Inhibitory effect of betahistine on polysynaptic neurons in the lateral vestibular nucleus

Summary Effects of betahistine, an antivertigo drug, were examined on the lateral vestibular nucleus (LVN) neurons of cats anesthetized with -chloralose. Spike generation of monosynaptic LVN neurons elicited by vestibular nerve stimulation remained unaffected with intravenous administration of betahistine up to 5 mg/kg and with iontophoretic application of the drug up to 200 nA. In contrast, the spike generation of polysynaptic I neurons in the LVN was dose-dependently inhibited by intravenous as well as iontophoretic application of betahistine. These results suggest that small doses of betahistine more selectively interfere with synaptic transmission in the polysynaptic I neurons than in the monosynaptic neurons.     

Saccular afferent fibers to the cochlear nucleus in the guinea pig

Summary After tracing the vestibular nerve of the guinea pig with horseradish peroxidase (HRP), a conspicuous fiber bundle was found that passed to the ipsilateral cochlear nucleus. HRP-labeled fibers were seen to leave the descending vestibular nucleus at a level caudal to subgroup y in a lateral direction. Travelling close to the restiform body, the axons terminated at cells lying between the dorsal and posteroventral cochlear nucleus. These cells could be distinguished cytoarchitecturally from surrounding cells of the cochlear nuclei. Several electrophysiological investigations have assumed that there is a direct connection between the vestibular and the cochlear system. Compared to these, the fibers under consideration might be the morphological basis for such a vestibulo-cochlear anastomosis.Presented at the First European Congress of Oto-Rhino-Laryngology and Cervico-Facial Surgery, Paris, 26–29 September 1988     

A study on vestibular-evoked myogenic potentials via galvanic vestibular stimulation in normal people

Objectives

The aim of our study is to examine vestibular-evoked myogenic potentials (VEMPs) elicited by the galvanic vestibular stimulation in the sternocleidomastoid muscle (SCM) in healthy subjects for clinical applications of auditory neuropathy or vestibular neuropathy in the future.

Neurochemical changes in the cholinergic system of the rat lateral vestibular nucleus following hemilabyrinthectomy

Summary The neurochemistry of the cholinergic system in the lateral vestibular nucleus (LVN) of the hemilabyrinthectomized rat was studied in view of the previous findings of other research showing that the process of vestibular compensation (VC) following hemilabyrinthectomy can be influenced by the administration of cholinergic agents. At 15 min, 2h, and 7 days after right hemilabyrinthectomy, animals were killed and the LVNs were removed from sections of the brain stem for various neurochemical measurements. The content of acetylcholine (ACh) and the activity of acetylcholinesterase in the LVN showed no significant changes at any time interval. In contrast, choline acetyltransferase activity decreased slightly in the nucleus on the unoperated side 15 min after the operation. These findings possibly implicate alterations in ACh synthesis in the LVN at an early stage of VC. However, there was no significant alteration in either high-affinity choline transport into the LVN or ACh release from the LVN 15 min after the operation. Furthermore, muscarinic ACh-receptor binding also showed no significant changes. These results suggest that the possible alterations in the function of cholinergic synapses in the course of VC indicated by previous pharmacological studies may take place in regions of the brain other than the LVN.     

Effects of stimulation of the vestibular nuclei on posterior hypothalamic neuron activity in guinea pigs

To clarify the differences among the four main vestibular nuclei in the vestibulo-autonomic reflex, we examined the effects of electrical stimulation of superior, lateral, medial and descending vestibular nuclei (SVN, LVN, MVN and DVN) on posterior hypothalamic area (PHA) neurons in the guinea pig. Ipsi- and contralateral SVN stimulation produced excitation in 30% and 25% of the PHA neurons tested, respectively. Twenty percent of the PHA neurons showed an excitatory response to ipsilateral LVN stimulation while 60% of the neurons tested responded to contralateral LVN stimulation, including excitation of 36% and inhibition of 24%. MVN and DVN stimulation produced little change in PHA neuron activity. These findings suggest that vestibular information processed in the SVN and the LVN is conveyed to the hypothalamus and may then contribute to activation of the vestibulo-autonomic reflex.     

