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At least 703 records · Page 39Linked to original sources
PubMed2004

Cochlear development: hair cells don their wigs and get wired.

PURPOSE OF REVIEW: Hair cells and spiral ganglion neurons form functional pairings in the cochlea that transduce the mechanical energy of sound into signals that are carried to the brainstem. Mutations of genes affecting the development and maintenance of these two cell populations cause deafness in humans and other animals. This review highlights recent findings regarding the development of hair cell stereocilia and spiral ganglion neurons in the cochlea. RECENT FINDINGS: Genes underlying Usher syndrome 1A have shed light on possible molecular participants in the development and structure of the hair cell stereocilia. Analysis of deaf mouse mutants have uncovered genes involved in stereocilia elongation and the orientation of the stereociliary bundles. Studies on the regulation of spiral ganglion neuronal survival and guidance suggest that the timing of expression of specific growth factors along the cochlear spiral is involved in maintaining the divergence of vestibular and cochlear nerve fibers. SUMMARY: Examining human and mouse genes affecting hearing has not only provided insight into causes of human deafness, but has also opened a window into how stereociliary bundles are constructed and spiral ganglion neurons are preserved and guided during development. Synthesis of information from diverse lines of research pinpoints genes for screening or repair in the genetic medicine of the future and dramatizes the intimate relationship between strict adherence to complex developmental programs and hearing. In addition, future improvements in the efficacy of cochlear implants may depend on the preservation and manipulation of adult spiral ganglion neurons. Developmental mechanisms promise to yield insight into possible interventions to redirect or reconnect spiral ganglion neurons in damaged cochlea.

Animals↗
PubMed1999

The prognostic value of intraoperative BAEP patterns in acoustic neurinoma surgery.

Based on a consecutive series of 70 hearing patients with unilateral acoustic neurinomas and intraoperative monitoring of brain-stem auditory evoked potentials (BAEP), 4 dynamic BAEP patterns could be characterized. These patterns correspond with early and late postoperative hearing outcome. All patients with stable wave V (pattern 1) showed definite hearing preservation, all patients with irreversible abrupt loss of BAEP (pattern 2) lost their hearing, despite early hearing preservation in two cases. All patients with irreversible progressive loss of either wave I or wave V (pattern 3) eventually suffered from definite postoperative hearing loss, despite early hearing preservation in two cases. Those cases with intraoperative reversible loss of BAEP (pattern 4) showed variable short and long term hearing outcome. In 34% hearing was preserved, 44% suffered from postoperative hearing loss, the remaining 22% showed postoperative hearing fluctuation, either as a delayed hearing loss or as reversible hearing loss. Postoperative hearing fluctuation indicates anatomical and functional preservation of the cochlear nerve during surgery and is suggestive of a pathophysiological mechanism initiated during the surgical procedure and continuing thereafter. Patients at risk for delayed hearing loss can be identified during surgery by a characteristic BAEP pattern and may benefit from vasoactive treatment.

Audiometry, Pure-Tone↗
PubMed2006

Preliminary results on correlation between neural response imaging and 'most comfortable levels' in cochlear implantation.

During cochlear implantation, precise placement of the cochlear electrodes against the cochlear nerve is one of the most important steps, necessary to enable the patient to be aware of the stimulus from the implanted device. Neural response imaging (NRI) is a new tool which measures the evoked compound action potential generated as a result of electrical stimulation of the cochlea by properly placed electrodes during surgery. The aim of this study was to examine the correlation between intra-operative NRI recordings and 'most comfortable levels' (M levels) measured during standard fitting with the SoundWave fitting software, in cochlear implantation patients. Seven adult subjects were included in the study. The average duration of profound bilateral deafness was seven years (range = 19 years) and the mean age at implantation was 24 years (range = 17-34 years). All subjects underwent implantation and reached the one-month fitting session; one patient reached the two-month fitting session. The intra-operative NRI threshold (tNRI) was observed to be much higher than the first fitting M levels. The tNRI was 203 per cent of the sequential M value and 246 per cent of the paired M value. All but one intra-operative tNRI values were greater than 150 clinical units (CU), and all first fitting M levels were on average below 100 CU. No obvious correlation was found between individual intra-operative tNRI and first fitting M levels. The M levels at one month were much higher than the first fitting M levels, with much more dispersion.

