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At least 1,279 records · Page 71Linked to original sources
PubMed1998

Induction of endolymphatic hydrops in the guinea pig by perisaccular deposition of sepharose beads carrying and not carrying immune complexes.

We tried to induce endolymphatic hydrops in guinea pig cochleas by unilateral, perisaccular deposition of sepharose beads carrying immune complexes. Controls consisted of the deposition of sepharose beads without immune complexes and the contralateral, untreated ear. The effects of the treatment were studied by light microscopy and electrophysiological recordings of the gross cochlear potentials 1, 2, and 6 weeks after treatment. Each condition included six animals. Analysis of variance of the morphometric data concerning the ears treated with deposition of the beads showed a statistically significant difference (P = 0.04) between the degree of hydrops found for the beads with immune complexes and for those without. The difference between the treated ears and the contralateral untreated ears was significant (P = 0.01) for the beads with immune complexes and not significant (P = 0.8) for those without immune complexes while there was no significant effect of post-treatment time interval. Analysis of variance of the electrophysiological data, collected in response to tone bursts at the apex of the cochlea, showed no significant differences between the results for the beads with and without immune complexes. Therefore these results were pooled. One week after treatment the pooled results for the compound action potential showed a small decrease in amplitude, just significant at 2 kHz, but not at 4 and 8 kHz. This decrease disappeared completely after 6 weeks. The pooled results for the negative summating potential (SP) showed a significant increase in magnitude at all frequencies decreasing with post-treatment interval. The cochlear microphonics did not demonstrate any change in amplitude after treatment. The results indicate that deposition of sepharose beads with immune complexes induces endolymphatic hydrops. Also, deposition of the sepharose beads itself may have induced hydrops together with enhancement of the SP. SP enhancement may be related to the development of endolymphatic hydrops rather than to the presence of hydrops as such. This may be based on pressure build-up while hydrops develops.

Action Potentials↗
PubMed1995

Peripheral basis for the auditory deficit in Belgian Waterslager canaries (Serinus canarius).

Recently, behavioural thresholds obtained in canaries of the Belgian Waterslager strain showed that these birds have an inherited auditory deficit. Canaries of this strain have absolute auditory thresholds at frequencies above 2.0 kHz that are as much as 40 dB above the threshold of canaries of other strains. We obtained audiograms from cochlear microphonics and from compound action potentials from the 8th nerve of Waterslager and non-Waterslager canaries and compare these results to previous behavioural data on hearing in this species. We also examined the growth of evoked potential amplitude-intensity functions in Waterslager and non-Waterslager canaries. Together with reflectance measurements of middle-ear function from both Waterslager and non-Waterslager canaries, we conclude that the origin of auditory deficit in Waterslager canaries lies in the cochlea.

Acoustic Stimulation↗
PubMed1998

Experimental study on the effects of gentamicin injection on the guinea-pig: electrophysiological studies.

The inner ear distortion induced by gentamicin (GM), a type of aminoglycoside antibiotic, was examined in guinea-pigs. Previous studies which investigated the function of the eighth cranial nerve and organ of Corti using cochlear microphonics (CM) and compound action potential (CAP) reported ototoxicity following experimental exposure to GM. In this report, the effects of GM on the cochlea and the eighth cranial nerve were investigated systematically by measuring CM, CAP, summating potentials induced by 90 dB (SPL) tone burst, endocochlear potential (EP) and K+ ion concentration of the endolymph. Guinea-pigs were treated with a daily intramuscular injection of GM (60 mg in 1.5 cc) at a dose of 60 mg/kg during different treatment periods. The maximum output voltage of AP was decreased by injection of GM (60 mg/kg x 24). A decrease in the CM maximum output voltage and the elevation of CM pseudothreshold were typically seen after GM injection at a test frequency of 8 kHz and a decrease in CAP was also observed. Changes in EP during 3 min anoxia were observed, in particular a decrease in the absolute value of the negative potential. The endolymph K+ ion concentration remained unchanged. These findings indicate that the diffusion potentials decreased at the same time as reduction of maximum output voltage in CM induced by GM injection.

