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PubMedDate not supplied

[Quantitative findings on the morphology of the vestibular nerve in Menière's disease].

In vestibular nerves of patients without any inner ear disease and from patients who suffered from Menière's disease, the number, diameter, and density of nerve fibres were determined in the whole nerve as well as in the different parts (pars superior and pars inferior). As regards normal values, the number of fibres in the whole nerve ranged between 17 097 and 23 088 (age group: 40-54 years). In nerves from Menière patients the number of nerve fibres was diminished: in cases of 5-7 years of duration by about 13-37%; in cases of 15-21 years of duration, by about 73%. The persisting nerve fibres showed an increase in the number of thinner fibres, but occasionally also some very thick ones with giant myelin sheaths could be observed. The number and density of nerve fibres were appreciably diminished in the nervus ampullaris anterior, posterior, and nervus saccularis. The degenerative changes in Menière's disease were more pronounced in the phylogenetically younger pars inferior with progression in the later stages of the disease.

Adult↗
PubMedDate not supplied

Projection of the vestibular nerve to the SI arm field in the cerebral cortex of the cat.

Evoked cortical focal potentials from electrical vestibular nerve stimulation were recorded in the Pcd-area in cats anaesthetized with Chloralose or Nembutal. For comparison, additional cortical projections were located for n. rad. superficialis and group Ia muscle afferents from n. rad. prof., n. fibularis prof., n. femuralis ramus muscularis and the motor nerve to the trapezoid muscle. Surface positive potentials, which reversed to negativity in middle cortical layers, were for vestibular nerve stimulation recorded in the S I forelimb field in a small area close to Pcd in the posterior medial part of the deep radial nerve projection field. The location of this field is compared with the vestibulo-cortical projections described earlier for rodents, squirrel monkey, and rhesus monkey. The histology shows that the field was within the cytoarchitectonic 3a area.

Animals↗
PubMed1999

A morphological and morphometric study of the peripheral process of the human vestibular nerve following posterior cranial fossa neurectomy.

Three vestibular nerve specimens removed at transmeatal neurectomy were studied in order to understand better retrograde degeneration and regeneration after vestibular neurectomy in the posterior cranial fossa. In two cases this procedure followed retrolabyrinthine retrosigmoid posterior fossa vestibular neurectomy. The subjects, three patients with Menière's disease, were compared with one another and two autopsy controls with no known otological problem. The specimens were obtained at the distal end of the internal auditory canal and transversely sectioned. Many collapsed Schwann cell basement membranes were observed. The ratio of small-diameter nerve fibres increased significantly after neurectomy. Onion bulb formation around myelinated nerve fibres with small diameters and Schwann cell proliferation around the soma of vestibular ganglion cells reflected remyelination. We conclude that peripheral processes of vestibular nerve fibres can undergo retrograde degeneration and subsequent regeneration after transection of the central process.

Aged↗
PubMed1984

Evidence for glutamate as a neurotransmitter in the cat vestibular nerve: radioautographic and biochemical studies.

Evidence that glutamate acts as a neurotransmitter in vestibular nerve fibers was sought (1) by electron microscope radioautographic identification of the uptake sites of [3H]-glutamic acid after incubation of slices of cat vestibular nuclei, and (2) by measuring changes in sodium-dependent high affinity glutamate uptake in nerve endings containing homogenates from normal and deafferented vestibular nuclei 8 to 11 days after unilateral vestibular nerve lesion. Electron microscopic radioautography revealed that glutamate had been taken up by numerous nerve endings projecting over the whole vestibular nuclear complex. The biochemical approach indicated that after section of the vestibular nerve, a significant decrease in high affinity glutamate uptake occurred in the vestibular nuclei, which lost their exclusively ipsilateral projection. This decrease varied from one area of the deafferented vestibular nuclei to another, reaching -58% in the lateral area of the central part corresponding to the ventral lateral vestibular nucleus and the rostral part of the descending vestibular nucleus. It is concluded that glutamate (or aspartate) is used by the vestibular nerve fibers as a neurotransmitter in the vestibular nuclei.

Animals↗
PubMed1995

Morphologic changes in superior vestibulo-ocular neurons and vestibular nerve following labyrinthectomy in the cat.

