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At least 1,135 records · Page 63Linked to original sources
PubMed2005

Fast adaptation in vestibular hair cells requires myosin-1c activity.

In sensory hair cells of the inner ear, mechanical amplification of small stimuli requires fast adaptation, the rapid closing of mechanically activated transduction channels. In frog and mouse vestibular hair cells, we found that the rate of fast adaptation depends on both channel opening and stimulus size and that it is modeled well as a release of a mechanical element in series with the transduction apparatus. To determine whether myosin-1c molecules of the adaptation motor are responsible for the release, we introduced the Y61G mutation into the Myo1c locus and generated mice homozygous for this sensitized allele. Measuring transduction and adaptation in the presence of NMB-ADP, an allele-specific inhibitor, we found that the inhibitor not only blocked slow adaptation, as demonstrated previously in transgenic mice, but also inhibited fast adaptation. These results suggest that mechanical activity of myosin-1c is required for fast adaptation in vestibular hair cells.

Adaptation, Physiological↗
PubMed2002

Imaging the intact guinea pig tympanic bulla by orthogonal-plane fluorescence optical sectioning microscopy.

Orthogonal-plane fluorescence optical sectioning (OPFOS) microscopy was developed for the purpose of making quantitative measurements of the intact mammalian cochlea and to facilitate 3D reconstructions of complex features. A new version of this imaging apparatus was built with a specimen chamber designed to accommodate samples as large as the intact guinea pig bulla. This method left the cochlear connections with the vestibular system and with the ossicles of the middle ear undisturbed, providing views within the cochlea with no breaches of its structural integrity. Since the features within the bulla were not physically touched during the preparation process, the risk of damage was minimized, and were imaged in relatively pristine condition with spatial resolution to 16 microm. A description of the imaging method and specimen preparation procedure is presented, as are images of features from the cochlea, ossicles, and vestibular system.

Animals↗
PubMedDate not supplied

Moving sound sources: techniques and applications.

A stimulating device for the application of moving acoustic signals of varying form and velocity is described. The apparatus functions on the principle of intensity stereophony and permits continuous smooth sound movements in a vast range of different forms and frequencies. Furthermore, simultaneous application of vestibular and optokinetic stimuli is possible. Cortically evoked potentials, voluntary and involuntary eye movements, and influences upon body sway from moving acoustic signals are offered as examples for applicability.

Acoustic Stimulation↗
PubMed1995

Cytological changes related to maturation of the organ of Corti and opening of Corti's tunnel.

Maturation of the organ of Corti in the gerbil was analyzed between 2 and 16 days after birth (DAB) by electron microscopy and immunostaining for beta-tubulin. At 2 DAB, the organ of Corti consisted of stratified epithelium bearing immature sensory hair cells (HCs) and supporting cells. Maturation of OHCs and Deiters cells progressed in a medial-to-lateral direction and cytoskeletal development in inner pillar cells preceded that in outer pillar cells at the single location studied along the frequency-place map. Pillar cell differentiation progressed through a unique stage characterized by the appearance and stratification of structural features apparently concerned with opening of Corti's tunnel and subsequently showed other structural changes related to maturity toward the adult form. Development of the microtubule cytoskeleton occurred first in the cell's apex and proceeded basally. Ruffling of a middle region of the cell surface by microvilli appeared to promote separation between inner and outer pillar cells and initiate tunnel opening at 4 DAB. Proliferation of distended cisternae of granular reticulum evidenced proteinaceous secretion by these cells between 4 and 8 DAB. Subsequent tunnel expansion at about 14 DAB coincided with appearance in outer pillar cells of tubulocisternal endoplasmic reticulum and associated Golgi complexes that are thought to mediate fluid and ion secretion. Sixteen days postnatally after disappearance of granular and tubulocisternal reticula and Golgi complexes and at the time of clearing of tunnel fluid, lysosomes interpreted as mediating catabolism of endocytosed protein congregated beneath the apical and apicolateral plasmalemmae of inner pillar cells. As with pillar cells, development of the microtubule system in Deiters cells proceeded from the cell's apex to base. Following differentiation of their microtubule system by 8 DAB, Deiters cells showed expansion of Golgi cisternae between 10 and 15 DAB and development of tubulocisternal endoplasmic reticulum at 15 DAB. Hair cells possessed abundant, distinctively large mitochondria from 4 to 10 DAB. The subsurface cisternae matured earlier in medial as opposed to lateral outer hair cells. Vesicles budding from underlying cisternae appeared associated with development of subsurface cisternae and at 16 DAB were still observed in third row but not in more mature first row HCs.

