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At least 307 records · Page 17Linked to original sources
PubMed1989

The origin of the low-frequency microphonic in the first cochlear turn of guinea-pig.

Low-frequency microphonic potentials (100 Hz to 2000 Hz) have been measured in the first turn of the guinea pig cochlea before and after a variety of manipulations of the cochlea. These included ablation of the apical turns, iontophoresis of streptomycin, dc current injection into the first turn, acoustic trauma and two-tone interference with pure tones. These manipulations indicate that the low-frequency microphonic measured in the first turn and at the round window is generated predominantly by the hair cells of this region. It is a convenient and relatively uncomplicated indicator of the integrity of the mechano-electrical transduction process of these cells.

Acoustic Stimulation↗
PubMed1989

Changes in cochlear microphonic and neural sensitivity produced by acoustic trauma.

The low-frequency (200 Hz) microphonic potentials at the round window and in the organ of Corti of the first turn of the guinea pig cochlea have been measured before and after acoustic overstimulation. Reductions in the amplitude of this microphonic after loud sound are highly correlated with neural threshold elevation in this region. The fall in the microphonic amplitude appears due to an inactivation of mechano-electrical transduction channels at the apex of the outer hair cells into a closed state. These results are consistent with the idea that the current through the outer hair cells controls the mechanical sensitivity of the organ of Corti, and that the temporary loss of mechanical and neural sensitivity following loud sound is due to a simple inactivation of the mechano-electrical transduction channels.

Action Potentials↗
PubMed1989

Perilymph composition in scala tympani of the cochlea: influence of cerebrospinal fluid.

A commonly used technique to obtain cochlear perilymph for analysis has been the aspiration of samples through the round window membrane. The present study has investigated the influence of the volume withdrawn on sample composition in the guinea pig. Samples of less than 200 nl in volume taken through the round window showed relatively high glycine content, comparable to the level found in samples taken from scala vestibuli. If larger volumes are withdrawn, lower glycine levels are observed. This is consistent with cerebrospinal fluid (having a low glycine content) being drawn into scala tympani through the cochlear aqueduct and contaminating the sample. The existence of a concentration difference for glycine between scala tympani perilymph and cerebrospinal fluid suggests the physiologic communication across the cochlear aqueduct is relatively small in this species. The observation of considerable exchange between cerebrospinal fluid and perilymph, as reported in some studies, is more likely to be an artifact of the experimental procedures, rather than of physiologic significance. Alternative sampling procedures have been evaluated which allow larger volumes of uncontaminated scala tympani perilymph to be collected.

Animals↗
PubMed1992

The development and interpretation of the summating potential response.

The development of cochlear responses in the mouse was investigated, recording from the round window. Positive summating potentials (SP) could be detected as early as 7 days after birth in some individuals, the first signs of negative SP occurred in mice aged 10 days, and compound action potentials were first detected at 11 days of age. These early responses were obtained with relatively low frequency stimuli (usually 6 kHz). All waveforms recorded from 20 day old mice could be interpreted as simple additions of positive and negative SP and compound action potentials, each with different amplitudes and latencies. Positive SP showed both fast and slow components. Our observations are consistent with the positive SP with only a fast component arising from the basal turn inner hair cells, the positive SP with fast and slow components being generated by both inner and outer hair cells in the basal turn, and the negative SP seen at low frequencies of stimulation originating from depolarisation of hair cells in the apical turn. Summating potentials may thus be useful for investigating inner and outer hair cell function separately in abnormal cochleas in which it is not known which cell type primarily is affected.

Acoustic Stimulation↗
PubMed1992

Round-window recorded potential of single-fibre discharge (unit response) in normal and noise-damaged cochleas.

Unit responses (URs) of eighth-nerve fibres have been determined at the round window by spike-triggered averaging in both normal and pathological guinea pig cochleas. The pathology was mainly noise-induced damage. The URs have been analysed with respect to their dependence on the fibre's threshold, characteristic frequency (CF) and spontaneous rate (SR). The results from normal cochleas confirmed earlier data (Prijs, 1986): the UR has a diphasic waveform and the amplitude of its negative first peak is about 0.1 microV. From the six parameters (amplitude, latency, and width of the two peaks) by which the UR was described only the amplitude of the positive peak showed a significant variation with CF: a small decrease with increasing CF (CF-range 0.1 to 20 kHz). This finding may possibly be caused by oscillations in the spike-triggered average for low CFs. URs for most low- and medium-SR fibres were found to be large (greater than 0.3 microV). However, this result is interpreted as an artefact caused by synchrony of fibre spontaneous activity. In damaged cochleas only slight changes of the UR were found: the waveform duration became significantly shorter and on some occasions the positive peak increased in amplitude, but latency and amplitude of the negative component of the UR remained unchanged.

