphilic hyperbranched polyphosphoester containing thioketal units, which scavenged ROS and disintegrate to release the encapsulated ATX. The ROS-sensitivity was confirmed by ¹H nuclear magnetic resonance spectroscopy, transmission electron microscopy and an H₂O₂ ON/OFF stimulated model. Enhanced release profiles stimulated by H₂O₂ were verified in artificial perilymph, the HEI-OC1 cell line and guinea pigs. In addition, ATX-PPS-NP efficiently inhibited cisplatin-induced HEI-OC1 cell cytotoxicity and apoptosis compared with ATX or PPS-NP alone, suggesting an enhanced effect of the combination of the natural active compound ATX and ROS-consuming PPS-NP. Moreover, ATX-PPS-NP attenuated outer hair cell losses in cultured organ of Corti. In guinea pigs, NiRe-PPS-NP verified a quick penetration across the round window membrane and ATX-PPS-NP showed protective effect on spiral ganglion neurons, which further attenuated cisplatin-induced moderate hearing loss. Further studies revealed that the protective mechanisms involved decreasing excessive ROS generation, reducing inflammatory chemokine (interleukin-6) release, increasing antioxidant glutathione expression and inhibiting the mitochondrial apoptotic pathway.

Conclusions

Thus, this ROS-responsive nanoparticle encapsulating ATX has favorable potential in the prevention of cisplatin-induced hearing loss.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12951-022-01485-8.

The Cl--channel TMEM16A is involved in the generation of cochlear Ca2+ waves and promotes the refinement of auditory brainstem networks in mice

Before hearing onset (postnatal day 12 in mice), inner hair cells (IHCs) spontaneously fire action potentials, thereby driving pre-sensory activity in the ascending auditory pathway. The rate of IHC action potential bursts is modulated by inner supporting cells (ISCs) of Kölliker’s organ through the activity of the Ca²⁺-activated Cl^--channel TMEM16A (ANO1). Here, we show that conditional deletion of Ano1 (Tmem16a) in mice disrupts Ca²⁺ waves within Kölliker’s organ, reduces the burst-firing activity and the frequency selectivity of auditory brainstem neurons in the medial nucleus of the trapezoid body (MNTB), and also impairs the functional refinement of MNTB projections to the lateral superior olive. These results reveal the importance of the activity of Kölliker’s organ for the refinement of central auditory connectivity. In addition, our study suggests the involvement of TMEM16A in the propagation of Ca²⁺ waves, which may also apply to other tissues expressing TMEM16A.

Cochlear protection against noise exposure requires serotonin type 3A receptor via the medial olivocochlear system

The cochlear efferent feedback system plays important roles in auditory processing, including regulation of the dynamic range of hearing, and provides protection against acoustic trauma. These functions are performed through medial olivocochlear (MOC) neurons. However, the underlying cellular and molecular mechanisms are not fully understood. The serotonin type 3A (5-HT3A) receptor is widely expressed throughout the nervous system, which suggests important roles in various neural functions. However, involvement of the 5-HT3A receptor in the MOC system remains unclear. We used mice in this study and found that the 5-HT3A receptor was expressed in MOC neurons that innervated outer hair cells in the cochlea and was involved in the activation of MOC neurons by noise exposure. 5-HT3A receptor knockout impaired MOC functions, potentiated noise-induced hearing loss, and increased loss of ribbon synapses following noise exposure. Furthermore, 5-HT3 receptor agonist treatment alleviated the noise-induced hearing loss and loss of ribbon synapses, which enhanced cochlear protection provided by the MOC system. Our findings demonstrate that the 5-HT3A receptor plays fundamental roles in the MOC system and critically contributes to protection from noise-induced hearing impairment.

Scanning laser optical tomography in a neuropathic mouse model : Visualization of structural changes

BACKGROUND

In the field of hearing research a variety of imaging techniques are available to study molecular and cellular structures of the cochlea. Most of them are based on decalcifying, embedding, and cutting of the cochlea. By means of scanning laser optical tomography (SLOT), the complete cochlea can be visualized without cutting. The Ca_v1.3^-/- mice have already been extensively characterized and show structural changes in the inner ear. Therefore, they were used in this study as a model to investigate whether SLOT can detect structural differences in the murine cochlea.

MATERIALS AND METHODS

Whole undissected cochleae from Ca_v1.3^-/- and wild-type mice of various postnatal stages were immunostained and analyzed by SLOT. The results were compared to cochlea preparations that were immunostained and analyzed by fluorescence microscopy. In addition, cochlea preparations were stained with osmium tetraoxide.

RESULTS

Visualization by SLOT showed that the staining of nerve fibers at P27 in Ca_v1.3^-/- mice was almost absent compared to wild-type mice and earlier timepoints (P9). The analysis of cochlea preparations confirmed a reduction of the radial nerve fibers. In addition, a significantly reduced number of ribbon synapses per inner hair cell (IHC) at P20 and P27 in the apical part of the cochlea of Ca_v1.3^-/- mice was detected.

CONCLUSION

The visualization of whole non-dissected cochleae by SLOT is a suitable tool for the analysis of gross phenotypic changes, as demonstrated by means of the Ca_v1.3^-/- mouse model. For the analysis of finer structures of the cochlea, however, further methods must be used.

[Scanning laser optical tomography in a neuropathic mouse model : Visualization of structural changes. German version]

BACKGROUND

In the field of hearing research a variety of imaging techniques are available to study molecular and cellular structures of the cochlea. Most of them are based on decalcifying, embedding, and cutting of the cochlea. By means of scanning laser optical tomography (SLOT), the complete cochlea can be visualized without cutting. The Ca_v1.3^-/- mice have already been extensively characterized and show structural changes in the inner ear. Therefore, they were used in this study as a model to investigate whether SLOT can detect structural differences in the murine cochlea.

MATERIALS AND METHODS

Whole undissected cochleae from Ca_v1.3^-/- and wildtype mice of various postnatal stages were immunostained and analyzed by SLOT. The results were compared to cochlea preparations that were immunostained and analyzed by fluorescence microscopy. In addition, cochlea preparations were stained with osmium tetraoxide.

RESULTS

Visualization by SLOT showed that the staining of nerve fibers at P27 in Ca_v1.3^-/- mice was almost absent compared to wildtype mice and earlier timepoints (P9). The analysis of cochlea preparations confirmed a reduction of the radial nerve fibers. In addition, a significantly reduced number of ribbon synapses per inner hair cell (IHC) at P20 and P27 in the apical part of the cochlea of Ca_v1.3^-/- mice was detected.

CONCLUSION

The visualization of whole non-dissected cochleae by SLOT is a suitable tool for the analysis of gross phenotypic changes, as demonstrated by means of the Ca_v1.3^-/- mouse model. For the analysis of finer structures of the cochlea, however, further methods must be used.

