Acoustic Cues for Sound Source Distance and Azimuth in Rabbits, a Racquetball and a Rigid Spherical Model

There are numerous studies measuring the transfer functions representing signal transformation between a source and each ear canal, i.e., the head-related transfer functions (HRTFs), for various species. However, only a handful of these address the effects of sound source distance on HRTFs. This is the first study of HRTFs in the rabbit where the emphasis is on the effects of sound source distance and azimuth on HRTFs. With the rabbit placed in an anechoic chamber, we made acoustic measurements with miniature microphones placed deep in each ear canal to a sound source at different positions (10–160 cm distance, ±150° azimuth). The sound was a logarithmically swept broadband chirp. For comparisons, we also obtained the HRTFs from a racquetball and a computational model for a rigid sphere. We found that (1) the spectral shape of the HRTF in each ear changed with sound source location; (2) interaural level difference (ILD) increased with decreasing distance and with increasing frequency. Furthermore, ILDs can be substantial even at low frequencies when distance is close; and (3) interaural time difference (ITD) decreased with decreasing distance and generally increased with decreasing frequency. The observations in the rabbit were reproduced, in general, by those in the racquetball, albeit greater in magnitude in the rabbit. In the sphere model, the results were partly similar and partly different than those in the racquetball and the rabbit. These findings refute the common notions that ILD is negligible at low frequencies and that ITD is constant across frequency. These misconceptions became evident when distance-dependent changes were examined.     

High-Frequency Sensorineural Hearing Loss and Its Underlying Genetics (<Emphasis Type="Italic">Hfhl1</Emphasis> and <Emphasis Type="Italic">Hfhl2</Emphasis>) in NIH Swiss Mice

Studies using inbred strains of mice have been invaluable for identifying alleles that adversely affect hearing. However, the efficacy of those studies is limited by the phenotypes that these strains express and the alleles that they segregate. Here, by selectively breeding phenotypically and genetically heterogeneous NIH Swiss mice, we generated two lines—the all-frequency hearing loss (AFHL) line and the high-frequency hearing loss (HFHL) line—with differential hearing loss. The AFHL line exhibited characteristics typical of severe, early-onset, sensorineural hearing impairment. In contrast, the HFHL line expressed a novel early-onset, mildly progressive, and frequency-specific sensorineural hearing loss. By quantitative trait loci (QTLs) analyses in these two lines, we identified QTLs on chromosomes 7, 8, and 10 that significantly affected hearing function. The loci on chromosomes 7 and 8 (Hfhl1 and Hfhl2, respectively) are novel and appear to adversely affect only high frequencies (≥30 kHz). Mice homozygous for NIH Swiss alleles at either Hfhl1 or Hfhl2 have 32-kHz auditory-evoked brain stem response thresholds that are 8–14 dB SPL higher than the corresponding heterozygotes. DNA sequence analyses suggest that both the Cdh23 ^ahl and Gipc3 ^ahl5 variants contribute to the chromosome 10 QTL detected in the AFHL line. The frequency-specific hearing loss indicates that the Hfhl1 and Hfhl2 alleles may affect tonotopic development. In addition, dissecting the underlying complex genetics of high-frequency hearing loss may prove relevant in identifying less severe and common forms of hearing impairment in the human population.     

Complex level alterations of the 2<Emphasis Type="Italic">f</Emphasis><Subscript>1</Subscript>−<Emphasis Type="Italic">f</Emphasis><Subscript>2</Subscript> distortion product due to hypoxia in the guinea pig

