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Results for “Cochlear Nerve”

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PubMed1996

Brain stem auditory-evoked potentials of mice with experimental allergic encephalomyelitis.

Experimental allergic encephalomyelitis (EAE) is an experimental model for multiple sclerosis. In order to study autoimmune retrocochlear hearing loss, we performed brain stem auditory-evoked potential (BAEP) studies on EAE mice. The EAE was induced in B10.PL and (PL/J x SJL)F1 mice. In the BAEP study, all of the peak and interpeak latencies were prolonged significantly in the diseased mice. Hearing thresholds were slightly elevated in the immunized mice during the acute phase. Inflammatory and phagocytic cell infiltration, demyelination, and V beta 8.1, 8.2 T-cell receptor-positive cells were observed in the cochlear nerves or their proximity by histologic study. It is suggested that immunologic reactions identified with EAE also occurred in the cochlear nerve, and that these reactions were responsible for the hearing problems. It appears that EAE is a useful model system for studying autoimmune insults on the neural portion of the auditory system.

Animals↗

PubMed1990

[Occult acoustic neurinoma].

A case of small occult schwannoma in a 73-year-old man is reported. Histopathological sections of the temporal bone revealed a tumor in the left internal auditory meatus. The tumor measured about 5 x 6 mm in size. There were whorls of spindle shaped cells with the typical palisading characteristic of acoustic neurinoma-Antoni A type. The posterior wall of the meatus had been eroded but the nerve fibers were intact. It seems to have raised from the cochlear nerve trunk and was displaced and compressed. Slight degeneration of the spiral ganglion cells and the cochlear nerve fibers was found. There was a very fine granular eosinophilic precipitate throughout the perilymphatic space. This probably represents increased protein content in the perilymph. Thickening of the walls of the internal auditory artery and some vessels of striae vasculares was also noted. The organs of Corti, the maculae of the utricle and saccule and the cristae of semicircular canals appeared normal.

Aged↗

PubMed1993

Ratio of variance to mean of action potential counts for an auditory nerve fiber model with second-order refractory behavior.

Sequences of interval times were generated with the first- and second-order interval probability dependence proposed by Gaumond et al. [J. Neurophysiol. 48, 856-873 (1982)] to characterize cochlear nerve fiber spontaneous action potential (AP) sequences. The ratio F(T) of the variance to the mean of the count of APs in bins of T s was computed for the simulated sequences, and compared to the corresponding measure for cochlear nerve fiber data presented by Lowen and Teich [J. Acoust. Soc. Am. 92, 803-806 (1992)]. The simulations were generally consistent with the data in the range 15 < T < 100 ms.

Cochlea↗

PubMed1983

Pathology as it relates to ear surgery II. Labyrinthectomy.

Five human temporal bones and three surgical VIIIth nerve biopsies from patients who had previously undergone labyrinthectomy, five months to ten years before examination, were studied by light and electron microscopy. Post-labyrinthectomy dizziness could be explained on the bases of inadequate surgical removal of the vestibular sense-organs, neuroma formation in the vestibule, and high regenerative potential of the vestibular nerve. Post-labyrinthectomy pressure sensation and tinnitus are most probably due to cochlear endolymphatic hydrops and need cochlear neurectomy. The severe atrophy in the sensorineural structures of the cochlea was not associated with retrograde degeneration of the cochlear nerve central axons. This may be of significance in the artificial electrical stimulation of the cochlear nerve in deaf patients.

Adult↗

PubMed2000

Expression of EphA4 in developing inner ears of the mouse and guinea pig.

