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PubMed1976

Horizontal vestibular nystagmus. I. Identification of medial vestibular neurones.

1. The properities of inputs from the horizontal semi-circular canal to neurones of the medial vestibular nucleus have been studied intracellularly in the unanaesthetized encéphale isolé cat. 2. Secondary neurones of the bestibulo-abducens reflex arc were identified by their orthodromic response to labyrinthine stimulation and by antidromic excitation from the contralateral abducens nucleus. 3. The responses of medial vestibular cells receiving only labyrinthine in puts are also described. These were seen to be predominantly excitatory though IPSPs were observed in a few cases. 4. Identified vestibular neurones were intracellularly injected with procion yellow and showed different morphological characteristics correlated with function.

Abducens Nerve↗
PubMed1999

Firing behavior of vestibular neurons during active and passive head movements: vestibulo-spinal and other non-eye-movement related neurons.

The firing behavior of 51 non-eye movement related central vestibular neurons that were sensitive to passive head rotation in the plane of the horizontal semicircular canal was studied in three squirrel monkeys whose heads were free to move in the horizontal plane. Unit sensitivity to active head movements during spontaneous gaze saccades was compared with sensitivity to passive head rotation. Most units (29/35 tested) were activated at monosynaptic latencies following electrical stimulation of the ipsilateral vestibular nerve. Nine were vestibulo-spinal units that were antidromically activated following electrical stimulation of the ventromedial funiculi of the spinal cord at C1. All of the units were less sensitive to active head movements than to passive whole body rotation. In the majority of cells (37/51, 73%), including all nine identified vestibulo-spinal units, the vestibular signals related to active head movements were canceled. The remaining units (n = 14, 27%) were sensitive to active head movements, but their responses were attenuated by 20-75%. Most units were nearly as sensitive to passive head-on-trunk rotation as they were to whole body rotation; this suggests that vestibular signals related to active head movements were cancelled primarily by subtraction of a head movement efference copy signal. The sensitivity of most units to passive whole body rotation was unchanged during gaze saccades. A fundamental feature of sensory processing is the ability to distinguish between self-generated and externally induced sensory events. Our observations suggest that the distinction is made at an early stage of processing in the vestibular system.

Animals↗
PubMedDate not supplied

[Morphologic and electrophysiologic characteristics of cultured vestibular ganglia neurons].

Vestibular afferent neurons have been classified on the basis of their spontaneous activity as regular and irregular; this has been attributed to their synaptic input, but it remains to be defined the participation of some intrinsical properties of the afferent neurons in the determination of their discharge pattern. In this work, we have developed tissue cultures of the rat vestibular ganglia. Isolated cells were plated using poly-D-lysine or collagen as substrates and L-15 or Neurobasal as culture media. After 48 hrs cells in the four experimental conditions give forth neurites of variable longitude. By using antibodies against the neurofilaments 160 kDa the cell structure was studied. Monopolar (30.6%), bipolar (63.9%) and multipolar (5.5%) cells were found. By using the voltage and current clamp procedures the voltage dependence and kinetics of the tetrodotoxin sensitive Na+ current was fully characterized. Cultured cells were shown to generate action potentials under electrical stimulation, and they were capable of repetitive spike discharge under the influence of 4-aminopyridine. These results demonstrate that tissue cultures constitute an excellent system to study the intrinsical properties of vestibular afferent neurons.

Action Potentials↗
PubMed1979

The postnatal development of functional properties of central vestibular neurons in the rat.

The postnatal development of the responses of rat central vestibular neurons to horizontal angular acceleration was studied in the time and frequency domain. The resting discharge was very low and irregular during the first postnatal days, increased gradually and became more regular throughout the first month and reached adult values approximately by the end of the first month. The relative distribution of type I and type II units was the same in all age groups. Threshold for frequency increase to angular acceleration and sensitivity of unit responses became lower and higher, respectively, as time elapsed after birth. Adult values were reached approximately by the end of the first month. There was a slight tendency towards shorter time constants and smaller phase lags in one-month-old animals when compared with the younger animals. The results are discussed in conjunction with similar work performed in vestibular afferents and correlated with known morphological and behavioral studies.

