Biomedical subjects

Y Cazals

Publications and source records attributed to Y Cazals.

At least 19 recordsLinked to original sources

PubMed1992

Differences in hair bundles associated with type I and type II vestibular hair cells of the guinea pig saccule.

Several studies have reported variations in shape and size of stereociliary bundles and in a limited number of observations have associated them to type I and type II hair cells. A systematic study has been undertaken for which a technique was developed in order to identify both cell types and their corresponding hair bundles. Numerous fissures were obtained in saccular epithelia and observed in scanning electron microscopy. Saccular type I and type II hair cells in the guinea pig were found to have distinctive hair bundles. The tallest stereocilia of almost all type I cells were longer than 6 microns, and were shorter in the striola compared to the periphery. In contrast, the tallest stereocilia of almost all type II cells were shorter than 6 microns and were not found to vary notably in size from the striola to the periphery. Hair bundles with stereocilia organized in straight or in staggered rows were found for both types of cells across the whole saccular epithelium, with no apparent particular distribution. Possible physiological significance of differences in hair bundles is discussed.

Animals↗

PubMed1992

Axo-somatic contacts in the postnatal developing white rat spiral ganglion.

Development of the spiral ganglion in white rats was followed during the first 2 weeks after birth and morphological characteristics of the two neuronal types (I and II) were examined. In some neurons different stages of partial degeneration leading to formation of residual bodies were found without observation of degenerated cell, supporting the idea that differentiation at this time is not associated with cell death. Contacts between cell body of type II neurons and neuronal endings is reported for the first time. Such axo-somatic contacts previously observed only in monkey and man, also exists in lower mammals.

Animals↗

PubMed1991

Effect of silence duration in intervocalic velar plosive on voicing perception for normal and hearing-impaired subjects.

For normally hearing subjects shortening the silence duration of an intervocalic voiceless plosive induces a misperception of voicing. The time boundary for this effect is about 60 ms, which corresponds to a possible forward masking effect at the frequency of voicing. If recovery from masking is indeed involved, hearing-impaired subjects, who may have prolonged forward masking, can be expected to show abnormally long time boundary for voicing misperception. This study investigated the perception of voicing of an intervocalic plosive for a natural speech sample "aka" as a function of occlusive silence duration for normally hearing and hearing-impaired subjects. To investigate a correlation with forward masking, a second test was performed on the subjects. The same first a of the "aka" was selected and at its end was concatenated a voiced murmur taken from an "aga" elocution from the same speaker, and the minimum duration of the voiced murmur necessary for it to be perceived was measured. About half of the hearing-impaired subjects needed an abnormally long silence duration to avoid voicing misperception. The data indicate a significant correlation between the results of the two tests with a slope of regression line close to unity, and thus support the hypothesis of a voicing perception ruled by recovery from forward masking. Increase in silence duration of voiceless plosives might then be a beneficial acoustical processing for some hearing-impaired subjects.

Adolescent↗

PubMed1991

Contribution of increased endolymphatic pressure to hearing loss in experimental hydrops.

After the induction of experimental hydrops there follows a strict sequence of compound action potential (CAP) audiogram changes. Within days a low-frequency loss (below 8 kHz) is detected; within weeks a very high-frequency loss (above 8 kHz) develops; and finally within months the 8-kHz region is also affected. Following the application of excess pressure, presumably to the endolymphatic spaces, via a cannula placed in the endolymphatic duct, a sequence of CAP audiogram changes occurs that is not similar to that observed with hydrops. There is first a very high-frequency loss (above 4 kHz), then a very low-frequency loss (below 4 kHz), and finally the 4 kHz region is also affected and thresholds for all frequencies become even more raised. The data thus suggest that a slow accumulation of endolymph as induced by blockage of the endolymphatic duct does not produce the same disorder as a rapid onset of a high pressure applied at the base of the cochlea. In addition the data suggest that raised endolymphatic pressure is not likely to be significant in early stages of hydrops, but could contribute to the later high-frequency sensitivity losses.

Animals↗

PubMed1991

Indication of a relation between speech perception and temporal resolution for cochlear implantees.

In order to better understand the reasons for success or failure of a cochlear implant system for various patients, it appears necessary to analyze the patients' basic psychophysical capacities in relation to speech perception. Five patients with intracochlear multichannel Ineraid implants were studied in terms of their performance on temporal analysis in relation to their perception of consonants. For temporal analysis we measured the detection of a silent gap in noise and of an interval between two clicks. For consonant perception we established a confusion matrix based on 12 consonants presented in a vowel-consonant-vowel context using the vowel /a/. The results showed a correlation between temporal resolution for two successive clicks at the most basal cochlear electrode used, and the perception of place of articulation of consonants. This finding indicates that delivering fine temporal coding can be crucial for the success of an implant and that for a given subject, optimal capacity for temporal resolution may serve as a criterion for choosing a basal electrode.