Fibroblast growth factor 12 is expressed in spiral and vestibular ganglia and necessary for auditory and equilibrium function

We investigated fibroblast growth factor 12 (FGF12) as a transcript enriched in the inner ear by searching published cDNA library databases. FGF12 is a fibroblast growth factor homologous factor, a subset of the FGF superfamily. To date, its localisation and function in the inner ear have not been determined. Here, we show that FGF12 mRNA is localised in spiral ganglion neurons (SGNs) and the vestibular ganglion. We also show that FGF12 protein is localised in SGNs, the vestibular ganglion, and nerve fibres extending beneath hair cells. Moreover, we investigated FGF12 function in auditory and vestibular systems using Fgf12-knockout (FGF12-KO) mice generated with CRISPR/Cas9 technology. Our results show that the inner ear morphology of FGF12-KO mice is not significantly different compared with wild-type mice. However, FGF12-KO mice exhibited an increased hearing threshold, as measured by the auditory brainstem response, as well as deficits in rotarod and balance beam performance tests. These results suggest that FGF12 is necessary for normal auditory and equilibrium function.

Trans-Tympanic Drug Delivery for the Treatment of Ototoxicity

The systemic administration of protective agents to treat drug-induced ototoxicity is limited by the possibility that these protective agents could interfere with the chemotherapeutic efficacy of the primary drugs. This is especially true for the drug cisplatin, whose anticancer actions are attenuated by antioxidants which provide adequate protection against hearing loss. Other current or potential otoprotective agents could pose a similar problem, if administered systemically. The application of various biologicals or protective agents directly to the cochlea would allow for high levels of these agents locally with limited systemic side effects. In this report, we demonstrate a trans-tympanic method of delivery of various drugs or biological reagents to the cochlea, which should enhance basic science research on the cochlea and provide a simple way of directing the use of otoprotective agents in the clinics. This report details a method of trans-tympanic drug delivery and provides examples of how this technique has been used successfully in experimental animals to treat cisplatin ototoxicity.

Activation of SIRT3 by the NAD⁺ precursor nicotinamide riboside protects from noise-induced hearing loss

Intense noise exposure causes hearing loss by inducing degeneration of spiral ganglia neurites that innervate cochlear hair cells. Nicotinamide adenine dinucleotide (NAD(+)) exhibits axon-protective effects in cultured neurons; however, its ability to block degeneration in vivo has been difficult to establish due to its poor cell permeability and serum instability. Here, we describe a strategy to increase cochlear NAD(+) levels in mice by administering nicotinamide riboside (NR), a recently described NAD(+) precursor. We find that administration of NR, even after noise exposure, prevents noise-induced hearing loss (NIHL) and spiral ganglia neurite degeneration. These effects are mediated by the NAD(+)-dependent mitochondrial sirtuin, SIRT3, since SIRT3-overexpressing mice are resistant to NIHL and SIRT3 deletion abrogates the protective effects of NR and expression of NAD(+) biosynthetic enzymes. These findings reveal that administration of NR activates a NAD(+)-SIRT3 pathway that reduces neurite degeneration caused by noise exposure.

Eeyore: a novel mouse model of hereditary deafness

Animal models that recapitulate human disease are proving to be an invaluable tool in the identification of novel disease-associated genes. These models can improve our understanding of the complex genetic mechanisms involved in disease and provide a basis to guide therapeutic strategies to combat these conditions. We have identified a novel mouse model of non-syndromic sensorineural hearing loss with linkage to a region on chromosome 18. Eeyore mutant mice have early onset progressive hearing impairment and show abnormal structure of the sensory epithelium from as early as 4 weeks of age. Ultrastructural and histological analyses show irregular hair cell structure and degeneration of the sensory hair bundles in the cochlea. The identification of new genes involved in hearing is central to understanding the complex genetic pathways involved in the hearing process and the loci at which these pathways are interrupted in people with a genetic hearing loss. We therefore discuss possible candidate genes within the linkage region identified in eeyore that may underlie the deafness phenotype in these mice. Eeyore provides a new model of hereditary sensorineural deafness and will be an important tool in the search for novel deafness genes.

Intracochlear electrical stimulation suppresses apoptotic signaling in rat spiral ganglion neurons after deafening in vivo

OBJECTIVE

To establish the intracellular consequences of electrical stimulation to spiral ganglion neurons after deafferentation. Here we use a rat model to determine the effect of both low and high pulse rate acute electrical stimulation on activation of the proapoptotic transcription factor Jun in deafferented spiral ganglion neurons in vivo.

STUDY DESIGN

Experimental animal study.

SETTING

Hearing research laboratories of the University of Iowa Departments of Biology and Otolaryngology.

METHODS

A single electrode was implanted through the round window of kanamycin-deafened rats at either postnatal day 32 (P32, n = 24) or P60 (n = 22) for 4 hours of stimulation (monopolar, biphasic pulses, amplitude twice electrically evoked auditory brainstem response [eABR] threshold) at either 100 or 5000 Hz. Jun phosphorylation was assayed by immunofluorescence to quantitatively assess the effect of electrical stimulation on proapoptotic signaling.

RESULTS

Jun phosphorylation was reliably suppressed by 100 Hz stimuli in deafened cochleae of P32 but not P60 rats. This effect was not significant in the basal cochlear turns. Stimulation frequency may be consequential: 100 Hz was significantly more effective than was 5 kHz stimulation in suppressing phospho-Jun.

CONCLUSIONS

Suppression of Jun phosphorylation occurs in deafferented spiral ganglion neurons after only 4 hours of electrical stimulation. This finding is consistent with the hypothesis that electrical stimulation can decrease spiral ganglion neuron death after deafferentation.

Characterization of a novel ENU-generated myosin VI mutant mouse strain with congenital deafness and vestibular dysfunction

Myosin VI (Myo6) is known to play an important role in the mammalian auditory and vestibular systems. We have identified a novel N-ethyl-N-nitrosourea mutagenised mouse strain, charlie, carrying an intronic Myo6 splice site mutation. This mutation (IVS5+5G > A) results in skipping of exon 5, and is predicted to cause a frameshift and premature termination of the protein. We detected essentially no Myo6 transcript in tissue from charlie homozygous mutant mice (Myo6(chl/chl)). Myo6(chl/chl) mice exhibit vestibular dysfunction and profound hearing impairment when first tested at four weeks of age. Analysis of vestibular and cochlear hair cells by scanning electron microscopy and immunohistochemistry revealed highly disorganised hair bundles with irregular orientation and kinocilium position at postnatal stage P2-P3. Within a few weeks, the majority of hair cell stereocilia are missing, or fused and elongated, and degeneration of the sensory epithelium occurs. This novel mouse strain will be an important resource in elucidating the role myosin VI plays in the mammalian auditory system, as well as its non-auditory functions.

Load regulates bone formation and Sclerostin expression through a TGFβ-dependent mechanism

Bone continually adapts to meet changing physical and biological demands. Osteoblasts, osteoclasts, and osteocytes cooperate to integrate these physical and biochemical cues to maintain bone homeostasis. Although TGFβ acts on all three of these cell types to maintain bone homeostasis, the extent to which it participates in the adaptation of bone to mechanical load is unknown. Here, we investigated the role of the TGFβ pathway in load-induced bone formation and the regulation of Sclerostin, a mechanosensitive antagonist of bone anabolism. We found that mechanical load rapidly represses the net activity of the TGFβ pathway in osteocytes, resulting in reduced phosphorylation and activity of key downstream effectors, Smad2 and Smad3. Loss of TGFβ sensitivity compromises the anabolic response of bone to mechanical load, demonstrating that the mechanosensitive regulation of TGFβ signaling is essential for load-induced bone formation. Furthermore, sensitivity to TGFβ is required for the mechanosensitive regulation of Sclerostin, which is induced by TGFβ in a Smad3-dependent manner. Together, our results show that physical cues maintain bone homeostasis through the TGFβ pathway to regulate Sclerostin expression and the deposition of new bone.