The expression of EphA4, an Eph-class receptor tyrosine kinase, was determined by immunohistochemistry in developing inner ears of the mouse and the guinea pig. In the mouse, EphA4 expression was visible in the fibroblasts of the spiral ligament and in the structures that were to become the osseous spiral lamina. Cochlear nerve ganglion cells expressed ephrin-B2, and the modiolus expressed mRNA coding for ephrin-B3, both transmembrane ligands for EphA4. In contrast, in the guinea pig, cells of the cochlear nerve ganglion expressed EphA4, as did supporting cells of the organ of Corti (Hensen's cells and inner pillar cells). There was also some expression in fibroblasts of the spiral ligament but none in the structures that were to become the osseous spiral lamina. It is suggested that in the mouse, EphA4 may help direct the cochlear innervation towards the organ of Corti by a repulsive interaction, but that this is highly species dependent.

Amino Acid Sequence↗

PubMed1993

[Effect of methamphetamine on the auditory system].

Four series of experiments were performed to evaluate the effects of methamphetamine on the auditory system of guinea pigs. Methamphetamine was administered to guinea pigs via intraperitoneal injection, and the time course of latencies of waves I, II, III, and IV, interpeak latencies of waves I-III, III-IV, and I-IV of the ABR, and the near-field potential of the inferior colliculus and cochlear nerve were measured. These physiological data were analyzed in comparison with the distribution of methamphetamine in the inferior colliculus and cochlea following its immunohistochemical staining, as well as the serum methamphetamine concentration. The following results were obtained; 1. The wave latencies and interpeak latencies of ABR decreased up to 120 minutes after the administration. 2. In the cochlear nerve recording, the amplitude of the response increased and the latency decreased up to 90 minutes after the administration. These changes in responses were, however more prominent in the inferior colliculus recording. 3. Immunohistochemical examination revealed that methamphetamine was present in the hair cells of the organ of Corti, spiral ligament, spiral ganglion cells and the inferior colliculus 30 minutes after the administration. 4. The serum concentration of methamphetamine rapidly reached its maximal level, and then dropped gradually, logarithmically, having become almost horizontal at a low level 6 hours later. These results suggest that methamphetamine does exert an effect on the peripheral auditory system, as well as on the central nervous system, which is generally regarded as the effector organ. It is assumed that the pharmacological effect of methamphetamine on the cochlea involves excitation of sensory cells, afferent nerve fibers and spiral ganglion cells.

Animals↗

PubMed2002

Pediatric cochlear implantation in auditory neuropathy.

OBJECTIVE: Auditory neuropathy (AN) is characterized by varying degrees of sensorineural hearing loss, an absent or severely abnormal auditory brainstem response, and normal otoacoustic emissions. The nomenclature for this condition reflects the concept that the site of lesion is proximal to the cochlea (e.g., cochlear nerve). Given this hypothesis, it is reasonable to expect limited benefit from cochlear implantation in patients with AN. However, a growing body of evidence shows the striking benefits of cochlear implantation in AN. To explore this topic, we reviewed our population of children with AN and, specifically, the performance results in those children having undergone cochlear implantation. STUDY DESIGN: A retrospective case review of those patients diagnosed with AN from 1993 to 2001. SETTING: A tertiary pediatric referral center. PATIENTS: A diagnosis of AN reported from the Center for Hearing and Deafness Research, Cincinnati, OH, database. RESULTS: Eighteen patients were diagnosed with AN (11 girls, 7 boys), with 3 sets of siblings, including 1 set of identical twins. Four patients with AN underwent implantation in the previous 5 years. Twelve out of the 18 patients had classic risk factors for AN (e.g., prematurity and hyperbilirubinemia). The degree of hearing loss varied in our patients, with a majority showing severe to profound deficits. All children with implants showed improvement in auditory and verbal development, but this improvement was variable. CONCLUSION: The success of cochlear implantation in these patients suggests that some children with AN have an auditory system lesion that can be compensated for by cochlear implantation. This implies either an inner hair cell or inner hair cell-cochlear nerve junctional pathology that can be overcome by direct electrical stimulation.

Audiometry, Pure-Tone↗

PubMed1997

Management of vestibular schwannomas (acoustic neuromas): auditory and facial nerve function after resection of 120 vestibular schwannomas in patients with neurofibromatosis 2.

