The utility of positron emission tomography in the evaluation of autoimmune hearing loss

OBJECTIVE

To evaluate positron emission tomography as an imaging tool in the diagnosis, evaluation, and management of autoimmune inner ear disease.

BACKGROUND

Autoimmune inner ear disease is a form of cochleovestibular disease associated with variable hearing loss and vertigo for which no reliable diagnostic tests are available.

METHODS

Pilot study of 10 patients with autoimmune inner ear disease and 5 sex-matched and age-matched control subjects without any history of autoimmune inner ear disease, who underwent limited positron emission tomography of the inner ear. Five patients with new or active autoimmune inner ear disease underwent serial positron emission tomography before and after 4 to 6 weeks of a high-dose tapering course of prednisone. The subjects had cranial magnetic resonance imagining, audiometric and vestibular studies, and heat-shock protein (HSP-70) measurements. Reading of the positron emission tomography scans was blinded.

RESULTS

Positron emission tomography was normal in 4 of 5 normal control subjects and abnormal in 1 with normal audiometric and vestibular studies and positive HSP-70. Of patients with established and stable autoimmune inner ear disease, 4 of 5 had no positron emission tomography abnormalities and negative HSP-70, and the one with abnormal positron emission tomography shortly thereafter manifested clinically active disease. Of the 5 patients with active autoimmune inner ear disease monitored serially, 4 had an initial abnormal positron emission tomography in at least one ear, which became normal in all but 1 patient after therapy. HSP-70 correlated with disease activity. Only 1 patient with clinically active autoimmune inner ear disease had a normal positron emission tomography before and after therapy (the HSP-70 was positive before therapy and negative after the therapy).

CONCLUSIONS

Positron emission tomography, especially when combined with HSP-70 determination, may be a useful technique for assessing disease in patients with autoimmune inner ear disease.

The interutricular distance determined from external landmarks

Knowledge of the exact distance between the utricles is important in new vestibular tests, such as the unilateral centrifugation (UC) test for the unilateral examination of the utricles. During this test, subjects are rotated at constant velocity and simultaneously laterally displaced along an interaural axis so that one labyrinth becomes aligned with the axis of rotation. When the axis of rotation crosses precisely through one labyrinth, only the opposite labyrinth is stimulated. To achieve this setup, precise knowledge of the interutricular distance is needed. The purpose of this study is to investigate the correlation between the interutricular distance (IUD), measured on T2-weighted magnetic resonance images, and specific external measures of head dimensions such as distance nasion-inion, intermastoid distance (IMD), distances between the temporomandibular joints and between the lateral margins of the orbits. Data have been collected in a series of 50 subjects (25 men and 25 women). On MR images we found a mean IUD of 7.22 cm (SD = 0.42 cm). There was a strong correlation between the IUD measured on MR images and the intermastoid distance. A linear combination of the IMD, nasion-inion distance and height of the subjects could predict the IUD very satisfactory (R = 0.85, adjusted R2=0.723). We also determined a measure of eccentricity of the vestibular labyrinths. The 95% prediction interval for the asymmetry appeared to be less than 4.3%.

Adaptations of the vestibular system to short and long-term exposures to altered gravity

Long-term space flight creates unique environmental conditions to which the vestibular system must adapt for optimal survival of a given organism. The development and maintenance of vestibular connections are controlled by environmental gravitational stimulation as well as genetically controlled molecular interactions. This paper describes the effects of hypergravity on axonal growth and dendritic morphology, respectively. Two aspects of this vestibular adaptation are examined: (1) How does long-term exposure to hypergravity affect the development of vestibular axons? (2) How does short-term exposure to extremely rapid changes in gravity, such as those that occur during shuttle launch and landing, affect dendrites of the vestibulocerebellar system? To study the effects of longterm exposures to altered gravity, embryonic rats that developed in hypergravity were compared to microgravity-exposed and control rats. Examination of the vestibular projections from epithelia devoted to linear and angular acceleration revealed that the terminal fields segregate differently in rat embryos that gestated in each of the gravitational environments.To study the effects of short-term exposures to altered gravity, mice were exposed briefly to strong vestibular stimuli and the vestibulocerebellum was examined for any resulting morphological changes. My data show that these stimuli cause intense vestibular excitation of cerebellar Purkinje cells, which induce up-regulation of clathrin-mediated endocytosis and other morphological changes that are comparable to those seen in long-term depression. This system provides a basis for studying how the vestibular environment can modify cerebellar function, allowing animals to adapt to new environments.

Histological studies on the vestibular organ of frog embryos and larvae after simulated weightlessness

The ontology of gravity receptors is discussed. As well as phylogenetic aspects of the question, we may ask whether the different gravity receptors in plants and animals derive from the same source; did they evolve from a general sensitivity of the living cell or do they represent parallel inventions. One may also ask whether during ontogeny of the receptor it receives information from gravity or whether the development of function of the organ is an autonomous process. In many cases ontogeny shows traces of phylogeny. Statoliths, e.g. the differentiating statolith membranes of the frog embryo, look somewhat like sedimentational structures. Furthermore the amphibian embryo in its relatively early stages takes up a special position in relation to the direction of gravity. Which mechanism is involved here? The materials studied were frog embryos and larvae which developed within a fast rotating clinostat. The results may help to answer the question as to whether the differentiation of the frog statolith membrane is an autonomous process.

[Diagnostic imaging of peripheral vertigo]

Clinical imaging investigation of vertigo is actually mainly performed using MRI, which offers a detailed analysis of cochieo-vestibular nerve and labyrinth. Computed tomography is reserved to the analysis of bony structures. Several causes of vertigo are described, e.g. tumours, labyrinthitis, malformations, Ménière's disease, otoscierosis, trauma, cholesteatomas and postoperative changes. The interest of imaging is discussed. The necessity to perform paraclinical tests prior to diagnostic imaging to optimise the choice of imaging is emphasized.

