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PubMed2001

Cochlear gene delivery through an intact round window membrane in mouse.

Cochlear gene transfer studies in animal models have utilized mainly two delivery methods: direct injection through the round window membrane (RWM) or intracochlear infusion through a cochleostomy. However, the surgical trauma, inflammation, and hearing loss associated with these methods lead us to investigate a less invasive delivery method. Herein, we studied the feasibility of a vector transgene-soaked gelatin sponge, Gelfoam, for transgene delivery into the mouse cochlea through an intact RWM. The Gelfoam absorbed with liposomes and adenovirus, but not with adeno-associated virus (AAV), was successful in mediating transgene expression across an intact RWM in a variety of cochlear tissues. The Gelfoam technique proved to be an easy, atraumatic, and effective, but vector-dependent, method of delivering transgenes through an intact RWM. Compared with the more invasive gene delivery methods, this technique represents a safer and a more clinically viable route of cochlear gene delivery in humans.

Adenoviridae↗
PubMed1991

Hyaluronan applied to lesioned round window membrane is free from cochlear ototoxicity.

Hyaluronan (HYA) in 1% solution was instilled into the round window (RW) niche of rats (n = 6) prior to perforating the round window membrane (RWM). Cochlear functioning and structure were then monitored by recording auditory brainstem responses (ABRs) at 2-31.5 kHz and by scanning electron microscopy. Perforation of the RWM alone (n = 6) resulted in immediate loss of ABR thresholds between 6 and 31.5 kHz in 2 of 6 animals. Similar results were obtained after instilling HYA into the RW niche and subsequent RWM perforation (n = 6). After 2 months, ABR thresholds were recorded at all frequencies in the HYA-treated animals, whereas in 2 of the controls no ABR thresholds could be elicited at 20 and 31.5 kHz. However, in both treatment groups the mean ABR thresholds and mean latencies for wave II at the ABR threshold returned to the pre-surgical (normal) range after 2 months. With respect to the cochlear morphology the results in both treatment groups were also alike including minor structural changes in hair cell stereociliae but no loss of hair cells. It is concluded that HYA, when instilled into the middle ear with the inner ear opened, is free from cochlear otoxicity.

Animals↗
PubMed1991

The use of intraoperative electrocochleography in Meniére's surgery.

Intra-operative electrocochleography was undertaken during surgery for Meniére's disease. It was found that the electrocochleogram (ECoG) provided a stable measure which accurately reflected changes within the inner ear during surgery. During salt osmosis of the round window, a rapid change in the summating potential versus action potential ratio (SP/AP) occurred which showed when the endolymphatic hydrops (ELH) had been altered. During a modified cochleostomy procedure, the ECoG showed when the cochlear duct had been ruptured. Forty ears were monitored during endolymphatic sac surgery. Twenty-five of these ears showed stable ECochG which did not alter at any time during the procedure; however, 8 of these ears showed normal SP/AP ratios during the surgery despite having been abnormal in the week prior to surgery. The SP/AP ratio was reduced in 8 ears, increased in 3 ears and showed other changes which were probably due to unstable electrode positioning in 4 ears. It was concluded that endolymphatic sac or duct surgery altered the inner ear physiology in a significant number of ears affected by endolymphatic hydrops.

Acoustic Stimulation↗
PubMedDate not supplied

Round window membrane permeability to human serum albumin in antigen-induced otitis media.

The round window membrane (RWM) permeability to human serum albumin (HSA) was investigated in both normal chinchillas and chinchillas sensitized with HSA. The effect of a corticosteroid agent (triamcinolone) on the RWM permeability was also analyzed. It was found that HSA could not be detected in either the perilymph or the cerebrospinal fluid of normal chinchillas within 1 hour after instillation into the middle ear bulla. Perilymph levels of HSA peaked 24 hours after instillation. In antigen-induced otitis media, the HSA level in the perilymph at 12 hours after challenge was significantly higher than that in normal chinchillas (P less than .01), but it did not increase with the development of otitis media. A significant difference of HSA level in the perilymph of animals with and without steroid treatment was noted (P less than .025 at 24 hours and P less than .05 at 48 hours). It is concluded that little HSA passes through the normal RWM in a short time and that the RWM permeability to HSA increases in the early stage (about 12 hours) of antigen-induced otitis media. Corticosteroids can affect the RWM permeability to HSA by reducing the level of antigen-induced otitis media.

