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PubMed1994

Peripheral innervation patterns of vestibular nerve afferents in the bullfrog utriculus.

Vestibular nerve afferents innervating the bullfrog utriculus differ in their response dynamics and sensitivity to natural stimulation. They also supply hair cells that differ markedly in hair bundle morphology. To examine the peripheral innervation patterns of individual utricular afferents more closely, afferent fibers were labeled by the extracellular injection of horseradish peroxidase (HRP) into the vestibular nerve after sectioning the vestibular nerve medial to Scarpa's ganglion to allow the degeneration of sympathetic and efferent fibers. The peripheral arborizations of individual afferents were then correlated with the diameters of their parent axons, the regions of the macula they innervate, and the number and type of hair cells they supply. The utriculus is divided by the striola, a narrow zone of distinctive morphology, into medial and lateral parts. Utricular afferents were classified as striolar or extrastriolar according to the epithelial entrance of their parent axons and the location of their terminal fields. In general, striolar afferents had thicker parent axons, fewer subepithelial bifurcations, larger terminal fields, and more synaptic endings than afferents in extrastriolar regions. Afferents in a juxtastriolar zone, immediately adjacent to the medial striola, had innervation patterns transitional between those in the striola and more peripheral parts of the medial extrastriola. Most afferents innervated only a single macular zone. The terminal fields of striolar afferents, with the notable exception of a few afferents with thin parent axons, were generally confined to one side of the striola. Hair cells in the bullfrog utriculus have previously been classified into four types based on hair bundle morphology (Lewis and Li: Brain Res. 83:35-50, 1975). Afferents in the extrastriolar and juxtastriolar zones largely or exclusively innervated Type B hair cells, the predominant hair cell type in the utricular macula. Striolar afferents supplied a mixture of four hair cell types, but largely contacted Type B and Type C hair cells, particularly on the outer rows of the medial striola. Afferents supplying more central striolar regions innervated fewer Type B and large numbers of Type E and Type F hair cells. Striolar afferents with thin parent axons largely supplied Type E hair cells with bulbed kinocilia in the innermost striolar rows.

Animals↗

PubMed1991

Histological changes of vestibular nerves and ganglion cells in the acoustic tumor in relation to clinical functions.

The superior vestibular nerves and vestibular ganglion cells were observed electron microscopically in acoustic tumors removed surgically from 15 patients. Furthermore, the sensory cells of the vestibular organs were examined. Histological changes of vestibular nerves and ganglion cells were compared with the caloric responses of the patients. In most cases, the degree of degeneration of myelinated nerve fibers was proportional to the reduced responses of vestibular nerves. The myelinated nerve fibers decreased in number and showed some features of demyelination. The alteration of vestibular ganglion cells was unremarkable in comparison with vestibular nerves. In some cases, the number of lipofuscin granules, vacuolar organelles and amorphous materials markedly increased in the ganglion cells. However, the sensory cells of the vestibular organs appeared normal.

Adolescent↗

PubMed1979

The brainstem projection of the vestibular nerve in the cat.

The projection of the vestibular nerve to the brainstem of the cat was re-examined with silver degeneration methods after complete lesions of the vestibular ganglion. Whereas previous investigations emphasize that only parts of the major vestibular nuclei are innervated by the vestibular nerve, the present investigation shows that only the dorsal division of the lateral vestibular nucleus is uninnervated. Thus, the terminal field of the vestibular nerve extends to the cytoarchitectonic boundaries of the superior, medial, descending, and the ventral division of the lateral vestibular nuclei. Vestibular nerve fibers were also traced to discrete terminal fields in the reticular formation lateral to the abducens nucleus and in the rostral, lateral parts of the accessory cuneate nucleus. These observations indicate a more widespread distribution of vestibular nerve fibers in the brainstem of the cat than previously believed.

Afferent Pathways↗

PubMed1998

Fiber grouping in the feline vestibular nerve before and after labyrinthectomy.

The vestibular nerve is composed of fibers with a wide spectrum of diameters. The fibers of largest diameter are known to innervate the type I hair cells of the cristae, while the small-diameter fibers innervate the type II hair cells. Midsized fibers (dimorphic fibers) represent neurons that innervate both type I and type II hair cells. Reports by others have commented on the tendency for clustering of fibers with like diameters. Rigorous statistical proof for or against clustering has not yet been presented. The explanation for this is, in part, the mathematic complexity of analyzing clustering in a system composed of three elements. We report a new method for analysis of fiber clustering and apply this method to large-, medium-, and small-diameter fibers in the feline vestibular nerve. The fiber grouping in the caudal and rostral ends of the vestibular nerves of six normal animals is compared to that in similar areas of the nerves of five animals 12 to 17 months after unilateral labyrinthectomy. No statistically significant clustering of fiber types was found in the rostral portion of either the control or the labyrinthectomized animals. In the caudal portion of the control nerves, clustering of the large fibers was demonstrated (p < .005, chi2 test). This clustering was not demonstrated after labyrinthectomy. An explanation of these findings is discussed. The method used in this study to analyze fiber clustering may be applicable to other nerve systems of greater complexity.

