Toadfish saccular hair cell bundle has a preferred orientation in the otolithic membrane

The macula of the saccule of the toadfish, Opsanus tau, is covered by an otolithic membrane containing sockets into which the stereocilia and kinocilia of the hair cells project. We have found that the hair cell bundle has a distinct eccentric orientation within this space of the otolithic socket. Although the sockets of the otolithic membrane are irregular in shape, all kinocilia are located closet to the same border of the sockets. Since the socket is a fluid or gel filled space through which the hair cell bundle moves, this orientation may have some significance for transduction since it leaves a larger space in the on direction for stereociliary movement.     

Conservative management of Tumarkin's otolithic crisis

Tumarkin's otolithic crisis (TOC), characterized by a sudden drop attack without accompanying loss of consciousness, vertigo or autonomic signs, is a rare phenomenon thought to be of peripheral origin and associated with late-stage Meniere's disease. The purpose of this paper is to describe the clinical course of TOC in our series; to discuss the relationship between TOC and the onset and symptomatology of pre-existent Meniere's disease, and to determine the management of patients with TOC.     

Computational models of hair cell bundle mechanics: II. Simplified bundle models

Simplified versions of hair cell bundles are mechanically modeled. The influence of various geometric and material combinations on bundle stiffness, link tensions and deformation shape are examined. Three models are analyzed within this paper: two stereocilia connected by one link, two stereocilia connected by a biologically realistic set of links, and a column of stereocilia connected by realistic links. Stereocilia are modeled using a distributed parameter model [J. Biomech. Eng. 122, 44]. Some fundamental rules for linking bundles emerge from these tests: (1) Links must have a threshold stiffness value for the bundle to deform as a whole. Beyond this value, the stereocilia are perfectly linked and variations in link stiffness do not significantly effect the bundle stiffness or link tension. (2) Decreasing the relative heights of successive stereocilia may increase link tension while decreasing bundle stiffness. (3) When lateral links exist, the top most lateral links carry the majority of tension. Lower links in single column model appear mechanically insignificant. (4) Extending the length of the bundle in a column does not increase the stiffness once the column reaches a certain length.     

Amplitude range analysis of otolithic organ responses

Benign paroxysmal positioning vertigo is easily diagnosed with the Dix-Hallpike maneuver. It is an ideal clinical condition in which to study the electrical response of the inner ear with electrocochleography techniques. Responses can be recorded during head tilt in roll and in pitch. With this technique we found that the amplitude range and scaling behavior of recorded raw data for the baseline resting position versus the stimulus position was statistically different in both patients and normal subjects. This can be demonstrated in the visual format of box plots. This technique promises to become a valuable addition to electrical examination techniques of the inner ear.     

Ultrastructural changes of statoconia after segmentation of the otolithic membrane

The chick vestibule transformed from a homogeneous epithelial layer at day 2 (stage 15) into a pseudo-stratified epithelial layer at day 4 (stage 24). The apical columnal appearance of sensory cells was evident by day 6 (stage 29). In the supporting cells of the saccule and utricle large rough endoplasmic reticulum cisterns filled with material similar to the primitive organic matrix. Fibrillar material of the otolithic membrane remained attached to the supporting cells and accumulated over the saccule and utricle. The primitive otolithic membrane acquired stress-like lines and statoconial units emerged from the upper surface without a central core. Statoconia thickened at the periphery and a central core formed. Calcium was deposited between the fibrils of older statoconia which were located on top of the segmenting membrane. DIAMOX inhibited statoconia formation and/or prevented calcium and the matrix from associating. Large statoconia (100-200 microns diameter) were formed in embryos injected with this carbonic anhydrase inhibitor. Gel electrophoresis of immature statoconial complexes yielded at least 5 major protein bands between 25 and 210 kDa. Ouabain-sensitive potassium-dependent p-nitrophenylphosphatase activity was demonstrated in the endolymphatic sac of newly hatched chicks.     