OBJECTIVE: Vestibular schwannomas (VSs) affect young patients with Neurofibromatosis 2 (NF-2) and cause very serious problems for hearing, facial expression, and brain stem function. Our objective was to determine a therapy concept for the right timing and indication of neurosurgical therapy. METHODS: In 1000 consecutive VS resections, 120 tumors in 82 patients with NF-2 were surgically treated by the same surgeon (MS) at the Department of Neurosurgery at Nordstadt Hospital from 1978 to 1993. The mean age of the patients was 27.5 years. Sixty tumors were surgically treated in 41 male patients, and 60 tumors were surgically treated in 41 female patients. Bilateral tumor resection was performed in 38 patients (76 operations, after previous partial surgery in 15 cases elsewhere), and unilateral operations were performed in 44 patients, 5 of whom had undergone ipsi- or contralateral surgery that was performed elsewhere. The operative and clinical findings are evaluated and compared with the data of patients without NF-2. RESULTS: In 105 cases, complete tumor resections were achieved. In 15 cases, deliberate subtotal resections were performed. These were for brain stem decompression in 4 cases and for hearing preservation in the last hearing ear in 11 cases, with successful preservation in 8 of the 11. Pre- and postoperative hearing rates were higher in male than in female patients (70% in male versus 65% in female patients before surgery and 40.5 versus 31%, respectively, after surgery). Hearing was preserved in 29 of 81 ears (36%). The rate of preservation was 24% in cases of large tumors and 57% in cases of small tumors (<30 mm). Twenty-one of 82 patients (26%) were bilaterally deaf before surgery. Twenty-five patients had uni- or bilateral hearing after surgery (i.e., 41 % of those with preoperative hearing or 30.5% of the whole group). Anatomic facial nerve preservation was achieved in 85%. The facial nerve was reconstructed intracranially at the cerebellopontine angle by sural grafting in 17 cases and by hypoglossal-facial reanimation in 5. Two deaths occurred 1 and 3 months postsurgically as a result of malignant tumor growth with brain stem dysfunction and respiratory problems. In summary, for patients with NF-2, the presentation ages are lower, tumor progression is faster, the chances of anatomic and functional nerve preservation are lower, the chances of good outcomes are best when surgery is performed early and when there is good preoperative hearing function, and the danger of sudden hearing loss is higher. The chances and danger often differ from side to side among individual patients. CONCLUSION: The indication and the timing of tumor resections are in some respects different from normal VS handling and are dependent on the tumor extension and related necessity of brain stem decompression and on the auditory function. As an optimal goal, completeness of resection with functional cochlear nerve preservation is formulated, and as an acceptable compromise, subtotal microsurgical resection with functional cochlear nerve preservation in the last hearing ear is suggested.

Adolescent↗

PubMed1990

Nerve fiber analysis and the aging process of the vestibulocochlear nerve.

Nerve fiber analyses were performed on the human vestibulocochlear nerve stained with Luxol fast blue-periodic acid-Schiff-hematoxylin with use of a combination of an image-analyzer and a computer. The axons were counted and their transverse (cross-sectional) areas were measured in 12 individuals. The average numbers of axons in each vestibular and cochlear nerve were 17,727 and 25,098, and the average transverse areas of their axons were 4.02 and 1.79 microns 2, respectively. Amyloid bodies and intervening Schwann cells in the vestibulocochlear nerve were also counted. The average number of amyloid bodies was 246 per transverse section of the nerve and their average size was 114 microns 2. The average number of intervening Schwann cells was 1,513. Our results indicated that the transverse axonal areas of the cochlear nerve became reduced with age, while the transverse areas of the amyloid bodies in the vestibulocochlear nerve increased with age. The number of vestibular nerve fibers did not seem to change with age.

Adult↗

PubMed1988

Uptake and release of glycine in the guinea pig cochlear nucleus after axotomy of afferent or centrifugal fibers.

