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At least 199 records · Page 11Linked to original sources
PubMed2003

Immunocytochemical study of alpha 1 and beta 2/3 subunits of GABAA receptors in freehand isolated vestibular Deiters' neurons.

Vestibular Deiters' neurons have been isolated from bovine brain by the Hydén's freehand dissection technique and challenged with monoclonal antibodies directed toward the alpha 1 and beta 2/3 subunits of the GABAA receptors. Subsequent challenge with fluorescent secondary antibodies and confocal microscopy allowed the study of the cellular distribution of such subunits. In Deiters' neurons the beta 2/3 subunit displayed a clear presence all along the cell body profile and the initial parts of the dendrites. The alpha 1 subunit was found highly present all over the cell interior except the nuclear profiles. The strong presence inside the cells possibly masked its presence on the plasma membrane. However, in part of the cells studied a distinct presence on the plasma membrane was evident. This subunit was visualized also all along the long dendrites of these neurons. The approach we describe here, involving freehand isolated mature neurons from adult animals, may allow a better characterization of the tridimensional distribution of different types of neuronal GABAA receptors in the respect of the approach with brain slices.

Animals↗
PubMed1999

Developmental changes in low and high voltage-activated calcium currents in acutely isolated mouse vestibular neurons.

1. The development of low voltage-activated (LVA) and high voltage-activated (HVA) calcium currents was studied in neurons acutely dissociated from mouse vestibular ganglia at embryonic stages (E)14, 15, 17 and birth using the whole-cell patch-clamp technique. 2. LVA current was present in almost all neurons tested at stages E14 to E17, although at birth this current was restricted to a few neurons. Two populations of neurons were characterized based on the amplitude of the LVA current. In the first population, LVA current densities decreased between E17 and birth by which time this current tended to disappear in most neurons. A second population of neurons with high density LVA current appeared at E17, and in this group the mean density increased during development. 3. Among HVA currents, the dihydropyridine-sensitive L-type current remained constant between E15 and birth. Over the same period, the density of N- and Q-type currents continuously increased as shown using omega-conotoxin-GVIA (N-type), and high concentrations of omega-agatoxin-IVA (Q-type). The P-type current, sensitive to low concentrations of omega-agatoxin-IVA, transiently increased between E15 and E17, and then both current density and its proportion of the global current decreased. 4. Our results reveal large modifications in the expression of voltage-dependent calcium channels during embryonic development of primary vestibular neurons. The changes in the expression of LVA current and the transient augmentation of P-type HVA current occur during a period characterized by massive neuronal growth and by the beginning of synaptogenesis. These results suggest a specific role of these currents in the ontogenesis of vestibular primary afferents.

Animals↗
PubMed1996

Basic fibroblast growth factor (FGF-2) affects development of acoustico-vestibular neurons in the chick embryo brain in vitro.

The effects of basic fibroblast growth factor (FGF-2) on presumptive auditory and vestibular neurons from the medulla were studied in primary cell cultures. The part of the rhombic lip that forms nucleus magnocellularis (homologue of the mammalian anteroventral cochlear nucleus) was explanted from white leghorn chicken embryos at Hamburger-Hamilton stage 28 (E5.5), the time when precursors of the magnocellularis bushy cells migrate and begin to differentiate in situ. In vitro the neuroblasts migrated onto 2-D substrates of purified collagen, differentiated, and expressed neuronal markers. One-half of the cultures were supplemented with human recombinant FGF-2 (10 ng/ml daily) for 5-7 days; the others, with fetal bovine serum. FGF-2 more than doubled the length of neurite outgrowth during the first 3 day treatment compared to serum, but the number of migrating neuroblasts was unaffected. Although neurites attained greater lengths in FGF-2, they usually degenerated after 4-5 days; in serum their growth continued for several weeks. Differentiation of neuronal structure, including axons and dendrites, began within 1-2 days in bFGF but required at least 5-7 days in serum. Histochemical observations in vitro and in situ with antibodies to FGF receptor demonstrated immunopositive patches on acoustico-vestibular neuroblasts at stage 28, when they are migrating and first forming their axons. The findings suggest that FGF-2 stimulates neurite outgrowth in the cochlear and vestibular nuclei. FGF-2 may accelerate cell death by overstimulating neuroblasts, but other factors are needed to sustain their further development.