Eye movements induced by lateral tilt and testing of otolithic function

In the last few years, we have studied ocular reflexes caused by tilting stimulations in test subjects placed in an upright sitting position on a chair apparatus which tilts continuously. In healthy persons, a weak nystagmus can be observed, and involves a nystagmus of minor amplitude and showing a small number of beats. The actual incidence of nystagmus in the younger group was minimal, but it tended to increase with age. This occurrence is considered to be due to age-related degeneration of the otolithic organ. Patients with vertigo and/or dizziness clearly develop nystagmus. These responses are classified as follows: type I is of fixed direction; type II is of changed direction; and type III is a combination of the first and second types. Among the peripheral vestibular disorders, particularly involving those patients with benign paroxysmal positional vertigo, a nystagmus of changed direction was found. This type was rarely seen in patients with other vestibular disorders, but was a common occurrence in healthy individuals who readily experienced motion sickness. These observations have led us to conclude that patients with benign paroxysmal positional vertigo have definite reactions which are similar to those of individuals with motion sickness, and that such depends on the susceptibility of the otolithic organs.     

Human otolithic function before and after unilateral vestibular neurectomy.

One index of otolith function is the so-called oculogravic "illusion" that during centrifugal stimulation a small luminous bar, fixed with respect to the observer, appears to be roll-tilted by the same amount that the observer feels to be roll-tilted. Many patients undergoing therapeutic unilateral vestibular nerve section show the illusion symmetrically for left and right roll-tilts prior to the operation, but at testing one week after vestibular nerve section show a large asymmetry: they perceive the illusion when the resultant force is directed toward their intact ear, but they perceive a much reduced illusion when the force is directed toward their operated ear. This roll-tilt perceptual response asymmetry appears similar to the asymmetrical horizontal semicircular canal vestibulo-ocular responses for symmetrical but opposite head accelerations that these same patients exhibit for values of head angular accelerations in the natural range (Ewald's second law), and the present paper suggests that a version of Ewald's second law may apply to the otolithic system: specifically, that there is a response asymmetry for linear accelerations. Anatomical and physiological evidence concerning such an otolithic asymmetry is reviewed.     

Eye movements induced by lateral tilt and testing of otolithic function

Summary In the last few years, we have studied ocular reflexes caused by tilting stimulations in test subjects placed in an upright sitting position on a chair apparatus which tilts continuously. In healthy persons, a weak nystagmus can be observed, and involves a nystagmus of minor amplitude and showing a small number of beats. The actual incidence of nystagmus in the younger group was minimal, but it tended to increase with age. This occurrence is considered to be due to age-related degeneration of the otolithic organ. Patients with vertigo and/or dizziness clearly develop nystagmus. These responses are classified as follows: type I is of fixed direction; type II is of changed direction; and type III is a combination of the first and second types. Among the peripheral vestibular disorders, particularly involving those patients with benign paroxysmal positional vertigo, a nystagmus of changed direction was found. This type was rarely seen in patients with other vestibular disorders, but was a common occurrence in healthy individuals who readily experienced motion sickness. These observations have led us to conclude that patients with benign paroxysmal positional vertigo have definite reactions which are similar to those of individuals with motion sickness, and that such depends on the susceptibility of the otolithic organs.     

The vertical component in a caloric nystagmus and the existence of a second phase of the nystagmus--the possibility of canal otolithic interaction in normal subjects]

To clarify the existence of the vertical component during a caloric nystagmus and the existence of a second phase of the nystagmus, 194 induced incidents of a caloric nystagmus in 29 normal subjects have been analyzed. Each nystagmus episode was recorded by using ENG and an infra-red video camera. The caloric stimuli were given by pouring 5 ml of water at 20 degrees C into the ear at an ear-up position. After irrigation, each subject then assumed a supine or a prone position, with the head bent 30 degrees forward in either position. All recordings contained vertical components that depended on the supine or prone head position and not on the side of the stimulated ear, i.e., an up-beating nystagmus resulted in the supine position and a down-beating nystagmus in the prone position. Further, the vertical component was far stronger in the prone position. In contrast, the horizontal component had larger velocities and was of longer duration in the supine position than in the prone position. When the first phase of the caloric nystagmus ended, the body position was changed 90 degrees, i.e., to a sitting position or a right-ear-down or left-ear-down position. All trials showed a horizontal component during the secondary phase when the head assumed the sitting position. As for the ear-down positions, only when the irrigated ear was moved upwards from the prone position during the secondary phase, an up-beating vertical nystagmus resulted in almost all the trials. These findings suggest that a caloric nystagmus may originate not only from the lateral semicircular canal but also from the vertical canals, and the second phase of a caloric nystagmus may be strongly influenced by the otolithic organs.     

