Supernumerary human hair cells-signs of regeneration or impaired development? A field emission scanning electron microscopy study

BACKGROUND

Current attempts to regenerate cochlear sensorineural structures motivate further inspection of the human organ of hearing. Here, we analyzed the supernumerary inner hair cell (sIHC), a possible sign of regeneration and cell replacement.

METHODS

Human cochleae were studied using field emission scanning electron microscopy (FESEM; maximum resolution 2 nm) obtained from individuals aged 44, 48, and 58 years with normal sensorineural pure-tone average (PTA) thresholds (PTA <20 dB). The wasted tissue was harvested during trans-cochlear approaches and immediately fixed for ultrastructural analysis.

RESULTS

All specimens exhibited sIHCs at all turns except at the extreme lower basal turn. In one specimen, it was possible to image and count the inner hair cells (IHCs) along the cochlea representing the 0.2 kHz-8 kHz region according to the Greenwood place/frequency scale. In a region with 2,321 IHCs, there were 120 scattered one-cell losses or 'gaps' (5%). Forty-two sIHCs were present facing the modiolus. Thirty-eight percent of the sIHCs were located near a 'gap' in the IHC row (±6 IHCs).

CONCLUSIONS

The prevalence of ectopic inner hair cells was higher than expected. The morphology and placement could reflect a certain ongoing regeneration. Further molecular studies are needed to verify if the regenerative capacity of the human auditory periphery might have been underestimated.

Guided growth of auditory neurons: Bioactive particles towards gapless neural - electrode interface

Cochlear implant (CI) is a successful device to restore hearing. Despite continuous development, frequency discrimination is poor in CI users due to an anatomical gap between the auditory neurons and CI electrode causing current spread and unspecific neural stimulation. One strategy to close this anatomical gap is guiding the growth of neuron dendrites closer to CI electrodes through targeted slow release of neurotrophins. Biodegradable calcium phosphate hollow nanospheres (CPHSs) were produced and their capacity for uptake and release of neurotrophins investigated using ¹²⁵I-conjugated glia cell line-derived neurotrophic factor (GDNF). The CPHSs were coated onto CI electrodes and loaded with neurotrophins. Axon guidance effect of slow-released neurotrophins from the CPHSs was studied in an in vitro 3D culture model. CPHS coating bound and released GDNF with an association rate constant 6.3 × 10³ M^-1s^-1 and dissociation rate 2.6 × 10^-5 s^-1, respectively. Neurites from human vestibulocochlear ganglion explants found and established physical contact with the GDNF-loaded CPHS coating on the CI electrodes placed 0.7 mm away. Our results suggest that neurotrophin delivery through CPHS coating is a plausible way to close the anatomical gap between auditory neurons and electrodes. By overcoming this gap, selective neural activation and the fine hearing for CI users become possible.

Neurosensory Differentiation and Innervation Patterning in the Human Fetal Vestibular End Organs between the Gestational Weeks 8-12

Balance orientation depends on the precise operation of the vestibular end organs and the vestibular ganglion neurons. Previous research on the assemblage of the neuronal network in the developing fetal vestibular organ has been limited to data from animal models. Insights into the molecular expression profiles and signaling moieties involved in embryological development of the human fetal inner ear have been limited. We present an investigation of the cells of the vestibular end organs with specific focus on the hair cell differentiation and innervation pattern using an uninterrupted series of unique specimens from gestational weeks 8-12. Nerve fibers positive for peripherin innervate the entire fetal crista and utricle. While in rodents only the peripheral regions of the cristae and the extra-striolar region of the statolithic organs are stained. At week 9, transcription factors PAX2 and PAX8 were observed in the hair cells whereas PAX6 was observed for the first time among the supporting cells of the cristae and the satellite glial cells of the vestibular ganglia. Glutamine synthetase, a regulator of the neurotransmitter glutamate, is strongly expressed among satellite glia cells, transitional zones of the utricle and supporting cells in the sensory epithelium. At gestational week 11, electron microscopic examination reveals bouton contacts at hair cells and first signs of the formation of a protocalyx at type I hair cells. Our study provides first-hand insight into the fetal development of the vestibular end organs as well as their pattern of innervation by means of immunohistochemical and EM techniques, with the aim of contributing toward our understanding of balance development.

The effect of pulsed electric fields on the electrotactic migration of human neural progenitor cells through the involvement of intracellular calcium signaling

Endogenous electric fields (EFs) are required for the physiological control of the central nervous system development. Application of the direct current EFs to neural stem cells has been studied for the possibility of stem cell transplantation as one of the therapies for brain injury. EFs generated within the nervous system are often associated with action potentials and synaptic activity, apparently resulting in a pulsed current in nature. The aim of this study is to investigate the effect of pulsed EF, which can reduce the cytotoxicity, on the migration of human neural progenitor cells (hNPCs). We applied the mono-directional pulsed EF with a strength of 250mV/mm to hNPCs for 6h. The migration distance of the hNPCs exposed to pulsed EF was significantly greater compared with the control not exposed to the EF. Pulsed EFs, however, had less of an effect on the migration of the differentiated hNPCs. There was no significant change in the survival of hNPCs after exposure to the pulsed EF. To investigate the role of Ca²⁺ signaling in electrotactic migration of hNPCs, pharmacological inhibition of Ca²⁺ channels in the EF-exposed cells revealed that the electrotactic migration of hNPCs exposed to Ca²⁺ channel blockers was significantly lower compared to the control group. The findings suggest that the pulsed EF induced migration of hNPCs is partly influenced by intracellular Ca²⁺ signaling.