Sodium- and potassium-activated ATPase in the mammalian vestibular system

Autoradiographic and cytochemical procedures were employed to determine the cellular distribution of the Na,K-ATPase enzyme in the mammalian vestibular system. A light-microscope survey of vestibular tissues incubated with [(3)H]ouabain shows high densities of ouabain binding sites within the dark cell epithelium (DC) of the ampullae of the semi-circular canals, and to a lesser extent, the DC of the utricular macula. A moderate number of binding sites was found in nerve fibers penetrating the connective tissue beneath the sensory epithelium (SE) of the ampullae and the maculae. A small number of binding sites is distributed in the deep portion of the SE, both in the ampullae and in the maculae. These latter binding sites seem to be associated with nerve terminals and receptor cells. At the ultrastructural level, the vestibular dark cells exhibit extensive basolateral membrane infolding, a morphological hallmark of cells engaged in trans-epithelial ion transport. The cytochemical reaction product is K(+)-dependent, ouabain inhibitable, and is restricted to the basolateral membrane extensions, with little or no product on the luminal membrane. The extent of membrane infolding in dark cells of the utricle is less pronounced than that of the ampullar dark cells and the intensity of the cytochemical reaction appears to correlate with the extent of membrane infolding. The results support the widely held hypothesis that the vestibular dark cells play a role in endolymph production. They also suggest that the vestibular sensory epithelia may be a site of ion exchange.

The vestibular complex in a prosimian primate (Galago senegalensis): morphology and spinovestibular connections

The morphology of, and distribution of spinal afferents to, the vestibular complex of a prosimian primate (lesser bushbaby, Galago senegalensis) were studied using cytoarchitectural, myeloarchitectural and selective silver impregnation methods. The vestibular complex of Galago consists of superior (SVN), lateral (LVN), medial (MVN) and spinal (SpVN) nuclei, each nucleus having cell populations of characteristic size, shape and distribution within its borders. There is morphological and experimental evidence for the existence of subgroups f, 1, x, y and z and a hitherto undescribed subgroup located in dorsomedial portions of the rostral two-thirds of the MVN. Following partial or complete hemisections at cord levels C1-L6 brain stem sections were impregnated according to the method of Fink and Heimer. Preterminal debris is concentrated mainly in subgroups x and z, relatively sparse in adjacent SpVN and moderate to sparse in LVN and MVN following hemisections at upper and mid-cervical levels. Axonal debris is noticeably absent from the MVN after lesions below the C8 spinal level; this indicates that the MVN receives spinal input from cervical levels only. Following lesions at C8 and progressively lower spinal levels, degeneration was found primarily in subgroups x and z and in LVN and SpVN although in lesser amounts; as lesions were placed at progressively lower levels there was a proportionate decrease in the amount of axonal debris found in these respective nuclei. No degeneration was found in SVN following lesions at any spinal level.

Complex vestibular macular anatomical relationships need a synthetic approach

Mammalian vestibular maculae are anatomically organized for complex parallel processing of linear acceleration information. Anatomical findings in rat maculae are provided in order to underscore this complexity, which is little understood functionally. This report emphasizes that a synthetic approach is critical to understanding how maculae function and the kind of information they conduct to the brain.

Squirrel monkeys and space motion sickness

Studies of the vestibular system in squirrel monkeys in consideration of space motion sickness (SMS) or space adaptation syndrome (SAS) were reviewed. First, the phylogenetic position of the squirrel monkey was considered. Then the anatomico-physiological studies of both the peripheral and the central vestibular systems were described, because the vestibular system is crucially important in the genesis of SMS (SAS). In this connection, the ablation studies of labyrinth, semicircular canals, and other SAS-related areas were referred to, and consideration was made for experiments about caloric irrigation of the ear. A hypothetic model was then proposed for the genesis of SAS.

Neuronal feedback between brain and inner ear for growth of otoliths in fish

Previous investigations revealed that fish inner ear otolith growth (concerning otolith size and calcium-incorporation) depends on the amplitude and the direction of gravity, suggesting the existence of a (negative) feedback mechanism. In search for the regulating unit, the vestibular nerve was unilaterally transected in neonate swordtail fish (Xiphophorus helleri) which were subsequently incubated in the calcium-tracer alizarin-complexone. Calcium incorporation ceased on the transected head sides, indicating that calcium uptake is neurally regulated.

[Functional organization of the vestibulospinal system in amphibians]

In experiments on the preparation of a frog perfused brain, using recording of intracellular potentials the vestibulospinal neurons were identified on the basis of excitatory postsynaptic potentials evoked by the stimulation of the ipsilateral vestibular nerve and antidromic activation from the stimulation of the cervical and lumbar enlargements of the spinal cord. The average conduction velocity determined for axons of C neurons was 10.67 m/s and for L neurons 15.84 m/s. The ratio of C and L neurons over the vestibular nuclear complex was very stimular to each other: 52% C neurons and 48% L neurons. The majority of both types of neurons were localized in the lateral vestibular nucleus (58.6%), to the lesser extent in the descending vestibular nucleus (30.7%) and very little in the medial vestibular nucleus (10.6%). Fast and slow cells were detected among the vestibulospinal neurons. The fast neurons of L cells did not prevail greatly over the slow ones, whereas the slow neurons of C cells prevailed comparatively largely over the fast neurons. Thus, it became possible to reconstruct spatial distribution of the identified vestibulospinal neurons. The results of spatial distribution of C and L vestibulospinal neurons in the frogs failed to conform to definite somatotopy, which is characteristic for mammalian vestibular nuclei. C and L neurons in the frog's vestibular nuclei as a source of vestibulospinal fibres, are scattered separately or more frequently in groups, so that they establish a "patch-like" somatotopy and do not form a distinctly designed fields as in mammals.

