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Results for “Vestibular Neuronitis”

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At least 361 records · Page 20Linked to original sources
PubMed1985

Projection of secondary vestibular neurons to the abducens nucleus in the carpet shark Cephaloscyllium isabella.

The abducens nucleus in carpet sharks is not a discrete delimited nucleus, as the dendrites of the motoneurons extend into the reticular formation and the medial longitudinal fasciculus. Injections of horseradish peroxidase (HRP) designed to trace the inputs to these neurons are therefore difficult to confine to this system alone. Despite this problem a consistent finding from injection of HRP in the area of the abducens nucleus is the retrograde labelling of a column of cells in the contralateral octaval nuclei. The column of cells is predominantly in the ventral portion of the descending octaval nucleus, but does straddle the entrance of nerve VIII, extending into the caudal part of the ascending octaval nucleus. Labelled cells correspond in location and morphology to those cells receiving input from horizontal canal afferent fibers, confirming the trineuronal nature of the horizontal vestibulo-ocular reflex arc in elasmobranch fishes.

Abducens Nerve↗
PubMed2004

Effects of gravity, hypergravity and microgravity on vestibular neurones of the crab.

Recordings were made from identified balancing system interneurones using implanted electrodes in crabs oscillated at 0.3 Hz during bouts of Parabolic flight. Repeatable non stabilized patterns of response firing were seen in head up and head down interneurones. During the hypergravity phases, the ratio of firing frequencies in the two directional categories of interneurones was altered showing that hypergravity produced effects normally seen during tilting of the crab, implying greater bending of the sensory thread hairs. During microgravity, firing levels remained low and constant or changed slowly towards initial firing levels.

Acceleration↗
PubMed2002

Role of the flocculus in mediating vestibular nucleus neuron plasticity during vestibular compensation in the rat.

We investigated the role of the cerebellar flocculus in mediating the adaptive changes that occur in the intrinsic properties of brainstem medial vestibular nucleus (MVN) neurons during vestibular compensation. Ipsi-lesional, but not contra-lesional, flocculectomy prevented the compensatory increase in intrinsic excitability (CIE) that normally occurs in the de-afferented MVN neurons within 4 h after unilateral labyrinthectomy (UL). Flocculectomy did not, however, prevent the down-regulation of efficacy of GABA receptors that also occurs in these neurons after UL, indicating that these responses of the MVN neurons to deafferentation are discrete, parallel processes. CIE was also abolished by intra-floccular microinjection of the metabotropic glutamate receptor (mGluR) antagonist AIDA, and the protein kinase C inhibitor bisindolymaleimide I (BIS-I). The serene-threonine kinase inhibitor H-7 had no effect when microinjected at the time of de-afferentation, but abolished CIE if microinjected 2 h later. These cellular effects are in line with the recently reported retardatory effects of BIS-I and H-7 on behavioural recovery after UL. They demonstrate that the increase in intrinsic excitability in MVN neurons during vestibular compensation is cerebellum dependent, and requires mGluR activation and protein phosphorylation in cerebellar cortex. Furthermore, microinjection of the glucocorticoid receptor (GR) antagonist RU38486 into the ipsi-lesional flocculus also abolished CIE in MVN neurons. Thus an important site for glucocorticoids in facilitating vestibular compensation is within the cerebellar cortex. These observations ascribe functional significance to the high levels of GR and 11-beta-HSD Type 1 expression in cerebellum.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗
PubMed1994

Distribution of glutamatergic receptors and GAD mRNA-containing neurons in the vestibular nuclei of normal and hemilabyrinthectomized rats.

Vestibular compensation is an attractive model for investigations of cellular mechanisms underlying post-lesional plasticity in the adult central nervous system. Immediately after hemilabyrinthectomy, the spontaneous activity in the deafferented second-order vestibular neurons falls to zero, resulting in a strong asymmetry between the resting discharge of the vestibular complexes on the lesioned and intact sides. This asymmetry most probably causes the static and dynamic vestibular deficits observed in the acute stage. After approximately 50 h, the deafferented vestibular neurons recover a quasi-normal resting activity which is thought to be the key of the compensation of the static vestibular syndromes. However, the molecular mechanisms underlying this recovery are unknown. In this study, we investigate possible changes in the distribution of glutamatergic N-methyl-D-aspartate (NMDA) and glutamate metabotropic receptors and of glutamate decarboxylase 67k (GAD 67k) mRNAs in the deafferented vestibular neurons induced by the labyrinthine lesion. Specific radioactive oligonucleotides were used to probe sections of rat vestibular nuclei according to in situ hybridization methods. Animals were killed at different times (5 h, 3 days and 3 weeks) following the lesion. Signal was detected by means of film or emulsion autoradiography. In the normal animals, several brainstem regions including the medial, lateral, inferior and superior vestibular nuclei were densely labelled by the antisense oligonucleotide NMDAR1 probe. However, the vestibular nuclei were not labelled by the glutamate metabotropic oligonucleotide antisense probe (mGluR 1). The GAD 67k antisense oligonucleotide probe labelled numerous small- to medium-sized central vestibular neurons but not the larger cell bodies in the lateral vestibular nucleus. This agrees with previous studies. In the hemilabyrinthectomized rats, no asymmetry could be detected, at either the autoradiographic or cellular levels, between the two medial vestibular nuclei whatever the probe used and whatever the delay following the lesion. However, for the NMDAR1 probe, the mean density of silver grains in both the deafferented and intact medial vestibular neurons was 20% lower 5 h after the lesion. Three days and 3 weeks later, the intensity of labelling over all cells was the same as in the control group. Further studies are necessary to confirm the relatively weak modification of the NMDAR1 mRNAs expression and to exclude a change of GAD 65 and of other NMDA subunit mRNAs during the vestibular compensation process.

