Monosynaptic vestibular nerve input to vestibular and adjacent reticular neurons projecting into the ascending medial longitudinal fasciculus.
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Eighth nerve in acoustic neuromas. Special reference to superior vestibular nerve function and histopathology.
Eighth nerve specimens were removed during acoustic neuroma surgery, and findings were related to cochlear and especially to superior vestibular nerve function as studied by conventional caloric testing in 21 cases. The origin of the tumor was in eight cases the inferior and in two cases the superior vestibular nerve, and in eight cases the vestibular nerve without more specific localization. In three advanced cases the exact site of origin could not be determined. Leaving age-related changes out of account, the utricle and horizontal canal ampulla appeared normal in all ears except one in which the ampulla was replaced by tumor tissue. In 11 ears the superior vestibular nerve was histologically intact and three of these ears also showed normal caloric responses. In seven ears there was a canal paresis, and in three no reaction was obtained. The ten ears with partial or total nerve invasion by tumor either showed a weak reaction or no response at all. It is likely that an early conduction block arises in both cochlear and vestibular nerves, and reduced reactions to appropriate stimuli do not warrant conclusions that the numbers of anatomically intact nerve fibers possibly are reduced.
Adult↗
The morphology of the vestibular nerve in a patient with normal vestibular function and in patients with Ménière's disease.
The morphology of the vestibular nerve was studied in three fresh nerve specimens obtained by surgery from two patients with Ménière's disease and one patient with tinnitus after an attack of sudden deafness. The number of nerve fibres appeared light microscopically normal. The vestibular ganglion cells of the Ménière-specimens showed, as a characteristic finding advanced vesiculation of the cytoplasm. This change was confirmed by electron microscopy and the vacuoles appeared to consist of widened endoplasmic reticulum cisternae. Numerous primary lysosomes and lipofuscin granules were observed in all vestibular ganglion cells but their number appeared increased in the specimens from Ménière-patients. Some of the vestibular ganglion cells of these patients showed a filamentous appearance and the number of glycogen granules seemed reduced in all of them. All vestibular ganglion cells observed were unmyelinated. The degenerative changes observed might explain the typical elevation of the threshold for vestibular stimulation in Ménière's disease.
Adult↗
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↗
[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.
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The cerebellar projection of the vestibular nerve in the cat.
The projection of the vestibular nerve to the cerebellum of the cat was examined with silver degeneration methods after complete lesions of the vestibular ganglion. The majority of the primary vestibular afferents were traced to the cortex of the ipsilateral nodulus and uvula, relatively fewer entering the ipsilateral flocculus. Fibers were not traced to the paraflocculus, lingula or lateral cerebellar nucleus. A sparse projection to the ipsilateral fastigial nucleus may exist, but it remains equivocal until confirmed with additional methods. Light microscopic examination of plastic sections confirmed these observations and showed further details of the organization of the primary vestibular projection to the nodulus and uvula. These results show that the region of the cerebellum densely innervated by primary vestibular afferents is smaller than previously believed.
Afferent Pathways↗
[Vestibular results before and after neurectomy of the vestibular nerve in cases of vertigo resistant to medical treatment (author's transl)].
25 patients suffering from vertigo due to peripheral-vestibular disorders resistant to medical treatment underwent neurectomy of the vestibular nerve. Präoperatively 24 showed a pathological result in the neurotological examination. In 83% of the cases an abnormal caloric reaction could be seen in the frequency-calorigram, which graphically represents the caloric test. The postoperative objective vestibular results always correlated with the subjective feeling of vertigo. We could see a decrease and finally a disappearance of the horizontal unidirectional spontaneous nystagmus. It is of value to examine the gaze nystagmus in none directions of gaze. In the positiogram, a quantitative scheme of the positional test, one could recongize a decrease of the nystagmus intensity in the follow-up examination. The same was found by testing the vestibulo-spinal reactions. Although the neurectomy of the vestibular nerve involves a serious operation it is nevertheless the first choice of treatment. 96% of the cases are free from vertigo. Postoperative there is a very low complication quota.
Adult↗
Middle fossa vestibular nerve section in the management of Ménière's disease.
The triad of fluctuating hearing loss, tinnitus, and episodic attacks of vertigo known as Ménière's disease can be a frustrating therapeutic problem. While most patients respond to a medical regime consisting of a low salt diet, diuretics, diazepam, and propantheline bromide, there is a significant group who remain refractory to conservative management. These individuals either continue to experience their distressing symptoms or undergo some type of surgical procedure in an attempt to seek relief. There are a multitude of such techniques available to the otologic surgeon and he must make the decision as to which procedure is best for any given individual. The authors' employ three surgical approaches for the management of Ménire's disease. These are the translabyrinthine labyrinthectomy, the endolymphatic subarachnoid shunt, and the middle fossa vestibular nerve section. In this paper the indications for surgery, technique, results and complications are covered in detail. Thirty-one patients are reviewed who have been followed from one to four years postoperatively. Seventeen had total and 14 had superior vestibular nerve sections. The results were much better in the total group, as 94 percent had complete relief of vertigo and 76 percent were able to maintain their preoperative hearing level. The authors feel the middle fossa vestibular nerve section is a valuable addition to the otologist's armamentarium in the treatment of the patient who is refractory to medical management.
Adult↗
Fine structure of the medial and descending vestibular nuclei in normal rats and after unilateral transection of the vestibular nerve.