Dimensions of the vestibular and tympanic scalae of the cochlea in selected mammals

The spiral shaped organ of hearing occurs only in mammals. This shape creates good conditions for the acoustic wave inside the cochlea. There are various forms of the cochlea in different species of mammal: the number of turns ranges from 1.5 to 4.5, a fact for which there seems no obvious explanation. In order to become more familiar with the geometry of the cochlear scalae in animals, a microanatomical study was carried out on 40 temporal bones, obtained from four common species of mammal: cat, dog, cattle and macaca. The bones were dissected with the aid of an operation microscope using standard otosurgical equipment, in which their perilymphatic spaces were filled with latex and further prepared in a formalin stain. Each of the rubber molds was removed from the osseous matrix and subsequently manually cut into 1 mm segments. The results, presented in diagrams, indicate that the vestibular and tympanic scalae present alternate dominance in their width and height, as was previously found in a study of humans. The change of this alternation domination appears two to five times on their entire length. The dimensions of the cochlear scalae are to a certain extent proportional to the weight of the animal: the largest were found in cattle and the smallest in the macaca.

Effects of microgravity on vestibular ontogeny: direct physiological and anatomical measurements following space flight (STS-29)

Does space flight change gravity receptor development? The present study measured vestibular form and function in birds flown as embryos for 5 days in earth orbit (STS-29). No major changes in vestibular gross morphology were found. Vestibular response mean amplitudes and latencies were unaffected by space flight. However, the results of measuring vestibular thresholds were mixed and abnormal responses in 3 of the 8 flight animals raise important questions.

Effects of vestibular nerve transection on the calcium incorporation of fish otoliths

Previous investigations revealed that the growth of fish inner ear otoliths (otolith size and calcium-incorporation) depends on the amplitude and the direction of gravity, suggesting the existence of a (negative) feedback mechanism. In search for the regulating unit, the vestibular nerve was transacted unilaterally in neonate swordtail fish (Xiphophorus helleri) which were subsequently incubated in the calcium-tracer alizarin-complexone. Calcium incorporation ceased on the transacted head sides, indicating that calcium uptake is neurally regulated. Grant numbers: 50 WB 9533, 50 WB 9997.

Does the endolymph pass through the base of the cupula?

Whether the endolymph of the semicircular canal passes the cupular partition or not was examined using the lateral semicircular canal system of adult pigeons (Columba livia). By applying various pressures by means of injection of a dye solution through the membranous canal, it was found that the dye solution, was seen to pass the cupula even under very low pressures when the pressure was increased gradually. When pulled by a magnet, the ultrafine particles of the dextran magnetite contained in the injected fluid were found to pass through the subcupular space without evident increase of the ampullary pressure.

High-Resolution Three-Dimensional Magnetic Resonance Imaging of the Vestibular Labyrinth in Patients with Atypical and Intractable Benign Positional Vertigo

Benign paroxysmal positional vertigo (BPPV) is a most common cause of dizziness and usually a self-limited disease, although a small percentage of patients suffer from a permanent form and do not respond to any treatment. This persistent form of BPPV is thought to have a different underlying pathophysiology than the generally accepted canalolithiasis theory. We investigated 5 patients who did not respond to physical treatment, presented with an atypical concomitant nystagmus or both with high-resolution three-dimensional magnetic resonance imaging of the inner ear. This method provides an excellent imaging of the inner ear fluid spaces. In all 5 patients, we found structural changes such as fractures or filling defects in the semicircular canals which we did not find in control groups. One patient clinically presented with the symptoms of a 'heavy cupula'. Whereas crosssections through the ampullary region and the adjoining utricle showed no abnormalities, there were significant structural changes in the semicircular canals, which are able to provide an explanation for the symptoms of a heavy cupula.

Volumetric and dimensional analysis of the guinea pig inner ear

The objective of this study was to provide accurate volumetric data on the fluid spaces and soft tissue in the guinea pig inner ear by measuring all histologic serial sections by means of Metamorph Imaging Software at 400x to 1,000x magnification. The total endolymph volume of the inner ear was 4.691 mm3, of which 1.501 mm3 was in the cochlea, 3.090 mm3 in the vestibular labyrinth, and 0.100 mm3 in the endolymphatic duct and sac. The total perilymph volume was 15.938 mm3, of which 8.867 mm3 was in the cochlea and 7.071 mm3 in the vestibular labyrinth. The volume of the organ of Corti per millimeter length increased toward the apex, but the volumes of the stria vascularis, spiral ligament, and spiral limbus decreased. The volume of the macula utriculi was larger than that of the macula sacculi. The measurement of the luminal surface area of the stria vascularis was 3.944 mm2, and that of the vestibular dark cells was 5.772 mm2.

Vestibular impairment

The measurement of vestibular impairment for medicolegal purposes represents a challenge. In the United States, the most widely employed system is that described in the American Medical Association's (AMA's) Guides to the Evaluation of Permanent Impairment. The fourth edition, published in 1993, represented a major step forward at that time, but room for improvement still exists. The problem areas in the Guides are discussed and appropriate modifications are suggested. Briefly, balance disorders are divided into two general categories, constant and recurrent (episodic). Using this novel approach, scales for quantification of the symptoms and signs (and laboratory tests for each), in increasing order of severity, are suggested. In this manner, an overall score may be derived for any individual with a permanent medicolegal balance impairment.

Effects of microgravity on vestibular development and function in rats: genetics and environment

Our anatomical and behavioral studies of embryonic rats that developed in microgravity suggest that the vestibular sensory system, like the visual system, has genetically mediated processes of development that establish crude connections between the periphery and the brain. Environmental stimuli also regulate connection formation including terminal branch formation and fine-tuning of synaptic contacts. Axons of vestibular sensory neurons from gravistatic as well as linear acceleration receptors reach their targets in both microgravity and normal gravity, suggesting that this is a genetically regulated component of development. However, microgravity exposure delays the development of terminal branches and synapses in gravistatic but not linear acceleration-sensitive neurons and also produces behavioral changes. These latter changes reflect environmentally controlled processes of development.

