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At least 1,117 records · Page 62Linked to original sources
PubMed1998

Magnetic resonance imaging of the inner ear in patients with idiopathic sudden sensorineural hearing loss.

Although gadolinium-enhanced magnetic resonance imaging (Gd-MRI) has been used to indicate the presence of a subclinical labyrinthitis in patients with idiopathic sudden sensorineural hearing loss (ISSHL), its sensitivity in daily clinical practice is unknown. We describe Gd-MRI findings in 27 ISSHL patients taking part in a prospective multicenter clinical trial. MRI findings were related to the severity of the hearing loss, vestibular involvement and the time interval between the occurrence of ISSHL and imaging. Pathological enhancement of the cochlea indicating a labyrinthitis was found in one patient with ISSHL. In 26 cases, no pathological enhancement could be established. Study results indicate that the present sensitivity of Gd-MRI is low for detecting subclinical viral labyrinthitis in patients with ISSHL. To improve the sensitivity of MRI in ISSHL, we recommend that imaging is performed as early as possible, preferably before treatment is started.

Adolescent↗
PubMed2000

Development of the gerbil inner ear observed in the hemicochlea.

A frequency-dependent change in hearing sensitivity occurs during maturation in the basal gerbil cochlea. This change takes place during the first week after the onset of hearing. It has been argued that the mass of a given cochlear segment decreases during development and thus increases the best frequency. Changes in mass during cochlear maturation have been estimated previously by measuring the changes in cochlear dimensions. Fixed, dehydrated, embedded, or sputter-coated tissues were used in such work. However, dehydration of the tissue, a part of most histological techniques, results in severe distortion of some aspects of cochlear morphology. The present experiments, using a novel preparation, the hemicochlea, show that hydrated structures, such as the tectorial membrane and the basilar membrane hyaline matrix, are up to 100% larger than estimated previous studies. Therefore, the hemicochlea was used to study the development of cochlear morphology in the gerbil between the day of birth and postnatal day 19. We used no protocols that would have resulted in severe distortion of cochlear elements. Consequently, a detailed study of cochlear morphology yields several measures that differ from previously published data. Our experiments confirm growth patterns of the cochlea that include a period of remarkably rapid change between postnatal day 6 and 8. The accelerated growth starts in the middle of the cochlea and progresses toward the base and the apex. In particular, the increase in height of Deiters' cells dominated the change, "pushing" the tectorial membrane toward scala vestibuli. This resulted in a shape change of the tectorial membrane and the organ of Corti. The tectorial membrane was properly extended above the outer hair cells by postnatal day 12. This time coincides with the onset of hearing. The basilar membrane hyaline matrix increased in thickness, whereas the multilayered tympanic cover layer cells decreased to a single band of cells by postnatal day 19. Before and after the period of rapid growth, the observed gross morphological changes are rather small. It is unlikely that dimensional changes of cochlear structures between postnatal days 12 and 19 contribute significantly in the remapping of the frequency-place code in the base of the cochlea. Instead, structural changes affecting the stiffness of the cochlear partition might be responsible for the shift in best frequency.

Animals↗
PubMed2002

Topological and developmental gradients of calbindin expression in the chick's inner ear.

Mobile intracellular calcium buffers play an important role in regulating calcium flux into mechanosensory hair cells and calbindin D-28k is expressed at high levels in the chick's basilar papilla. We have used RT-PCR, in situ hybridization, and immunohistology to demonstrate that calbindin expression varies systematically according to hair cell position and developmental age. RT-PCR using microdissected quarters of the posthatch basilar papilla showed that mRNA levels were lowest in the (low frequency) apex and higher in basal quadrants. In situ hybridization revealed calbindin mRNA in posthatch hair cells and supporting cells, with more intense labeling of hair cells from basal (high frequency) positions. A similar topology was obtained with calbindin antibodies. Neither calbindin riboprobe nor calbindin antibody labeled cochlear neurons. In contrast, a subset of large vestibular neurons and their calyciform endings onto Type I vestibu lar hair cells were strongly labeled by the calbindin antibody, while vestibular hair cells were negative for calbindin immunoreactivity. Likewise, calbindin in situ hybridization was negative for vestibular hair cells but positive in a subset of larger vestibular neurons. Calbindin mRNA was detected in hair cells of the basal half of the papilla at embryonic day 10 (E10) and calbindin immunoreactivity was detected at E12. Hair cells in the apical half of the papilla had equivalent calbindin expression two days later. Immunoreactivity appeared in abneural supporting cells days later than in hair cells, and not until E20 in neurally located supporting cells. These results demonstrate that calbindin message and protein levels are greater in high-frequency hair cells. This "tonotopic" gradient may result from the stabilization of a basal-to-apical developmental gradient and could be related at least in part to calcium channel expression along this axis.

