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PubMed1982

Optokinetic, vestibular, and optokinetic-vestibular responses in albino and pigmented rats.

Horizontal eye movements and neuronal activity in the vestibular nuclei and pretectum were recorded in albino and pigmented rats in response to optokinetic, vestibular (VS), combined visual-vestibular (VVS) sinusoidal stimulations. 1. VOR slow phase velocity in VS condition leads head velocity. This phase lead is smaller in albino than in pigmented rats. 2. Presence of vision (VVS) improves the phase angle of the VOR in both strains, especially at low frequencies. In pigmented rats the VOR is perfectly compensatory with respect to phase at all frequencies whereas in albinos the eye velocity still leads the head velocity. 3. There is no difference in the response characteristics of vestibular nuclear neurons (VN) to VS between albino and pigmented rats which could explain the difference in their VORs. 4. In the pigmented rat, there is a strong optokinetic input to VN which provokes a shift of the response peak towards peak head velocity. These visual-vestibular interactions at VN level are in agreement with the changes in the phase angle of the VOR. 5. In albino rat, there are no differences in the response characteristics of VN between VS and VVS, thus the decrease of the VOR phase lead observed in VVS compared to VS is due either to visual-vestibular interactions outside of the vestibular nuclei or to some general arousing effect of light. 6. Recording of responses of pretectal neurons to visual stimulation in albino rats has shown that they are activated in a phasic or tonic way by light on ("On cells") or off ("Off cells"). Contrary to the pigmented rat, pretreated neurons in albino exhibited no detectable direction specific optokinetic responses.

Animals↗
PubMed1997

Cellular basis of vestibular compensation: changes in intrinsic excitability of MVN neurones.

A systematic survey of the intrinsically generated in vitro discharge rates of rat medial vestibular nucleus (MVN) neurones was carried out in slices from normal animals and animals undergoing vestibular compensation over 48 h after unilateral labyrinthectomy (UL). Isolation of the individual MVN in vitro revealed that the tonic discharge rates of neurones in the rostral MVN ipsilateral to the lesion were not different from control 2 h post-UL, but increased significantly at 4 h post-UL and remained significantly higher until 24 h post-UL. There were no significant changes in the in vitro discharge rates of MVN cells in the contralateral nucleus. The increase in excitability of the ipsilateral MVN cells after UL may be accounted for by a down-regulation of GABA receptors on these cells, following their sustained exposure to excessive commissural inhibition after labyrinthectomy. We suggest that the increased intrinsic excitability of the ipsilateral MVN cells is responsible for the restoration of the resting discharge in these cells after UL and the consequent recovery of static vestibular function.

Animals↗
PubMed1995

Immunohistochemical localization of neurocalcin in the rat inner ear.

Localization in the rat inner ear of neurocalcin, a three EF-hand calcium-binding protein, was examined immunohistochemically. Neurocalcin-like immunoreactivity was restricted to neurons in neuroepithelial receptor organs, while hair cells and supporting cells showed no such immunoreactivity. In the organ of Corti, both afferent and efferent nerve terminals, which formed synapses on both inner and outer hair cells, showed distinct immunoreactions. Spiral ganglion neurons and cochlear nerves were immunopositive. In the cristae ampullaris, macula utriculi and macula sacculi, afferent nerve terminals forming nerve calices or terminal boutons were strongly immunopositive. Efferent nerve terminals making synapses either on nerve calices or on hair cells showed an intense immunoreactivity. Vestibular ganglion neurons were strongly immunopositive. In electron microscopy, immunoreaction products were diffuse in the cytoplasm of ganglion neurons and nerve terminals. Neurocalcin-like immunoreactivity occurred in association with microtubules, outer mitochondrial membranes, synaptic vesicles and synaptic membranes. It is thus likely that neurocalcin is involved in neural functions in each type of afferent and efferent transmission in the inner ear.

Animals↗
PubMed2004

Dissociating self-generated from passively applied head motion: neural mechanisms in the vestibular nuclei.

