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PubMed1975

[The acute vestibular paralysis (author's transl)].

Acute vestibular paralysis may not be considered as a nosologic entity but as a syndrome. Symptomatology (vertigo, spontaneous and provoked vestibular nystagmus, absence of cochlear signs) shows an uniform picture. The results of the caloric test as well as the nystagmic responses induced by galvanic stimulation and the development of central vestibular compensation however indicate that the site of the lesion is not only confined to the labyrinth but may also occur at the level of the peripheral neuron or even the vestibular nuclei. Etiology and pathology are still vague. Our own clinical observations as well as the scarce data in literature about morphological and experimental studies suggest in a way that vascular and infectious disorders are of importance as primary releasing factors. Hypothetically, vestibular loss of function may either be caused by a disturbance of labyrinthine microcirculation, initiated in a great majority of cases by infection, or by a direct lesion of the peripheral neuron as well as the vestibular nuclei. Retrolabyrinthine lesions may be due to menigoencephalitis, caused by a neurotropic virus or other infectious agents such as Toxoplasma gondii. Acute vestibular paralysis should be strictly distinguished from vestibular neuronitis. While vestibular paralysis is a syndrome, vestibular neuronitis must be considered as a nosologic entity, including a lesion of the peripheral neuron as well as evidence of an infectious event.

Adolescent↗
PubMed2001

Differential sensorimotor processing of vestibulo-ocular signals during rotation and translation.

Rotational and translational vestibulo-ocular reflexes (RVOR and TrVOR) function to maintain stable binocular fixation during head movements. Despite similar functional roles, differences in behavioral, neuroanatomical, and sensory afferent properties suggest that the sensorimotor processing may be partially distinct for the RVOR and TrVOR. To investigate the currently poorly understood neural correlates for the TrVOR, the activities of eye movement-sensitive neurons in the rostral vestibular nuclei were examined during pure translation and rotation under both stable gaze and suppression conditions. Two main conclusions were made. First, the 0.5 Hz firing rates of cells that carry both sensory head movement and motor-like signals during rotation were more strongly related to the oculomotor output than to the vestibular sensory signal during translation. Second, neurons the firing rates of which increased for ipsilaterally versus contralaterally directed eye movements (eye-ipsi and eye-contra cells, respectively) exhibited distinct dynamic properties during TrVOR suppression. Eye-ipsi neurons demonstrated relatively flat dynamics that was similar to that of the majority of vestibular-only neurons. In contrast, eye-contra cells were characterized by low-pass filter dynamics relative to linear acceleration and lower sensitivities than eye-ipsi cells. In fact, the main secondary eye-contra neuron in the disynaptic RVOR pathways (position-vestibular-pause cell) that exhibits a robust modulation during RVOR suppression did not modulate during TrVOR suppression. To explain these results, a simple model is proposed that is consistent with the known neuroanatomy and postulates differential projections of sensory canal and otolith signals onto eye-contra and eye-ipsi cells, respectively, within a shared premotor circuitry that generates the VORs.

Action Potentials↗
PubMed1995

Posterior canal-activated excitatory vestibuloocular relay neurons participate in the vestibulocortical pathways in cats.

We have previously reported that axon collaterals of posterior canal-activated excitatory vestibular (PC) neurons project to the contralateral oculomotor nucleus, and rostrally to the thalamus. To elucidate the vestibulothalamocortical pathways we investigated the synaptic connections of the PC neurons with the thalamic neurons by post-spike averaging of compound potentials triggered by spikes of the PC neuron in anesthetized cats. The averaged field potential evoked in the ventrobasal complex (VBC) revealed a spike followed by a negative wave. Latencies of the wave ranged from 0.8 to 1.5 ms. Next, we examined the location and axonal projection of 36 thalamic neurons which were activated by nose-up head rotation and by contralateral labyrinth stimulation. Most of them were located in the VBC and some in the medial geniculate body. Thirteen of the 36 neurons were antidromically activated from the anterior suprasylvian sulcus or postcruciate dimple of the cortex. These results suggest that the PC neurons participate, at least in part, in the vestibulocortical pathways contributing to spatial orientation.

Animals↗
PubMed2001

Holger Hydén's technique of preparation of single Deiters' neurons and study of permeability characteristics of their plasma membranes.

The protocols described here refer to Hydén's technique of isolation and microdissection of vestibular Deiters' neurons from adult mammals. The isolation of Deiters' cells from bovine is described and an example is given of the immunocytochemical visualization of their GABA(A) receptors by monoclonal antibodies against the beta(2/3) subunit. In addition, the protocol of the method for isolation of Deiters' cells from adult rabbit brain stem, the preparation of their plasma membranes and the study of their permeability characteristics is presented. Also in this case, examples of its application to the determination of chloride permeability and its modulation by GABA are given.

Animals↗
PubMed1975

Functional organization of vestibulofastigial projection in the horizontal semicircular canal system in the cat.