Adjuvants, Immunologic↗
PubMed2006

Dehiscent high jugular bulb: a pitfall in middle ear surgery.

OBJECTIVE: The aim of this study was to present our experience on facing the dehiscent high jugular bulb (HJB) during middle ear surgery in the past 2 decades. STUDY DESIGN: Retrospective review. SETTING: Secondary referral hospital. PATIENTS: From January 1982 to June 2002, consecutive 1,657 patients underwent surgical intervention for middle ear cleft diseases, a total of 1,857 operations. Of them, 10 ears (0.5%) in nine patients were proven to have dehiscent HJB during operation for adhesive otitis media in four ears and for chronic otitis media with cholesteatoma in six ears. MAIN OUTCOME MEASURES: Each patient underwent otoscopic examination, radiographic examination, and audiometry before and 6 months after operation. RESULTS: Otoscopic examination revealed atrophic changes in the pars tensa with adhering to the promontory in two ears, attic retraction in one ear, and both findings in seven ears. All lesions were located beneath the basal turn of the cochlea and the round window niche at anteroinferior and/or posteroinferior quadrants. Active bleeding was encountered in two ears (20%) while elevating the tympanomeatal flap, which was treated by pressure compression associated with gelfoam sheet, then covered with an autologous cartilage to protect the dehiscent bulb. For the remaining eight ears, the bulbs were reinforced with fascia, perichondrium, or autologous cartilage. All 10 ears were allowed completion of the planned surgery without complications. CONCLUSION: HJB is not a contraindication for middle ear surgery. Awareness of this pitfall may lessen the operation risk.

Adult↗
PubMed1987

Mathematical analysis of VIIIth nerve cap with a linearly-fitted experimental unit response.

The compound action potential (CAP) recorded at the round window has for some time been investigated in order to determine the underlying temporal spike sequence: the firing probability density (FPD) function of the fibres. Charlet de Sauvage et al. [(1980) Hear. Res. 2, 343-346; (1983) J. Acoust. Soc. Am. 73, 616-627] have previously described a close estimate of the far-field unit response (UR) by presenting to the ear a transient electrical stimulation combined with an acoustical masking noise. A linear model of UR, free of noise or extrinsic potentials and based on both experimental data and on the dipole principle of Teas et al. [(1962) J. Acoust. Soc. Am. 34, 1438-1459], was proposed [(1985) Hear. Res. 18, 121-125]. Using the UR model, deconvolutions were performed on CAPs recorded in various conditions of stimulation and of cochlear pathologies in the guinea pig. The principal findings were: (1) a plateau was observed in the amplitude function around 60-70 dB above normal threshold both for click-evoked CAPs and for the corresponding FPDs; (2) FPDs resulting from the deconvolution of high-frequency derived responses showed 2 main peaks with a 0.7 ms interval followed by a second homologous pair with lower amplitude. Convolution computations confirmed the need for the second set with peaks 2 and 3 being only 0.3 ms apart. These findings are interpreted in terms of mechanical excitation pattern.

Animals↗
PubMed1990

The prognostic value of round window electrical stimulation in cochlear implant patients.