Inner ear morphology is perturbed in two novel mouse models of recessive deafness

Human MYO7A mutations can cause a variety of conditions involving the inner ear. These include dominant and recessive non-syndromic hearing loss and syndromic conditions such as Usher syndrome. Mouse models of deafness allow us to investigate functional pathways involved in normal and abnormal hearing processes. We present two novel mouse models with mutations in the Myo7a gene with distinct phenotypes. The mutation in Myo7a^I487N/I487N ewaso is located within the head motor domain of Myo7a. Mice exhibit a profound hearing loss and manifest behaviour associated with a vestibular defect. A mutation located in the linker region between the coiled-coil and the first MyTH4 domains of the protein is responsible in Myo7a^F947I/F947I dumbo. These mice show a less severe hearing loss than in Myo7a^I487N/I487N ewaso; their hearing loss threshold is elevated at 4 weeks old, and progressively worsens with age. These mice show no obvious signs of vestibular dysfunction, although scanning electron microscopy reveals a mild phenotype in vestibular stereocilia bundles. The Myo7a^F947I/F947I dumbo strain is therefore the first reported Myo7a mouse model without an overt vestibular phenotype; a possible model for human DFNB2 deafness. Understanding the molecular basis of these newly identified mutations will provide knowledge into the complex genetic pathways involved in the maintenance of hearing, and will provide insight into recessively inherited sensorineural hearing loss in humans.

Viral vector tropism for supporting cells in the developing murine cochlea

Gene-based therapeutics are being developed as novel treatments for genetic hearing loss. One roadblock to effective gene therapy is the identification of vectors which will safely deliver therapeutics to targeted cells. The cellular heterogeneity that exists within the cochlea makes viral tropism a vital consideration for effective inner ear gene therapy. There are compelling reasons to identify a viral vector with tropism for organ of Corti supporting cells. Supporting cells are the primary expression site of connexin 26 gap junction proteins that are mutated in the most common form of congenital genetic deafness (DFNB1). Supporting cells are also primary targets for inducing hair cell regeneration. Since many genetic forms of deafness are congenital it is necessary to administer gene transfer-based therapeutics prior to the onset of significant hearing loss. We have used transuterine microinjection of the fetal murine otocyst to investigate viral tropism in the developing inner ear. For the first time we have characterized viral tropism for supporting cells following in utero delivery to their progenitors. We report the inner ear tropism and potential ototoxicity of three previously untested vectors: early-generation adenovirus (Ad5.CMV.GFP), advanced-generation adenovirus (Adf.11D) and bovine adeno-associated virus (BAAV.CMV.GFP). Adenovirus showed robust tropism for organ of Corti supporting cells throughout the cochlea but induced increased ABR thresholds indicating ototoxicity. BAAV also showed tropism for organ of Corti supporting cells, with preferential transduction toward the cochlear apex. Additionally, BAAV readily transduced spiral ganglion neurons. Importantly, the BAAV-injected ears exhibited normal hearing at 5 weeks of age when compared to non-injected ears. Our results support the use of BAAV for safe and efficient targeting of supporting cell progenitors in the developing murine inner ear.

An ENU-induced mutation of Cdh23 causes congenital hearing loss, but no vestibular dysfunction, in mice

Mutations in the human cadherin 23 (CDH23) gene cause deafness, neurosensory, autosomal recessive 12 (DFNB12) nonsyndromic hearing loss or Usher syndrome, type 1D (characterized by hearing impairment, vestibular dysfunction, and visual impairment). Reported waltzer mouse strains each harbor a Cdh23-null mutation and present with hearing loss and vestibular dysfunction. Two additional Cdh23 mouse mutants, salsa and erlong, each carry a homozygous Cdh23 missense mutation and have progressive hearing loss. We report the identification of a novel mouse strain, jera, with inherited hearing loss caused by an N-ethyl-N-nitrosourea-induced c.7079T>A mutation in the Cdh23 gene. The mutation generates a missense change, p.V2360E, in Cdh23. Affected mice have profound sensorineural deafness, with no vestibular dysfunction. The p.V2360E mutation is semidominant because heterozygous mice have milder and more progressive hearing loss in advanced age. The mutation affects a highly conserved Ca(2+)-binding motif in extracellular domain 22, thought to be important for Cdh23 structure and dimerization. Molecular modeling suggests that the Cdh23(V2360E/V2360E) mutation alters the structural conformation of the protein and affects Ca(2+)-binding properties. Similar to salsa mice, but in contrast to waltzer mice, hair bundle development is normal in jera and hearing loss appears to be due to the loss of tip links. Thus, jera is a novel mouse model for DFNB12.

Cytomegalovirus-induced sensorineural hearing loss with persistent cochlear inflammation in neonatal mice

Congenital cytomegalovirus (CMV) infection is the leading cause of sensorineural hearing loss (SNHL) in children. During murine (M)CMV-induced encephalitis, the immune response is important for both the control of viral dissemination and the clearance of virus from the brain. While the importance of CMV-induced SNHL has been described, the mechanisms surrounding its pathogenesis and the role of inflammatory responses remain unclear. This study presents a neonatal mouse model of profound SNHL in which MCMV preferentially infected both cochlear perilymphatic epithelial cells and spiral ganglion neurons. Interestingly, MCMV infection induced cochlear hair cell death by 21 days post-infection, despite a clear lack of direct infection of hair cells and the complete clearance of the virus from the cochlea by 14 dpi. Flow cytometric, immunohistochemical, and quantitative PCR analysis of MCMV-infected cochlea revealed a robust and chronic inflammatory response, including a prolonged increase in reactive oxygen species production by infiltrating macrophages. These data support a pivotal role for inflammation during MCMV-induced SNHL.

A mutation in synaptojanin 2 causes progressive hearing loss in the ENU-mutagenised mouse strain Mozart

Background

Hearing impairment is the most common sensory impairment in humans, affecting 1∶1,000 births. We have identified an ENU generated mouse mutant, Mozart, with recessively inherited, non-syndromic progressive hearing loss caused by a mutation in the synaptojanin 2 (Synj2), a central regulatory enzyme in the phosphoinositide-signaling cascade.

Methodology/Principal Findings

The hearing loss in Mozart is caused by a p.Asn538Lys mutation in the catalytic domain of the inositol polyphosphate 5-phosphatase synaptojanin 2. Within the cochlea, Synj2 mRNA expression was detected in the inner and outer hair cells but not in the spiral ganglion. Synj2^N538K mutant protein showed loss of lipid phosphatase activity, and was unable to degrade phosphoinositide signaling molecules. Mutant Mozart mice (Synj2^N538K/N538K) exhibited progressive hearing loss and showed signs of hair cell degeneration as early as two weeks of age, with fusion of stereocilia followed by complete loss of hair bundles and ultimately loss of hair cells. No changes in vestibular or neurological function, or other clinical or behavioral manifestations were apparent.

Conclusions/Significance

Phosphoinositides are membrane associated signaling molecules that regulate many cellular processes including cell death, proliferation, actin polymerization and ion channel activity. These results reveal Synj2 as a critical regulator of hair cell survival that is essential for hair cell maintenance and hearing function.