Cells and neuropil are of similar structure in the descending and medial vestibular nuclei. Two cell types were found: small neurons and larger cells. Three types of axon terminals have been defined: small and large terminals containing spherical vesicles (SV) and terminals with elongated vesicles (EV). Small SV terminals contact perikarya and dendrites, whereas large SV terminals contact fine dendritic branches. EV terminals contact neurons at perikarya and large as well as small dendritic profiles. SV terminals can be presynaptic to EV terminals. Vestibular nerve transection resulted in degeneration of small SV terminals which were found from the first to fifth postoperative day in the ipsilateral nuclei. Glycogen granules were found in various types of axon terminals bilaterally in the vestibular nuclei 3-5 days after right vestibular transection. They were not observed in normal animals or in degenerating vestibular afferent terminals.
Animals↗
Superior vestibular nerve sectioning. Experimental studies in squirrel monkeys.
Spontaneous, positional, and paroxysmal positional nystagmus were studied before and after sectioning the superior division of the vestibular nerve and the anterior vestibular artery in squirrel monkeys. Histopathologic study of the temporal bones confirmed the degeneration of the macula utriculi with release of statoconia, but failed to identify the released utricular statoconia within the vestibular endolymphatic space in any animal. Postoperatively the animals consistently demonstrated direction-fixed spontaneous nystagmus until the end of the experiment (five months). Positional tests and Dix-Hallpike maneuver occasionally changed the intensity of the spontaneous nystagmus, but never elicited paroxysmal positional nystagmus. Possible reasons for not demonstrating paroxysmal positional nystagmus in the squirrel monkey are as follows: a resorption of statoconia; slight morphological alteration of the sensory epithelia of the posterior cristae; interference of the posterior crista function due to partial collapse of the membranous ampulla; the existence of interspecies difference; or possibly a faulty hypothesis regarding the etiologic mechanism of benign paroxysmal positional vertigo.
Animals↗
Middle fossa vestibular nerve section. A histopathological report.
A patient with Meniere's disease underwent a middle fossa superior and inferior vestibular nerve section with excision of Scarpa's ganglia. Studies of this patient's temporal bone, conducted two and one-half years post-operatively, showed normal cochlear and facial nerves. The internal auditory canal showed fibrosis and new periosteal bone formation. There was complete denervation of the vestibular labyrinth except for the posterior semicircular canal crista. Fibrous and osteoid tissue filled the superior and lateral semicircular canals. In this case, these severe degenerative changes, presumably associated with biochemical changes in the vestibular labyrinth, altered the natural course of Meniere's disease. Vertigo was completely relieved, tinnitus improved, and hearing thresholds stabilized during the course of post-operative follow-up.
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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.
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A new stimulation technique of the crista ampullaris of the lateral canal in the adult cat: study of the action potential of the vestibular nerve.
The stimulation of the crista ampullaris of the lateral canal by a short ampullopetal liquid flux produces on the pre-ganglionic vestibular fibres the appearance of a bimodal action potential. The amplitude of this action potential increases with the intensity of the stimulation. This stimulation also provokes the birth of an evoked potential at the level of the vestibular nuclei as well as an ocular jerk.
Action Potentials↗
Ipsilateral utricular and semicircular canal interactions from electrical stimulation of individual vestibular nerve branches recorded in the descending medial longitudinal fasciculus.
Interactions from electrical stimulation of individual vestibular end organ nerves recorded from second order vestibular neurons projecting caudally in the medial longitudinal fasciculus (MLF) have been investigated in unanesthetized, decerebrate decerebellate cats. Canal-canal and utricle-canal interactions were recorded using various condition-test parameters. The brain stem was sectioned to eliminate influence of the contralateral vestibular nuclei, and the condition-test experiments were repeated. The type of interaction observed (inhibition or facilitation) and the degree to which it occurred were dependent on the MLF recording site. Also, in the case of utricular interactions, these were dependent on the site of utricular stimulation. These dependencies indicate a topological arrangement from receptor cell through the second order neuronal projection pathways. Sectioning of the brain stem produced changes in the interaction patterns, indicating masking and/or balancing of the ipsilateral interactions. In interactions between the anterior and posterior canals, instances of no apparent interaction occurring before sectioning converted to inhibition after sectioning. This indicates that some facilitative interaction occurs involving feedback from the contralateral vestibular nuclei, and this facilitation masks or balances ipsilateral inhibition. In interactions between the anterior and horizontal canals, contralateral inhibitory influence masks ipsilateral facilitatory interactions. Contralateral facilitatory influence again balances ipsilateral inhibition in interactions between the horizontal and posterior canals. The degree of inhibition and facilitation observed indicates that considerably more polysynaptic ipsilateral convergence on second order vestibular neurons occurs than has been demonstrated in intracellular studies. Only inhibition was observed when the anterior canal was conditioned by stimulation of the utricular nerve after sectioning. In all other pairings, mixed effects were observed. It is suggested that this is related to known functional connections of semicircular canal second order neurons with neck motoneurons. Not only is canal output affected by utricular activity, but each canal affects utricular output in a different manner.
Afferent Pathways↗
[Surgical approach to the separate branches of the vestibular nerve in the cat].
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Animals↗
Cerebral cortex and vestibular nerve.
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Afferent Pathways↗
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.
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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.
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