The use of preoperative round window stimulation has been advocated for its possible predictive value in cochlear implant patients. We have attempted to correlate cause of deafness, preoperative radiologic study, and postoperative stimulability and performance with preoperative stimulation. Round window stimulation procedures consisted of measurements of electrical thresholds and comfort levels, gap detection, and temporal difference limen. Radiologic studies were performed using high-resolution computerized semi-axial and coronal tomography with 1.5-millimeter overlapping cuts. Patient performance was measured using a standard audiologic test battery. Sixteen postlingually, profoundly deaf adults who received the Nucleus multichannel cochlear implant were studied. All 16 patients who responded to preoperative stimulation had acceptable CT scans for the ear operated on and stimulated postoperatively with the prosthesis. The lowest level at which a patient could reliably detect a gap between two signals ranged from 10 to 150 milliseconds, which was not predictive. For the temporal difference limen task, the patients who could reliably identify the longer of two pulses when the difference was less than 100 milliseconds did achieve varying amounts of open-set speech discrimination postoperatively. In summary, results indicate that the preoperative psychoacoustic electrical stimulation test battery provides useful information in predicting postoperative performance.

Cochlea↗
PubMed1988

Histopathology of chloroform-induced inner ear damage.

Inner ear function loss was caused in guinea pigs and rats by injecting chloroform into the middle ear. After symptoms for cochlear and vestibular deficit had been registered, the animals were permitted to survive for one day to five months. Ear histopathology was then studied in celloidin sections. In both species, hair cells and afferent nerve fibers were intact at all survival times. The acute stage of functional loss in guinea pigs was associated with inner ears of normal histological appearance. Within days after chloroform injection a severe otitis media developed which led to fibrous occlusion of the round window and eventually to new bone growth in the middle ear space around the otic capsule. A secondary labyrinthitis was also observed, resulting in endolymphatic hydrops at longer survival times. Different histopathological changes were seen in rats. The tectorial membrane appeared swollen in all cases, the swelling being more severe in more apical turns at longer survival times. It is concluded that only secondary sequela of the initial functional insult can be detected by standard light microscopic histopathology. Chloroform does not cause a chemical labyrinthectomy as previously assumed, although it is severely ototoxic.

Animals↗
PubMed2005

Communication between the perilymphatic scalae and spiral ligament visualized by in vivo MRI.

We evaluated the transport of Gadolinium-diethylenetriaminepentaacetate-bismethylamide (Gd-DTPA-BMA) through the round window (RW) membrane into the perilymphatic space with 4.7-T MRI in an animal study and 1.5-T MRI in humans. After administration of Gd-DTPA-BMA onto the intact RW membrane of guinea pig, Gd-DTPA-BMA uptake was observed in the basal turn and part of the second turn within 40 min. The scala tympani, scala vestibuli, the fibrous part of the spiral ligament and semicircular canal all showed uptake of Gd-DTPA-BMA. All turns of the cochlea were filled with Gd within 10 min in the perforated RW membrane administration group and within 30 min in the intravenous administration group. In patients who accepted middle ear injection of Gd-DTPA-BMA, uptake was observed within 2 h in the basal turn and semicircular canal. After 12 h the apex did still not show any uptake. Gd-DTPA-BMA is transported from the RW to the semicircular canal, the scala tympani and scala vestibuli without passing the helicotrema.

Animals↗
PubMed1994

Loss of perilymph affects electrocochleographic potentials in the guinea pig.

Alterations of electrocochleographic (ECoG) potentials recorded from guinea pig cochleae have been reported to occur following round window (RW) membrane perforation (perilymphatic fistula). To further evaluate the pathophysiology of perilymphatic fistula, a study was conducted of the short-term effects of acute RW membrane perforation on the amplitude of the summating potential (SP) and the action potential (AP), and the SP:AP ratio. Acute RW membrane perforation was produced in 15 Hartley guinea pigs. The animals were placed in a head dependent position, so that some perilymph would drain from the inner ear following RW perforation. For both click and low frequency tone burst stimuli (2 kHz), the mean AP amplitudes showed variable but progressive deterioration with time following RW membrane perforation. Action potential latencies showed a significant increase with time for both click and tone burst stimuli. Summating potential amplitudes for click and tone burst were typically stable or slightly decreased. Interanimal variability of all measures was typically high. However, AP and SP amplitudes in the same animal were consistently and differentially affected by perforation of the RW membrane. There also were differential effects on the positive and the negative components of the SP, suggesting the interplay of several generator mechanisms. The authors conclude that AP amplitude and, consequently, the SP:AP ratio are sensitive to the creation of a perilymphatic fistula. These results provide support for the use of ECoG tests in the diagnosis of perilymphatic fistula.