Up-regulation of Nob1 in the rat auditory system with noise-induced hearing loss

The Nob1 gene is assumed to be associated with transcription regulation and may play important roles in mediating some physiological and pathological functions. Here, the rats were randomized equally into experimental group and control group. In experimental group, all subjects were exposed to 4-kHz octave-band noise at 110 dB SPL, 8 h per day for 7 days consecutively. Auditory thresholds were assessed by auditory brainstem response, prior to and 1 h after the cessation of noise exposure. Then, we investigated for the first time the expression of Nob1 in noise-exposed and noise-unexposed rats by quantitative polymerase chain reaction. The distribution of Nob1 in rat cochlea was further examined by immunohistochemistry. The results indicated that the hearing threshold was significantly higher in the noise-injured group than in the uninjured group after noise exposure. Nob1 mRNA was present at higher levels in regions of the noise-injured cochlea. As for noise-exposed rats, Nob1 expression was positive in the inner and outer hair cells of the organ of Corti and spiral ganglion neurons, but it undetectable in the uninjured cochlea. Therefore, Nob1 may play an important role in auditory function following acoustic trauma and can be used as a new target for the treatment of noise-induced hearing loss.

Spontaneous association of glial cells with regrowing neurites in mixed cultures of dissociated spiral ganglia

Evidence from developmental and regeneration studies of the cochlea and other tissues gives reason to hypothesize a role for nonneural cells in the growth and regeneration of cochlear spiral ganglion nerve fibers. We examined the spontaneous associations of regrowing neurites and nonneural cells in mixed cultures of dissociated newborn mouse spiral ganglia. After 7 days in vitro, nonneural cells formed a confluent layer in the culture well. Regrowing neurites grew atop this layer, forming non-uniform patterns that were similar to those formed by endogenously expressed laminin-1, entactin and integrin beta4, but not fibronectin or tenascin. In cultures grown for 42 h and maintained in three different growth media, all regrowing neurites were preferentially associated with spindle-shaped nonneural cells. The spindle-shaped cells incorporated bromodeoxyuridine in culture and were immunoreactive for the proteins S100, laminin-1, laminin-2, SRY-related high-mobility-group box 10 transcription factor (Sox10), neurotrophin receptor (P75) and connexin29 but negative for fibronectin and glial fibrillary acidic protein. These cells existed in the culture within a much larger, general population of fibronectin positive cells. Immunolabeling of fixed cochleas from neonatal mice localized Sox10, P75 and connexin29, to peripheral nerve bundles. The observed expressions of protein markers and the bipolar, spindle shape of the neurite-associated cells indicate that they are derived in vitro from the original Schwann or satellite cells in the ganglion or spiral lamina. The spontaneous and preferential association of neurites in culture with mitotic Schwann cells highlights the potential contribution neurite-Schwann cell interactions may have in promoting the growth and regrowth of damaged spiral ganglion neurons in the cochlea.

The expression of NOB1 in spiral ganglion cells of guinea pig

OBJECTIVE

NOB1 was a transcription-associated protein, consisting of one zinc ribbon domain. This study aimed to investigate the NOB1 expression in spiral ganglion cells of normal guinea pigs and deaf ones.

METHODS

Twelve guinea pigs were randomized equally into experimental group and control group. In experimental group, guinea pigs received a single intramuscular injection of gentamicin, while the control group was treated with physiological saline. Auditory brainstem responses (ABR) test was performed before and 10 days after injection, respectively. Guinea pigs of both groups were sacrificed and temporal bones were removed. The expression of NOB1 in the spiral ganglion was evaluated by immunohistochemistry.

RESULTS

NOB1 staining was found expressed in spiral ganglion cells from the basal turn to the apical turn of the cochlea. The expression of NOB1 was found significantly stronger in spiral ganglion cells of deaf guinea pigs as compared with that in normal ones.

CONCLUSIONS

The NOB1 was presented in spiral ganglions cells of the guinea pig and might play a role in hearing transduction.

A protocol for cryoembedding the adult guinea pig cochlea for fluorescence immunohistology

Green fluorescent protein (GFP) has been used extensively to label cells in vitro and to track them following their transplantation in vivo. During our studies using the mouse embryonic stem cell line R1 B5-EGFP, we observed variable levels of fluorescence intensity of the GFP within these transfected cells. The variable fluorescence of this protein coupled with the innately autofluorescent nature of several structures within the cochlea collectively made the in vivo identification of these transplanted stem cells difficult. We have modified previously published protocols to enable the discrimination of an authentic GFP signal from autofluorescence in the adult guinea pig cochlea using fluorescence-based immunohistochemistry. The protocol described can also be used to label tissues of the cochlea using a chromogen, such as 3,3'-diaminobenzidine tetrahydrochloride (DAB). Moreover, the described method gives excellent preservation of structural morphology making the tissues useful for both morphological and quantitative studies in combination with robust immunohistochemistry in the adult guinea pig cochlea.

Effect of resuscitation after selective cerebral ultraprofound hypothermia on expressions of nerve growth factor and glial cell line-derived neurotrophic factor in the brain of monkey

OBJECTIVE

To investigate the expression of nerve growth factor (NGF) and glial cell line-derived neurotrophic factor (GDNF) in monkeys of resuscitation after selective cerebral ultraprofound hypothermia and blood flow occlusion.

METHODS

The monkeys were immediately removed brain after death in operation of group A (identical temperature perfusion group) and group B (ultraprofound hypothermia perfusion group). Immunohistochemical technique was used to determine frontal cellular expression of NGF and GDNF. Statistics were analyzed by ANOVA analyses with significance level at P < 0.05.

RESULTS

The expressions of NGF and GDNF in the group B were significantly higher than those in the group A (P < 0.05).

CONCLUSION

NGF and GDNF increased significantly in the monkeys of resuscitation after selective cerebral ultraprofound hypothermia and blood flow occlusion. It may be a protective mechanism for neuron survival and neural function recovery.

Cochlear neuronal tracing for frequency mapping with DiI, NeuroVue, and Golgi methods

CONCLUSIONS

Labeling experiments using NeuroVue Red dye allowed us to demonstrate individual afferent fiber tracks in the cochlea from the synaptic region of the inner hair cell in the organ of Corti (OC) to the spiral ganglion in Rosenthal's canal. Further optimization is necessary to obtain 3-dimensional (3D) neural distribution in the apical region for frequency mapping.

OBJECTIVES

We intend to develop a method by which the radial fibers of the spiral ganglion (SG) can be individually visualized and tracked in 3D from the base to the apex of the cochlea. The combined trajectories of fibers from each cochlea could then be calculated for modeling of the 3D relationship of OC and SG in cochlear implant studies to assist in the optimization of cochlear implants for music and speech perception in noise.

MATERIALS AND METHODS

We tested three different methods to visualize cochlear nerve fibers from OC to SG. Adult rat and mouse ears were stained with DiI dye, modified Golgi-Cox method or NeuroVue dye, sectioned or whole-mounted, and viewed with confocal or standard light microscope.

RESULTS

In DiI staining, spacial resolution and the number of neurons to be stained are too low to utilize this method to create a characteristic frequency map of the cochlea. The Golgi method mainly stained efferent nerve fibers, resulting in less information on cochlear nerve distribution. NeuroVue Red dye allowed clear tracking of individual fibers when combined with DAPI counterstaining.