Cochlear Implants↗

PubMed1991

[Evaluation of voice quality. Experimental approach and modeling of the prosthetic voice of laryngectomized patients].

The authors describe their initial results with the parametric assessment of voice quality, which still is mainly subjective. This analysis will be used both in audiology and phonology. A first approach is made on the experimental model of a laryngectomee with a Bordeaux-type phonatory implant. Such patients allow a simpler analysis of voice production both incoustics and with an electromyographic control. The analysis of the data and their statistical validation is based on the use of original computer software.

Acoustics↗

PubMed1990

GABA immunoreactivity of calyceal nerve endings in the vestibular system of the guinea pig.

Neurotransmitters involved in the vestibular system are largely uncharacterized. On the basis of results of earlier electrophysiological and immunohistochemical experiments, glutamate and gamma-amino-butyric acid (GABA) have been proposed in both mammalian and non-mammalian species as afferent transmitters between the sensory cell and the afferent dendrite. GABA is also suspected to act as an efferent neurotransmitter in the cochlea. We describe in this study the immunocytochemical localization of GABA within the vestibular end organs in the guinea pig. GABA immunoreactivity was found in the calyceal nerve endings surrounding type I hair cells of the vestibular epithelia. The most significant labelings were obtained in the crista ampullaris. Labeling was more difficult to observe in the utricular and saccular macula. These results contribute to the recent proposal that the calyx has a secretory function, and suggest that GABA may have a modulatory influence upon the type I hair cells.

Animals↗

PubMed1990

Evidence for potassium-induced motility in type I vestibular hair cells in the guinea pig.

In higher vertebrates, vestibular epithelia contain two types of hair cells, type I and type II cells. Physiological properties of single nerve units have been correlated to the corresponding hair cell type and a better knowledge of the hair cell static and dynamic properties should help in understanding transduction and coding in the vestibular system. For the auditory system, isolated outer cochlear hair cells (OHCs) have provided a useful approach for electrophysiological studies and for observations of motile processes involved in the active control of cochlear micromechanics. The present study tests the hypothesis of motile properties in guinea-pig vestibular hair cells, using stimuli known to elicit motile events in OHCs. After exposure to a medium containing a high concentration in potassium (125 mM or 80 mM KCl), 19 of 26 type I hair cells showed an irreversible tilt of the neck region often accompanied by an obvious swelling of the cell body. In contrast, no shape changes were detected in type II cells. In response to extracellular electrical stimulation, no motility was observed in either type I or type II cells.

Animals↗

PubMed1990

Alterations of CAP audiogram by increased endolymphatic pressure and its relation to hydrops.

Most current theories regarding the inner ear pathology of Menières disease assume that there is an augmentation of the endolymphatic pressure due to the presence of hydrops. In this study normal hearing pigmented guinea pigs were employed to investigate the effect of increased endolymphatic pressure on the compound action potential (CAP) audiogram. All animals were implanted with an electrode on the round window and the CAP audiogram was determined prior to further surgery. The endolymphatic canal was then visualised by a posterior fossa intra-dural surgical approach. A hole was pierced in the canal and a cannula inserted. The CAP audiogram was again determined before, and at frequent intervals after, the application of hydrostatic pressure (0.5-1 cm Hg). A similar sequence of CAP sensitivity losses was observed within 2 h for 0.5 cm Hg or 15 min for 1 cm Hg. There was at first a very high frequency loss, followed by a very low frequency loss and finally a mid frequency sensitivity loss rendered the audiogram flat and lying around 50 dB sound pressure level. Given that the first characteristic index for experimental hydrops is a low frequency loss the present data suggest that an increase in endolymphatic pressure, as in these experiments, is likely to be a rather late pathological feature of hydrops. Indeed we have shown that a high frequency loss develops at a second phase during the evolution of hydrops.

Action Potentials↗

PubMed1990

Multi-channel cochlear implant patients with different open speech understanding show some similar basic psychophysical results.