Primary vestibular projections in the chinchilla

Summary The central projections of fibers from the vestibular nerve were studied in 19 chinchillas after horseradish peroxidase labelling. In addition, the limits of the vestibular nuclei and the anatomical characteristics of their neurons were also studied. All five vestibular nuclei received primary afferents, but there were extensive areas of them that received very little or no projections at all, such as the rostral part of the superior vestibular nucleus, the dorsocaudal part of the lateral vestibular nucleus, the caudal half of the medial vestibular nucleus and the caudalmost aspect of the dorsal vestibular nucleus.Presented at the First European Congress of Oto-Rhino-Laryngology and Cervico-Facial Surgery, Paris, 26–29 September 1988     

Second-order neural responses after contralateral vestibular nerve sectioning

The characteristics of the response to an 8 degrees/sec2 acceleration of 41 neurons in the medial vestibular nucleus of the cat following vestibular nerve sectioning were compared with those of 73 control neurons at the same site. In 14 of the vestibular nerve-sectioned animals the same neuron was recorded before and after sectioning. No difference was found between the resting discharge rates, maximal response rates, and rates of adaptation of the two groups. Following contralateral vestibular nerve sectioning Type II neurons were still plentiful, suggesting many receive ipsilateral labyrinthine innervation.     

Comparison of VEMPs,VHIT and caloric test outcomes after vestibular neurectomy in Menière’s disease

Objective

Selective unilateral vestibular neurectomy (VN) is considered a reliable surgical treatment in case of recurrent vertigo in Menière’s disease (MD) because of hearing preservation and a minimally invasive posterior fossa retrosigmoid approach. The present study aimed to assess the quality of life and the long-term vestibular function in patients submitted to yearly follow-up after VN because of intractable MD.

Optokinetic nystagmus and vestibular stimulation in squirrel monkey model

Summary Simultaneous application of the rotatory stimulus with a constant angular acceleration (1/sec²) did not clearly improve the optokinetic pursuing ability in squirrel monkeys, even though the directions of vestibular and visual stimuli matched.When the directions of vestibular stimulus and visual stimulus conflicted, the optokinetic pursuing ability markedly declined regardless of the stimulus magnitude. The inter-individual difference was large in that situation.For the vestibular-visual coordination, the active head movement condition is considered to be natural and important as a biological function.This study was supported in part by NASA Contract NAS-9-14546, and NINCDS grants: NS-10940 and NS-07237     

Prednisolone excitation of medial vestibular nucleus neurons in cats

An electrophysiological study was performed to determine whether prednisolone hydrochloride directly influenced neuronal activities of the medial vestibular nucleus (MVN) in -chloralose-anesthetized cats. Single neuronal activities of MVN were recorded extracellularly with a glass-insulated silver wire microelectrode attached along a seven-barreled micropipette. Each barrel was filled with prednisolone, glutamate, glutamic acid diethylester (GDEE) or COCl₂. Except for prednisolone, which was administered both intravenously and microiontophoretically, other chemicals were applied microiontophoretically to the immediate vicinity of the target neurons. These MVN neurons were classified as type I and 11 neurons according to their responses to horizontal and sinusoidal rotations. Intravenous prednisolone (up to 5 mg/kg) enhanced spontaneous and rotation-induced neuronal firings of both type I and II neurons in a dose-dependent manner. In a similar tendency, microiontophoretically applied prednisolone (50–200 nA) dose-dependently increased spontaneous and rotation-induced firings of both type I and II neurons. Microiontophoretic GDEE, a non-selective glutamate receptor antagonist, inhibited glutamate- and rotation-induced neuronal discharges without affecting prednisolone-induced increases in neuronal responses of MVN. In addition, iontophoretically applied CoCl₂, a Ca²⁺ channel blocker, did not affect prednisolone-, glutamate- and rotation-induced neuronal firings of MVN. These results suggest that prednisolone induces excitation of type I and II neurons, probably by acting directly on the membrane of MVN neurons. Thus, glucocorticoids such as prednisolone may be effective for the treatment of vertigo resulting from hypofunction of vestibular nucleus neurons.     

Adaptation of the vertical vestibulo-ocular reflex in cats during low-frequency vertical rotation

Objective

We examined plastic changes in the vestibulo-ocular reflex (VOR) during low-frequency vertical head rotation, a condition under which otolith inputs from the vestibular system are essential for VOR generation.

Vestibular function outcomes after vestibular neurectomy in Meniere disease: Can vestibular neurectomy provide complete vestibular deafferentation?

Objective

Vestibular neurectomy is considered the reference treatment of incapacitating vertigo accompanying Meniere disease, with an efficiency rate of 85–95% in most literature reports.The aim of this study is to evaluate if vestibular neurectomy can provide a complete vestibular deafferentation by investigating complete vestibular function after surgery.

