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At least 793 records · Page 44Linked to original sources
PubMed1990

Cochlear nucleus anatomy related to central electroauditory prosthesis implantation.

The central electroauditory prosthesis is now used to stimulate the cochlear nuclei to obtain auditory perception in patients with bilateral cochlear nerve transection who are undergoing bilateral acoustic tumor removal. In this study, we used fixed cadaver specimens to identify visible landmarks for accurate placement of the central electroauditory prosthesis through a combined suboccipital-translabyrinthine opening. Histologic features of the regions of probable implantation of the central electroauditory prosthesis were also investigated. We found that the following landmarks might have surgical significance: (1) the tenia of the inferior velum of the fourth ventricle, which crosses the surface of the ventral cochlear nucleus and the vestibulocochlear nerve; (2) the angle between the vestibulocochlear and glossopharyngeal nerves; and (3) the foramen of Luschka. It is suggested that an incision be made in the tenia for insertion of the prosthesis into the lateral recess and eventual placement on the ventral cochlear nucleus surface. To study regions of potential stimulation, we injected ink into different sites on the exposed surface of the cochlear nuclei. We then histologically examined neuronal populations adjacent to the sites. We found that a portion of the ventral cochlear nucleus localized within the lateral recess might be the most appropriate location for placement of the central electroauditory prosthesis.

Cochlea↗
PubMedDate not supplied

Apoptosis in auditory brainstem neurons after a severe noise trauma of the organ of Corti: intracochlear GDNF treatment reduces the number of apoptotic cells.

We have studied the morphological and cellular changes in the cochlear nucleus (CN) after cochlear nerve degeneration and whether these changes can be prevented by rescuing the primary cochlear neurons from degeneration with local glial cell line derived neurotrophic factor (GDNF) treatment. Degeneration of spiral ganglion neurons was seen to lead to a reduction of the volume of the anteroventral cochlear nucleus (AVCN); the size of the cell nuclei in the AVCN also was reduced. No differences were observed in cell density. After intrascalar GDNF treatment the volume of the AVCN was significantly larger when compared to the untreated side, and the size of the cell nuclei in the AVCN was significantly larger on the treated side. After degeneration of spiral ganglion neurons, an increased number of apoptotic cell nuclei were seen in ipsilateral CN and superior olivary complex. This increase was significantly smaller after intrascalar GDNF treatment. Degeneration of primary cochlear neurons seems to lead to an increase in the number of CN neurons undergoing apoptotic cell death. This can be prevented partially by rescuing primary cochlear neurons from degeneration with local GDNF treatment.

Animals↗
PubMed1998

[The effect of white noise on activity of nitric oxide synthase in cochlear nuclei of guinea pigs].

This experiment adopted lipoic amido dehydrogenase (NADPH-d) histochemistry method and image pattern analysis technique to investigate the relationship between nitric oxide synthase (NOS) neurons and activity of NOS and auditory threshold, and to explore the possible role of NOS neurone in cochlear nuclei of guinea pigs after exposed to white noise. The results showed that the quantity and staining intensity of positive NOS neurons in cochlear nuclei increased obviously after exposed to noise. It reached the peak 2 weeks later and remained high expression during 3-4 weeks. It restored 5 weeks later but was still higher than normal. Within 7 days after exposed to noise, activity of NOS in cochlear nuclei deviated from ABR threshold. After 7 days, activity of NOS had a positive correlation with ABR threshold (r = 0.9571, P < 0.01). It is suggested that NOS in cochlear nuclei might play double role after exposed to white noise. On one hand, a certain range of activity of NOS might help to restore injured neurons. On the other hand, over expression of NOS might exacerbate the injury of cochlear nerves.

Animals↗
PubMed1988

Masked cochlear whole-nerve response intensity functions altered by electrical stimulation of the crossed olivocochlear bundle.

