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Biomedical subjects

H P Zenner

Publications and source records attributed to H P Zenner.

At least 19 recordsLinked to original sources
PubMed2000

Human studies of a piezoelectric transducer and a microphone for a totally implantable electronic hearing device.

OBJECTIVE: For the surgical treatment of patients with moderate and severe sensorineural hearing loss, the authors have developed a totally implantable hearing device, the totally integrated cochlea amplifier (TICA). To evaluate the effectiveness of transducer and microphone of this device, three separate human studies were conducted. STUDY DESIGN: The first study using transducer prototypes involved self experiments in investigators with normal hearing. The second study used the transducer prototypes in patients with hearing loss, and the third study involved the temporary implantation of the final transducer prototype and microphone in patients undergoing otologic surgery. PATIENTS: In routine middle ear surgery, transducer prototypes were coupled to the ossicular chain of 28 patients. In addition to the transducer, in 5 patients the microphone was placed beneath the skin of the auditory canal, allowing the skin to cover the microphone membrane completely. RESULTS: The piezoelectric transducer reached an equivalent sound pressure level of 145 dB SPL < or =10 kHz. The dynamics for music reached 32 dB, which was identical with the results of the preoperative investigations using high-fidelity headsets (33 dB). The low nonlinear distortions of <0.1% and the frequency range of 10 kHz are reflected in the positive evaluation of the sound quality by 84% of the patients involved. When phonetically balanced speech material and music were presented under free field conditions at a sound level of 65 dB SPL, understanding of the phonetically balanced speech material was 100%. Most patients judged the presentations of music as clear and undistorted with all broadband components. CONCLUSIONS: Data in humans on the performance of the two main components of the TICA implant, the transducer and the microphone, are reported.

Amplifiers, Electronic↗
PubMed1999

Differential expression of trkB.T1 and trkB.T2, truncated trkC, and p75(NGFR) in the cochlea prior to hearing function.

Prior to the onset of hearing, synchronous cellular, neuronal, and morphogenetic processes participate in the development of a functional cochlea. We have studied the expression of different splice forms of trkB and trkC as well as p75(NGFR) in rat and mouse cochlea within this critical developmental period, using in situ hybridization, PCR, Northern blotting, and immunohistochemical analyses. An antibody to full-length trkB receptors proved to detect full-length trkB receptors as well as truncated trkB.T2 but not trkB. T1 isoforms. Full-length trkB and trkC isoforms as well as trkB.T2 but not trkB.T1 receptors were noted in cochlear neurons. A transient expression of trkB.T1 and trkB.T2 was observed at the epithelial-mesenchymal border of the spiral ligament during this time. A sequential appearance of trkB.T1, the low-affinity neurotrophin receptor p75(NGFR), and trkB.T2 in epithelial cochlear cells correlated with the formation of the inner sulcus of the organ. A differential expression of presumptive trkB.T2 in hair and supporting cells was observed concomitant with the maturation of the distinct innervation pattern of these cells. A gradual shift from p75(NGFR) to truncated trkC receptors in Pillar cells occurred during the formation of the tunnel of Corti. A distinct expression of full-length trkC correlated with the time of differentiation of the stria vascularis. Finally, an expression of trkB.T1 and trkB.T2 in oligodendrocytes, full-length trkB and trkC in nerve fibers, and p75(NGFR) in Schwann cells was noted at the glial interface of the VIIIth nerve during the establishment of the glial transition zone. These various transitory neurotrophin receptor expression patterns, which were related to final maturation processes of the cochlea, may provide new insights into the as yet obscure role of neurotrophin receptors in nonneuronal tissue.

Animals↗
PubMed1999

Gene expression of P2X-receptors in the developing inner ear of the rat.

Reverse transcription-polymerase chain reaction (RT-PCR) was used to characterize the expression of P2X receptor subunits (P2X1-P2X7) in different inner ear tissues. The present study revealed the presence of P2X2, P2X3, P2X4 and P2X7-mRNA in rat organ of Corti, vestibular organ and spiral ganglion at different postnatal developmental stages (PD1-PD16), with slight differences in the onset of expression. Expression of P2X1, P2X5 and P2X6-mRNA was not detectable in the inner ear tissues. In addition, single cell RT-PCR experiments with outer hair cells (OHC) revealed the expression of either the P2X2 or the P2X2-2 splice variant or coexpression of both isoforms in individual cells. Our data suggest that extracellular adenosine-5'-triphosphate (ATP) may play an important role in signal transduction in the inner ear.

Aging↗
PubMed1999

A changing pattern of brain-derived neurotrophic factor expression correlates with the rearrangement of fibers during cochlear development of rats and mice.