Adolescent↗
PubMed1996

Responsiveness of alpha 1 and beta 1 cochlear Na, K-ATPase isoforms to thyroid hormone.

The effects of thyroid hormone on Na, K-ATPase subunit isoforms under euthyroid (EUTH), hypothyroid (HYPO) and hyperthyroid (HYPER) states were investigated via immunocytochemistry and the use of polyclonal antibodies specific to each isoform (alpha 1, alpha 2, alpha 3 and beta 1, beta 2). In HYPO animals, there was a distinct decrease in Na, K-ATPase alpha 1 isoform immunoreactivity in the stria vascularis (SV), spiral ganglion (SG) cells, spiral limbus (SLi) and cochlear nerve (CN) as compared with that in EUTH animals by the 17th day of the experiment. Immunostaining of the alpha 1 isoform increased in HYPER animals as compared with that in HYPO animals, and reached a level comparable to that in EUTH animals after 2 days of triiodothyronine (T3) treatment. Levels of alpha 2, alpha 3 and beta 2 isoforms did not appear to be affected by T3 administration. By the 19th day of a low I2 diet, the immunoreactive intensity of the beta 1 isoform was reduced in cochlear tissues of HYPO animals as compared with that in EUTH animals. The immunoreactivity of the beta 1 isoform increased after treatment with T3 for 4 days and was comparable with levels in EUTH animals. These data indicate that alpha 1 and beta 1 isoforms within specific cochlear regions of the adult rat are responsive to thyroid hormone.

Animals↗
PubMed1999

Temporal bone histopathologic findings in a case of interstitial deletion of the long arm of chromosome 2 [del(2) (q31q33)].

The temporal bones of a 24-day-old female neonate with an interstitial deletion of the long arm of chromosome 2 [del(2)(q31q33)] were studied histopathologically, focusing mainly on the inner ear. This is, to our knowledge, the first report of a temporal bone study in a case of this chromosomal aberration. The abnormalities included a shortened cochlea with underdeveloped modiolus in both ears. Total absence of the spiral ganglion cells and the cochlear nerve bundle, accompanied by obliteration of the fundus of the internal auditory meatus by a bony plate, and dislocation of some geniculate ganglion cells to the internal auditory meatus were also observed in the right ear. The absence of the spiral ganglion cells is considered to be the result of some complication in the early fetal life, such as dysgenesis or early degeneration of the neuronal cells. The organ of Corti in the right ear was well-developed and preserved in the middle turn, suggesting that the differentiation of the cochlear sensory epithelium in humans is not dependent upon the innervation, at least on the gross level.

Abnormalities, Multiple↗
PubMedDate not supplied

How OHC lesions can lead to neural cochlear hypersensitivity.

Several laboratories, including ours, have found that damage to OHCs--but not to IHCs--can produce hypersensitivity of cochlear nerve afferents to low-frequency sound in the presence of hyposensitivity at the characteristic frequency (CF). It is possible to explain the paradox by a mechanical coupling of the OHCs and IHCs through the tectorial membrane, for which there is accumulating experimental evidence. No direct contact between the IHC stereocilia and the tectorial membrane is required.

Animals↗
PubMed1994

Subtotal petrosectomy with external canal overclosure in the management of chronic suppurative otitis media.

