Electrophysiologic consequences of flexible electrode insertions in gerbils with noise-induced hearing loss.

HYPOTHESIS: Flexible electrode interaction with intracochlear structures in a noise-damaged region of the cochlea can lead to measureable electrophysiologic changes. BACKGROUND: An emerging goal in cochlear implantation is preservation of residual hearing subsequently allowing for combined electric and acoustic stimulation (EAS). However, residual hearing is at least partially lost in most patients as a result of electrode insertion. A gerbil model was used to examine changes to acoustically evoked cochlear potentials during simulated cochlear implantation. METHODS: Gerbils were partially deafened by noise exposure to mimic residual hearing in human cochlear implant candidates. After 1 month, round window and intracochlear recordings during flexible electrode insertion were made in response to 1 kHz tone burst stimuli at 80 dB SPL. After the insertion, the cochleas were histologically examined for hair cell loss because of the noise exposure and trauma because of the electrode insertion. RESULTS: Anatomic damage from the flexible electrode was not observable in most cases. However, insertions caused response declines that were, on average, greater than the controls, although some losses were similar to the controls. The CM was more sensitive than the CAP for detecting cochlear disturbance. CONCLUSION: Because response reductions occurred in the absence of anatomic damage, disturbances in the fluid at the base appear to affect responses from the apex. The losses were less than in previous experiments where the basilar membrane was penetrated.

The use of Nucleus CI422 in a ski-slope high-frequency hearing loss and chronic external ear pathology: a case study.

OBJECTIVE AND IMPORTANCE: This case report illustrates the ongoing extending criteria for cochlear implantation (CI). It reinforces the statement that patients who do not fulfill the standard criteria for CI should be carefully considered on an individual basis. CLINICAL PRESENTATION: The patient on this report presented with a ski-slope high-frequency hearing loss and chronic external ear canal infections. The latter precluded the consistent use of hearing aids with moulds. His speech discrimination in quiet and in noise was poor and his hearing loss was interfering with his ability to work. INTERVENTION: After years of frustration, this patient decided to risk losing his low-frequency residual hearing and was implanted with the new Nucleus CI422 (Cochlear Ltd). CONCLUSION: Hearing preservation was achieved and he gained a remarkable improvement in his hearing performance. It is thought that his outcomes are the result of the combination of hearing presentation surgery, electrode design, and intensive auditory training.

Stem cell transplantation in noise induced hearing loss.

OBJECTIVE: To investigate efficacy of bone marrow stem cell implantation in rehabilitation of noise induced hearing loss in rats. MATERIALS AND METHODS: Hearing loss was induced in male rats by a continuous wide-band noise (8-16 kHz/120 dB/120 min). Ten microliter of stem cell containing solution was injected by a Hamilton syringe with 30 G needle through the round window membrane. Hearing status was examined by, distortion product otoacoustic emissions using DP-OAE. Animals were studied in 4 different groups: (1) Normal hearing animals, undergoing sham surgery (no injection done, only round window membrane ruptured and sealed). (2) Deaf animals, undergoing sham surgery. (3) Deaf animals undergoing surgery and injection of solvent (artificial perilymph). (4) Deaf animals undergoing surgery and injection of artificial perilymph containing BMSCs. RESULTS: DP-Gram in rat with normal hearing undergoing sham surgery show that procedure has neither negative impact on normal cochlear nor on deaf cochleas. No significant difference (p=0.25) between ears excludes artificial perilymph as a confounding factor. There is no significant difference between ears in animals receiving BMSCs. CONCLUSIONS: Implanted cells with normal histologic structures have no physiologic function and hearing rehabilitation. Further studies by monitoring the survival of these cells with histologic and appropriate biomarkers will help to investigate differentiation process of these cells.

Intravenous administration of human mesenchymal stem cells after noise- or drug-induced hearing loss in rats.