Action Potentials↗
PubMed2000

Characterization of the ototoxicity of difluoromethylornithine and its enantiomers.

Difluoromethylornithine (DFMO) is an irreversible inhibitor of ornithine decarboxylase (ODC), the essential enzyme in mammalian polyamine biosynthesis (Pasic et al., 1997, Arch. Otolaryngol. Head Neck Surg. 123[12], 1281-1286). This cancer chemotherapeutic agent has significant ototoxic potential. Because the DFMO enantiomers differ in their ability to block ODC, the present study was designed to compare the ototoxic potential of each enantiomer with the racemic form of this drug for the rat and guinea pig. Determining differential ototoxicity of the enantiomers is one preliminary step in determining the optimal form of DFMO to use in human cancer chemotherapy. Daily intubation with D,L-DFMO does not produce any auditory dysfunction in rats with doses between 200 mg/kg/day and 1. 2 g/kg/day for up to 8 weeks, despite the fact that doses of 800 and 1200 mg/kg/day depressed body weight gain. In contrast to the data observed in rats, substantial ototoxicity was observed when guinea pigs were injected ip with doses of D,L-DFMO between 500 mg/kg/day and 1 g/kg/day. D,L-DFMO produced loss of compound action potential sensitivity, but not of cochlear microphonic amplitude. This finding correlated with histological data revealing loss of both outer and inner hair cells in the cochlea with inner more affected than outer hair cells, particularly in the basal turn. Higher exposure doses (2-3 g/kg/day) resulted in significant general toxicity including impaired growth and some mortality. When the enantiomers were evaluated in the guinea pig, it was found that 1 g/kg/day D-DFMO did not produce any significant hearing impairment, whereas 1 g/kg/day of the L-enantiomer of DFMO generated a threshold shift that surpassed that of 1 g/kg/day of the D,L-DFMO treatment.

Animals↗
PubMed1991

[Familial deafness showing hearing pattern of low-tone losses].

Clinical and electrocochleographic studies of low tone familial deafness were carried out in 19 patients of 10 families. These hearing impairments were characterized by an upward-sloping pure tone audiogram with 50dB to 60dB hearing threshold below 2000Hz and with normal or near-normal hearing threshold above this frequency. The type of inheritance in these families showed autosomal dominant mode and no associated malformation. In 7 patients, hearing tests were repeated, it was observed that hearing threshold was not elevated. The short increment sensitivity index (SISI) tests were positive suggesting a hair cell lesion in tested 7 patients. The caloric tests were normal in tested 3 patients. No abnormal internal ear configuration was found in both X-ray and high-resolution computed tomography. Twelve patients with these familial low tone deafness (FLTD), 19 patients with Ménière's disease, and 9 patients with low tone sudden deafness (LTSD) were studied using the transtympanic electrode technique of electrocochleography. All patients of FLTD showed normal negative summating potential (-SP) amplitude, and the cochlear microphonics (CM) showed a nearly same detection threshold as hearing level of the pure tone audiogram at 1 kHz and 0.5 kHz. The evidence suggested that the hearing impairment resulted from a localized abnormality of the cochlear apex, and without endolymphatic hydrops. On the other hand, patients with Ménière's disease and LTSD showed a high -SP amplitude and a satisfactory detection threshold of CM compared with hearing level of the pure tone audiogram. These findings suggest that both Ménière's disease and LTSD relate to endolymphatic hydrops.

Adolescent↗
PubMedDate not supplied

[A study of damaged acoustic biopotentials in guinea pigs following exposure to white noise].

62 guinea-pigs were treated twice exposed to white noise, 105 dB SPL, 20 to 20 000 cps for 40 minutes with a break of 24 hours in between. The cochlear microphonics (CM), the compound action potentials of the acoustic nerve (NAP) and the slow evoked potentials (SEP) were recorded. There were different degrees of damage to be seen in the acoustic biopotentials. The CM showed little damages only whereas the compound action potentials of the hearing nerve showed significant impairments in excitation and in adaptation. In the SEP excitation was decreased. From this, we may conclude that the CM must not be the only criterion for judging damages in the acoustic system after acoustic trauma. Furthermore we see that the central acoustic pathway is capable to compensate peripheric hearing damages within a short time. An additional exposure to noise does not necessarily add or cumulate the degrees of damage.

