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Results for “Cochlear Nerve”

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At least 505 records · Page 28Linked to original sources

PubMed1990

Hearing conservation in acoustic neuroma surgery via the posterior fossa.

An increasing number of patients with an acoustic neuroma present with useful hearing in the tumour ear. Surgical removal of these tumours via the posterior fossa route may enable preservation of the cochlear nerve and otic capsule without increasing the morbidity to the facial nerve. The results of treating 51 cases of acoustic neuroma via the posterior fossa is presented. Forty four tumours measured less than 20 mm in diameter in the cerebellopontine angle and surgery was undertaken with hearing preservation as a principle objective. In 26 cases, the cochlear nerve was preserved anatomically and post-operative hearing at levels better than mean pure tone threshold of 50 dB or 50 per cent speech discrimination was recorded in 14 patients. The preservation of hearing represents a worthwhile surgical goal in selected patients with an acoustic neuroma without increasing the operative morbidity.

Cochlear Nerve↗

PubMed1985

Algorithms for removing recovery-related distortion from auditory-nerve discharge patterns.

The probability that a cochlear nerve fiber discharges during some specified time interval depends on both the acoustic stimulus and on refractory effects due to earlier spike discharges. With the objective of separating the stimulus-related effects from refractory-related effects seen in poststimulus-time histograms, various maximum-likelihood estimation schemes have been developed. By modeling auditory-nerve fiber discharges as a self-exciting point process in which the intensity depends on both the time during stimulation and the history of discharge, we have been able to independently verify the likelihood estimates of Gaumond et al. [J. Acoust. Soc. Am. 74, 1392-1398 (1983)] under conditions when the recovery function is known. Secondly by maximizing the likelihood function of the neural event process subject to periodic stimulus constraints we have derived estimates which as the number of stimulus presentations and or stimulus periods increase are free from the effects of both absolute and relative recovery-related distortion. Under conditions when the recovery function is unknown, a recursive algorithm is proposed that yields the joint maximum-likelihood estimates of both the stimulus-and recovery-related components in the response histograms. We state the conditions under which unique maximum-likelihood estimates exist and prove that the recursive algorithm converges to those unique estimates.

Acoustic Stimulation↗

PubMed1977

Evidence that catecholamines are not the afferent transmitter in the cochlea.

Beta-receptor blocking agents (practolol, propranolol) and alpha-receptor blocking agents (phenoxybenzamine, phentolamine), when applied intracochlearly do not eliminate the afferetn discharges or compound action potential of the cochlear nerve. Under the assumption that the drugs used reach the synaptic site, it is therefore concluded that these drugs do not interfere with afferent synaptic transmission. Phentolamine,, however, has a toxic effect upon the cochlea independent from the synaptic process. Local application of catecholamines does not increase spontaneous activity of single fibres of the cochlear nerve. These findings show that catecholamines are not likely to be the afferent transmitter.

Acoustic Stimulation↗

PubMed1988

Morphology of cochlear root neurons in the rat.

The morphology of large neurons in the cochlear nerve root of albino rat has been studied with a variety of techniques including Nissl and cell-myelin staining, Golgi impregnation, horseradish peroxidase back-filling of severed axons, transmission electron microscopy, and morphometry. The cells, called root neurons, resemble the globular cells of the ventral cochlear nucleus in having an oval cell body, an eccentric nucleus, an axon that projects centrally via the trapezoid body, and in receiving many primary-like axosomatic boutons. The root neurons, however, are larger than globular cells, and they have at least two types of dendrites oriented, respectively, parallel and across the cochlear nerve fibres. The soma, moreover, has less finely dispersed Nissl material, is less completely covered with terminals, and receives a smaller proportion of presumably inhibitory synapses. So far, this particular type of neuron has been observed only in rat and mouse.

Animals↗

PubMed1979

Vestibular, auditory, and somatic input to the posterior thalamus of the cat.