It is controversially discussed inasmuch acute hearing disorders might originate from impaired cochlear circulation. Hypoxia-specific alterations of inner ear parameters measurable in patients with acute sensorineural hearing loss would therefore be of great interest. Aim of this study was to characterize hypoxia-related alterations of the 2f ₁−f ₂ distortion product. Nine guinea pigs were anaesthetized by i.m. administration of Midazolam, Medetomidin and Fentanyl. For introduction of hypoxia, the spontaneously breathing animals were offered a gas mixture of N₂O and O₂ containing either 21 or 12–13% O₂. Distortion product otoacoustic emissions (DPOAEs) were continuously monitored at f ₂ = 16 kHz; f ₂/f ₁ = 1, 2; DP-definition = 2f ₁−f ₂; L ₁ = 65 dB and L ₂ = 55 dB, while inhaled oxygen was switched from 21 to 12–13% and back. Oxygen saturation (SaO₂) was continuously monitored. Data from an hypoxic interval were only used for further data processing if DPOAE levels were stable before and after hypoxia. Six hypoxic intervals in five animals fulfilled the stability criterion. During the hypoxic interval with the highest measured SaO₂ (75%), no alterations of DPOAE levels were observed. During the remaining five hypoxic intervals, when SaO₂ ranged between 57 and 70%, DPOAE levels were on average lower with an increased standard deviation compared to mean pre-hypoxic levels. Mean decrease correlated with the decrease of SaO₂ (r = 0.90, P = 0.014). Alterations followed a characteristic time course—when hypoxia was started, DPOAE levels exhibited a short increase before they decreased and remarkably destabilized. After re-oxygenation DPOAE levels showed a pronounced level decrease, while SaO₂ already had recovered to pre-hypoxic values. After reaching a minimum, DPOAE levels slowly recovered to pre-hypoxic values. The decrease of DPOAE levels during hypoxia and the post-hypoxic level alterations have similarly been described by other authors before, while the distinct destabilization and transiently increased DPOAE levels have not been explicitly mentioned. A micromechanical mechanism that might explain a transient level increase and the post-hypoxic DPOAE level changes is discussed.     

Tonsillectomy <Emphasis Type="Italic">à chaud</Emphasis> for quinsy: revisited

In a prospective study involving 16 patients over a 12 month period, we determined whether tonsillectomy à chaud is an acceptable alternative to interval tonsillectomy for patients with quinsy. Guidelines for the acute surgical management of quinsy (or peritonsillar abscess) were established following a departmental audit. Sixteen patients were admitted with a quinsy plus an indication for tonsillectomy; 12 were evaluated prospectively. Each was treated either by incision and drainage or needle aspiration, rehydration, analgesia and intravenous antibiotic therapy, followed by a tonsillectomy à chaud (immediate tonsillectomy) within 30 h of the acute admission. Despite initial drainage, a high incidence of pus was detected intra-operatively. A much larger group of patients had peritonsillitis rather than peritonsillar abscess. Of the 16 patients admitted with a quinsy and indication for tonsillectomy over a 12 month period, 12 consented to tonsillectomy à chaud. Aspiration was used to confirm the presence of a quinsy in seven patients (58%), and incision and drainage in the remaining five. There were no complications, and further hospitalisations were avoided thus reducing patient morbidity and costs. We propose that tonsillectomy à chaud remains a justifiable alternative to interval tonsillectomy for such patients when personnel and theatre facilities permit.     

Short-term antibiotics treatment in patients with nasal polyps and enterotoxins producing <Emphasis Type="Italic">Staphylococcus aureus</Emphasis> strains

Enterotoxins produced by Staphylococcus aureus (SA) can act as super-antigens and thus influence the course of chronic rhinosinusitis with nasal polyps (NP). The aim of this study was to determine if antibiotic treatment administered after endoscopic sinus surgery (ESS) for NP can positively influence the course of the disease compared to placebo. After ESS, 23 patients who tested positive, in a perioperative culture, for SA strains producing enterotoxins A–E and TSST-1, were randomized into two groups. Group A which in addition to standard treatment received oral anti-staphylococcal antibiotics for 3 weeks. Group B received a placebo. Both groups were compared preoperatively, and at 3 and 6 months after surgery using a symptom-specific score, an endoscopic score and the SNOT-22 quality of life questionnaire. Slightly better results were achieved in patients who received antibiotic therapy. However, the differences were not statistically significant. Regardless of post-operative treatment, approximately 30% of patients had a SA-negative culture 6 months after surgery.     

Audiological Evaluation of Affected Members from a Dutch DFNA8/12 (<Emphasis Type="Italic">TECTA</Emphasis>) Family