The ability to distinguish sensory inputs that are a consequence of our own actions from those that result from changes in the external world is essential for perceptual stability and accurate motor control. To accomplish this, it has been proposed that an internal prediction of the consequences of our actions is compared with the actual sensory input to cancel the resultant self-generated activation. Here, we provide evidence for this hypothesis at an early stage of processing in the vestibular system. Previous studies have shown that neurons in the vestibular nucleus, which receive direct inputs from vestibular afferent fibers, are responsive to passively applied head movements. However, these same neurons do not reliably encode head velocity resulting from self-generated movements of the head on the body. In this study, we examined the mechanism that underlies the selective elimination of vestibular sensitivity to active head-on-body rotations. Individual neurons were recorded in monkeys making active head movements. The correspondence between intended and actual head movement was experimentally controlled. We found that a cancellation signal was gated into the vestibular nuclei only in conditions in which the activation of neck proprioceptors matched that expected on the basis of the neck motor command. This finding suggests that vestibular signals that arise from self-generated head movements are inhibited by a mechanism that compares the internal prediction of the sensory consequences by the brain to the actual resultant sensory feedback. Because self-generated vestibular inputs are selectively cancelled early in processing, we propose that this gating is important for the computation of spatial orientation and control of posture by higher-order structures.

Animals↗
PubMed1996

Central and peripheral myelin in the rat cochlear and vestibular nerves.

In the bipolar neurons of vertebrate cochlear and vestibular nerves, the myelin envelopes without interruption the axon, the perikaryon and the dendrite. The perikaryal myelin is thin and partially loose, whereas axon and dendrite are enveloped by compacted myelin. The expression of protein 0 and myelin basic protein, constituents of peripheral and central myelin respectively, has been investigated in the rat by immunohistochemical study at the light microscopic level. Our data indicate that both in the cochlear and vestibular nerves the myelin of the perikaryon and dendrite is composed by specific peripheral myelin proteins. The axon segment between the perikaryon and the transitional zone expresses peripheral myelin proteins in the cochlear nerve, while both types of myelin proteins are present in the vestibular nerve. Between the transitional zone and the brainstem the myelin of the axon is exclusively of the central type. The peripheral-central myelin transitional zone is in close proximity to the axonal pole in the vestibular ganglion cells, while in the cochlear nerve it is near the spiral foramina, at variable distance from the axonal pole of ganglion cells.

Animals↗
PubMed1995

Inputs from the ipsilateral and contralateral vestibular apparatus to behaviorally characterized abducens neurons in rhesus monkeys.

1. We made extracellular recordings from neurons in the abducens nuclei of alert rhesus monkeys during electrical stimulation of the vestibular labyrinths with brief current pulses and during smooth pursuit, steady fixation, and the vestibuloocular reflex (VOR) evoked by passive head turns. The responses to electrical stimuli were compared with quantitative measures of the sensitivity of each neuron to eye position and eye velocity. We also compared the strengths of the vestibular inputs from the labyrinths ipsilateral and contralateral to the side of recording. 2. Abducens neurons showed transient excitation after a current pulse was applied to the contralateral labyrinth and transient inhibition after stimulation of the ipsilateral labyrinth. The latency of excitation had a mean value of 1.7 ms and a median value of 1.5 ms. Latency was unimodally distributed with little variation among neurons. Neurons with large responses showed a second phase of excitation that started 2.5 ms after the stimulus. 3. In two of three monkeys, the excitatory responses of abducens neurons to electrical stimulation of the contralateral labyrinth were approximately 3 times as large as their inhibitory responses to stimulation of the ipsilateral labyrinth. The difference in response size was not observed in the third monkey. The asymmetry in the size of the electrically evoked inputs from the two labyrinths was associated with a smaller asymmetry in responses of abducens neurons during the VOR evoked by passive head turns. The increase in firing rate during head rotation away from the side of the recording was almost always larger than the decrease in firing rate during head rotation toward the side of the recording. 4. The size of the neuronal response to electrical stimulation was correlated with the magnitude of the change in discharge rate during eye movements. Single or multiple regression of measures of response amplitude against eye position threshold, sensitivity to eye position, sensitivity to eye velocity, and baseline discharge rate yielded correlation coefficients that ranged from 0.26 to 0.92 in different monkeys. The existence of positive correlations is consistent with a role of the intrinsic properties of abducens neurons in determining recruitment order. However, the existence of large amounts of variability within most of the samples suggests that the recruitment order of abducens neurons also depends on the discharge properties of the afferents to each abducens neuron.

Abducens Nerve↗
PubMedDate not supplied

Quantitative study of human Scarpa's ganglion and vestibular sensory epithelia.

Methods for counting vestibular ganglion cells and determining the densities of hair cells and intraepithelial basophilic inclusions (IBI) in samples of cross-sectioned vestibular sensory epithelia are described. Data obtained by means of these methods in vestibular sensory epithelia and Scarpa's ganglia in individual temporal bones from subjects at different ages are presented. Both vestibular hair cells and nerve cells in Scarpa's ganglia are found numerically reduced in ears of aged individuals. Changes in the vestibular sensory epithelia appear to precede those seen in Scarpa's ganglion. The incidence of intraepithelial basophilic inclusions correlates with degeneration in the respective vestibular sensory epithelia. There are no striking differences in hair cells densities of the different vestibular sense organs of the same ear and from subjects at about the same age.