Amino Acid Sequence↗
PubMed1983

Vestibular neuronitis; a neurological and neurophysiological evaluation.

Neurological and neurophysiological findings were retrospectively reviewed in a group of 50 patients with vestibular neuronitis (VN). The onsets of VN were found to be clustered in the period from August to January. A preceding infection was reported by 36% of the patients. Neurological examinations did not reveal any other relevant signs than a spontaneous nystagmus during the acute phase. The results of routine laboratory tests and cerebrospinal fluid tests were within normal limits. EEG was recorded in 37 patients; 15 patients had a definitely abnormal EEG, with a slowing of the dominant occipital rhythm or more generalized diffuse slowing in 12 cases. 5 patients, 3 of them without slowing of the background activity, had a distinct focal disturbance of intermittent slow activity in the temporal region. In control recordings, an improvement was seen in the slowing of the background activity but not in the focal disturbances. Brainstem auditory evoked responses (BSER) were recorded in 12 patients, 5 of whom had abnormal responses. The seasonal clustering of VN onsets and the association of VN with overt infections further suggest its infectious pathogenesis. The observed EEG and BSER disturbances suggest a subclinical brainstem involvement in some cases of VN.

Adolescent↗
PubMed1984

Responses of cat vestibular neurons to stimulation of the frontal cortex.

To study the neural basis for the regulation of vestibulocollic reflexes during voluntary head movements, the effects of stimulation of the precruciate cortex near the presylvian sulcus (neck area of the motor cortex) and the frontal eye fields (FEF) on vestibular neurons were studied in cerebellectomized cats anesthetized with alpha chloralose. Neurons were recorded in the medial and descending vestibular nuclei and antidromically identified from C1. Stimulation of the FEF and precruciate cortex fired 29 and 13% of neurons that did not exhibit spontaneous activity. About 80% of spontaneously discharging neurons were influenced by stimulation of either of the two. Stimulation of the precruciate cortex or FEF suppressed or facilitated labyrinthine evoked monosynaptic activation of vestibulospinal neurons, suggesting that the frontal cortical neurons have the properties to regulate the vestibulocollic reflexes.

Animals↗
PubMed1995

Central disorders in vestibular neuronitis.

Between 1972 and 1993 equilibrium and audiological examinations were made on 73 patients who had been diagnosed to suffer from vestibular neuronitis. In 23 of these patients, central nervous disorders (CND) were suspected from the result of tests of positional and positioning nystagmus, smooth pursuit, optokinetic nystagmus or auditory brainstem response. In this group of patients the frequency of associated disorders and vertiginous symptoms (dizziness) was statistically higher than in the remainder 50 patients who did not have CND. In the CND group the time interval between the onset and improvement or disappearance of all vertiginous symptoms, nystagmus and canal paresis was longer than in the non-CND group.

Adolescent↗
PubMed1993

Follow-up of square drawing test in vestibular neuronitis.

The square drawing test (SDT) devised by Sekitani (1975), which is a modification of Fukuda's vertical writing test, was performed to evaluate vestibular dysfunction in 15 patients with vestibular neuronitis followed up for a long period. In particular, two parameters (distance and total length) were analyzed in the present study. Distance was analyzed by dividing the 15 cases into 3 groups. The largest group showed a tendency to shorten at an early stage. Total length was examined by dividing the 15 cases into 3 groups. The largest group showed a tendency towards macrographism at an early stage. It was found that as the degree of caloric responses recovered, the range of distance and total length decreased. Considering the correlation between parameters of the SDT (distance and total length) and caloric responses we concluded that the SDT is a feasible method to evaluate and follow up patients with vestibular dysfunction.

Adolescent↗
PubMed2006

Bone conducted vibration selectively activates irregular primary otolithic vestibular neurons in the guinea pig.