Glycine may be an inhibitory transmitter in the mammalian cochlear nucleus (CN). This study attempts to determine if cochlear and/or centrifugal projections to the CN use glycine as a transmitter. The high-affinity uptake and electrically evoked release of exogenous [14C]glycine were measured in vitro in the three major subdivisions of the guinea pig CN: the anteroventral, posteroventral, and dorsal cochlear nuclei (AVCN, PVCN, and DCN, respectively). [14C]Glycine (3.4 microM) was taken up by each subdivision, reaching tissue concentrations six to seven times that in the medium. Subsequent electrical stimulation evoked a Ca2+-dependent release of [14C]glycine from each subdivision. These activities were compared in subdivisions fr0m unlesioned animals, and from animals with lesions of centrifugal or cochlear projections to the CN. Two knife-cut lesions were made to interrupt centrifugal projections to the CN lying in the right acoustic striae and trapezoid body. In one group of animals, centrifugal fibers projecting mainly to the right AVCN and PVCN were severed, which reduced [14C]glycine uptake and release by 44-53% in these subdivisions, but not in the right DCN. In another group of animals, fibers projecting mainly to the right PVCN and DCN were severed, which reduced [14C]glycine uptake and release by 33-47% in these subdivisions, but not in the right AVCN. In CN subdivisions contralateral to either lesion there was no significant change in [14C]glycine uptake or release. Neither of these lesions altered the uptake or release of D-[3H]aspartate in the right or the left CN. Ablation of the left cochlea, which presumably destroyed cochlear nerve fibers unilaterally, had no effect on [14C]glycine uptake and release. These observations suggest that centrifugal projections contribute a proportion of the glycinergic synaptic endings in the CN. In addition, some glycinergic endings probably arise from neurons intrinsic to the CN. The cochlear nerve contains very few, if any, glycinergic fibers.

Afferent Pathways↗

PubMed1979

Electrocochleography and experimentally induced loudness recruitment.

The relationship between changes in loudness and the cochlear whole-nerve potential following experimentally produced deafness was studied in an animal model. Reaction time of a subject's response to an auditory stimulus has been shown to be an index of loudness in human experiments and has been adapted to nonhuman primates. In a series of experiments, four macaque monkeys were operantly conditioned to respond to 8-kHz tones over a range of 3--80 dB SPL, and their reaction times to pure tone stimuli were measured. Whole-nerve cochlear action potentials were recorded from chronic inner-ear electrodes. The relationship between behavioral and electrical measures of loudness recruitment were examined in animals with both temporary and permanent noise-induced hearing loss. Loudness recruitment was demonstrated experimentally after a 1-h exposure to a high-intensity 8-kHz octave band of noise. Excellent agreement was observed between the reaction time function and the action potential input-output function at intervals of 0.5, 12, 24, 48, and 84 h after exposure. Permanent hearing loss was produced in some of these animals by a much longer duration of exposure to the 8-kHz octave band of noise. Recruitment was observed in both the behavioral and the electrical measures. Histological studies of these damaged cochleas revealed primarily outer hair cell destruction, with a relative sparing of inner hair cells and nerve supply. The findings of this study are interpreted as strong support for the clinical electrocochleogram as an objective indicator of the presence of loudness recruitment.

Action Potentials↗

PubMed2006

The effect of Gaussian noise on the threshold, dynamic range, and loudness of analogue cochlear implant stimuli.

