[Show abstract][Hide abstract] ABSTRACT: Auditory sensitivity and frequency resolution depend on the physical properties of the basilar membrane in combination with outer hair cell-based amplification in the cochlea. The physiological role of the tectorial membrane (TM) in hair cell transduction has been controversial for decades. New insights into the TM structure and function have been gained from studies of targeted gene disruption. Several missense mutations in genes regulating the human TM structure have been described with phenotypic expressions. Here, we portray the remarkable gradient structure and molecular organization of the human TM. Ultrastructural analysis and confocal immunohistochemistry were performed in freshly fixed human cochleae obtained during surgery. Based on these findings and recent literature, we discuss the role of human TMs in hair cell activation. Moreover, the outcome proposes that the α-tectorin-positive amorphous layer of the human TM is replenished and partly undergoes regeneration during life.
Full-text · Article · Jun 2015 · Cell and Tissue Research
[Show abstract][Hide abstract] ABSTRACT: Systemic pharmacotherapies have limitation due to blood-labyrinth barrier, so local delivery via the round window membrane opens a path for effective treatment. Multifunctional nanoparticle (NP)-mediated cell specific drug delivery may enhance efficacy and reduce side effects. Different NPs with ligands to target TrkB receptor were tested. Distribution, uptake mechanisms, trafficking, and bioefficacy of drug release of rolipram loaded NPs were evaluated.
We tested lipid based nanocapsules (LNCs), Quantum Dot, silica NPs with surface modification by peptides mimicking TrkB or TrkB activating antibodies. Bioefficacy of drug release was tested with rolipram loaded LNCs to prevent cisplatin-induced apoptosis. We established different cell culture models with SH-SY-5Y and inner ear derived cell lines and used neonatal and adult mouse explants. Uptake and trafficking was evaluated with FACS and confocal as well as transmission electron microscopy.
Plain NPs show some selectivity in uptake related to the in vitro system properties, carrier material, and NP size. Some peptide ligands provide enhanced targeted uptake to neuronal cells but failed to show this in cell cultures. Agonistic antibodies linked to silica NPs showed TrkB activation and enhanced binding to inner ear derived cells. Rolipram loaded LNCs proved as effective carriers to prevent cisplatin-induced apoptosis.
Most NPs with targeting ligands showed limited effects to enhance uptake. NP aggregation and unspecific binding may change uptake mechanisms and impair endocytosis by an overload of NPs. This may affect survival signaling. NPs with antibodies activate survival signaling and show effective binding to TrkB positive cells but needs further optimization for specific internalization. Bioefficiacy of rolipram release confirms LNCs as encouraging vectors for drug delivery of lipophilic agents to the inner ear with ideal release characteristics independent of endocytosis.
Full-text · Article · May 2015 · Frontiers in Aging Neuroscience
[Show abstract][Hide abstract] ABSTRACT: This presentation aims to display some important anatomical characteristics and variations of the human cochlea that may influence outcomes with cochlear implants. I will describe the complexity of the “hook” region and how it may challenge atraumatic insertion of an electrode array. In addition, I will discuss advantages and disadvantages of various cochleostomy approaches and of various trajectories for insertions. These anatomical considerations are informed by micro dissections of human temporal bones and plastic casts of different parts of the bones. In addition, the studied microanatomy of the basilar membrane may inform insertions and insertion depths needed to preserve cochlear structures. In particular, the studies suggest that the vulnerability of the membrane may be greatest at the apex and this possibility has implications for electrode designs and insertions. Also, the apical region may be most susceptible to inflammation and fibrosis due to its anatomy. The anatomical considerations for safe insertions of electrodes, including preservation of the remaining neural tissue, will be discussed. This work was supported by grants from Uppsala University Hospital and Uppsala University; the Tysta Skolan Foundation; the Swedish Deafness Foundation; the European Community 7th Framework Programme; and kind private donations from Börje Runögård.
No preview · Article · Apr 2015 · The Journal of the Acoustical Society of America
[Show abstract][Hide abstract] ABSTRACT: 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.
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.
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.
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.
Full-text · Article · Feb 2015 · Cell and Tissue Research
[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.
Electronic supplementary material
The online version of this article (doi:10.1007/s00441-013-1735-2) contains supplementary material, which is available to authorized users.
Full-text · Article · Nov 2013 · Cell and Tissue Research
[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.
[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.
Full-text · Article · Jun 2013 · Journal of Controlled Release
[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.
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.
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%).
Extracapsular spread depicted on computed tomography using strict criteria has high specificity.
No preview · Article · Jun 2013 · European journal of radiology
[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.
No preview · Article · Feb 2013 · Disease Models and Mechanisms
[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 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.
Full-text · Article · Jul 2012 · International Journal of Nanomedicine
[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.
No preview · Article · Apr 2012 · Otology & neurotology: official publication of the American Otological Society, American Neurotology Society [and] European Academy of Otology and Neurotology