Animals↗
PubMed2006

Efficacy of gene transfer through the round window membrane: an in vitro model.

The viral vector-transgene soaked gelatin-sponge method has been shown to be successful in mediating transgene expression across an intact round window membrane (RWM) in mouse in vivo. However, there are many confounding factors which make it difficult to evaluate the role of the RWM in gene transfer. We have created an in vitro model to test the feasibility of gene delivery through an intact RWM. The round window including the bony niche of a CD1 mouse was removed under an operating microscope and fixed with adhesive on the base of a petri dish through which a hole had been drilled. Toluidine blue was injected into the niche containing a hyaluronic acid ester sponge against the round window membrane. The niche was closed with a fascia. A plastic tube containing PBS was fixed on the opposite side, from where the samples were collected at different time points. The concentration of toluidine blue was evaluated spectrophotometrically. An adenoviral vector containing green fluorescent protein (GFP) marker gene was injected into the niche. Samples were collected from the opposite side at different time points. The presence of the vector was studied with GFP PCR. We also modulated the permeability of the RWM by treating it with clinically applicable detergents, histamine or silver nitrate. Silver nitrate and trichloracetic acid caused destruction of the surface epithelium of the RWM as shown by light microscopy. Both toluidine blue and adenoviral vectors passed through the RWM in a time-dependent fashion. RWM cells expressed GFP after Ad-GFP treatment. The permeability of the RWM was decreased after treatment with different detergents, histamine or silver nitrate. RWM offers an atraumatic route to the inner ear. Compared with more invasive gene delivery methods, this technique represents a safer and clinically more viable route of cochlear gene delivery.

Animals↗
PubMed2004

Imaging of the guinea pig cochlea following round window gadolinium application.

Precise, non-invasive determination of the aetiology and site of pathology of inner ear disorders is difficult. The aim of this study was to describe an alternative method for inner ear visualization, based on local application of the paramagnetic contrast agent gadolinium. Using a 4.7 T MRI scanner, high contrast images of all four cochlear turns were obtained 3.5 h after placing gadolinium on the round window membrane. Gadolinium cleared from the cochlea within 96 h. Auditory brainstem response measurements performed on a separate group of animals showed no significant threshold shifts after the application, indicating that gadolinium is non-toxic to the guinea pig cochlea.

Acoustic Stimulation↗
PubMed1988

Directional hearing in the barn owl (Tyto alba).