Prosurvival and proapoptotic intracellular signaling in rat spiral ganglion neurons in vivo after the loss of hair cells

Neurons depend on afferent input for survival. Rats were given daily kanamycin injections from P8 to P16 to destroy hair cells, the sole afferent input to spiral ganglion neurons (SGNs). Most SGNs die over an approximately 14-week period after deafferentation. During this period, the SGN population is heterogeneous. At any given time, some SGNs exhibit apoptotic markers--TUNEL and cytochrome c loss--whereas others appear nonapoptotic. We asked whether differences among SGNs in intracellular signaling relevant to apoptotic regulation could account for this heterogeneity. cAMP response element binding protein (CREB) phosphorylation, which reflects neurotrophic signaling, is reduced in many SGNs at P16, P23, and P32, when SGNs begin to die. In particular, nearly all apoptotic SGNs exhibit reduced phospho-CREB, implying that apoptosis is due to insufficient neurotrophic support. However, >32% of SGNs maintain high phospho-CREB levels, implying access to neurotrophic support. By P60, when approximately 50% of the SGNs have died, phospho-CREB levels in surviving neurons are not reduced, and SGN death is no longer correlated with reduced phospho-CREB. Activity in the proapoptotic Jun N-terminal kinase (JNK)-Jun signaling pathway is elevated in SGNs during the cell death period. This too is heterogeneous: <42% of the SGNs exhibited high phospho-Jun levels, but nearly all SGNs undergoing apoptosis exhibited elevated phospho-Jun. Thus, heterogeneity among SGNs in prosurvival and proapoptotic signaling is correlated with apoptosis. SGN death following deafferentation has an early phase in which apoptosis is correlated with reduced phospho-CREB and a later phase in which it is not. Proapoptotic JNK-Jun signaling is tightly correlated with SGN apoptosis.

Improved cryosections and specific immunohistochemical methods for detecting hypoxia in mouse and rat cochleae

The present study was undertaken to develop an improved cryoembedding method for analysis of mice and rat cochleae, which permits high-quality cryosections and preserves overall structure and cellular resolution as shown by hematoxylin/eosin staining. The preservation of morphology and antigenicity is mandatory to achieve optimal results. A total of 20 male cd/1 mice and 14 male Sprague-Dawley rats were used in experiments for optimization of preservation, fixative, decalcification, embedding and cryosectioning of cochleae from adult and aged rodents. In addition, a novel immunohistochemical procedure (using Hydroxyprobe-1 kit) was developed for detecting regions of hypoxia in mice and rat cochlea. This method employs a primary fluorescent-conjugated monoclonal antibody directed against pimonidazole protein adducts that are created in hypoxic tissues. Subsequent studies of hypoxia inducible factor-1alpha (HIF-1alpha) by immunofluorescence in the cochlea of these animals were performed in order to confirm that immunochemical detection of pimonidazole protein is representative of a hypoxic environment. We conclude that the present method results in high-quality cryosections of cochlear tissues presenting good anatomical and histological preservation. Furthermore, our optimized procedures provide novel tools for the investigation of neuro-sensory-epithelium in physio-pathological situations associated with hypoxia and/or ischemia, such as inner ear development, plasticity, regeneration and senescence.

Selectivity of neural stimulation in the auditory system: a comparison of optic and electric stimuli

Pulsed, mid-infrared lasers were recently investigated as a method to stimulate neural activity. There are significant benefits of optically stimulating nerves over electrically stimulating, in particular the application of more spatially confined neural stimulation. We report results from experiments in which the gerbil auditory system was stimulated by optical radiation, acoustic tones, or electric current. Immunohistochemical staining for the protein c-FOS revealed the spread of excitation. We demonstrate a spatially selective activation of neurons using a laser; only neurons in the direct optical path are stimulated. This pattern of c-FOS labeling is in contrast to that after electrical stimulation. Electrical stimulation leads to a large, more spatially extended population of labeled, activated neurons. In the auditory system, optical stimulation of nerves could have a significant impact on the performance of cochlear implants, which can be limited by the electric current spread.

Sendai Virus Vector-Mediated Transgene Expression in the Cochlea in vivo

We injected a recombinant Sendai virus (SeV) vector into the guinea pig cochlea using two different approaches--the scala media and scala tympani--and investigated which cell types took up the vector. The hearing threshold shift and distribution of transfected cells in animals using the scala media approach were different compared to those using the scala tympani approach. SeV can transfect very different types of cells, including stria vascularis, spiral ganglion neurons, and sensory epithelia of the organ of Corti, and fibrocytes of the scala tympani. Because SeV vectors can potentially deliver stimuli to the cochlea to induce hair cell regeneration, it may be a powerful tool for repairing the organ of Corti.

Gene expression changes during step-wise differentiation of embryonic stem cells along the inner ear hair cell pathway

CONCLUSION

Our study outlines an alternative approach for the selection and investigation of genes involved in inner ear function.

OBJECTIVE

To gain understanding of the gene pathways involved in the development of the normal cochlea.

MATERIALS AND METHODS

Microarray technology currently offers the most efficient approach to investigate gene expression and identify pathways involved in cell differentiation. Epidermal growth factor (EGF) induces cultures derived from the organ of Corti to proliferate and produce new hair cells. Since pluripotent embryonic stem (ES) cells have the capacity to generate all tissues, we induced murine ES cells to differentiate towards ectodermal and neuroectodermal cell types and from there investigated their commitment towards the hair cell lineage in the presence of EGF. Cells were collected at three points along the differentiation pathway and their expression profiles were determined using the Soares NMIE mouse inner ear cDNA library printed in microarray format.

RESULTS

Three genes up-regulated after addition of EGF (serine (or cysteine) proteinase inhibitor, clade H, member 1 (Serpinh1), solute carrier family 2 (facilitated glucose transporter), member 10 (Slc2a10) and secreted acidic cysteine-rich glycoprotein (Sparc)) were selected for further analysis and characterization. Of the three genes, Serpinh1 and Slc2a10 have never been implicated in the hearing process.

Acid-sensing ion channel-1b in the stereocilia of mammalian cochlear hair cells

We investigated whether amiloride-blockable proton-gated cation channels ASIC1a (acid-sensing ion channel-1a) and ASIC1b are expressed in the stereocilia of mouse cochlear hair cells. In-situ hybridization studies showed that ASIC1b transcripts, but not ASIC1a transcripts, were expressed in the inner and outer hair cells. Fluorescent immunohistochemical and immunogold electron microscopic analyses revealed that the ASIC1b channels were located at the insertions of the stereocilia into the hair cells. Our findings provide a novel molecular key to the understanding of cochlear physiology and pathophysiology.

