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At least 577 records · Page 32Linked to original sources
PubMed1999

Acoustic neuroma surgery: absent auditory brainstem response does not contraindicate attempted hearing preservation.

OBJECTIVE: Absence of auditory brainstem response (ABR) waveforms has been associated with a poor likelihood of hearing preservation following resection of acoustic neuromas. Our experience is reviewed for patients with absent preoperative ABR regarding hearing preservation, hearing improvement, and return of ABR. STUDY DESIGN: Retrospective review of 22 cases of acoustic neuroma resection. Nine patients with absent preoperative ABR were identified. All underwent tumor resection utilizing intraoperative cochlear nerve action potential (CNAP) monitoring. Postoperative hearing results and ABR waveforms were examined. METHODS: Charts were reviewed and tabulated for age, sex, tumor side, tumor size, preoperative and postoperative audiometric and ABR results, intraoperative monitoring results by ABR and CNAP, and surgical complications. RESULTS: Hearing preservation was achieved in seven of nine patients (78%) with absent preoperative ABR, as well as six of seven patients (86%) with tumors less than or equal to 20 mm in greatest dimension. Although intraoperative ABR monitoring was not possible in any of these patients, CNAP monitoring was successful in all. Return of ABR waveforms was observed in four of the six patients (67%) tested from 3 to 22 months postoperatively. Four of the seven patients (57%) enjoyed improvement in hearing class as defined by the guidelines of the American Academy of Otolaryngology-Head and Neck Surgery. CONCLUSIONS: Absent ABR waveforms have not been a negative prognostic sign regarding hearing preservation. CNAP monitoring is possible in these patients and likely helps to minimize iatrogenic cochlear nerve trauma. Patients with no ABR waveforms have hope of hearing preservation and even improvement following acoustic neuroma resection performed utilizing CNAP monitoring and hearing preservation surgical techniques.

Aged↗
PubMed1981

Electrocochleographic study of patients with cerebral vascular lesions.

Electrocochleographies were performed on three patients with deafness resulting from cerebral vascular lesions. Recording was made by the transtympanic needle electrode technique. In a patient who had anterior-inferior cerebellar artery aneurysm that showed fluctuating hearing loss, auditory nerve action potential (AP), cochlear microphonics (CM), and summating potential fluctuate in amplitude in concert with episodes of ischemic hearing loss. This indicates the pathophysiology of reversible impairment of the cochlear nerve and of sensory epithelium of the inner ear caused by disturbance of blood flow into the inner ear. It was also conjectured that the cochlea is hardly impaired in the case with normal AP and CM responses despite the increased threshold in pure-tone audiometry and that the cochlea undergoes irreversible organic changes in the patient who has no AP or CM response in tests after a long period.

Action Potentials↗
PubMed1999

Expression of membrane-bound and cytosolic guanylyl cyclases in the rat inner ear.

Membrane-bound guanylyl cyclases (GCs) are peptide hormone receptors whereas the cytosolic isoforms are receptors for nitric oxide. In the inner ear, the membrane-bound GCs may be involved in the regulation of fluid homeostasis and the cytosolic forms possibly play a role in signal processing and regulation of local blood flow. In this comprehensive study, we examined, qualitatively and quantitatively, the transcription pattern of all known GC isoforms in the inner ear from rat by RT-PCR. The tissues used were endolymphatic sac, stria vascularis, organ of Corti, organ of Corti outer hair cells, cochlear nerve, Reissner's membrane, vestibular dark cells, and vestibular sensory cells. We show that multiple particulate (GC-A, GC-B, GC-D, GC-E, GC-F and GC-G) and several subunits of the heterodimeric cytosolic GCs (alpha1, alpha2, beta1 and beta2) are expressed, albeit at highly different levels. GC-C was not found. GC-A and the soluble subunits alpha1 and beta1 were transcribed ubiquitously. GC-B was present in all tissues except stria vascularis, which contained GC-A and traces of GC-E and GC-G. GC-B was by far the predominant membrane-bound isoform in the organ of Corti (86%), Reissner's membrane (75%) and the vestibulum (80%). Surprisingly, GC-E, a retinal isoform, was detected in significant amounts in the cochlear nerve (8%) and in the organ of Corti (4%). Although the cytosolic GC is a heterodimer composed of an alpha and a beta subunit, the mRNA transcription of these subunits was not stoichiometric. Particularly in the vestibulum, the transcription of the beta1 subunits was at least four-fold higher than of the alpha1 subunit. The data are compatible with earlier suggestions that membrane receptor GCs may be involved in the control of inner ear electrolyte and fluid composition whereas NO-stimulated GC isoforms mainly participate in the regulation of blood flow and supporting cell physiology.