A series of tests was recently undertaken on three multi-channel cochlear implant patients showing different degrees of open speech understanding in order to try to determine underlying differences in inner ear excitation. First we wanted to determine whether these patients showed notable differences in basic psychophysical tasks. This article reports a series of measures including absolute and differential thresholds, simultaneous and forward masking, and some polarity and phase perception. Absolute and differential sensitivities were found to be similar. In forward or simultaneous masking, the patients often showed no masking at all and in cases of masking, no frequency selectivity. In forward masking, their time constants were found to be longer than those in normal hearing. Multi-harmonic signals differing only in phase relations to produce large differences in peak amplitude did not seem to elicit different perceptions. In stimulating with very low-frequency square waves, only negative going fronts were perceived. The similarity of results for the 3 patients in this study suggest that individual differences lie in more complex stimulus processing and perhaps in qualitative aspects of perception.

Adult↗

PubMed1989

Auditory frequency selectivity and tinnitus.

In the majority of cases tinnitus has a high pitch and can be matched rather precisely to an objective high frequency sound. However, it is well known that tinnitus can be masked by different tones without any frequency selectivity. We wondered whether objective tones matched to tinnitus would show a more significant deterioration of frequency selectivity than could be expected from any associated hearing loss. Psychoacoustic tuning curves were obtained using simultaneous pure-tone masking and revealed a broadening of frequency selectivity. In cases of comparable bilateral hearing losses with unilateral tinnitus, the broadening associated with the tinnitus was particularly conspicuous. This broadening strongly suggests that tinnitus originates in the cochlea, although some involvement of central pathways may also occur. Tinnitus-induced broadening of frequency selectivity as a possible sign of cochlear origin deserves further consideration in future studies.

Adult↗

PubMed1989

Acoustic responses recorded from the saccular bundle on the eighth nerve of the guinea pig.

Previous studies have demonstrated the existence of acoustic responses from the saccule in guinea pigs for stimulus intensities above 75 dB SPL. It is well known that the saccule receives a double afferent innervation: a bundle of the superior branch of the eighth nerve reaches its anterior part and another bundle of the inferior branch innervates its posterior part. These two bundles join just at the exit of the internal auditory meatus. An electrophysiological experiment was performed to investigate whether saccular acoustic responses could be similarly recorded from both bundles. Recordings from an electrode tip of 0.2 mm diameter were obtained in normal animals and also in animals with a complete and selective destruction of the cochlear sensory epithelium induced by treatment with an ototoxic antibiotic combined with a loop diuretic. In both normal and treated animals acoustic responses with the peculiar very short latency were specifically recorded in the area of the junction of the two bundles, they were of maximal amplitude on the bundle of the inferior branch. These data confirm in a more direct way the saccular origin of the short latency acoustic responses and indicate that they are probably conveyed in both saccular nerve bundles but mostly in that of the inferior branch of the eighth nerve. Finally these data show unequivocally that saccular acoustic responses exist in normal guinea pig ears.

Animals↗

PubMed1989

Distortion products in early stage experimental hydrops in the guinea pig.

The swelling of the endolymphatic spaces in experimental hydrops is likely to induce mechanical changes all along the cochlea. The selective atrophy of short and middle stereocilia on the outer hair cell above the first cochlear turn is expected to alter micromechanics and transduction. Two tone stimuli were employed in the present study to investigate cochlear distortion products in hydropic ears. Despite a substantial low frequency sensitivity loss on the CAP audiogram, 2f1-f2 distortion products recorded in the RWCM and the CAP were similar in hydropic ears and normal control ears which reflect the probable common origin of these responses--the base of the cochlea where no threshold shifts can be detected. On the other hand this distortion product in the otoacoustic emissions was considerably reduced in hydropic cochleas when the primary tones lay within the pathological part of the audiogram. The reduction of CDT emissions cannot be accounted for by hair cell loss since at the early stage of hydrops described here there is only discrete hair cell loss which is restricted to the apex of the cochlea. On the other hand the reduction in the amplitude of the CDT might reflect disturbance in hair cell function and/or cochlear mechanics above the first cochlear turn.

Action Potentials↗

PubMed1989

Asymmetry of evoked rotatory nystagmus in the guinea pig after experimental induction of endolymphatic hydrops.