Animals↗
PubMed1994

Ultrastructure of the epithelial cells of the endolymphatic duct in the rat.

The ultrastructure of the epithelial cells of the endolymphatic duct in the rat is described, following vascular perfusion-fixation of live, anaesthetised and artificially respirated animals. The animals were fixed by means of a pressure feed-back controlled peristaltic pump and an isotonic perfusate-fixative containing glutaraldehyde and Dextran. The endolymphatic duct was isolated by microdissection after the perfusion-fixation, to omit the step of a demineralization procedure. The proximal, intermediate and juxta-saccular parts of the endolymphatic duct were embedded, sectioned and studied separately in the electron microscope. Postfixation in a solution containing OsO4 and potassium ferricyanide revealed a well-developed tubulo-cisternal endoplasmic reticulum (TER), not previously described. Serial sectioning and computerized three-dimensional reconstruction demonstrated a continuity of the TER through the cell from subsurface cisterns abutting on the apical cell membrane to subsurface cisterns abutting on the basolateral cell membrane. The TER resembles that found in solute transporting epithelia, e.g., renal proximal tubule, gall bladder, small intestine and choroid plexus. A fluid resorptive capacity of the epithelial cells of the endolymphatic duct is compatible with the fine structure revealed in the present study. Epithelial cells in the juxta-saccular part of the duct display morphological indications of a secretory activity; furthermore, multivesicular bodies were observed in the epithelial cells throughout the endolymphatic duct.

Animals↗
PubMed1991

Prediction of space motion sickness susceptibility by disconjugate eye torsion in parabolic flight.

The hypothesis of asymmetric otolith function asserts that physiological or anatomical differences in the two sides of the bilateral gravity-sensing otolith apparatus of the inner ear may be well compensated on Earth, but when exposed to novel gravitational states, the prior compensatory stratagems may be ineffective, leading to unstable vestibular responses and causing the phenomenon of space motion sickness. To investigate this hypothesis, spontaneous eye torsion, a reflex governed by the otolith organs, was examined in the upright position during the hypo- and hypergravity of parabolic flight aboard NASA's KC-135 aircraft in nine former astronauts whose history of space motion sickness was revealed after data analysis had been completed. Results showed that astronauts who had been sick in space had significantly higher scores of disconjugate eye torsion in parabolic flight, and that their responses were consistently different in 1.8 G relative to 0 G compared to astronauts who had not been sick in space. In 1 G, there were no differences in disconjugate eye torsion between the subjects. The results support the asymmetry hypothesis and offer a possible predictive test of space motion sickness.

Disease Susceptibility↗
PubMed1989

[Cooperation and substitution of the saccadic system and the reflexes of vestibular origin: should the "reflex" concept be revised?].

Neuronal mechanisms of production of ocular saccadic movements are discussed, together with stabilizing movements of vestibular origin, and descriptions given of several neuronal elements constituting the tecto-reticulo-spinal system, the generator of horizontal saccadic movements in the brain stem, the vestibulo-ocular pathway, etc... Analysis of these pathways and of the signals travelling through them suggests that the overall apparatus is not constituted of isolated reflex modules but acts as a true functional unit for cooperation between orientation and stabilization mechanisms. In addition, coordination of synergies between eye and head movements appear to be based on the activity of clearly identifiable neurons. This neuronal implementation of the concept of synergy is completed further by a remarkable functional flexibility. The latter allows substitution by the brain, for example, fo saccades instead of vestibular reflex movements when the latter are deficient because of lesions or disturbances in the coherence of sensory information. The principal conclusion reached is that cognitive factors, which imply representations of body movements in space activated as a function of the subject's goals, must be considered when ocular movement, and gaze control is described.

Animals↗
PubMed2001

Herpes simplex virus in the vestibular ganglion and the geniculate ganglion-role of loose myelin.