The reorganization of specific neuronal connections is a typical feature of the developing nervous system. It is assumed that the refinement of connections in sensory systems requires spontaneous activity before the onset of cochlear function and selective sensory experience during the ensuing period. The mechanism of refinement through sensory experience is currently postulated as being based on the selective reinforcement of active projections by neurotrophins. We studied a presumed role of neurotrophins for rearrangement of afferent and efferent fibers before the onset of sensory function in the precisely innervated auditory end organ, the cochlea. We observed a spatiotemporal change in the localization of brain-derived neurotrophic factor (BDNF) protein and mRNA, which correlated with the reorganization of fibers. Thus, BDNF decreased in target hair cells during fiber retraction and was subsequently upregulated in neurons, target hair cells, and adjacent supporting cells concomitant with the formation of new synaptic contacts. Analysis of the innervation pattern in BDNF gene-deleted mice by immunohistochemistry and confocal microscopy revealed a failure in the rearrangement of fibers and a BDNF dependency of distinct neuronal projections that reorganize in control animals. Our data suggest that, before the onset of auditory function, a spatiotemporal change in BDNF expression in sensory, epithelial, and neuronal cells may guide the initial steps of refinement of the innervation pattern.

Afferent Pathways↗
PubMed1999

Gene disruption of p27(Kip1) allows cell proliferation in the postnatal and adult organ of corti.

Hearing loss is most often the result of hair-cell degeneration due to genetic abnormalities or ototoxic and traumatic insults. In the postembryonic and adult mammalian auditory sensory epithelium, the organ of Corti, no hair-cell regeneration has ever been observed. However, nonmammalian hair-cell epithelia are capable of regenerating sensory hair cells as a consequence of nonsensory supporting-cell proliferation. The supporting cells of the organ of Corti are highly specialized, terminally differentiated cell types that apparently are incapable of proliferation. At the molecular level terminally differentiated cells have been shown to express high levels of cell-cycle inhibitors, in particular, cyclin-dependent kinase inhibitors [Parker, S. B., et al. (1995) Science 267, 1024-1027], which are thought to be responsible for preventing these cells from reentering the cell cycle. Here we report that the cyclin-dependent kinase inhibitor p27(Kip1) is selectively expressed in the supporting-cell population of the organ of Corti. Effects of p27(Kip1)-gene disruption include ongoing cell proliferation in postnatal and adult mouse organ of Corti at time points well after mitosis normally has ceased during embryonic development. This suggests that release from p27(Kip1)-induced cell-cycle arrest is sufficient to allow supporting-cell proliferation to occur. This finding may provide an important pathway for inducing hair-cell regeneration in the mammalian hearing organ.

Acoustic Stimulation↗
PubMed1999

Distinct thyroid hormone-dependent expression of TrKB and p75NGFR in nonneuronal cells during the critical TH-dependent period of the cochlea.

Analyzing the thyroid hormone (TH)-dependent period of the inner ear, we observed that the presence of triiodothyronine (T3) between postnatal day 3 (P3) and P12 is sufficient for functional maturation of the auditory system. Within this short time period, an unusual transient TH-dependent expression of nonneuronal neurotrophin receptors (NT-R) trkB and p75(NGFR) was observed in correlation with neuronal and morphogenetic processes. The availability of thyroid hormone was revealed to be invariably correlated with (a) a transient expression of full-length trkB in TRalpha1-, TRalpha2- and TRbeta1-expressing hair cells concomitant to the segregation of afferent fibers and the synaptogenesis of efferent fibers; and (b) a transient expression of p75(NGFR) in TRalpha1- and TRbeta1-expressing great epithelia ridge cells in direct spatiotemporal correlation with the appearance of apoptotic cells and morphogenetic maturation of the organ. For the first time, these data suggest a TH dependency of the expression of neurotrophin receptors in nonneuronal cells. A potential role of these peculiar neurotrophin receptor expression for the conversion of the biological function of TH on innervation patterning and morphogenesis during the critical TH-dependent period of the inner ear may be considered.

Animals↗
PubMed1999

[Hearing loss caused by leisure noise].

Although noise in general can induce hearing loss, environmental noise represents an important risk for children, teenagers and young adults. Epidemiological investigations now support the occurrence of an increasing number of irreversible hearing losses in these groups. Major causes of hearing loss are toys (guns), explosives and electroacoustically amplified music delivered by head sets or heard in discotheques and open air concerts. Clinical indications are discussed.

Adolescent↗
PubMed1999

[Hearing disorders].

Explore the source record for details and available documents.

Cochlear Implantation↗
PubMed1999

Comparative study of visual, auditory, and olfactory function in Usher syndrome.