Acceleration↗
PubMed1998

Spike discharge regularity of vestibular neurons in labyrinthectomized guinea pigs.

Single unit activity of second-order vestibular neurons was recorded in alert guinea pigs. Here, we compared the spike discharge regularity (measured by calculating the coefficient of variation (CV)) of neurons from control animals with those from animals labyrinthectomized 1 week before. The mean CV (+/-SD) were the same in both groups (0.72+/-0.43 vs. 0.70+/-0.39). Furthermore, in both groups, the CV was related to the resting rate (RR) according to the same law (CV = 4/square root of RR). Because the discharge of a neuron is more regular when it is due to a pacemaker activity than when it is due to the synaptic drive, we conclude that restoration in the firing rate after labyrinthectomy is due to increase in the synaptic drive rather than to increase in the (intrinsic) pacemaker activity.

Action Potentials↗
PubMed1994

Second-order vestibular neuron morphology of the extra-MLF anterior canal pathway in the cat.

Second-order vestibular neurons form the central links of the vestibulo-oculomotor three-neuron arcs that mediate compensatory eye movements. Most of the axons that provide for vertical vestibulo-ocular reflexes ascend in the medial longitudinal fasciculus (MLF) toward target neurons in the oculomotor and trochlear nuclei. We have now determined the morphology of individual excitatory second-order neurons of the anterior semicircular canal system that course outside the MLF to the oculomotor nucleus. The data were obtained by the intracellular horseradish peroxidase method. Cell somata of the extra-MLF anterior canal neurons were located in the superior vestibular nucleus. The main axon ascended through the deep reticular formation beneath the brachium conjunctivum to the rostral extent of the nucleus reticularis tegmenti pontis, where it crossed the midline. The main axon continued its trajectory to the caudal edge of the red nucleus from where it coursed back toward the oculomotor nucleus. Within the oculomotor nucleus, collaterals reached superior rectus and inferior oblique motoneurons. Some axon branches recrossed the midline within the oculomotor nucleus and reached the superior rectus motoneuron subdivision on that side. Since these neurons did not give off a collateral toward the spinal cord, they were classified as being of the vestibulo-oculomotor type and are thought to be involved exclusively in eye movement control. The signal content and spatial tuning characteristics of this anterior canal vestibulo-oculomotor neuron class remain to be determined.

Animals↗
PubMedDate not supplied

Effects of ketamine on the adaptive responses of second-order vestibular neurons of the cat.

The adaptive characteristics of 80 neurons in the vestibular nuclei of ketamine-anesthetized cats were investigated. All types I and II neurons responded to stimulation of the horizontal semicircular canals by an 8 degree/sec2 stepwise angular acceleration of 40 sec. For the purpose of this study, vestibular adaptation was defined as a decline in response at a rate of greater than -0.01 spikes/sec/sec. According to this criterion, 71 neurons (89 per cent) behaved as adapting neurons, and nine (11 per cent) showed either no adaptation or reverse adaptation. The rate of adaptation varied from neuron to neuron; the average rate was -0.312 spikes/sec/sec. The average resting discharge rate, the maximum response level, and the average adaptation rate were compared with similar neural responses in barbiturate-anesthetized cats. Although the average resting discharge rates of the two groups showed no significant difference, the average adaptation rate and the maximum response level of the ketamine-anesthetized group were significantly higher than those of the barbiturate-anesthetized group. These data suggest that the gain of the second-order neurons is higher and more actively modulated in more alert (ketamine-anesthetized) cats than in barbiturate-anesthetized cats.

Animals↗
PubMed1995

Responses of guinea pig primary vestibular neurons to clicks.