Methods

Prospective study. Twenty-four patients suffering from incapacitated Meniere vertigo crisis beneficiated from a vestibular neurectomy by retrosigmoid approach. The average time between surgery and vestibular evaluation was 1 year. We performed (i) kinetic test, (ii) caloric test and (iii) vibration-induced nystagmus (VIN) at 30, 60 and 100 Hz under videonystagmography recording, (iv) vestibular evoked myogenic potentials (VEMP), (v) video head impulsed test (VHIT) for each semicircular canals and (vi) an evaluation of visual vertical and horizontal subjective (VVS and HVS).

Results

On clinical evaluation, all the patients except one had never experienced any recurrence of vertigo crisis after surgery. The 24 patients would definitely undergo the surgery again. On vestibular evaluation, on the operated side, all patients showed a total areflexia at caloric test; 23 patients had no VEMP response; 23 patients had abolished canals response to VHIT. All the patients had VVS and HVS deviated towards the operated side; 23 patients had a high velocity VIN from 30 to 60 Hz.

Conclusion

This study proves that vestibular neurectomy can provide a complete vestibular deafferentation. We discuss this vestibular evaluation protocol and the main difficulties encounter during surgery, which could lead to partial nerve section and partial relief, and explain residual vestibular function after vestibular neurectomy.     

Convergence of olfactory and nasotrigeminal inputs and possible trigeminal contributions to olfactory responses in the rat thalamus

Summary To elucidate the role of trigeminal input on the olfactory system, field-evoked potentials were measured following electrical stimulation of the nasociliary branch of the trigeminal nerve in the olfactory-related structures in the rat brain. Significant potential changes were recorded in the mediodorsal nucleus of the thalamus and the lateral hypothalamic area. In the mediodorsal nucleus of the thalamus, the neurons responding to olfactory bulb electrical stimulation also responded to trigeminal nerve stimulation. Single neuronal responses of mediodorsal thalamic neurons following odorant stimulation were enhanced by blockade of the trigeminal nerve with procaine. These results suggest that olfactory and trigeminal pathways converge on the same neural elements within the mediodorsal nucleus of the thalamus and that the trigeminal input may modulate olfactory input in this nucleus.Correspondence to: A. Inokuchi     

Experimental study on the eye movements induced by the electrical stimulation of the cerebellar nucleus in the rabbit

The purpose of this study is to investigate the induced eye movements by the cerebellar nuclei stimulation in the rabbits. Forty-five pigmented rabbits were used in this experiments. The cerebellar nuclei, especially medial nucleus, were stimulated electrically and the induced eye movements were observed. The results were as follows. 1. The horizontal nystagmus was produced by the electrical stimulation of the medial, anterior interposed, or posterior interposed nuclei. 2. The horizontal nystagmus towards the ipsilateral to the stimulated side was observed when the caudal portion of the medial nucleus was stimulated. On the other hand, the horizontal nystagmus towards the contralateral to the stimulated side was observed when the rostral portion of the medial nucleus was stimulated. 3. The latency of the field potential in the vestibular nucleus by stimulating the medial cerebellar nucleus, and that in the reverse situation, were 0.7 to 1.1 msec. 4. After the destruction of the lateral vestibular nucleus, no nystagmus was elicited by the stimulation of the medial cerebellar nucleus. From these results, it can be concluded that there is the monosynaptic connection between the medial cerebellar nucleus and the lateral vestibular nucleus. This indicates that the stimulation of the medial cerebellar nucleus produces the excitation of the vestibular nucleus via the cerebello-vestibular fibers and produces the nystagmus in the pigmented rabbits.     

Die Aktivität motorischer Einheiten des Musculus Splenius Capitis bei peripheren vestibulären Läsionen

Summary The activity of single motor units of the splenius-capitis muscle of healthy human subjects and patients with unilateral vestibular lesions was recorded by means of microelectrodes. The major part of these units reacted to vestibular stimulation in the same way as primary and secondary vestibular neurones of other vertebrates. The reactions of these units to trapezoidale stimuli is identical to that of vestibular neurones.An angular acceleration of more than 0.6°/s² is for these units a stimulus which is above threshold, this too corresponds to findings in the vestibular nerve. In patients with unilateral vestibular lesions the threshold for rotatory stimuli is markedly increased on the side of the lesion, whereas the threshold on the other side remains constant.This method is very sensitive and vestibular lesions can be detected which cannot be seen using the common technics for vestibular examination.