Biofunctionalized peptide-based hydrogels provide permissive scaffolds to attract neurite outgrowth from spiral ganglion neurons

Cochlear implants (CI) allow for hearing rehabilitation in patients with sensorineural hearing loss or deafness. Restricted CI performance results from the spatial gap between spiral ganglion neurons and the CI, causing current spread that limits spatially restricted stimulation and impairs frequency resolution. This may be substantially improved by guiding peripheral processes of spiral ganglion neurons towards and onto the CI electrode contacts. An injectable, peptide-based hydrogel was developed which may provide a permissive scaffold to facilitate neurite growth towards the CI. To test hydrogel capacity to attract spiral ganglion neurites, neurite outgrowth was quantified in an in vitro model using a custom-designed hydrogel scaffold and PuraMatrix^®. Neurite attachment to native hydrogels is poor, but significantly improved by incorporation of brain-derived neurotrophic factor (BDNF), covalent coupling of the bioactive laminin epitope IKVAV and the incorporation a full length laminin to hydrogel scaffolds. Incorporation of full length laminin protein into a novel custom-designed biofunctionalized hydrogel (IKVAV-GGG-SIINFEKL) allows for neurite outgrowth into the hydrogel scaffold. The study demonstrates that peptide-based hydrogels can be specifically biofunctionalized to provide a permissive scaffold to attract neurite outgrowth from spiral ganglion neurons. Such biomaterials appear suitable to bridge the spatial gap between neurons and the CI.

Effects of Intratympanic Injection of Latanoprost in Meniere's Disease: A Randomized, Placebo-Controlled, Double-Blind, Pilot Study

OBJECTIVE: To determine the short-term effects of latanoprost, a selective FP prostanoid receptor agonist, in Meniere's disease.

STUDY DESIGN AND METHODS: Latanoprost was administered by intratympanic injection once daily for 3 days. Before the first injection (day 1) and on days 5 and 15, hearing and tinnitus were determined. The patients assessed vertigo on a visual analogue scale on days 1-15. The study was randomized, doubleblind, and placebo-controlled.

RESULTS: Latanoprost reduced vertigo/dysequilibrium around 30% ( P >0.05), and improved speech discrimination around 15% ( P >0.05). Tinnitus loudness deteriorated after injection of placebo (P >0.01) but not after latanoprost. Side effects were few.

CONCLUSION AND SIGNIFICANCE: Latanoprost alleviated vertigo/dysequilibrium and improved hearing. The results indicate that the drug potentially could be useful for treatment of Meniere's disease.

Scanning Electron Microscopic Examination of the Extracellular Matrix in the Decellularized Mouse and Human Cochlea

Decellularized tissues have been used to investigate the extracellular matrix (ECM) in a number of different tissues and species. Santi and Johnson JARO 14:3-15 (2013) first described the decellularized inner ear in the mouse, rat, and human using scanning thin-sheet laser imaging microscopy (sTSLIM). The purpose of the present investigation is to examine decellularized cochleas in the mouse and human at higher resolution using scanning electron microscopy (SEM). Fresh cochleas were harvested and decellularized using detergent extraction methods. Following decellularization, the ECM of the bone, basilar membrane, spiral limbus, and ligament remained, and all of the cells were removed from the cochlea. A number of similarities and differences in the ECM of the mouse and human were observed. A novel, spirally directed structure was present on the basilar membrane and is located at the border between Hensen and Boettcher cells. These septa-like structures formed a single row in the mouse and multiple rows in the human. The basal lamina of the stria vascularis capillaries was present and appeared thicker in the human compared with the mouse. In the mouse, numerous openings beneath the spiral prominence that previously housed the root processes of the external sulcus cells were observed but in the human there was only a single row of openings. These and other anatomical differences in the ECM between the mouse and human may reflect functional differences and/or be due to aging; however, decellularized cochleas provide a new way to examine the cochlear ECM and reveal new observations.

Experiences from Auditory Brainstem Implantation (ABIs) in four paediatric patients

INTRODUCTION

Indications for auditory brainstem implants (ABIs) have been widened from patients with neurofibromatosis type 2 (NF2) to paediatric patients with congenital cochlear malformations, cochlear nerve hypoplasia/aplasia, or cochlear ossification after meningitis. We present four ABI surgeries performed in children at Uppsala University Hospital in Sweden since 2009.

METHODS

Three children were implanted with implants from Cochlear Ltd. (Lane Cove, Australia) and one child with an implant from MedEl GMBH (Innsbruck, Austria). A boy with Goldenhar syndrome was implanted with a Cochlear Nucleus ABI24M at age 2 years (patient 1). Another boy with CHARGE syndrome was implanted with a Cochlear Nucleus ABI541 at age 2.5 years (patient 2). Another boy with post-ossification meningitis was implanted with a Cochlear Nucleus ABI24M at age 4 years (patient 3). A girl with cochlear aplasia was implanted with a MedEl Synchrony ABI at age 3 years (patient 4). In patients 1, 2, and 3, the trans-labyrinthine approach was used, and in patient 4 the retro-sigmoid approach was used.

RESULTS

Three of the four children benefited from their ABIs and use it full time. Two of the full time users had categories of auditory performance (CAP) score of 4 at their last follow up visit (6 and 2.5 years postoperative) which means they can discriminate consistently any combination of two of Ling's sounds. One child has not been fully evaluated yet, but is a full time user and had CAP 2 (responds to speech sounds) after 3 months of ABI use. No severe side or unpleasant stimulation effects have been observed so far. There was one case of immediate electrode migration and one case of implant device failure after 6.5 years.

CONCLUSION

ABI should be considered as an option in the rehabilitation of children with similar diagnoses.