The responses of 157 neural units in the magnocellular (mc) and parvocellular (pc) components of the medial geniculate nucleus (MG) and other nuclei of the posterior (PO) thalamic group were recorded and analyzed. Units were tested for a response to electrical stimulation of the vestibular nerve, natural auditory and electrical cochlear nerve stimulation, and natural stimulation of joint, muscle, and cutaneous receptors of the limbs, trunk, and neck (somatic stimulation). Only 45% of the units responded to these stimuli. Twenty-four percent of the responsive units were multimodal, responding to more than one stimulus. All multimodal units were activated by auditory stimuli. More units responding to vestibular stimulation were found in mcMG than in pcMG or other components of the PO group. Potentials evoked by vestibular nerve stimulation were recorded in all 3 regions with latencies of 5--25 msec. No evidence was found for a thalamic relay from vestibular nerve to cortex in the area investigated, since the recorded latency for activity from vestibular nerve stimulation was longer than the latency of responses recorded in the cortex. This region of the thalamus appears to be important for reception of auditory information and integration with vestibular and somatic modalities.

Acoustic Stimulation↗

PubMed2005

Influence of supporting cells on neuronal degeneration after hair cell loss.

In sensorineural hearing loss, hair cell loss is often followed by loss of cochlear nerve fibers, which can continue for years after the insult. The degree and time course of neuronal loss varies, but the reasons for this variation are unclear. The present study addresses this issue with a quantitative analysis of hair cell, supporting cell, and neuronal survival in animals with long-term survival of up to 5.5 years from two types of drug-induced hair cell loss: aminoglycoside antibiotics and platinum-containing chemotherapeutics. To complement the analysis of the effects of organ of Corti damage on neuronal survival, cases of primary neuronal degeneration, via auditory nerve section, are also assessed. Analysis shows that (1) long-term neuronal survival is enhanced when supporting cells in the inner hair cell (IHC) area remain intact; (2) after hair cell loss, the time course of neuronal loss is slower in the apex than in the base; (3) primary loss of cochlear nerve fibers does not lead to secondary degeneration of sensory cells or supporting cells in the organ of Corti; and (4) after auditory nerve section, there can be a massive reinnervation of the IHC region, especially in the apex. Results are consistent with the idea that supporting cells participate in the regulation of neuronal survival and neuronal sprouting in the organ of Corti.

Aminoglycosides↗

PubMed2000

Preoperative cochlear implant imaging: is magnetic resonance imaging enough?

OBJECTIVE: To investigate the accuracy of magnetic resonance imaging (MRI) as a preoperative imaging technique for cochlear implant candidates. STUDY DESIGN: Retrospective, blinded. SETTING: Tertiary medical center. PATIENTS: 31 cochlear implant candidates with various causes of hearing loss. INTERVENTION: Cochlear implant patients received preoperative high-resolution temporal bone computed tomography (CT), and high-resolution T2-weighted fast spin echo MRI (FSE-MRI). The images were read independently of each other and in a blinded manner by two neuroradiologists. The imaging results were also correlated with intraoperative findings. MAIN OUTCOME MEASURES: Lack of agreement between the findings for either imaging technique; also, lack of agreement between imaging findings and intraoperative findings. RESULTS: FSE-MRI is equal to CT imaging in the detection of abnormalities of cochlear patency. It is better than CT imaging in detecting cochlear dysplasia and large vestibular aqueducts, and in determining the presence of the cochlear nerve. CONCLUSION: FSE-MRI is accurate in predicting inner ear anomalies and obstruction of the cochlear lumen. It also adds information not gathered from CT imaging, such as the presence and size of the cochlear nerve.

Cochlear Implantation↗

PubMed1996

Cochlear implantation in an intralabyrinthine acoustic neuroma patient after resection of an intracanalicular tumour.

This case study describes a therapeutic strategy using a cochlear implant for a bilateral acoustic neuroma deafened patient. The cochlear nerve had previously been sacrificed on one side during tumour removal, but on the remaining side a functioning cochlear nerve was assessed by electric promontory stimulation in spite of a neuroma extending into the vestibular labyrinth. The patient was successfully stimulated with a Nucleus 22-channel implant after removal of the intracanalicular portion of the neuroma via a middle fossa approach.

Cochlear Implants↗

PubMed2004

Optico-cochleo-dentate degeneration associated with severe peripheral neuropathy and caused by peroxisomal D-bifunctional protein deficiency.

