Evidence of local antibody response against Alloiococcus otitidis in the middle ear cavity of children with otitis media

Alloiococcus otitidis is a recently discovered bacterium frequently associated with otitis media. However, no study is available as to whether A. otitidis has a pathogenic role and induces local immune response in the middle ear as a true pathogen. Whole bacterial sonicate of A. otitidis was separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), and transferred to a nitrocellulose membrane. Then, Western blot analysis was performed with supernatant of the middle ear effusions from children with A. otitidis-positive otitis media. SDS-PAGE of the bacterial sonicate showed several protein bands, designated A1-A11. Western blot analysis revealed the presence of IgG, secretory IgA, IgG2, and IgM against A. otitidis in the middle ear effusions. Absorption of the specimens with sonicates of other major middle ear pathogens did not alter the reactivity of antibodies against the alloiococcal antigens. The results suggest that specific local immune response against A. otitidis is induced during middle ear infection of the organism as a true pathogen. A5, A6 or A11 is expected to be a main antigenic determinant. This is the first report to show evidence of local antibody response against A. otitidis and to disclose antigenic components of A. otitidis.     

Isolation of Alloiococcus otitidis from Indigenous and non-Indigenous Australian children with chronic otitis media with effusion

During the last decade Alloiococcus otitidis has been identified in specimens from patients with chronic otitis media with effusion. Whereas most of those studies employed molecular techniques, we used minor modifications of conventional microbiological methods to isolate and identify A. otitidis in samples obtained from 20/50 (40%) children referred for myringotomy. Alloiococcus otitidis was isolated from 10/22 (45%) Indigenous and 10/28 (36%) non-Indigenous children. This is the first report of isolation of A. otitidis from Australian children with chronic otitis media. All isolates were sensitive to penicillin, but 14/20 (70%) of the isolates were resistant or partially resistant to erythromycin as assessed by the E-test.     

Bacterial etiology of otitis media with effusion; focusing on the high positivity of Alloiococcus otitidis

The etiology of otitis media with effusion (OME) is unclear. The bacterial analyses of middle ear effusion (MEE) in OME may reveal important information regarding its etiology. Alloiococcus otitidis, Heamophilus influenzae, Streptococcus pneumoniae and Moraxella catarrhalis were investigated by using microbiologic culture and a multiplex PCR method in the middle ear fluid of 32 children (54 samples) with chronic OME. PCR yielded positive results in 18 (33.3%) middle ear effusions while culture resulted positive for 3 (5.6%). The PCR method detected A. otitidis in 10 (18.5%) specimens, H. influenzae in 7 (13%), M. catarrhalis in 4 (7.4%) and S. pneumoniae in 2 (3.7%) specimens. The multiplex PCR method enhances the detection rate significantly compared to that of the conventional culture method. A. otitidis is the most common detected pathogen in the MEE of the OME.     

Induction of CD69 expression and Th1 cytokines release from human peripheral blood lymphocytes after in vitro stimulation with Alloiococcus otitidis and three middle ear pathogens

Alloiococcus otitidis is a recently discovered pathogen of otitis media. However, only a limited number of studies are available about the pathogenic and immunological role of A. otitidis. The aim of this study was to investigate the activation and the cytokine production of human peripheral blood lymphocytes at the early immune response after stimulation with A. otitidis. After stimulation of whole human peripheral blood lymphocytes for 18 h with whole killed A. otitidis or the three major middle ear pathogens (Streptococcus pneumoniae, Haemophilus influenzae and Moraxella catarrhalis), the expression of CD69 and the production of cytokines were analyzed. The expression of CD69 on T cells and B cells was dose-dependently enhanced after stimulation with A. otitidis. The release of interleukin (IL)-12 was induced after stimulation with A. otitidis, whereas the release of IL-4 was not induced after stimulation with A. otitidis. In addition, the release of interferon (IFN)-gamma was induced after stimulation with A. otitidis. Although the release of IFN-gamma started within 18 h after stimulation with A. otitidis, intracellular production of IFN-gamma was not observed in either CD4+ T cells or CD8+ T cells within 18 h upon stimulation. The patterns of CD69 expression and T helper-type 1 (Th1)-promoting cytokines production were similarly shown when human peripheral blood lymphocytes were stimulated with the other three major pathogens. Our results suggest that A. otitidis has sufficient immunogenic potential to modulate a host immune response, like the other three major middle ear pathogens, and also suggest that the immunogenicity of A. otitidis is very similar, at the early immune response, to that of the three major middle ear pathogens.     