Strategy towards independent electrical stimulation from cochlear implants: Guided auditory neuron growth on topographically modified nanocrystalline diamond

Cochlear implants (CI) have been used for several decades to treat patients with profound hearing loss. Nevertheless, results vary between individuals, and fine hearing is generally poor due to the lack of discrete neural stimulation from the individual receptor hair cells. A major problem is the deliverance of independent stimulation signals to individual auditory neurons. Fine hearing requires significantly more stimulation contacts with intimate neuron/electrode interphases from ordered axonal re-growth, something current CI technology cannot provide. Here, we demonstrate the potential application of micro-textured nanocrystalline diamond (NCD) surfaces on CI electrode arrays. Such textured NCD surfaces consist of micrometer-sized nail-head-shaped pillars (size 5×5μm(2)) made with sequences of micro/nano-fabrication processes, including sputtering, photolithography and plasma etching. The results show that human and murine inner-ear ganglion neurites and, potentially, neural progenitor cells can attach to patterned NCD surfaces without an extracellular matrix coating. Microscopic methods revealed adhesion and neural growth, specifically along the nail-head-shaped NCD pillars in an ordered manner, rather than in non-textured areas. This pattern was established when the inter-NCD pillar distance varied between 4 and 9μm. The findings demonstrate that regenerating auditory neurons show a strong affinity to the NCD pillars, and the technique could be used for neural guidance and the creation of new neural networks. Together with the NCD's unique anti-bacterial and electrical properties, patterned NCD surfaces could provide designed neural/electrode interfaces to create independent electrical stimulation signals in CI electrode arrays for the neural population.

STATEMENT OF SIGNIFICANCE

Cochlear implant is currently a successful way to treat sensorineural hearing loss and deafness especially in children. Although clinically successful, patients' fine hearing cannot be completely restored. One problem is the amount of the electrodes; 12-20 electrodes are used to replace the function of 3400 inner hair cells. Intense research is ongoing aiming to increase the number of electrodes. This study demonstrates the use of nanocrystalline diamond as a potential nerve-electrode interface. Micrometer-sized nanocrystalline diamond pillars showed high affinity to regenerated human neurons, which grew into a pre-defined network based on the pillar design. Our findings are of particular interest since they can be applied on any silicon-based implant to increase electrode count and to achieve individual neuron stimulation patterns.

Regulation of the perilymphatic-endolymphatic water shunt in the cochlea by membrane translocation of aquaporin-5

Volume homeostasis of the cochlear endolymph depends on radial and longitudinal endolymph movements (LEMs). LEMs measured in vivo have been exclusively recognized under physiologically challenging conditions, such as experimentally induced alterations of perilymph osmolarity or endolymph volume. The regulatory mechanisms that adjust LEMs to the physiological requirements of endolymph volume homeostasis remain unknown. Here, we describe the formation of an aquaporin (AQP)-based "water shunt" during the postnatal development of the mouse cochlea and its regulation by different triggers. The final complementary expression pattern of AQP5 (apical membrane) and AQP4 (basolateral membrane) in outer sulcus cells (OSCs) of the cochlear apex is acquired at the onset of hearing function (postnatal day (p)8-p12). In vitro, hyperosmolar perfusion of the perilymphatic fluid spaces or the administration of the muscarinic agonist pilocarpine in cochlear explants (p14) induced the translocation of AQP5 channel proteins into the apical membranes of OSCs. AQP5 membrane translocation was blocked by the muscarinic antagonist atropine. The muscarinic M3 acetylcholine (ACh) receptor (M3R) was identified in murine OSCs via mRNA expression, immunolabeling, and in vitro binding studies using an M3R-specific fluorescent ligand. Finally, the water shunt elements AQP4, AQP5, and M3R were also demonstrated in OSCs of the human cochlea. The regulation of the AQP4/AQP5 water shunt in OSCs of the cochlear apex provides a molecular basis for regulated endolymphatic volume homeostasis. Moreover, its dysregulation or disruption may have pathophysiologic implications for clinical conditions related to endolymphatic hydrops, such as Ménière's disease.

Self-reported benefit, sound perception, and quality-of-life in patients with auditory brainstem implants (ABIs)

CONCLUSION

The majority of the patients used their auditory brainstem implants (ABIs) all the time, reporting that he/she would make the decision to receive an implant again if the decision were reconsidered. The findings support that the ABI is a valuable treatment in patients with type 2 neurofibromatosis (NF2) and in children with congenital inner ear and nerve anomalies or cochlear ossification.

OBJECTIVE

To evaluate the patients who underwent ABI implantation in Uppsala during 1993-2013. This study analyzed patients' implant use, perception of environmental sounds, perceived benefit from the implant, and quality-of-life (QoL).

METHOD

The NF2-patients (n = 20) comprised the majority of the patients, and there were a few non-NF2 pediatric patients (n = 4). The exclusion criteria included deceased patients (n = 4) and patients with no hearing sensations from the implant, or those with an inactivated ABI (n = 2). The data were collected from a questionnaire survey.

RESULTS

Eleven adult patients and two pediatric patients answered the questionnaires. Eight of the adult patients used their implants 'always'. The two children always used their implants. Hearing problems had the largest negative effect on the QoL. The non-users and the users scored equally on the NFTI-QoL.

Immunohistochemical localization of OCT2 in the cochlea of various species

Objective

To locate the organic cation transporter 2 (OCT2) in the cochlea of three different species and to modulate the ototoxicity of cisplatin in the guinea pig by pretreatment with phenformin, having a known affinity for OCT2.

Study Design

Immunohistochemical and in vivo study.

Methods

Sections from the auditory end organs were subjected to immunohistochemical staining in order to identify OCT2 in cochlea from untreated rats, guinea pigs, and a pig. In the in vivo study, guinea pigs were given phenformin intravenously 30 minutes before cisplatin administration. Electrophysiological hearing thresholds were determined, and hair cells loss was assessed 96 hours later. The total amount of platinum in cochlear tissue was determined using mass spectrometry.