CONCLUSION: Systemic application of human mesenchymal stem cells (hMSCs) may be another effective tool for stem cell supply to the inner ear. OBJECTIVES: Most researchers have used local application to provide the inner ear with stem cells. In spite of their efficacy, these methods can potentially cause irreversible damage to the inner ear. A homing phenomenon of systemically administered MSCs to the ischemic myocardium and brain was recently reported. Moreover, hMSCs have several advantages over conventional neural or embryonic stem cells. Thus we hypothesized that intense noise or ototoxic injury to the cochlea could induce the homing of hMSCs. METHODS: We harvested hMSCs from bone marrow of the iliac crest of five normal individuals. Then hMSCs at a dose of 4 × 10(6) cells were given via intravenous injection of cell suspension into rats with cochleae damaged by noise or ototoxic drugs. Histological analysis was undertaken 30 days later. RESULTS: Systemically delivered hMSCs were usually largely entrapped in the lungs. However, we documented the homing of some hMSCs to the cochlea with degenerated inner hair cells. The recruitment of hMSCs was limited to the spiral ganglion area only. The migration of donor cells into the cochlea was accompanied by the expression of brain-derived neurotrophic factor (BDNF).

Detection of intracochlear damage with cochlear implantation in a gerbil model of hearing loss.

HYPOTHESIS: Cochlear trauma due to electrode insertion can be detected in acoustic responses to low frequencies in an animal model with a hearing condition similar to patients using electroacoustic stimulation. BACKGROUND: Clinical evidence suggests that intracochlear damage during cochlear implantation negatively affects residual hearing. Recently, we demonstrated the usefulness of acoustically evoked potentials to detect cochlear trauma in normal-hearing gerbils. Here, gerbils with noise-induced hearing loss were used to investigate the effects of remote trauma on residual hearing. METHODS: Gerbils underwent high-pass (4-kHz cutoff) noise exposure to produce sloping hearing loss. After 1 month of recovery, each animal's hearing loss was determined from auditory brainstem responses and baseline intracochlear recording of the cochlear microphonic and compound action potential (CAP) obtained at the round window. Subsequently, electrode insertions were performed to produce basal trauma, whereas the acoustically generated potentials to a 1-kHz tone-burst were recorded after each step of electrode advancement. Hair cell counts were made to characterize the noise damage, and cochlear whole mounts were used to identify cochlear trauma due to the electrode. RESULTS: The noise exposure paradigm produced a pattern of hair cell, auditory brainstem response, and intracochlear potential losses that closely mimicked that of electrical and acoustic stimulation patients. Trauma in the basal turn, in the 15- to 30-kHz portion of the deafened region, remote from preserved hair cells, induced a decline in intracochlear acoustic responses to the hearing preserved frequency of 1 kHz. CONCLUSION: The results indicate that a recording algorithm based on physiological markers to low-frequency acoustic stimuli can identify cochlear trauma during implantation. Future work will focus on translating these results for use with current cochlear implant technology in humans.

Effect of epithelial stem cell transplantation on noise-induced hearing loss in adult mice.

Noise trauma in mammals can result in damage to multiple epithelial cochlear cell types, producing permanent hearing loss. Here we investigate whether epithelial stem cell transplantation can ameliorate noise-induced hearing loss in mice. Epithelial stem/progenitor cells isolated from adult mouse tongue displayed extensive proliferation in vitro as well as positive immunolabelling for the epithelial stem cell marker p63. To examine the functional effects of cochlear transplantation of these cells, mice were exposed to noise trauma and the cells were transplanted via a lateral wall cochleostomy 2 days post-trauma. Changes in auditory function were assessed by determining auditory brainstem response (ABR) threshold shifts 4 weeks after stem cell transplantation or sham surgery. Stem/progenitor cell transplantation resulted in a significantly reduced permanent ABR threshold shift for click stimuli compared to sham-injected mice, as corroborated using two distinct analyses. Cell fate analyses revealed stem/progenitor cell survival and integration into suprastrial regions of the spiral ligament. These results suggest that transplantation of adult epithelial stem/progenitor cells can attenuate the ototoxic effects of noise trauma in a mammalian model of noise-induced hearing loss.

Evaluation of the usefulness of a silicone tube connected to a microphone in monitoring noise levels induced by drilling during mastoidectomy and cochleostomy.