Interleukin-8 secretion of human epithelial and monocytic cell lines induced by middle ear pathogens

Otitis media with effusion (OME) is one of the most common diseases in children. Alloiococcus otitidis, a new gram-positive bacterial species, was isolated from the middle ear fluid of children with OME; however, the pathogenic role of this bacteria is yet unknown. In this study, the ability of cultured epithelial cell lines (Hep-2 and Hela) and monocytic cell lines (THP-1 and U 937) to secrete chemokine interleukin-8 (IL-8) in response to the A. otitidis organism and three bacterial organisms mainly detected from middle ear fluid in OME, and bacterial cell components was investigated. When stimulated with four viable bacterial cells, epithelial cells and monocytes secreted IL-8 in a time-dependent manner. The monocytes produced significantly higher levels of IL-8 than the epithelial cells. Compared with that by viable bacterial cells, IL-8 secretion by stimulated epithelial cells and monocytes was reduced when the bacteria were heated and treated with glutaraldehyde. With bacterial stimulations, cell treatment of interferon-gamma caused monocytes to increase the induction of IL-8 production, however, the induction of monocyte differentiation caused monocytes to reduce the induction of IL-8 production. Furthermore, epithelial cells and monocytes stimulated by four viable bacterial organisms physically separated from cultured cells reduced the induction of IL-8 compared with directly stimulated cells, and monocytes stimulated with soluble extracts prepared from A. otitidis organisms produced IL-8 in a dose-dependent manner. These results suggest that part of the IL-8 stimulation of the A. otitidis organism may exist in a diffusable factor released by the bacteria or soluble components of the bacteria itself.     

Effect of Alloiococcus otitidis and three pathogens of otitis media in production of interleukin-12 by human monocyte cell line

Alloiococcus otitidis is detected in middle ear effusion of otitis media with effusion (OME). Only a limited number of studies are available concerning the immunological profile of A. otitidis. We have studied the ability of A. otitidis and three other representative pathogens of otitis media to stimulate the production of interleukin-12 (IL-12) from a monocytic cell line THP-1. Viable A. otitidis induced the production of IL-12 in THP-1 cells but IL-12 production was reduced if glutaraldehyde-fixed bacteria were used as stimulants. When viable bacteria were physically separated from THP-1 cells during the stimulation period, remarkable reductions of IL-12 secretion were shown after challenge with gram-positive bacteria A. otitidis and S. pneumoniae. When stimulated with soluble extracts of A. otitidis, THP-1 secreted IL-12 in a dose-dependent manner. The subfraction with a molecular mass over 100 kDa showed a strong ability to induce IL-12 production. Our results show that A. otitidis has immunostimulatory capacity with regard to IL-12 production. We also show that soluble antigen(s) of A. otitidis can modulate the immune response in OME.     

A polysaccharide of Alloiococcus otitidis, a new pathogen of otitis media: chemical structure and synthesis of a neoglycoconjugate thereof