The clinical, neuroradiological, neuropathological and biochemical findings in a patient with optico-cochleo-dentate degeneration (OCDD; OMIM 258700) are presented in a severe case succumbing at the age of 4 years. The electron microscopic and biochemical data showed for the first time that OCDD may occur as the phenotypic expression of D-bifunctional protein deficiency, i.e., a peroxisomal disorder. The boy was born as the first child of healthy, consanguineous parents of Turkish origin. No other family members were affected. The main clinical symptoms consisted of muscle hypotonia ("floppy infant"), generalized epileptic fits, hypacusis, rotatory nystagmus, insufficient pupillary reactions, and mental retardation. Fibroblast cultures revealed D-bifunctional protein deficiency. Neuropathological examination displayed moderate frontoparietal and insular microgyria, and atrophy of the cerebellum. Loss of neurons was severe in the granular layer, the Purkinje cell band of the cerebellum, and rather complete in the dentate nucleus. A corresponding loss of myelinated fibers associated with characteristic periodic acid-Schiff-positive macrophages was most prominent in the white matter of the cerebellum. There was additional severe loss of myelinated fibers in the central portions of the optic nerve, reduction of the nerve fiber density in the cochlear nerve, and reduction of myelinated nerve fibers by about 80-90% in the sural nerve, which has not been studied in previous cases. At the electron microscopic level, characteristic inclusions mainly in perivascular macrophages and astrocytes were the most prominent finding. The inclusions usually showed a bilaminar structure, whereas trilaminar structures, typically seen in adrenoleukodystrophy, and multilaminar structures were less frequently seen.

3-Hydroxyacyl CoA Dehydrogenases↗

PubMedDate not supplied

[Effect of microphone potential feedback on formation of adjusted curves of the hearing periphery].

The model of the formation of the exiting factor on the neuron endings of the cochlear nerve taking into consideration the feedback mechanisms described in recent experimental investigations is proposed. It is shown that the functioning of the feedback in the model give the possibility to explain the principle of action of the mechanism of enhancement of mechanical duct tuning which produce exquisite tuning, reflected in the tuning properties of cochlear nerve fibers. At the same time the utilisation in the model the mechanism of the lateral inhibition provide it the property similar to the effect of inhibition of the neurone response to a given tone signal when another tone signal arises in a nearby frequency region.

Animals↗

PubMed1993

Investigations in electrophysiology and morphology of the VIII cranial nerve.

The morphological and functional changes of the eighth nerve in patients undergoing cerebello-pontine angle (CPA) surgery are under investigation in the ENT Department of the University of Verona. The main aspects of the research are: ultrastructural examination of the eighth nerve in normals and subjects operated on for vestibular or cochleo-vestibular neurectomy and for acoustic neuroma; monitoring cochlear nerve function during CPA surgery by monopolar and bipolar recording of cochlear nerve action potential (CNAPs). The specific aims of this research are: to acquire information on the pathophysiology of a number of peripheral cochleo-vestibular disorders; to evaluate the role of intraoperative recording of the eighth nerve in preserving hearing.

Evoked Potentials, Auditory↗

PubMed1991

Effect of isepamicin dosing scheme on concentration in cochlear tissue.

To investigate the possible effect of the dosing scheme of aminoglycosides on their concentration in the cochlear tissue, we gave two groups of 12 guinea pigs subcutaneous doses of 45 mg of isepamicin (ca. 30 mg of active product) per kg of body weight daily for eight consecutive days. The first group received the drug by continuous infusion, while the second group received it by single daily injection. On the final day of administration, the animals were sacrificed and the cochlear tissue was removed. The tissues from the cochleas of pairs of guinea pigs were pooled. The isepamicin concentrations in the cochlear duct tissue (organ of Corti plus lateral wall) and the cochlear nerve tissue were determined separately. Hearing levels before and after treatment were assessed by means of frequency-specific auditory brain stem responses (ABR). The creatinine level in serum was determined on the last day of the administration. None of the animals in either group showed signs of renal insufficiency or of hearing impairment. The median isepamicin concentration in the cochlear duct was 2.40 micrograms/mg of protein after continuous administration and 2.50 micrograms/mg of protein after once-daily administration, compared with the concentration in the cochlear nerve, where it was 1.93 micrograms/mg of protein after continuous administration and 2.59 micrograms/mg of protein after once-daily administration. These differences are statistically insignificant. The results give evidence for linear uptake kinetics of isepamicin in the inner ear tissue and may be directly relevant to the clinical dosing of the drug.

Animals↗

PubMed1982

Uptake and transport of horseradish peroxidase by cochlear spiral ganglion neurons.