Molecular characterization and expression of maternally expressed gene 3 (Meg3/Gtl2) RNA in the mouse inner ear

The pathways responsible for sound perception in the cochlea involve the coordinated and regulated expression of hundreds of genes. By using microarray analysis, we identified several transcripts enriched in the inner ear, including the maternally expressed gene 3 (Meg3/Gtl2), an imprinted noncoding RNA. Real-time PCR analysis demonstrated that Meg3/Gtl2 was highly expressed in the cochlea, brain, and eye. Molecular studies revealed the presence of several Meg3/Gtl2 RNA splice variants in the mouse cochlea, brain, and eye. In situ hybridizations showed intense Meg3/Gtl2 RNA staining in the nuclei of type I spiral ganglion cells and in cerebellum near the dorsal vestibular region of the cochlea. In embryonic mouse head sections, Meg3/Gtl2 RNA expression was observed in the otocyst, brain, eye, cartilage, connective tissue, and muscle. Meg3/Gtl2 RNA expression increased in the developing otocyst and localized to the spiral ganglion, stria vascularis, Reissner's membrane, and greater epithelial ridge (GER) in the cochlear duct. RT-PCR analysis performed on cell lines derived from the organ of Corti, representing neural, supporting, and hair cells, showed significantly elevated levels of Meg3/Gtl2 expression in differentiated neural cells. We propose that Meg3/Gtl2 RNA functions as a noncoding regulatory RNA in the inner ear and that it plays a role in pattern specification and differentiation of cells during otocyst development, as well as in the maintenance of a number of terminally differentiated cochlear cell types.

Gene expression analysis of distinct populations of cells isolated from mouse and human inner ear FFPE tissue using laser capture microdissection--a technical report based on preliminary findings

Laser Capture Microdissection (LCM) allows microscopic procurement of specific cell types from tissue sections that can then be used for gene expression analysis. We first tested this method with sections of adult mouse inner ears and subsequently applied it to human inner ear sections. The morphology of the various cell types within the inner ear is well preserved in formalin fixed paraffin embedded (FFPE) sections, making it easier to identify cell types and their boundaries. Recovery of good quality RNA from FFPE sections can be challenging, however, recent studies in cancer research demonstrated that it is possible to carry out gene expression analysis of FFPE material. Thus, a method developed using mouse FFPE tissue can be applied to human archival temporal bones. This is important because the majority of human temporal bone banks have specimens preserved in formalin and a technique for retrospective analysis of human archival ear tissue is needed. We used mouse FFPE inner ear sections to procure distinct populations of cells from the various functional domains (organ of Corti, spiral ganglion, etc.) by LCM. RNA was extracted from captured cells, amplified, and assessed for quality. Expression of selected genes was tested by RT-PCR. In addition to housekeeping genes, we were able to detect cell type specific markers, such as Myosin 7a, p27(kip1) and neurofilament gene transcripts that confirmed the likely composition of cells in the sample. We also tested the method described above on FFPE sections from human crista ampullaris. These sections were approximately a year old. Populations of cells from the epithelium and stroma were collected and analyzed independently for gene expression. The method described here has potential use in many areas of hearing research. For example, following exposure to noise, ototoxic drugs or age, it would be highly desirable to analyze gene expression profiles of selected populations of cells within the organ of Corti or spiral ganglion cells rather than a mixed population of cells from whole inner ear tissue. Also, this method can be applied for analysis of human archival ear tissue.

Where is the spike generator of the cochlear nerve? Voltage-gated sodium channels in the mouse cochlea

The origin of the action potential in the cochlea has been a long-standing puzzle. Because voltage-dependent Na+ (Nav) channels are essential for action potential generation, we investigated the detailed distribution of Nav1.6 and Nav1.2 in the cochlear ganglion, cochlear nerve, and organ of Corti, including the type I and type II ganglion cells. In most type I ganglion cells, Nav1.6 was present at the first nodes flanking the myelinated bipolar cell body and at subsequent nodes of Ranvier. In the other ganglion cells, including type II, Nav1.6 clustered in the initial segments of both of the axons that flank the unmyelinated bipolar ganglion cell bodies. In the organ of Corti, Nav1.6 was localized in the short segments of the afferent axons and their sensory endings beneath each inner hair cell. Surprisingly, the outer spiral fibers and their sensory endings were well labeled beneath the outer hair cells over their entire trajectory. In contrast, Nav1.2 in the organ of Corti was localized to the unmyelinated efferent axons and their endings on the inner and outer hair cells. We present a computational model illustrating the potential role of the Nav channel distribution described here. In the deaf mutant quivering mouse, the localization of Nav1.6 was disrupted in the sensory epithelium and ganglion. Together, these results suggest that distinct Nav channels generate and regenerate action potentials at multiple sites along the cochlear ganglion cells and nerve fibers, including the afferent endings, ganglionic initial segments, and nodes of Ranvier.

Survival and morphology of auditory neurons in dissociated cultures of newborn mouse spiral ganglion

We have systematically characterized neuronal survival and growth in cultures derived from newborn/postnatal day 1 mouse cochlea. Dissociated cultures of the cochlear spiral ganglion provide an experimental environment in which to examine molecular mechanisms of survival, development and physiology of auditory neurons. To relate survival to the total number of neurons present in the source tissue, three cochleas from different newborn CD-1 mice were embedded in Araldite resin and serially sectioned at 5 mum thickness. All neurons were counted. To avoid overcounting, each section served as a lookup section for the next, giving 8240+/-423 (S.D.) neurons per ganglion. Cultures maintained in the presence of adjacent non-neural tissue, brain-derived neurotrophic factor, neurotrophin 3, leukemia inhibitory factor (LIF) and 10% fetal bovine serum returned the best overall survival (30%) at 42 h post-plating. Best overall survival required the continuous presence of a serum component(s) larger than 100,000 MW. Plating efficiency (number of neurons that attach to the well after 4 h) was similar in the presence or absence of LIF. Inclusion of LIF maintained 100% survival of plated neurons over 42 h of culture; without LIF, a large fraction of the neurons did not survive. LIF appeared to maintain survival by preferentially preserving a population of bipolar neurons, while having little effect on the number of monopolar neurons. This work provides quantitative measures of survival and morphology of auditory neurons in vitro. The results support the idea that survival of spiral ganglion neurons in vivo may depend on interactions with adjacent, non-neural tissue and raise the possibility that maintenance of bipolar morphology after hair cell damage may require biochemical mechanisms in addition to those induced by neurotrophins.

Biotinidase reveals the morphogenetic sequence in cochlea and cochlear nucleus of mice

Hearing loss affects children with biotinidase deficiency, an inherited metabolic disorder in the recycling of biotin. The deficit appears shortly after birth during development of the auditory system. Using a mouse model, we sought to discover where and when biotinidase is expressed in the normal development of the cochlea and cochlear nucleus. In the process, we reconstructed the normal morphogenetic sequences of the constituent cells. Immunolabeling for biotinidase was localized to neurons and other cells of the adult and immature mouse, including the embryonic precursors of these regions dating from the stage of the otocyst. Its distribution was compared to the particular morphological changes occurring at each developmental stage. Biotinidase was localized in cells and their processes at the critical stages in their proliferation, migration, structural differentiation, and innervation, covering the entire span of their development. The prevalence of immunostaining peaked in the adult animal, including hair cells and ganglion cells of the cochlea and neurons of the cochlear nucleus. The findings suggest that biotinidase plays a role in the normal development of the auditory system. Besides the pattern of localization of biotinidase, this study provides the first systematic account of each developmental stage in a mammalian auditory system.