The main objective of this study was to determine whether bone-conducted vibration (BCV) is equally effective in activating both semicircular canal and otolith afferents in the guinea pig or whether there is preferential activation of one of these classes of vestibular afferents. To answer this question a large number (346) of single primary vestibular neurons were recorded extracellularly in anesthetized guinea pigs and were identified by their location in the vestibular nerve and classed as regular or irregular on the basis of the variability of their spontaneous discharge. If a neuron responded to angular acceleration it was classed as a semicircular canal neuron, if it responded to maintained roll or pitch tilts it was classified as an otolith neuron. Each neuron was then tested by BCV stimuli-either clicks, continuous pure tones (200-1,500 Hz) or short tone bursts (500 Hz lasting 7 ms)-delivered by a B-71 clinical bone-conduction oscillator cemented to the guinea pig's skull. All stimulus intensities were referred to that animal's own auditory brainstem response (ABR) threshold to BCV clicks, and the maximum intensity used was within the animal's physiological range and was usually around 70 dB above BCV threshold. In addition two sensitive single axis linear accelerometers cemented to the skull gave absolute values of the stimulus acceleration in the rostro-caudal direction. The criterion for a neuron being classed as activated was an audible, stimulus-locked increase in firing rate (a 10% change was easily detectable) in response to the BCV stimulus. At the stimulus levels used in this study, semicircular canal neurons, both regular and irregular, were insensitive to BCV stimuli and very few responded: only nine of 189 semicircular canal neurons tested (4.7%) showed a detectable increase in firing in response to BCV stimuli up to the maximum 2 V peak-to-peak level we delivered to the B-71 oscillator (which produced a peak-to-peak skull acceleration of around 6-8 g and was usually around 60-70 dB above the animal's own ABR threshold for BCV clicks). Regular otolithic afferents likewise had a poor response; only 14 of 99 tested (14.1%) showed any increase in firing rate up to the maximum BCV stimulus level. However, most irregular otolithic afferents (82.8%) showed a clear increase in firing rate in response to BCV stimuli: of the 58 irregular otolith neurons tested, 48 were activated, with some being activated at very low intensities (only about 10 dB above the animal's ABR threshold to BCV clicks). Most of the activated otolith afferents were in the superior division of the vestibular nerve and were probably utricular afferents. That was confirmed by evidence using juxtacellular injection of neurobiotin near BCV activated neurons to trace their site of origin to the utricular macula. We conclude there is a very clear preference for irregular otolith afferents to be activated selectively by BCV stimuli at low stimulus levels and that BCV stimuli activate some utricular irregular afferent neurons. The BCV generates compressional and shear waves, which travel through the skull and constitute head accelerations, which are sufficient to stimulate the most sensitive otolithic receptor cells.

Acoustic Stimulation↗
PubMed1990

NMDA receptors contribute to the resting discharge of vestibular neurons in the normal and hemilabyrinthectomized guinea pig.

Excitatory amino acids (EAA) like L-Glutamate or L-Aspartate have been suggested to be the neurotransmitters at the synapses between primary vestibular afferents and second-order vestibular neurons. In the first part of our work, we have tested the possibility that EAA receptors are implicated in the control of posture by vestibular nuclei. Normal guinea pigs were implanted with minipumps delivering EAA antagonists in the vestibular nuclei. Their resting posture was monitored during the perfusion by using an X-ray photographic method. Chronic infusion of D-L-2-amino-5-phosphonovaleric acid (APV), a specific antagonist of NMDA receptors, in the vestibular nuclei induced a postural and oculomotor syndrome similar to the one observed following acute vestibular deafferentation. Administration of 6-cyano-7-nitro-quinoxaline-2-3-dione (CNQX), a specific antagonist of kainate and quisqualate receptors, failed to induce any postural syndrome or eye deviation. These results suggest that, under physiological conditions, N-methyl-D-aspartate (NMDA) receptors, contrary to kainate and quisqualate receptors, are essential for the maintenance of a symmetric posture and of a normal eye position at rest. Previous electrophysiological studies have demonstrated that following unilateral labyrinthectomy the recovery of a resting discharge in the deafferented vestibular nuclei plays a key role in the compensation of postural disorders. In the second part of this study, we have tested whether NMDA receptors could be implicated in this postural recovery. APV mini-pumps were implanted in hemilabyrinthectomized guinea pigs after complete compensation. A postural decompensation was induced, which occurred after delivery of the same amount of APV which provoked a vestibular syndrome in intact guinea pigs.(ABSTRACT TRUNCATED AT 250 WORDS)

2-Amino-5-phosphonovalerate↗
PubMed1992

A model for the characterization of the spatial properties in vestibular neurons.