Besonderer Dank gilt der Firma Tönnies, Freiburg, die diese Untersuchungen durch leihweises Überlassen von Geräten und Hilfestellung bei der Lösung technischer Probleme erleichtert hat.     

Stereotactic radiotherapy in three weekly fractions for the management of vestibular schwannomas

Purpose

This study evaluates the rates of tumor control, hearing preservation and cranial nerve toxicity with the use of CyberKnife stereotactic radiotherapy consisting of 2100?cGy to the 80% isodose line delivered in three weekly fractions to treat vestibular schwannomas.

Emotional and analytic music perception in cochlear implant users after optimizing the speech processor

The present study examined transmitters that regulate commissural inhibition. Extracellular spikes of a single vestibular neuron were recorded in decerebrated cats. Multibarreled electrodes were filled with transmitter candidates (GABA and glycine), their specific antagonists (bicuculline, strychnine) and 2 M NaCl for extracellular recording. After isolation of a type I neuron, chemicals were iontophoretically applied to examine their effects on the activity of the neuron. The results were as follows. Commissural inhibition caused by electrical stimulation of the contralateral labyrinth was not abolished by the application of strychnine (a glycine antagonist), but was abolished by bicuculline (a GABA antagonist). Commissural inhibition was not abolished by phaclofen. Some bicuculline-sensitive neurons, with a short-latency commissural inhibition (presumably disynaptic inhibition), showed spacial summation when the conditioning stimulation (contralateral vestibular nerve stimulation) was applied with the test stimulation (vestibular nucleus stimulation). It was concluded that commissural inhibition was activated by the GABA_A receptor, but not by the GABA_B receptor, that the inhibitory type I neurons located in the contralateral vestibular nucleus were GABAergic, and that inhibitory type II neurons were also GABAergic neurons.     

The Efficiency of Simultaneous Binaural Ocular Vestibular Evoked Myogenic Potentials: A Comparative Study with Monaural Acoustic Stimulation in Healthy Subjects

Objectives

To evaluate the test-retest reliability and convenience of simultaneous binaural acoustic-evoked ocular vestibular evoked myogenic potentials (oVEMP).

Methods

Thirteen healthy subjects with no history of ear diseases participated in this study. All subjects underwent oVEMP test with both separated monaural acoustic stimulation and simultaneous binaural acoustic stimulation. For evaluating test-retest reliability, three repetitive sessions were performed in each ear for calculating the intraclass correlation coefficient (ICC) for both monaural and binaural tests. We analyzed data from the biphasic n1-p1 complex, such as latency of peak, inter-peak amplitude, and asymmetric ratio of amplitude in both ears. Finally, we checked the total time required to complete each test for evaluating test convenience.

Results

No significant difference was observed in amplitude and asymmetric ratio in comparison between monaural and binaural oVEMP. However, latency was slightly delayed in binaural oVEMP. In test-retest reliability analysis, binaural oVEMP showed excellent ICC values ranging from 0.68 to 0.98 in latency, asymmetric ratio, and inter-peak amplitude. Additionally, the test time was shorter in binaural than monaural oVEMP.

Conclusion

oVEMP elicited from binaural acoustic stimulation yields similar satisfactory results as monaural stimulation. Further, excellent test-retest reliability and shorter test time were achieved in binaural than in monaural oVEMP.     

A Model of Electrically Stimulated Auditory Nerve Fiber Responses with Peripheral and Central Sites of Spike Generation

A computational model of cat auditory nerve fiber (ANF) responses to electrical stimulation is presented. The model assumes that (1) there exist at least two sites of spike generation along the ANF and (2) both an anodic (positive) and a cathodic (negative) charge in isolation can evoke a spike. A single ANF is modeled as a network of two exponential integrate-and-fire point-neuron models, referred to as peripheral and central axons of the ANF. The peripheral axon is excited by the cathodic charge, inhibited by the anodic charge, and exhibits longer spike latencies than the central axon; the central axon is excited by the anodic charge, inhibited by the cathodic charge, and exhibits shorter spike latencies than the peripheral axon. The model also includes subthreshold and suprathreshold adaptive feedback loops which continuously modify the membrane potential and can account for effects of facilitation, accommodation, refractoriness, and spike-rate adaptation in ANF. Although the model is parameterized using data for either single or paired pulse stimulation with monophasic rectangular pulses, it correctly predicts effects of various stimulus pulse shapes, stimulation pulse rates, and level on the neural response statistics. The model may serve as a framework to explore the effects of different stimulus parameters on psychophysical performance measured in cochlear implant listeners.