Cochlear spiral ganglion neurons in the cat have been classified as type I and type II. The type II neurons are of special interest since they are reported to provide the afferent innervation to three-quarters of the cochlear hair cells, and also because of a recent assertion that they do not project to the brain. In the present study the neuronal marker horseradish peroxidase (HRP) was utilized to re-examine these issues. HRP was injected into the intranuclear cochlear nerve root of adult cats. 18 to 48 h post-injection HRP reaction product was observed in both type I and type II neurons. The majority of labeled cells were characterized by granular reaction product, while a smaller number of cells were also diffusely filled with HRP, resulting in intense staining of the cell soma and its processes. These data indicate that the central axons of type II neurons are constituents of the cochlear nerve root at the level of the brainstem and thus do project centrally. In the organ of Corti HRP-filled fibers to both inner and outer hair cells were observed and demonstrated in electron microscopy to be afferent neurons. This intra-axonal accumulation of the HRP by outer hair cell afferents constitutes direct evidence of the functional projection of these neurons to the cochlear nucleus.

Animals↗

PubMed1979

The development of some peripheral and central auditory responses in the neonatal cat.

The development of cochlear nerve action potential thresholds at different frequencies (AP audiograms) and inferior colliculus (IC) single unit thresholds and tuning was examined in barbiturate-anaesthetized kittens. AP thresholds decreased over the whole frequency spectrum during the first 5 weeks of life. Thresholds to high-frequency stimulation remained higher in 7-week-old animals than in adults. These results are in contrast to previous reports which have suggested that the AP response and gross cochlear anatomy are mature by the end of the second week. These differences may be due to the fact that the AP audiogram technique provides a measure of the activity of discrete regions along the cochlear partition. IC units in animals younger than 3.5 weeks had significantly elevated thresholds and broader tuning than those of the adult cat. Comparison of AP audiogram and IC unit thresholds in the adult revealed that these indices show similar frequency-dependent sensitivity. The slower maturation revealed by the AP audiogram may be due to the greater number and/or synchrony of cochlear nerve discharges needed to produce the gross AP. If this were the case, perception of suprathreshold sounds might not develop as quickly as thresholds for sound detection.

Acoustic Stimulation↗

PubMedDate not supplied

Conflicting electrophysiological and anatomical data from drug-impaired guinea pig cochleas.

In guinea pigs that had been treated with very large doses of the aminoglycoside amikacin (14 x 450 mg/kg/day, i.m.) clear, short-latency responses to various click stimuli could be recorded at the round window. When the same cochleas were examined histologically, no outer or inner hair cells could be found along the entire length of the basilar membrane, save for a very few outer hair cells remaining at the apex. The response patterns resembled that of the compound action potential, and various characteristics suggest that they were of neural origin. Vestibular function, investigated by electronystagmography during rotation, appeared normal, as did most of the saccular and utricular hair cells. Transmission electron microscopy revealed a significant number of cochlear nerve fibres still innervating the remnants of Corti's organ. In other cochleas with similarly extensive destruction induced by another aminoglycoside (sisomycin, 14 x 125 mg/kg/day, 15 days as well as 3 months post-Rx), no responses could be recorded from the round window. Cochleas that were less affected, with the upper turns preserved, gave only small, long-latency responses. These preliminary observations are confirmed by further experiments now in progress. They suggest that unless a considerable number of inner hair cells remained undetected in the lower basal turn, a possibility that appears highly unlikely, there was either a direct mechanical excitation of cochlear nerve fibres, or an acoustical stimulation of vestibular sense organs.

Acoustic Stimulation↗

PubMed1997

Frequency tuning and spontaneous activity in the auditory nerve and cochlear nucleus magnocellularis of the barn owl Tyto alba.