Quantitative study of the static and dynamic response properties of some otolith-sensitive neurons has been difficult in the past partly because their responses to different linear acceleration vectors exhibited no "null" plane and a dependence of phase on stimulus orientation. The theoretical formulation of the response ellipse provides a quantitative way to estimate the spatio-temporal properties of such neurons. Its semi-major axis gives the direction of the polarization vector (i.e., direction of maximal sensitivity) and it estimates the neuronal response for stimulation along that direction. In addition, the semi-minor axis of the ellipse provides an estimate of the neuron's maximal sensitivity in the "null" plane. In this paper, extracellular recordings from otolith-sensitive vestibular nuclei neurons in decerebrate rats were used to demonstrate the practical application of the method. The experimentally observed gain and phase dependence on the orientation angle of the acceleration vector in a head-horizontal plane was described and satisfactorily fit by the response ellipse model. In addition, the model satisfactorily fits neuronal responses in three-dimensions and unequivocally demonstrates that the response ellipse formulation is the general approach to describe quantitatively the spatial properties of vestibular neurons.

Animals↗
PubMed1981

Properties of secondary vestibular neurons fired by stimulation of ampullary nerve of the vertical, anterior or posterior, semicircular canals in the cat.

Experiments on cats were performed to study the pathway and location of the secondary vestibulo-ocular neurons in response to stimulation of the ampullary nerves of the vertical, anterior or posterior, semicircular canals. Experiments on the medial longitudinal fasciculus transection disclosed that vertical canal-evoked, disynaptic excitation and inhibition were transmitted to the extraocular motoneurons through the contra- and ipsilateral medial longitudinal fasciculus respectively. Secondary vestibular neurons, which receive input from the ampullary nerve of the vertical semicircular canals and send their axons to contralateral medial longitudinal fasciculus, were intermingled in the rostral half of the descending and lateral part of the medial vestibular nuclei. A direct excitatory connection of some of these neurons to the target extraocular motoneurons was confirmed by means of a spike-triggered signal averaging technique. It was also found that neurons activated by antidromic stimulation of ipsilateral medial longitudinal fasciculus were located in the superior vestibular nucleus, some of which made direct inhibitory connections to the target extraocular motoneurons. Both excitatory and inhibitory vestibuloocular neurons made synaptic contact in about half of the impaled target motoneurons.

Animals↗
PubMed1986

Influence of standing on vestibular neuronal activity in awake cats.

Single-unit activity of vestibular nuclear neurons was recorded in chronically prepared, awake cats. To examine the influence of tonic activation of limb proprioception on vestibular function, the vestibular modulation by horizontal rotation (0.2 Hz, 17 deg) and head-tilt (0.1 Hz, 7 deg) was recorded in animals with freely hanging limbs and was compared with the modulation in standing cats. Of 29 examined cells responding to horizontal rotation, only about 30% were affected during standing, with most exhibiting a decrease of the mean discharge rate and gain. In contrast, about 70% of the 28 tilt-modulated cells showed pronounced effects during standing with a decrease of the gain and an increase of the mean discharge rate. The increase of the mean discharge rate in tilt cells may be caused by the excitatory spinovestibular afferent fibers or by the efferent vestibular system. For the observed inhibitory effects on the gain different mechanisms may be responsible: cerebellar inhibition and/or efferent vestibular receptor control. This control of labyrinthine information by somatosensory afferent fibers may serve for the stability of equilibrium in the moving animal.

Animals↗
PubMed1993

Interpretation of the combined galvanic test. Findings from cases with vestibular neuronitis.

The combined galvanic test (CGT) was developed in our department for simultaneous recording of galvanic eye movement test (GEMT) and galvanic body sway test (GBST). Twelve cases of vestibular neuronitis were studied first with the caloric test, and then with the CGT. The findings of the caloric test corresponded to those of the GEMT, but did not always correspond to those of the GBST. Thus we suggest that the GBST reflects an abnormality in a system different from that reflected by the caloric test and GEMT. It is likely that the caloric response mainly originates from the semicircular canal system. Thus the GEMT may reflect an abnormality in the semicircular canal system, while the GBST reflects an abnormality in the otolithic system. The CGT may thus be a feasible method of differentiating the disorders of the semicircular canal system from those of the otolithic system in the vestibular nervous system.