In DFNA8/12, an autosomal dominantly inherited type of nonsyndromic hearing impairment, the TECTA gene mutation causes a defect in the structure of the tectorial membrane in the inner ear. Because DFNA8/12 affects the tectorial membrane, patients with DFNA8/12 may show specific audiometric characteristics. In this study, five selected members of a Dutch DFNA8/12 family with a TECTA sensorineural hearing impairment were evaluated with pure-tone audiometry, loudness scaling, speech perception in quiet and noise, difference limen for frequency, acoustic reflexes, otoacoustic emissions, and gap detection. Four out of five subjects showed an elevation of pure-tone thresholds, acoustic reflex thresholds, and loudness discomfort levels. Loudness growth curves are parallel to those found in normal-hearing individuals. Suprathreshold measures such as difference limen for frequency modulated pure tones, gap detection, and particularly speech perception in noise are within the normal range. Distortion otoacoustic emissions are present at the higher stimulus level. These results are similar to those previously obtained from a Dutch DFNA13 family with midfrequency sensorineural hearing impairment. It seems that a defect in the tectorial membrane results primarily in an attenuation of sound, whereas suprathreshold measures, such as otoacoustic emissions and speech perception in noise, are preserved rather well. The main effect of the defects is a shift in the operation point of the outer hair cells with near intact functioning at high levels. As most test results reflect those found in middle-ear conductive loss in both families, the sensorineural hearing impairment may be characterized as a cochlear conductive hearing impairment.     

Mucin in middle ear effusions inhibits attachment of <Emphasis Type="Italic">Haemophilus influenzae</Emphasis> to mucosal epithelial cells

Although otitis media with effusion is often preceded by an infection of the tympanic cavity, when cultured, many effusions show no culturable bacteria. Based on the hypothesis that the effusion might play a protective role in the course of infection, the influence of this fluid on adhesion of H. influenzae (Hi) type-b strain 770235 and nontypeable H. influenzae (NTHi) strains to buccal epithelial cells was investigated. Effusions were classified as mucoid, seromucoid and serous. Mucoid secretions inhibited adhesion to a significantly greater extent (62%) than did seromucous (52%) and serous effusions (47%) ( P<0.001). The glycoprotein and high-molecular-weight fractions showed similar levels of inhibition. Sialic acid concentration, and, to a lesser extent, protein concentration, correlated with the level of inhibition. Desialylated effusions lost their ability to block bacterial attachment. Thus, middle ear effusion fluid exhibits an inhibitory effect that is due to mucins, which determine viscosity and represent the sialylated high-molecular-weight glycoprotein fraction of the effusion.     

Dynamic Expression of <Emphasis Type="Italic">Lgr5</Emphasis>, a Wnt Target Gene,in the Developing and Mature Mouse Cochlea

The Wnt signaling pathway is a recurring theme in tissue development and homeostasis. Its specific roles during inner ear development are just emerging, but few studies have characterized Wnt target genes. Lgr5, a member of the G protein-coupled receptor family, is a Wnt target in the gastrointestinal and integumentary systems. Although its function is unknown, its deficiency leads to perinatal lethality due to gastrointestinal distension. In this study, we used a knock-in reporter mouse to examine the spatiotemporal expression of Lgr5 in the cochlear duct during embryonic and postnatal periods. In the embryonic day 15.5 (E15.5) cochlear duct, Lgr5-EGFP is expressed in the floor epithelium and overlapped with the prosensory markers Sox2, Jagged1, and p27(Kip1). Nascent hair cells and supporting cells in the apical turn of the E18.5 cochlear duct express Lgr5-EGFP, which becomes downregulated in hair cells and subsets of supporting cells in more mature stages. In situ hybridization experiments validated the reporter expression, which gradually decreases until the second postnatal week. Only the third row of Deiters’ cells expresses Lgr5-EGFP in the mature organ of Corti. Normal cochlear development was observed in Lgr5^EGFP/EGFP and Lgr5^EGFP/+ mice, which exhibited normal auditory thresholds. The expression pattern of Lgr5 contrasts with another Wnt target gene, Axin2, a feedback inhibitor of the Wnt pathway. Robust Axin2 expression was found in cells surrounding the embryonic cochlear duct and becomes restricted to tympanic border cells below the basilar membrane in the postnatal cochlea. Both Lgr5 and Axin2 act as Wnt targets in the cochlea because purified Wnt3a promoted and Wnt antagonist suppressed their expression. Their differential expression among cell populations highlights the dynamic but complex distribution of Wnt-activated cells in and around the embryonic and postnatal cochlea.     