Adolescent↗
PubMed2000

Properties of utricular and saccular nerve-activated vestibulocerebellar neurons in cats.

Properties of otolith inputs to vestibulocerebellar neurons were investigated in 14 adult cats. In the vestibular nuclei, we recorded single-unit activities that responded orthodromically after stimulation of the utricular and/or saccular nerves and antidromically after stimulation of the cerebellum (uvula-nodulus and anterior vermis). Descending axonal projections to the spinal cord were also examined by antidromic stimulation of the caudal end of the C1 segment. Forty-seven otolith-activated neurons that projected to the uvula-nodulus were recorded. Thirteen (28%) of the 47 neurons received convergent inputs from the utriculus and sacculus. The remaining 34 (72%) vestibular neurons were non-convergent neurons: 18 (38%) received utricular input alone, and 16 (34%) received saccular input alone. Most (35/47) vestibulocerebellar neurons were located in the descending vestibular nucleus and only one of these projected to the spinal cord. Seven of the 47 vestibulocerebellar neurons were located in the lateral vestibular nucleus and most of these neurons projected to the spinal cord. The remaining neurons were located in group X (two neurons) and the superior vestibular nucleus (three neurons). In a different series of experiments, 37 otolith-activated vestibular neurons were tested to determine whether they projected to the uvula-nodulus and/or the anterior vermis. Nineteen of the 37 neurons projected to the anterior vermis, 13/37 projected to the uvula-nodulus, and 5/37 projected to both. The utricular and/or saccular nerve-activated vestibulocerebellar neurons projected to not only the uvulanodulus, but also to the anterior vermis. In summary, the results of this study showed that vestibular neurons receiving inputs from the utriculus and/or sacculus projected to the cerebellar cortex. This indirect otolith-cerebellar pathway terminated both in the anterior lobe and in the uvula/nodulus.

Animals↗
PubMed1995

Developing inner ear sensory neurons require TrkB and TrkC receptors for innervation of their peripheral targets.

The trkB and trkC genes are expressed during the formation of the vestibular and auditory system. To elucidate the function of trkB and trkC during this process, we have analysed mice carrying a germline mutation in the tyrosine kinase catalytic domain of these genes. Neuroanatomical analysis of homozygous mutant mice revealed neuronal deficiencies in the vestibular and cochlear ganglia. In trkB (-/-) animals vestibular neurons and a subset of cochlear neurons responsible for the innervation of outer hair cells were drastically reduced. The peripheral targets of the respective neurons showed severe innervation defects. A comparative analysis of ganglia from trkC (-/-) mutants revealed a moderate reduction of vestibular neurons and a specific loss of cochlear neurons innervating inner hair cells. No nerve fibres were detected in the sensory epithelium containing inner hair cells. A developmental study of trkB (-/-) and trkC (-/-) mice showed that some vestibular and cochlear fibres initially reached their peripheral targets but failed to maintain innervation and degenerated. TrkB and TrkC receptors are therefore required for the survival of specific neuronal populations and the maintenance of target innervation in the peripheral sensory system of the inner ear.

Animals↗
PubMed1983

Responses of units in the rat cerebellar flocculus during optokinetic and vestibular stimulation.