Alloiococcus otitidis is a recently discovered Gram-positive bacterium that has been linked with otitis media (middle ear infections). In this study, we describe the structure of a novel capsular polysaccharide (PS) expressed by the type-strain of A. otitidis, ATCC 51267, and the synthesis of a glycoconjugate composed of the capsule PS and bovine serum albumin (BSA). The capsule PS of A. otitidis type-strain was determined to be a repeating trisaccharide composed of 3-substituted N-acetyl-D-glucosamine (GlcpNAc), 6-substituted N-acetyl-D-galactosamine (GalpNAc), and 4-substituted D-glucuronic acid (GlcpA), of which the majority was amidically decorated with L-glutamic acid (Glu): {-->6)-beta-GalpNAc-(1-->4)-[Glup-->6]-beta-GlcpA-(1-->3)-beta-GlcpNAc-(1}n. Monomeric analysis performed on other A. otitidis strains revealed that similar components were variably expressed, but Glu appeared to be a regular constituent in all the strains examined. Due to the suitable presence of GlcpA and Glu, our approach for glycoconjugate synthesis employed a carbodiimide-based strategy with activation of available carboxyl groups by 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC), which afforded direct coupling between the capsule PS and BSA. Analysis by mass spectrometry indicated that this A. otitidis capsule PS-BSA conjugate was composed of BSA units that carried up to seven capsule PSs. This work represents the first report in the literature describing an A. otitidis cell-surface carbohydrate and the synthesis of a glycoconjugate preparation thereof. Presently, we are formulating plans to immunologically evaluate this A. otitidis glycoconjugate vaccine in animals.     

Correction of low-set ear: superoposterior mobilization of the ear as a transposition flap pivoted on the ear canal with burring of the superoposterior canal wall

In a number of congenital, developmental, and postoperative conditions, many patients have a difference in the vertical and anteroposterior position of the ears. On correction of this deformity, the most difficult problem is the low and anterior location of the external auditory canal. To overcome this unyielding limitation, the authors perform superoposterior transposition of the low-set ear pivoted on the ear canal after making a new path for the canal by burring of the thick superoposterior canal wall. A mastoid hairline incision is followed by three-quarters circumferential subpericranial dissection around the bony ear canal posteriorly. A preauricular incision is followed by subcutaneous dissection anteriorly. By using the natural deformability of the cartilaginous ear canal, the S-shaped canal can be straightened through a new path made by burring of the thick superoposterior wall. Then the low-set ear can be mobilized superoposteriorly as a transposition flap pivoted on the ear canal with minimal tension by straightening of the canal. The corrected auricular position can be maintained by (1) several permanent sutures between the cavum conchae and the mastoid and deep temporal fascia, (2) a suspensory temporoparietal fascial loop, and (3) a skin support provided by the repair in an elevated position and V-Y-plasty or Z-plasty on the lower pole of the ear. From December of 1997 to October of 1998, three cases with a maximum follow-up of 15 months were examined. Symmetric ear position was achieved and maintained on both frontal and lateral views after the operation in all cases. This new technique for correction of low-set ear produces symmetric ear position in both vertical and anteroposterior dimensions for a long time. In addition, it can be performed with various other surgical procedures safely and simultaneously in a variety of pathologic conditions.     

Finite element modelling of human auditory periphery including a feed-forward amplification of the cochlea

A three-dimensional finite element model is developed for the simulation of the sound transmission through the human auditory periphery consisting of the external ear canal, middle ear and cochlea. The cochlea is modelled as a straight duct divided into two fluid-filled scalae by the basilar membrane (BM) having an orthotropic material property with dimensional variation along its length. In particular, an active feed-forward mechanism is added into the passive cochlear model to represent the activity of the outer hair cells (OHCs). An iterative procedure is proposed for calculating the nonlinear response resulting from the active cochlea in the frequency domain. Results on the middle-ear transfer function, BM steady-state frequency response and intracochlear pressure are derived. A good match of the model predictions with experimental data from the literatures demonstrates the validity of the ear model for simulating sound pressure gain of middle ear, frequency to place map, cochlear sensitivity and compressive output for large intensity input. The current model featuring an active cochlea is able to correlate directly the sound stimulus in the ear canal with the vibration of BM and provides a tool to explore the mechanisms by which sound pressure in the ear canal is converted to a stimulus for the OHCs.     

Mechanisms of sound reception and conduction in the dolphin

Morphology of the dolphin’s lower jaw, model and behavioral experiments are discussed with the aim of exploring the mechanisms of sound reception and conduction to the lower jaw canals, taking into account the known concepts of acoustics and the theory of grouped antennas. It is shown that the left and right rows of mental foramens with the respective mandibular canal and tissues of the canals are forming the new external ear and the new external auditory duct whereby sound (in the frequency band of 0.1–160 kHz) is transmitted into the middle ear, in contrast to the dolphin’s nonfunctional outer ear. This new external ear is created by nature as a receiving array of traveling-wave antennas located in the throat of an acoustic horn (the respective mandibular canal). The results give reason to assume the existence of a similar new external ear in Odontoceti.     

