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PubMed1974

The projection of the vestibular nerve to the cerebral cortex in the cat.

1. The cerebral cortex in the cat has been examined for responses to contra-lateral vestibular nerve shocks and to natural stimuli.2. Stimulation of the nerve produces short latency (3.5 msec) surface positive responses in very restricted areas. Within these areas, unitary discharges occur during the equivalent negative phase below the surface.3. It has not been possible to evoke unitary activity in these areas by natural stimulation during light anaesthesia with pentobarbitone, chloralose or urethane.4. The distribution and properties of the shock evoked responses have been studied with special attention to the problem of stimulus spread. They are shown to be overlapped by somato-sensory and auditory projections, but to be distinguishable from them. Evidence is presented that previously reported longer latency responses were probably due to stimulus spread.5. Reasons are discussed for the extreme sensitivity of the vestibulocortical pathway to anaesthesia.

Anesthesia, General↗
PubMedDate not supplied

Effects of cholinergic agonists and antagonists of nucleus vestibularis lateralis unit discharge to vestibular nerve stimulation in the cat.

Unit discharge in nucleus vestibularis (NVL) was studied in locally anesthetized cats. The mean firing rate +/-S.E. of spontaneous unitary discharges of NVL neurons was 19.8+/-0.9 Hz and that of spinal-transected animals was 18.0+/-1.6 Hz. The mean firing rate of these neurons in animals with cerebellum ablation and the administration of scopolamine in a dose of 0.5 mg/kg i.v. was relatively low. After administration of physostigmine in a dose of 25 mug/kg i.v. the firing rate was enhanced. The effects of physostigmine were antagonized by scopolamine. About 95% of NVL neurons activated by single electrical shocks to the ipsilateral vestibular nerve showed regular firing following administration of physostigmine. These neurons changed to a gamma distribution at lambda=2 following administration of scopolamine.

Animals↗
PubMed2005

Combined retrosigmoid retrolabyrinthine vestibular nerve section: results of our experience over 10 years.

OBJECTIVE: We aimed to evaluate the results of our experience in vestibular nerve sectioning (VN), which was performed using combined retrosigmoid-retrolabyrinthine approach. STUDY DESIGN: Medical records of 280 patients who were consecutively operated on for incapacitating peripheral vertigo were retrospectively evaluated, and 210 patients who completed 2 years follow-up and had adequate follow-up data were found to be suitable for inclusion in the study. METHODS: Hearing results, vertigo control rates, and complications of the retrosigmoid-retrolabyrinthine VN were evaluated. RESULTS: The patients were suffering from vertigo for a mean period of 32.2 months. Bilateral Meniere's disease occurred in 5.7% of the patients in the follow-up period. A complete or substantial vertigo control could be achieved in 94.4% of the patients (191 [90.1%] in Class A and 9 [4.3%] in Class B). Preoperative speech reception threshold, pure-tone average, and speech discrimination score of the patients were 56.5 dB, 47.4 dB, and 73.6%, respectively. Postoperative corresponding values were 62.2 dB, 43.4 dB, and 68.5%, respectively (p > 0.05). The complication rate was low (2.5%). Most common complication was abdominal hematoma, which was seen in 4.5%. CONCLUSION: VN performed using retrosigmoid-retrolabyrinthine approach has low complication and high vertigo control and hearing preservation rates. It can be applied as an initial surgery or reserved as the last step when the other surgical treatments have failed to control vertigo.

Adolescent↗
PubMed2006

Response of vestibular-nerve afferents to active and passive rotations under normal conditions and after unilateral labyrinthectomy.