The simple (SS) and complex spike (CS) responses of Purkinje (P-cells) and non-Purkinje (non P-cells) in the cerebellar flocculus were studied in alert pigmented rats (DA-HAN) during binocular and monocular optokinetic stimulation (OKS), vestibular stimulation and a combination of the two. Of a total of 98 P-cells whose SS discharges were activated by rotary stimulation of the horizontal canal in the dark (type I and type II P-cells), the vast majority (72%) responded to constant velocity binocular OKS that was produced by means of a horizontal shadow projector system. The remaining P-cells responded only to vestibular stimulation (19%), to OKS or to the presumed fast components of optokinetic and vestibular nystagmus (9%). The optokinetic responses of P-cells were generally bidirectional but asymmetrical, i.e., the increases in rate in one direction were larger in magnitude than decreases on opposite OKS and were synergistic with the semicircular canal input. During constant velocity OKS, the discharge of a few P-cells rose approximately exponentially, outlasted the stimulus by as much as 10-13.5s and, thus, resembled OKS responses of vestibular nucleus neurons. However, the majority exhibited a phasic-tonic response governed by a short "time constant" of from 0.5-3s. The velocity tuning curves of vestibular/OKS responding P-cells showed peak sensitivities with retinal slip velocities of 1.5-2 degrees/s. This is higher than the ca. 1 degree/s determined for other relay nuclei of the horizontal optokinetic pathway. The responses of non P-cells suggest that they originate from mossy fiber projections from vestibular, visual (optokinetic) and saccadic eye movement-related areas of the brainstem. Most of the units carried a combined vestibular and optokinetic signal. The majority showed a bidirection-selective response to OKS, and a small percentage showed unidirectional responses only. Monocular testing of P-cells revealed that most received a bidirection-selective, but asymmetrical, OKS input. Slightly more than half of these had a strongest OKS drive from the contralateral eye; the remaining units were driven most strongly by the ipsilateral eye. Unidirection-selective P-cells, driven by OKS to the ipsi- or contralateral eye, were uncommon; yet this class is common among other portions of the horizontal optokinetic system (e.g., vestibular nuclei, praepositus hypoglossi nucleus, nucleus reticularis tegmenti pontis).(ABSTRACT TRUNCATED AT 400 WORDS)

Acoustic Stimulation↗
PubMed1984

The modifiable neuronal network of the cerebellum.

Recent data of neuronal network structures of the cerebellum are reviewed and experimental evidence is presented for the hypothesis that parallel fiber synapses on Purkinje cells retain plasticity which provides a memory device to the cerebellar cortical network. A corticonuclear microcomplex, consisting of a small area of the cerebellar cortex, a small group of cerebellar and vestibular nuclear neurons, and a small group of inferior olive neurons, which are interconnected, is proposed to form a functional unit of the cerebellum. The idea that a corticonuclear microcomplex endows an extracerebellar system with subtle control capabilities such as coordination, prediction, and adaptation-learning is supported with experimental data on the cerebellar control of the vestibulo-ocular reflex.

Animals↗
PubMed2005

Immunocytochemical and pharmacological characterization of metabotropic glutamate receptors of the vestibular end organs in the frog.

Using immunocytochemistry and multiunit recording of afferent activity of the whole vestibular nerve, we investigated the role of metabotropic glutamate receptors (mGluR) in the afferent neurotransmission in the frog semicircular canals (SCC). Group I (mGluR1alpha) and group II (mGluR2/3) mGluR immunoreactivities were distributed to the vestibular ganglion neurons, and this can be attributed to a postsynaptic locus of metabotropic regulation of rapid excitatory transmission. The effects of group I/II mGluR agonist (1S,3R)-1-aminocyclopentane-trans-1,3-dicarboxylic acid (ACPD) and antagonist (R,S)-alpha-methyl-4-carboxyphenylglycine (MCPG) on resting and chemically induced afferent activity were studied. ACPD (10-100 microM) enhanced the resting discharge frequency. MCPG (5-100 microM) led to a concentration-dependent decrease of both resting activity and ACPD-induced responses. If the discharge frequency had previously been restored by L-glutamate (L-Glu) in high-Mg2+ solution, ACPD elicited a transient increase in the firing rate in the afferent nerve suggesting that ACPD acts on postsynaptic receptors. The L-Glu agonists, alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA) and N-methyl-D-aspartate (NMDA), were tested during application of ACPD. AMPA- and NMDA-induced responses were higher in the presence than absence of ACPD, implicating mGluR in the modulation of ionotropic glutamate receptors. These results indicate that activation of mGluR potentiates AMPA and NMDA responses through a postsynaptic interaction. We conclude that ACPD may exert modulating postsynaptic effects on vestibular afferents and that this process is activity-dependent.

Animals↗
PubMed1991

Response properties of gerbil otolith afferents to small angle pitch and roll tilts.

The responses from isolated single otolith afferent fibers were obtained to small angle sinusoidal pitch and roll tilts in anesthetized gerbils. The stimulus directions that produced the maximum (response vector) and minimum response sensitivities were determined for each otolith afferent, with response vectors for the units being spread throughout the horizontal plane, similar to those reported for other species. A breadth of tuning measure was derived, with narrowly tuned neurons responding maximally to stimulation in one direction and minimally along an orthogonal ('null') direction. Most (approximately 80%) otolith afferents are narrowly tuned, however, some fibers were broadly tuned responding significantly to stimulations in any direction in the horizontal plane. The number of broadly tuned otolith afferents (approximately 20%) differs significantly from the more substantial number of broadly tuned vestibular nuclei neurons (88%) recently reported in rats.