Action Potentials↗
PubMedDate not supplied

Electrocochleography in deaf subjects.

Electrocochleography using the transtympanic electrode technique was performed on 86 deaf ears. Auditory nerve action potential was detected in 9 ears, in 5 of which deafness was caused by cerebellopontine angle tumor or surgery. A low threshold of the cochlear microphonics' response was also observed in some of the cases with deafness caused by mumps or cerebellopontine angle tumor. Various pathophysiological states of the inner ear can be observed, even in cases showing the same total deafness when measured by audiometer.

Acoustic Stimulation↗
PubMed1999

Auditory brainstem responses, electrocochleograms, and cochlear microphonics in the myelin deficient mutant hamster 'bt'.

Electrophysiological studies of the auditory pathway were performed on the mutant hamster 'bt' which is known to have myelin deficiencies in the central nervous system. Auditory brainstem responses (ABRs), electrocochleograms (EcochGs), and cochlear microphonics (CMs) were recorded. ABRs in 'bt' demonstrated markedly transformed waveforms with significantly prolonged latencies. EcochG in 'bt' showed significantly prolonged N1 latencies of the compound action potentials (CAPs) while 'bt' showed normal CMs. The myelin deficient mutant hamster 'bt' may have myelin deficiencies not only in the brainstem auditory pathway but also in the cochlear nerve.

Animals↗
PubMed1982

Modulation of responses of spiral ganglion cells in the guinea pig cochlea by low frequency sound.

Period histograms were generated from single unit data obtained from the spiral ganglion of the first turn of the guinea pig cochlea in response to continuous tones between 40 and 500 Hz. With the lowest intensities used, spontaneous activity was suppressed during basilar membrane displacement (inferred from cochlear microphonic phase) towards scala vestibula and activity was enhanced during displacement towards scala tympani. At higher intensities the response changed to excitation during maximal basilar membrane velocity towards scala vestibuli. These patterns were delayed by about 0.5 ms producing large phase delays at the higher frequencies. We postulate that the displacement response is produced by cochlear microphonic originating from the outer hair cells acting on the inner hair cell membrane. In contrast, the velocity response is produced by the inner hair cell receptor potential. The effect of a 40 Hz tone on activity evoked by tones above, at, and below the characteristic frequency was investigated by generating period histograms synchronous with the 40 Hz tone. We found that activity evoked by tones around the characteristic frequency of the cell was suppressed during displacement of the basilar membrane towards scala tympani and enhanced in the opposite direction at 40 Hz intensities that had no effect on spontaneous activity. Further increase in the 40 Hz intensity produced suppression during scala vestibuli displacement with activity remaining only during the zero crossings. Still further increase produces the 40 Hz tone alone response. Activity evoked by tones in the low frequency 'tails' of the frequency threshold curve was not similarly modulated. This phenomenon is though to be related to basilar membrane nonlinearity for frequencies close to the cut-off. Investigation of the effect of a 40 Hz tone on the threshold of the compound action potential confirmed data obtained from single units.

Animals↗
PubMed1980

The responses of inner hair cells to basilar membrane velocity during low frequency auditory stimulation in the guinea pig cochlea.

Intracellular receptor potentials were recorded from inner hair cells in the basal turn of the guinea pig cochlea in response to low frequency tones. These were compared with the cochlear microphonic (CM) recorded from the scala tympani and sound pressure at the tympanic membrance. The CM is symmetrical and behaves as if it responds to basilar membrane displacement. The depolarizing phase of the inner hair cell receptor potential exceeds the hyperpolarizing phase with a ratio of about 3:1 in response to sinusoidal stimulation. Below 100 Hz inner hair cell receptor potentials phase lead sound pressure by 180 degrees and their amplitudes increase at a rate of 12 dB/octave. Above 200 Hz their receptor potentials are in phase with CM. The capacitative impedances of the hair cells delay and attenuate the intracellular receptor potentials at frequencies above 178-873 Hz. We conclude that CM is dominated by the responses of outer hair cells, and that a frequencies below 100-200 Hz inner hair cells respond to basilar membrance velocity. Above this they respond to basilar membrane displacement.

