[Show abstract][Hide abstract] ABSTRACT: 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 (NMSC) 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) non-myelinated Schwann cells (NMSC) 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 NMSC 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.
[Show abstract][Hide abstract] ABSTRACT: Human spiral ganglion (SG) neurons show remarkable survival properties and maintain electric excitability for a long time after complete deafness and even separation from the organ of Corti, features essential for cochlear implantation. Here, we analyze and compare the localization and distribution of gap junction (GJ) intercellular channels and connexin 43 (Cx43) in cells surrounding SG cell bodies in man and guinea pig by using transmission electron microscopy and confocal immunohistochemistry. GJs and Cx43 expression has been recognized in satellite glial cells (SGCs) in non-myelinating sensory ganglia including the human SG. In man, SG neurons can survive as mono-polar or "amputated" cells with unbroken central projections following dendrite degeneration and consolidation of the dendrite pole. Cx43-mediated GJ signaling between SGCs is believed to play a key role in this "healing" process and could explain the unique preservation of human SG neurons and the persistence of cochlear implant function.
Cell and Tissue Research 11/2013; · 3.33 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Our knowledge about the neural code in the auditory nerve is based to a large extent on experiments on cats. Several anatomical differences between auditory neurons in human and cat are expected to lead to functional differences in speed and safety of spike conduction.
Confocal microscopy was used to systematically evaluate peripheral and central process diameters, commonness of myelination and morphology of spiral ganglion neurons (SGNs) along the cochlea of three human and three cats. Based on these morphometric data, model analysis reveales that spike conduction in SGNs is characterized by four phases: a postsynaptic delay, constant velocity in the peripheral process, a presomatic delay and constant velocity in the central process. The majority of SGNs are type I, connecting the inner hair cells with the brainstem. In contrast to those of humans, type I neurons of the cat are entirely myelinated. Biophysical model evaluation showed delayed and weak spikes in the human soma region as a consequence of a lack of myelin. The simulated spike conduction times are in accordance with normal interwave latencies from auditory brainstem response recordings from man and cat. Simulated 400 pA postsynaptic currents from inner hair cell ribbon synapses were 15 times above threshold. They enforced quick and synchronous spiking. Both of these properties were not present in type II cells as they receive fewer and much weaker ((∼)26 pA) synaptic stimuli.
Wasting synaptic energy boosts spike initiation, which guarantees the rapid transmission of temporal fine structure of auditory signals. However, a lack of myelin in the soma regions of human type I neurons causes a large delay in spike conduction in comparison with cat neurons. The absent myelin, in combination with a longer peripheral process, causes quantitative differences of temporal parameters in the electrically stimulated human cochlea compared to the cat cochlea.
PLoS ONE 11/2013; 8(11):e79256. · 3.53 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: 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.
[Show abstract][Hide abstract] ABSTRACT: Numerous studies on nanocarriers use fluorescent dye labeling to investigate their biodistribution or cellular trafficking. However, when the fluorescence dye is not grafted to the nanocarrier, the question of the stability of the labeling arises. How can it be validated that the fluorescence observed during an experiment corresponds to the nanocarriers, and not to the free dye released from the nanocarriers? Studying the integrity of the labeling is challenging. Therefore, an innovative approach to confirm the labeling stability was developed, based on the transfer of a fluorescent dye from its hosting nanocarrier to a lipophilic compartment. Lipid nanocapsules (LNC) and triglyceride oil were used as models. The protocol involved mixing of LNC suspension and oil, and then separation by centrifugation. The quality of the separation was controlled by light scattering, using the derived count rate tool. Dye transfer from loaded LNCs to the lipophilic compartment or from a lipophilic compartment containing dye to non-loaded LNC was investigated by varying the nature of the dye and the oil, the oil volume and the LNC dilution. Tensiometry was used to define the dye location in the nanocarrier. Results showed that when dyes such as Nile Red and Coumarin-6 are located in oily core, the transfer occurred in a partition-dependent manner. In contrast, when the dye was entrapped in the surfactant shell of LNCs such as lipophilic indocarbocyanines (i.e. DiO, DiI and DiD), no transfer was observed. Dye diffusion was also observed in cell culture, with Nile Red inside lipid bodies of HEI-OC1 cells, without uptake of LNCs. In contrast, DiO-loaded LNCs had to be internalized to observe fluorescence inside the cells, providing a further confirmation of the absence of transfer in this case, and the stability of fluorescence labeling of the LNCs.