Localization of beta1-adrenergic receptors in the cochlea and the vestibular labyrinth

Sympathetic activation in a "fight or flight reaction" may put the sensory systems for hearing and balance into a state of heightened alert via beta1-adrenergic receptors (beta1-AR). The aim of the present study was to localize beta1-AR in the gerbil inner ear by confocal immunocytochemistry, to characterize beta1-AR by Western immunoblots, and to identify beta1-AR pharmacologically by measurements of cAMP production. Staining for beta1-AR was found in strial marginal cells, inner and outer hair cells, outer sulcus, and spiral ganglia cells of the cochlea, as well as in dark, transitional and supporting cells of the vestibular labyrinth. Receptors were characterized in microdissected inner ear tissue fractions as 55 kDa non-glycosylated species and as 160 kDa high-mannose-glycosylated complexes. Pharmacological studies using isoproterenol, ICI-118551 and CGP-20712A demonstrated beta1-AR as the predominant adrenergic receptor in stria vascularis and organ of Corti. In conclusion, beta1-AR are present and functional in inner ear epithelial cells that are involved in K+ cycling and auditory transduction, as well as in neuronal cells that are involved in auditory transmission.

Hearing loss following Gata3 haploinsufficiency is caused by cochlear disorder

Patients with HDR syndrome suffer from hypoparathyroidism, deafness, and renal dysplasia due to a heterozygous deletion of the transcription factor GATA3. Since GATA3 is prominently expressed in both the inner ear and different parts of the auditory nervous system, it is not clear whether the deafness in HDR patients is caused by peripheral and/or central deficits. Therefore, we have created and examined heterozygous Gata3 knockout mice. Auditory brainstem response (ABR) thresholds of alert heterozygous Gata3 mice, analyzed from 1 to 19 months of age, showed a hearing loss of 30 dB compared to wild-type littermates. Neither physiological nor morphological abnormalities were found in the brainstem, cerebral cortex, the outer or the middle ear. In contrast, cochleae of heterozygous Gata3 mice showed significant progressive morphological degeneration starting with the outer hair cells (OHCs) at the apex and ultimately affecting all hair cells and supporting cells in the entire cochlea. Together, these findings indicate that hearing loss following Gata3 haploinsufficiency is peripheral in origin and that this defect is detectable from early postnatal development and maintains through adulthood.

Characterisation of DRASIC in the mouse inner ear

Within the cochlea, the hair cells detect sound waves and transduce them into receptor potential. The molecular architecture of the highly specialised cochlea is complex and until recently little was known about the molecular interactions which underlie its function. It is now clear that the coordinated expression and interplay of hundreds of genes and the integrity of cochlear cells regulate this function. It was hypothesised that transcripts expressed highly or specifically in the cochlea are likely to have important roles in normal hearing. Microarray analyses of the Soares NMIE library, consisting of 1536 cDNA clones isolated from the mouse inner ear, suggested that the expression of the mechanoreceptor DRASIC was enriched in the cochlea compared to other tissues. This amiloride-sensitive ion channel is a member of the DEG/ENaC superfamily and a potential candidate for the unidentified mechanoelectrical transduction channel of the sensory hair cells of the cochlea. The cochlear-enriched expression of amiloride-sensitive cation channel 3 (ACCN3) was confirmed by quantitative real-time polymerase chain reaction. Using in situ hybridisation and immunofluorescence, DRASIC expression was localised to the cells and neural fibre region of the spiral ganglion. DRASIC protein was also detected in cells of the organ of Corti. DRASIC may be present in cochlear hair cells as the ACCN3 transcript was shown to be expressed in immortalised cell lines that exhibit characteristics of hair cells. The normal mouse ACCN3 cDNA and an alternatively spliced transcript were elucidated by reverse transcription polymerase chain reaction from mouse inner ear RNA. This transcript may represent a new protein isoform with an as yet unknown function. A DRASIC knockout mouse model was tested for a hearing loss phenotype and was found to have normal hearing at 2 months of age but appeared to develop hearing loss early in life. The human homologue of ACCN3, acid-sensing ion channel 3, maps to the same chromosomal region as the autosomal recessive hearing loss locus DFNB13. However, we did not detect mutations in this gene in a family with DFNB13 hearing loss.

Cochlear immunochemistry--a new technique based on gelatin embedding

Histological processing of the cochlea for immunochemistry is often a compromise between good anatomical resolution and preservation of antigenicity. Techniques able to preserve tissue architecture invariably demand elevated temperatures and harsh chemicals or a combination of both. The likely result is reduced antigenicity, enzyme activity and nucleic acid integrity. We have modified an existing embedding medium for use in the cochlea that operates at physiological temperature and avoids denaturing agents and organic solvents. Tissue antigenicity is maximised and anatomical detail preserved, normally two mutually exclusive goals. The method is attractive because of its simplicity, speed and transparency for easy cochlear orientation. It is also likely to be adaptable for the infiltration of other heterogeneous structures prone to distortion during frozen sectioning.

Embedding media for cryomicrotomy: an applicative reappraisal

We reassess here the formulation of cryoembedding media in connection with recent developments in commercial cryomicrotomes. Water-based solutions of polyvinyl alcohols were our starting media, and each of 2 different polymers (56-98, MW approximately 195000; and 6-98, MW approximately 47000) showed a critical concentration for optimum sectioning. At higher or lower polymer concentrations, wrinkles and folds became apparent in tissue areas of sections, or in the sectioned embedding medium areas between tissues, respectively. Addition of polyethylene glycol (MW 380-420) further facilitated and improved sectioning, resulting in frozen tissue blocks that cut well in the 2 to 100 microm range and further, using disposable blades throughout. Applying a wide temperature differential between tissue specimen (-11 degrees C to -13 degrees C) and cutting knife (-33 degrees C to -35 degrees C), serial adjacent sections were reproducibly obtained at a 2-microm setting, singly or in short ribbons. Embedding media of low and high viscosity were obtained, depending on the polyvinyl alcohol polymer used, and could be applied sequentially for tissue infiltration followed by embedding with precise sample orientation. When required, media were made semisolid by addition of carboxymethylcellulose.

Glial cell line-derived neurotrophic factor and chronic electrical stimulation prevent VIII cranial nerve degeneration following denervation

As with other cranial nerves and many CNS neurons, primary auditory neurons degenerate as a consequence of loss of input from their target cells, the inner hair cells (IHCs). Electrical stimulation (ES) of spiral ganglion cells (SGCs) has been shown to enhance their survival. Glial cell line-derived neurotrophic factor (GDNF) has also been shown to increase survival of SGCs following IHC loss. In this study, the combined effects of the GDNF transgene delivered by adenoviral vectors (Ad-GDNF) and ES were tested on SGCs after first eliminating the IHCs. Animal groups received Ad-GDNF or ES or both. Ad-GDNF was inoculated into the cochlea of guinea pigs after deafening, to overexpress human GDNF. ES-treated animals were implanted with a cochlear implant electrode and chronically stimulated. A third group of animals received both Ad-GDNF and ES (GDNF/ES). Electrically evoked auditory brainstem responses were recorded from ES-treated animals at the start and end of the stimulation period. Animals were sacrificed 43 days after deafening and their ears prepared for evaluation of IHC survival and SGC counts. Treated ears exhibited significantly greater SGC survival than nontreated ears. The GDNF/ES combination provided significantly better preservation of SGC density than either treatment alone. Insofar as ES parameters were optimized for maximal protection (saturated effect), the further augmentation of the protection by GDNF suggests that the mechanisms of GDNF- and ES-mediated SGC protection are, at least in part, independent. We suggest that GDNF/ES combined treatment in cochlear implant recipients will improve auditory perception. These findings may have implications for the prevention and treatment of other neurodegenerative processes. .