Results

Organic cation transporter 2 was found in the supporting cells and in type I spiral ganglion cells in the cochlea of all species studied. Pretreatment with phenformin did not reduce the ototoxic side effect of cisplatin. Furthermore, the concentration of platinum in the cochlea was not affected by phenformin.

Conclusions

The localization of OCT2 in the supporting cells and type I spiral ganglion cells suggests that this transport protein is not primarily involved in cisplatin uptake from the systemic circulation. We hypothesize that OCT2 transport intensifies cisplatin ototoxicity via transport mechanisms in alternate compartments of the cochlea.

Level of Evidence

N/A. Laryngoscope, 125:E320–E325, 2015

Macromolecular organization and fine structure of the human basilar membrane - RELEVANCE for cochlear implantation

INTRODUCTION

Cochlear micromechanics and frequency tuning depend on the macromolecular organization of the basilar membrane (BM), which is still unclear in man. Novel techniques in cochlear implantation (CI) motivate further analyses of the BM.

MATERIALS AND METHODS

Normal cochleae from patients undergoing removal of life-threatening petro-clival meningioma and an autopsy specimen from a normal human were used. Laser-confocal microscopy, high resolution scanning (SEM) and transmission electron microscopy (TEM) were carried out in combination. In addition, one human temporal bone was decellularized and investigated by SEM.

RESULTS

The human BM consisted in four separate layers: (1) epithelial basement membrane positive for laminin-β2 and collagen IV, (2) BM "proper" composed of radial fibers expressing collagen II and XI, (3) layer of collagen IV and (4) tympanic covering layer (TCL) expressing collagen IV, fibronectin and integrin. BM thickness varied both radially and longitudinally (mean 0.55-1.16 μm). BM was thinnest near the OHC region and laterally.

CONCLUSIONS

There are several important similarities and differences between the morphology of the BM in humans and animals. Unlike in animals, it does not contain a distinct pars tecta (arcuate) and pectinata. Its width increases and thickness decreases as it travels apically in the cochlea. Findings show that the human BM is thinnest and probably most vibration-sensitive at the outer pillar feet/Deiter cells at the OHCs. The inner pillar and IHCs seem situated on a fairly rigid part of the BM. The gradient design of the BM suggests that its vulnerability increases apical wards when performing hearing preservation CI surgery.

3-D gel culture and time-lapse video microscopy of the human vestibular nerve

CONCLUSIONS

Human inner ear neurons have an innate regenerative capacity and can be cultured in vitro in a 3-D gel. The culture technique is valuable for experimental investigations of human inner ear neuron signaling and regeneration.

OBJECTIVES

To establish a new in vitro model to study human inner ear nerve signaling and regeneration.

METHODS

Human superior vestibular ganglion (SVG) was harvested during translabyrinthine surgery for removal of vestibular schwannoma. After dissection tissue explants were embedded and cultured in a laminin-based 3-D matrix (Matrigel™). 3-D growth cone (GC) expansion was analyzed using time-lapse video microscopy (TLVM). Neural marker expression was appraised using immunocytochemistry with fluorescence and laser confocal microscopy.

RESULTS

Tissue explants from adult human SVG could be cultured in 3-D in a gel, indicating an innate potential for regeneration. Cultured GCs were found to expand dynamically in the gel. Growth cone expansion and axonal Schwann cell alignment were documented using TLVM. Neurons were identified morphologically and through immunohistochemical staining.

On the anatomy of the 'hook' region of the human cochlea and how it relates to cochlear implantation

BACKGROUND

The optimal insertion route for an electrode array in hearing preservation cochlear implantation (CI) surgery is still tentative. Both cochleostomy (CO) and round window (RW) techniques are used today. In the present study we analyzed size variations and topographic anatomy of the 'hook' region of the human cochlea to better comprehend the Testo effects of various electric array insertion modes.

MATERIAL AND METHODS

Size variations of the cochlear 'hook' region were assessed in 23 human, microdissected temporal bones by measuring the distances between the oval and round windows, also outlining the spiral ligament/spiral lamina. Influence of size variations on spiral ligament position and fundamentals for different surgical approaches were evaluated in a subset of 'small' and 'large' cochleae performing different types of CO. In addition, the relationship between the microdissected accessory canal housing the inferior cochlear vein and the RW was analyzed.

RESULTS

The lateral vestibular wall and the cochlear 'hook' displayed large anatomic variations that greatly influenced the size of the potential surgical area. RESULTS showed that only very inferiorly located CO entered the scala tympani without causing trauma to the spiral ligament and spiral lamina. An inferior approach may challenge the inferior cochlear vein.

CONCLUSION

Preoperative assessment of the distance between the round and oval windows may direct the surgeon before CI hearing-preservation surgery. CO techniques, especially in 'small' ears, may lead to frequent damage to the inner ear structures. In those cases with substantial residual hearing, CI surgery may be better performed through a RW approach.