Cochlear whole-nerve response (CAP) intensity functions were recorded from the guinea pig round window. The intensity functions were obtained in the presence of masking noise, with electrical stimulation of the crossed olivocochlear bundle (COCB), and the combination of masking noise and COCB stimulation. Electrical stimulation of the COCB produced the expected reduction of CAP magnitude for low- to moderate-intensity tone bursts. Masking noise produced reductions in CAP magnitude over the whole signal intensity range used in this study. The combination of electrical stimulation of the COCB with the masking noise produced CAP magnitude changes graded between reduction and enhancement dependent on signal and masker levels. In general, at low signal levels, the masked CAP magnitude is reduced compared to the masked alone condition. At high signal levels, the masked CAP is increased in magnitude. These results confirm and extend the earlier observations of Nieder and Nieder [Exp. Neurol. 28, 174-188 (1970); also, Nature 227, 184-185 (1970)].

Animals↗
PubMed1975

Degenerative alterations in the ventral cochlear nucleus of the guinea pig after impulse noise exposure. A preliminary light and electron microscopic study.

Guinea pigs were exposed to the noise of 40 shots of an alarm pistol held at a distance of about 60 cm. The ventral cochlear nuclei were studied in phase contrast and electron microscopy after both survival periods and longer periods of up to 55 days survival. Marked degeneration of primary cochlear nerve endings and of synapting secondary neurons of the posterior caudal part of the ventral cochlear nucleus (AVCN) and the octupus cell area (OCA) of the posterior ventral cochlear nucleus (PVCN) was found most distinctly after 5-55 days. As criteria of degeneration of the second neuron of the afferent auditory pathway we used: 1. The loss of the synapting nerve endings, mainly 'shrinking". 2. The formation of huge mitochondria in the second order neurons and their dendrites. 3. The phagocytosis by glial cells of nerve endings, of the second order neurons and of their dendrites. After 5 days survival time no distinct changes were found in the granular cell area of PVCN, where as all stages of degeneration could be found in OCA at this time. In the discussion of these findings it is concluded that additional studies of the morphology of the cochlear nuclei seem necessary, as these may lead to a better understanding of the pathology of hearing following heavy noise exposure.

Animals↗
PubMed2000

Vestibular function in auditory neuropathy.

Auditory neuropathy is characterized by mild-to-moderate pure-tone hearing loss, poor speech discrimination out of proportion with this loss, absent or abnormal auditory brainstem responses and normal outer hair cell function as measured by otoacoustic emissions and cochlear microphonics. We followed three patients in our clinic whom we classified as auditory neuropathy patients. These patients also complained of balance disorders and we report our auditory and vestibular system analyses of these patients. The data presented herein include results of audiometric tests (serial pure-tone audiometry and speech discrimination tests), otoacoustic emissions, auditory-evoked brainstem responses and vestibular function tests (clinical tests of balance, electronystagmography, damped rotation tests and vestibular-evoked myogenic potentials). In all patients, pure-tone audiometry revealed mild-to-moderate sensorineural hearing loss, markedly poor speech discrimination scores and absent auditory-evoked brainstem responses, all in the presence of normal otoacoustic emissions. Balance tests (caloric tests and damped rotation test) were abnormal. Saccades, smooth pursuit eye movements and optokinetic nystagmus were normal in all patients. Neurological and motor system evaluations were normal in all patients. These three auditory neuropathy patients manifest a disorder of cochlear nerve function in the presence of normal outer hair cell activity. They additionally manifest a disorder of the vestibular nerve and its end organs. We conclude that, in patients with isolated auditory neuropathy, the vestibular branch of the VIIIth cranial nerve and its innervated structures may also be affected. We suggest the use of the term "cochlear neuropathy" to characterize those patients with involvement of only the auditory branch of the VIIIth cranial nerve and its innervation.

Aged↗
PubMed1989

The small acoustic tumour; a chance to preserve hearing.