Animals↗

PubMedDate not supplied

Vestibular nerve findings in 150 neurectomized patients.

Vestibular nerve specimens obtained at neurectomy were studied by light and electron microscopy in 150 patients with various neuro-otological disorders. The vestibular nerve was considered morphologically normal in only 20% of the cases but the changes observed in most cases were interpreted as artifacts or physiological changes of aging. In nearly half of the cases there was excessive fibrosis of the perineurium or endoneurium of the vestibular nerve, or occurrence of glial tissue within or near Scarpa's ganglion. When these changes are of moderate or severe degree, they may be of pathological significance. Severe nerve cell destruction with subsequent fibrosis, indicating primary neuropathy, was found in four cases.

Adult↗

PubMed1996

Vestibular nerve section following previous mastoidectomy.

Vestibular neurectomy is an effective procedure in the management of vertigo due to active labyrinthine disease. Various approaches have been developed for selectively sectioning the vestibular nerve, in order to preserve serviceable hearing and avoid facial nerve injury. In patients who have a mastoid cavity, from previous surgery for chronic otitis media, the approach to the vestibular nerve has to be modified. Considerations taken into account are cavity infection, hearing status, and the presence of associated loud tinnitus. Vestibular or vestibulo-cochlear nerve section has been undertaken, by the senior author, in eight patients with a mastoid cavity from previous surgery for chronic otitis media. Translabyrinthine, retrosigmoid and middle fossa approaches have all been used; strategies for selection of each specific technique are considered, and the aetiology of post-chronic suppurative otitis media (CSOM) peripheral vestibular disease discussed.

Adult↗

PubMed2002

The effect of vestibular nerve section upon tinnitus.

This paper reviews the published evidence regarding the effect of vestibular nerve section upon tinnitus. This is of relevance not only for those performing and undergoing this procedure, but also for those considering the hypothesis that auditory efferent system dysfunction may be influential in tinnitus perception. The auditory medial efferent fibres within the internal auditory canal run within the inferior vestibular nerve, only joining the cochlear nerve at the anastomosis of Oort, a bundle of 1300 fibres running from the saccular branch of the inferior vestibular nerve to the cochlear nerve. Vestibular nerve section procedures therefore section this efferent olivocochlear pathway, and ablate efferent influence upon that cochlear. If auditory efferent dysfunction is involved in tinnitus perception, this ablation might influence the tinnitus status of that patient. A literature search identified 18 papers mentioning tinnitus status after vestibular nerve section, describing the experiences of a total of 1318 patients. The proportion of patients in whom tinnitus was said to be exacerbated postoperatively ranged from 0% to 60%, with a mean of 16.4% (standard deviation 14.0). The proportion of patients in whom tinnitus was unchanged was 17% to 72% (mean 38.5%, standard deviation 15.6), and in whom tinnitus was said to be improved was 6% to 61% (mean 37.2%, standard deviation 15.2). In the majority of patients undergoing this procedure, ablation of auditory efferent input (and thus total efferent dysfunction) to the cochlea was not associated with an exacerbation of tinnitus. The finding of this review is that efferent dysfunction after vestibular nerve section does not consistently worsen tinnitus.

Humans↗

PubMed1987

Surgical approach to the superior vestibular nerve in guinea pigs.

The superior vestibular nerve carries homo- and contra-lateral efferent fibers to the cochlea. The subarcuate fossa, a tube-like structure in the temporal bone of the guinea pig, can be used to reach the superior vestibular nerve at the level of the internal acoustic meatus. Normally, this structure accommodates the dorsal and ventral floccular extension of the cerebellum. This technique has several advantages. Firstly, a reduced cranial opening is necessary; secondly, less cerebellar tissue is sacrificed. Then there is the relative insulation of the operative field, and finally, it presents a straight guide to the internal auditory meatus and vestibular nerve.

Animals↗

PubMed1987

Morphological aspects of the vestibular nerve of the squirrel monkey.