The deliberate addition of Gaussian noise to cochlear implant signals has previously been proposed to enhance the time coding of signals by the cochlear nerve. Potentially, the addition of an inaudible level of noise could also have secondary benefits: it could lower the threshold to the information-bearing signal, and by desynchronization of nerve discharges, it could increase the level at which the information-bearing signal becomes uncomfortable. Both these effects would lead to an increased dynamic range, which might be expected to enhance speech comprehension and make the choice of cochlear implant compression parameters less critical (as with a wider dynamic range, small changes in the parameters would have less effect on loudness). The hypothesized secondary effects were investigated with eight users of the Clarion cochlear implant; the stimulation was analogue and monopolar. For presentations in noise, noise at 95% of the threshold level was applied simultaneously and independently to all the electrodes. The noise was found in two-alternative forced-choice (2AFC) experiments to decrease the threshold to sinusoidal stimuli (100 Hz, 1 kHz, 5 kHz) by about 2.0 dB and increase the dynamic range by 0.7 dB. Furthermore, in 2AFC loudness balance experiments, noise was found to decrease the loudness of moderate to intense stimuli. This suggests that loudness is partially coded by the degree of phase-locking of cochlear nerve fibers. The overall gain in dynamic range was modest, and more complex noise strategies, for example, using inhibition between the noise sources, may be required to get a clinically useful benefit.

Adult↗

PubMed1999

Physiologic identification of eighth nerve subdivisions: direct recordings with bipolar and monopolar electrodes.

The purpose of this study was to determine stimulation and recording parameters that maximize differences in evoked responses recorded between the cochlear nerve and the surrounding tissues. Click-evoked potentials were obtained using monopolar and bipolar recording electrodes placed directly on the exposed eighth nerve of anesthetized cats. Responses were compared as stimulus intensity, electrode location, and bipolar electrode orientation and interelectrode spacing were systematically varied. Wave amplitudes increased monotonically with intensity for both monopolar and bipolar configurations, but bipolar configurations exhibited greater selectivity in differentiating cochlear from vestibular subdivisions. The optimal stimulus intensity was 70 to 80 dB peak sound pressure level (pSPL). Monopolar recordings were often confounded by activity originating at remote sites, typically the cochlear nucleus and (for recording sites on the vestibular nerve) the cochlear nerve. Bipolar response amplitudes increased with interelectrode spacing and were largest when electrodes were oriented parallel to the long axis of the nerve. Extrapolation of empirical data indicated that amplitudes of bipolar responses would be maximal at an electrode separation of 7.5 mm. Cochlear nerve conduction velocity, calculated from wave latencies at each of the two monopolar electrodes, was 11.6 +/- 1.6 m/sec.

Animals↗

PubMed1971

Human auditory attention: a central or peripheral process?

The click-evoked electrical responses of the human cochlear nerve were recorded from the external ear canal concurrently with the cortical evoked potentials from the scalp. Paying attention to the clicks during a discrimination task resulted in a highly significant enhancement of the cortical response but no change in the cochlear nerve response. Hence no evidence was obtained for the operation of a peripheral gating mechanism during attention in man.

Action Potentials↗

PubMed2003

Intralabyrinthine schwannomas.

OBJECTIVE: To describe the patient presentation, radiographic findings, and treatment results in a series of eight patients with a diagnosis of intralabyrinthine schwannoma, and to review the presentation of other cases of intralabyrinthine schwannoma in the English otolaryngologic literature. METHODS: Retrospective review of patient records, operative reports, and radiologic studies, and review of the literature. RESULTS: Eight patients with a variety of otologic symptoms including progressive hearing loss, episodic vertigo, and tinnitus were found to have a schwannoma involving the vestibule or cochlea. Surgery was performed to remove the tumors from four patients with nonserviceable hearing. The patients experienced significant improvement in their vertigo and tinnitus after surgery. Observation and serial magnetic resonance imaging were adequate treatment of the four patients with serviceable hearing. In the literature review, 447 cases of intralabyrinthine schwannoma were identified, and the presentations were similar to those in the cases described here. CONCLUSION: Intralabyrinthine schwannomas are rare tumors that arise from the distal portion of either the vestibular nerve or the cochlear nerve. Consequently, the cochlea, the semicircular canals, the vestibule, or a combination of these structures may become involved with these lesions. Transmastoid labyrinthectomy or a transotic approach can be used to remove intralabyrinthine tumors from patients with nonserviceable hearing and severe vertigo or tinnitus. In addition, these surgical approaches should be used if the tumor grows to involve the internal auditory canal. Observation is an appropriate option for patients who have serviceable hearing.

