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PubMed1996

Central and peripheral myelin in the rat cochlear and vestibular nerves.

In the bipolar neurons of vertebrate cochlear and vestibular nerves, the myelin envelopes without interruption the axon, the perikaryon and the dendrite. The perikaryal myelin is thin and partially loose, whereas axon and dendrite are enveloped by compacted myelin. The expression of protein 0 and myelin basic protein, constituents of peripheral and central myelin respectively, has been investigated in the rat by immunohistochemical study at the light microscopic level. Our data indicate that both in the cochlear and vestibular nerves the myelin of the perikaryon and dendrite is composed by specific peripheral myelin proteins. The axon segment between the perikaryon and the transitional zone expresses peripheral myelin proteins in the cochlear nerve, while both types of myelin proteins are present in the vestibular nerve. Between the transitional zone and the brainstem the myelin of the axon is exclusively of the central type. The peripheral-central myelin transitional zone is in close proximity to the axonal pole in the vestibular ganglion cells, while in the cochlear nerve it is near the spiral foramina, at variable distance from the axonal pole of ganglion cells.

Animals↗
PubMed1997

Vestibular nerve pathology in cases of intractable vertigo: an electronmicroscopic study.

OBJECTIVE: This study aimed to determine the absence or presence and the nature of pathology of the vestibular nerve in case of intractable vertigo. STUDY DESIGN: This was a prospective study. SETTING: The study was performed at a private practice tertiary referral center. PATIENTS: There-were 42 patients with intractable vertigo in the study. INTERVENTIONS: All patients received thorough diagnostic examinations and surgical excision of the vestibular nerves. MAIN OUTCOME MEASURES: Segments of the superior and inferior vestibular nerves were surgically removed, preserved in glutaraldehyde, examined by electronmicroscopy, and the findings were correlated with the clinical diagnosis. RESULTS: A variety of different types of pathologic lesions were identified, including axon and supporting cell degeneration, herpes zoster virus, other viruses, results of bacterial infection, and regrowth of nerve after surgical resection. CONCLUSION: The vestibular nerves were found to be histologically normal in lesions primarily involving the end organ such as most early Meniere's disease cases, benign paroxysmal postural vertigo (BPPV), and mild labyrinthine concussion. Vestibular nerve degeneration was seen with advanced Meniere's disease, severe labyrinthine concussion, and with vascular loops in the internal auditory canal. Herpes zoster involves Scarpa ganglion in herpes zoster oticus. Viruses were found in the nuclei of vestibular nerve cells in a patient with delayed hydrops. Regrowth of the vestibular nerve after surgical resection was confirmed in three cases.

Adult↗
PubMed1997

Vestibular nerve section: long-term follow-up.

Vestibular nerve section is considered an effective modality in the treatment of refractory and incapacitating vertigo. Typically nerve section results are described on the basis of short-term follow-up. We have reviewed 41 cases of vestibular nerve section spanning an 18-year period. Although the majority of cases involved classic Meniere's disease, delayed endolymphatic hydrops, vestibular neuritis, and Meniere's syndrome secondary to head trauma were also included. Surgical approaches included translabyrinthine (20 cases), retrolabyrinthine (14 cases), retrosigmoid (six cases), and middle fossa (one case) procedures. Postoperative follow-up time averaged 102 months, with 46% of patients followed for a minimum of 9 years. Results are reported according to standards set forth by the American Academy of Otolaryngology--Head and Neck Surgery. Vertigo was cured or markedly improved in 88% of cases (90% in patients with Meniere's disease) at 18 to 24 months postoperatively. These vertigo results were sustained at the time of latest follow-up. Functional level was also preserved over time despite the development of bilateral symptoms in several cases. The rate of bilateral disease reached 22% of cases. Although vertigo results remained stable, long-term follow-up of successful hearing preservation cases demonstrated deterioration over time. Postoperative continuation of medical treatment is urged to optimize and sustain the vestibular neurectomy result.