The pre- and post-somatic segments of the human type I spiral ganglion neurons--structural and functional considerations related to cochlear implantation

Human auditory nerve afferents consist of two separate systems; one is represented by the large type I cells innervating the inner hair cells and the other one by the small type II cells innervating the outer hair cells. Type I spiral ganglion neurons (SGNs) constitute 96% of the afferent nerve population and, in contrast to other mammals, their soma and pre- and post-somatic segments are unmyelinated. Type II nerve soma and fibers are unmyelinated. Histopathology and clinical experience imply that human SGNs can persist electrically excitable without dendrites, thus lacking connection to the organ of Corti. The biological background to this phenomenon remains elusive. We analyzed the pre- and post-somatic segments of the type I human SGNs using immunohistochemistry and transmission electron microscopy (TEM) in normal and pathological conditions. These segments were found surrounded by non-myelinated Schwann cells (NMSCs) showing strong intracellular expression of laminin-β2/collagen IV. These cells also bordered the perikaryal entry zone and disclosed surface rugosities outlined by a folded basement membrane (BM) expressing laminin-β2 and collagen IV. It is presumed that human large SGNs are demarcated by three cell categories: (a) myelinated Schwann cells, (b) NMSCs and (c) satellite glial cells (SGCs). Their BMs express laminin-β2/collagen IV and reaches the BM of the sensory epithelium at the habenula perforata. We speculate that the NMSCs protect SGNs from further degeneration following dendrite loss. It may give further explanation why SGNs can persist as electrically excitable monopolar cells even after long-time deafness, a blessing for the deaf treated with cochlear implantation.

Auditory brainstem implants (ABIs)--20 years of clinical experience in Uppsala, Sweden

CONCLUSIONS

Even though sound perception may be limited after treatment with an auditory brainstem implant (ABI), it provides benefits and should be selectively offered to patients. Importantly the patients must be motivated, given reasonable expectations of outcome and offered long-term rehabilitation with a considerable 'learn to listen' period with the implant device.

OBJECTIVES

To describe the clinical experiences and results of 24 ABI surgeries performed in Uppsala University Hospital between 1993 and 2013.

METHODS

Most patients (n = 20) suffered from neurofibromatosis type 2 (NF2); a few patients (n = 4) were paediatric non-NF2 patients. The files were searched for information on the presurgery size of the vestibular schwannoma, whether the patient had undergone gamma knife treatment, the surgical approach, the side effects of the surgery and of the use of the implant, the electrode activation pattern and implant use, and categories of auditory performance (CAP) score.

RESULTS

Our results show that many patients greatly benefited from an ABI, and most of the patients used their implants even though the hearing improvements usually consisted of awareness of surrounding sounds and improved lip-reading. No severe side effects were observed from implant stimulation.

Differentiation of human neural progenitor cell-derived spiral ganglion-like neurons: a time-lapse video study

CONCLUSIONS

Human neural progenitor cells can differentiate into spiral ganglion-like cells when exposed to inner ear-associated growth factors. The phenotype bears resemblance to human sphere-derived neurons.

OBJECTIVE

To establish an in vitro model for the human auditory nerve to replace and complement in vivo animal experiments and ultimately human in vivo transplantation.

METHODS

Human neural progenitors were differentiated under conditions developed for in vitro survival of human primary spiral ganglion culture with media containing growth factors associated with inner ear development. Differentiation was documented using time-lapse video microscopy. Time-dependent marker expression was evaluated using immunocytochemistry with fluorescence and laser confocal microscopy.

RESULTS

Within 14 days of differentiation, neural progenitors adopted neural phenotype and expressed spiral ganglion-associated markers.

Nanomedicine strategies for drug delivery to the ear

The highly compartmentalized anatomy of the ear aggravates drug delivery, which is used to combat hearing-related diseases. Novel nanosized drug vehicles are thought to overcome the limitations of classic approaches. In this article, we summarize the nanotechnology-based efforts involving nano-objects, such as liposomes, polymersomes, lipidic nanocapsules and poly(lactic-co-glycolic acid) nanoparticles, as well as nanocoatings of implants to provide an efficient means for drug transfer in the ear. Modern strategies do not only enhance drug delivery efficiency, in the inner ear these vector systems also aim for specific uptake into hair cells and spiral ganglion neurons. These novel peptide-mediated strategies for specific delivery are reviewed in this article. Finally, the biosafety of these vector systems is still an outstanding issue, since long-term application to the ear has not yet been assessed.

Water permeability of the mammalian cochlea: functional features of an aquaporin-facilitated water shunt at the perilymph-endolymph barrier

The cochlear duct epithelium (CDE) constitutes a tight barrier that effectively separates the inner ear fluids, endolymph and perilymph, thereby maintaining distinct ionic and osmotic gradients that are essential for auditory function. However, in vivo experiments have demonstrated that the CDE allows for rapid water exchange between fluid compartments. The molecular mechanism governing water permeation across the CDE remains elusive. We computationally determined the diffusional (PD) and osmotic (Pf) water permeability coefficients for the mammalian CDE based on in silico simulations of cochlear water dynamics integrating previously derived in vivo experimental data on fluid flow with expression sites of molecular water channels (aquaporins, AQPs). The PD of the entire CDE (PD = 8.18 × 10(-5) cm s(-1)) and its individual partitions including Reissner's membrane (PD = 12.06 × 10(-5) cm s(-1)) and the organ of Corti (PD = 10.2 × 10(-5) cm s(-1)) were similar to other epithelia with AQP-facilitated water permeation. The Pf of the CDE (Pf = 6.15 × 10(-4) cm s(-1)) was also in the range of other epithelia while an exceptionally high Pf was determined for an epithelial subdomain of outer sulcus cells in the cochlear apex co-expressing AQP4 and AQP5 (OSCs; Pf = 156.90 × 10(-3) cm s(-1)). The Pf/PD ratios of the CDE (Pf/PD = 7.52) and OSCs (Pf/PD = 242.02) indicate an aqueous pore-facilitated water exchange and reveal a high-transfer region or "water shunt" in the cochlear apex. This "water shunt" explains experimentally determined phenomena of endolymphatic longitudinal flow towards the cochlear apex. The water permeability coefficients of the CDE emphasise the physiological and pathophysiological relevance of water dynamics in the cochlea in particular for endolymphatic hydrops and Ménière's disease.