Treatment of tripod fracture of zygomatic bone by <Emphasis Type="Italic">N</Emphasis>-2-butyl cyanoacrylate glue fixation,and its effects on the tissues

The standard treatment of zygomatic bone fractures is fixation by microplates or miniplates and screws today. It is very difficult to place plates and screws into thin bones or small bone fragments especially in the facial bones and bones adjacent to important structures. Cyanoacrylate is used as a hemostatic agent, an embolic agent, in retinal tears, in corneal ulcers, in fixation of mandibular osteotomies and in craniofacial surgery. N-2-Butyl cyanoacrylate is a form of cyanoacrylate which is bioabsorbable and biocompatible. It is easily applied to the tissues. We aimed to determine the effect of N-2-butyl cyanoacrylate in the fixation of displaced zygomatic bone fractures. We examined the histotoxicity and the effects on healing and foreign body reaction of N-2-butyl cyanoacrylate. Eight New Zealand white rabbits underwent zygomatic osteotomies bilaterally. The fractures on left sides of the rabbits were determined as study site and right sides as control site. Knight and North classification of zygomatic bone fractures were used and group 4 fractures were made bilaterally. Open reduction of fractures was performed bilaterally and N-2-butyl cyanoacrylate was applied only on left sides. No fixation was made on right sides representing the control group. Postoperatively in the first, second, third and fourth weeks, two rabbits were sacrificed and the fracture sites were examined macroscopically and histopathologically. In the glued study group, fixation was obtained in all cases whereas in the control group, all the fractures were seen to be displaced. Tissue reaction was similar in the study and the control groups.     

The efficacy of <Emphasis Type="Italic">N</Emphasis>-2-butyl cyanoacrylate in the fixation of nasal septum to the anterior nasal spine in rabbits: experimental study

In nasal septal surgery, fixing the caudal portion of the nasal septum to the anterior nasal spine is difficult with the present techniques. N-2-butyl cyanoacrylate is a form of cyanoacrylate which is bioabsorbable and biocompatible. The feasibility and efficacy of the compound, which is easy to apply to the tissues, for the above purpose is investigated in this experimental study. Fourteen New Zealand rabbits were included in the study. The nasal septum was exposed with the open approach (transcolumellar). In the study group (n = 10), the septum was detached from the nasal floor and attached to a point 3 mm lateral to the nasal spine on the right side, using 2-butyl cyanoacrylate. In control group (n = 4) it was deviated 3 mm to the right side and left for spontaneous healing without using any fixation method. Beginning on the third postoperative week, one animal was sacrificed under general anesthesia, every week in the study group and every third week in the control group, and the septum was analysed. Foreign body reaction, histotoxicity, and the structure of the regenerative tissue in the junction of bone and cartilage were analysed with histopathology. The success of stabilization in the study group, where the septum was attached with N-2-butyl cyanoacrylate, was significantly superior to the control group where no fixation method was used (P < 0.05). Histopathologically, there were no differences between the two groups with respect to foreign body reaction, histotoxicity, and the tissue that formed between the bone and cartilage (P > 0.05). This study demonstrated that N-2-Butyl cyanoacrylate was successful in the fixation of the caudal edge of the nasal septum to the anterior nasal spine. No serious infections, foreign body reaction, necrosis or histotoxicity were observed.     

Structure and Growth of the Utricular Macula in the Inner Ear of the Slider Turtle <Emphasis Type="Italic">Trachemys scripta</Emphasis>

In general, postembryonic production of inner ear vestibular hair cells (HCs) is believed to occur in all nonmammalian vertebrates. However, no study on this topic has been published on reptiles and, consequently, it is not known whether this also applies to these vertebrates. Therefore, the present study applied stereological methods in order to estimate the total number of HCs in turtles of varying sizes. The findings are that in prehatchlings the utricular macula (UM) contains approximately 4000 HCs as compared to approximately 5000 in juveniles, approximately 8000 in medium-sized turtles, and approximately 12,000 in large, sexually mature turtles. Scanning electron microscopy (SEM) reveals that presumably newly generated HCs with small surface areas and thin stereovilli are found in all regions of the UM. Furthermore, it reveals that utricular HCs can be classified as belonging to a specific region from the morphology of their apical structure. Striolar HCs have a large free oval-to-ovoid surface, a hair bundle with numerous stereovilli, and a short kinocilium. Rampary and cotillary HCs have smaller and slimmer free surfaces, comparatively fewer stereovilli, but much longer kinocilia. In conclusion, the current study demonstrates that postembryonic production of HCs does occur in reptiles and thereby supports the general view that this is a common trait in all nonmammalian vertebrates.     