Adult↗
PubMed1995

Time course of vestibular function in patients with menière's disease following vestibular nerve section.

Harmonic acceleration rotational test and vestibular autorotation test (VAT) were performed on 8 patients with Menière's disease before and after vestibular nerve section. Sinusoidal rotations of 0.01-0.64 Hz were used in the HA rotational test. VAT was performed at frequencies between 0.5 and 6 Hz. Two weeks after operation, almost all the patients consistently showed response asymmetry toward the healthy ear at all stimulus frequencies and a reduction in sensitivity to rotational stimuli at 0.01 Hz in the HA rotational test. Prior to surgery, the time constant of the vestibulo-ocular reflex (VOR) varied according to the residual vestibular function of each patient. The time constant then dropped to a mean of 4.2 s after the operation. In the VAT, almost all the patients showed a gain reduction at all frequency ranges on the seventh postoperative day. These findings suggest that response asymmetry and gain at 0.01 Hz in the HA rotational test are valuable for evaluating the time course of the compensation of the vestibular function after surgery and that the VOR time constant is useful in detecting whether the vestibular nerve has been sectioned correctly.

Adult↗
PubMed1990

[Histopathology of the vestibular nerve in Menière's disease].

Histological and morphometrical investigations of the vestibular nerve were performed on surgical specimens from 19 patients suffering from Ménière's disease and on 5 autopsy preparations from patients without inner ear disease. The number of lipofuscin granules and vacuoles in the ganglion cells of specimens from Ménière patients was not increased compared with control specimens of a similar age, nor did the amount of endoneuronal connective tissue in the vestibular nerve specimens differ between the two groups. The density of capillaries in Scarpa's ganglion and vestibular nerve was significantly increased in the Ménière patients compared with the control specimens. Furthermore, the ratio of nerve fibres with a larger diameter was higher in specimens from Ménière patients than in control preparations. There was no difference in the density of myelinated fibres between the two groups.

Capillaries↗
PubMed1984

Relation between discharge regularity and responses to externally applied galvanic currents in vestibular nerve afferents of the squirrel monkey.

Most vestibular nerve afferents can be classified as regularly or irregularly discharging. Two factors are theoretically identified as being potentially responsible for differences in discharge regularity. The first, ascribable to synaptic noise, is the variance (sigma v2) characterizing the transmembrane voltage fluctuations of the axon's spike trigger site, i.e., the place where impulses normally arise. The second factor is the slope (dmuv/dt) of the trigger site's postspike recovery function. Were (dmuv/dt) a major determinant of discharge regularity, the theory predicts that the more irregular the discharge of a unit, the greater should be its sensitivity to externally applied galvanic currents and the faster should be the postspike recovery of its electrical excitability. The predictions would not hold if differences in the discharge regularity between units largely reflected variations in sigma v. To test these predictions, the responses of vestibular nerve afferents to externally applied galvanic currents were studied in the barbiturate-anesthetized squirrel monkey. Current steps of 5-s duration and short (50 microsecond) shocks were delivered by way of the perilymphatic space of the vestibule. Results were similar regardless of which end organ an afferent innervated. The regularity of discharge of each unit was expressed by a normalized coefficient of variation (CV*). The galvanic sensitivity (beta p) of a unit, measured from its response to current steps, was linearly related to discharge regularity (CV*), there being approximately 20-fold variations in both variables across the afferent population. Various geometric factors--including fiber diameter, position of individual axons within the various nerve branches, and the configuration of unmyelinated processes within the sensory epithelium--are unlikely to have made a major contribution to the positive relation between beta P and CV*. The postspike recovery of electrical excitability was measured as response thresholds to shocks, synchronized to follow naturally occurring impulses at several different delays. Recovery in irregular units was more rapid than in regular units. Evidence is presented that externally applied currents acted at the spike trigger site rather than elsewhere in the sensory transduction process. We argue that the irregular discharge of some vestibular afferents offers no functional advantage in the encoding and transmission of sensory information. Rather, the irregularity of discharge is better viewed as a consequence of the enhanced sensitivity of these units to depolarizing influences, including afferent and efferent synaptic inputs.