We investigated the possible contribution of signals carried by vestibular-nerve afferents to long-term processes of vestibular compensation after unilateral labyrinthectomy. Semicircular canal afferents were recorded from the contralesional nerve in three macaque monkeys before [horizontal (HC) = 67, anterior (AC) = 66, posterior (PC) = 50] and 1-12 mo after (HC = 192, AC = 86, PC = 57) lesion. Vestibular responses were evaluated using passive sinusoidal rotations with frequencies of 0.5-15 Hz (20-80 degrees /s) and fast whole-body rotations reaching velocities of 500 degrees /s. Sensitivities to nonvestibular inputs were tested by: 1) comparing responses during active and passive head movements, 2) rotating the body with the head held stationary to activate neck proprioceptors, and 3) encouraging head-restrained animals to attempt to make head movements that resulted in the production of neck torques of < or =2 Nm. Mean resting discharge rate before and after the lesion did not differ for the regular, D (dimorphic)-irregular, or C (calyx)-irregular afferents. In response to passive rotations, afferents showed no change in sensitivity and phase, inhibitory cutoff, and excitatory saturation after unilateral labyrinthectomy. Moreover, head sensitivities were similar during voluntary and passive head rotations and responses were not altered by neck proprioceptive or efference copy signals before or after the lesion. The only significant change was an increase in the proportion of C-irregular units postlesion, accompanied by a decrease in the proportion of regular afferents. Taken together, our findings show that changes in response properties of the vestibular afferent population are not likely to play a major role in the long-term changes associated with compensation after unilateral labyrinthectomy.

Animals↗
PubMed2004

[Inferior vestibular nerve impairment in auditory neuropathy].

OBJECTIVE: To investigate if auditory neuropathy have inferior vestibular nerve (IVN) lesion and to explore the relation between AN and the IVN lesion by vestibular evoked myogenic potentials (VEMPs). METHODS: VEMPs were observed in 13 patients with auditory neuropathy. And the relation among the duration, hearing threshold of lower frequency and speech discrimination score with VEMPs were observed. RESULTS: Fifty-four percent patients in auditory neuropathy had abnormal VEMPs. They took the form of lower amplitude and no response. The statistical analysis showed that the abnormality of VEMPs had no correlation with lower frequency hearing loss, the duration and speech discrimination score. CONCLUSIONS: The IVN dysfunction may coexist with auditory neuropathy, having lesion in the IVN. However, there was no significant relation between the severity of AN and VEMPs, which meant that AN and inferior vestibular neuropathy had their independence to some extent.

Adolescent↗
PubMed1981

Human vestibular nerve morphology and labyrinthectomy.

Surgical labyrinthectomy leads to extensive and degenerative changes in the membranous labyrinth and is often followed by fibrosis and ossification of the vestibule and neuroma formation. After labyrinthectomy the distal processes of the vestibular nerve degenerate, but the nerve trunk within the internal auditory canal, including Scarpa's ganglion, does not show an obvious loss of neurons. Electron microscopic examination of the cells of Scarpa's ganglion revealed many changes similar to those of chromatolysis, indicating increased cell metabolism and probable regenerative changes. Many nerve fibers appeared to be in the process of regeneration. Some ganglion cells were fibrotic and showed ultrastructural features similar to those of cells that had undergone atrophy but survived in a sublethal state.

Adult↗
PubMedDate not supplied

[Morphologic aspects of the vestibular nerve of the chinchilla].

A quantitative study was made of the number of fibers, their diameters and patterns of distribution in 14 ampullar nerves of chinchilla. The nerves were processed for osmium staining, embedded in plastic and cut serially in 1-micron-thick sections for histologic evaluation. Quantitative evaluation of nerve-fiber characteristics was made with the aid of a laboratory computer and specific programs. The number of the nerve fibers ranged between 1,877 and 2,175. The diameters of the fibers could be as large as 8 microns. The fibers between 2 and 2.5 microns were the most abundant, representing 29.6% of the fiber population. The distribution of fibers in the cristae was size-dependent: 80% of the thin fibers were located at the ends of the nerves, while most of the thick fibers were distributed through the central and intermediate areas.

Animals↗
PubMedDate not supplied

[Light and electron microscopic study of the vestibular nerve and Scarpa's ganglion in Ménière's disease].

