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At least 109 records · Page 6Linked to original sources
PubMed2003

Hyperthermia exacerbates and hypothermia protects from noise-induced threshold elevation of the cochlear nerve envelope response in the C57BL/6J mouse.

The scalp-recorded cochlear nerve envelope response (CNER) reflects the ability of high frequency cochlear nerve axons to fire in a phase-locked fashion to low frequency modulations of the acoustic envelope of high frequency stimuli. This property might be useful in evaluating the adverse effects of noise exposure on the ability of the ear to detect acoustic changes characteristic of vocalizations and speech. Hyperthermia (40 degrees C rectal) per se had no observable influence on the CNER in C57BL/6 mice. Hypothermia (30 degrees C) elevated CNER thresholds elicited by high frequency stimuli, although these stimuli still generated an auditory brainstem response. Mice exposed to noise when hyperthermic had greater threshold elevations than those exposed when euthermic (36 degrees C); those exposed when hypothermic had smaller threshold elevations than those exposed when euthermic. These observations were discussed in terms of the interaction of temperature and noise on oxidative processes within the cochlea.

Animals↗
PubMed1980

Relationship between the dynamic range of cochlear nerve fibres and their spontaneous activity.

The dynamic ranges of cochlear nerve fibres in cats were determined automatically and were related to the fibres' rates of spontaneous activity, in both pooled data and data from individual cochlear nerves. The dynamic range represents the range of levels of a tone at the characteristic frequency of the fibre evoking mean discharge rates between spontaneous and saturated activity. In common with the findings of other investigators, the distribution of spontaneous discharge rates was bimodal. The total population could be divided into two sub-populations with spontaneous discharge rates above and below 15 spikes/s, respectively. The mean dynamic range of fibres having spontaneous discharge rates in excess of 15 spikes/s, was 41 dB (+/- 0.65 S.E.); that for fibres with rates below 15 spikes/s was 50 dB (+/- 1.2 S.E.). While the distributions of dynamic ranges of the two populations overlapped, they were significantly different, and dynamic ranges in excess of 60 dB were only found in substantial numbers (23%) in the population having low spontaneous discharge rates. Some of these were not saturated at the highest stimulus levels used.

Animals↗
PubMed1999

Profound hearing loss attributable to cochlear nerve disease: diagnosis with combination of otoacoustic emission and magnetic resonance imaging.

OBJECTIVE: To detect the causes of deafness based on the combined findings of auditory brainstem response (ABR), distortion product otoacoustic emissions (DPOAEs), and three-dimensional Fourier transformation-constructive interference in steady state (3DFT-CISS) magnetic resonance imaging (MRI). STUDY DESIGN: Retrospective review of the medical records of 13 patients with unilateral profound hearing loss since childhood. METHODS: Subjects were tested with pure-tone audiometry, ABR, DPOAEs, and 3DFT-CISS imaging. RESULTS: No significant components of ABR were observable in any of the deaf ears. In 10 cases, the cochlear nerves of the deaf ears were found to be as normal as the healthy sides by 3DFT-CISS imaging, and no significant levels of DPOAEs were recorded. In the other three cases, no apparent cochlear nerves were identified by 3DFT-CISS imaging. Although no significant levels of DPOAEs were observable in two cases with cochlear nerves invisible by the MRI study, almost the same level of DPOAEs as that in the healthy side was recorded in the last case. CONCLUSIONS: In the last particular case, the cochlear nerve seemed to be mainly responsible for the profound deafness. 3DFT-CISS imaging in combination with preexisting audiological measures may provide direct evidence for the cochlear nerve disease. steady state, internal auditory canal, cochlear nerve disease.

Audiometry, Pure-Tone↗
PubMed2003

Effect of topically applied basic fibroblast growth factor on injured cochlear nerve.