CONCLUSION: The use of a silicone tube and a microphone enables peroperative noise recordings in cadavers and should be safe to apply in vivo. Our preliminary data indicate that noise levels during inner ear surgery reach levels that can cause noise-induced hearing loss. Our method is easily performed and enables future uncomplicated and safe noise recordings and we suggest future application in vivo to expand knowledge regarding peroperative noise levels. OBJECTIVES: To evaluate the safety and utility of a silicone tube connected to a microphone probe in noise recordings during middle ear surgery and to achieve preliminary results regarding drill-related noise levels. METHODS: Peroperative noise recordings were obtained during mastoidectomy and at the round window during cochleostomy in a cadaver model by means of a silicone tube connected to a microphone and a Matlab(®) computer program. RESULTS: Our method enabled recordings of radiated noise levels close to the drill ranging from 84 to 125 dB SPL during drilling in cortical bone and from 85 to 117 dB during drilling in the mastoid cavity. During cochleostomy noise levels ranged from 114 to 128 dB SPL when recordings were made close to the round window. Maximal noise levels were underestimated due to microphone overload above 80 Pa.

Neural stem cells injected into the sound-damaged cochlea migrate throughout the cochlea and express markers of hair cells, supporting cells, and spiral ganglion cells.

Most cases of hearing loss are caused by the death or dysfunction of one of the many cochlear cell types. We examined whether cells from a neural stem cell line could replace cochlear cell types lost after exposure to intense noise. For this purpose, we transplanted a clonal stem cell line into the scala tympani of sound damaged mice and guinea pigs. Utilizing morphological, protein expression and genetic criteria, stem cells were found with characteristics of both neural tissues (satellite, spiral ganglion, and Schwann cells) and cells of the organ of Corti (hair cells, supporting cells). Additionally, noise-exposed, stem cell-injected animals exhibited a small but significant increase in the number of satellite cells and Type I spiral ganglion neurons compared to non-injected noise-exposed animals. These results indicate that cells of this neural stem cell line migrate from the scala tympani to Rosenthal's canal and the organ of Corti. Moreover, they suggest that cells of this neural stem cell line may derive some information needed from the microenvironment of the cochlea to differentiate into replacement cells in the cochlea.

[Rupture of the round window--detection with fluorescence endoscopy]. / Rundfensterruptur--Nachweis mittels Fluoreszenzendoskopie.

Rupture of the round window membrane as a special cause of inner ear deafness is widely accepted after changing pressure levels, e.g. in diving. However, even without a barotrauma before, the spontaneous rupture of the round window membrane is suspected occasionally in patients with sudden hearing loss and/or vertigo and tinnitus. To carry through the tympanotomy is decided by ENT surgeons often in cases of progressive hearing loss despite infusion therapy. Perilymph fistulas have been detected relatively seldom, compared to the number of reported operations by several authors. However, covering the round niche with connective tissue leads to the improvement of symptoms sometimes even in cases without microscopical evidence of fistula. Within the last 3 years 14 patients suffering sudden hearing loss of one ear underwent tympanotomy in our department. Of these patients 8 reached restitution of the hearing ability. Especially 2 patients with sudden deafness caused by spontaneous rupture of the round window membrane are reported in the following article. Perilymph fistulas were detected in these cases by IV-application of fluorescein and fluorescence endoscopy of the middle ear. Both patients obtained a normal hearing curve within 1 week after surgical intervention and obliteration of the round niche.

[Future cure of hearing disorders? Gene therapy and stem cell implantation are possible new therapeutic alternatives]. / Framtida bot för hörselskador? Genterapi och implantation av stamceller möjliga nya behandlingsvägar.

Hearing loss is a very common disorder; nearly 10 per cent of the population is affected. Recently, a few findings such as the roles of neurotrophins, nitric oxide, reactive oxygen species and glutamate receptors in the peripheral hearing system have been highlighted. In this review, focus is set on possible mechanisms of peripheral hearing disorders, and on recent advances to prevent and treat hearing loss. Clinically useful treatment strategies, especially gene therapy and the use of embryonic stem cells, are particularly stressed.