Adult↗
PubMed2005

Spatial properties of central vestibular neurons of monkeys after bilateral lateral canal nerve section.

Thirty-seven neurons were recorded in the superior vestibular nucleus (SVN) of two cynomolgus monkeys 1-2 yr after bilateral lateral canal nerve section to test whether the central neurons had spatially adapted for the loss of lateral canal input. The absence of lateral canal function was verified with eye movement recordings. The relation of unit activity to the vertical canals was determined by oscillating the animals about a horizontal axis with the head in various orientations relative to the axis of rotation. Animals were also oscillated about a vertical axis while upright or tilted in pitch. In the second test, the vertical canals are maximally activated when the animals are tilted back about -50 degrees from the spatial upright and the lateral canals when the animals are tilted forward about 30 degrees . We reasoned that if central compensation occurred, the head orientation at which the response of the vertical canal-related neurons was maximal should be shifted toward the plane of the lateral canals. No lateral canal-related units were found after nerve section, and vertical canal-related units were found only in SVN not in the rostral medial vestibular nucleus. SVN canal-related units were maximally activated when the head was tilted back at -47 +/- 17 and -50 +/- 12 degrees (means +/- SD) in the two animals, close to the predicted orientation of the vertical canals. This indicated that spatial adaptation of vertical canal-related vestibular neurons had not occurred. There were substantial neck and/or otolith-related inputs activating the vertical canal-related neurons in the nerve-sectioned animals, which could have contributed to oculomotor compensation after nerve section.

Action Potentials↗
PubMed1989

Primary afferent excitatory transmission recorded intracellularly in vitro from rat medial vestibular neurons.

Intracellular recordings were made from rat medial vestibular nucleus (MVN) neurons in transverse brain slices containing the root of the vestibular nerve (N. VIII). Electrical stimuli applied to the N. VIII tract evoked an orthodromic excitatory postsynaptic potential (EPSP) that lasted about 50 ms following a 0.5 to 1.5 ms delay between the stimulus artifact and synaptic potential. These orthodromic EPSPs were insensitive to the following antagonists: atropine, hexamethonium, diphenhydramine, and caffeine. Based on these results we conclude that the primary afferent excitatory transmitter is not acetylcholine, histamine, or adenosine, respectively. However, kynurenic acid, a general excitatory amino acid receptor antagonist, blocked the orthodromic EPSP while having no effect on the resting membrane potential, input resistance, or action potential configuration of MVN neurons. Our data suggest that an excitatory amino acid, or amino acid-like substance, is responsible for primary afferent excitatory transmission in the rat medial vestibular nucleus.

Action Potentials↗
PubMed1985

Canal-neck interaction in vestibular neurons of the cat's cerebral cortex.

Interaction of semicircular canal and neck proprioceptive inputs was studied in the cerebral cortex of awake, intact cats. Neuronal responses were recorded extracellularly in the anterior suprasylvian gyrus of the left hemisphere. Stimulations consisted of horizontal rotations in the dark applied as sinusoids or position ramps. There were three stimulus conditions: (1) Pure canal stimulation; rotation of whole body. (2) Pure neck stimulation; rotation of trunk about stationary head. (3) Canal-neck interaction; rotation of head about stationary trunk. We recorded 105 neurons with either Type I or Type II canal response. These showed often pronounced non-linearities such as a clear firing increase upon rotation in the "on-direction" and hardly any decrease in the opposite direction. The responses reflected mostly angular velocity, but angular position signals were also obtained. In 79 neurons, either Type I or Type II neck responses were obtained. They coded either angular velocity, velocity plus position, or position. Canal-neck convergence was found in 67 of 88 neurons tested. In the majority of neurons, interaction was "antagonistic" in the sense that the canal and neck responses tended to cancel each other during rotation of the head about the stationary trunk. These neurons could signal trunk rotation in space rather than head in space or head relative to trunk. Most of the remaining neurons showed a "synergistic" interaction such that the response upon head rotation was enhanced as compared to whole body or trunk rotation. These neurons might be involved in the dual task of monitoring head rotation in space and relative to trunk. Interaction was compatible with linear summation of canal and neck inputs in 70% of the neurons. In part of these, however, the assumption had to be made that the interaction had taken place already at some stage prior to the cortical neurons investigated. The response characteristics of cortical canal neurons are discussed in comparison to vestibular nuclear neurons. Furthermore, parallels are drawn between the observed canal-neck interactions in the cortical neurons and (i) interactions of canal and neck dependent postural reflexes in the decerebrate cat, and (ii) interactions of canal and neck induced turning sensations in man.