Journal of Controlled Release 06/2013; · 7.63 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: BACKGROUND: Extracapsular spread of cervical lymph nodes deteriorates the prognosis of patients with head and neck squamous cell carcinoma. Postoperative radiochemotherapy is superior to postoperative radiotherapy alone in patients with histologically proven extracapsular spread. If extracapsular spread can be detected preoperatively, patients may favor primary radiochemotherapy instead of primary surgery plus postoperative radiochemotherapy. METHODS: Computed tomography (CT) scans of nodal positive head and neck squamous cell carcinoma patients treated between 2008 and 2010 with comprehensive neck dissection as part of first line surgical treatment were retrospectively scanned for extracapsular spread by two blinded radiologists. If a positive lymph node was identified by the pathologist, CT scans were assessed for extracapsular spread retrospectively. CT criteria for Extracapsular spread were apparent fat and soft tissue infiltration or infiltration of sternocleidomastoid muscle, internal jugular vein or carotid artery. Radiologic judgment was compared with histological evidence of extracapsular spread and specificity and sensitivity of CT detection was calculated. RESULTS: Forty-nine patients with histologically proven positive lymph nodes (pN+) were included. Extracapsular spread was histologically proven in 17 cases; the number of all affected lymph nodes was not listed. Radiologist 1 found extracapsular spread in CT scans of 15/49 patients and radiologist 2 in 16/49 patients (Cohen's kappa=0.86; p<0.01). Sensitivity of radiologic extracapsular spread detection was 73% (95% confidential index (CI): 44.0-89.7%) and specificity 91% (75.0-98.0%). CONCLUSION: Extracapsular spread depicted on computed tomography using strict criteria has high specificity.
European journal of radiology 06/2013; · 2.65 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Hearing loss is a frequent finding in intensive care patients due to several causes. However, sepsis has not been examined as a possible cause. The aim of the study is to assess the influence of experimental sepsis on hearing thresholds and to evaluate pathologic changes in the cochlea. Eighteen sepsis mice, 13 sham and 13 control animals were included into the study using cecal ligation puncture technique. Prior to the induction of sepsis and at the peak of the disease the hearing thresholds of the animals were evaluated with auditory evoked brainstem responses. Immediately after the second measurement the mice were sacrificed, the inner ears harvested and prepared for further evaluation. The cochleae were examined with light microscopy, electron microscopy and immunohistochemistry for Bax, cleaved Caspase 3 and Bcl 2. The sepsis mice showed a significant hearing loss but not the control groups. Induction of apoptosis could be shown in the supporting cells of the organ of Corti. Furthermore, excitotoxicity could be shown at the basal pole of the inner hair cells. In this murine model sepsis leads to significant hearing impairment. The physiologic alteration could be linked to apoptosis in the supporting cells of the organ of Corti and to a disturbance of the inner hair cells synapses.
Disease Models and Mechanisms 02/2013; · 4.96 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Background: Due to their biochemical versatility, nanoparticles (NPs) have become one of the most important future carriers for drugs and genes. NP-mediated delivery could enable an effective pharmacotherapy to the inner ear and combat hearing loss. Aims: This study investigates the endocytic trafficking of silica NPs within HEI-OC1 cells, a cell line derived from the inner ear. Materials & methods: To investigate the interaction between 50-, 70- and 100-nm silica NPs and the cells, the authors employed a set of commonly available methods involving light and electron microscopy, and sample processing methods, which preserve the native cell shape and the fragile endocytic structures. Results: The authors observed that 50-nm NPs were the most efficiently internalized. They also identified macropinocytosis as the dominant mechanism of uptake, showed localization of NPs in the early endosome and observed that silica NPs were delayed during trafficking to the lysosomes, where these NPs stayed confined, showing no endosomal escape. Conclusion: These silica NPs mostly rely on macropinocytosis for internalization. A successful use of silica NPs as vectors would involve smaller NPs and an endosomal escape strategy. Original submitted 21 December 2011; Revised submitted 23 May 2012.
[Show abstract][Hide abstract] ABSTRACT: The unique, unmyelinated perikarya of spiral ganglion cells (SGCs) in the human cochlea are often arranged in functional units covered by common satellite glial cells. This micro anatomical peculiarity presents a crucial barrier for an action potential (AP) travelling from the sensory receptors to the brain. Confocal microscopy was used to acquire systematically volumetric data on perikarya and corresponding nuclei in their full dimension along the cochlea of two individuals. Four populations of SGCs within the human inner ear of two different specimens were identified using agglomerative hierarchical clustering, contrary to the present distinction of two groups of SGCs. Furthermore, we found evidence of a spatial arrangement of perikarya and their accordant nuclei along the cochlea spiral. In this arrangement, the most uniform sizes of cell bodies are located in the middle turn, which represents the majority of phonational frequencies. Since single-cell recordings from other mammalians may not be representative to humans and human SGCs are not accessible for physiological measurements, computer simulation has been used to quantify the effect of varying soma size on single neuron response to electrical micro stimulation. Results show that temporal parameters of the spiking pattern are affected by the size of the cell body. Cathodic stimulation was found to induce stronger variations of spikes while also leading to the lowest thresholds and longest latencies. Therefore, anodic stimulation leads to a more uniform excitation profile among SGCs with different cell body size.