The acoustical properties of the external ear of the barn owl (Tyto alba) were studied by measuring sound pressure in the ear canal and outer ear cavity. Under normal conditions, pressure amplification by the external ear reaches about 20 dB between 3-9 kHz but decreases sharply above 10 kHz. The acoustic gain curve of the outer ear cavity alone is close to that of a finite-length exponential horn between 1.2-13 kHz with maximum gain reaching 20 dB between 5-9 kHz. Pressure gain by the facial ruff produces a maximum of 12 dB between 5-8 kHz and decreases rapidly above 9 kHz. The directional sensitivity of the external ear was obtained from pressure measurements in the ear canal. Directivity of the major lobe is explained, to a first approximation, by the sound diffraction properties of a circular aperture. Aperture size is based on the average radius (30 mm) of the open face of the ruff. Above 5 kHz, the external ear becomes highly directional and there is a 26 degree disparity in elevation between the acoustic axis of the left and right ear. In azimuth, directivity patterns are relocated closer to the midline as frequency increases and the acoustic axis moves at a rate of 20 degree/octave between 2-13 kHz. Movement of the axis can be explained, to a first approximation, by the acoustical diffraction properties of an obliquely truncated horn, due to the asymmetrical shape of the outer ear cavity. The directional sensitivity of the barn owl ear was studied by recording cochlear microphonic (CM) potentials from the round window membrane. Between 3-9 kHz, CM directivity patterns are clearly different to the directivity patterns of the external ear; CM directionality is abruptly lost above 10 kHz. Above 5 kHz, CM directivity patterns are characterized by an elongated major lobe containing the CM axis, forming a tilted band of high amplitude but low directionality (CM axial plane), closely bordered by minima or nulls. The highest directionality is found in the CM directional plane, approximately perpendicular to the CM axial plane. The left and right ear axial planes are symmetrical about the interaural midline (tilted 12 degrees to the right of the midline of the head) and inclined by an average of 60 degrees to the left and right respectively. In azimuth, the CM axis moves towards the midline at a rate of 37 degrees/octave as frequency increases from 2-9 kHz, crossing into contralateral space near 7 kHz.(ABSTRACT TRUNCATED AT 400 WORDS)

Acoustic Stimulation↗
PubMed1979

Measurement of the hydrostatic pressures of the cochlear compartments.

A micropressure transducer (sensitive 0.1 cm H2O) utilizing a manual servo nulling system and a micropipette (tip diameter 12-20 micron) was designed in order to measure endolymphatic and perilymphatic hydrostatic pressures in the inner ear of the guinea pig. Perilymphatic pressures were measured through the round window membrane in animals in which the ossicular structures had been removed and in those in which the middle ear structures were intact. Endolymphatic pressures were measured after removal of the middle ear structures. There was a significant (p less than 0.001) difference between perilymphatic pressures in the presence (4.7 +/- 0.36 cm H2O) and absence (2.43 +/- 0.22 cm H2O) of the middle ear structures. The endolymphatic pressure was 0.00 cm H2O when measured through the basilar membrane after disruption of the scala tympani, and was 3.34 +/- 0.57 when monitored through the spiral ligament and stria vascularis. In order to verify the accuracy of these measurements, we monitored pressures in animals whose perilymphatic pressures were artificially maintained by an external source. Recoveries were always 95-100% of the artificially applied pressure. The injection of purified cholera toxin into the scala media through the basilar membrane resulted in a significant (p less than 0.001) increase in endolymphatic pressure.

Animals↗
PubMed2002

Similar half-octave TTS protection of the cochlea by xylazine/ketamine or sympathectomy.

Cochlear efferents, sympathetic control and stress conditions have been shown to influence sound-induced hearing loss. These factors are also known to be modified by sedation/anesthesia. We tested here the effect of sedation/anesthesia on temporary threshold shift (TTS) compared to that in the same awake animals. The effect of sympathectomy was also tested. We employed awake guinea pigs with a chronically implanted electrode on the round window of each of the cochleae. Each ear was tested for its sensitivity to TTS induced by a 1 min or a 10 min exposure to an 8 kHz pure tone at 96 dB sound pressure level. After an intramuscular injection of xylazine or ketamine together with xylazine, TTS at half-octave frequencies was reduced compared to that in awake animals. The second half-octave frequencies were less affected. This specific pattern of protection was also observed here after surgical ablation of a superior cervical ganglion. The data lead to the speculation that protection from TTS under sedation/anesthesia might be due to diminished sympathetic influence. Xylazine is a pre-synaptic alpha2-adrenoreceptor agonist which blocks noradrenaline release from the sympathetic system. Ketamine is a N-methyl-D-aspartic acid receptor antagonist which could reduce glutamate excitotoxicity as well as reduce sympathetic activity.

Adrenergic alpha-Agonists↗
PubMed2024

A base editor for the long-term restoration of auditory function in mice with recessive profound deafness.