Acoustic Stimulation↗
PubMed1994

Cochlear blood flow measured by averaged laser Doppler flowmetry (ALDF).

This report describes a new approach to estimate the hydromechanical properties of a vascular system. Averaged laser Doppler flowmetry (ALDF) was developed by averaging the flux signal of a laser Doppler flowmeter (LDF) synchronized to the heart cycle. The usefulness of this method was verified by manipulation of the cochlear microvasculature. Twelve pigmented guinea pigs under pentobarbital/fentanyl anesthesia were used. The cochlea was surgically exposed and the LDF probe placed on the bony surface of the first turn to monitor cochlear blood flow (CBF). The LDF flux signal (0.2 s time constant) was sampled by an A/D board at 2 kHz for 255 ms and averaged with synchronization to the heart beat. The mean blood flow, peak to peak amplitude, and time (phase) delay of pulsatile flow were measured from the averaged signal. According to a transmission line model of the vascular system, under a given perfusion pressure, mean flow reflects resistance while amplitude and time delay of the pulsatile flow are related to the reactance component of the impedance of the vascular system. During the formation of photochemically-induced thrombosis in the cochlear microvasculature, there was a dramatic mean flux decrease (90.1 +/- 3.4% from baseline (BL), N = 6). Additionally, a time-dependent decrease in amplitude and time delay of pulsatile flow were indicated by ALDF. These results suggest a large increase in vascular resistance and significant decrease in compliance.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1995

Auditory nerve neurophonic recorded from the round window of the Mongolian gerbil.

In the Mongolian gerbil, round window (RW) recordings of averaged responses to phase-locked acoustic stimuli which are not alternated in polarity can include both the cochlear mirophonic (CM) and auditory nerve neurophonic (ANN). The ANN can dominate the recordings when the RW electrode is referenced to some portion of the body that allows the two electrodes to straddle the auditory nerve. Concentric bipolar RW electrodes are biased in favor of the CM. When there is a substantial ANN component in the RW response, as the sinusoidal stimulus intensity increases there is a non-monotonic increase of amplitude and a pronounced change of phase of the response. When the phase-locked stimuli are alternated in polarity in order to cancel the CM, a residual response is often observed. This residual response has twice the frequency of the stimulus and is decreased in amplitude by forward masking. It also shows a pattern of amplitude decrement following the stimulus onset, resembling adaptation of the firing rate of cochlear nerve axons. Tetrodotoxin (TTX) eliminates the non-monotonic RW amplitude input-output (I/O) function, reduces the phase changes of the response as the stimulus intensity is increased, eliminates the residual non-canceled response to alternated stimuli, and the time-limited amplitude decrements which resemble adaptation. Following application of TTX, the RW response of the gerbil to stimuli with non-alternated polarity much more closely resembles the CM responses of other animals. It is concluded that the gerbil's residual response following cancellation of the CM is the ANN, and that the RW of the gerbil is a convenient site for recording measures of phase-locked cochlear axonal activity.

Acoustic Stimulation↗
PubMedDate not supplied

Three-dimensional reconstruction of the cochlea from two-dimensional images of optical sections.

This paper describes a methodology for three-dimensional (3D) computer-aided reconstruction of the guinea pig cochlea using orthogonal-plane fluorescence optical sectioning. Specimens are sectioned optically, allowing them to remain intact during observation. Equations to correct the data for specimen translation and rotation are developed and 3D reconstructions of the scala tympani, round window membrane, and cochlear aqueduct are presented. The error associated with the reconstruction is estimated to be < 19 microns.

Animals↗
PubMed2006

Development and surgical anatomy of the round window niche.

The round window niche is a bony pouch of the tympanic cavity and clinically frequently explored, therefore its topography has fundamental impact on microsurgery. A total of 783 macerated and formalin-fixed temporal bones were used to study the normal anatomy of the round window and its development. The ossification of the niche starts in the 16th fetal week and is complete at birth. A process of the otic capsule, called the cartilage bar, forms the inferior wall of the round window niche. The anterior and superior walls of the niche form by intramembranous ossification, whereas the posterior and inferior walls predominantly form by enchondral ossification. The uneven growth of different walls of the round window niche can alter the shape of the entrance, which results in eight different types of niches: extremely narrow, descending tegmen, anterior septum, bony membrane, open fundus, exostosis, jugular dome and trabeculae.

Adolescent↗
PubMedDate not supplied

Labyrinthitis secondary to experimental otitis media.