OBJECTIVE: Trauma-induced hearing loss after cerebellopontine angle manipulation has been regarded as having a hopeless natural course once it occurs. To challenge such a pessimistic view, we investigated whether pharmacological interventions with basic fibroblast growth factor (bFGF) could ameliorate trauma-induced cochlear nerve degeneration. METHODS: The cerebellopontine angle portion of the cochlear nerve of rats was quantitatively compressed, and bFGF was topically administered for 2 weeks with a bFGF-soaked absorbable sponge and an osmotic minipump. The animals were killed 2 weeks after the compression procedure. The effect of bFGF in ameliorating cochlear neuronal death was evaluated from the residual number of spiral ganglion cells. RESULTS: Cerebellopontine angle cisternal application of bFGF ameliorated cochlear nerve degeneration after the compression. Immunocytochemical studies of FGF receptors indicated that topically administered bFGF was internalized by a receptor-mediated mechanism through FGF receptor-1 and/or FGF receptor-2. CONCLUSION: This report demonstrated that therapeutic application of bFGF was feasible to ameliorate trauma-induced cochlear nerve degeneration. Recent technological advances for deafened ears, such as cochlear implants and auditory brainstem implants, in combination with neurotrophic and/or growth factor therapeutic intervention, would be of great potential benefit for patients with hearing loss.

Animals↗
PubMed1991

Auditory nerve of the normal and jaundiced rat. I. Spontaneous discharge rate and cochlear nerve histology.

Hyperbilirubinemia is a major problem in neonatal intensive care. Hearing impairment is one of its sequelae. Although lesions of the central auditory pathways are known to be associated with this disorder in both humans and homozygous Gunn rats, the presence of cochler pathology is still controversial. The purpose of this study was to examine the functional integrity of the peripheral auditory system in the Gunn rat. The Gunn rat is a mutant of the Wistar strain with congenital deficiency of the liver enzyme uridine diphosphoglucuronyl transferase which is essential for bilirubin conjugation. This deficiency is inherited as an autosomal recessive trait, with the homozygous animals (jj) showing evidence of bilirubin encephalopathy. The heterozygotes (Jj) have 50% enzyme deficiency and are not jaundiced. The Long-Evans rat served as a control. The approach was to study the discharge characteristics fo single auditory nerve fibers using standard procedures in a closed and calibrated sound system. Various response measurements which would reveal pathological processes in the cochlea were analyzed. In this study, spontaneous discharge rate distribution and interspike interval statistics derived from Gunn rat auditory nerve recordings were found to be within the normal range, and cochlear nerve histology showed no evidence of neuropathy.

Action Potentials↗
PubMed1986

Frequency selectivity of single cochlear-nerve fibers based on the temporal response pattern to two-tone signals.

The physiological basis of auditory frequency selectivity was investigated by recording the temporal response patterns of single cochlear-nerve fibers in the cat. The characteristic frequency and sharpness of tuning was determined for low-frequency cochlear-nerve fibers with two-tone signals whose frequency components were of equal amplitude and starting phase. The measures were compared with those obtained with sinusoidal signals. The two-tone characteristic frequency (2TCF) is defined as the arithmetic-center frequency at which the fiber is synchronized to both signal frequencies in equal measure. The 2TCF closely corresponds to the characteristic frequency as determined by the frequency threshold curve. Moreover, the 2TCF changes relatively little (2%-12%) over a 60-dB intensity range. The 2TCF generally shifts upward with increasing intensity for cochlear-nerve fibers tuned to frequencies below 1 kHz and shifts downward as a function of intensity for units with characteristic frequencies (CF's) above 1 kHz. The shifts in the 2TCF are considerably smaller than those observed with sinusoidal signals. Filter functions were derived from the synchronization pattern to the two-tone signal by varying the frequency of one of the components over the fiber's response area while maintaining the other component at the 2TCF. The frequency selectivity of the two-tone filter function was determined by dividing the vector strength to the variable frequency signal by the vector strength to the CF tone. The filter function was measured 10 dB down from the peak (2T Q 10 dB) and compared with the Q 10 dB of the frequency threshold curve. The correlation between the two measures of frequency selectivity was 0.72. The 2T Q 10 dB does change as a function of intensity. The magnitude and direction of the change is dependent on the sharpness of tuning at low and moderate sound-pressure levels (SPL's). The selectivity of the more sharply tuned fibers (2T Q 10 dB greater than 3) diminishes at intensities above 60 dB SPL. However, the broadening of selectivity is relatively small in comparison to discharge rate-based measures of selectivity. The selectivity of the more broadly tuned units remains unchanged or improves slightly at similar intensity levels. The present data indicate that the frequency selectivity and tuning of low-frequency cochlear-nerve fibers are relatively stable over a 60-dB range of SPL's when measured in terms of their temporal discharge properties.

