[A virus in the vestibular nerve].
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Humans↗
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Myelin-sheath abnormalities in the vestibular nerves of chronically diabetic rats.
Electron microscopic examination of the saccular and utricular nerves of rats with streptozocin-induced diabetes mellitus revealed differences from age-matched control animals, mainly related to myelin sheaths. Nerves from diabetic rats had a high incidence of a variety of osmiophilic inclusion bodies, often associated with disrupted myelin-sheath lamellae, lysosomal bodies, and periaxonal expansions of Schwann cell cytoplasm. The occurrence of osmiophilic inclusion bodies within nerve profiles was correlated with the severity of diabetes as measured by blood glucose levels (p < 0.001, linear-regression ANOVA). Duration of diabetes was not related to incidence of inclusion bodies. No evidence of demyelination/remyelination or neuronal degeneration was observed. An unusual Schwann cell reaction was noted, involving lysosomal digestion of large, pinched-off portions of myelinated nerve fibers of some diabetic rats. Both this Schwann cell reaction and the high incidence of inclusion bodies may be due to increased nonenzymatic glycosylation of myelin proteins in the diabetic animals.
Animals↗
Vestibular nerve section for Ménière's disease.
In summary: (i) the fact that VNS spares auditory function makes it preferable to labyrinthectomy. A comparison of VNS and the "conservative" operations on the inner ear shown that they have much the same effect on hearing. VNS by controlling vertigo may also provide an additional benefit by eliminating one of the stress factors concerned in the perpetuation of hydrops; (2) in the treatment of vertigo, VNS is now the most effective method of treatment. Because of elimination of vertigo is what chiefly concerns most of our patients, we suggest that when medical treatment fails to control vertigo, VNS is the surgical method of choice.
Adult↗
The nuclei of the vestibular nerve of the red kangaroo, Megaleia rufus.
The preceeding account describes vestibular nuclei of the kangaroo which conform to the general mammalian pattern. Certain pecularities such as subdivisions of the medial vestibular nuclei are reported but cannot be assigned functional importance. The four major vestibular nuclei and the cerebellum receive vestibular root fibers in like manner as in other mammalian brains. The nuclear patterns and the secondary connections of the vestibular complex in the kangaroo are likewise consistent with those described in other mammals. This is so evident from the description of these regions in the kangaroo and the reports in the literature that the statement needs no further documentation. However, there are certain differences which are significant. Unusual size and/or differentiation of a center, together with an increase in the projection path arising from it, is often reflected in the behavioral patterns of the animal. Thus the lateral vestibular nucleus and the ventrolateral vestibulospinal tract are conspicuously large in the kangaroo in which the methods of locomotion and the manner in which he fights must require frequent orientation in space. It is obvious that the locomotion capabilities of the kangaroo are in large measure due to his well developed vestibular complex and its descending connection. Studies of the sort represented here, then, emphasize the specializations in certain systems and provide information with regard to the interrelations between the anatomic patterns and functional specilization in these systems. They also supplement our knowledge of the course of differentiation within the mammalian phylum. It is to be noticed that specialization at a given level may occur at any place in the evolutionary scale but cephalization is an indication of a relatively progressive development from lower to higher forms.
Animals↗
Alternating episodes of vestibular nerve excitation and failure.
Recurrent episodes of oscillopsia, rotational vertigo, and postural imbalance were elicited and modulated by changing the horizontal head positions of a patient with an arachnoid cyst in the right cerebellopontine angle that distorted the vestibulocochlear nerve. Oculomotor analysis revealed two different types of attacks depending on the particular head position: 1) episodes of vestibular hypofunction (minutes to several hours) with normal head position and 2) paroxysmal vestibular excitation (seconds) with head rotation to the left. The most likely cause is a transition from conduction block to ectopic discharges, which occurs when various peripheral nerves are compressed. One week after resection of the cyst and decompression of the eighth cranial nerve the patient was symptom free, and the electronystagmogram was normal.