The effect of hair bundle shape on hair bundle hydrodynamics of inner ear hair cells at low and high frequencies

The relationship between size and shape of the hair bundle of a hair cell in the inner ear and its sensitivity at asymptotically high and low frequencies was determined, thereby extending the results of an analysis of hair bundle hydrodynamics in two dimensions (Freeman and Weiss, 1990. Hydrodynamic analysis of a two-dimensional model for micromechanical resonance of free-standing hair bundles. Hear. Res. 48, 37-68) to three dimensions. A hemispheroid was used to represent the hair bundle. The hemispheroid had a number of advantages: it could represent shapes that range from thin, pencil-like shapes, to wide, flat, disk-like shapes. Also analytic methods could be used in the high frequency range to obtain an exact solution to the equations of motion. In the low frequency range, where an approximate solution was found using boundary element methods, the sensitivity of the responses of hair cells was mainly proportional to the cube of the heights of their hair bundles, and at high frequencies, the sensitivity of the hair cells was mainly proportional to the inverse of their heights. An excellent match was obtained between measurements of sensitivity curves in the basillar papilla of the alligator and bobtail lizards and the model's predictions. These results also suggest why hair bundles of hair cells in vestibular organs which are sensitive to low frequencies have ranges of heights that are an order of magnitude larger than the range of heights of hair bundles of hair cells found in auditory organs.

Topographic distribution of nicotinic acetylcholine receptors in the cristae of a turtle

The neurochemical basis of cholinergic efferent modulation of afferent function in the vestibular periphery remains incompletely understood; however, there is cellular, biochemical and molecular biological evidence for both muscarinic and nicotinic acetylcholine (ACh) receptors (nAChRs) in this system. This study examined the topographic distribution of alpha-bungarotoxin (alpha-BTX) nAChRs in the cristae of a turtle species. Cristae were perfusion-fixed, cut at 20 micrometer on a cryostat and incubated with alpha-BTX or polyclonal antibodies raised against Torpedo nAChR. Light microscopy showed abundant specific labeling of nAChR in the central zone of each hemicrista on the calyx-bearing afferents surrounding type I hair cells and on the base of the type II hair cells. Within the peripheral zone, dense labeling of type II hair cells near the torus and sparse or no label was observed on type II hair cells near the planum. The alpha-BTX binding showed a similar pattern within the cristae. The similarity between the topographic distribution of alpha-BTX binding nAChR and of efferent inhibition of afferents supports the notion that the inhibitory effect of afferents is mediated by nAChR.

Imaging of the osseous, membranous, and perilymphatic labyrinths

The inner ear is located within the petrous portion of the temporal bone and consists of the membranous, perilymphatic, and the outer osseous labyrinths. Together, these structures form the end organs for mediating hearing and balance. This article provides a detailed review of the neonatal anatomy and development of these structures, knowledge of which derives in great part from advances in CT and sophisticated MR imaging. Current research should soon enable clinicians to identify a wide variety of subtle lesions of the inner ear that heretofore have been inaccessible to imaging diagnosis.

[An anatomical investigation relating to the stapes elevation surgery]

OBJECTIVE

For the purpose of improving patient's hearing in stapes elevation surgery.

METHOD

The anatomical features relating to this operation were observed and measured in 30 ears of fresh cadavers, which included the length of lenticular process, the highness of stapes head and neck, the thickness of lower border of footplate, the angle of incudostapecial joint and the gradients of upper and lower wall of vestibular niche. The relation between two types of the present operation and the investigation were discussed.

RESULT

The two types of present operations were in accord with the physiologicoanatomical features of the stapes and incus.

CONCLUSION

In order to improve the patient's hearing, making use of biobinder for strengthening the incudostapedial connexion as a routine is suggested.

Cochlear fluid space dimensions for six species derived from reconstructions of three-dimensional magnetic resonance images

OBJECTIVES

To establish the dimensions and volumes of the cochlear fluid spaces.

STUDY DESIGN

Fluid space volumes, lengths, and cross-sectional areas were derived for the cochleas from six species: human, guinea pig, bat, rat, mouse, and gerbil.

METHODS

Three-dimensional reconstructions of the fluid spaces were made from magnetic resonance microscopy (MRM) images. Consecutive serial slices composed of isotropic voxels (25 microm3) representing the entire volume of fixed, isolated cochleas were obtained. The boundaries delineating the fluid spaces, including Reissner's membrane, were resolved for all specimens, except for the human, in which Reissner's membrane was not consistently resolved. Three-dimensional reconstructions of the endolymphatic and perilymphatic fluid spaces were generated. Fluid space length and variation of cross-sectional area with distance were derived by an algorithm that followed the midpoint of the space along the length of the spiral. The total volume of each fluid space was derived from a voxel count for each specimen.

RESULTS

Length, volume, and cross-sectional areas are provided for six species. In all cases, the length of the endolymphatic fluid space was consistently longer than that of either perilymphatic scala, primarily as a result of a greater radius of curvature. For guinea pig specimens, the measured volumes of the fluid spaces were considerably lower than those suggested by previous reports based on histological data.

CONCLUSIONS

The quantification of cochlear fluid spaces provided by this study will enable the more accurate calculation of drug and other solute movements in fluids of the inner ear during experimental or clinical manipulations.

