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PubMed2002

GluR2-R4 AMPA subunit study in rat vestibular nuclei after unilateral labyrinthectomy: an in situ and immunohistochemical study.

In the present investigation, we address the question of whether the expression of GluR2-R4 subunits mRNAs and GluR2 and GluR4 subunits protein of the alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA)-selective glutamate receptors are modulated in the vestibular nuclei following unilateral labyrinthectomy. Specific GluR2-R4 radioactive oligonucleotides were used to probe sections of rat vestibular nuclei according to in situ hybridization methods. The signal was detected by means of film or emulsion photography. GluR2 and GluR4 subunit expression were also measured in control and operated rats by use of specific monoclonal GluR2 and GluR4 antibodies. Animals were killed at different stages following the lesion: 1, 3 or 8 days for the in situ hybridization study and 4 and 8 days for the immunohistochemical study. In normal animals, several brainstem regions including the lateral, medial, superior and inferior vestibular nuclei expressed all the GluR2, GluR3 and GluR4 subunit mRNAs. Moreover, numerous vestibular nuclei neurons are endowed with AMPA receptors containing the GluR2 and the GluR4 subunits. In unilaterally labyrinthectomized rats, no asymmetry could be detected on autoradiographs between the two medial vestibular nuclei probed with the GluR2 and the GluR4 oligonucleotide probes regardless of the delay following the lesion. However, compared to control, a bilateral decrease (-22%) in GluR3 gene expression was observed in the medial vestibular nuclei 3 days after the lesion followed by a return to normal at day 8 post-lesion. No significant asymmetrical changes in the density of GluR2- and GluR4-immunopositive cells could be detected between the intact and deafferented sides in any part of the vestibular nuclear complex and at any times (day 4 or day 8) following the lesion. Our data show that the removal of glutamatergic vestibular input induced an absence of modulation of GluR2 and GluR4 gene and subunits expression. This demonstrates that GluR2 and GluR4 expression do not play a role in the recovery of the resting discharge of the deafferented medial vestibular nuclei neurons and consequently in the functional restoration of the static postural and oculomotor deficits. The functional role of the slight and bilateral GluR3 mRNA decrease in the vestibular nuclei remains to be elucidated.

Animals↗
PubMed1997

Differential expression of alpha2-7, alpha9 and beta2-4 nicotinic acetylcholine receptor subunit mRNA in the vestibular end-organs and Scarpa's ganglia of the rat.

To further characterize the pattern of expression of the nicotinic acetylcholine receptor (nAChR) subunits in the peripheral vestibular system, we conducted RT-PCR of all known mammalian nAChR alpha and beta subunits in mRNA extracted from adult rat vestibular primary afferent neurons (Scarpa's ganglia) and vestibular end-organs. Transcripts encoding the alpha2-7 and beta2-4 nAChR subunits were found in the vestibular ganglia, while alpha3, alpha5-7, alpha9 and beta2-4 nAChR subunits were expressed in the vestibular end-organs. These results support previous electrophysiological, immunocytochemical and molecular biological data, and also provide a more complete understanding of the role of nAChRs in the neurochemical transmission subserving the efferent-afferent interaction in the vestibular periphery.

Animals↗
PubMed1987

Input-output relations of lobules I and II of the cerebellar anterior lobe vermis in connexion with neck and vestibulospinal reflexes in the cat.