[Show abstract][Hide abstract] ABSTRACT: Currently, no large animal model exists for surgical-experimental exploratory analysis of implantable hearing devices. In a histomorphometric study, we sought to investigate whether sheep or pig cochleae are suitable for this purpose and whether device implantation is feasible.
Skulls of pig and sheep cadavers were examined using high-resolution 128-slice computed tomography (CT) to study anatomic relationships. A cochlear implant and an active middle ear implant could be successfully implanted into the sheep's inner and middle ear, respectively. Correct device placement was verified by CT and histology. The cochlear anatomy of the sheep was further studied by micro-CT and histology.
Our investigations indicate that the sheep is a suitable animal model for implantation of implantable hearing devices. The implantation of the devices was successfully performed by access through a mastoidectomy. The histologic, morphologic, and micro-CT study of the sheep cochlea showed that it is highly similar to the human cochlea. The temporal bone of the pig was not suitable for these microsurgical procedures because the middle and inner ear were not accessible owing to distinct soft and fatty tissue coverage of the mastoid.
The sheep is an appropriate large animal model for experimental studies with implantable hearing devices, whereas the pig is not.
Otology & neurotology: official publication of the American Otological Society, American Neurotology Society [and] European Academy of Otology and Neurotology 04/2012; 33(3):481-9. · 1.44 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: 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.
Cell and Tissue Research 03/2012; 348(3):407-15. · 3.33 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Experimental murine malaria has been shown to result in significant hearing impairment. Microscopic evaluation of the temporal bones of these animals has revealed regular morphology of the cochlea duct. Furthermore, the known vascular pathologic changes being associated with malaria could not be found. Immunohistochemistry for ICAM1 showed a strong marking in the stria vascularis, indicating a disturbance of the endocochlear potential. The aim of this study was to evaluate the role of apoptosis and the disturbance of the blood labyrinth barrier in the murine malaria associated hearing impairment.
The temporal bones of seven mice with cerebral malaria-four with hearing impairment, three without hearing impairment-were evaluated with immunohistochemistry for cleaved caspase 3 to detect apoptosis and connexin 26, a gap junction protein being a cornerstone in the endocochlear potassium recirculation. Furthermore five animals with cerebral malaria were treated with Evans blue prior to sacrification to detect disturbances of the blood labyrinth barrier.
Cleaved caspase 3 could clearly be detected by immunohistochemistry in the fibrocytes of the spiral ligament, more intensively in animals with hearing impairment, less intensively in those without. Apoptosis signal was equally distributed in the spiral ligament as was the connexin 26 gap junction protein. The Evans blue testing revealed a strong signal in the malaria animals and no signal in the healthy control animals.
Malfunction of the fibrocytes type 1 in the spiral ligament and disruption of the blood labyrinth barrier, resulting in a breakdown of the endocochlear potential, are major causes for hearing impairment in murine cerebral malaria.
[Show abstract][Hide abstract] ABSTRACT: The neurotrophic receptor tyrosine kinase B (TrkB) has diverse signaling roles in neurons and tumor cells. Accordingly, its suppressive targeting is of interest in neuroblastoma and other tumors, whereas its role in improving survival is focused in neurons. Here we describe targeting of TrkB-binding peptide-conjugated liposomes (PCL) to the TrkB-expressing mouse macrophage-like cell line RAW264, and to all-trans-retinoic acid-treated neuron-like TrkB⁺ SH-SY5Y human neuroblastoma cells.
Binding and internalization of PCL was monitored by flow cytometry and confocal fluorescence microscopy.
Internalization of TrkB-targeted PCL by RAW264 cells was enhanced and faster when compared with PCL having the corresponding scrambled peptide. Likewise, binding and augmented uptake were confirmed for TrkB⁺ SH-SY5Y cells, with targeted PCL appearing in the cytoplasm after 20 minutes of incubation.
We demonstrate here the feasibility of targeting liposomes to TrkB-expressing cells by 18-mer peptides, promoting cellular uptake (at least partly into endosomes) via receptor-mediated pathways.