Arachnoid Cysts↗
Connections of the facial and vestibular nerves: an anatomic study.
The facial and vestibulocochlear nerves emanate from the brain stem and then run parallel to each other within the internal auditory canal prior to their more peripheral distribution. Although anatomic connections between the facial and cochlear nerves have been described, reports outlining facial-vestibular anastomoses are few and may be found primarily in the non-English literature. The present study documents the existence of vestibulofacial neural connections as part of an anatomic dissection of 17 fresh human temporal bones.
Facial Nerve↗
Anatomic and physiological correlates in bullfrog vestibular nerve.
1. The correlations between anatomic and physiological characteristics of primary afferent neurons innervating the anterior semicircular canal in the bullfrog were investigated. These characteristics were examined separately in large groups of neurons, and the direct correlations between them were established in a subset of neurons by means of intraaxonal recording and labeling. 2. Anatomic features of the anterior canalicular nerve that were related with fiber diameter were studied. This nerve was composed of an average of 1,142 fibers (standard deviation of 171 in 5 samples), of which 42% were less than 2 microns in diameter and 8% were greater than 7 microns. The nerve branched into 6 clearly defined bundles, whose fiber diameter-dependent composition could be determined in 5 samples. In the 2 center bundles, 32% of the fibers had diameters greater than 7 microns. In contrast, these thick fibers comprised only 4% of the fiber population in the 2 lateralmost bundles, in which 44% of the fibers had diameters less than 2 microns. The projections of labeled afferent fibers were traced into the neuroepithelium, and it was demonstrated that all thick fibers, even those of the lateral bundles, turned toward more central regions of the crista. Consequently, in the bullfrog, there is a clear predominance of thick afferent fibers innervating the anterior crista's central region and thin fibers in the peripheral region. 3. The dendritic morphology of the broad classes of afferent fibers (i.e., thick and thin) was elucidated. Individually labeled thick afferents possessed dendrites forming short, thick, clawlike extensions to contact a few hair cells. The thinnest afferents were labeled through extracellular horseradish peroxidase (HRP) injections. In contrast to the thick fibers, thin afferents were characterized by an unbranched trajectory with serially located bouton-like structures that were apposed to successive hair cells. 4. The characteristics of spontaneous firing and the responses to rotational stimuli were determined for 138 anterior canalicular neurons. Spontaneous firing rates ranged from 0 to 95 spikes.s-1. The coefficient of variation (CV) of spontaneous firing ranged from 0.12 to 2.5. Response gains to high- (0.5 and 0.4 Hz) and medium- (0.05 Hz) frequency sinusoidal acceleration stimuli were positively correlated with CV (P less than 0.001) for neurons with a CV value less than or equal to 0.5. The gain of neurons characterized by more irregular spontaneous firing (CV values greater than 0.5) was uncorrelated with CV.(ABSTRACT TRUNCATED AT 400 WORDS)
Animals↗
The vestibular nerve of the chinchilla. IV. Discharge properties of utricular afferents.