Responses of single neurons in the vestibular nerve to high-intensity clicks were studied by extracellular recording in anaesthetised guinea pigs. One hundred and two neurons in the posterior division of the superior branch or in the inferior branch of the vestibular nerve were activated at short latency by intense clicks. The latency of activation was short (median 0.9 ms) and the threshold was high: the click intensity for evoking the response of these cells was around 60 dB above the auditory brainstem response threshold. Animals were tilted and rotated to identify physiologically the sensory region of the labyrinth from which the activated neurons originated. Seventeen neurons responded to static tilt as well as clicks. These results show that vestibular receptors, probably the otoliths, respond to clicks at intensities corresponding to those used in a new clinical test of the vestibulo-collic pathway.

Acoustic Stimulation↗
PubMed1994

Ascending projections of posterior canal-activated excitatory and inhibitory secondary vestibular neurons to the mesodiencephalon in cats.

The axonal projections of 62 posterior canal (PC)-activated excitatory and inhibitory secondary vestibular neurons were studied electrophysiologically in cats. PC-related neurons were identified by monosynaptic activation elicited by electrical stimulation of the vestibular nerve and activation following nose-up rotation of the animal's head. Single excitatory and inhibitory neurons were identified by antidromic activation following electrical stimulation of the contralateral and ipsilateral medial longitudinal fasciculus, respectively. The oculomotor projections of identified neurons were confirmed with a spike-triggered averaging technique. The axonal projections of the identified neurons were then studied by systematic, antidromic stimulation of the mesodiencephalon. Excitatory neurons showed two main types of axonal projections. In one type, axonal branches were issued to the interstitial nucleus of Cajal, central gray, and thalamus including the ventral posterolateral, ventral posteromedial, ventral lateral, ventral medial, centromedian, central lateral, lateral posterior, and ventral lateral geniculate nuclei. The other type was more frequently observed, giving off axon collaterals to the above-mentioned regions and to Forel's field H as well. Inhibitory neurons issued axonal branches to limited areas which included the central gray, interstitial nucleus of Cajal, its adjacent reticular formation and caudalmost part of Forel's field H, but not the rostral part of the Forel's field H and the thalamus. These results suggest that PC-related excitatory neurons participate in the genesis of vertical eye movements and in the perception of the vestibular sensation, and that PC-related inhibitory neurons seem to take part only in the genesis of vertical eye movements.

Animals↗
PubMed1991

A clinical study of vestibular neuronitis.

By means of clinical and neurotological findings in 38 patients with vestibular Neuronitis, an analysis of the clinical-pathological manifestations, that may be included into this denomination, has been carried out. The probable etiology of this disease and the results of the tests performed have also been analyzed. In the light of these results the vestibular compensatory mechanisms, studied with later periodic tests, are discussed, and the conclusions on the prognosis and treatment of this entity derived.

Adolescent↗
PubMed1988

Response of vestibular neurons to head rotations in vertical planes. I. Response to vestibular stimulation.

1. We have studied, in decerebrate cats, the responses of neurons in the lateral and descending vestibular nuclei to whole-body rotations in vertical planes that activated vertical semicircular canal and utricular receptors. Some neurons were identified as vestibulospinal by antidromic stimulation with floating electrodes placed in C4. 2. The direction of tilt that caused maximal excitation (response vector orientation) of each neuron was determined. Neuron dynamics were then studied with sinusoidal stimuli closely aligned with the response vector orientation, in the range 0.02-1 Hz. A few cells, for which we could not identify a response vector, probably had spatial-temporal convergence. 3. On the basis of dynamics, neurons were classified as receiving their input primarily from vertical semicircular canals, primarily from the otolith organs, or from canal+otolith convergence. 4. Response vector orientations of canal-driven neurons were often near +45 degrees or -45 degrees with respect to the transverse (roll) plane, suggesting these neurons received excitatory input from the ipsilateral anterior or posterior canal, respectively. Some neurons had canal-related dynamics but vector orientations near roll, presumably because they received convergent input from the ipsilateral anterior and posterior canals. Few neurons had their vectors near pitch. 5. In the lateral vestibular nucleus, neurons with otolith organ input (pure otolith or otolith+canal) tended to have vector orientations closer to roll than to pitch. In the descending nucleus the responses were evenly divided between the roll and pitch quadrants. 6. We conclude that most of our neurons have dynamics and response vector orientations that make them good candidates to participate in vestibulospinal reflexes acting on the limbs, but not those acting on the neck.