Immunolocalization of Bone Morphogenetic Protein-2 and -3 and Osteogenic Protein-1 during murine tooth root morphogenesis and in other craniofacial structures

The distribution of Bone Morphogenetic Protein-2, and -3 (BMP-2 and BMP-3) and Osteogenic Protein-1 (OP-1, also known as BMP-7) during root morphogenesis and in other craniofacial structures was examined in sections of 12- to 18-d-old mouse heads using polyclonal and monoclonal antibodies. BMP-3 and OP-1 were localized in alveolar bone, cementum, and periodontal ligament, whereas BMP-2 was only localized in the alveolar bone of periodontium. All three BMPs were localized in predentine, dentine, odontoblasts, osteoblasts, osteocytes, osteoid, cartilage, chondrocytes and spiral limbus. BMP-2 and OP-1 were also localized in spiral ligament and interdentate cells of the cochlea, whilst BMP-3 was restricted to the spiral ganglion. BMP-3 was also localized in ducts of submandibular and sublingual salivary glands, acini of the lacrimal gland, Purkinje cells in the cerebellum, nerve fibres of the cerebellum and brain, afferent cells of the dorsal root ganglia, inferior alveolar nerve, and peripheral processes of the vestibulocochlear nerve. OP-1 was also localized in hair and whisker follicles, sclera of the eye and in ameloblasts. The demonstration of BMP-3 in the nervous system suggests that this protein may be neurotrophic during development and maintenance of the nervous system. The composite expression of BMPs/OPs during periodontal tissue morphogenesis suggests that optimal therapeutic regeneration may entail the combined use of different BMPs/OPs.

Dimensions of the human vestibular and tympanic scalae

The cochlear scalae provide a practical access route for the insertion of cochlear implant electrodes. A microanatomical study was carried out on 25 human temporal bones obtained from cadavers. These bones were dissected with the aid of an operation microscope, in which their perilymphatic spaces were filled with coloured latex and further prepared in a formalin stain. Each of the rubber moulds was removed from the osseous matrix using standard otosurgical equipment, and subsequently cut into 1 mm segments. The height and width of the vestibular and tympanic scalae were measured. The results, presented in diagrams, indicate that the vestibular scala is less prominent than the tympanic scala in the basic and middle coil of the cochlea and in the upper coil, they display greater dimensions which could serve as a place for electrode insertion in cochlear implant procedures. In addition, the vestibular and tympanic scalae present alternate dominance in their width and height as corroborated by the calculated coefficients. The results obtained in this study supplement our knowledge of the anatomy of the cochlea thus far lacking a full investigation of the scalae, and could serve as a basis for other studies dealing with the physiology of the organs of hearing.

Peripherin immunoreactivity labels small diameter vestibular 'bouton' afferents in rodents

Recent morphophysiological studies have described three different subpopulations of vestibular afferents. The purpose of this study was to determine whether peripherin, a 56-kDa type III intermediate filament protein present in small sensory neurons in dorsal root ganglion and spiral ganglion cells, would also label thin vestibular afferents. Peripherin immunohistochemistry was done on vestibular sensory organs (cristae ampullares, utriculi and sacculi) of chinchillas, rats, and mice. In these sensory organs, immunoreactivity was confined to the extrastriolar region of the utriculus and the peripheral region of the crista. The labelled terminals were all boutons, except for an occasional calyx. In vestibular ganglia, immunoreactivity was restricted to small vestibular ganglion cells with thin axons. The immunoreactive central axons of vestibular ganglion cells form narrow bundles as they pass through the caudal spinal trigeminal tract. As they exit this tract, several bundles coalesce to form a single, narrow bundle passing caudally through the ventral part of the lateral vestibular nucleus. Finally, we conclude that all labelled axons and terminals were vestibular afferents rather than efferents, as no immunoreactivity in the vestibular efferent nucleus of the brainstem was observed.

Dizziness in the elderly and age-related degeneration of the vestibular system

The peripheral and central vestibular systems exhibit an age-related structural deterioration which may be responsible for vestibular reflex deficits and dizziness in the elderly. However, it seems likely that the central nervous system is capable of compensating for a certain degree of decline in function, since not all elderly people are impaired to the extent that the clinical signs of vestibular dysfunction are apparent. Dizziness and other vestibular disorders may develop only when the degree of deterioration of the vestibular system exceeds the ability of the nervous system to compensate. If dizziness does eventuate, it can have profound psychological consequences, particularly in terms of loss of confidence in independent activity, and may lead to the development of anxiety disorders. Vestibular rehabilitation programs may help to minimise the effects of age-related deterioration of the vestibular system and its psychological impact.

Morphological, morphometric, and functional differences in the vestibular organ of different breeds of the rat (Rattus norvegicus)

In the laboratory rat, differences in shape, dimension and function of the cochlea have been reported for various breeds. In contrast, no comparable investigations to date have been undertaken for the vestibular organ in different breeds of the rat. Vestibular organs of two breeds of rat (Wistar, Sprague-Dawley) were analyzed morphologically and morphometrically by means of microdissection techniques in order to determine the mechanical sensitivity of the cupula according to Oman et al; (Acta Otolaryngol., 1987;103:1-13, 1987). Differences in shape of the lateral semicircular duct exist between the two breeds and the cupular mechanical sensitivity is significantly higher in Wistar than in Sprague-Dawley rats. With respect to the other semicircular ducts, no differences in shape were found between the two strains. The cupular mechanical sensitivity of the anterior semicircular duct, however, is higher in Wistar than in Sprague-Dawley rats. The breeds also differ in the shape of their utriculus; obviously a correlation exists between the latter and the cupular mechanical sensitivity of the semicircular ducts. There are differences in the vestibular organs between the two breeds of the laboratory rat investigated. The cupular mechanical sensitivity of the semicircular duct does not seem to be correlated to body mass. The size and morphology of the utriculus influence the mechanical sensitivity of a single duct, but differences only become significant if other parameters also differ.