Morphologic changes in ipsilateral superior vestibulo-ocular neurons (SVON) and the vestibular nerve were measured in 4 cats 8 weeks after labyrinthectomy and 4 cats 1 year after labyrinthectomy. There is a 20% decrease in SVON size and 30% decrease in rough endoplasmic reticulum and ribosomes with no change in the volume fractions of Golgi apparatus or mitochondria. In the central nervous system degeneration of the vestibular nerve terminals ipsilateral to the labyrinthectomy was represented by a 25% loss of synaptic profiles (SP) on SVON at 8 weeks and 57% loss of SP at 1 year after labyrinthectomy. There was no significant loss of fiber number in the vestibular nerve at 8 weeks post lesion but a 35% loss of fibers primarily of the large size at 1 year post lesion.

Animals↗
PubMed2002

Demyelination of vestibular nerve axons in unilateral Ménière's disease.

We conducted a study to determine whether vestibular nerves in patients with unilateral Ménière's disease whose symptoms are refractory to medical management exhibit neuropathologic changes. We also endeavored to determine whether retrocochlear abnormalities are primary or secondary factors in the disease process. To these ends, we obtained vestibular nerve segments from five patients during retrosigmoid (posterior fossa) neurectomy, immediately fixed them, and processed them for light and electron microscopy. We found that all five segments exhibited moderate to severe demyelination with axonal sparing. Moreover, we noted that reactive astrocytes produced an extensive proliferation of fibrous processes and that the microglia assumed a phagocytic role. We conclude that the possible etiologies of demyelination include viral and/or immune-mediated factors similar to those seen in other demyelinating diseases, such as multiple sclerosis and Guillain-Barré syndrome. Our findings suggest that some forms of Ménière's disease that are refractory to traditional medical management might be the result of retrocochlear pathology that affects the neuroglial portion of the vestibular nerve.

Adult↗
PubMed1984

Retrolabyrinthine section of the vestibular nerve.

When symptoms of dizziness and episodic vertigo cannot be controlled through medical management or drainage procedures such as endolymphatic subarachnoid shunt operations, selective vestibular nerve section may be necessary. In the 1920s eighth cranial nerve sections were performed by neurosurgeons through the suboccipital approach but were frequently associated with hearing loss and facial paralysis. The middle fossa approach has been popularized by Dr. William House and others as a method of selectively sectioning the vestibular nerve and preserving facial and cochlear function. More recently the suboccipital retrolabyrinthine approach has been described as a method of selectively sectioning the vestibular nerve. We have reviewed 42 cases of suboccipital retrolabyrinthine selective section of the vestibular nerve performed at the Otologic Medical Group over the past 2 years. The shortest follow-up on these patients has been 6 months. Thirty-two patients had preoperative diagnosis of Meniere's disease, and of these patients 25 had had previous endolymphatic subarachnoid shunt surgery. Eighty-five percent (27 patients) experienced complete relief of vertigo following surgery, while 6% (two patients) stated they were improved. Three patients reported no relief. There were 10 patients with dizziness who had a diagnosis other than Meniere's disease. In this diverse group three experienced complete relief of vertigo, five were improved, and two reported no improvement of vertigo following surgery. None of the patients lost his hearing as a result of the surgery and there was no facial weakness. One patient had postoperative CSF rhinorrhea and another had meningitis.

Dizziness↗
PubMed2003

A small vestibular schwannoma arising from the inferior vestibular nerve.

The investigation of a complaint of unilateral right sensorineural hearing loss led to the identification of a right 3 mm vestibular schwannoma arising from the inferior division of the right vestibular nerve. On investigation the patient was found to have normal caloric function, this being mediated by the superior vestibular nerve. Both transient and distortion product otoacoustic emissions were absent in the right ear, and ABR was abnormal on this side. These findings are of interest as they indicate that this small lesion produced a hearing loss that was both cochlear and retrocochlear. The anatomical finding that the medial auditory efferents run within the inferior vestibular nerve is considered. This patient did not experience tinnitus or hyperacusis despite the site of the lesion arising from the inferior vestibular nerve.

Gadolinium↗
PubMed2003

Brainstem projections of different branches of the vestibular nerve: an experimental study by transganglionic transport of horseradish peroxidase in the cat. III. The saccular nerve.