Degenerative changes in both the nervus vestibularis and in Scarpa's ganglion depending on the duration of Meniére's disease are visualized by light and electron microscopy. The specimens were obtained by transtemporal neurectomy in patients with Meniére's disease and were fixed quickly. On the thick nerve fibres (pars superior) a splintering of the myelin lamellae, an increase in the nerve fibre diameter and the formation of myelin globes were found. On the thin nerve fibres (pars inferior) protrusion and introversion of whole parts of the myelin sheath had been observed. In the later stages of the disease, losses of axons and decay of myelin sheath were evident. In Scarpa's ganglion, different stages of ganglion cell degeneration were found. The degenerative morphological changes in the nerve and ganglion were more obvious in later stages of the disease.

Adult↗
PubMed1992

Hearing results following posterior semicircular canal injury during antesigmoid retrolabyrinthine selective vestibular nerve section.

The disastrous hearing results in six patients whose posterior semicircular canal was entered during antesigmoid mastoid craniotomy for retrolabyrinthine selective vestibular nerve section were reviewed. The injury occurred during skeletonization of the posterior semicircular canal to maximize intracranial exposure of the eighth nerve. All patients had Meniere's disease. Four patients were deafened, and in two, there was either no serviceable hearing or severe hearing impairment in the operated ear. Caution is urged in posterior semicircular canal labyrinthotomy for vertigo and attempted hearing preservation if a patient has symptoms of endolymphatic hydrops.

Craniotomy↗
PubMed1985

[Synaptic action of vestibular nerve afferents on reticular neurons of the isolated medulla oblongata of the goldfish].

Excitatory post-synaptic potentials (EPSPs) were evoked in reticular neurons of isolated goldfish brian stem by stimulation of the ipsilateral vestibular nerve or by direct intra-axonal activation of single vestibular fibres. Composite EPSPs displayed usually two components. Ca2+-deficient, Mn2+-containing solution abolished the delayed chemical components of EPSPs, but did not affect the short latency responses suggesting dual (electrical-chemical) mode of transmission between some vestibular afferents and reticular neurons.

Animals↗
PubMed1980

Efferent activity in the goldfish vestibular nerve and its influence on afferent activity.

Out of 326 fibres in the horizontal semicircular canal branch of the goldfish vestibular nerve, 7 fibres could be identified as efferents. They showed irregular spontaneous activity and responded to rotatory stimuli with double frequency. Additionally in the central stump of the dissected nerve, efferent fibres were found, the spontaneous and stimulus modulated activity of which could not be differentiated from afferents. Efferents could be driven by a number of stimuli (vestibular, visual, somatosensory). Disruption of the efferent influence upon the receptors by dissection of the nerve or by pharmacological means (Gallamine) led to an increase of spontaneous afferent activity by 50%, showing that there is tonic efferent inhibition. Transfer functions of afferents were not changed after release from efferent influence. Electrical stimulation of efferents in 41% of the fibres led to an increase of afferent activity instead of the expected inhibition, which was seen in another 32%.

Animals↗
PubMed1992

Responses of neurons in the caudal medullary raphe nuclei of the cat to stimulation of the vestibular nerve.

In the decerebrate cat, recordings were made from neurons in the caudal medullary raphe nuclei to determine if they responded to electrical stimulation of the vestibular nerve and thus might participate in vestibulosympathetic reflexes. Many of these cells projected to the upper thoracic spinal cord. The majority (20/28) of raphespinal neurons with conduction velocities between 1 and 4 m/s received vestibular inputs; 13 of the 20 were inhibited, and 7 were excited. Since many raphespinal neurons with similar slow conduction velocities are involved in the control of sympathetic outflow, as well as in other functions, these cells could potentially relay vestibular signals to sympathetic preganglionic neurons. The onset latency of the vestibular effects was long (median of 15 ms), indicating the inputs were polysynaptic. In addition, 34 of 42 raphespinal neurons with more rapid conduction velocities (6-78 m/s) also received long-latency (median of 10 ms) labyrinthine inputs; 26 were excited and 8 were inhibited. Although little is known about these rapidly-conducting cells, they do not appear to be involved in autonomic control, suggesting that the function of vestibular inputs to raphe neurons is not limited to production of vestibulosympathetic reflexes. One hypothesis is that raphe neurons are also involved in modulating the gain of vestibulocollic and vestibulospinal reflexes; this possibility remains to be tested.