A morphological study of the vestibular nerve of a primate, the squirrel monkey, revealed a systematic organization of neurons according to fiber diameter. At the center of the cristae, thick fibers align in two parallel rows along the long axis; in the periphery of the cristae, thin fibers predominate. Within the superior vestibular nerve the thick fibers of the anterior and horizontal semicircular canals and utricle are situated in the anterosuperior area, the thin fibers in the posterior part. A similar segregation occurs with fibers of the posterior ampullary nerve and the saccule within the inferior vestibular nerve. The fibers continue to segregate at the root entry zone where they lose their Schwann's cell ensheathing and begin to divide into secondary central branches. There is a correspondence between the volume of the ganglion cell and the fiber diameter; hence, a segregation of ganglion cells according to their size also takes place in the vestibular nerve. The organization of the primate's vestibular nerve is similar to that found earlier in an anuran. The relevance of the phylogenetic preservation of the vestibular nerve's anatomical organization is discussed in terms of current physiological findings, which support the differential role of fibers of different diameters in vestibular function.

Animals↗

PubMed1992

Inputs from regularly and irregularly discharging vestibular nerve afferents to secondary neurons in squirrel monkey vestibular nuclei. III. Correlation with vestibulospinal and vestibuloocular output pathways.

1. A previous study measured the relative contributions made by regularly and irregularly discharging afferents to the monosynaptic vestibular nerve (Vi) input of individual secondary neurons located in and around the superior vestibular nucleus of barbiturate-anesthetized squirrel monkeys. Here, the analysis is extended to more caudal regions of the vestibular nuclei, which are a major source of both vestibuloocular and vestibulospinal pathways. As in the previous study, antidromic stimulation techniques are used to classify secondary neurons as oculomotor or spinal projecting. In addition, spinal-projecting neurons are distinguished by their descending pathways, their termination levels in the spinal cord, and their collateral projections to the IIIrd nucleus. 2. Monosynaptic excitatory postsynaptic potentials (EPSPs) were recorded intracellularly from secondary neurons as shocks of increasing strength were applied to Vi. Shocks were normalized in terms of the threshold (T) required to evoke field potentials in the vestibular nuclei. As shown previously, the relative contribution of irregular afferents to the total monosynaptic Vi input of each secondary neuron can be expressed as a %I index, the ratio (x100) of the relative sizes of the EPSPs evoked by shocks of 4 x T and 16 x T. 3. Antidromic stimulation was used to type secondary neurons as 1) medial vestibulospinal tract (MVST) cells projecting to spinal segments C1 or C6; 2) lateral vestibulospinal tract (LVST) cells projecting to C1, C6; or L1; 3) vestibulooculo-collic (VOC) cells projecting both to the IIIrd nucleus and by way of the MVST to C1 or C6; and 4) vestibuloocular (VOR) neurons projecting to the IIIrd nucleus but not to the spinal cord. Most of the neurons were located in the lateral vestibular nucleus (LV), including its dorsal (dLV) and ventral (vLV) divisions, and adjacent parts of the medial (MV) and descending nuclei (DV). Cells receiving quite different proportions of their direct inputs from regular and irregular afferents were intermingled in all regions explored. 4. LVST neurons are restricted to LV and DV and show a somatotopic organization. Those destined for the cervical and thoracic cord come from vLV, from a transition zone between vLV and DV, and to a lesser extent from dLV. Lumbar-projecting neurons are located more dorsally in dLV and more caudally in DV. MVST neurons reside in MV and in the vLV-DV transition zone.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1991

Retrolabyrinthine vestibular nerve section: efficacy in disorders other than Menière's disease.

The retrolabyrinthine vestibular nerve section has evolved as an effective treatment for intractable vertigo of peripheral vestibular origin when hearing preservation is desired. This report studies the efficacy of retrolabyrinthine vestibular nerve section for control of vertigo due to causes other than Meniere's disease. This report details our experience with 42 patients with a wide variety of diagnoses. The reduced success rate of retrolabyrinthine vestibular nerve section in these patients is difficult to evaluate, as very few patients have been analyzed with respect to their specific diagnoses. Of patients who underwent retrolabyrinthine vestibular nerve section for control of vertigo, 23 patients had uncompensated vestibular neuritis and 19 others had a wide range of other diagnoses. For patients with uncompensated vestibular neuritis (n = 23), the physician record noted that 39% of patients were cured and 30% improved. This compares to our series of patients with Meniere's disease (n = 48), where 94% were cured and 2% improved. The true vestibular abnormality may be less reliably identified in patients with uncompensated vestibular neuritis, contributing to the less effective results. Since the development of a vestibular rehabilitation program, retrolabyrinthine vestibular nerve section for uncompensated vestibular neuritis has been all but abandoned. Retrolabyrinthine vestibular nerve section appears to achieve a high cure rate in patients with sensorineural hearing loss associated with their vestibular abnormalities. While retrolabyrinthine vestibular nerve section is helpful for control of vertigo in some diagnoses, a substantial incidence of persistent postoperative dysequilibrium was noted.