The brainstem projection of the saccular nerve was investigated by transganglionic tracing with horseradish peroxidase in the cat. The labeled fibers were located most caudally and laterally (dorsolaterally) in the vestibular nerve root. This was unique when compared with the locations of the fibers from the nerves of the other vestibular-end organs that were studied by the present authors by the same approach previously. In addition, such a comparison revealed a specific location, from lateral to medial, for the fibers from each of the five divisions of the vestibular nerve. In the present study, labeled fibers from the sacculus, of fine caliber, were found close to the restiform body, both medially and laterally, some even penetrating through this structure. Labeled terminals were present in cell group "y". This was unique, compared with the nerves from the other end organs. Such terminals were also found in the four main vestibular nuclei, except for the medial vestibular nucleus, where no labeled terminals could be detected. No labeled terminals were found in the interstitial nucleus of the vestibular nerve. Together with the findings from our previous studies, this suggests that, in contrast to the ampullar nerves, the nerves from the maculae do not project to this structure. This study confirms, but also extends, findings reported from a previous investigation in the cat, using an experimental degeneration technique.

Animals↗
PubMed1983

Survival of function in the deafferentated vestibular nerve.

After it has been deafferentated, spontaneous spike activity in the vestibular nerve is not abolished, but is drastically reduced 1-3 months post-op. If the nerve stump is cut again in the compensated animal, similarly directed postural asymmetries are re-induced, although of milder intensity. Electrical stimulation of the vestibular nerve stump evokes monosynaptic excitation in the vestibular nuclei and a vestibulo-ocular reflex at normal thresholds despite partial degeneration in the nerve. Therefore, the deafferentated nerve is capable of exerting compensatory influences upon the central nervous system.

Action Potentials↗
PubMedDate not supplied

Binocular counterrolling during sustained body tilt in normal humans and in a patient with unilateral vestibular nerve section.

Two normal persons and a patient with unilateral vestibular nerve section were held motionless for ten minutes in the upright position, at 60 degrees tilt right ear down, and at 60 degrees tilt left ear down. In addition, one normal subject was held for ten minutes at each of 30, 60, and 90 degrees tilt left ear down. Photographs were taken of both eyes every ten seconds. Measurements of ocular counterrolling during these trials revealed torsional eye movements in all positions, including the upright, even though the head and body were stationary. Variations in torsion in the upright position ranged up to 2.75 degrees. At the tilt positions, variations ranged up to 4 degrees. Disconjugate movements were seen in all subjects in all positions. There were no significant differences in measurements of ocular counterrolling during static tilt between the normal subjects and the patient with the vestibular nerve section, in contrast to measures obtained during slow velocity dynamic testing.

Adult↗
PubMed2004

Responses of irregularly discharging chinchilla semicircular canal vestibular-nerve afferents during high-frequency head rotations.

Mammalian vestibular-nerve afferents innervating the semicircular canals have been divided into groups according to their discharge regularity, gain at 2-Hz rotational stimulation, and morphology. Low-gain irregular afferents terminate in calyx endings in the central crista, high-gain irregular afferents synapse more peripherally in dimorphic (bouton and calyx) endings, and regular afferents terminate in the peripheral zone as bouton-only and dimorphic endings. The response dynamics of these three groups have been described only up to 4 Hz in previous studies. Reported here are responses of chinchilla semicircular canal vestibular-nerve afferents to rotational stimuli at frequencies up to 16 Hz. The sensitivity of all afferents increased with increasing frequency with the sensitivity of low-gain irregular afferents increasing the most and matching the high-gain irregular afferents at 16 Hz. All afferents increased their phase lead with respect to stimulus velocity at higher frequencies with the highest leads in low-gain irregular afferents and the lowest in regular afferents. No attenuation of sensitivity or shift in phase consistent with the presence of a high-frequency pole over the range tested was noted. Responses were best fit with a torsion-pendulum model combined with a lead operator (tau(HF1)s + 1)(tau(HF2)s + 1). The discharge regularity of individual afferents was correlated to the value of each afferent's lead operator time constants. These findings suggest that low-gain irregular afferents are well suited for encoding the onset of rapid head movements, a property that would be advantageous for initiation of reflexes with short latency such as the vestibulo-ocular reflex.

Animals↗
PubMed1989

[Relationship between directions of cerebellar retractions and cochlear and vestibular nerve injuries].

It is said that lateral-to-medial retraction of the cerebellar hemisphere is hazardous because, by this retraction, avulsion injury of the cochlear nerve and internal auditory artery may be caused. Caudal-to-rostral retraction of the cerebellar hemisphere is, therefore, recommended in operations in the CP angle such as microvascular decompression procedures. From the results of our present study, however, it can be said caudal-to-rostral retraction can easily cause vestibular nerve damage. However, rostral-to-caudal retraction may damage the cochlear nerve just as lateral-to-medial retraction does. These differences of the eighth nerve injuries according to directions of cerebellar retractions are explicable from the fact that the vestibule and vestibular nerve are located posterior to the cochlea and cochlear nerve. Most of dysequilibrium appearing after manipulations in the CP angle may be due to vestibular nerve damage-avulsion of the vestibular nerve and its accompanying vessels from the vestibular apparatus.