Animals↗
PubMed1992

[Electrophysiological identification of the cochlear and vestibular nerves in the cerebellopontine angle: experimental study and clinical implication].

Electrical stimulation was applied on the surface of the eighth cranial nerve in the cerebellopontine angle of dogs and the evoked potentials were recorded with surface electrodes on the scalp. The shape of the evoked potentials recorded was different according to the portion of the nerve stimulated electrically. It was, therefore, possible to precisely identify the nerve stimulated from the surface recorded evoked potentials. This electrophysiological method may be helpful for the surgeon to precisely locate the cochlear and vestibular nerves in various operations in the cerebellopontine angle in human. Our preliminary experience of this monitoring method in acoustic neuroma excision was presented.

Animals↗
PubMed1996

The contribution of the vertical semicircular canals to high-velocity horizontal vestibulo-ocular reflex (VOR) in normal subjects and patients with unilateral vestibular nerve section.

We have examined to what extent the vertical semicircular canals contribute to the nonlinearity of the horizontal VOR imposed by the driving of primary vestibular afferents into inhibitory cutoff at high velocities of head rotation (Ewald's second law). The gain (eye velocity/head velocity) of the horizontal component of the VOR with the head pitched down 30 degrees and pitched up 30 degrees was examined during constant-velocity rotations in normal subjects and patients following unilateral vestibular nerve section. In normal subjects, VOR gain decreases as chair velocity increases from 60-300 degrees/s when the head is pitched up, but VOR gain remains constant when the head is pitched down. This finding implies that the mechanism by which the gain of the horizontal VOR gain remains constant at all velocities of rotation depends upon the pattern of labyrinthine stimulation. Following unilateral nerve section, we found that the directional preponderance (DP) in horizontal VOR depends upon whether the head is pitched up 30 (mean asymmetry = 5%) or pitched down 30 degrees (mean asymmetry = 20%). This is what is expected based on the degree to which the lateral and vertical semicircular canals sense horizontal head acceleration with the head in different degrees of pitch. Hence, following unilateral vestibular lesions, the DP of horizontal VOR gain is most easily elicited at high velocities of head rotation and with the head pitched down 30 degrees. Evidence for DP at the bedside using the "head-shaking nystagmus" technique may be optimally elicited with the head pitched down 30 degrees.

Acceleration↗
PubMed1994

[An experimental herpes simplex virus infection in the vestibular nerve].

The author succeeded in producing vestibular ganglionitis by inoculating herpes simplex virus type 1 (HSV-1) into the back of the auricle of a new-born mouse. Postural deviation to the inoculated side was observed in 14 of 275 mice (5.1%) 6 to 10 days after the inoculation. In 6 of the 14 mice (42.9%) with postural deviation, HSV antigens were demonstrated immunohistochemically in the vestibular ganglion cells of the inoculated side. No antigens were identified in the animals with normal posture or in controls. Vestibular functions were evaluated in 5 animals suffering from postural deviation by the following test procedures. 1. behavior in an open field, 2. righting reflex, 3. transversing a narrow path, 4. ascending a rope, 5. negative geotaxis, 6. grasping a rod, 7. swimming. None could perform these tasks due to impairment of vestibular function. Histopathological and immunohistochemical examinations showed degeneration of the vestibular ganglion cells in 4 of the 5 mice, while HSV-1 antigens were recognized in 2 of them. The results of the present study show that inoculation of HSV into the back of the auricle of a new-born mouse can cause infection of the vestibular ganglion resulting in symptoms similar to those of vestibular neuritis, though the incidence is low compared to that of facial paralysis.

Animals↗