Animals↗
PubMed1993

The mammalian vestibular ganglion cells and the myelin sheath surrounding them.

Morphological findings of the vestibular ganglia of small animals and human temporal bones are reported. For light microscopy, the ganglia were fixed with Levi's solution and stained with iron-hematoxylin and/or azan. The ganglia of bats were studied with electron microscopy. For scanning laser microscopy, human temporal bones were fixed in 10% formalin, decalcified, and embedded in paraffin, then stained with laxol fast blue. The ganglia were found as nodules among the VIIIth cranial nerve. The vestibular ganglion cells were seen in myelinated and unmyelinated nerve fibres, loose collagen fibres, and capillaries, separated from each other. These cells were bipolar and spindle shaped and varied in size, in contrast to spiral ganglion cells. The cell bodies (perikarya) were surrounded by myelin sheaths. Under electron microscopy, the myelin sheath could be seen between a vestibular ganglion cell body and a Schwann cell and consisted of 3-7 major lines in bats, and of about 10 in rabbits. The structure thus depends on species. The myelin sheath of human vestibular ganglion cells was seen in Levi-azan sections with a light microscope and in LFB (and/or HE) mirror slides with a scanning laser microscope.

Animals↗
PubMed1986

[Lymphocyte subpopulations and HLA-DR determinations in diseases of the inner ear and Bell's palsy].

Thymus lymphocytes-subpopulations (T-helper T4 and T-suppressorcells T8) were determined in inner ear diseases (e.g. sudden hearing loss, neuronitis vestibularis, Morbus Menière, Bell's Palsy) by specific monoclonal antibodies. T-cell subset ratio (T4/T8) was elevated (less than 3) in about 50% of all patients. DR-typifying was performed because of the well-known control of the immunoregulation through the class II HLA-DR antigens. There was a relative risk of 5.2 in peripheral vestibular lesion (neuronitis vestibularis). The relative risk of autoimmune diseases is found at this level.

Autoimmune Diseases↗
PubMed1988

The NMDA antagonists MK801 and CPP disrupt compensation for unilateral labyrinthectomy in the guinea pig.

Unilateral labyrinthectomy results in eye movement and postural disorders which diminish over time in a process of behavioral recovery called vestibular compensation. This compensation process is due to CNS plasticity which generates a renewal of spontaneous activity in vestibular nucleus neurons ipsilateral to the labyrinthectomy. However, the mechanisms responsible for the induction and maintenance of this neural recovery are unknown. The present results show that i.p. injections of the N-methyl-D-aspartate (NMDA) receptor antagonists MK801 [( (+)-5-methyl-10,11-dihydro-5H- dibenzo[a,d]-cyclohepten-5,10-imine maleate]) and CPP (3-[+/- )-2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid) disrupt the maintenance of compensation following unilateral labyrinthectomy, producing a reappearance of eye movement symptoms after compensation has been attained. These results suggest that NMDA receptors may be involved in the maintenance of the neural changes responsible for vestibular compensation.

Adaptation, Physiological↗
PubMed1988

The incidence of fibrosis in the vestibular ganglia in Menière's disease.

The vestibular ganglia in 11 temporal bones from subjects with known premortem unilateral Meniere's disease were studied for evidence of increased fibrosis. Tissue sections were treated with Gomori's trichrome stain and were examined independently by each of seven persons experienced in histological study. The averaged ratings for the amount of fibrous tissue in the vestibular ganglia showed no significant differences for ears with Meniere's disease, the opposite uninvolved ears, and the controls.

Aged↗
PubMed2002

Unorthodox view of the functioning of a GABAA synapse.

1. Studies about the permeation of labelled chloride and GABA across single plasma membranes microdissected from vestibular Deiters' neurons have yielded two unexpected results: (a) intracellular GABA stimulates chloride permeation in an asymmetric fashion (efflux being favoured); (b) under certain conditions GABA permeates by a diffusion mechanism in the out-->in direction across these plasma membranes. 2. These two main results have been obtained over many years together with a host of other indications about the fine mechanism of these events. Thus, a picture has emerged of their physiological meaning within the context of the functioning of the GABAA synapses between the Purkinje cells and the Deiters' neurons. 3. In short, it is proposed that at these synapses GABA accumulates into the postsynaptic neuron after its release and activation of the postsynaptic receptors. GABA accumulated in the Deiters' neurons is involved in the process of chloride extrusion to build an inward directed electrochemical gradient for chloride.

Animals↗