Action Potentials↗
PubMed1993

Vestibular nerve disorder in patients suffering from sudden deafness with vertigo and/or vestibular dysfunction.

Vestibular nerve disorder (VND) in cases suffering from sudden deafness with vertigo was studied. Between 1987 and 1991, we observed 46 patients suffering from sudden deafness with or without vertigo, who had undergone the caloric test and galvanic body sway test (GBST). Twenty-seven patients had vertigo and canal paresis (CP) upon the caloric test, 6 vertigo without CP and 13 CP without vertigo. VND was detected in 12 of the 46 patients. All those with VND had vertigo and CP upon the caloric test, 12/27 (44%). The degree of hearing loss in those with VND was significantly (p < 0.05) more severe and their recovery of hearing loss was poorer than in patients without VND. These results indicate that VND is a common finding in cases of sudden deafness with vertigo especially in those with severe hearing loss.

Caloric Tests↗
PubMed2005

Efferent-mediated fluctuations in vestibular nerve discharge: a novel, positive-feedback mechanism of efferent control.

We compared the background discharge of vestibular nerve afferents in barbiturate-anesthetized and unanesthetized, decerebrate chinchillas. Based on their interspike-interval statistics, units were categorized as regular, intermediate, or irregular. Background discharge rates were higher in irregular units from decerebrates compared to anesthetized preparations; no such difference was observed for regular or intermediate units. Large fluctuations in discharge rate were confined to intermediate and irregular units in decerebrates, but were not seen at all in anesthetized animals. The most prominent examples of fluctuations consisted of oscillations with periods exceeding 500 s and peak-to-peak amplitudes as large as 300 spikes/s. Several observations show that the fluctuations are mediated by the efferent vestibular system (EVS): (1) they are abolished when the vestibular nerve is cut proximal to the recording electrode; (2) their amplitude is correlated with the size of efferent-mediated rotational responses in individual units; and (3) they occur even when vital signs are stable. Previous studies had provided evidence that the EVS involves positive feedback: vestibular nerve afferents and EVS neurons excite one another. To study how oscillations could be produced, we developed a nonlinear model of positive feedback in which afferent feed-forward discharge was nonlinearly related to its inputs from hair cells and the EVS, while these inputs declined (adapted) as discharge was prolonged. Provided that the gain of the efferent feedback loop was sufficiently large, the model showed oscillations similar to those observed experimentally. Although large fluctuations in afferent discharge are unlikely to occur under physiological circumstances, positive feedback may be a normal feature that can amplify the influence of the EVS.

Animals↗
PubMedDate not supplied

Ultrastructural study of the human utricular macula and vestibular nerve in meniére's disease.

The authors have carried out an ultrastructural study of the human utricular macula and the vestibular nerve in the internal acoustic meatus of four patients suffering from Meniere's disease. They confirm the presence of degenerative alterations in the utricular sensory epithelium. The nervous fibers situated in the supporting connective tissue of the neuro-epithelium showed modifications in the Schwann cell cytoplasm and in the arrangement of the myelin sheaths. The same alterations appear in the vestibular nerve in the internal acoustic meatus in 2 of our cases. In the other 2, the vestibular nerve was formed by a granular matrix with several myelin figures in the proximity of possible Schwann cell nucleus debris.

Adult↗
PubMed1997

Skew deviation following vestibular nerve surgery.

Eighteen consecutive patients undergoing vestibular nerve surgery underwent pre- and postoperative examination of ocular motility. Five patients developed a skew deviation following surgery, with the lower eye on the operated side and an incomitant pattern of deviation in all cases. Three patients experienced diplopia lasting from 1 day to 6 months. The magnitude of skew deviation was increased by head tilt away from the operated side in only 1 case. The development of skew deviation was not determined by preoperative ocular alignment or binocular function, or any particular type or pattern of vestibular disease. There was an association with large changes in ocular torsion and subjective visual vertical, which correlated with lesser degrees of canal paresis to preoperative caloric testing on the operated side. No patient developed a head tilt postoperatively. There is a gradation of responses to surgical vestibular deafferentation in humans, skew deviation only occurring in patients suffering marked changes in subjective visual vertical and ocular torsion.

Adult↗