Acoustic Stimulation↗
PubMedDate not supplied

Cochlear potentials and their modulation by low-frequency sound in early endolymphatic hydrops.

Seventeen guinea pigs were unilaterally operated to produce endolymphatic hydrops. After 2 wk (9 animals) or 4 wk (8 animals), extracochlear electrophysiological responses to tone bursts of several frequencies were recorded in both the operated and non-operated ears. In addition, modulation by low-frequency (29 Hz sinusoidal bias) sound of the responses to 8 kHz tonebursts was measured. After the electrophysiological measurements, the animals were killed and examined histologically. Four weeks after the operation, cochlear microphonics in response to a 500 Hz tone burst and to the 29 Hz bias were significantly smaller in the operated ears. The summating potential showed a tendency to be larger in the operated ears. The compound action potential input-output curves for 2 kHz probes showed a small threshold shift accompanied by steep slopes, reminiscent of recruitment. Modulation of summating potentials by the low-frequency bias was smaller on the operated side. In most cochleae an endolymphatic hydrops was observed. Three cochleae showed a collapse of Reissner's membrane.

Acoustic Stimulation↗
PubMed1976

Morphological and physiological findings on hair cells with impaired metabolism (nitrogen, monoiodoacetate) in Caiman crocodilus with reference to sudden deafness.

Morphological and physiological studies were carried out on Caiman crocodilus under experimentally produced metabolic changes. During N2-respiration the cochlear potentials responded differently. The negative component (CM-) of the cochlear microphonics decreased continuously, whereas the CM+ component showed only a little change. The summation action potential (AP) exhibited a similar behaviour to that of CM-. These alterations were reversible up to periods of 30 min N2-respiration. The morphological findings, after N2-respiration, showed an intracellular oedema of the hair cells. The afferent synaptic contacts are always recognizable. Different degrees of disintegration within the presynaptic structures were seen. Efferent axosomal and axodendritic synapses were unchanged. MIA-perfusion led to an irreversible decrease of the cochlear potentials (CM+; CM-; AP) and morphologically to a total destruction of the papilla basilaris. The changes in the presynaptic structures during anaerobic metabolism offer the possibility of a new explanation for the reversibility of sudden deafness.

Action Potentials↗
PubMed1979

[Relationship between cochlear fatigue and the asymmetrical non-linearity of microphonic responses in the guinea pig (author's transl)].

It is classically considered that cochlear fatigue and acoustic trauma occur when intensity is such that the ear is saturated, i.e. when the microphonic potential fails to increase in a linear fashion in relation to intensity and when distorsion appears. The present report concerns a study in the guinea pig of the relationship between the non-linearity of microphonic responses, and their fatigability. The results show that fatigability is related not only to non-linearity but also to the asymmetry of responses. The asymmetry of microphonic responses may be interpreted as reflecting an asymmetrical ionic flow at the upper pole of hair cells, resulting in an accumulation of potassium ions within and around hair cells and thereby creating a depression of responses.

Animals↗
PubMed1987

Reliability of cochlear microphonics in clinical electrocochleography.

A study was made on the reliability of cochlear microphonics (CM) recorded in clinical electrocochleography (ECochG) by the transtympanic electrode technique. In normal-hearing subjects, the CM shift increased as the frequency was lowered at the same sound pressure, and as the sound pressure was lowered at the same frequency. The CM shift for the frequencies from 8 to 0.5 kHz was greater as the sound pressure was lowered. The above results suggest that clinical ECochG CM responses may well reflect the potential of the cochlea.

Acoustic Stimulation↗
PubMed1979

The uptake of methyl mercury in guinea pig cochlea in relation to its ototoxic effect.