Animals↗
PubMed2006

Development of synapses and expression of a voltage-gated potassium channel in chick embryonic auditory nuclei.

The potassium channel protein, Kv3.1, is abundantly expressed in the chick auditory pathway. Its b-isoform is found in nucleus magnocellularis, which receives the cochlear input, both before and after the establishment of synaptic connections. It is also present in cell cultures in the absence of any peripheral input. However, the expression of this isoform in the embryo has been shown to increase with development. Here, we address the question of the correlation between maturation of synapses in the auditory pathway and the pattern of expression of the b-isoform in a series of embryos prepared for immunohistochemistry at Hamburger-Hamilton stages equivalent to E10, E12, E14, and E17. We show here that this subunit translocates from the perinuclear cytoplasm to the cell membrane domain in nucleus magnocellularis at the time that cochlear nerve endings emerge as endbulbs of Held (E17). In nucleus laminaris, by this time, while abundant Kv3.1b occurs in the perinuclear cytoplasm, a translocation to the cell membrane domain has not yet occurred, and the mature peri-synaptic localization is delayed to a later stage. This difference suggests a hierarchy in the developmental expression of Kv3.1. An unexpected finding is the expression of the a-isoform of Kv3.1 in astrocytes, especially those which surround the developing nuclei and their connecting fibers. We also report here for the first time the presence of Kv3.1b in the initial segments of axons at the times when they begin to form. Our observations suggest that the Kv3.1 channel protein is regulated through mechanisms linked to the development of synaptic activity.

Animals↗
PubMed1990

Mechanisms that degrade timing information in the cochlea.

Action potentials of cochlear nerve fibers are synchronized to the temporal variations of sounds, but this synchronization is attenuated for high-frequency sounds. In cochleas from a number of vertebrates, the frequency dependence of synchronization can be represented as a lowpass filter process whose order is at least three (Weiss and Rose, 1988a); i.e. at least three first-order kinetic processes may be responsible for the loss of synchronization. In this paper we assess the extent to which calcium processes, that are essential for chemical transmission at the hair-cell neuron junction, contribute to this attenuation of synchronization. We analyze a model of calcium processes in hair cells (Lewis, 1985; Hudspeth and Lewis, 1988a) for sinusoidal receptor potentials. We show that: (1) the relation between the receptor potential and the calcium current, which is nonlinear, acts approximately as a first-order lowpass filter whose cut-off frequency decreases with increasing receptor potential magnitude; (2) the relation between calcium current and calcium-concentration is a first-order, lowpass filter with constant cutoff frequency. These two calcium processes plus the lowpass-filter process resulting from the electrical resistance and capacitance of the hair-cell membrane - which limits the rate at which the receptor potential can change (Weiss and Rose, 1988b) - can account for much, although perhaps not for all, of the loss of synchronization of cochlear nerve fibers.

Acoustic Stimulation↗
PubMed1992

Branchio-oto-renal syndrome: further delineation of an underdiagnosed syndrome.

We report on a woman who was diagnosed with branchio-oto-renal (BOR) syndrome after 2 pregnancies complicated by oligohydramnios due to renal hypoplasia and agenesis. Both babies died neonatally of pulmonary hypoplasia. Histopathology of the temporal bones of the second child showed marked immaturity of the middle ear cleft, ossicles, facial nerve and canal, and cochlear nerve. Maternal renal ultrasound study was normal although intravenous pyelography indicated renal hypoplasia. The frequency of BOR syndrome among cases of recurrent fetal renal hypoplasia/dysplasia or agenesis is unknown, and parental renal ultrasonography may not identify a heritable renal defect. Investigations should include a family history, and examination of relatives to look for preauricular pits, lacrimal duct stenosis, and branchial fistulae and/or cysts. Hearing studies and IVP may be indicated.

Abnormalities, Multiple↗
PubMed1989

MINIMAC: a totally numeric 15 channel implanted stimulator.