Subtotal petrosectomy with external canal overclosure has been used in the management of 10 patients with chronic suppurative otitis media in the past four years. These patients fall into two categories. One group consisted of patients with end-stage chronically discharging mastoid cavities, despite aggressive medical therapy. The other group comprised patients who had developed disabling peripheral vestibular symptoms and had a mastoid cavity from past surgery for chronic otitis media. In both groups the affected ear had absent or poor auditory function. In the second group, a translabyrinthine section of the vestibular and/or cochlear nerves was performed in conjunction with subtotal petrosectomy. The procedure has been very successful in relieving the persistent otorrhoea, giving the patient an ear without a cavity that would need regular care. No restriction on swimming and participation in other water sports is an additional advantage. Illustrative cases are used to discuss the technique and indications.

Adult↗
PubMedDate not supplied

Properties of derived cochlear action potentials in forward tonal masking in guinea pigs.

Chronic experiments on guinea pigs were used to study the characteristics of cochlear nerve action potentials and the derived potential in conditions of forward masking. The auditory nerve action potential was recorded from the round window of the cochlea. The derived potential was obtained by subtracting the action potential recorded with masking from the response obtained in silence. These studies showed that the derived potential showed higher sensitivity to masking than the traditional measure of masking, i.e., the decrement in the amplitude of the auditory nerve action potential. The derived potential reflects not only changes in the action potential during masking, but also changes in its shape. Differences between the derived potential and the action potential decrement provide evidence that the amplitude and time changes in the derived potential provide more complete information on the nature of activity in the auditory fibers.

Action Potentials↗
PubMed2003

[The role of MRI in suspected inner ear malformations].

PURPOSE: This is a prospective analysis of the value of MRI in suspected inner ear malformations. MATERIALS AND METHODS: In 50 patients (43 children and young adults, 7 adults) with suspected inner ear malformation MRI (1.5 T) was performed. In addition, 42 of these patients underwent CT. For the analysis of the inner ear structures, the constructive interference in steady state (CISS) sequence with 0.7 mm slice thickness was used. Functional tests revealed a sensorineural hearing loss or deafness in 82 temporal bones (TB) and a combined hearing loss in 4 TB. The hearing loss was unilateral in 14 patients. MRI and CT findings were compared. RESULTS: Imaging findings were normal in 58 TB. The pathological findings included inner ear malformations (35 TB), inflammatory changes (4 TB), partial obliteration of labyrinth (2 TB) and congenital aural atresia (1 TB). An isolated absence of the cochlear nerve (1 TB) could only be found by MRI. In the remaining cases, an inner ear malformation was diagnosed by MRI and CT with the same confidence but MRI was superior in displaying the fine details. CONCLUSIONS: MRI will become the method of choice in the diagnosis of inner ear malformations.

Adolescent↗
PubMedDate not supplied

Effect of intracochlear aminooxyacetic acid on cochlear potentials and endolymph composition.

Summary--Aminooxyacetic acid (AOAA; 1 MM) when perfused through the scala tympani of guinea pigs produced a biphasic reduction in the endocochlear potential, together with a shift in the input-output functions of the cochlear microphonics and the compound action potential of the cochlear nerve. Since the ionic (Na+, K+) content of the scala media was not alerted, it appears that such changes did not underlie the reduction recorded in the endocochlear potential. The negative direct current potential recorded in the organ of Corti did not appear to be affected by the drug. Attempts to antagonize the effects of AOAA with pyridoxine failed.

Acetates↗
PubMed2001

Auditory nerve fiber differences in the normal and neurofilament deficient Japanese quail.