Animals↗
PubMed2000

Spatiotemporal processing of linear acceleration: primary afferent and central vestibular neuron responses.

Spatiotemporal convergence and two-dimensional (2-D) neural tuning have been proposed as a major neural mechanism in the signal processing of linear acceleration. To examine this hypothesis, we studied the firing properties of primary otolith afferents and central otolith neurons that respond exclusively to horizontal linear accelerations of the head (0.16-10 Hz) in alert rhesus monkeys. Unlike primary afferents, the majority of central otolith neurons exhibited 2-D spatial tuning to linear acceleration. As a result, central otolith dynamics vary as a function of movement direction. During movement along the maximum sensitivity direction, the dynamics of all central otolith neurons differed significantly from those observed for the primary afferent population. Specifically at low frequencies (</=0.5 Hz), the firing rate of the majority of central otolith neurons peaked in phase with linear velocity, in contrast to primary afferents that peaked in phase with linear acceleration. At least three different groups of central response dynamics were described according to the properties observed for motion along the maximum sensitivity direction. "High-pass" neurons exhibited increasing gains and phase values as a function of frequency. "Flat" neurons were characterized by relatively flat gains and constant phase lags (approximately 20-55 degrees ). A few neurons ("low-pass") were characterized by decreasing gain and phase as a function of frequency. The response dynamics of central otolith neurons suggest that the approximately 90 degrees phase lags observed at low frequencies are not the result of a neural integration but rather the effect of nonminimum phase behavior, which could arise at least partly through spatiotemporal convergence. Neither afferent nor central otolith neurons discriminated between gravitational and inertial components of linear acceleration. Thus response sensitivity was indistinguishable during 0.5-Hz pitch oscillations and fore-aft movements. The fact that otolith-only central neurons with "high-pass" filter properties exhibit semicircular canal-like dynamics during head tilts might have important consequences for the conclusions of previous studies of sensory convergence and sensorimotor transformations in central vestibular neurons.

Acceleration↗
PubMed2003

Dynamics of vestibular neurons during rotational motion in alert rhesus monkeys.

The temporal processing in the encoding of head rotation was investigated by comparing the dynamics of vestibular nuclei neurons with those of the regularly and irregularly firing semicircular canal afferents in alert rhesus monkeys. During earth-vertical axis rotations, neurons without eye movement sensitivity differed in their response dynamics from both regularly and irregularly firing semicircular canal afferents. At high frequencies, central responses increased in sensitivity and maintained phase leads of nearly 30 degrees relative to head velocity. These persistent high-frequency phase leads resembled those of irregularly firing (but not regularly firing) semicircular canal afferents. However, at low frequencies, central responses exhibited significantly smaller phase leads than those of irregularly firing semicircular canal afferents, and dynamics resembled more those of the regularly firing afferents. The response dynamics of central non-eye movement cells were significantly different from those of position-vestibular-pause and eye-head neurons (collectively referred to as eye movement cells). In contrast to the persistent phase leads of non-eye movement neurons, all eye movement cells modulated closely in phase with head velocity at all frequencies down to 0.05 Hz during visual suppression tasks. Vertical canal non-eye movement neurons that were insensitive to both translations and static head tilts led head velocity by approximately 5-30 degrees during high-frequency earth-horizontal axis rotations. Unlike the earth-vertical axis responses that led head velocity at low frequencies by as much as 20-40 degrees, vertical canal neurons only slightly led or even lagged behind head velocity during low-frequency earth-horizontal axis rotations. Posterior canal central non-eye movement cells lagged behind head velocity significantly more than anterior canal neurons. These frequency dependencies of central vestibular neurons in comparison with those of the afferents suggest that both low- and high-pass filtering might be necessary to convert primary semicircular canal afferent response dynamics to central neuron ones.

Action Potentials↗