In the anaesthetized cat, lobules I and II of the cerebellar anterior lobe vermis were examined to determine their role in the vestibulospinal and neck-vestibulospinal reflexes with respect to: the somatotopic representation of afferent inputs from labyrinth, neck and tail; and the inhibitory influence on vestibulospinal tract (VST) neurones receiving vestibular and neck afferent inputs. After electrical stimulation of the vestibular nerve and of neck afferents, almost identical responses via mossy fibres were evoked in the lobules, with the prominent response in lobules I and IIa of Larsell. Stimulation of the nerve supplying the dorsal region of the tail induced primarily the mossy fibre response, but also the climbing fibre response, in lobule II. The most responsive areas to tail and neck afferent stimulation did not overlap each other. In the lateral vestibular nucleus, 163 antidromically identified VST neurones were recorded extra- or intracellularly. On the basis of the response pattern to contralateral neck afferent stimulation, they were classified into 3 groups: neurones with excitation (n = 45); neurones with inhibition (n = 71); and neurones with no modulation (n = 47). Stimulation of lobules I-IIa inhibited the activities of 44 VST neurones. Out of them, 41 neurones belonged to the first group. They made up 91% of the group. Twenty-nine of these neurones, i.e. neurones receiving excitatory inputs from the neck and inhibitory inputs from the lobules, received additional excitatory input from the labyrinth. Although lobules I-IIa may be regarded as neck area in the anterior lobe vermis from the viewpoint of sensory input, they did not exert inhibitory influence only exceptionally on vestibulocollic neurones, but predominantly on VST neurones sending their axons to lower thoracic or more caudal segments in the spinal cord. It is suggested from these results that lobules I-IIa have a close relationship with the neck reflex and/or interaction of neck and vestibulospinal reflexes being concerned with the postural adjustment of a rather wide area of the body.

Animals↗
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↗
PubMed1977

Linear addition of optokinetic and vestibular signals in the vestibular nucleus.

A simple model of the vestibuloocular reflex and the optokinetic system was used to simulate recent data on visual and vestibular responses of neurons in the vestibular nucleus. Contrary to a previous interpretation, the results support the hypothesis that the optokinetic and semicircular canal signals are combined simply by linear addition on the cells of the vestibular nucleus.

Animals↗
PubMed1979

Functional deficits in the optokinetic system of albino rats.

Vestibular nuclear neurons of the horizontal canal system (Vn) of albino rats (Wistar) failed to respond to optokinetic stimulation. Similarly, optokinetic nystagmus (OKN) could not be elicited in these animals. Brown (DA--HAN) rats, however, consistently showed optokinetic responses of Vn and OKN to identical stimuli.

Animals↗
PubMed1960

The neurologic aspects of vertigo: analysis of 400 cases.

Of almost 8,000 patients referred for neurological consultation, 6.1 per cent had "dizziness" as a presenting complaint. Dizziness is a nonspecific complaint, used loosely to describe funny feelings in the head or lightheadedness by anxious or depressed patients; or it may mean vertigo-a hallucination of movement of self or surroundings in horizontal, rotatory or vertical direction. An analysis of 400 cases showed the complaint "dizziness" to be functional in about 25 per cent of patients. The cause in the remaining cases varied from epilepsy from cortical lesions, to lesion of the brain stem, such as tumors, vascular insufficiency, and multiple sclerosis, or to the peripheral neurone from Meniere's disease, and vestibular neuritis. Leading the patient out in a description of the kind of dizziness he feels may give clues that will help differentiate between true vertigo and functional disorder, particularly when considered against the information that is obtained in neurological examination.

Brain Stem↗
PubMed1992

Antidromic and synaptic activation of Deiters' neurons induced by stimulation of red nucleus in the cat.

Antidromic and orthodromic action potentials of neurons located in the lateral vestibular nucleus of Deiters' evoked by stimulation of red nucleus were studied in anaesthetized cats. Vestibulospinal neurons were identified by stimulation of the lateral vestibulospinal tract. The 'second-order' vestibular neurons were revealed by mean of stimulation of the ipsilateral VIIIth nerve. Stimulation of the red nucleus is shown to lead mainly to antidromic, as well as mono-, oligo- and polysynaptic activation of Deiters' neurons. Not any inhibitory reaction was observed in vestibular neurons in response to stimulation of the red nucleus. Ascending axon collaterals of the vestibulospinal neurons to this brainstem structure were revealed. The peculiarities and functional significance of the effects mentioned are discussed.

Action Potentials↗
PubMed1985

Effect of tilt on the response of neuronal activity within the cat vestibular nuclei during slow and constant velocity rotation.

The responses of neurons sensitive to static tilt in the vestibular nuclei were examined in decerebrate cats during slow and constant velocity rotations about an axis tilted at various angles from the vertical. During any 360 degrees rotation, each unit showed a modulation of their firing rate, with a position-dependent maximum and minimum. Changes in amplitude of head displacement from 5 degrees to 25 degrees decreased the response gain of the units without affecting the locations of the discharge maxima and minima.