Numerical simulation of wave propagation in a realistic model of the human external ear

In this study, a numerical investigation is performed to evaluate the effects of high-pressure sinusoidal and blast wave's propagation around and inside of a human external ear. A series of computed tomography images are used to reconstruct a realistic three-dimensional (3D) model of a human ear canal and the auricle. The airflow field is then computed by solving the governing differential equations in the time domain using a computational fluid dynamics software. An unsteady algorithm is used to obtain the high-pressure wave propagation throughout the ear canal which is validated against the available analytical and numerical data in literature. The effects of frequency, wave shape, and the auricle on pressure distribution are then evaluated and discussed. The results clearly indicate that the frequency plays a key role on pressure distribution within the ear canal. At 4 kHz frequency, the pressure magnitude is much more amplified within the ear canal than the frequencies of 2 and 6 kHz, for the incident wave angle of 90° investigated in this study, attributable to the ‘4-kHz notch’ in patients with noise-induced hearing loss. According to the results, the pressure distribution patterns at the ear canal are very similar for both sinusoidal pressure waveform with the frequency of 2 kHz and blast wave. The ratio of the peak pressure value at the eardrum to that at the canal entrance increases from about 8% to 30% as the peak pressure value of the blast wave increases from 5 to 100 kPa for the incident wave angle of 90° investigated in this study. Furthermore, incorporation of the auricle to the ear canal model is associated with centerline pressure magnitudes of about 50% and 7% more than those of the ear canal model without the auricle throughout the ear canal for sinusoidal and blast waves, respectively, without any significant effect on pressure distribution pattern along the ear canal for the incident wave angle of 90° investigated in this study.     

Directional hearing in the barn owl (Tyto alba)

Summary 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° 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°/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 theCM directional plane, approximately perpendicular to the CM axial plane. The left and right ear axial planes are symmetrical about the interaural midline (tilted 12° to the right of the midline of the head) and inclined by an average of 60° to the left and right respectively. In azimuth, the CM axis moves towards the midline at a rate of 37°/octave as frequency increases from 2–9 kHz, crossing into contralateral space near 7 kHz. In the CM directional plane, the directivity of the major lobe suggests that a pressure gradient may occur at the TM. The region of frontal space mapped by movement of the CM axis in azimuth closely matches the angle of sound incidence which would be expected to produce the maximum driving pressure at the TM. It is suggested that acoustical interference at the TM results from sound transmission through the interaural canal and therefore the ear is inherently directional. It is proposed that ear directionality in the barn owl may be explained by the combined effect of sound diffraction by the outer ear cavity and a pressure gradient at the TM.Abbreviations CM cochlear microphonic - RMS root mean square - SPL sound pressure level - TM tympanic membrane     

Anatomy and physics of the exceptional sensitivity of dolphin hearing (Odontoceti: Cetacea)

During the past 50 years, the high acoustic sensitivity and the echolocation behavior of dolphins and other small odontocetes have been studied thoroughly. However, understanding has been scarce as to how the dolphin cochlea is stimulated by high frequency echoes, and likewise regarding the ear mechanics affecting dolphin audiograms. The characteristic impedance of mammalian soft tissues is similar to that of water, and thus no radical refractions of sound, nor reflections of sound, can be expected at the water/soft tissue interfaces. Consequently, a sound-collecting terrestrial pinna and an outer ear canal serve little purpose in underwater hearing. Additionally, compared to terrestrial mammals whose middle ear performs an impedance match from air to the cochlea, the impedance match performed by the odontocete middle ear needs to be reversed to perform an opposite match from water to the cochlea. In this paper, we discuss anatomical adaptations of dolphins: a lower jaw collecting sound, thus replacing the terrestrial outer ear pinna, and a thin and large tympanic bone plate replacing the tympanic membrane of terrestrial mammals. The paper describes the lower jaw anatomy and hypothetical middle ear mechanisms explaining both the high sensitivity and the converted acoustic impedance match.     