Expression and localization of heat shock factor (Hsf) 1 in the rodent cochlea

Activation of heat shock factors (Hsfs) is one of the potential mechanisms for regulating the transcription of the heat shock proteins (Hsps) and certain other stress-responsive genes. Reverse transcription polymerase chain reaction (RT-PCR), Western blot and immunocytochemistry were used to examine the expression and localization of Hsf1, the stress-responsive member of the Hsf family, in the rat and mouse cochlea. Cerebellum was used as a positive control. Semi-quantitative RT-PCR of cochlear RNA revealed that Hsf1 was more highly expressed in a subfraction containing sensorineural epithelium and lateral wall than in a subfraction containing modiolus, with the alpha splice form predominant over the beta in both subfractions. Immunocytochemistry showed selective staining in the rodent cochlea. Hsf1 immunostaining was found in the nuclei of inner and outer hair cells in the organ of Corti, spiral ganglion cells in the modiolus, and cells in the marginal and intermediate layers of the stria vascularis. This is largely consistent with where Hsp70 induction is reported. Hsf1 activation following heat shock was examined by Western blot. Hyperthermia resulted in stress-induced Hsf1 hyperphosphorylation in cochlea as well as cerebellum. This hyperphosphorylation as well as the correlation of its localization with Hsp70 induction supports a role for Hsf1 in the cochlear stress response.

Gene transfer into supporting cells of the organ of Corti

To utilize the rapidly accumulating genetic information for developing new therapeutic technologies for inner ear disease, it is necessary to design technologies for expressing transgenes in the inner ear, especially in the organ of Corti. We examined the outcome of an adenovirus gene transfer into the organ of Corti via the scala media in guinea pigs. The transgene insert is the bacterial lacZ gene driven by a cytomegalovirus promoter. We demonstrate that the inoculation is detrimental to the hair cells that surround the site of inoculation, but the supporting cells in the organ of Corti survive and retain the ability to express the reporter transgene beta-gal. The ability to deliver transgenes that are expressed in the supporting cells is an important step in the development of clinically applicable treatments that involve hair cell regeneration.

Transgene expression in neonatal mouse inner ear explants mediated by first and advanced generation adenovirus vectors

The mouse serves as a valuable model for treatment leading to the prevention and therapy of inner ear disease. Transgenic correction of genetic inner ear disease in mice may help develop treatment for human genetic inner ear disease. In mutations involving hair cells (HCs) or supporting cells (SCs), it is necessary to insert the wild-type transgenes directly into these cells. We used inner ear explants to characterize the transgenic expression using adenovirus-mediated reporter genes (bacterial lacZ). The variable parameters were the age of the explants (P1-P5), the type of vector (first and advanced generation adenovirus) and the genotype of the mouse (wild-type versus shaker-2 mutant). Transduction of cochlear HCs was detected at P1 and in some of the P3 cochleae. Low efficiency transduction of SCs was observed in P1 explants, but the efficiency increased with age and reached high levels at P5. The pattern of transduction was similar regardless of the genotype and the type of vector used. The data demonstrate that differentiating HCs and SCs in mouse explants can be transduced by adenovirus vectors, suggesting that cultures of mouse ears are a valuable model for developing inner ear gene therapy protocols.

Cochlear whole mount in situ hybridization: identification of longitudinal and radial gradients

The morphology of the organ of Corti has a radial asymmetry and also changes longitudinally from base to apex. Cellular localization of transcripts within the inner ear has relied primarily on the use of sectioned tissue with in situ hybridization. However, radial and longitudinal gradients of expression are not readily recognized using sectioned tissue owing to problems in visualization of signals with varying intensities. Herein, we describe the use of whole mount in situ hybridization for identification of cochlear longitudinal and radial expression gradients in the neurosensory epithelium, hair cells. Not only can these hair cell gradients be shown in adult tissues, but also the developmental up-regulation and down-regulation of genes and their associated spatio-temporal expression patterns can be demonstrated.

The functional and structural outcome of inner ear gene transfer via the vestibular and cochlear fluids in mice

Mice present an ideal model for inner ear gene therapy because their genome is being rapidly sequenced, their generation time is relatively short, and they serve as a valuable model for human hereditary inner ear disease. However, the small size of the mouse inner ear poses a particular challenge for surgical procedures. We have developed a new approach for viral inoculation into the mature mouse inner ear, using a replication-deficient adenovirus expressing the bacterial gene lacZ. We administered the virus through the posterior semicircular canal (canalostomy) and into the cochlea (cochleostomy). Both approaches caused lacZ to be expressed in cells lining the perilymphatic space. One canalostomy case showed gene expression in sensory cells of the crista ampullaris, whereas the cochleostomy group showed gene expression in the sensory cells in the organ of Corti and saccule. Functional tests after the surgery showed that the canalostomy preserved hearing, whereas the cochleostomy did not. Any vestibular function transiently lost after the canalostomy was recovered. Our findings indicate that inoculation of adenovirus vectors into the mouse inner ear through the semicircular canal has the potential to efficiently introduce transgenes to the vestibular system and the cochlea without compromising hearing.

Decreased cochlear DNA receptor staining in MRL.MpJ-Fas(lpr) autoimmune mice with hearing loss

OBJECTIVES

Previous studies of decreased cochlear DNA binding in autoimmune mice suggested that antibodies against a cochlear cell surface DNA receptor cause autoimmune hearing loss. However, the presence of a cochlear DNA receptor has not been determined. Therefore, immunohistochemistry with an anti-DNA receptor antibody was performed on MRL.MpJ-Fas(lpr) (MRL/lpr) autoimmune mice to determine 1) which inner ear structures contain DNA receptors and 2) whether the receptor staining pattern changes as autoimmune disease progresses and hearing thresholds increase.

STUDY DESIGN

A prospective study of the progression of hearing loss in autoimmune mice and correlated alterations in immunostaining for the inner ear DNA receptor.

METHODS

One group of MRL/lpr mice (n = 10) was allowed to develop autoimmune disease, and auditory brainstem response (ABR) audiometry was performed at 4, 6, and 9 months of age to measure the progression of hearing loss. A second group (n = 5) was tested for ABR thresholds at 2 months of age and immediately killed to assess receptor staining before the onset of autoimmune disease and hearing loss. The inner ears from all mice were immunohistochemically stained with an anti-DNA receptor antibody, and a qualitative analysis of the staining of cochlear structures was performed.

RESULTS

Auditory brainstem response audiometry revealed a significant 20- to 30-dB elevation of thresholds as systemic disease progressed. Anti-DNA receptor staining was heaviest in the spiral ligament and less intense in the spiral ganglion and cochlear nerve. Both groups showed a similar pattern of staining in these structures. The stria vascularis and hair cells also stained in both groups. However, the stria cells of normal-hearing mice showed diffuse intracellular immunoreactivity, whereas older mice displayed less staining that was confined to the cell membranes.

CONCLUSIONS

The inner ears of MRL/lpr mice contain DNA receptors. Autoimmune hearing loss was correlated with weaker overall intracellular staining in the stria vascularis and hair cells but increased staining of the cell membranes. This suggested DNA receptors have impaired endocytosis and more receptors remain on the cell membrane, possibly as a result of binding by circulating autoantibodies.