Animals↗
PubMed1982

[Origin of N1 wave of the cochlear nerve action potential recorded at the bony wall of the cochlea].

As an objective audiometry, the cochlear nerve action potential (AP) evoked by tone stimulation has been clinically utilized. But the origin of AP wave is still obscure. In order to know the origin of the N1 wave of AP, the author intended to compare the AP waves (AP(W)) recorded at the bony wall of the cochlea with action potentials of the individual spiral ganglion cell (spikes) and group of the spiral ganglion cells (AP(R)) in the Rosenthal canal of the guinea pig. Spikes and AP(R) were recorded by glass pipettes filled with 2M NaCl. The results showed that waves of AP(R) demonstrated a wide monophasic negative wave in contrast to diphasic AP(W) wave. The Input-Output Curves (I.O.C.) of the AP(W) and AP(R) were compared in order to ascertain whether both APs were derived from the cochlear nerve or not. The I.O.C. of latency, onset, amplitude, offset and width of both AP(R) and AP(W) N1 waves showed a same pattern with high correlation coefficient. So it was confirmed that both AP(R) and AP(W) N1 waves were the direct and indirect cochlear nerve action potential respectively. The thresholds of both AP(W) and AP(R) at the characteristic frequency of a single ganglion cell showed a high correlation. The time of onset and latency of AP(R) were longer than those of AP(W). Based on anatomy and electrophysiology, it is concluded that AP(W) N1 wave originates from the action potential generated at the habenula perforata, where spikes are first produced. The curves of the AP(R) were flat in respect of frequency-threshold relationship. The threshold was the lowest in the spiral ganglion cell followed by AP(R) and AP(W).

Acoustic Stimulation↗
PubMed1976

Tuning of single fibers in the cochlear nerve of the alligator lizard: relation to receptor morphology.

(1) The general anatomy of the peripheral portion of the cochlear nerve in the alligator lizard is described. (2) Spike discharges of single units were recorded with micropipets placed in the peripheral portion of the cochlear nerve of anesthetized lizards. (3) In response to tone bursts, each unit is maximally sensitive to a charactertistic frequency (CF). There are two distinct populations of units having different CFs: a low CF population (CF in the range 0.2-0.8 kHz) recorded in the portion of the nerve that enters the apical region of the basilar papilla and a high CF population (CF in the range 0.9-4.0 kHz) recorded in the portion of the nerve that enters the basal region. The low CF units are more sharply tuned than the high CF units. (4) Comparison of cochlear nerve units of the alligator lizard with those of mammals shows that the tuning of low CF units resembles that of mammalian units of the same CF. The tuning of high CF lizard units differs significantly from mammalian units. (5) The distinct differences in tuning of low and high CF units are correlated with distinct differences in the structure of the basilar papilla in the apical and basal regions rather than with differences in the width of the basilar membrane.

Animals↗
PubMed1978

Neural correlates of auditory fatigue: frequency-dependent changes in activity of single cochlear nerve fibers.

1. These experiments were designed to test whether intense pure tones produced greater depression of cochlear nerve fibers tuned to the exposure frequency or of those tuned to frequencies above the exposure frequency. Spike discharges of single fibers were studied in anesthetized cats before, during, and after exposures lasting 1 min. Exposure frequency was varied relative to each fiber's characteristic frequency (CF), and was either at the CF or 1/2 octave above (+1/2 oct) or 1/2 octave below (-1/2 oct) the CF. Exposure levels were 85 or 90 dB SPL. Effects of the various exposures on driven discharge rates were evaluated using standard test stimuli at each fiber's CF. In addition, nonevoked discharges were measured during the brief quiet intervals between test stimuli ("interstimulus activity") as well as during extended quiet periods ("resting activity"). Major results were as follows: 2. All the exposures resulted in depression of the driven discharge rates; however, these effects were strongly dependent on the exposure frequency. The depression was greatest and endured the longest following -1/2 oct exposures at 90 dB. The CF exposures at 85 and 90 dB were much less depressant, as were exposures at -1/2 oct at 85 dB; these three exposures resulted in very similar recovery functions. The +1/2 oct exposures produced little or no depression, whether at 85 or 90 dB. 3. Interstimulus activity was depressed immediately following all exposures, but recovered to normal quickly than did driven discharge rates. Following exposures at -1/2 oct at 90 dB, recovery was non-monotonic in that an extended period of supernormality preceded the return to normal rates. During this period of elevated activity, the interstimulus activity approached but never exceeded the resting rate of the same fiber. 4. Resting activity recovered even more rapidly than interstimulus activity, being completely normal by 1 min following all exposures. 5. These results constitute the first demonstration that the CF is not necessarily the most depressant exposure frequency for a given cochlear nerve fiber. Further, the results imply that the half-octave (or greater) shifts of the point of maximum hearing loss, so characteristic of auditory fatigue, may be accounted for by frequency-dependent alterations in the responsiveness of cochlear nerve fibers.