Animals↗
PubMed1990

GABA, glycine, aspartate, glutamate and taurine in the vestibular nuclei: an immunocytochemical investigation in the cat.

The distributions of five amino acids with well-established neuroexcitatory or neuroinhibitory properties were investigated in the feline vestibular complex. Consecutive semithin sections of plastic-embedded tissue were incubated with antisera raised against protein-glutaraldehyde conjugates of GABA, glycine, aspartate, glutamate and taurine. This approach allowed us to study the relative densities of the different immunoreactivities at the level of individual cell profiles. The results indicate that in the vestibular nuclei, neuronal colocalization of two or more neuroactive amino acids is the rule rather than an exception. Colocalization was found of immunoreactivities for GABA and glycine; glycine, aspartate and glutamate; glycine and aspartate, and glutamate and aspartate. GABA immunoreactive neurons were generally small and were found scattered throughout the vestibular complex. Glycine immunoreactive neurons were similarly distributed, except in the superior nucleus where the latter type of neuron could not be detected. Neuronal profiles colocalizing immunoreactivities for GABA and glycine occurred in all nuclei, but were most numerous in the lateral nucleus. The vast majority of the neurons showed noteworthy staining for glutamate and aspartate, although the level of immunoreactivities varied (e.g., the large neurons in the lateral and descending nuclei were more intensely aspartate immunoreactive than the smaller ones). Taurine-like immunoreactivity did not occur in neuronal cell bodies but appeared in Purkinje cell axons and in glial cell profiles. The functional significance of the complex pattern of amino acid colocalization remains to be clarified. In particular it needs to be distinguished between metabolic and transmitter pools of the different amino acids. The present results call for caution when attempts are made to conclude about transmitter identity on the basis of amino acid contents alone.

Amino Acids↗
PubMed2000

Effects of nitric oxide on the vestibular functional recovery after unilateral labyrinthectomy.

The effects of nitric oxide on the vestibular function recovery following unilateral labyrinthectomy were studied. Male Sprague-Dawley rats treated with N-omega-nitro-L-arginine methyl ester (L-NAME), a nitric oxide synthase (NOS) inhibitor, were subjected to destruction of the unilateral vestibular apparatus and spontaneous nystagmus was observed. To explore the role of nitric oxide on the potassium current, the whole cell patch clamp technique was applied on isolated medial vestibular nuclear neurons. The frequency of spontaneous nystagmus that appeared in L-NAME-treated rats was higher and maintained longer than in control animals. Potassium currents in the isolated medial vestibular nucleus were inhibited by nitric oxide liberating agents, sodium nitroprusside and S-nitroso-N-acetylpenicillamine. After blockade of calcium dependent potassium currents by high EGTA (11 mM)-containing pipette solution, sodium nitroprusside did not inhibit the outward potassium currents. 8-Bromoguanosine 3,5-cyclic monophosphate, a membrane-permeable cGMP analogue, produced similar effects to inhibit the outward potassium currents as sodium nitroprusside. These results suggest that nitric oxide production after unilateral labyrinthectomy would help to facilitate vestibular compensation by inhibiting calcium-dependent potassium currents through increasing intracellular cyclic GMP, thereby increasing excitability in ipsilateral vestibular nuclear neurons.

Animals↗
PubMed1997

Prevalence of head-shaking nystagmus in patients according to their diagnostic classification in a dizziness unit.

OBJECTIVE: In a previous publication, the authors documented the prevalence and characteristics of head-shaking nystagmus (HSN) in over 1300 consecutive dizzy patients during formal electronystagmography (ENG) at the combined Otologic Function Unit (OFU) of the Toronto and Mount Sinai Hospitals. This companion study was done to prospectively analyze a subgroup of 300 patients with known clinical diagnoses belonging to the senior author (J.R.). METHODS: The prevalence of HSN in this series of patients with a known diagnosis is prospectively compared to the presence of HSN in a series of normal controls. RESULTS: Results indicate that HSN is seen significantly (p < .05) in those patients with peripheral vestibular dysfunction and that the more globally the peripheral vestibular disorder involves end-organ (i.e., Meniere's) or primary afferent-neuron function (i.e., vestibular neuronitis), the more likely HSN will be present. CONCLUSION: We further comment on the usefulness of the head-shake test and its clinical relevance in the bedside examination of the dizzy patient.