How to predict cochlear length before cochlear implantation surgery

CONCLUSIONS

The basal turn diameter of the human cochlea predicts the outer wall length of the basal and two first turns relatively well but there was less correlation for the total cochlear length. The linear regression graph defines the length of the basal turn within an error of ± 1 mm and could be used clinically to distinguish small and large cochleae.

OBJECTIVE

The human cochlea varies in size. The preoperative assessment of cochlear length can be crucial for non-traumatic electrode insertion and hearing preservation. In this study, we estimated the external cochlear wall length by assessing the basal turn diameter.

METHODS

A total of 51 non-selected, human inner ear moulds were analysed. A line was drawn from the midpoint of the round window through the cochlear mid-portion to the opposite side (A) and correlated to the cochlear turn lengths. Linear regression analyses were carried out.

RESULTS

Mean diameter A was 9.3 mm. The mean basal turn length was 22.8 mm, the two first turns were 35.1 mm and the total length was 41.2 mm. Linear regression analyses indicated a coefficient of determination (R(2)) of 0.74 for diameter A and the basal turn length, R(2) = 0.70 for the two-turn length and R(2) = 0.39 for the total length.

Round window vibroplasty in chronic ear surgery: comparison with conventional hearing rehabilitation

CONCLUSION

Functional hearing results with round window vibroplasty in chronically disabled middle ears were comparable and, at high frequencies, superior to the results achieved with previously used conventional hearing aids even after extended surgery. Soft tissue transfer appears to be more important than floating mass transducer (FMT) alignment with the round window membrane (RWM) for efficient coupling or sonoinversion.

OBJECTIVES

To evaluate the functional hearing results of an active middle ear implant (AMEI) to the round window niche (RWN). The results were compared with previously used conventional hearing aids. The position of the FMT was determined by cone-beam computed tomography (CBCT).

METHODS

This was a prospective cohort study carried out in a tertiary referral center. Seven patients with severe middle ear disease were implanted with an AMEI with round window application. The postoperative hearing outcome was compared with preoperative hearing using unaided and conventionally aided conditions. The results were correlated with the physical/geometric relation of the FMT to the RWM as determined with CBCT.

RESULTS

Dislocation of the FMT was not observed. One patient was re-implanted due to accidental damage to the electrode. In all patients, the pertinent functional hearing results were achieved and were comparable to previous rehabilitation results.

Non-echo planar diffusion-weighted MRI increases follow-up accuracy after one-step step canal wall-down obliteration surgery for cholesteatoma

CONCLUSION

Non-echo planar (non-EPI) diffusion-weighted (DW) magnetic resonance imaging (MRI) increases the number of detected cholesteatoma after one-step canal wall-down (CWD) obliteration surgery for cholesteatoma compared with clinical evaluation alone.

OBJECTIVE

To evaluate the use of DW-MRI for detection of cholesteatoma after surgical treatment using a CWD obliteration technique.

METHODS

Thirty-eight adult patients (41 ears) treated with an identical one-step CWD obliteration surgical technique were included in a prospective and blinded study. All patients were investigated with non-EPI and EPI DW-MRI 1-9 months after the clinical examination. Follow-up time after primary surgery varied between 10 and 234 months. DW-MRI was assessed by two neuroradiologists and compared with clinical results. Inter-rater agreement was calculated. Positive non-EPI DW-MRI cases underwent revision surgery within 18-159 days after imaging.

RESULTS

Seven of 41 cases were evaluated as positive for cholesteatoma on non-EPI DW-MRI. Since one patient refused surgery six of these seven cases underwent surgical revision and all were verified. There was agreement between clinical and non-EPI findings in five of eight cases. EPI findings correlated poorly with non-EPI and clinical findings. Inter-rater agreement (Cohen's kappa) was 0.91 for non-EPI DW-MRI (p < 0.001) and -0.062 for EPI DW-MRI (p = 0.43).

Surgical treatment of adult cholesteatoma: long-term follow-up using total reconstruction procedure without staging

CONCLUSIONS

A total of 330 cases of adult cholesteatoma were operated with canal-wall down (CWD) and total reconstruction procedure (TRP) without staging. Independent of preoperative middle ear conditions, cholesteatoma extent and localization, long-term improvement of hearing with a low incidence of residual and recurrent disease were achieved.

OBJECTIVES

To evaluate long-term surgical and hearing results using a well-defined surgical technique without staging in adult cholesteatoma.

METHODS

The same CWD surgical technique, including obliteration of the mastoid cavity, reconstruction of the canal wall, and ossiculoplasty with autologous bone, was used by three senior surgeons (1982-2004). Preoperative and postoperative pure tone average (PTA) for air conduction (AC), bone conduction (BC), and air-bone gap (ABG) were assessed and compared 1, 3, and 6 years after surgery. Various prognostic factors with potential influence on long-term hearing outcome were evaluated.

RESULTS

Recurrence of AC occurred in 10%, residual disease in 3%. Six years after surgery all patients except one had a dry ear and over 92% of all cases were water resistant. Three patients developed complete deafness. Long-lasting improvement and/or preservation of hearing, with maintenance of PTA-ABG closure in 68% of all cases within 20 dB, were obtained. Sixty-four (19%) ossicular revisions were performed.