A primary axonal disease affecting the central and peripheral nervous system was discovered in a mutant strain of the Japanese quail, named quiver (Quv). We have previously demonstrated altered auditory evoked potentials in the neurofilament (NF) deficient quail. In this current study we attempt to find relationships between the auditory evoked potential results and the histo-pathological abnormalities of the auditory neurons. No abnormalities in the external auditory meatus and tympanic cavity were observed in either Quv or control quails and the ganglion cell bodies and their nuclei appeared normal by light microscopy. The myelin staining pattern was found to be similar in both strains with hematoxylin and eosin and Klüver-Barrera staining. The frequency histograms of fiber and axonal diameters of myelinated fibers showed an unimodal pattern in both strains. In Quv quails myelinated fibers and their axoplasm were smaller in diameter than in controls resulting in smaller neural tissue mass. In electron microscopic observation the axons of the Quv quail were composed of mitochondria and microtubules and smooth endoplasmic reticuli. In Quv quail electron micrographs of cochlear nerve myelinated fibers NFs were not seen in the axons and the neuronal cell bodies. Our current findings indicate that the previously reported reduction of conduction velocity of auditory evoked potentials may be due to smaller fiber and/or axonal diameter. The g-ratio, myelin thickness and fiber circularity were found to be the same for both strains. In conclusion, loss of axonal cytoskeletal elements (NFs) correlates well with our electrophysiological findings. Reduced conduction velocity and severely distorted auditory evoked potentials in NF deficient quails seem to be primarily due to axonal hypotrophy.

Animals↗
PubMed1994

Stapedotomy with stapedius tendon preservation: technique and long-term results.

From 1975 to 1992, a total of 1459 primary stapedoplasty operations (i.e., stapedectomy, stapedotomy with tendon section, and stapedotomy with tendon preservation) were performed in 1323 subjects at the Ear, Nose, and Throat Department of the University of Verona. Pure-tone audiometry was carried out in all subjects who were operated on and who underwent 6-month and 10-year follow-ups. To evaluate the influence of stapedius tendon preservation on functional outcome, we randomly selected subgroups of patients using the three different stapedioplasty techniques and tested them by multiple-frequency tympanometry, psychoacoustic tuning curves, and speech discrimination in noise. Finally, to assess the effect of prosthesis diameter on middle ear transfer function, we used the electrocochleographic technique and examined the threshold and latency of cochlear nerve compound action potentials recorded during surgery from the round window. The results of this study show that the best auditory performance in otosclerotic subjects is achieved by performing a stapedotomy of 0.7 mm diameter, using a 0.6 wire-Teflon piston, and preserving the stapedius tendon.

Acoustic Impedance Tests↗
PubMed1993

Hearing preservation in cerebellopontine angle tumor surgery: the NYU experience 1974-1991.

Between 1974 and 1991, hearing preservation surgery was attempted on 161 of 476 patients with a variety of cerebellopontine (CPA) tumors, at New York University School of Medicine. This included 146 unilateral acoustic neuromas, seven meningiomas, and six cases of neurofibromatosis. The suboccipital/retrosigmoid approach was used almost exclusively. The cochlear nerve was anatomically preserved in 131 cases, 32 percent of whom had successful hearing preservation. In the most successful group, hearing was preserved in 9 of 12 patients (75%). Success was defined as a postoperative pure-tone average (PTA) or speech reception threshold (SRT) of no more than 50 dB, and a speech discrimination score (SDS) of at least 50 percent. In those patients whose preoperative hearing was worse that this, success was based on a loss of no more than 10 dB in PTA or SRT, and 10 percent in SDS. Success was dependent mostly on extracanalicular (EC) tumor size, with the smallest tumors yielding the best results. When controlled for EC size, intracanalicular size and preoperative hearing were statistically significant variables. Origin from the superior vestibular nerve was also a favorable prognostic indicator. The character and duration of hearing loss, the patient's age, and the histology of the tumor did not have prognostic value. Auditory monitoring with either auditory brainstem response (ABR) or direct eighth nerve electrodes did not have a significant impact on success. Complications were somewhat increased by attempted hearing preservation. Facial nerve function was type I or II in 93 percent of patients. Cerebrospinal fluid leaks occurred in 15 percent of cases, but only 4 percent required surgical repair. There was one death, a patient with a 2.5-cm tumor. Early in the series, when a classic long vertical nuchal incision was used, headache and neck pain were common.