A prevalent recessive mutation (c.2485C>T, p.Q829X) within the OTOF gene leads to profound prelingual hearing loss. Here we show that in Otof mice harbouring a mutation (c.2482C>T, p.Q828X) homozygous to human OTOF that faithfully mimics the hearing-loss phenotype, a base editor (consisting of the deaminase ABE7.10max and the Cas9 variant SpCas9-NG) packaged in adeno-associated viruses and injected into the inner ear of the mice via the round-window membrane effectively corrected the pathogenic mutation, with no apparent off-target effects. The treatment restored the levels of the otoferlin protein in 88% of the inner hair cells and stably rescued the auditory function of the mice to near-wild-type levels for over 1.5 years while improving synaptic exocytosis in the inner hair cells. We also show that an adenine base editor that targets the prevalent human OTOF mutation restored hearing in humanized mice to levels comparable to those of the wild-type counterparts. Base editors may be effective for the treatment of hereditary deafness.

Animals↗
PubMed2001

Intratympanic dexamethasone for sudden sensorineural hearing loss: clinical and laboratory evaluation.

OBJECTIVE: To discuss the value of intratympanic dexamethasone (IT-DEX) perfusion for sudden sensorineural hearing loss (SSNHL), clinically and in an animal model. STUDY DESIGN: Retrospective case review of 10 patients with SSNHL treated with IT-DEX. The findings are correlated with this institution's previous findings from a study of IT-DEX in guinea pigs. SETTING: Ambulatory tertiary otologic referral center. PATIENTS: Sequential patients with SSNHL who chose IT-DEX treatment. INTERVENTIONS: Dexamethasone 0.5 mg was injected transtympanically and bathed the round window for 20 minutes. Animal study: 79 ears were randomized into five groups: control, IT-DEX versus intravenous (IV)-DEX, IT-DEX with histamine, IT-DEX with hyaluronic acid, and IT-DEX with dimethylsulfoxide. MAIN OUTCOME MEASURES: Clinical study: postprocedure audiometry. Animal study: perilymph steroid concentration. RESULTS: IT-DEX results in significant hearing improvement and in significantly higher perilymph concentration of steroid than IV-DEX. CONCLUSIONS: IT-DEX is an appropriate treatment option for the treatment of SSNHL. Further study of dosages and frequency of administration is warranted.

Administration, Topical↗
PubMed2005

m-Chlorophenylpiperazine exacerbates perception of salicylate-induced tinnitus in rats.

The serotonin receptor 5-HT2c agonist m-chlorophenylpiperazine (mCPP) has been widely used to induce anxiety-like states in animals and anxiety in humans. We here addressed the effect of an intraperitoneal injection of mCPP on the perception of tinnitus in a behavioural protocol based on an active avoidance paradigm. In control saline-treated animals, mCPP did not change compound action potential audiograms or measurable tinnitus. In contrast, mCPP to animals demonstrating salicylate-induced tinnitus exacerbated tinnitus perception by nearly twofold. We went on to test whether manipulation of the peripheral generator of tinnitus (i.e. the cochlea) could extinguish this exacerbated perception by applying the N-methyl-d-aspartate (NMDA) antagonist 7-chlorokynurenate (7-CK) into cochlear fluids using a 7-CK-soaked Gelfoam ball placed on the round window of each of the animals' two ears. In addition to blocking the tinnitus induced by salicylate alone, 50 microm of 7-CK clearly abolished tinnitus in animals receiving salicylate and an injection of mCPP. The demonstration that cochlear NMDA receptor blockade abolishes the exacerbated perception of tinnitus is highly relevant in terms of treatment. In addition to psychotherapeutic treatment that may help to attenuate an individual's perception of tinnitus, targeting cochlear NMDA receptors represents a promising therapeutic strategy, even in depressed or chronically anxious patients.

Animals↗