Human cochlea: anatomical characteristics and their relevance for cochlear implantation

This is a review of the anatomical characteristics of human cochlea and the importance of variations in this anatomy to the process of cochlear implantation (CI). Studies of the human cochlea are essential to better comprehend the physiology and pathology of man's hearing. The human cochlea is difficult to explore due to its vulnerability and bordering capsule. Inner ear tissue undergoes quick autolytic changes making investigations of autopsy material difficult, even though excellent results have been presented over time. Important issues today are novel inner ear therapies including CI and new approaches for inner ear pharmacological treatments. Inner ear surgery is now a reality, and technical advancements in the design of electrode arrays and surgical approaches allow preservation of remaining structure/function in most cases. Surgeons should aim to conserve cochlear structures for future potential stem cell and gene therapies. Renewal interest of round window approaches necessitates further acquaintance of this complex anatomy and its variations. Rough cochleostomy drilling at the intricate "hook" region can generate intracochlear bone-dust-inducing fibrosis and new bone formation, which could negatively influence auditory nerve responses at a later time point. Here, we present macro- and microanatomic investigations of the human cochlea viewing the extensive anatomic variations that influence electrode insertion. In addition, electron microscopic (TEM and SEM) and immunohistochemical results, based on specimens removed at surgeries for life-threatening petroclival meningioma and some well-preserved postmortal tissues, are displayed. These give us new information about structure as well as protein and molecular expression in man. Our aim was not to formulate a complete description of the complex human anatomy but to focus on aspects clinically relevant for electric stimulation, predominantly, the sensory targets, and how surgical atraumaticity best could be reached.

Assessment of Meniere's disease from a radiological aspect - saccular otoconia as a cause of Meniere's disease?

CONCLUSION

Significant reduced visualization of the reuniting duct (ductus reuniens; RD), saccular duct (SD) and endolymphatic sinus (ES) in Meniere's disease (MD) compared with normal control ears on three-dimensional (3D) CT imaging suggests the blockage of endolymphatic flow there with radiodense substances, which may be explained by dislodged otoconia from the saccule. These structures could be involved in the pathogenesis of MD.

OBJECTIVE

This study was designed to visualize and assess the RD, SD and ES in patients with MD using 3D CT.

METHODS

Sixty-two patients with a definite diagnose of unilateral MD, based on criteria proposed by the Committee on Hearing and Equilibrium of the American Academy of Otolaryngology-Head and Neck Surgery (AAO-HNS), were compared with contralateral ears and normal controls (26 ears) using 3D CT. The RD, SD and ES were scrutinized for patency on 3D CT images.

RESULTS

MD ears showed loss of continuity of the RD, SD and ES based on evaluation of 3D CT images, and differed significantly from normal healthy control ears (p < 0.01).

Cochlear implantation and hearing preservation: Results in 21 consecutively operated patients using the round window approach

CONCLUSION

Prevalent hearing conservation may be achieved after round window (RW) cochlear implantation using soft and flexible electrode arrays if variations of RW anatomy, topography, and facial nerve position are considered. The most favorable electrode insertion depth remains to be established.

OBJECTIVES

We assessed the incidence of cochlear function after cochlear implant (CI) electrode insertion through the RW in our first 21 consecutively operated patients aimed at hearing conservation.

METHODS

Eleven patients had a preoperative low frequency hearing suitable for electro-acoustic stimulation. Hearing was preserved in an additional nine patients at their request with the intention to use full frequency CI stimulation. Anatomic variations of the RW were carefully considered using our temporal bone collection of micro-dissected ears. Electrode extension was assessed on X-ray by measuring the insertion angle of the first electrode and intra-cochlear length and correlated with audiometric data.

RESULTS

There was no incidence of total loss of residual hearing in any of the patients. A slight deterioration of low frequency thresholds occurred in some patients. Mean hearing loss at 125-500 Hz was 14.4 dB at 1 month following surgery and 15.6 dB after 1 year. Insertion angle (300-540°) and depth (17.5-28.5 mm) were not statistically correlated to hearing loss.

High frequency hearing following stapes surgery

CONCLUSION

Our results indicate that a pre-existing sensorineural hearing loss (SNHL) is not a potential risk factor for further hearing loss in stapes surgery.

OBJECTIVE

The study evaluated whether pre-existing SNHL in otosclerosis constitutes a risk factor for further hearing loss in stapedotomy.

METHODS

Preoperative and postoperative audiometric evaluation including air (AC) and bone conduction (BC) hearing levels were assessed together with collection of surgical records from 338 consecutively operated cases for primary otosclerosis using a database. Patients were operated by the same surgeon between 2000 and 2006. In all, 291 patients were operated on 1 side and 47 patients were operated on both sides. Ages ranged from 16 to 76 years. Stapedotomy was performed in all cases except five (stapedectomy). Cases were separated into four different groups based on preoperative AC hearing levels at 4, 6, and 8 kHz: group I, <30 dB HL; group II, 30-50 dB HL; group III, 51-70 dB HL; group IV, >70 dB HL).

RESULTS

Hearing deterioration at 4, 6, and 8 kHz (>10 dB) was observed in 6.5% of all cases. Patients with normal preoperative hearing were found to be more prone to further SNHL 4, 6, and 8 kHz (range 13-25 dB) at surgery, while patients in group IV, with preoperative SNHL impairment, remained unaffected.

Distribution of P75 neurotrophin receptor in adult human cochlea--an immunohistochemical study

Mechanisms underlying the unique survival property of human spiral neurons are yet to be explored. P75 (p75(NTR)) is a low affinity receptor for neurotrophins and is known to interact with Trk receptors to modulate ligand binding and signaling. Up-regulation of this receptor was found to be associated with apoptosis as well as with cell proliferation. Its distribution and injury-induced change in expression pattern in the cochlea have been mainly studied in rodents. There is still no report concerning p75(NTR) in post-natal human inner ear. We analyzed, for the first time, p75(NTR) expression in five freshly fixed human cochleae by using immunohistochemistry techniques, including myelin basic protein (MBP) as a myelin sheath marker and TrkB as the human spiral neuron marker, and by using thin optical sectioning of laser confocal microscopy. The inner ear specimens were obtained from adult patients who had normal pure tone thresholds before the surgical procedures, via a trans-cochlear approach for removal of giant posterior cranial fossa meningioma. The expression of p75(NTR) was investigated and localized in the glial cells, including Schwann cells and satellite glial cells in the Rosenthal canal, in the central nerve bundles within the modiolus, and in the osseous spiral lamina of the human cochleae. The biological significance of p75(NTR) in human cochlea is discussed.