Adult↗

PubMed1996

Evidence for reactive astrocytes in rat vestibular and cochlear nuclei following unilateral inner ear lesion.

We investigated whether unilateral removal of the labyrinthine and cochlear receptors induces a macroglial reaction in rat vestibular and cochlear nuclei using vimentin and glial fibrillary acidic protein (GFAP) immunochemical markers. Antibody binding was visualized using the avidin-biotin method and 3,3'-diaminobenzidine as the peroxidase substrate. In addition, double-labelling experiments were performed using specific secondary fluorescent antibodies. Potentially degenerating axon terminals were also studied using a silver impregnation method. In normal adult rats, vimentin was found only in ependymal cells, tanicytes around the fourth ventricle, endothelial cells in the blood vessels and Bergmann glia in the molecular layer of the cerebellum. In lesioned rats, all deafferented vestibular and ventral cochlear nuclei showed strong vimentin immunoreactivity. Furthermore, double-labelling experiments demonstrated that these vimentin-positive cells were also GFAP-positive. The reaction became evident on the second day after the lesion, was intense for 3-8 days and then declined until day 21. No vimentin immunoreactivity could be detected at the level of the ipsilateral dorsal cochlear nucleus. Therefore, unilateral inner ear lesion induced an astroglial reaction within the deafferented vestibular and cochlear nuclei. The decrease in the resting discharge of the primary vestibular afferents and/or in the deafferented central vestibular neurons may induce the glial reaction in the vestibular complex, whereas both degeneration and silence of the cochlear nerve and central cochlear neurons are most probably responsible for the cochlear vimentin-immunoreactive staining. The role of the reactive astrocytes in the vestibular compensation process remains to be determined.

Animals↗

PubMedDate not supplied

[Vestibular nerves and nuclei throughout history].

Throughout the evolution of the concepts concerning the peripheral nerves, different ideas have dominated at different moments in history. The studies and demonstrations conducted in an attempt to further our knowledge of our own constitution and working at the same time enabled us to gain a better understanding of the make-up and specific functioning of the vestibular nerves, together with their central connecting elements in the brainstem: the vestibular nuclei. It may be that the first references to vestibular nerves are now lost in time, yet the Ancient Greeks already attempted to understand their functional nature by carrying out studies essentially focused on neuroanatomical aspects, but heavily influenced by philosophical concepts. It was not until the 18th century that researchers came to understand that there were differences between the vestibular nerve and the cochlear nerve --until then they were believed to be one single nerve. Another century went by before attempts were made to clarify the role it plays in balance and not in hearing. The differences between the distinct vestibular nuclei situated between the medulla oblongata and the pons were established in the 19th and 20th centuries when a number of authors, backed by previous microscopic studies, contributed to clarifying the fuzzy limits of cells separating the four classic nuclear groups and four others taken as being accessory.

History, Ancient↗

PubMed1994

[Study on the bilaterally recorded ABR in the experimental model of acoustic tumor].

The ABRs were bilaterally recorded with monaural stimulation from the animal model of acoustic tumor in 10 rats. It was found that the waveform of ABRs recorded from the right dura was different from the left one. A major feature of right ABRs was that the amplitudes of wave II and wave III were decreased by 3.53 +/- 1.21 microV and 3.94 +/- 1.16 microV respectively, and that the latencies of wave IV and wave V were increased by 0.88 +/- 0.11ms and 1.37 +/- 0.10ms respectively. It suggested that the cochlear nerve near the cochlear nucleus was pressured. A major feature of left ABRs was that the amplitudes of wave III were prominently reduced by 7.02 +/- 0.73 microV and wave IV and V were mixed together. The results implied that the waves generated after wave III might be affected by the bilateral auditory pathway.

Acoustic Stimulation↗