BACKGROUND: Usher syndrome is a genotypically and phenotypically heterogeneous group of autosomal recessive diseases featuring retinitis pigmentosa (RP) and sensorineural hearing loss. A general ciliary dysfunction has been suspected following reports of a mutated cytoskeletal protein (myosin VIIA) in type IB, and preliminary data has suggested an olfactory deficit. The purpose of this study was to quantitatively assess olfactory function in Usher syndrome patients and to search for a correlation between the degree of impairment of the three sensory systems as indication of an underlying ciliary defect. METHODS: 39 patients with Usher syndrome (8 type I, 31 type II) were examined. The ophthalmologic protocol included patient history, visual acuity, eye morphology, Goldmann perimetry, and electroretinography. The ENT protocol included a thorough examination, speech-recognition test, pure-tone audiometry and an olfactory function test. RESULTS: In both groups, visual acuity was typically 20/40, the remaining visual field area was small, and the ERG responses were low to non-detectable. Average hearing loss was 100% in type I and 40% in type II. Olfactory thresholds were normal [median 9.7 (I) and 8.5 (II) vs. 8.5 in the control group]. There were multiple significant correlations between parameters of the same organ, but no relationship between parameters of different sensory systems. CONCLUSION: Almost all Usher syndrome patients in this study had an advanced form of RP. In contrast, auditory function differed considerably between type I and type II. An impairment of the olfactory system could not be detected, and there was no correlation between parameters representing visual function, hearing ability, and olfactory sense.

Adult↗
PubMed1999

Determination of hair cell degeneration and hair cell death in neomycin treated cultures of the neonatal rat cochlea.

The spatial-temporal course of hair cell degeneration and hair cell death was examined in the mammalian cochlea following aminoglycoside treatment. Organotypic cultures were established from postnatal rats (P3) and treated with 1 mM neomycin sulfate for 12-48 h and analyzed using a live/dead assay under epifluorescence microscopy. Live hair cells were labeled with calcein, a probe whose fluorescence and cellular retention depends upon intracellular esterase activity and cell-membrane integrity, respectively. Hair cell death was determined by ethidium homodimer-1, a probe that can enter cells with compromised cell membranes only. Inside the cell it binds to DNA. Hair cell morphology was also examined using phalloidin labeling, scanning electron microscopy and semi-thin section analysis. Results showed that hair cell degeneration and hair cell death occurred in a time dependent gradient from base to apex. After 48 h of neomycin treatment, most apical hair cells survived while most basal hair cells died. Calcein labeling provides a sensitive functional assay for measuring hair cell survival.

Animals↗
PubMed1999

Expression pattern of adenylyl cyclase isoforms in the inner ear of the rat by RT-PCR and immunochemical localization of calcineurin in the organ of Corti.

Most studies concerning adenylyl cyclases in the inner ear were carried out before the advent of molecular biology. In a PCR approach using cDNAs of six inner ear tissues (stria vascularis, endolymphatic sac, organ of Corti, vestibulum, cochlear and vestibular nerve) we found tissue specific expression of adenylyl cyclase isoforms. Adenylyl cyclases types 2 and 4 are predominant in the fluid controlling tissues, i.e. in the stria vascularis and endolymphatic sac. In the organ of Corti and vestibulum the Ca2+-modulated isoforms types 1, 6 and 9 were expressed. The regulation of adenylyl cyclase 9, which is the major isoform expressed in the organ of Corti, proceeds via the Ca2+-activated protein phosphatase 2B (calcineurin, PPP3). PCR with specific primers for calcineurin demonstrated its abundant expression in the organ of Corti. Using a monoclonal antibody we localized calcineurin immunochemically to the cochlear nerve, the nerve fibers and the inner hair cells. In the cochlear and vestibular nerves a characteristic neuronal expression pattern of adenylyl cyclase isoforms was observed, i.e. adenylyl cyclases types 2, 3 and 8. The functional consequences of the adenylyl cyclase expression pattern in the inner ear are discussed in conjunction with its unique sensory performance.

Adenylyl Cyclases↗
PubMed1999

Clinical evidence for dystrophin dysfunction as a cause of hearing loss in locus DFN4.

OBJECTIVE: Locus DFN4 is an X-linked nonsyndromic hearing loss locus originally mapped to Xp21.2. Recently, we have mapped deafness in a second family from Turkey to the same region, refining the location to within the Duchenne muscular dystrophy (DMD) locus. The objective of this study was to characterize the clinical phenotype of the Turkish family with comprehensive audiovestibular testing and high-resolution temporal bone computerized tomography. METHODS: Fourteen members of a three-generation family were studied in detail including two deaf affected males. Members of the family underwent general physical and otologic examination, vestibular testing, pure-tone audiometry, otoacoustic emissions, and immitance testing. An affected male underwent high-resolution computerized tomography of the temporal bone, electroretinogram (ERG), electromyography, electroneurography, and determination of serum creatinine phosphokinase level. RESULTS: Affected males were congenitally deaf with normal vestibular function. Carrier females showed a mild sensorineural hearing loss affecting all frequencies and absent otoacoustic emissions. Otoacoustic emissions in a younger, 3-year-old carrier girl were normal. In an affected male, ERG demonstrated subnormal scotopic b-wave typically seen in DMD. Computerized tomography of the temporal bone was normal. With the exception of the ERG finding, there was no clinical or laboratory evidence of DMD or Becker muscular dystrophy (BMD). CONCLUSION: The abnormal ERG in the Turkish family in conjunction with mapping of the DFN4 locus to within DMD strongly suggests that a defect in dystrophin is responsible for the hearing loss in this family. Patients with DMD and BMD should be screened systematically for sensorineural hearing loss. This family provides additional evidence for the critical role of cytoskeletal proteins in normal hearing.