The authors report their experience in the surgical management of small (less than 1.5 cm diameter) acoustic neuromas. Twenty-nine patients were treated. They had suffered symptoms of unilateral eighth nerve dysfunction on average for 37 months. High resolution CT with iv contrast was the primary investigation. In equivocal cases, air meatography was performed. All operations were performed by the senior author (LS). All tumours were totally removed, there were no deaths and all patients had an excellent result. There were 6 complications (CSF leak 3; meningitis 2; deep venous thrombosis 1). The facial nerve was preserved in 26 cases (and functioned adequately in all) and the cochlear nerve in 62%. In 4 cases with hearing pre-operatively, the decibel loss was the same or less post operatively. In 8 cases speech discrimination remained above 35%.

Adolescent↗
PubMed1999

Neurovascular compression syndrome of the eighth cranial nerve. Can the site of compression explain the symptoms?

Considerable skepticism still exists concerning the concept of neurovascular compression (NVC) syndromes of the eighth cranial nerve (8th N). If such syndromes exist, the sites of compression of the nerve must explain the symptoms encountered. We recorded compound action potentials of the cochlear nerve (CCAPs) during neurovascular decompression (NVD) to examine the topography of the three components of the 8th N. The sites of compression of the 8th N in cases of NVC syndrome confirmed at surgery were superimposed on the topography of the CN and vestibular nerve (VN) in order to determine the relationship between the sites of compression and the symptoms. CCAPs were clearly and consistently recorded on the caudal surface of the 8th N along the midline. In patients with vertigo and tinnitus there was vascular compression of the rostroventral (VN) and caudal surface (CN) of the nerve, respectively. In patients with both vertigo and tinnitus, there was compression of both VN and CN. Our findings clearly demonstrate that the symptoms of NVC of the 8th N depend on the part of the nerve that is compressed by blood vessels, and they support the concept of NVC syndrome of the 8th N.

Action Potentials↗
PubMed2004

Auditory brainstem implant as a salvage treatment after unsuccessful cochlear implantation.

OBJECTIVE: The present article investigates on an individual basis the performance achieved with the auditory brainstem implant in patients who had been treated unsuccessfully with a cochlear implant. STUDY DESIGN: An intrasubject comparison between results achieved with the cochlear implant and the auditory brainstem implant is reported. SETTING: Tertiary referral care. PATIENTS: Five subjects were fitted with an auditory brainstem implant in our department because of the poor results achieved with cochlear implants. Two were children, one with bilateral cochlear nerve aplasia and one suffering from auditory neuropathy. Three were adults with complete cochlear ossification. INTERVENTION: A retrosigmoid approach was used in all subjects. Electrically evoked auditory brainstem responses and neural response telemetry were used to monitor electrode positioning. RESULTS: No complications were observed due to implantation surgery or related to activation or long-term use of the auditory brainstem implant. Auditory sensations were induced in all patients with varying numbers of electrodes (from 9-16). In all three adults, the cochlear implant did not allow either word/sentence discrimination or speech tracking, whereas the auditory brainstem implant permitted discrimination of two- or three-syllable words with scores from 85 to 100%. In the two adults with a follow-up of 5 and 6 months after auditory brainstem implant activation, the open-set sentence recognition scores (auditory-only mode) were 70% and 100%, respectively, and the speech-tracking scores were 27 and 40 words/min, respectively. One patient with a follow-up of only 3 months scored 0% in both sentence recognition and speech tracking. The two children who had achieved no hearing ability with the cochlear implant were already able to detect sounds and words as early as 2 months after activation of the auditory brainstem implant and are showing progressive improvement in their performance. CONCLUSION: Auditory brainstem implantation may be a very powerful rehabilitative treatment after cochlear implant failure. The possibility of using the auditory brainstem implant as first-choice therapy in some categories of deaf patients (e.g., subjects with auditory neuropathy or cochlear ossification) who are currently treated with cochlear implantation is discussed.

Adult↗
PubMed1988

Afferent influences on brain stem auditory nuclei of the chicken: presynaptic action potentials regulate protein synthesis in nucleus magnocellularis neurons.