Acoustic Stimulation↗
PubMed1978

Temporal and spatial sequence of anterograde degeneration in the cochlear nerve fibers of the cat. A light microscopic study.

This study deals with anterograde degeneration in the cochlear nerve fibers following cochlear lesions. The observations are based on 2-mum thick sections of material embedded in resin according to procedures used in electron microscopy and stained with toluidine blue. Among the various operative approaches used in this study, sparing of the modiolus afforded the least local reaction and furnished the material best suited for anterograde degneration studies in this nerve only 2 mm long. The anterograde degeneration of the cochlear nerve is characterized by segmental swelling of myelinated nerve fibers followed by shrinkage of the axoplasm and collapse of the distended myelin sheaths. The swelling, which begins at the nodal-paranodal region of the axon, is preceded by accumulation in the cytoplasm of granular organelles, presumably mitochondria and lysosomes. The portions of the cochlear fibers situated in the nerve root, i.e., within the cochlear nuclei and including the axon terminals, follow essentially the same pattern of degeneration as those in the peripheral portion of the nerve. Both peripherally and centrally degenerative changes occur first in the basal, high frequency fibers and centrally degenerative changes occur first in the basal, high frequency fibers and progress to the apical, low frequency fibers. The difference between the two extremes in the onset of degeneration is, approximately, 24 hours. Once initiated, however, the pace of degeneration is the same along the whole fiber spectrum.

Animals↗
PubMedDate not supplied

Cochlear processes reflected in responses of the cochlear nerve.

The effects of sound frequency, intensity, and duration on responses of cochlear-nerve fibers and inner hair cells (IHCs) are reviewed and compared. The frequency selectivity observed in the nerve is already present in the IHC receptor potential but synaptic transmission appears to influence some other properties of the nerve response. First, the average rate-intensity function of a nerve fiber spans a smaller operating range than the IHC input-output characteristic. However, nerve fibers with different sensitivities can innervate the same IHC and respond over different regions of its characteristic. Second, adaptation is present in the nerve-fiber response but not observed in the IHC. It appears to result from a decrease in synaptic transmission and produces temporal contrast and a decrease in operating range. Interactions among the various effects have important influences on the spatiotemporal pattern of cochlear-nerve responses to complex stimuli.

Acoustic Stimulation↗
PubMedDate not supplied

Involvement of cochlear nerve in acoustic tumours.

With conventional light and transmission electronmicroscopy we studied 10 cases of acoustic nerve tumour, 3 of which proved to be instances of von Recklinghausen neurofibroma and 7 of schwannoma. Schwannomas were not found to infiltrate the cochlear nerve. Hearing loss, if present in cases of schwannoma, could be related to non-specific lesions of the uninfiltrated cochlear nerve in the vicinity of the vestibular nerve tumour. Only neurofibromas were found to infiltrate the cochlear nerve. Distinction between tumour infiltration and non-specific lesion could be made by electron microscopy.

Adolescent↗
PubMed1980

Mechanical and neural interactions between binaurally applied sounds in cat cochlear nerve fibers.

Most single fibers of the cochlear nerve (CN) in 22 cats exhibited effects of mechanical interaction in one cochlea between two sounds applied binaurally, similarly to results in two cats in which the contralateral CN was transected. In 11 of 189 fibers, the spontaneous and/or the sound-evoked activity was suppressed by a contralateral intense best-frequency sound; this indicates an interaural neural inhibition, probably through the olivocochlear bundle (OCB). The inhibited fiber population was small, and the intensity differences between the binaural sounds were exceptionally large, so that a simple negative feed-back function via the OCB is not likely.