Dystrophin↗
PubMed1999

Monitoring noise susceptibility: sensitivity of otoacoustic emissions and subjective audiometry.

The capacity of different audiological methods to detect a high noise susceptibility was examined in 20 normally hearing and 26 especially noise-susceptible subjects. The latter were selected from 422 soldiers in field studies: they had shown a temporary threshold shift (TTS) in pure tone audiometry (PTA) after regular training with firearms. In laboratory experiments, the TTS-positive soldiers were re-examined using greatly reduced sound intensities, which caused no TTS in a control subject group. Before and after acoustic stimulation, different subjective (PTA, high frequency audiometry (HFA), upper limit of hearing (ULH)) and objective (transiently evoked otoacoustic emissions (TEOAE), distortion products (DPOAE)) audiological tests were performed. After exposure to low impact noise in the laboratory, in both PTA and HFA, a TTS was observed in 11.5% (N = 3) of the noise-susceptible group (compared to 0% in the control group). In the TTS-positive group, deterioration of the ULH occurred in 28% (N = 7) (compared to 15% (N = 3) in the control group). An ULH improvement occurred in only one subject (3.8%) (compared to 25% (N = 5) in the control group). Significant alterations of click-evoked OAE-amplitudes were found in 26.9% (N = 7) of the selected groups, whereas stable emissions were observed in all but one subject (5%) of the control group. However, DPOAE alterations were seen in 19.2% (N = 5) of the TTS-positive soldiers but also in 25% (N = 5) of the control group. These results suggest that TEOAE provides a more sensitive and more objective method of detecting a subtle noise-induced disturbance of cochlear function than do PTA or DPOAE.

Adolescent↗
PubMed1998

A second family with nonsyndromic sensorineural hearing loss linked to Xp21.2: refinement of the DFN4 locus within DMD.

X-linked inherited hearing impairment is a group of heterogeneous disorders accounting for less than 2% of hereditary hearing loss. DFN4, a sex-linked hearing impairment associated with profound sensorineural hearing loss, has been previously mapped to Xp21.2, a region containing the DMD locus. We have identified a family from Turkey with deafness in which the disease maps to and refines the DFN4 locus. In contrast to the previous family, the crossover points are entirely within the DMD locus. Two-point lod score analysis for the markers DXS 997, DXS 1214, and DXS 1219 showed a lod score of 2. 59. 5' and 3' crossovers were between DMD 44 and DXS 1219 and between DXS 1214 and DXS 985, respectively, suggesting that DFN4 is either an allele of DMD or a mutation in a DMD nested gene. The restriction of the DFN4 locus to DMD suggests that dystrophin may play an important role in hearing.

Chromosome Mapping↗
PubMed1998

Evidence for opening of hair-cell transducer channels after tip-link loss.

The mechanosensitive transducer channels of hair cells have long been proposed to be gated directly by tension in the tip links. These are thin, elastic extracellular elements connecting the tips of adjacent stereocilia located on the apical surface of the cell. If this hypothesis is true, the channels should close after destruction of tip links. The hypothesis was tested pharmacologically using receptor currents obtained in response to mechanical stimulation of the stereociliary bundle of outer hair cells isolated from the adult guinea pig cochlea. Application of elastase (20 U/ml) or 1,2-bis(2-aminophenoxy)ethane-N,N,N', N'-tetra-acetic acid (BAPTA; 5 mM), both of which are known to disrupt tip links in other hair-cell preparations, led to the expected irreversible loss of receptor currents. However, the cells then displayed a maintained inward current, implying that channels were left permanently open. This current was similar in magnitude to the receptor current before treatment and was reduced reversibly by known blockers of mechanosensitive channels, namely, dihydrostreptomycin (100 microM), amiloride (300 microM), and gadolinium ions (1 mM). These observations suggest that the maintained current flows through the mechanosensitive channels. Electron microscopical analysis of isolated hair cells, exposed to the same concentrations of elastase or BAPTA as in the electrophysiological experiments, demonstrated an almost total loss of tip links in hair bundles that showed no evidence of other mechanical damage. It is concluded that although the tip links are required for mechanoelectrical transduction, the channels are not gated directly by the tip links.

Animals↗