1. Extracellular recording techniques were used in the chinchilla to study the discharge properties of utricular afferents, including their discharge regularity, background discharge, and responses to both externally applied galvanic currents and centrifugal forces. 2. A normalized coefficient of variation (CV*), independent of discharge rate, was used to classify units as regularly (CV* less than 0.10), intermediate (0.10 less than or equal to CV* less than or equal to 0.20), or irregularly discharging (CV* greater than 0.20). In some circumstances, it was useful to recognize a group of very regularly discharging afferents (CV* less than 0.05). The CV* ranged from less than 0.020 to greater than 0.60. Regular units outnumbered irregular units by an approximate 3:1 ratio. The distribution of CV*s was bimodal: there was a major peak at CV* = 0.03 and a minor peak at CV* = 0.3. 3. Background rates were measured with the head in a horizontal position. Those of regular units usually fell between 40 and 80 spikes/s (mean: 54 spikes/s); those of irregular units were more broadly distributed (mean: 47 spikes/s). 4. Units were categorized in terms of the tilt directions resulting in increased discharge. There is a broad distribution of excitatory tilt directions with some units excited by ipsilateral rolls, others by contralateral rolls, some by nose-up pitches, and still others by nose-down pitches. In the chinchilla, there are almost equal numbers of units excited by ipsilateral or contralateral tilts. This is in contrast to previous findings in the cat and squirrel monkey, where the former units predominant by a 3:1 ratio. The difference can be related to the fact that the medial zone of the macula, where units excited by ipsilateral tilts reside, makes up a smaller proportion of the sensory epithelium in the chinchilla than in the monkey. 5. Galvanic sensitivity (beta *) and discharge regularity (CV*) were related by a power law, beta* = (CV*), with an exponent, b = 0.70. 6. Responses to sinusoidal centrifugal forces in the frequency range, f, between DC and 2 Hz were characterized by their gains (gf) and phases (phi f), taken with respect to peak linear force. Response linearity was studied by varying the amplitude of a 0.1-Hz sinusoid from 0.05 to 0.4 g. Nonlinear distortion was small (approximately 10%), as was the variation of gain (+/- 10%) and phase (+/- 5 degrees) with amplitude. 7. Response dynamics vary with discharge regularity. Very regular units are tonic. Their gains are typically 50 spikes.s-1/g and almost constant (+/- 10%) over the entire frequency range. Phases hover near zero with small (5 degrees) phase leads at low frequencies and slightly larger (10 degrees) phase lags at high frequencies. Irregular units are more phasic.(ABSTRACT TRUNCATED AT 400 WORDS)
Action Potentials↗
Responses of afferent and efferent neurons to visual inputs in the vestibular nerve of the frog.
In the frog immobilized by intralymphatic injection of D-tubocurarine, stimulation of the visual apparatus with either electrical shocks applied to the optic chiasma or light pulses elicited, in many cases, an increase and a decrease of firing of efferent and afferent vestibular neurons, respectively, recorded from the horizontal semicircular canal nerve. Optokinetic stimulation was completely inefficient in modulating the efferent and afferent discharge. These results show that stimulation of the visual system can modify vestibular apparatus fuctioning at the most peripheral level. However, it is likely that the effects observed were due to an arousal phenomenon or/and to a motor corollary discharge.
Action Potentials↗
Tympanic and transtympanic electrocochleography in acoustic neuroma and vestibular nerve section surgery.
Eighth nerve action potential (AP) amplitudes and latencies and cochlear microphonic (CM) amplitudes were compared using tympanic and transtympanic electrocochleography (ECOG) in two patient groups. Tympanic ECOG was performed with a wick electrode placed on the tympanic membrane (TM). Transtympanic ECOG was performed with a needle electrode placed on the promontory of the anesthetized patient. Eighteen subjects were tested by tympanic ECOG as part of a preoperative assessment for either acoustic neuroma removal or transection of the vestibular portion of the eighth cranial nerve. Surgery occurred within 1 week of the preoperative evaluation. Intraoperative auditory monitoring was performed using transtympanic ECOG. Baseline recordings were compared to the preoperative tympanic ECOG data. Stimuli were condensation and rarefaction clicks and tone bursts, presented by an insert earphone. As expected, the two methods resulted in essentially identical response latencies and large amplitude differences, although the response amplitudes were extremely variable. The AP amplitude and the CM amplitude did not increase by the same factor with the transtympanic (TT) electrode compared to the tympanic electrode. On comparison of preoperative and intraoperative response amplitudes with regard to stimulus polarity, tympanic electrocochleography appears to be a useful method of gathering preliminary information on the status of the patient's auditory system. In this study, tympanic ECOG was found to have some predictive value when trying to ascertain the best intraoperative monitoring situation.
Acoustic Stimulation↗
Vascular compression syndrome of the vestibular nerve: a critical analysis.