Restoring hearing with active hearing implants.

Due to shortcomings of conventional hearing aid technology, such as unsatisfactory sound quality due to limited frequency range and undesired distortion, occlusion of the outer ear canal, and acoustic feedback with high amplification, but also psychological aspects of stigmatization, a significant of patients in need of hearing aids are actually not wearing them. Active hearing implants can be distinguished in: (1) impedance transformation implants (ITI), (2) cochlear amplifier implants (CAI), (3) cochlear implants (CI), and (4) brain stem implants (BSI). Whereas ITI are designed for patients with middle ear hearing loss, CAI are intended to restore hearing in patients with inner ear hearing loss. Advantages of CAI may be: (1) improved sound fidelity, (2) no occlusion of the outer ear canal, (3) no feedback, and (4) invisibility. However, not all features are true for every device. CI replace inner ear function in deaf or almost deaf patients. This article gives an overview on the range of active hearing implants to restore hearing and outlines the future use of computer and robot aided surgery.     

A previously unidentified <Emphasis Type="Italic">Chorioptes</Emphasis> species infesting outer ear canals of moose (<Emphasis Type="Italic">Alces alces</Emphasis>): characterization of the mite and the pathology of infestation

Background  

During the past decade, Chorioptes mites occupying the outer ear canals have been a common finding at routine necropsies of moose (Alces alces) in Sweden, but neither the taxonomy of the mites nor lesions from the infestation have been investigated. In this study, the mites are characterized by morphological and molecular techniques, and the histopathology of the skin of the outer ear canal is described.     

Evaluation on masks with exhaust valves and with exhaust holes from physiological and subjective responses

The purpose of this study was to compare the effects of wearing different kinds of masks on the ear canal temperature, heart rate, clothing microclimate, and subjective perception of discomfort. Ten subjects performed intermittent exercise on a treadmill while wearing the protective masks in a climatic chamber controlled at an air temperature of 25 degrees C and a relative humidity of 70%. Two types of mask-mask A, with exhaust valves and mask B, with exhaust holes-were used in the study. The results of this study indicated: (1) The subjects had a tendency toward lower maximum heart rate when wearing mask A than when wearing mask B. (2) Temperatures and absolute humidities (the outer surface of mask, the microclimate inside the mask, the chest wall skin and microclimate) of mask A were significantly lower than those of mask B. (3) The ear canal temperature increased significantly in mask B as compared to that in mask A. (4) The ear canal temperature showed significant augmentation along with increased temperature and humidity inside the mask microclimate. The mask microclimate temperature also affected significantly the chest microclimate temperature. (5) Mask A was rated significantly lower for perception of humidity, heat, breath resistance, tightness, unfitness, odor, fatigue, and offered less overall discomfort than mask B. (6) Subjective preference for mask A was higher. (7) The ratings of subjective overall discomfort showed significant augmentation along with increased wetness and fatigue. We discuss how the ventilation properties of masks A and B induce significantly different temperature and humidity in the microclimates of the masks and the heat loss of the body, which have profound influences on heart rate, thermal stress, and subjective perception of discomfort.     

Study of middle ear disease using tympanometry in general practice.

Tympanometry was used to provide evidence of middle ear effusions in a prospective study of middle ear disease in 264 children aged 3 months to 6 years in general practice. Adequate measurements on both ears were obtained in 220 children, of whom 68 (31%) had evidence of middle ear effusion in one ear (29 children) or both ears (39 children) at entry to the study. In 28 (42%) of the 68 children persistence of the tympanometric findings was recorded for at least three months. Children of European descent were more likely to have evidence of middle ear effusion at the initial examination compared with African and West Indian children, as were those children whose siblings had a positive history of otitis media compared with those whose siblings had no such history. Children under 3 years were more likely to have evidence of an effusion than older children. Middle ear effusion as shown by tympanometry was not associated with a previous history of otitis media in the child but was associated with recent symptoms of respiratory infection or otalgia. A previous consultation for otitis media was, however, strongly associated with a greater likelihood of a consultation for otitis media during the follow up period. Comparing evidence of effusion by tympanometry with that by pneumatic otoscopy showed that using the appearance of the eardrum alone the sensitivity of otoscopy was 55%; the addition of mobility improved the sensitivity to 76% with little reduction in specificity. Further studies on populations using tympanometry are needed to determine the natural history, aetiology, and indications for referring children with middle ear effusion.     