Adolescent↗
PubMed1977

Evidence that GABA is not the afferent transmitter in the cochlea.

The GABA antagonists picrotoxin, bicuculline and bicuculline-methochloride, when applied intracochlearly, do not affect the compound action potential of the cochlear nerve. It is therefore concluded that these drugs do not interfere with afferent synaptic transmission, and therefore that GABA is not the afferent transmitter. With very high doses, picrotoxin as well as bicuculline-methochloride partially block the efferent synapses. This effect is most likely to be unspecific, but shows that with the technique used the agents can reach the synaptic site.

Acoustic Stimulation↗
PubMed1975

Microsurgical approach to the cerebellopontine angle.

Various sections of the IXth, Vth, vestibular and cochlear nerves have been performed on twenty patients. The technique we used was an 'a minima' approach to the cerebellopontine angle. This operation is atraumatic and quick to perform, and the postoperative period is always excellent. It seems very useful for patients with Ménière's disease or intractable pains in the glossopharyngeal or trigeminal fields. It can be used for diagnosis if a small neurinoma in the cerebellopontine angle is suspected.

Aged↗
PubMed1996

Early and late postoperative hearing preservation in patients with acoustic neuromas.

OBJECTIVE: To examine the incidence of postoperative hearing preservation and the factors that influence early and late postoperative hearing in patients with acoustic neuromas. METHODS: We reviewed the results of surgery and follow-up in 73 consecutive patients. RESULTS: Of 73 patients, 51 demonstrated preoperative hearing levels equal to or better than Class 3, according to the classification system of Gardner and Robertson (8). After surgery, 21 (41.2%) of the 51 patients retained Class 1, 2, or 3 hearing. Hearing was more likely to be preserved after surgery if the tumor was small and if the preoperative hearing was good. The early postoperative hearing grade declined in 7 (33.3%) of the 21 patients, compared with the preoperative hearing level. The long-term follow-up of 17 patients in whom measurable hearing was retained after surgery indicated that 3 (17.6%) experienced delayed worsening of hearing, without evidence of tumor recurrence. The extent of hearing loss in patients with successful hearing preservation was not correlated with tumor size, preoperative hearing, patient age, or the shape of the cochlear nerve on the tumor surface. Hearing at long-term follow-up was significantly better in patients with excellent preoperative hearing. CONCLUSION: Postoperative long-term preservation of hearing is more likely if surgery is performed while the tumor is still small and hearing is still excellent. Under these circumstances, it is more likely that the early and late hearing loss will be compensated.

Adult↗
PubMed1975

Adenosine triphosphate and phosphocreatine levels in cochlear structures. Use rate and effect of salicylates.

Guinea pigs were injected with various dosages of salicylate for varying time periods. The temporal bones were removed, frozen quickly, freeze-dried, and the cochlea was dissected into essential auditory component parts and subjected to microchemical analysis for phospho-creatine (P-creatine) and adenosine triphosphate (ATP) levels. It was found that high energy phosphates were not decreased by therapeutic or acutely toxic levels of salicylate. Only when chronic intoxication with salicylate was accomplished was there a reduction in ATP and P-creatine. The data presented do not provide support for the widely held view that uncoupling of oxidative phosphorylation or inhibition of enzymes involved in energy generation in the inner ear structures studied (organ of Corti, stria vascularis, Reissner's membrane, modiolar blood vessels, cochlear nerve and spiral ganglion) are the mechanisms by which salicylates cause reversible hearing loss. The study confirms the existence of a P-creatine gradient opposite to the well known glycogen gradient in the organ of Corti (Krzanowski JJ Jr, Matschinsky M: J Histochem 19:321, 1971) and suggests a relatively uniform energy use rate of this tissue for all four turns (20 mmoles of approximately phosphorus used/kg dry weight/min).

Adenosine Triphosphate↗