Adolescent↗

PubMed1997

Morphologic changes in the vestibular nerves and nuclei after labyrinthectomy in the cat: a case for the neurotrophin hypothesis in vestibular compensation.

Morphological changes in the vestibular nerves and superior vestibulocular neurons (SVON) after unilateral labyrinthectomy in cats revealed a progressive loss of axons in the ipsilateral vestibular nerve (35%) and synaptic profiles (SP) on ipsilateral SVON (60%) up to a 1-year survival period. Although the ipsilateral vestibular nerve showed further degeneration (45%) at 2 years post ablation, the number of SP on ipsilateral SVON increased to 60% of normal (40% loss). These SP likely represent sprouting from crossing commissural or cerebellar pathways. Contralateral vestibular nerves at 1 and 2 years post ablation revealed normal numbers and size spectrum, but the number of SP contacting the contralateral SVON at 8 weeks, 1 and 2 years paralleled the levels of SP found on ipsilateral SVON. The symmetry in adjustment of SP on the SVON of both sides of the brainstem after ablation may be explained by the neurotrophin hypothesis.

Adaptation, Physiological↗

PubMed2004

Vestibular nerve section versus intratympanic gentamicin for Meniere's disease.

OBJECTIVES/HYPOTHESIS: Vestibular nerve section and transtympanic gentamicin administration are procedures with proven efficacy in the treatment of vertigo associated with Meniere's disease refractory to medical management. Hearing loss is a known complication of each of these procedures; however, there has not been a report of hearing results of both treatments from a single institution. STUDY DESIGN: Retrospective review. METHODS: Review was made of 25 patients undergoing gentamicin injection and 39 patients undergoing vestibular nerve section for Meniere's disease. Rate of vertigo control and pretreatment and post-treatment pure-tone average values and speech discrimination scores were reported. RESULTS: The mean preoperative pure-tone average for patients having vestibular nerve section was 47.2 dB, with a speech discrimination score of 75.4%. In these patients, the postoperative pure-tone average was 49.1 dB and the speech discrimination score was 75%. Patients undergoing gentamicin injection had a mean pretreatment pure-tone average of 55.9 dB and a speech discrimination score of 62%. The post-treatment pure-tone average and speech discrimination score for the gentamicin group were 68.8 dB and 49.3%, respectively. Five of 25 patients (20%) in the gentamicin treatment group and 1 of 39 (3%) in the vestibular nerve section treatment group had an increase in bone-conduction threshold greater than 30 dB. The amount of postprocedure hearing loss was significantly greater in the gentamicin treatment group (P =.006). Control of vertigo was good to excellent in 95% of the patients treated with vestibular nerve section and in 80% of the patients treated with gentamicin. CONCLUSION: Although vestibular nerve section and transtympanic gentamicin are both acceptable treatment options for vertigo associated with Meniere's disease, gentamicin causes a higher level of hearing loss related to treatment and vestibular nerve section has higher vertigo control rates.

Anti-Bacterial Agents↗

PubMedDate not supplied

[Distribution of vestibular nerve fiber endings in the ventral vestibular nucleus of the stato-acoustic complex of the medulla oblongata in Rana temporaria frogs].

Electronmicroscopic studies have been made on the distribution of the primary vestibular afferents after sectioning the VIIIth nerve in the frog Rana temporaria. The projections of the vestibular nerve fibers extend ipsilaterally. Some of the primary vestibular afferents are connected with the second-order neurons by means of electrotonic contacts. Degeneration of postsynaptic components was found in axo-axonal synapses. Some of the vestibular neurons send axons to the labyrinth. Possible functional significance of these findings is discussed.

Animals↗

PubMedDate not supplied

The influence of middle ear pressure on the vestibular nerve activity in cats.

The influence of middle ear pressure on the vestibular nerve activities was investigated in anesthetized cats. The vestibular nerve activities were recorded intraaxonally and positive or negative pressure was applied to the middle ear cavity through a tympanic membrane perforation. The firing of vestibular nerve fibers, especially the regular type nerve that responded to horizontal semicircular canal stimulation, increased with positive pressure and decreased with negative pressure. Most vestibular nerves that responded to anterior or posterior semicircular canal stimulation were not influenced by changes in the middle ear pressure. These results indicate that middle ear pressure load is transmitted to the vestibular end organs and then to vestibular nerve.