Animals↗
PubMed1987

Cat vestibular neurons that exhibit different responses to active and passive yaw head rotations.

Neurons in the vestibular nuclei were recorded in alert cats during voluntary yaw rotations of the head and during the same rotations delivered with a turntable driven from a record of previous voluntary movements. During both voluntary and passive rotations 35% (6/17) of neurons tested responded at higher rates or for a larger part of the movement during voluntary movements than during the same rotations delivered with the turntable. Neck sensory input was evaluated separately in many of these cells and can account qualitatively for the extra firing present during active movement.

Animals↗
PubMed1979

Vestibular neuronitis; a follow-up study.

Forty-three patients suffering from vestibular neuronitis were examinated during the acute attack and on an average 3.2 years afterwards. In the follow-up examination there was no caloric reactions in 7 patients, lowered in 15 patients and normal symmetric reactions in 21 persons. In the first examination all had normal symmetric hearing, in the follow-up examination there was 5 to 10 db hearing loss in 4.6 and 8 kHz on the diseased side in 24 patients.

Adolescent↗
PubMed2001

In vitro effects of acetyl-DL-leucine (tanganil) on central vestibular neurons and vestibulo-ocular networks of the guinea-pig.

For 40 years, the amino acid acetyl-DL-leucine (or isoleucine/Tanganil) has been used in clinical practice to reduce the imbalance and autonomic signs associated with acute vertigo crises. In animal models, acetyl-DL-leucine was shown to accelerate vestibular compensation following unilateral labyrinthectomy, while having only minor effects on normal vestibular function. However, the underlying mechanisms are unknown. In this study, the effect of acetyl-DL-leucine on the activity of central vestibular neurons of the medial vestibular nucleus (MVN) and/or the overall activity of vestibular-related networks was electrophysiologically measured in brainstem slices and in the isolated, in vitro whole brain (IWB) of guinea-pig. Only moderate effects were obtained in normal animals, where both excitatory and inhibitory actions of acetyl-DL-leucine were obtained. However, intracellular recordings from MVN neurons revealed that the nature of the response depended on the resting membrane potential. The neurons excited by acetyl-DL-leucine were significantly hyperpolarized compared to nonsensitive cells, whereas the neurons inhibited by this compound tended to display higher than normal membrane potentials. In accordance with these data, acetyl-DL-leucine reduced the prominent asymmetry characterizing the vestibular-related networks of IWBs taken from previously labyrinthectomized animals, by decreasing the activity of the abnormally depolarized neurons on the hyperactive side. Altogether, our results suggest that acetyl-DL-leucine might act mainly on abnormally hyperpolarized and/or depolarized MVN neurons, by bringing back their membrane potential towards a mean value of -65 to -60 mV. Since in animal models, acute vestibular disorders are associated with asymmetrical spontaneous activities of MVN neurons, this study suggests how acetyl-DL-leucine may reduce acute, vestibular-related imbalances in humans.

Abducens Nerve↗
PubMedDate not supplied

Responses of frog vestibular neurons to combined temperature microstimulation of the semicircular canals.