PURPOSE: Analysis of labyrinthitis in a model of otitis media. MATERIALS AND METHODS: Morphologic study in 20 Wistar rats in which otitis media was induced by transbullar inoculation of Pseudomonas aeruginosa with obstruction of the eustachian tube. RESULTS: Seventy percent of rats showed vestibular signs. Histologic changes ranged from nonaffected labyrinths to suppurative labyrinthitis. CONCLUSIONS: Dissemination of infection probably occurs through round window membrane. A thinner round window membrane typical of rodents would be the reason for a more severe clinical and morphologic picture in rats when compared to human beings.

Animals↗
PubMed2004

Round window membrane motion with air conduction and bone conduction stimulation.

The vibration patterns of the round window (RW) membrane in human cadaver temporal bone specimens were assessed by measurements of the velocity of reflective targets placed on the RW membrane with an approximate spacing of 0.2 mm. The velocity was measured in the frequency range 0.1-10 kHz by a laser Doppler vibrometer in four specimens with air conduction (AC) stimulation and in four specimens with bone conduction (BC) stimulation. The response pattern was investigated by analyzing the velocity response of all targets on the RW membrane, by making iso-amplitude and iso-phase contour plots of the membrane surface, and by creating animations of the surface vibration at several frequencies. Similar response pattern was found with AC and BC stimulations. At frequencies below 1.5 kHz, the RW membrane vibrates nearly as a whole in an in-and-out motion and above 1.5 kHz, the membrane moves primarily in two sections that vibrate with approximately 180 degrees difference. Indication of some traveling wave motion of the RW membrane at those frequencies was also found. At higher frequencies, above 3 kHz, the membrane motion is complex with a mixture of modal and traveling wave motion. An increase of the stimulation level did not alter the vibration pattern; it only gave an increase of the RW membrane vibration amplitude corresponding to the increase in stimulation. When the mode of stimulation at the oval window was altered, by the insertion of a 0.6 mm piston, the vibration pattern of the RW membrane changed.

Acoustic Stimulation↗
PubMed2005

Cochlear structure and function after round window application of ototoxins.

Topical round window application of ototoxic agents has been a useful method for studying ototoxicity and hearing loss in the mammalian cochlea. For example, species-specific differences in cochlear susceptibility to damage have been documented using this technique. Carboplatin has been characterized in the literature as a selective inner hair cell (IHC) toxin in chinchillas, while cisplatin has been characterized as a selective outer hair cell (OHC) toxin. The present experiment quantified dose-dependent damage to cochlear hair cells in the chinchilla after a single direct round window application of either cisplatin or carboplatin. Detailed cytocochleograms were obtained for the entire cochlear duct, for a range of doses, along with auditory brainstem response thresholds. In agreement with the literature, although there was variability, at the lowest concentrations tested (2 and 3 mg/ml), carboplatin produced substantial IHC damage with no OHC damage. In contrast, the effects of cisplatin were more variable, and contrary to published reports, across the range of doses producing OHC damage, IHC damage was always observed. Limitations of direct round window ototoxin treatments are discussed, in addition to their potential application in the study of tinnitus.

Animals↗
PubMed2005

Simultaneous measurement of electrocochleography and cochlear blood flow during cochlear hypoxia in rabbits.

In this study, a new monitoring system is developed to measure cochlear blood flow (CBF) and electrocochleography (ECochG) during transient ischemic episodes of the cochlea. A newly designed otic probe was used for the simultaneous recordings of laser-Doppler CBF and ECochG directly from the round window (RW). The probe enabled the recording of high amplitude compound action potentials (CAP) and cochlear microphonics (CM) with few averages. Experiments were conducted on rabbits to generate episodes of cochlear ischemia by using timed compressions of the internal auditory artery (IAA). The computer monitoring system extracted and measured CAP and CM components from ECochG in real-time. Results indicate that CM and CAP generally followed CBF during compressions and releases of IAA. Both CBF values and CAP amplitudes showed an overshoot following the reperfusion. CAP amplitude measures were found to be very sensitive to ischemia showing very rapid amplitude, latency and morphological changes. CM amplitude decreased more slowly than the CAP and CBF. Simultaneous recordings of CBF and ECochG using the otic probe provide a valuable neuromonitoring tool to investigate the dynamic behavior of the cochlea during ischemia.

Acoustic Stimulation↗
PubMed2006

Reversible and controlled peripheral vestibular loss by continuous infusion of ropivacaine (Narop) into the round window niche of rats.