After CHORIMAC-8 and CHORIMAC-12 a new multichannel cochlear implant is presented, characterized by its totally numeric sound signal processing. Owing to FFT the whole speech information is cut into 15 channels, then sequentially transmitted to an implanted receptor and electrode bearer. This digital processing provides the new system with several advantages: 1. miniaturization of outside emitter end implanted receiver; 2. compatibility of this new emitter with the 12 channel receivers implanted in the last 10 years; 3. increasing the number of stimulating electrodes from 12 to 15; 4. simple emitter programming with an IBM-PC; 5. option to postoperatively program the number (1 to 15) and the value (80 to 3,800 Hz) of the peak filters, and the amplification (6, 10, 18 dB) of each electrode. The next implanted device will have: a. constant current; b. programming of a particular current value for each electrode; and c. stimulation of the cochlear nerve through an extra cochlear electrode bearer, allowing deep implantation without deafness.

Cochlear Implants↗
PubMed1990

Response timing constraints on the cortical representation of sound time structure.

The precision of spike response timing of 94 primary auditory cortex neurons was studied using conventional extracellular recording techniques in barbiturate-anesthetized cats to which tone- and/or noise-burst stimuli were presented using sealed sound delivery systems. Precision of spike timing was indexed using the standard deviation of the first-spike latent period in responses evoked by repeated presentation of tonal stimuli systematically varied in frequency, amplitude, and/or repetition rate. Within a neuron, variability of first-spike timing was usually proportional to the mean first-spike latency, in agreement with previous reports. In cases where there was a systematic relation between the precision of response timing and the mean latency, a linear correlation accounted for up to 90% of the data variance. Across the 94 neurons, standard deviations seen in responses of minimum latency were related to minimal mean latencies, and were typically in the range from 0.15-1.5 ms. The data suggest that responses to transients in the cortex show a precision of spike timing which is only slightly worse than that seen in cochlear-nerve fibers. This, however, is in dramatic contrast to previous evidence on the steady-state temporal response of cortical cells, which is at least an order of magnitude poorer than that seen in auditory-nerve fibers and many cochlear nucleus cells. These observations may be directly relevant to the known consequences of auditory cortex pathology in man.

Animals↗
PubMedDate not supplied

Relation between the waveform of the cochlear whole nerve action potential and its intensity function.

The whole-nerve action potential (AP) was recorded by intracochlear electrodes in the guinea-pig. As is well known, in normal conditions, the AP elicited by tone bursts displays negative and positive deflections. Inactivation of the central end of the nerve at the internal auditory meatus (IAM), by introduction of a few drops of KC1 solution, or by mechanical pressure, produces a change in the wave shape of AP which is transformed into a single negative deflection. The relation of the amplitude of the monophasic AP to the intensity of the tone burst is monotonic, in contrast to the classical two-slope variation observed in normal conditions. These results are interpreted by the disappearance of a positive component of the response produced at the IAM. The convolution of the monophasic unit AP would explain the monotonic intensity function.

Acoustic Stimulation↗
PubMed1998

Regeneration of cochlear efferent nerve terminals after gentamycin damage.

Chickens recover auditory function after hair cell loss caused by ototoxic drug damage or acoustic overstimulation, indicating that mechanisms exist to reestablish appropriate neuronal connections to regenerated hair cells. However, despite similar hair cell regeneration times, hearing recovery takes substantially longer after aminoglycoside than after sound damage. We have therefore begun examining damage and regeneration of efferent nerve terminals by immunolabeling whole-mount cochleae for differentially localized synaptic proteins and by visualizing the distribution of label with confocal microscopy. In undamaged cochleae, the synaptic proteins synapsin and syntaxin show similar distribution patterns corresponding to the large cup-like terminals on short hair cells. After gentamycin administration, these terminals are disrupted as hair cells are lost, leaving smaller, more numerous synapsin-reactive structures in the sensory epithelium. Syntaxin reactivity remains associated with the extruded hair cells, indicating that the presynaptic membrane is still attached to the postsynaptic site. In contrast, after sound damage, both synapsin and syntaxin reactivity are lost from the epithelium with extruded hair cells. As regenerated hair cells differentiate after gentamycin treatment, the synapsin labeling associated with cup-like efferent endings reappears but is not completely restored even after 60 d of recovery. Thus, efferent terminals are reestablished much more slowly than after sound damage (), consistent with the prolonged loss of hearing function. This in vivo model system allows comparison of axonal reconnection after either complete loss (sound damage) or partial disruption (gentamycin treatment) of axon terminals. Elucidating the differences in recovery between these injuries can provide insights into reinnervation mechanisms.