Proteins of the gelatinous layer of the trout saccular otolithic membrane.

Although the otolithic membrane is thought to play an important role in the stimulation of vestibular hair cells, little is known about its chemical composition. We analyzed proteins of the gelatinous layer of this structure from the trout saccule, a probable organ of hearing in fish, by SDS-polyacrylamide gel electrophoresis. A relatively small number of major proteins were detected in homogenates of the 'membrane' layer, with apparent molecular weights ranging from 35 to greater than 300 kDa. Six bands, with molecular weights of 35, 43, 65, 94, 100, and 160 kDa, were particularly prominent. Periodic acid-Schiff (PAS) staining indicated that the 43, 94, 100, and 160 kDa bands were glycoproteins. Lectin binding on nitrocellulose blots confirmed the PAS results, and further suggested that the 35 and 65 kDa bands may be glycoproteins. Incubation of blots with human anti-collagen type II antibodies suggested that the 94 kDa band was a component of collagen type II or a related protein.     

Computational models of hair cell bundle mechanics: I. Single stereocilium

A distributed parameter model for describing the response of a stereocilium to an applied force is presented. This model is based on elasticity theory, plus the geometry and material properties of the stereocilium. The stereocilia shaft above the taper is not assumed to be perfectly rigid. It is assumed to be deformable and that two separate mechanisms are involved in its deformation: bending and shear. The influence of each mode of deformation is explored in parametric studies. Results show that the magnitude of tip deflection depends on the shear compliance of the stereocilium material, the degree of base taper, and stereocilium height. Furthermore, the deformation profiles observed experimentally will occur only if there are constraints on the geometry and material properties of the stereocilium.     

Electrostatic interaction between stereocilia: II. Influence on the mechanical properties of the hair bundle

This paper is based on our model [Dolgobrodov et al., 2000. Hear. Res., submitted for publication] in which we examine the significance of the polyanionic surface layers of stereocilia for electrostatic interaction between them. We analyse how electrostatic forces modify the mechanical properties of the sensory hair bundle. Different charge distribution profiles within the glycocalyx are considered. When modelling a typical experiment on bundle stiffness measurements, applying an external force to the tallest row of stereocilia shows that the asymptotic stiffness of the hair bundle for negative displacements is always larger than the asymptotic stiffness for positive displacements. This increase in stiffness is monotonic for even charge distribution and shows local minima when the negative charge is concentrated in a thinner layer within the cell coat. The minima can also originate from the co-operative effect of electrostatic repulsion and inter-ciliary links with non-linear mechanical properties. Existing experimental observations are compared with the predictions of the model. We conclude that the forces of electrostatic interaction between stereocilia may influence the mechanical properties of the hair bundle and, being strongly non-linear, contribute to the non-linear phenomena, which have been recorded from the auditory periphery.     

Motion sickness susceptibility and the utilisation of visual and otolithic information for orientation

Summary Movement of large portions of the visual field can induce a static observer to experience illusory self-motion, changes in perceived orientation and motion sickness. Two experiments were performed to determine whether susceptibility to motion sickness might be related to an inability to ignore misleading visual information for orientation, measured here in terms of the magnitude of the apparent tilt of the vertical induced by rotation of the visual field about the line of sight. Significant and additive effects of sex and motion sickness susceptibility were demonstrated. Females susceptible to motion sickness proved highly inaccurate when attempting to set a line to the vertical with rotation of the background, while males resistant to motion sickness were the most accurate at this task. Two possible explanations are discussed, the first suggesting subclinical intersubject differences in otolithic sensitivity, and the second postulating deficiencies in intersensory integration. Parallels are drawn with the patterns of multisensory coordination for postural orientation seen in children and in patients with benign paroxysmal positional vertigo.