This study presents the first direct evidence for herpes simplex virus type 1 (HSV-1) infection in the neurons of the vestibular ganglion. Although many investigators have reported electron microscopic evidence of HSV-1 infection in sensory ganglia, HSV-1 infection in the vestibular ganglion has not been described. Vestibular ganglion neurons have a unique structure, with a loose myelin sheath instead of the satellite cell sheath that is seen in other ganglia. This loose myelin is slightly different from compact myelin which is known as too tight for HSV-1 to penetrate. The role of loose myelin in terms of HSV-1 infection is completely unknown. Therefore, in an attempt to evaluate the role of loose myelin in HSV-1 infection, we looked for HSV-1 particles, or any effects mediated by HSV-1, in the vestibular ganglion as compared with the geniculate ganglion. At the light microscopic level, some neurons with vacuolar changes were observed, mainly in the distal portion of the vestibular ganglion where the communicating branch from the geniculate ganglion enters. At the electron microscopic level, vacuoles, dilated rough endoplasmic reticulum and Golgi vesicles occupied by virus were observed in both ganglia neurons. In contrast, viral infections in Schwann and satellite cells were observed only in the geniculate ganglion, but not in the vestibular ganglion. These results suggest that loose myelin is an important barrier to HSV-1 infection, and it must play an important role in the prevention of viral spread from infected neurons to other cells.

Animals↗
PubMedDate not supplied

[Effect of angular accelerations on the sensory and motor components of fixation eye movements].

The effect of angular accelerations on the eye fixation function and concomitant sensory reactions was investigated under special conditions. An illusion of target distortion towards the rapid component of the vestibular nystagmus developed in these situations. Changes in the eye fixation movements and "sensation of target" were coordinated and depended on the direction of the vestibular nystagmus. The findings indicate that during an exposure to angular accelerations the stability of target perceptions is disturbed and objectively recorded errors of its fixation by the optic apparatus are made.

Acceleration↗
PubMed1994

The extent of adaptation in bullfrog saccular hair cells.

Positive deflection of the sensory hair bundle of a vertebrate hair cell opens transduction channels to depolarize the cell. In bullfrog saccular hair cells, there is a subsequent adaptation process, whereby the proportion of transduction channels that are open, and thus the receptor current, declines toward the resting value. This occurs because the sensitivity curve, relating open probability to bundle deflection, shifts along the deflection axis in response to bundle deflections, in a manner consistent with a relaxation of mechanical tension on transduction channels. In this study we determined the extent of adaptation, measured as the shift of the sensitivity curve following deflection of the hair bundle. The shift was determined both by comparison of the receptor current in the adapted state to the resting sensitivity curve, and by comparison of pre- and postadapted sensitivity curves. The adaptive shift approached steady state with a time constant of 20-30 msec, and was at steady state within 150 msec. For all positive and for small negative deflections, both methods showed a shift that was approximately 80% of the deflection. For larger negative deflections, the shift reached a fixed limit that was 100-500 nm negative to the freestanding bundle position. The limited extent of adaptation confers a time-dependent sensitivity: the cell has an instantaneous or phasic sensitivity curve that is steep, and steady-state or tonic sensitivity curve that is about five times broader. It also suggests the existence of two additional structural elements within the transduction apparatus. A revised quantitative theory accommodates these elements.

Adaptation, Physiological↗
PubMed1997

Injury-stimulated neurogenesis in sensory systems.

Injury-induced repair of sensory cells does occur in mammals in the sense that partial replacement can transpire in sensory ganglion cells and in visual photoreceptors. In the somatosensory system, functional replacement of the peripheral processes of sensory cells can occur when the cell body is not severely damaged. In the visual system, the outer segments of photoreceptors are replaced under physiologic conditions, but complete replacement after injury occurs only in cold-blooded animals. In the olfactory system, complete replacement of sensory nerve cells has evolved as the means by which animals, including mammals, can retain olfactory function with a receptor apparatus that is highly vulnerable to injury. In the taste system, the sensory cells are also disposable and are completely replaced within less than 2 weeks. In the auditory and vestibular systems, replacement is not physiologic and when it does occur, appears to be injury-induced.

Animals↗
PubMedDate not supplied

Caloric responses after horizontal canal inactivation.

Horizontal eye movements in squirrel monkeys were recorded in response to ice-water caloric stimuli before and after horizontal canal (HC) inactivation, achieved by a plugging procedure. Calorics were presented with the subjects supine and prone, and the maximum slow phase eye velocity (SPEV) of the induced nystagmus was assessed. SPEV responses from normal ears were always directed toward the stimulated side when the monkeys were supine, and toward the opposite side when they were prone. Supine responses were always greater than prone ones. After HC-plug, which abolishes the canal's mechanical response to rotatory or convection current stimulation, small SPEV responses were routinely observed. However, they were always directed toward the stimulated side, regardless of head orientation. The results are consistent with the notion that the normal caloric response is composed of the sum of a convention current component which is dependent upon head orientation, a smaller position-dependent component of unclear origin, and a direct temperature effect on the canal's sensory apparatus which is independent of head orientation.

Animals↗