Animals↗
PubMed1990

Changes in intracochlear and intracanalicular nerves after acoustic neurinoma excision confirmed by magnetic resonance imaging.

Postoperative magnetic resonance imaging findings related to the vestibulocochlear and facial nerves within the internal auditory canal were analyzed in acoustic neurinomas. T1- and proton-weighted magnetic resonance images showed that the vestibulocochlear nerves distal to the internal auditory meatus increased in signal intensity after surgical intervention. These nerves were conspicuously enhanced after intravenous administration of gadolinium diethylene-triamine-pentaacetic acid. The preserved facial nerves were also markedly enhanced postoperatively. As a possible cause of these findings, we suggest operative disruption of the blood-nerve barrier with ensuing nerve edema, although the operative procedures were carefully carried out using a surgical microscope. The clinical significance of traumatic disruption of the blood-nerve barrier and subsequent nerve edema are discussed from the standpoint of preservation of cochlear nerve function.

Cochlear Nerve↗
PubMedDate not supplied

Expression of subtypes NF-L, NF-M and NF-H of neurofilament triplet proteins in the developing rat inner ear.

The expression of each subtype (NF-L, NF-M and NF-H) of neurofilament (NF) triplet proteins in the developing rat inner ear was analysed using the immunofluorescence method (FITC). On the 15th gestational day (GD), immunostaining of NF subtypes did not occur in the otic region. On the 18th GD, positivity for NF-L and NF-M occurred in nerve fibres in both the sensory and the subepithelial layers of the inner ear but was lacking for NF-H. At 4 days after birth immunoreactivity was present for each NF subtype but with topographic differences in their distribution. The cell bodies of (different?) subpopulations of vestibular and spiral ganglion cells were immunostained with monoclonal antibodies for NF-L and NF-M, but a subpopulation of both vestibular and spiral ganglion cells showed immunoreactivity for all three NF subtypes. The vestibular nerve fibres and ganglion cells evidenced stronger positivity than cochlear nerve fibres and spiral ganglion cells. This study confirms that the cytoskeletal maturation of inner ear nerve fibres precedes the onset of at least the auditory function by several days.

Animals↗
PubMed1988

Synaptic endfeet in the 'acoustic nerve nucleus' of the rat. An electron microscopic study.

The medial portion of the cochlear nerve of the rat contains astrocytes, oligodendrocytes and neurons. These neurons form what has been called the 'acoustic nerve nucleus'. This nucleus has been studied here at the electron microscopic level. Its neurons are large and round, showing an eccentric nucleus, fibrillary bodies and rough endoplasmic reticulum which is not arranged in stacks. The somata and dendrites receive synaptic endfeet which can be classified into three groups according to vesicle size and shape. In general, the ultrastructural characteristics of these cells are similar to those of bushy cells as reported by other authors. The 'acoustic nerve nucleus' can be considered to be the most peripheral part of the anterior ventral cochlear nucleus.

Animals↗
PubMed1982

Cochlear potentials in the Bronx waltzer mutant mouse.

The Bronx waltzer mutant mouse has a unique cochlear abnormality in which the outer hair cells appear normal but the inner hair cells are absent. Potentials recorded from the round window indicate that the gross cochlear nerve action potential is very small or absent and cochlear microphonics are present but of small amplitude. Positive and negative summating potentials can both be recorded, indicating that mammalian outer hair cells are capable of producing both positive and negative DC potentials.

Animals↗
PubMed1965

Degeneration in the efferent nerve endings in the cochlea after axonal section.

Both roots of the olivo-cochlear nerve bundle to one ear were transected in the brain stems of 12 chinchillas. The animals were sacrificed at times ranging from 2 to 35 days after surgery. The normal olivo-cochlear terminals on the external hair cells in the cochleas of the control ears contained many mitochondria and small vesicles of constant size. The earliest evidence for degeneration was the presence of fine 100 A filaments in the proximal parts of the terminals. These were visible at 2 days. Animals sacrificed at later times showed a greater number of filaments and fewer vesicles, but few mitochondrial changes. After 1 week, disintegration of the terminals was more prominent. A few terminals showed mitochondrial swelling and lysis of the plasma membrane but few or no filaments within the first week. These latter terminals were interpreted as representing a more rapid process of disintegration than those terminals characterized by numerous filaments and seemingly unchanged mitochondria.

Animals↗