Nasal vestibule wall elasticity: interactions with a nasal dilator strip

We studied the effect of an adhesive external nasal dilator strip (ENDS) on external nasal geometry in 20 healthy Caucasian adults (10 men, 10 women; age 21-45 yr). The recoil force exerted by ENDS was estimated by bending the device (n = 10) with known weights. In the horizontal direction, a small/medium-sized ENDS in situ exerted a unilateral recoil force of 21.4-22.6 g. Application of ENDS resulted in a displacement of the lateral nasal vestibule walls that had both anterosuperior and horizontal components and that was maintained over an 8-h period. The resultant unilateral nasal vestibule wall displacement at the tip of the device was at 47.6 +/- 2.0 degrees to the horizontal (as related to the plane of the device when in situ) and had a magnitude of 3.5 +/- 0.1 mm. ENDS increased external nasal cross-sectional area by 23.0-65.3 mm2. Nasal vestibule wall compliance was estimated at 0.05-0.16 mm/g. Thus ENDS applies a relatively constant abducting force irrespective of nasal width. Variable responsiveness to ENDS may be related to differences in elastic properties of the nasal vestibule wall.

Hybrid rendering and virtual endoscopy of the auditory and vestibular system

A hybrid rendering method (color-coded 3D shaded-surface and volume display) with the possibility of virtual endoscopy using image data sets from HR-SCT was developed. To show the possible advantages and benefits of the improved rendering algorithm we have specifically highlighted the use in relation to the auditory and vestibular system. Postprocessing image visualization offers improved morphological analysis, and will benefit radiological diagnostics, medical education, surgical planning, surgical training and postoperative assessment.

Importance of type IV collagen, laminin, and heparan sulfate proteoglycan in the regulation of labyrinthine fluid in the rat cochlear duct

The distribution of major components of the basement membrane, such as type IV collagen, laminin, and heparan sulfate proteoglycan (HSPG), was investigated in the rat cochlear duct. Immunofluorescence demonstrated that type IV collagen, laminin and HSPG were distributed along capillaries in the cochlear duct, including the stria vascularis, spiral ligament, spiral prominence and spiral limbus. Additionally, type IV collagen, laminin and HSPG were found to be distributed from the basement membrane of Reissner's membrane to that of the spiral prominence in a linear pattern. The scala media was surrounded by these basement membrane components, demarcating endolymph from perilymph, along epithelial cells except at the stria vascularis. These findings suggest that type IV collagen, laminin and HSPG create the anatomical separation between endolymph and perilymph, thus indicating that they may be involved in the regulation of fluid transport between the endolymph and perilymph.

Surgical exposure of the fundus of the internal auditory canal: anatomic limits of the middle fossa versus the retrosigmoid transcanal approach

OBJECTIVE

To define the anatomic limitations and advantages of the middle cranial fossa and the retrosigmoid transcanal approaches in the exposure of the fundus of the internal auditory canal (IAC).

STUDY DESIGN

A series of 15 cadaver temporal bone specimens were dissected and the measurements of the lateral recess of the IAC were made with a millimeter rule and rounded to the nearest quarter millimeter.

METHODS

Retrospective case review, surgical observation, review, and measurements recorded from magnetic resonance scans. Surgical observations and measurements recorded from cadaver specimens.

RESULTS

These results were compared with historical studies of the retrosigmoid transcanal approach. The results utilizing a combination of these approaches to remove acoustic neuromas at a tertiary referral center during the preceding 11 years are also presented. Previous studies have shown that for the retrosigmoid transcanal approach, it is impossible to expose 3 to 4 mm of the lateral recess of the IAC without violating the vestibule and/or the endolymphatic duct. This has led some authors to advocate the middle cranial fossa approach to the IAC when hearing preservation is a consideration. The current study shows that the falciform crest obscures the inferior half of the fundus. This creates a pocket that cannot be visualized, which on average is 1.82 x 2.33 mm.

CONCLUSION

The fundus of the IAC cannot be completely exposed without violating the labyrinth through either the posterior fossa or middle fossa approach. The clinical implications of these studies are unknown at this time. Low recurrence rates are achieved with both approaches. The anatomic limitations of both approaches must still be considered when planning or performing these approaches, to minimize the risk of recurrence.

Topographical organization of inferior olive cells projecting to translation and rotation zones in the vestibulocerebellum of pigeons

Previous electrophysiological studies in pigeons have shown that the vestibulocerebellum can be divided into two parasagittal zones based on responses to optic flow stimuli. The medial zone responds best to optic flow resulting from self-translation, whereas the lateral zone responds best to optic flow resulting from self-rotation. This information arrives from the retina via a projection from the accessory optic system to the medial column of the inferior olive. In this study we investigated inferior olive projections to translational and rotational zones of the vestibulocerebellum using the retrograde tracer cholera toxin subunit B. Extracellular recordings of Purkinje cell activity (complex spikes) in response to large-field visual stimuli were used to identify the injection sites. We found a distinct segregation of inferior olive cells projecting to translational and rotational zones of the vestibulocerebellum. Translation zone injections resulted in retrogradely labeled cells in the ventrolateral area of the medial column, whereas rotation zone injections resulted in retrogradely labeled cells in the dorsomedial region of the medial column. Motion of any object through space, including self-motion of organisms, can be described with reference to translation and rotation in three-dimensional space. Our results show that, in pigeons, the brainstem visual systems responsible for detecting optic flow are segregated into channels responsible for the analysis of translational and rotational optic flow in the inferior olive, which is only two synapses from the retina.

Cerebral functional magnetic resonance imaging of vestibular, auditory, and nociceptive areas during galvanic stimulation

Cerebral activation was investigated with functional magnetic resonance imaging (fMRI) during galvanic stimulation of the mastoid in 6 normal volunteers. Cutaneous stimulation at the neck C4-5 level served as a control. During mastoid stimulation, bilateral vestibular activation occurred in the posterior insula (parietoinsular vestibular cortex, PIVC), the transverse temporal (Heschl's) gyrus, and thalamic pulvinar. The cutaneous pain elicited by galvanic stimulation caused bilateral activity of the medial part of the insula and the anterior median thalamus. Thus, galvanic stimulation at the mastoid level activates cortical areas of three different sensory systems in the insulathalamic region, the vestibular, the auditory, and the nociceptive systems.