Single-unit recordings were obtained from the brain stem of the barn owl at the level of entrance of the auditory nerve. Auditory nerve and nucleus magnocellularis units were distinguished by physiological criteria, with the use of the response latency to clicks, the spontaneous discharge rate, and the pattern of characteristic frequencies encountered along an electrode track. The response latency to click stimulation decreased in a logarithmic fashion with increasing characteristic frequency for both auditory nerve and nucleus magnocellularis units. The average difference between these populations was 0.4-0.55 ms. The average most sensitive thresholds were approximately 0 dB SPL and varied little between 0.5 and 9 kHz. Frequency-threshold curves showed the simple V shape that is typical for birds, with no indication of a low-frequency tail. Frequency selectivity increased in a gradual, power-law fashion with increasing characteristic frequency. There was no reflection of the unusual and greatly expanded mapping of higher frequencies on the basilar papilla of the owl. This observation is contrary to the equal-distance hypothesis that relates frequency selectivity to the spatial representation in the cochlea. On the basis of spontaneous rates and/or sensitivity there was no evidence for distinct subpopulations of auditory nerve fibers, such as the well-known type I afferent response classes in mammals. On the whole, barn owl auditory nerve physiology conformed entirely to the typical patterns seen in other bird species. The only exception was a remarkably small spread of thresholds at any one frequency, this being only 10-15 dB in individual owls. Average spontaneous rate was 72.2 spikes/s in the auditory nerve and 219.4 spikes/s for nucleus magnocellularis. This large difference, together with the known properties of endbulb-of-Held synapses, suggests a convergence of approximately 2-4 auditory nerve fibers onto one nucleus magnocellularis neuron. Some auditory nerve fibers as well as nucleus magnocellularis units showed a quasiperiodic spontaneous discharge with preferred intervals in the time-interval histogram. This phenomenon was observed at frequencies as high as 4.7 kHz.

Acoustic Stimulation↗

PubMed2006

Magnetic resonance appearance of the inner ear after hearing-preservation surgery.

OBJECTIVE: To determine whether the appearance of the inner ear on T2-weighted follow-up magnetic resonance imaging correlates with hearing status after hearing-preservation surgery for vestibular schwannoma. STUDY DESIGN: Retrospective chart review. SETTING: Tertiary referral medical center. PATIENTS: The study includes patients undergoing hearing-preservation surgery for vestibular schwannoma from 1998 to 2003. INTERVENTION: Diagnostic evaluation with magnetic resonance imaging and audiometric evaluation. MAIN OUTCOME MEASURES: Hearing results as reported in charts was correlated with appearance of membranous labyrinth on T2-weighted magnetic resonance images obtained at least 1 year after surgery. RESULTS: Twenty-nine patients were identified, 16 of whom satisfied the inclusion criteria. All 16 of the patients underwent middle fossa removal of vestibular schwannoma. Serviceable hearing according to American Academy of Otolaryngology-Head and Neck Surgery criteria was preserved in eight patients (50%). Of the eight patients without serviceable hearing, six had the cochlear nerve sacrificed at the time of surgery. All patients with serviceable hearing had normal appearing cochleovestibular signal on T2-weighted images, whereas six of eight patients (75%) with no hearing or poor hearing had abnormal low signal in the inner ear, suggesting inner ear ossification. The positive predictive value of a normal labyrinth for preserved hearing was 90%, whereas the negative predictive value of an abnormal labyrinth for no hearing was 100%. All but one patient who had the cochlear nerve sacrificed showed abnormal morphology of the labyrinth on T2-weighted magnetic resonance imaging. CONCLUSION: We describe the T2-weighted magnetic resonance findings after hearing-preservation surgery for acoustic tumor removal. Loss of inner ear signal on T2-weighted images correlates with loss of hearing postoperatively, whereas preserved inner ear signal correlates with hearing preservation after middle fossa surgery for vestibular schwannoma removal.

Auditory Threshold↗

PubMed1978

Organization and development of the brain stem auditory nuclei of the chicken: primary afferent projections.

The pattern of primary auditory projections to the brain stem of young chickens was investigated using terminal degeneration methods and orthograde transport of horseradish peroxidase (HRP) or tritiated amino acid. Of particular interest was the question of whether nucleus laminaris (NL) receives primary afferents. A study of silver-stained degeneration pattersn in nucleus magnocellularis (NM) and NL at three intervals following unilateral interruption of the cochlear nerve revealed that by 48 hours after the lesion, degenerating terminals were found only in the ipsilateral nucleus angularis (NA), NM and lagenar projection areas but not in NL. Five- and eight-day survival times, however, also revealed degeneration bilaterally in NL. The appearance of terminal degeneration in NL at the longer survival times is attributed to the previously-reported severe and rapid transneuronal degeneration of neurons in NM following deafferentation and not to the presence of cochlear nerve terminals in NL. Injection of HRP or tritiated proline into the basilar papilla produced patterns of labeling similar to that seen in the 2-day degeneration material; HRP reaction product or autoradiographic label were seen only in the ipsilateral NA and NM and in the ipsilateral projection areas of the macula lagena but not in either NL. The patterns of primary auditory projections revealed by the three methods were quite similar to each other and to that previously reported for the pigeon and confirm the conslucion that the laminar nucleus of chickens does not receive primary afferents.

Animals↗