The temperature microstimulation of the semicircular canal (heat bursts lasting about 2 sec with a peak amplitude of 0.5-5.0 degrees C) can be regarded as an analog of angular acceleration acting within the cavity of the given canal; the combination of temperature microstimulations targeted simultaneously on several canals can serve as a physical model of accelerated rotation having complex spatial characteristics. The recording of the activity of neurons of the vestibular nuclei of the frog (n = 278) in response to temperature microstimulation of the canals showed that 80% of the neurons have inputs from one to two canals and only 20% from three to six canals. The distribution of laterality was characterized by the predominance of ipsilateral inputs: 201 neurons (72.3%) had only ipsilateral inputs; 14 neurons (5%) had only contralateral inputs; 63 neurons (22.7%) had both inputs. The ipsilateral horizontal (67.6%) and the posterior (61.9%) were the most effective inputs; while among the contralateral, the posterior (21.2%) canals were the most effective; the least effective were the contralateral horizontal (8.6%) and the anterior (5.0%) canals. The presence of latent canal inputs (both excitatory and inhibitory) which showed up in combination with effective inputs was demonstrated.

Animals↗
PubMed1987

An in vitro brain slice preparation to study the pharmacology of central vestibular neurons.

The purpose for development of this preparation was to allow detailed studies of the pharmacological and electrophysiological properties of individual central vestibular neurons. The pharmacology of the central afferent synapses of the vestibular system has not been examined at the level of the neuronal membrane, and as a result few definitive reports are available. The best studies have used in situ extracellular recording techniques that are difficult to interpret. For instance, recent literature still supports the concept that excitatory transmission at the N. VIII to vestibular nuclei synapse is cholinergic. Our data refute this hypothesis and suggest that an excitatory amino acid is the most likely candidate for the eighth nerve to medial vestibular nucleus in the rat. We believe this preparation combined with an intracellular electrophysiological approach will shed information of value to both the basic scientist and the clinician with interest in the vestibular system.

Action Potentials↗
PubMed1994

Compartmental models of type A and type B guinea pig medial vestibular neurons.

1. We have developed compartmental models of guinea-pig medial vestibular nuclei neurons (MVNns). The structure and the parameters of the model cells were chosen to reproduce the responses of type A and type B MVNns as described in electrophysiological recordings. 2. Dynamics of membrane potentials were modeled in 46 and 61 branched electrical compartments for Type A and Type B MVNns, respectively. Each compartment was allowed to contain up to nine active ionic conductances: a fast inactivating sodium conductance, gNa, a persistent sodium conductance, gNap, a low-voltage activated calcium conductance, gCa(LVA), a high-voltage activated calcium conductance, gCa(HVA), a fast-voltage activated potassium conductance, gK(fast), a slowly relaxing voltage activated potassium conductance, gK(slow), a fast transient potassium channel, gK(A), a slowly relaxing mixed sodium-potassium conductance activating at hyperpolarized membrane potentials, gH, and a calcium-activated potassium conductance gK(AHP). The kinetics of these conductances were derived from voltage-clamp studies in a variety of preparations. Kinetic parameters as well as distribution and density of ion channels were adjusted to yield the reported electrophysiological behavior of medial vestibular neurons. 3. Dynamics of intracellular free [Ca2]i were modeled by inclusion of a Ca(2+)-pump and a Na(+)-Ca2+ exchanger for extrusion of calcium. Diffusion of calcium between submembraneous sites and the center of an electrical compartment was modeled by 25 and 6 shell-like chemical compartments for the cell body and the proximal dendrites, respectively. These compartments also contained binding sites for calcium. 4. The dynamics of active conductances were the same in both models except for gK(fast). This was necessary to achieve the different shape of spikes and of spike afterhyperpolarization in type A and type B MVNns. An intermediate depolarizing component of the spike afterhyperpolarization of type B neurons in part depended on their dendritic cable structure. 5. Variation of the low threshold calcium conductance, gCa(LVA), shows that the ability to generate low-threshold spike bursts critically depends on the density of this conductance. Sodium plateaus were generated when increasing the density of gNap. 6. The type B model cell generated rhythmic bursts of spiking activity under simulation of two distinct experimental conditions.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