Measurement of guinea pig basilar membrane using computer-aided three-dimensional reconstruction system

Cochleas are known to have the ability to analyze a frequency widely, and this ability seems to be owed mostly to the basilar membrane (BM) configuration. However, the relationship between the cochlear frequency-position map and the BM configuration is not clear. Therefore, in this paper, the internal structures of a guinea pig cochlea, especially the BM configuration, were reconstructed and measured using a computer-aided three-dimensional (3-D) reconstruction system. Then, an attempt was made to examine the influence of the BM configuration on the cochlear frequency-position map. The measurement results indicate that the width of the BM increased and its thickness decreased with an increase in the distance from the basal turn towards the apical turn. Theoretical consideration reveals that the wide frequency-position of the cochlea is achieved by not only the BM configuration change along the length of the cochlea but also the change of the Young's modulus of the BM along the length of the cochlea.

Physiological Principles of Vestibular Function on Earth and in Space

Physiological mechanisms underlying vestibular function have important implications for our ability to understand, predict, and modify balance processes during and after spaceflight. The microgravity environment of space provides many unique opportunities for studying the effects of changes in gravitoinertial force on structure and function of the vestibular system. Investigations of basic vestibular physiology and of changes in reflexes occurring as a consequence of exposure to microgravity have important implications for diagnosis and treatment of vestibular disorders in human beings. This report reviews physiological principles underlying control of vestibular processes on earth and in space. Information is presented from a functional perspective with emphasis on signals arising from labyrinthine receptors. Changes induced by microgravity in linear acceleration detected by the vestibulo-ocular reflexes. Alterations of the functional requirements for postural control in space are described. Areas of direct correlation between studies of vestibular reflexes in microgravity and vestibular disorders in human beings are discussed. (Otolaryngol Head Neck Surg 1998;118:S5-S15.)

Vestibular-hippocampal interactions

Since the early 1960s, researchers have speculated that the vestibular system, the sensory system concerned with the perception of balance and self-motion, contributes to spatial information processing and the development of spatial memory in the hippocampus. Anatomical studies have suggested that various parts of the thalamus are likely to transmit vestibular information to the hippocampus, perhaps via the parietal cortex; however, more direct pathways are possible. Over the last 2-3 years there have been a number of direct electrophysiological demonstrations that vestibular stimulation affects head direction cells in the anterior thalamic nuclei and place cells in the hippocampus. These studies demonstrate the importance of vestibular-hippocampal interactions for hippocampal function but also raise the possibility that the hippocampus may be important for compensation of vestibular function following peripheral or central vestibular lesions.

The evolution of tetrapod ears and the fossil record

In the earliest tetrapods, the fenestra vestibuli was a large hole in the braincase wall bounded by bones of different embryological origins: the otic capsule and occipital arch components, and also, in all except the Devonian Acanthostega, the dermal parasphenoid. This means that the hole lay along the line of the embryonic metotic fissure. Early tetrapod braincases were poorly ossified internally, and no specialized opening for a perilymphatic duct is evident. It is arguable that the earliest tetrapods had neither a perilympllatic duct crossing the otic capsule nor a specialized auditory receptor in a separate lagenar pouch. The primitive tetrapod condition is found in the earliest amniotes, and the separate development of (1) a fenestra vestibuli confined to the limits of the otic capsule, (2) a specialized pressure relief window also derived from components on the line of the metolic fissure, (3) a nonstructural, vibratory stapes and (4) increased internal ossification of the internal walls of the otic capsule, can be traced separately in synapsids, lepidosauromorph diapsids, archosauromorph diapsids, probably turtles, and amphibians. This suggests separate development of true tympanic ears in each of these groups. Developments indicating the existence of a true tympanic ear in amniotes are first found in animals from the Triassic period, and a correlation with the evolution of insect sound production is suggested.

Corticovestibular interactions: anatomy, electrophysiology, and functional considerations

This review summarizes anatomical and electrophysiological observations related to corticovestibular interactions as a step toward understanding their possible functions. Vestibular information is represented in at least three distinct regions of the cerebral cortex in cats and monkeys: the parietal and somatosensory cortex and the parietoinsular vestibular cortex. In addition, vestibular-related signals are found in more extensive regions, including the motor and premotor regions and frontal eye fields. Most of these regions also project directly to the vestibular nuclei. In monkeys, at least six cortical regions have been identified, including the motor, somatosensory, parietal and temporal areas. Most of these regions receive vestibular projections via the thalamus. Most neurons in those cortical areas respond to head velocity and receive converging vestibular, visual and somatosensory input. Electrical stimulation of some of these cortical areas in anesthetized cats influences the activity of many vestibular nuclear neurons including those projecting to the spinal cord. Lesions of the parietal vestibular regions impair the vestibulo-ocular reflex (VOR) and visual suppression of the VOR as well as vestibular-related cognitive functions such as spatial perception and memory in human subjects. Diffuse cortical damage also results in similar impairment of the VOR and suppression of the VOR and possibly the vestibulo-collic reflex. Such impairments after cortical lesions may well be due in part to interruption of cortico-vestibular connections. Future studies in alert animals should focus on the role of different cortical regions projecting to the vestibular nuclei, specifically on how each affects the processing of vestibular signals that mediate vestibulo-motor reflexes and that are used for vestibular related cognitive processes.