Middle-ear dynamics before and after ossicular replacement

The mechanism of hearing involves conduction of mechanical vibrations along the ossicular chain to the inner ear. An acoustic wave is collected and transformed as it passes down the ear canal and impacts on the tympanic membrane (ear drum). The drum is connected to the inner-ear by three ossicle bones (malleus, incus, and stapes) in a complex arrangement, which serves to further transform the mechanical vibration before it reaches the cochlea of the inner ear. What is the mechanical function of the ossicular chain, and what are the biomechanical consequences of surgical reconstruction with prostheses? To answer these questions, a three-dimensional finite element model of the outer ear canal and middle ear was generated. The dynamical behaviour was predicted for the normal ear, and an ear reconstructed with partial and total ossicular replacement prostheses. For the normal ear, stapes amplitudes of 1x10(-8) m at low frequencies decrease to 4x10(-10)m at approximately 3kHz with several resonance peeks in between, most significantly at approximately 1kHz. Thereafter a further resonance is predicted at 4kHz associated with the ear canal. The behaviour is changed fundamentally by adding a prosthesis; the partial replacement increases the vibratory coupling of the drum and the stapes compared to the normal ear whereas the total replacement does the opposite, and is predicted to have the disadvantage of bringing several new resonances of the ossicular chain into the hearing range. It is hypothesised that the function of the malleus-incus-stapes arrangement is to link the drum to the oval window with the flexibility required for impedance matching but the rigidity to prevent unconstrainable resonances from occurring in the hearing range. If this is true, then the structural stiffness of ossicular chain is the critical design variable for middle-ear replacement prostheses.     

Functional morphology of the ear in fossorial rodents, Microtus arvalis and Arvicola terrestris

Functionally relevant features and parameters of the outer, middle, and inner ear were studied morphologically and morphometrically in two species of voles, smaller Microtus arvalis and larger Arvicola terrestris. The findings in these fossorial (i.e., burrowing) rodents with components of surface activity were compared with respective findings reported for taxonomically related muroid rodents representing the same size classes but different eco-morphotypes: obligate subterranean rodents (Ellobius talpinus and Spalax ehrenbergi superspecies) and generalized rodents (Mus domesticus and Rattus norvegicus). The ear in voles was characterized by traits reported for subterranean rodents. The eardrum was round, without a distinct pars flaccida, and had an area of 5.4 mm2 in M. arvalis and 9 mm2 in A. terrestris. The middle ear exhibited reduced goniale, enlarged incus nearly parallel to the manubrium of the malleus. The malleus-incus lever ratio amounted to 2.1 (M. arvalis) and 2.0 (A. terrestris). The malleus-incus complex weighed about 0.8 mg in both vole species. The stapedial footplate had an area of 0.3 mm2 in M. arvalis and 0.4 mm2 in A. terrestris. The cochlea had 2.3 coils in both vole species; the basilar membrane was 8.5 mm and 10.5 mm long in M. arvalis and A. terrestris, respectively. There were on average 1,030 (M. arvalis) and 1,220 (A. terrestris) inner hair cells, and 3,760 (M. arvalis) and 4,250 (A. terrestris) outer hair cells in the organ of Corti. In quantitative terms, all these (as well as some further) traits and parameters were intermediate (related to body size) between those reported for generalized rodents on the one hand and subterranean ones on the other. The sound transmission system of the ear seems to be best tuned to frequencies of about 8-16 kHz with a high-frequency cut-off at about 50-60 kHz. The ear of A. terrestris seems to be tuned to somewhat lower frequencies than that in M. arvalis. In this aspect as well as regarding hearing sensitivity (as judged from the mechanical transmission parameters), voles can be considered intermediate not only in their lifestyle but also in their hearing abilities between the subterranean rodents (mole-vole and blind mole-rat) and the surface dwellers (house mouse and Norway rat).