Studies of the avian auditory system indicate that neurons in nucleus magnocellularis (NM) and nucleus laminaris of young animals are dramatically altered by changes in the auditory receptor. We examined the role of presynaptic activity on these transneuronal regulatory events. TTX was used to block action potentials in the auditory nerve. TTX injections into the perilymph reliably blocked all neuronal activity in the cochlear nerve and NM. Far-field recordings of sound-evoked potentials revealed that responses returned within 6-12 hr after a single TTX injection. Changes in protein synthesis by NM neurons were measured by determining the incorporation of 3H-leucine using autoradiography. NM neurons on the side of the brain ipsilateral to the TTX injection were compared to normally active cells on the other side of the same tissue section. Grain counts over individual neurons revealed that a single injection of TTX produced a 40% decrease in grain density in ipsilateral NM neurons within 1.5 hr after the TTX injection. However, by 24 hr after a single TTX injection, grain densities were not different on the 2 sides of the brain. Continuous activity blockade for 6 hr caused the cessation of amino acid incorporation in a portion of NM neurons and a 15-20% decrease in the remaining neurons. These changes in amino acid incorporation are comparable to those following complete removal of the cochlea (Steward and Rubel, 1985). We also examined NM for neuron loss and soma shrinkage after blocking eighth nerve action potentials. TTX injected every 12 hr for 48 hr caused a 20% neuron loss and an 8% shrinkage of the remaining neurons. Similar reductions were found following cochlea removal (Born and Rubel, 1985). It is concluded that neuronal activity plays a major role in the maintenance of normal NM neurons. Furthermore, these results suggest that transneuronal morphological changes seen in neurons following deafferentation or alterations of sensory experience are a result of changes in the level of presynaptic activity.

Action Potentials↗
PubMedDate not supplied

[Mechanism of the effect of neuronal response suppression in the auditory nerve during exposure to bitonal stimuli].

It is supposed that interreceptor currents existing due to microphonic and summating potentials are the exiting factors for the neuron endings of the cochlear nerve. A model is proposed of the formation of the cochlear neuron responses under the stimulation of the hearing system by a tone signal with a changing frequency and by a signal consisting of two tones. It is shown that the proposed model explains the effect of inhibition of the neuron response to a given tone signal when another tone signal of proper intensity arises in a definite frequency region.

Hearing↗
PubMed2000

[Cochlear implants].

A cochlear implant is a technologically advanced medical device that simulates sound in the cochlea by electrically stimulating the hearing nerve. Cochlear implants are designed to help severely or totally deaf individuals who gain little or no benefit from hearing aids. Hearing aids and assistive listening devices amplify sounds. The sounds produced by even the most sophisticated hearing aids may not offer much benefit to people with a severe-to-profound or profound hearing loss in both ears. A cochlear implant is an electronic device that provides the function of the damaged or absent hair cells by providing electrical stimulation to the remaining nerve fibers. The implant provides useful hearing and improved communication abilities to the implant user.

Adult↗
PubMed2003

Thapsigargin suppresses cochlear potentials and DPOAEs and is toxic to hair cells.

Thapsigargin, a drug that inhibits sarco-endoplasmic reticulum Ca(2+) ATPases (SERCAs), was infused into the perilymph compartment of the guinea pig cochlea in increasing concentrations (0.1-10 microM) while sound evoked cochlear potentials were monitored. Thapsigargin significantly suppressed the compound action potential of the auditory nerve, cochlear microphonics, and increased N(1) latency at low (56 dB SPL) and high intensity (92 dB SPL) levels of sound, suppressed low intensity sound evoked summating potential (SP) and greatly increased the magnitude of the high intensity sound evoked SP. At 10 microM, the drug suppressed the cubic distortion product otoacoustic emissions (2f(1)-f(2)=8 kHz, f(2)=12 kHz) evoked by both high and low intensity primaries (45, 60, 70 dB SPL). Thapsigargin (10 microM; 30 min) increased the endocochlear potential slightly (5 mV). In chronic animals, thapsigargin (10 microM; 60 min) destroyed many outer hair cells and some inner hair cells, especially in the basal turns. These effects are consistent with the hypothesis that the inhibition of the SERCAs affects the function of the cochlear amplifier and outer hair cells to a greater degree than it affects other functions of the cochlea.