This paper describes a method for achieving a peripheral vestibular blockade in rats by instillation of local anaesthetics over the round window membrane through a permanently implanted cannula. Being rapidly reversible, the effect of the anaesthetic drug is easily controlled by a single continuous infusion, which can be repeated at any time. The method offers a unique opportunity to study the consequence of single or repeated transient vestibular loss without any use of general anaesthetics, which may be a severe confounding factor. Such studies might shed light on balance disorders related to permanent vestibular loss or episodic vestibular dysfunction. To evaluate the method, spontaneous horizontal eye movements were recorded during the first 4 h of continuous infusion. Unilateral infusion of ropivacaine gave rise to a high-frequency spontaneous nystagmus, reaching levels that have not been documented after a surgical labyrinthectomy under general anaesthesia. This vestibulo-oculomotor behaviour is consistent with a previous report using a single intratympanic instillation of lidocaine to achieve a short-lasting vestibular blockade. In the present study, it was demonstrated that the initial high-frequency nystagmus decreased during the first 100 min of infusion before stabilizing at the same level as recorded when the effect of general anaesthesia has worn off after a surgical ablation. When the transient vestibular blockade was repeated by a second infusion during the following day, the nystagmus frequency saturated on a significantly lower level than during the first blockade. Also, serial single infusions, with recovery between each functional vestibular loss, gave rise to a less severe nystagmus. It is suggested that this phenomenon is an expression of the behavioural concept of 'vestibular habituation', the neural substrate of which is rather unknown.

Adaptation, Physiological↗
PubMed2004

Intratympanic perfusion for the treatment of tinnitus.

Intratympanic treatment of tinnitus with corticosteroids or gentamicin should be considered as an option of treatment in selected tinnitus patients, alone or in combination with standard modalities of management such as tinnitus retraining therapy, masking, and hearing aid amplification. Review of the literature and the authors' experience suggest the following points regarding intratympanic treatment for tinnitus: 1. Lidocaine, although effective in decreasing tinnitus, has been largely abandoned because of its severe side-effect profile and need for inpatient administration. 2. Corticosteroids have been associated with few if any side effects. 3. The good results reported in the literature with intratympanic steroids for treating tinnitus of various causes should be viewed with caution,because most are retrospective and uncontrolled studies. 4. Some Meniere's disease patients with tinnitus may experience tinnitus improvement following intratympanic steroids. This treatment may be considered in such patients, especially for those with good hearing. 5. Gentamicin is effective in eliminating or reducing tinnitus in a significant number of patients with Meniere's disease and may be considered especially for those with nonserviceable hearing. 6. Further prospective, randomized, and controlled studies to evaluate the effect of intratympanic perfusion for the treatment of tinnitus are warranted.

Administration, Topical↗
PubMed2004

Intratympanic corticosteroids for Meniere's disease and vertigo.

Hearing loss can be caused by acoustic trauma, aging, ototoxic medications, and various other causes. At the cellular level hearing loss seems to be mediated by reactive oxygen species and ultimately through the activation of apoptotic mechanisms. This article explains the cellular and molecular mechanisms of hearing loss and presents medications that could be used in the intratympanic treatment of hearing loss.

Administration, Topical↗
PubMed2004

Intratympanic gentamicin for the treatment of Meniere's disease and other forms of peripheral vertigo.

Titration therapy with intratympanic gentamicin offers class A or B control of vertigo in 87% (range, 75%-100%) of patients with unilateral Ménière's disease. The risk of additional hearing loss is about 21% (range,0-37%). Vertigo may recur, however, in nearly one third of patients over time. These recurrences can also be treated by intratympanic gentamicin with a similar risk of hearing loss. The salient effect of intratympanic gentamicin is probably the reduction of vestibular function through damage to hair cells, but a complete ablation of function does not seem to be necessary for vertigo control.

Administration, Topical↗
PubMed1997

Cochlear implants in children: what constitutes a complication?

The surgeon must ultimately accept the responsibility for any complications that occur as the result of a cochlear implant. Listening to the cochlear implant team members and responding to their needs may enhance the child's progress. Surgical complications, (i.e., skinflap problems, infection, and facial paralysis) are indeed infrequent, but nonsurgical problems are not. Surgical and nonsurgical experiences were reviewed in 55 children. Ages ranged from 23 months to 18 years at the time of cochlear implantation, which occurred from 1984 to 1995. There were no surgical complications. However, the most common surgical obstacle was ossification, which was present in 40% and undetected by computed tomographic scanning in 16.3% of children. Ossification occurred at the round window and scala tympani in 32.7% and involved the cochlea more extensively in 7.3% of children. In only one child was the cochlea entirely ossified. There were, however, many nonsurgical problems that were viewed as complications in patient management. The single most important complication was device failure. This occurred in 10.9% (5/46) of children with the Cochlear Corporation multichannel implant. Head banging and other temper tantrums, parental interference with rehabilitation, socioeconomic factors, poor compliance by the family unit, equipment problems, educational deficiencies, and impatience with habilitative training were some of the other problems.

Adolescent↗