Animals↗
PubMed1997

Ultrastructural analysis of the vestibular nerve in Ménière's disease.

Numerical analysis of the vestibular nerve in Méniè's disease was performed. Vestibular nerve specimens were obtained from three patients with classical clinical findings of Ménière's disease during retrosigmoid vestibular neurectomy. For each patient, an ultrathin section, including an entire cross-section of the nerve specimen, was examined. Fiber counts of nerve specimens with definite pathologic findings were compared with caloric testing results. A significant correlation was found between reduced vestibular response and the incidence of abnormal nerve fibers and also the density of the abnormal nerve fibers. However, the number of nerve fibers with pathologic findings was small. Results of the present study demonstrate no general degeneration of nerve fibers caused by the disease process of Ménière's disease.

Adult↗
PubMed1996

Vestibular neuritis spares the inferior division of the vestibular nerve.

Acute unilateral vestibulopathy, or vestibular neuritis, is the second most common cause of vertigo. To quantify the involvement of the different semicircular canal (SCC) afferents in this disease, we studied the three-dimensional (3D) properties of the vestibuloocular reflex (VOR) in 16 patients 3-10 days after onset of symptoms. Using 3D magnetic search coil eye movement recordings, we measured the speed and axis of eye rotation during spontaneous nystagmus and during rotation in the planes of the different SCCs. In all patients, spontaneous nystagmus axes clustered between the direction expected with involvement of just one horizontal SCC and the direction expected with combined involvement of the horizontal and anterior SCC on one side. Likewise, dynamic asymmetries were found only during rotations about axes which stimulated the ipsilesional horizontal or ipsilesional anterior SCCs. No asymmetry was found when the ipsilesional posterior SCC was stimulated. Thus, both measurements suggest that vestibular neuritis is a partial and not a complete unilateral vestibular lesion and that this partial lesion affects the superior division of the vestibular nerve which includes the afferents from the horizontal and anterior SCCs.

Adult↗
PubMed1991

Histochemical evidence that cochlear efferents are carried with the inferior vestibular nerve in guinea pigs.

Histochemical methods were employed to determine the course of the olivocochlear bundle (OCB) within the vestibular nerve of guinea pigs. Following transection of the inferior vestibular nerve, cholinesterase staining in the cochlea was greatly reduced. Transection of the superior vestibular nerve, however, yielded no detectable change in staining. It is concluded that the cochlear efferent innervation in guinea pigs is carried in the inferior vestibular nerve, at the point of entry into the medial bulla.

Animals↗
PubMed1996

The outcome of vestibular nerve section for intractable vertigo: the patient's point of view.

To document the outcome of vestibular nerve section from the patient's point of view we reviewed 102 patients who had undergone vestibular nerve section 1 to 10 years after operation. Only 3 patients had experienced further vertigo attacks: 2 of these were cured by a further, this time translabyrinthine vestibular nerve section; 1 patient developed multiple sclerosis. In contrast, about 50% of patients developed some subjective problem with balance while standing or walking; in 15% it was present all the time and of moderate severity. Despite this, over 85% of patients reported that they felt much better or back to normal after the operation and were satisfied with the outcome. The development and application of objective preoperative measures of vestibular and, in particular, vestibulospinal function might improve patient selection for vestibular nerve section and thus reduce the number of dissatisfied patients.

Female↗
PubMed1996

Absent vestibular evoked myogenic potentials in vestibular neurolabyrinthitis. An indicator of inferior vestibular nerve involvement?

