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At least 217 records · Page 12Linked to original sources
PubMed1993

[Cochlear nerve conduction block restoration of hearing after removal of cerebellopontine tumors].

Hearing restoration after removal of cerebellopontine tumors has only infrequently been observed. We present 5 cases with dramatic improvement of both pure tone threshold and speech threshold after excision of tumors. Two patients had acoustic neuroma, 2 meningioma and one cerebellar hemangioblastoma. Preoperatively, the patients suffered severe sensorineural hearing loss and had no measurable speech discrimination score. Recordings of the auditory brain stem response were absent or showed only wave I. However, results of the electrocochleogram were within normal limits. After removal of the tumors, their hearing returned to normal and remained stable thereafter. The data are consistent with the hypothesis that pressure from the tumor causes cochlear nerve conduction block and hearing impairment.

Adult↗
PubMed1997

Involvement of glibenclamide-sensitive potassium channels in vasorelaxation by cochlear nerve stimulation.

Rabbit aortic rings relaxed with an increase in cyclic guanosine monophosphate and cyclic adenosine monophosphate content in response to exposure to organ fluid of isolated cochleas of the guinea pig following field stimulation (50 Hz, 80 V, 0.2 ms). Relaxations were blocked by 30 microM N(G)-nitro-L-arginine methyl ester added to the vessel rings. This inhibitory effect was reversed by 3 mM L-arginine. Removal of the vascular endothelium also blocked the relaxation response. Glibenclamide attenuated vasorelaxation in a concentration-dependent manner. We conclude that cochlear nerve stimulation induces an endothelium-dependent vasorelaxation involving activation of adenosine triphosphate-sensitive potassium channels.

Animals↗
PubMed2003

A nonlinear filter-bank model of the guinea-pig cochlear nerve: rate responses.

The aim of this study is to produce a functional model of the auditory nerve (AN) response of the guinea-pig that reproduces a wide range of important responses to auditory stimulation. The model is intended for use as an input to larger scale models of auditory processing in the brain-stem. A dual-resonance nonlinear filter architecture is used to reproduce the mechanical tuning of the cochlea. Transduction to the activity on the AN is accomplished with a recently proposed model of the inner-hair-cell. Together, these models have been shown to be able to reproduce the response of high-, medium-, and low-spontaneous rate fibers from the guinea-pig AN at high best frequencies (BFs). In this study we generate parameters that allow us to fit the AN model to data from a wide range of BFs. By varying the characteristics of the mechanical filtering as a function of the BF it was possible to reproduce the BF dependence of frequency-threshold tuning curves, AN rate-intensity functions at and away from BF, compression of the basilar membrane at BF as inferred from AN responses, and AN iso-intensity functions. The model is a convenient computational tool for the simulation of the range of nonlinear tuning and rate-responses found across the length of the guinea-pig cochlear nerve.

Animals↗
PubMed1997

Calretinin expression in the chick brainstem auditory nuclei develops and is maintained independently of cochlear nerve input.

The expression of the calcium-binding protein calretinin (CR) in the chick brainstem auditory nuclei angularis (NA), laminaris (NL), and magnocelularis (NM) was studied during normal development and after deafening by surgical removal of the otocyst (embryonic precursor of the inner ear) or columella (middle ear ossicle). CR mRNA was localized by in situ hybridization by using a radiolabeled oligonucleotide chick CR probe. CR immunoreactivity (CR-IR) was localized on adjacent tissue sections. CR mRNA signal in the auditory nuclei was expressed at comparable levels at embryonic day (E)9 and E11 and increased thereafter to reach the highest levels in posthatch chicks. CR-IR neurons were apparent in NM and NA at E11 and in NL by E13, and CR-IR increased in all three auditory nuclei thereafter. Neither unilateral nor bilateral otocyst removal caused detectable changes in the intensity of CR mRNA expression or CR-IR in the auditory nuclei at any of the several ages examined. Similarly, columella removal at posthatching day 2 or 3 failed to significantly affect CR mRNA or CR-IR levels at 3 hours, 1 day, or 3-4 days survival times. We conclude that cochlear nerve input is not necessary for expression of either calretinin mRNA or protein and that the profound decrease in sound-evoked activity caused by columella removal does not affect the maintenance of CR expression after hatching.

Acoustic Stimulation↗
PubMed1994

Vestibular Neurectomy and Microvascular Decompression of the Cochlear Nerve in Meniere's Disease.

Vestibular neurectomy (VN) results in a high success rate in the control of vertigo in Meniere's disease, although the subsequent fate of auditory function is fairly unpredictable. The present investigation reports the postoperative results obtained in a group of 30 subjects with a clinical diagnosis of Meniere's disease and vascular cross-compression of cranial nerve VIII. All subjects underwent VN using a retrosigmoid approach, and in half of them microvascular decompression (MVD) of the cochlear nerve with interposition of autogenous muscle was performed at the same time. All patients had complete relief from vertigo. Hearing was significantly improved in the VN-MVD group (46.7% of subjects). In this group tinnitus and aural fullness also improved significantly, with values of 62.6% and 66.6%, respectively.

Journal Article↗
PubMed1991

Effects of L-glutamine, glutaminase and glutamine synthetase on CAP threshold of cochlear nerve of guinea pig.

Negative direct current (-DC 300 microA) stimulation was applied to the round window of the guinea pig cochlea to exhaust the pre-synaptic intracellular reserves of the transmitter in hair cells, and then the scala tympani was perfused respectively with L-glutamine, glutamine synthetase and glutaminase. Experimental results showed that the negative DC electrical stimulation applied to the round window elevated the CAP threshold of the cochlear nerve in the basal turn of the cochlea, which recovered over a period of approximately 17-39 min. The perfusion of L-glutamine apparently elevated the CAP threshold. The recovery of the CAP threshold following electrical stimulation, however, was accelerated by the perfusion of 10 mmol/L L-glutamine. The time for recovery only took about 5-6 min. The perfusion of enzyme glutamine synthetase elevated the CAP threshold by 50 dB, while glutaminase had little effect. These results suggest that the effect of L-glutamine on the CAP threshold in the cochlea of the guinea pig appears to be that of a potent depolarizing agent which accelerates the recovery of the CAP threshold during the depletion of the transmitter, and L-glutamine may be the candidate for the afferent excitatory transmitter.

Animals↗
PubMed2001

In vivo visualization of the cochlear nerve and nuclei with fluorescent axonal tracers.

In recent years multichannel neuroprostheses have been developed which directly stimulate the central auditory pathway. Substantially these have been used in cases of total hearing loss caused by neurofibromatosis type 2 where bilateral damage to the auditory nerve prevents more peripheral stimulation. The electrode carrier of the auditory brainstem implant (ABI) is designed to be placed on the cochlear nucleus complex residing at the lateral brainstem surface. Despite altered anatomy due to tumor growth or preceding surgery, correct electrode placement is essential to maximize the variety of pitch percept elicited during electrical stimulation with the ABI without producing side-effects. In order to assist intraoperative identification of the proximal auditory nerve and cochlear nuclei, the non-toxic fluorescent axonal tracers Fast Blue or Fluorogold were injected into the cochlea of rats and Java monkeys. Four to seven days after tracer application, labeling of the eighth cranial nerve, its entrance into the brainstem and the primary radiation of auditory fibers into the cochlear nucleus could be demonstrated as colored fluorescence on the living brain under appropriate ultraviolet illumination. Additional histological processing revealed groups of retrogradely labeled neuronal cell bodies in both species. Our results suggest that this method could also be used in humans in order to aid surgeons with the proper positioning of the electrode array.

Amidines↗