Acoustic Stimulation↗
PubMed2005

Engraftment of embryonic stem cell-derived neurons into the cochlear modiolus.

This study aimed to evaluate the potential of embryonic stem cell-derived neural progenitors for use as transplants for the replacement of the auditory primary neurons, spiral ganglion neurons. Mouse embryonic stem cell-derived neural progenitors were implanted into the base of the cochlear modiolus of normal or deafened guinea pigs, which contains spiral ganglion neurons and cochlear nerve fibers. Histological analysis demonstrated the survival and neural differentiation of transplants in the cochlear modiolus and active neurite outgrowth of transplants toward host peripheral or central auditory systems. Functional assessments indicated the potential of transplanted embryonic stem cell-derived neural progenitors to elicit the functional recovery of damaged cochleae. These findings support the hypothesis that transplantation of embryonic stem cell-derived neural progenitors can contribute to the functional restoration of spiral ganglion neurons.

Animals↗
PubMed2006

Cavernous angiomas within the internal auditory canal.

OBJECT: The aim of this study was to describe the symptomatology, radiological features, and surgical treatment of patients with cavernous angiomas within the internal auditory canal (IAC). METHODS: The authors reviewed the cases of seven patients with cavernous angiomas in the IAC that had been surgically treated in the 22-year period between 1983 and 2005. All the patients had presented with sensorineural hearing loss, and four suffered from tinnitus. Four patients also reported facial symptoms such as hemispasm or progressive palsy; one of these patients had presented with sudden facial paresis due to intrameatal tumor hemorrhage. According to computed tomography (CT) results, the lesions caused enlargement of the IAC. Interestingly, these same angiomas showed variable features on magnetic resonance (MR) imaging, making their differentiation from intrameatal vestibular schwannomas (VSs) sometimes impossible. In all patients the lesions were totally removed via the suboccipital retrosigmoid approach. They could be dissected away from the facial nerve in five cases, whereas in two cases, because of the location of the lesion, the seventh cranial nerve had to be sectioned and repaired with a sural nerve graft. Transient worsening of seventh cranial nerve symptoms occurred in two patients, with postoperative improvement in each of them. The cochlear nerve could not be functionally preserved because of its extreme adherence to the tumor, although its continuity was preserved in four patients. Complete deafness was the only postoperative complication. CONCLUSIONS: Cavernous angiomas of the IAC are very uncommon lesions that can imitate the symptoms of VSs. Although it is the most sensitive study available, MR imaging does not show sufficiently specific findings to differentiate the two lesion types. Thus, the preoperative diagnosis must be based on patient symptoms plus the CT and MR imaging features.

Adult↗
PubMed1975

[Functional survival of the human Corti organ after dissection of the eight nerve (author's transl)].

The behaviour of the functional unit haircell - peripheral neurit before and after the dissection of the cochlear nerve in two cases of cerebello-pontine angle tumors is described. An immediate alteration does not seem to be found when the blood supply via internal acoustic meatus is not severed. The survival time after the dissection of the acoustic nerve is somewhat more than seven weeks. This is longer than related morphological findings indicate in the cat where the morphological survival time of fibre population I (95% of all fibres) is not more than four weeks. On the other hand, morphological survival time of fibre population II (5% of all fibres) in cat is up to 14 months. The functional survival time in man under pure tumor pressure is longer than 10 years. Discrepancies between morphological and functional findings may indicate that morphological and functional behaviour do not necessarily coincide.

Adult↗
PubMed1987

Kynurenic acid and gamma-D-glutamylaminomethylsulfonic acid suppress the compound action potential of the auditory nerve.

Kynurenic acid and gamma-D-glutamylaminomethylsulfonic acid, two excitatory amino acid antagonists, were perfused through the guinea pig cochlea while monitoring various cochlear potentials. Both drugs (0.6-10 mM) reduced the magnitude of the compound action potential (CAP) of the cochlear nerve without much effect on other potentials. The results are consistent with the hypothesis that the hair cell transmitter is an excitatory amino acid, possibly L-glutamate.

Action Potentials↗