Animals↗
PubMed1984

Optimal response planes and canal convergence in secondary neurons in vestibular nuclei of alert cats.

Responses to natural stimulation were studied in electrically identified secondary vestibular neurons of awake cats. A class of neurons was identified whose response dynamics and responses to rotations in several vertical and horizontal planes indicated that they received semicircular canal input. Each canal neuron had clearly defined planes of maximal and null sensitivity to rotation. The orientation of these planes indicated that 44% of the neurons received input from one pair of canals, 40% from two, and 16% from all 3 canal pairs. Many cells also had oculomotor-related discharges and/or responded weakly to neck rotation.

Animals↗
PubMed1996

Decision making in vestibular neurectomy.

Indications for vestibular neurectomy have traditionally included intractable Meniere's disease, chronic vestibular neuronitis, vestibular hydrops, and posttraumatic vertigo. Between 1990 and 1993, 28 retrosigmoid vestibular neurectomies were performed for various peripheral vestibulopathies for which medical management failed. These were divided into two groups: Meniere's disease and non-Meniere's disease. The non-Meniere's disease group included the diagnosis of vestibular hydrops and chronic vestibular neuronitis. Results were analyzed by using the 1985 American Academy of Otolaryngology (AAO) criteria for Meniere's disease. Statistical analysis revealed a highly significant difference (chi 2 Fischer, p = 0.001), with the Meniere's group being highly successful and the non-Meniere's group being unsuccessful. We conclude that retrosigmoid vestibular neurectomy is a safe and effective modality for the management of Meniere's disease for which medical management failed. Patients with non-Meniere's vestibulopathies should be treated with other modalities.

Adult↗
PubMed1987

Dynamic characteristics of vestibular nuclear neurons responses to vestibular and optokinetic stimulation during vestibular compensation in the rat.

In albino rats and pigmented rats, neurons were recorded extracellularly in the vestibular nuclei during the first 2 weeks after unilateral labyrinthectomy in order to study the neuronal events occurring during vestibular compensation and the effect of unilateral vestibular lesion on the optokinetic responses of neurons in the vestibular nuclei. It was found in albino rats that a re-equilibration took place in the gains of type I neurons between both lesioned and intact sides. The gain of the rare type I neurons on the deafferented side, which was low just after the lesion (t less than 48 h) subsequently increased (48 h less than t less than 14 d) while on the intact side the gain was greater just after the lesion, and then decreased. This re-equilibration of the gains of type I neurons is considered to be the neuronal equivalent of behavioural effects which occur after hemilabyrinthectomy. In pigmented rats, most type I and II VN neurons recorded on both sides 24 to 96 h after the lesion did not respond to pure horizontal OKS, while in controls almost all of them responded. It seems evident that the tonic activation of VN neurons by vestibular afferences is necessary for their responsiveness to pure OKS. However, when comparing the gain/phase of their responses to pure, vestibular and combined optokinetic-vestibular stimulations, it was found that optokinetic inputs improved the performance of type I and II VN neurons on both lesioned and intact sides. Finally, the time course of vestibular compensation is shorter in pigmented rats than in albino rats, since the re-equilibration in gains between the two sides was already reached 4 days after the lesion in the former.

Animals↗
PubMed2004

[Connection of efferent neurons and afferent vestibular nuclei in rat].

OBJECTIVE: To study the connection between the efferent and afferent vestibular neurons in the center neural system. METHODS: In the present study, a retrograde neuron tracer horseradish peroxidase (HRP) was injected into the surrounding of efferent vestibular neurons located in the inner side of the facial genu of the rat and after following 48 hours for the retrograde axonal transport of this tracer, then its presence in neurons of the brain stem was demonstrated histochemically. RESULTS: Neurons labeled with HRP were found bilaterally in both Medial vestibular nuclei (MVe) and lateral vestibular nuclei (LVe). Approximately 80% of the neurons in each were located in the MVe on the side ipsilateral to the injection. CONCLUSIONS: There is a direct connection between the efferent and afferent vestibular neurons. These findings suggest that there is an afferent-efferent feedback regulatory mechanism in the vestibular system.

Animals↗