Age-Dependent Changes of Gap Detection in the Mongolian Gerbil (<Emphasis Type="Italic">Meriones unguiculatus</Emphasis>)

Gap detection using broadband noise was characterized in a group of young gerbils from the breeding colony of the University of Regensburg (RB gerbils), old RB gerbils, and old gerbils from the breeding colony of the University of South Carolina (SC gerbils). Data from old RB and old SC gerbils were not significantly different and were subsequently combined for a comparison with data from the group of young RB gerbils. Level dependence of gap-detection thresholds in young and old domesticated gerbils resembled the typical mammalian pattern of level dependence. Gap-detection thresholds of old gerbils were significantly elevated at 30 dB SL and 50 dB SPL as compared with young gerbils. Compared with young gerbils tested at 30 dB SL and 50 dB SPL, the distribution of gap-detection thresholds in old gerbils was broader with a spread to higher gap-detection thresholds. Some old animals retained excellent temporal resolution, while some showed impaired gap detection. The gap-detection data collected in young and old gerbils resemble previously published data from humans of different age and confirm that gerbils are a useful model to study age-dependent changes in temporal processing.     

Neomycin-Induced Hair Cell Death and Rapid Regeneration in the Lateral Line of Zebrafish (<Emphasis Type="Italic">Danio rerio</Emphasis>)

Mechanoreceptive hair cells are extremely sensitive to aminoglycoside antibiotics, including neomycin. Hair cell survival was assessed in larval wild-type zebrafish lateral line neuromasts 4 h after initial exposure to a range of neomycin concentrations for 1 h. Each of the lateral line neuromasts was scored in live fish for the presence or absence of hair cells using the fluorescent vital dye DASPEI to selectively label hair cells. All neuromasts were devoid of DASPEI-labeled hair cells 4 h after 500 µM neomycin exposure. Vital DASPEI staining was proportional to the number of hair cells per neuromast identified in fixed larvae using immunocytochemistry for acetylated tubulin and phalloidin labeling. The time course of hair cell regeneration in the lateral line neuromasts was also analyzed following neomycin-induced damage. Regenerated hair cells were first observed using live DASPEI staining 12 and 24 h following neomycin treatment. The potential role of proliferation in regenerating hair cells was analyzed. A 1 h pulse-fix protocol using bromodeoxyuridine (BrdU) incorporation was used to identify S-phase cells in neuromasts. BrdU incorporation in neomycin-damaged neuromasts did not differ from control neuromasts 4 h after drug exposure but was dramatically upregulated after 12 h. The proliferative cells identified during a 1 h period at 12 h after neomycin treatment were able to give rise to new hair cells by 24–48 h after drug treatment. The results presented here provide a standardized preparation for studying and identifying genes that influence vertebrate hair cell death, survival, and regeneration following ototoxic insults.     

Distortion Product Otoacoustic Emissions and Auditory Evoked Potentials in the Hedgehog Tenrec, <Emphasis Type="Italic">Echinops telfairi</Emphasis>

The hedgehog tenrec, Echinops telfairi, has certain basal mammalian features, like a cloaca and a sparsely differentiated brain with smooth cerebral hemispheres. The peripheral auditory capabilities of this species were investigated by means of distortion product otoacoustic emissions (DPOAE). For comparison, we determined auditory evoked potentials (AEP) in the inferior colliculus and the auditory cortex. Both methods show that the auditory range of E. telfairi extends well into ultrasonic frequencies, with a region of highest sensitivity at around 16 kHz. The total auditory range spans about 4 octaves at 40 dB SPL. The low-frequency limit of auditory processing is found at frequencies of about 2–3 kHz. The DPOAE and the AEP thresholds of E. telfairi do not run fully parallel in the high-frequency range. For a threshold value of 40 dB SPL, cochlear mechanical thresholds as measured with DPOAE extend up to 50 kHz, whereas neuronal thresholds reach the high-frequency limit at about 30 kHz. Frequency tuning, as assessed from DPOAE suppression tuning curves, was low to moderate with Q _10dB values ranging from 1.7 to 8. The lack of discontinuity in the group delay (derived from DPOAE measurements) reveals that cochlear frequency representation is tonotopic without any region of specialized mechanical tuning. Markus Drexl, Michael Faulstich, and Boris von Stebut contributed equally to the data presented in this study.