International Journal of Nanomedicine 01/2012; 7:3475-85. · 4.20 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Activation of tyrosine kinase receptor B (TrkB), a neurotrophin receptor, has been shown to increase neuronal cell survival and promote regeneration. Stimulation of the TrkB receptor by neurotrophic growth factors has been identified as a possible therapeutic target for the treatment of neurodegenerative disorders. However, growth factor delivery is problematic because of a short half-life in vivo. We have conjugated hNgf-EE, a short peptide mimetic of NGFβ to the surface of polymersome nanoparticles and shown that they are capable of activating the TrkB receptor in vitro in the SHSY-G7 cell line. We propose that polymersomes could act as a scaffold for the delivery of TrkB activating moieties and that the polymersome size and polyethylene glycol surface have been shown to increase in vivo retention time. These multifunctional nanoparticles have potential for the treatment of neurodegenerative disorders by TrkB activation. From the ClinicaL Editor: Tyrosine kinase receptor B activation has been shown to promote regeneration and survival of neurons. However, growth factor delivery to stimulate these receptors remains problematic. The authors demonstrate that a peptide mimetic of NGFβ conjugated to the surface of polymersome nanoparticles is capable of activating the TrkB receptors. These nanoparticles may offer a novel treatment strategy for a variety of neurodegenerative disorders.
Nanomedicine: nanotechnology, biology, and medicine 12/2011; 8(3):271-4. · 6.93 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Hearing loss is a very significant health problem. The methods currently available for inner ear drug delivery are limited and a noninvasive cell-specific drug delivery strategy needs to be found. Aim: In this study we investigated the ability of polymersomes, lipid core nanocapsules and hyperbranched poly-L-lysine to cross the round window membrane. Materials & Methods: Nanoparticles (NPs) used in this study have different size and chemical compositions. Freshly frozen human temporal bones were used for this investigation. Intact human round window membrane within the freshly frozen human temporal bone served as an excellent model to test the membrane permeation and distribution within the tissues. Results: In this investigation we were able to visualize the NPs across the round window membrane. The NPs were subsequently found to be distributed in the sensory hair cells, nerve fibers and to other cells of the cochlea. Conclusion: This finding raises hope in terms of future multifunctional NP-based drug delivery strategy to the human inner ear.
[Show abstract][Hide abstract] ABSTRACT: Objective To evaluate the pathophysiologic changes in the inner ear during the course of severe cerebral malaria in an established animal model, C57 BL/6J mice.Methods This study aims to examine the hearing threshold, the histological changes and ICAM-1 expression in the murine cochlea.Results Four of seven mice showed an expected hearing loss of 20 dB or more. The light microscopy of the inner ear did not show any morphologic alterations. The immunohistochemical analysis for ICAM-1 showed intensive staining in the stria vascularis of sick animals and hardly any reaction in healthy controls.Conclusion The up-regulation of ICAM-1 in the stria vascularis – generating the endocochlear potential – suggests its involvement in plasmodial infection.Objectif: Evaluer les modifications physiopathologiques de l’oreille interne au cours de la malaria cérébrale sévère dans un modèle animal établi, souris C57 BL/6J.Méthodes: Evaluation du seuil auditif, décrivant les modifications histologiques et l’expression de ICAM-1 dans la cochlée des souris.Résultats: Quatre souris sur sept ont montré une perte d’audition attendue de 20 dB ou plus. La microscopie optique de l’oreille interne n’a pas montré de modifications morphologiques. L’analyse immunohistochimique de l’ICAM-1 a montré une coloration intense de la strie vasculaire des animaux malades et presque aucune réaction chez les témoins sains.Conclusion: La régulation positive de ICAM-1 dans la strie vasculaire - générant le potentiel endocochléaire - suggère son implication dans l’infection plasmodique.
Tropical Medicine & International Health 05/2011; 16(8):914 - 922. · 2.30 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Nanoparticles as potential carriers for local drug transfer are an alternative to systemic drug delivery into the inner ear. We report on the first in vitro tests of a new ferrogel consisting of superparamagnetic iron oxide nanoparticles (SPIONs) and a Pluronic(®) F127 (PF127) copolymer. Pluronic copolymers possess a unique viscosity-adjustable property that makes PF127 gels easy to handle compared to conventional cross-linked hydrogels. This ferrogel was successfully tested in cadaver human temporal bones as well as in organotypic explant cultures of mouse inner ears. SPIONs were identified by light microscopy and localized with different imaging modes in energy-filtered transmission electron microscopy. Our approach shows a promising possibility to use iron oxide nanoparticles, which are suitable for visualization and characterization at both the light- and electron-microscopic levels. FROM THE CLINICAL EDITOR: The authors report the first in vitro tests of a new ferrogel consisting of superparamagnetic iron oxide nanoparticles (SPIONs) and a Pluronic® F127 (PF127) copolymer for drug delivery in the inner ear, demonstrasting a promising possibility to use iron oxide nanoparticles, which are suitable for visualization and characterization at both the light- and electron-microscopic levels.
Nanomedicine: nanotechnology, biology, and medicine 12/2010; 7(3):360-9. · 6.93 Impact Factor