We have previously shown by chronic implantation of round window electrodes, that after the experimental induction of endolymphatic hydrops by surgical blockade of the endolymphatic canal, in the guinea pig, there is a low/mid-frequency fluctuant hearing loss, followed by a very high frequency loss and after a few months the audiogram is flat. This evolution reproduces exactly that observed in Meniere's patients. The aim of this study was to investigate the evolution of one aspect of vestibular function in parallel with audiogram changes. The nystagmic responses in the dark were tested every month during the 4 months which followed hydrops induction. There was considerable variation in the number of evoked saccades for different control animals and even between different recordings for the same control animal. However, in general, the number of saccades to right and left rotation was symmetrical for control animals, whereas for hydropic animals there was a period, within the first 2 months post-operation, when there was a reduction of saccades to the left (operated side) with sometimes an increase to the right. This asymmetry which occurred in the period of fluctuant hearing losses did not however appear synchronized with audiogram fluctuations. The nystagmic responses tended to become symmetrical over the 4 months post-operation. Oral administration of glycerol to animals whose nystagmus was asymmetric brought the vestibular response towards symmetry in 50% of the cases. Although episodes of vertigo, as known in Meniere's disease, were never observed in operated guinea pigs, these data indicate that they have some functional vestibular disturbance.

Animals↗

PubMed1988

Evolution of recruitment at different frequencies during the development of endolymphatic hydrops in the guinea pig.

The study of human temporal bones has identified endolymphatic hydrops as a common feature of several diseases. In particular it is systematically found in those bones removed from patients with premortem Menière's disease. Menière's disease is known to induce sensorineural pathology with recruitment, which changes with the evolution of the hearing loss, and is suspected to induce a cochlear conductive loss by a possible increase in static pressure of endolymph. Amplitude/intensity functions of sensorineural responses can reflect recruitment and/or conduction loss. Experimentally induced hydrops in animals provokes cochlear physiological alterations, some of which closely resemble certain features of Menière's disease. In the present study using a guinea-pig animal model, we have examined amplitude/intensity functions at the round window for cochlear microphonics (RWCM), summating potentials (RWSP) and action potentials (CAP) at different stages of hearing loss in experimentally induced hydrops. During the period of fluctuating thresholds there was reduction of maximal RWCM amplitude, no change in RWSP and recruitment on the CAP. At a later stage when the audiogram was flat and fluctuations were no longer seen, RWCM remained unchanged. At this time RWSP could show recruitment while CAP amplitudes at all intensities were reduced, indicating either a cochlear conductive loss and/or a general depression of neural activity.

Animals↗

PubMed1988

Acute effects of noradrenalin related vasoactive agents on the ototoxicity of aspirin: an experimental study in the guinea pig.

Aspirin is known to be ototoxic when administered at high doses. Its mode of action is unknown but an alteration of the vascular function has been suspected. To further document this hypothesis, acute effects of some vasoactive agents on the ototoxicity of aspirin were tested in experiments on the guinea pig using sensori-neural electrophysiological responses and morphometry of the vessels of the stria and the spiral lamina. Electrophysiological measures showed no modification of sensory responses but neural responses revealed clear changes after administration of noradrenalin related agents, limited modifications after a drug acting partly as a serotonin antagonist, and no change after a dopaminergic agent. Morphometric studies showed no modification of the strial but some effect on the spiral vessels. The results are compatible with the hypothesis of a vascular involvement in the ototoxicity of aspirin and they point toward an interaction with the noradrenergic sympathetic cochlear system in the spiral lamina.

Animals↗

PubMed1988

Atrophy of middle and short stereocilia on outer hair cells of guinea pig cochleas with experimentally induced hydrops.

Scanning electron microscopy was employed to investigate hair cell morphology at different stages in the development of experimentally induced hydrops in the guinea pig. A particular form of morpho-pathology, never before described, was identified as characteristic of hydropic cochleas. The pathology was characteristically identified as atrophy of the short and middle stereocilia on the outer hair cells while the inner hair cell stereocilia did not have such a pathology. The atrophy was restricted to the upper cochlear turns in remarkable correspondence with the low/middle frequency sensitivity loss and was detected only at the end of the period of fluctuating thresholds. These stereocilia perturbations appear therefore to be linked with the threshold fluctuations and represent the first evidence for a clear correlation between hair cell morphology and physiology in the experimental model of endolymphatic hydrops. Such a morphopathology might also be expected to occur in cochleas of Menière's patients but may have been overlooked in the past because of the discrete nature of the pathology.

Animals↗

PubMed1988

Neuroanatomical study of Galen's anastomosis (nervus laryngeus) in the dog.

To further knowledge of the laryngeal nerves, the nerve fibers of Galen's anastomosis were studied using two neuroanatomical methods, namely nerve degeneration and horseradish peroxidase labeling. It is demonstrated that the superior laryngeal nerve forms part of the tracheal and esophageal nervous system. The value of the results in relation to physiological laryngeal studies and to human laryngeal diseases is discussed.

Animals↗