Acoustic Stimulation↗
PubMed1992

Electrical promontory stimulation in patients with intact cochlear nerve and anacusis following acoustic neuroma surgery.

Anacusis following hearing preservation surgery for acoustic neuroma removal in which the cochlear nerve was preserved has been explained on the basis of neural or vascular compromise. In the absence of pathologic evidence for either theory, a physiologic model was chosen. Electrical promontory stimulation with monitoring of subjective and electrically evoked auditory brainstem responses was undertaken. A positive response to stimulation suggests a vascular impairment of the cochlea sparing the cochlear nerve and spiral ganglion. The absence of response suggests loss of neural integrity at the level of the spiral ganglion or cochlear nerve. Six patients who suffered anacusis following hearing preservation surgery for acoustic neuroma were studied. Data regarding electrical promontory stimulation, auditory brainstem responses, and implications of the possible role of cochlear implantation are discussed.

California↗
PubMed2004

Cochlear nerve demyelination causes prolongation of wave I latency in ABR of the myelin deficient (md) rat.

In this study, we examined the auditory brainstem responses (ABRs), distortion product of otoacoustic emissions (DPOAEs) and cochlear morphology of the myelin deficient (md) rat, which completely lacks central myelin but not peripheral myelin. ABRs showed a marked prolongation not only wave II-IV latencies but also wave I latency. Cochlear nerve fibers near the modiolus lost their myelin halfway into the internal auditory canal. DPOAEs also decreased at a lower frequency of the combined tone. Since nerve fibers ending at the apical turn of the cochlea passed through central portion of the cochlear nerve, wave I prolongation of ABRs and decrease of DPOAEs at a lower frequency might originate mainly from the demyelinated CNS part of the cochlear nerve and efferent olivocochlear bundle in the internal auditory canal.

Animals↗
PubMed1999

Distribution of rate-intensity function types in chick cochlear nerve after exposure to intense sound.

Intense sound exposure to the chick ear produces cochlear damage and losses in auditory function. At twelve days post exposure there is considerable structural repair, although a defect on the sensory epithelium remains in the form of an incompletely healed 'patch' lesion. Auditory function significantly recovers 12 days after the exposure, but it, too, is incomplete. In this paper we describe the relationship between stimulus intensity and cochlear nerve discharge rate (the rate-intensity function) in two groups of chicks. One is exposed to damaging sound levels but allowed 12 days to recover, while the other is a group of non-exposed and age-matched control animals. Three different types of rate-intensity functions were identified; saturating, sloping, and straight. The percentage of saturating and sloping functions was compared across all characteristic frequencies in both groups of animals. A significant change was observed in the distribution of these types for recovered units with characteristic frequencies within the region of the patch lesion. In addition, the rate-intensity functions of these units exhibited a steeper slope and a higher maximum response. The distribution of rate-intensity function types and their slope and maximum responses, for units with characteristic frequencies outside of the patch lesion, was similar to those found in control ears. The changes in the cochlear nerve response in exposed chicks may be due to alterations in cochlear mechanics, hair cell or synaptic membrane properties, hair cell innervation, or the loss of a tonic suppression of afferent activity exerted by the damaged short hair cells.

Acoustic Stimulation↗
PubMed1982

Asymptomatic schwannoma of the cochlear nerve.

During systematic study of temporal bone histopathology at The Deafness Foundation, Memphis, we found an unsuspected small schwannoma arising solely from the cochlear nerve, compressing the facial nerve within the internal auditory canal. The primary temporal bone pathologic finding was bilateral otosclerosis. Compression of the facial nerve by schwannomas of the cochlear nerve is well know to occur at a late stage and produce a lower motor neuron facial paralysis but, in the present case, although the growth of th tumor compressed the facial nerve trunk, no paralysis was noted. Hearing test of the ear associated with the tumor, performed ten months before death, revealed a mixed conductive-sensorineural deafness. Surprisingly, the speech reception threshold was 75 dB, with a speech discrimination score of 70%.

Aged↗