Action Potentials↗

PubMed2004

Preservation of tap vestibular evoked myogenic potentials despite resection of the inferior vestibular nerve.

Sound and skull-tap induced vestibular evoked myogenic potentials (VEMP) were studied in a 43-year-old man following inferior vestibular neurectomy. Surgery was performed because of a small acoustic neuroma. Postoperative caloric testing suggested sparing of superior vestibular nerve function on the operated side. In response to sound stimulation there were no VEMP on the operated side, irrespective of whether sounds were presented by air- or bone-conduction. This suggests sound-induced VEMP to be critically dependent on inferior vestibular nerve function and this is in agreement with present knowledge. However, VEMP were obtained in response to forehead skull taps, i.e. positive-negative VEMP not only on the healthy side but also on the operated side. This suggests remnant vestibular function on the operated side of importance for forehead skull tap VEMP, because with complete unilateral vestibular loss there are no (positive-negative) VEMP on the lesioned side. Thus, forehead skull-tap VEMP depend, at least partly, on the superior vestibular nerve function.

Acoustic Stimulation↗

PubMed1991

A light and electron microscopic study of the development of the Mauthner cell and vestibular nerve in the axolotl.

Vestibular axons form synapses on a restricted area of the lateral dendrite of the Mauthner cell, a large, identified brainstem neuron found in fish and amphibians. The differentiation of the vestibular nerve, medullary neuropil, and Mauthner cell of the axolotl (Ambystoma mexicanum) was studied to understand better the means by which this synaptic specificity arises. The Mauthner cell first extends a medial process and then a lateral dendrite. The latter initially elongates as a simple process and later sends out branches. As the lateral dendrite grows, vestibular axons enter the brainstem to form one of the earliest of several discrete axon fascicles that course longitudinally through the neuropil. The fascicles, many of which are identifiable on the basis of their location and axonal morphology, are the precursors of the longitudinal tracts of the mature salamander. The lateral dendrite grows dorsally over the orthogonally oriented fascicles, making contact with each at a characteristic time and place. The first afferents to form synapses do so on the soma and proximal lateral dendrite; subsequent afferent groups terminate more distally. Axons within a given fascicle form synapses with the Mauthner cell in a discrete and initially homogeneous domain. As dendritic branches form and the organization of the longitudinal fascicles becomes more complex, the homogeneity of axons terminating on a given region of the Mauthner cell surface is lost, but no major rearrangement or migration of terminals is apparent. These observations are consistent with both active recognition and passive spatiotemporal models of synaptic site specificity.

Ambystoma mexicanum↗

PubMed2002

Vestibular nerve sectioning for intractable vertigo: efficacy of simplified retrosigmoid approach.

OBJECTIVE: To determine the surgical efficacy of a simplified retrosigmoid approach for vestibular nerve sectioning. STUDY DESIGN: A retrospective analysis. SETTING: Tertiary academic referral center. PATIENTS: Twenty-eight consecutive patients who underwent vestibular nerve sectioning for intractable peripheral vestibular disorders. INTERVENTION: All patients had a simplified retrosigmoid approach for vestibular nerve sectioning. MAIN OUTCOME MEASURES: Functional outcome after vestibular nerve sectioning was analyzed with respect to improvement in patient disability from vertigo and reduction in the frequency of definitive vertigo attacks. Resolution of lightheadedness provided an additional outcome measure. The incidence of surgical complications, including postoperative headache, was determined, and the operative time was reviewed. RESULTS: Twenty-six patients (92.9%) had an improved functional level postoperatively, 21 (75.0%) had excellent improvement, 4 (14.3%) had significant improvement, 1 (3.6%) had limited improvement, and 2 (7.1%) had no change. No patient was worse postoperatively. Eighteen of 23 Ménière's patients (78.3%) had complete control of definitive vertigo attacks after vestibular nerve sectioning. Improvement in lightheadedness was seen in 23 patients (82.1%), 11 (39.3%) of whom reported complete resolution. Postoperative headache developed in 1 (3.6%) patient. No patients experienced infection, facial weakness, or leakage of cerebrospinal fluid. Mild hearing deterioration was seen in 2 patients (7.1%). The mean operative time was 76.3 minutes. CONCLUSION: With excellent efficacy, short operative time, and a low incidence of postoperative hearing loss or headache, this simplified retrosigmoid technique should be considered for vestibular nerve sectioning in patients with intractable peripheral vestibular disorders.

Adult↗