Expression of myelin basic protein in the human auditory nerve - an immunohistochemical and comparative study

OBJECTIVE

The aim of this study is to analyse the expression and distribution of myelin basic protein (MBP or Myelin A1 protein) in the human spiral ganglion and auditory nerve.

MATERIALS AND METHODS

Cryostat sections were made from freshly fixed human cochlear specimens removed at surgery in patients with life-threatening petro-clival meningiomas compressing the brain stem. The sections were subjected to immunohistochemistry using antibodies against MBP, S-100 and Tubulin. The immunoreaction was documented using laser confocal microscopy.

RESULTS

Type I spiral ganglion nerve somata (SGN) were surrounded by so-called "satellite glial cells" (SGCs) that lacked expression of MBP consistent with earlier light and electron microscopic findings indicating that these cells are non-myelinating. S-100 labeling showed that the SGCs form a continuous network in the apical region.

CONCLUSIONS

The pattern of myelination in human spiral ganglion is different from that in other species' spiral ganglion. The striking differences in myelin outline should be investigated further in combination with its influence on signal coding and preservation properties in man.

Histology and synchrotron radiation-based microtomography of the inner ear in a molecularly confirmed case of CHARGE syndrome

CHARGE (Coloboma of the iris or retina, heart defects, atresia of the choanae, retardation of growth and/or development, genital anomalies, ear anomalies) syndrome (OMIM #214800) affects about 1 in 10,000 children and is most often caused by chromodomain helicase DNA-binding protein-7 (CHD7) mutations. Inner ear defects and vestibular abnormalities are particularly common. Specifically, semicircular canal (SCC) hypoplasia/aplasia and the presence of a Mondini malformation can be considered pathognomonic in the context of congenital malformations of the CHARGE syndrome. We obtained a temporal bone (TB) of a patient with CHARGE syndrome who died from bacteremia at 3 months of age. The clinical diagnosis was confirmed in the patient by direct DNA sequencing and the detection of a de novo, truncating CHD7 mutation, c.6169dup (p.R2057fs). We assessed changes of the TB and the degree of neural preservation, which may influence the potential benefit of cochlear implantation. The TB was analyzed using synchrotron radiation-based micro computed tomography, and by light microscopy. The vestibular partition consisted of a rudimentary vestibule with agenesis of the SCCs. The cochlea was hypoplastic with poor or deficient interscaling and shortened (Mondini dysplasia). The organ of Corti had near normal structure and innervation. Modiolus and Rosenthal's canal were hypoplastic with perikarya displaced along the axon bundles into the internal acoustic meatus, which may be explained by the arrest or limited migration and translocation of the cell nuclei into the cochlear tube during development.

Antisecretory factor-inducing therapy improves the clinical outcome in patients with Ménière's disease

CONCLUSION

Intake of antisecretory factor (AF)-inducing SPC-flakes significantly reduced vertigo in patients suffering from Ménière's disease (MD). The positive effect may be due to a modulation of the transport of water and ions in the endolymphatic space.

OBJECTIVE

To evaluate the effects of a 3-month treatment period with SPC-flakes in patients suffering from MD.

PATIENTS AND METHODS

A prospective, double-blind, placebo-controlled study was performed. A total of 51 adult patients with MD were included in the study: 27 subjects treated with SPC-flakes and 24 subjects with control cereals. The patients received SPC-flakes or control cereals (1 g per kg body weight per 24 h in two servings) for 3 months. Otoneurological examinations were carried out before and after this period.

RESULTS

The severity of MD was classified according to the American Academy of Otolaryngology-Head and Neck Surgery (AAO-HNS) grading system. Fourteen of the 27 patients randomized to intake of the AF-inducing SPC-flakes reported decreased vertigo, compared with 2 of 24 in the control group (p < 0.001). No consistent change in the otoneurological examinations could be demonstrated in any of the groups of patients.

Ganglion cell and 'dendrite' populations in electric acoustic stimulation ears

BACKGROUND/AIMS

The electric acoustic stimulation (EAS) technique combines electric and acoustic stimulation in the same ear and utilizes both low-frequency acoustic hearing and electric stimulation of preserved neurons. We present data of ganglion cell and dendrite populations in ears from normal individuals and those suffering from adult-onset hereditary progressive hearing loss with various degrees of residual low-frequency hearing. Some of these were potential candidates for EAS surgery. The data may give us information about the neuroanatomic situation in EAS ears.

METHODS

Dendrites and ganglion cells were calculated and audiocytocochleograms constructed. The temporal bones were from the collection at the House Ear Institute in Los Angeles, Calif., USA. Normal human anatomy, based on surgical specimens, is presented.

RESULTS

Inner and outer hair cells, supporting cells, ganglion cells and dendrites were preserved in the apical region. In the mid-frequency region, around 1 kHz, the organ of Corti with inner and outer hair cells was often conserved while in the lower basal turn, representing frequencies above 3 kHz, the organ of Corti was atrophic and replaced by thin cells. Despite loss of hair cells and lamina fibers ganglion cells were present even after 28 years of deafness.

CONCLUSIONS

Conditions with profound sensorineural hearing loss and preserved low-frequency hearing may have several causes and the pathology may vary accordingly. In our patients with progressive adult-onset sensorineural hearing loss (amalgamated into 'presbyacusis'), neurons were conserved even after long duration of deafness. These spiral ganglion cells may be excellent targets for electric stimulation using the EAS technique.