The development of vestibular connections in rat embryos in microgravity

Existing experimental embryological data suggests that the vestibular system initially develops in a very rigid and genetically controlled manner. Nevertheless, gravity appears to be a critical factor in the normal development of the vestibular system that monitors position with respect to gravity (saccule and utricle). In fact several studies have shown that prenatal exposure to microgravity causes temporary deficits in gravity-dependent righting behaviors, and prolonged exposure to hypergravity from conception to weaning causes permanent deficits in gravity-dependent righting behaviors. Data on hypergravity and microgravity exposure suggest some changes in the otolith formation during development, in particular the size although these changes may actually vary with the species involved. In adults exposed to microgravity there is a change in the synaptic density in the optic sensory epithelia suggesting that some adaptation may occur there. However, effects have also been reported in the brainstem. Several studies have shown synaptic changes in the lateral vestibular nucleus and in the nodulus of the cerebellum after neonatal exposure to hypergravity. We report here that synaptogenesis in the medial vestibular nucleus is retarded in developing rat embryos that were exposed to microgravity from gestation days 9 to 19.

Age-related changes of the globular substance in the otoconial membrane of mice

The globular substance, which occurs in the vestibular macula as a precursor of otoconia, was examined in aged mice in comparison with young adult mice. Dissected otoconial membrane from the utricular macula of C57BL/6J mice was loaded with fluo-3-AM, and directly observed under a confocal laser scanning microscope. Internal free Ca2+ concentration ([Ca2+]i) of the globular substance was determined through in situ calibration performed by superfusion with ionomycin and Mn2+. Total area of the otoconial membrane, average diameter of the globular substance, and [Ca2+]i showed no significant differences between young adult and aged groups. However, the number of globular substances in young adult mice was significantly larger than those of aged mice. These results suggest a reduced rate of otoconial formation in the aged vestibule, which would result in the sparseness of otoconia in the aged vestibule and lead to balance disorders commonly seen in elderly persons.

Projections from the subdivisions of the fastigial nucleus to the vestibular complex and the prepositus hypoglossal nucleus in the albino rat: an anterograde tracing study using biocytin

Differential projections from the subdivisions of the fastigial nucleus to the vestibular complex and the prepositus hypoglossal nucleus were investigated by an anterograde tracing method using biocytin in the albino rat. The caudomedial subdivision of the nucleus projected ipsilaterally to the dorsal and medial parts of the superior vestibular nucleus (Su Ve), the dorsomedial part of the lateral vestibular nucleus (LVe), and the dorsal parts of the medial (MVe) and spinal (Sp Ve) vestibular nuclei, and projected contralaterally to the ventrolateral corners of the Su Ve and LVe, the ventral part of the MVe, and the lateral part of the Sp Ve. The bilateral prepositus hypoglossal nuclei received sparse projections from the caudomedial subdivision. The middle subdivision of the fastigial nucleus projected ipsilaterally to the dorsal and/or ventral parts of the Su Ve, the dorsomedial pats of the LVe and Sp Ve, and the dorsolateral part of the MVe, and projected contralaterally to the dorsal margin of the Su Ve, the ventrolateral part of the LVe, and the lateral part of the Sp Ve. The dorsolateral protuberance of the fastigial nucleus projected ipsilaterally to the dorsal margin of the Su Ve, the dorsomedial part of the LVe, the dorsal or lateral parts of the Sp Ve, and the lateral part of the MVe, and projected contralaterally to the ventrolateral part of the LVe and the lateral part of the Sp Ve. The subnuclei x, y, and f, interstitial nucleus of the vestibular nerve, and the infracerebellar nucleus received bilateral or ipsilateral fastigiovestibular projections.

Secondary vestibulo-oculomotor projections in larval sea lamprey: anterior octavomotor nucleus

The ventral octavolateral area of lampreys contains three nuclei: the anterior, intermediate and posterior octavomotor nuclei, formed of large neurons that are contacted by thick primary vestibular fibres. We used horseradish peroxidase (HRP) or fluorescein-dextran-amine (FDA) labelling to study the projections of the anterior octavomotor nucleus (AON) in the larval sea lamprey, Petromyzon marinus. The tracers were injected either in the AON, the oculomotor nucleus or the rostralmost spinal cord. HRP injection in the AON labelled thick axons that coursed to the basal mesencephalic tegmentum, where most decussate and project to the oculomotor nucleus and the third Müller cell. Electron microscopy confirmed that AON axons contact with the contralateral third Müller cell and with oculomotor neurons. Some AON axons run in the mesencephalic tegmentum and the ventral diencephalon. An AON axon was observed to run close to the axon of the contralateral third Müller cell, establishing what appeared to be en passant contacts. HRP injection in the AON also revealed commissural fibres projecting to the contralateral octavolateral area. HRP or FDA injections in the oculomotor nucleus labelled both large and small neurons of the AON, mostly contralateral to the injection site, as well as of cells in the intermediate octavomotor nucleus, mainly ipsilateral. HRP injection in the AON or in the rostral spinal cord did not reveal any projections from the AON to the spinal cord. Our results indicate that the pattern of octavo-oculomotor connections in the lamprey is different from that observed in other vertebrates.

Transmission between the type I hair cell and its calyx ending

The long, uninterrupted apposition between the type I hair cell and the calyx ending has implications for the intercellular communication between these structures. Conventional synaptic transmission will be compromised unless the impedance of the ending is made relatively high. The apposition also creates the possibility of ephaptic transmission between the hair cell and the ending. Ephaptic transmission from the hair cell to the outer face of the calyx ending is too weak to make more than a minor contribution to sensory coding. Basolateral currents associated with hair-cell transduction can result in a substantial accumulation of K+ ions in the intercellular space. The accumulation can alter conventional transmission by depolarizing the hair cell and can alter afferent firing by depolarizing the ending. Reasons were presented suggesting that K+ accumulation may play an essential role in transduction involving type I hair cells, including the linearization of input-output relations and an increase in the maximal rate of discharge.