Adolescent↗
PubMed1980

Vestibular input to visual tracking neurons in the posterior parietal association cortex of the monkey.

Single unit recordings were made in the posterior parietal association cortex (area 7) of the behaving monkey. Visual tracking neurons were identified by the discharge pattern during the task of pursuit of moving visual objects. Vestibular inputs to these tracking neurons were examined by sinusoidal rotation of the turntable, on which the monkey was seated. The activity of more than half of horizontal tracking neurons was modulated by horizontal rotation in the dark. Most of them responded to the head rotation with the same preferred direction as visual tracking. It was concluded that visual tracking neurons of area 7 receive vestibular input and therefore are likely to integrate visual and vestibular informations.

Animals↗
PubMed2003

The development of vestibulo-ocular circuitry in the chicken embryo.

This article reviews studies of the organization and development of the vestibulo-ocular reflex arc in the chicken embryo. It summarizes some of the principal features that characterize the development of this circuit, including the gradual clustering of motoneurons in the oculomotor nucleus into functionally identifiable motoneuron pools, the patterning of vestibular projection neurons into coherent clusters with specific axonal trajectories and terminations onto the oculomotor motoneuron pools, the reverse order of synapse formation during development (motoneuron to muscle, then vestibular projection neuron to motoneuron), and the selectivity of initial synaptic termination at both the ultimate and penultimate relays within the reflex arc. Reference to studies in other vertebrate species is made to provide a comparative context, and potential mechanisms are discussed that may contribute to the underlying synaptic specificity in this circuit.

Animals↗
PubMedDate not supplied

[Segmentary organisation of the efferents of the vestibular complex in chicken embryos: is this an example of the general case?].

INTRODUCTION: In this paper we present, from the perspective of the embryological segmentary layout of the hindbrain, the topographic layout of the vestibular projection neurons that sustain the vestibulospinal, vestibulo ocular and vestibulocerebellous efferents, in correlation with the classic vestibular nuclei. AIMS: Four vestibular nuclei are usually described superior, lateral, medial and inferior. These originate in at least nine successive rhombomeric segments or pseudosegments, which suggests the possibility of a more precise analysis of their neuronal populations and of their respective connections and functions. It has recently been observed that the vestibular projection neurons identified for a particular target tend to appear aggregated in discrete accumulations, which have been proved to correlate either with rhombomeric units, where they apparently develop, or with internal subdivisions within them. Each projection has its own particular organisation. Comparing them with the resulting connective mosaic in different species shows that various aspects of this organisation are conserved throughout evolution in vertebrates. It is argued that certain genes that control the development of the rhombomeric units in the brain stem may determine, among other aspects, the specific properties of the different neuronal subpopulations related with their axonal navigation and synaptogenesis. CONCLUSIONS: This type of analysis furthers our understanding of how the functional circuitry of a complex system, such as the vestibular system, is generated and is a line of reasoning that in principle can be applied to the whole neural tube.

Animals↗
PubMed1995

Vestibular inputs to the lateral tegmental field of the cat: potential role in autonomic control.

The lateral tegmental field (LTF), which is comprised of the lateral reticular formation near the obex, is an important integrative area involved in cardiovascular control and the production of emesis. Using neuroanatomical and electrophysiological techniques, we tested the hypothesis that LTF neurons receive vestibular inputs; the neurons studied included those projecting into the subretrofacial rostral ventrolateral medulla (sRVLM), which contains cells that make direct connections with sympathetic preganglionic neurons. Injections of the anterograde tracer PHA-L into the medial and inferior vestibular nuclei produced labeled terminals in the LTF. Electrical stimulation of the vestibular nerve affected the firing rate of LTF neurons, including approximately one-third of those antidromically activated from the sRVLM. The response latencies ranged from 1.5 to 20 ms, suggesting that the neurons received both direct and polysynaptic vestibular inputs from the vestibular nuclei. The LTF may be involved in the production of vestibulosympathetic reflexes and vestibular-elicited vomiting.

Animals↗