Aging↗
PubMed2002

Relationship between inner-ear fluid pressure and semicircular canal afferent nerve discharge.

The present study was designed to determine (1) the transcupular fluid pressure (deltaP) generated across the semicircular canal cupula in response to sinusoidal head rotation, (2) the translabyrinthine dilational pressure (P0) generated across the membranous labyrinth in response to an increase in endolymph fluid volume (hydrops), (3) afferent nerve discharge patterns generated by these distinct pressure stimuli and, (4) threshold values of deltaP and P0 required to elicit afferent neural responses. The experimental model was the oyster toadfish, Opsanus tau. Micromechanical indentation of the horizontal canal (HC) duct and utricular vestibule was used to simulate sinusoidal head rotation and fluid volume injection. Single-unit neural spike trains and endolymph pressure within the ampulla, on both sides of the cupula, were recorded simultaneously. deltaP averaged 0.013 Pa per 1 degrees/s of sinusoidal angular head velocity and P0 averaged 0.2 Pa per 1 nL of endolymph volume injection. The most responsive afferents had a threshold sensitivity to deltaP of 10(-3) Pa and to P0 of 5 x 10(-2) Pa based on a discharge modulation criterion of 1 impulse/s per cycle for 2 Hz pressure stimuli. Neural sensitivity to AP was expected on the basis of transverse cupular and hair bundle deflections. Analysis of mechanics of the end organ, neuronal projections into the crista, and individual neural firing patterns indicates that P0 sensitivity resulted from pressure-induced distension of the ampulla that led to a nonuniform cupular deformation pattern and hair bundle deflections. This explanation is consistent with predictions of a finite element model of the end organ. Results have implications regarding the role of deltaP in angular motion transduction and the role of P0 under transient hydropic conditions.

Action Potentials↗
PubMed1981

Evolution of inner-ear auditory apparatus in the frog.

The morphology of typical anuran amphibian papillae is thoroughly distinct from that of urodeles. However, the morphological discontinuity lies not between the frogs and the salamanders, but between the most primitive living frog, Ascaphus truei, and the more derived anurans. Three features distinguishing the papillae of more derived anurans from that of Ascaphus apparently provide peripheral tonotopy in the former. The adaptive significance of a fourth feature, kinociliary bulbs, is not clear.

Animals↗
PubMed1982

The origin of efferent fibers to the inner ear in a turtle (Terrapene ornata). A horseradish peroxidase study.

The origin of efferent acoustic and vestibular fibers was determined in the turtle Terrapene ornata. After injection of an aqueous solution of horseradish peroxidase (HRP) into either the cochlear duct or into the ampullae of the horizontal and anterior semicircular canals, neurons in the medullary reticular formation were labeled by the reaction production of retrogradely transported HRP. These neurons were located bilaterally in the medial reticular nucleus. The majority were found ipsilateral to the injection site. There was no demonstrable difference in size, shape, and labeling pattern between efferent acoustic and efferent vestibular neurons. The crossed component component of efferent acoustic fibers, however, was rather sparsely developed.

Animals↗
PubMed1981

The origin of centrifugal fibers to the inner ear in Caiman crocodilus. A horseradish peroxidase study.

The origin of acoustic and vestibular efferent fibers was investigated in Caiman crocodilus. After injection of horseradish peroxidase (HRP) into the cochlear duct or into the ampullae of the horizontal and anterior semi-circular canals, cells in the medulla oblongata exhibited retrogradely transported HRP reaction product. Efferent vestibular fibers were found in the medial reticular nucleus, at the level of the oliva superior. There were more labeled neurons ipsilateral to the injection site. Efferent acoustic neurons were found close to or inside the rostroventral division of the oliva superior. They spread out into the medial reticular nucleus bilaterally, More labeled efferent acoustic neurons occurred contralateral to the injection site.

Alligators and Crocodiles↗
PubMed1984

Hair cell orientation and a possible intraepithelial growth of the macula lagenae in the inner ear of the European eel.

The hair cell orientation of the macula lagenae in eels at three different stages of life was examined with the light microscope. Part of the posterior periphery of all three stages was occupied by a few rows of sensory cells having their kinocilium pointing in a direction opposite to the direction of the adjacent sensory cells. The width of this peripheral belt remained the same at all three stages of life, in spite of a considerable growth of the sensory epithelium, and the belt was always confined to the margin. This indicates an intraepithelial growth of at least part of the neuroepithelium of the lagenar macula of the European eel.

Acoustic Maculae↗