BACKGROUND: Benign paroxysmal positioning vertigo (BPPV) is generally thought to be caused by canalolithiasis in the posterior semicircular canal, an organ that is innervated by the inferior vestibular nerve. We hypothesized that absent vestibular evoked myogenic potentials (VEMPs) would indicate involvement of the inferior vestibular nerve and that posterior semicircular canal-type BPPV could not develop after vestibular neurolabyrinthitis (VNL) in patients with absent VEMPs. OBJECTIVE: To find out if VEMPs could be helpful in evaluating involvement of the inferior vestibular nerve in acute VNL. DESIGN: We reviewed the VEMP findings in 47 patients (34 men and 13 women) with acute VNL, 10 of whom had then developed posterior semicircular canal-type BPPV. RESULTS: While p13-n23, the first positive-negative peak of the VEMP, was ipsilaterally present on stimulation of the unaffected side in all patients, it was absent on the affected side in 16 patients (34%). The absence or presence of p13-n23 was independent of the results of caloric tests, pure tone audiometry, and auditory brain-stem responses. Typical posterior semicircular canal BPPV developed in 10 of the 47 patients after the acute attack of VNL, always on the same side as the neurolabyrinthitis. The p13-n23 potentials were preserved on stimulation of the affected ear in all 10 patients with BPPV. CONCLUSIONS: These results suggest that if VEMPs are absent from an ear that has suffered acute VNL, then posterior semicircular canal BPPV is unlikely to develop as a consequence of the VNL. The reason for this appears to be that the absence of VEMPs is due to involvement of the inferior vestibular nerve or involvement of the structures that it innervates.

Acoustic Stimulation↗
PubMed1975

Bilateral effects of vestibular nerve stimulation on activity in the lumbar spinal cord.

These experiments were designed to study the effects of vestibular nerve stimulation on the activity of hindlimb motoneuron pools. Two techniques were used to stimulate the vestibular nerves of precollicularly decerebrated cats. In one set of experiments the individual semicircular canals were stimulated via bipolar electrodes placed near the canal nerves. In the second series of experiments the whole vestibular nerve was stimulated with an electrode placed on the intradural nerve. Activity in the hindlimb motoneuron pools was ascertained by evoking monosynaptic reflexes in the various hindlimb nerves. Stimulation of the individual semicircular canals produced response patterns that varied with both the vestibular branch being stimulated and the hindlimb nerve being conditioned. Intradural stimulation of the vestibular nerve, on the other hand, evoked similar response patterns in the antagonist ankle flexor and extensor nerves. The most common pattern consisted of facilitation followed by a period of inhibition. Lesions of descending fiber tracts produced results which suggest the presence of a diffuse pathway, involving the recitular formation, which mediates the observed responses. It is suggested that the biphasic response pattern is analogous to the startle response and the function of the responses is discussed in that context.

Animals↗
PubMed1987

Vestibular nerve and nuclei unit responses and eye movement responses to repetitive galvanic stimulation of the labyrinth in the rat.

Two-second cathodal current pulses were applied at one-minute intervals at a point external to the round window in the ear of each albino rat subject. Responses were recorded in the vestibular nerve ganglion, the vestibular nuclei (single units), or in the eye movements (search coil recording method) of anaesthetized, decerebrated, or alert rats. The unit responses to the galvanic stimuli were characterized and compared with responses to galvanic and rotational stimuli reported in the literature. The main focus of the study, however, was effects of stimulus repetition. In both the vestibular nerve and vestibular nuclei recordings, the responses of many units were substantially larger or smaller at the end of a 13-pulse stimulus train than at the beginning. In the vestibular nuclei, but not in the nerve, there was a slight bias towards a decrease in response magnitude, with 10/88 units showing decreases great enough to be considered as reflecting an habituation process. In contrast, the eye movement responses showed more consistent response decrements, especially in the alert condition, but also in the other conditions (none of the unit recordings were done in alert rats). It is concluded that some of the modifications underlying habituation of the vestibuloocular reflex probably occur in portions of the neuronal reflex pathways that are downstream from the vestibular nuclei.

Animals↗