Guinea pigs were treated for 7 days by daily subcutaneous injection of methyl mercury chloride labeled with 14C, the total dose of which was 17 mg Hg/kg. In these animals the cochlear microphonics and whole-nerve action potentials were suppressed in the basal turn but there was no marked losses in the third turn of the cochlea. The endocochlear potential was not decreased in magnitude. At the end of the treatment there was no accumulation of mercury in the perilymph, endolymph and cerebrospinal fluid. Uptake and elimination of mercury in the cochlear fluids were studied in guinea pigs which were treated by a single intravenous injection of 203Hg-labeled methyl mercury, the dose of which ranged from 0.2 to 17 mg Hg/kg. The results indicated that mercury concentration ratio of the blood relative to cochlear fluids was comparable with the blood to plasma ratio reported previously. In contrast to lack of accumulation in the extra cellular environment, it is likely that tissues of the sensory end organs in the cochlea accumulated methyl mercury.

Action Potentials↗
PubMed2005

Changes in distortion of two-tone cochlear microphonic and otoacoustic emission signals during an acute endolymphatic hydrops in the guinea pig.

An acute endolymphatic hydrops was induced by the injection of 1.1 mul of artificial endolymph into the scala media of guinea pig cochleas. This volume corresponds with an acute endolymphatic hydrops of 23%. During and after the injection, cochlear function was assessed by measuring the 2f(1)-f(2 )and f(2)-f(1) distortion products in cochlear microphonics (CMDP) and the 2f(1)-f(2) distortion product otoacoustic emission (DPOAE). A reversible pressure increase of 23 Pa and a relatively stable endocochlear potential (EP) were accompanied by a mean decrease in 2f(1)-f(2) DPOAE of only 3.4 dB. Similarly, the 2f(1)-f(2) CMDP amplitude change was minimal during and after the injection. The only substantial change was measured in the f(2)-f(1) CMDP amplitude. The measured range of distortion amplitudes during an acute endolymphatic hydrops can be related to small changes in the cochlear transducer operating point.

Acute Disease↗
PubMed2003

Vanilloid receptors in hearing: altered cochlear sensitivity by vanilloids and expression of TRPV1 in the organ of corti.

Capsaicin, the vanilloid that selectively activates vanilloid receptors (VRs) on sensory neurons for noxious perception, has been reported to increase cochlear blood flow (CBF). VR-related receptors have also been found in the inner ear. This study aims to address the question as to whether VRs exist in the organ of Corti and play a role in cochlear physiology. Capsaicin or the more potent VR agonist, resiniferatoxin (RTX), was infused into the scala tympani of guinea pig cochlea, and their effects on cochlear sensitivity were investigated. Capsaicin (20 microM) elevated the threshold of auditory nerve compound action potential and reduced the magnitude of cochlear microphonic and electrically evoked otoacoustic emissions. These effects were reversible and could be blocked by a competitive antagonist, capsazepine. Application of 2 microM RTX resulted in cochlear sensitivity alterations similar to that by capsaicin, which could also be blocked by capsazepine. A desensitization phenomenon was observed in the case of prolonged perfusion with either capsaicin or RTX. Brief increase of CBF by capsaicin was confirmed, and the endocochlear potential was not decreased. Basilar membrane velocity (BM) growth functions near the best frequency and BM tuning were altered by capsaicin. Immunohistochemistry study revealed the presence of vanilloid receptor type 1 of the transient receptor potential channel family in the hair cells and supporting cells of the organ of Corti and the spiral ganglion cells of the cochlea. The results indicate that the main action of capsaicin is on outer hair cells and suggest that VRs in the cochlea play a role in cochlear homeostasis.

Acoustic Stimulation↗
PubMed1981

Stimulated acoustic emissions in the ear canal of the gerbil.

Ear-canal sound pressure and cochlear potentials were monitored inthe anesthetized gerbil to study the origins of acoustic emissions produced by transient and continuous stimuli. No evidence was found of any delayed emissions (echoes) originating within the cochlea in the acoustic or cochlear microphonic (CM) waveforms. However, strong acoustic and CM distortion products occurred when two primary tones of moderate levels were presented to the ear; the site of origin of these products was traced to the cochlea. Further, the levels of distortion followed a complex time course after anoxia, often becoming stronger after animal death for up to one hour, then decaying to the noise floor of the system. The disappearance of the distortion products was coincident with elimination of both the negative endocochlear potential and the CM response to a fundamental tone.

Acoustic Stimulation↗