The rationale, indications, and surgical results of microvascular decompression for the treatment of vertigo are reviewed, and a critical analysis is made. The syndrome of disabling positional vertigo is discussed. It is concluded that (1) vascular compressive vestibular neuropathy may exist, (2) the current published diagnostic criteria for this disorder are insufficient to firmly establish the diagnosis, and (3) further work delineating this syndrome should be undertaken.
Brain↗
Responses to somatosensory input by afferent and efferent neurons in the vestibular nerve of the frog.
In the frog, we have recorded the activity of efferent and afferent fibers in the nerve of the horizontal semicircular canal in response to somatosensory stimulation. Recordings were made extracellularly by means of glass micropipettes filled with 2 M NaCl, and somatosensory stimulation was produced either by electrical stimulation of the sciatic nerve (ipsi- or contralateral to the recording side) or by vibratory stimulation of the gastrocnemius. The discharge frequency of 43% of the efferent fibers recorded was significantly increased by such stimulation, while the activity of the others was unaffected. The discharge rate of the afferent fibers was either significantly increased (in about 11% of the cases when the results were pooled together) or significantly decreased (in about 22% of the cases) by stimulation of the somatosensory system. The latencies of the responses ranged from 5 to 50 ms. These results show that: somatosensory input can influence the activity of the vestibular apparatus at the most peripheral level; modulation of the afferent discharge is mediated by the efferent vestibular system (EVS); the influence of the EVS on the vestibular afferent activity is both inhibitory and facilitatory, and the responses to somatosensory stimulation are mediated by both long-latency polysynaptic and short-latency oligosynaptic pathways. The functional significance of these two pathways is discussed.
Animals↗
Quantitative determinations of neurons and glial cells in the nuclei of the facial and vestibular nerves in man, monkey and dog.
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Adult↗
Postsynaptic influences on the vestibular non-deiters nuclei from primary vestibular nerve.
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Cerebellum↗
[The differential diagnostic significance of provoked vestibular nerve reactions].
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Brain Neoplasms↗
Are There Parallel Channels in the Vestibular Nerve?
A popular concept in neurobiology is that sensory information is transmitted to the central nervous system over parallel channels of neurons that play different functional roles. But alternative organizing schemes are possible, and it is useful to ask whether some other framework might better account for the diversity of vestibular primary afferents.
Journal Article↗
NT-3 replacement with brain-derived neurotrophic factor redirects vestibular nerve fibers to the cochlea.
Survival of inner ear sensory neurons depends on two neurotrophins, BDNF and NT-3, and their respective receptors, TrkB and TrkC. Because both receptors are present in the same neuron, it has been suggested that BDNF and NT-3 are functionally redundant in promoting neuronal survival. Knock-in of one ligand into the locus of the other one confirmed this hypothesis for the cochlea, leaving open the question of why two neurotrophins are required for proper innervation of the mammalian ear. Here, we show that the precise spatiotemporal pattern of expression of the two neurotrophins is essential for proper patterning of the inner ear innervation. Mice expressing BDNF under the control of the NT-3 promoter develop exuberant projections of vestibular sensory neurons to the basal turn of the cochlea. This projection can be enhanced by combining the transgene with a null mutation of BDNF. However, vestibular fibers rerouted into the cochlea do not reach hair cells and remain outside the organ of Corti, suggesting a chemotactic role for neurotrophins on these fibers. Our data provide genetic evidence that neurotrophins in the ear exert both survival and axon guidance roles.
Animals↗
Synaptogenesis of the efferent vestibular nerve endings of the cat: ultrastructural study.
The maturation of the innervation of the sensory hair cells of the cristae ampullares was studied in the newborn cat. The essential characteristics of the adult are already present in the type II cells at this age. The type I cells on the contrary reveal different degrees of maturation. It was observed that in the immature stages the efferent endings which were already filled with synaptic vesicles were in direct contact with the membrane of the sensory cell. The nerve chalice as it settles into place breaks this contact and simultaneously a synapse is created between the efferent endings and the afferent chalice.
Animals↗