Spike potentials of fastigial nucleus neurons were recorded extracellularly in decerebrate, unanesthetized cats. The neurons responding to head rotation in the horizontal plane with a type I fashion were located mainly in the middle and caudal regions of the fastigial nucleus. Three fourth of these fastigial type I neurons were antidromically activated by stimulation of the contralateral vestibular nuclei. These neurons were excited transsynaptically from the ipsilateral vestibular nerve or nuclei. Intra cellular recordings were made from those neurons which were located in the caudal half of the fastigial nucleus and were activated antidromically from the contralateral vestibular nuclei. Stimulation of the ipsilateral vestibular nerve produced EPSPs in these neurons with latencies of 1.0-6.6 msec. The shortest conduction time along primary vestibular aggerents from the labyrinth to the ipsilateral fastigial nucleus was 0,7 msec. The EPSPs with the shortest latency of 1.0 msec were therefore postulated to be due to monosynaptic connections of primary vestibular afferents with fastigial neurons. Stimulation of ipsilateral vestibular nuclei also produced monosynaptic EPSPs in fastigial neurons. These EPSPs were facilitated by conditioning stimulation of the ipsilateral vestibular nerve, indicating the existence of polysynaptic activation of fastigial neurons from the ipsilateral vestibular nerve through the vestibular nuclei.

Animals↗
PubMed2006

Oscillatory and intrinsic membrane properties of guinea pig nucleus prepositus hypoglossi neurons in vitro.

Numerous models of the oculomotor neuronal integrator located in the prepositus hypoglossi nucleus (PHN) involve both highly tuned recurrent networks and intrinsic neuronal properties; however, there is little experimental evidence for the relative role of these two mechanisms. The experiments reported here show that all PHN neurons (PHNn) show marked phasic behavior, which is highly oscillatory in approximately 25% of the population. The behavior of this subset of PHNn, referred to as type D PHNn, is clearly different from that of the medial vestibular nucleus neurons, which transmit the bulk of head velocity-related sensory vestibular inputs without integrating them. We have investigated the firing and biophysical properties of PHNn and developed data-based realistic neuronal models to quantitatively illustrate that their active conductances can produce the oscillatory behavior. Although some individual type D PHNn are able to show some features of mathematical integration, the lack of robustness of this behavior strongly suggests that additional network interactions, likely involving all types of PHNn, are essential for the neuronal integrator. Furthermore, the relationship between the impulse activity and membrane potential of type D PHNn is highly nonlinear and frequency-dependent, even for relatively small-amplitude responses. These results suggest that some of the synaptic input to type D PHNn is likely to evoke oscillatory responses that will be nonlinearly amplified as the spike discharge rate increases. It would appear that the PHNn have specific intrinsic properties that, in conjunction with network interconnections, enhance the persistent neural activity needed for their function.

Action Potentials↗
PubMed1977

Vestibular nuclei activity during optokinetic after-nystagmus (OKAN) in the alert monkey.

Neurons which receive an input from the horizontal semicircular canals were recorded from the vestibular nuclei in chronically prepared monkeys (Macaca mulatta) during optokinetic after-nystagmus (OKAN). In complete darkness the vestibular neurons showed activity changes which closely paralleled the strength of nystagmus. The activity of vestibular units returned to baseline levels of spontaneous discharge only when all after-nystagmus had ceased, or when it was inhibited by stationary visual stimuli. The possible role of vestibular neurons in the generation of OKAN and its significance in vestibulo-visual interaction is discussed.

Animals↗
PubMed2006

Intrinsic and synaptic plasticity in the vestibular system.

The vestibular system provides an attractive model for understanding how changes in cellular and synaptic activity influence learning and memory in a quantifiable behavior, the vestibulo-ocular reflex. The vestibulo-ocular reflex produces eye movements that compensate for head motion; simple yet powerful forms of motor learning calibrate the circuit throughout life. Learning in the vestibulo-ocular reflex depends initially on the activity of Purkinje cells in the cerebellar flocculus, but consolidated memories appear to be stored downstream of Purkinje cells, probably in the vestibular nuclei. Recent studies have demonstrated that the neurons of the vestibular nucleus possess the capacity for both synaptic and intrinsic plasticity. Mechanistic analyses of a novel form of firing rate potentiation in neurons of the vestibular nucleus have revealed new rules of plasticity that could apply to spontaneously firing neurons in other parts of the brain.

Action Potentials↗
PubMed1996

Expression of nicotinic acetylcholine receptor mRNA in the adult rat peripheral vestibular system.

The mRNA expression of the neuronal nicotinic acetylcholine receptor subunits was determined in adult rat vestibular end-organs and in Scarpa's ganglion (SCG) by in situ hybridization with [35S] riboprobes. Neurons in the SCG expressed the alpha 4-7 and beta 2-3 mRNAs, but not alpha 3 or beta 4 mRNAs. Not all SCG neurons expressed every mRNA found in SCG. The alpha 6 and beta 2-3 riboprobes labeled all neurons, but alpha 4, alpha 5, and alpha 7 mRNAs were selectively expressed in one or more subpopulations of SCG neurons. Vestibular sensory hair cells, in contrast, expressed only alpha 9 mRNA.

Animals↗
PubMed1990

Compensation of horizontal canal related activity in the medial vestibular nucleus following unilateral labyrinth ablation in the decerebrate gerbil. II. Type II neurons.

The spontaneous activity and dynamic responses to sinusoidal horizontal head angular acceleration of type II horizontal semicircular canal related neurons in the medial vestibular nucleus (MVN) were recorded bilaterally in decerebrate Mongolian gerbils (Meriones unguiculatus) under three experimental conditions: normal labyrinths intact, acutely following unilateral labyrinthine lesion, and four to seven weeks following labyrinthine lesion. The number of type II neurons detected contralateral to the lesion was greatly reduced both in the acutely hemilabyrinthectomized animals and following compensation. The gain of the responses was depressed bilaterally acutely following the lesion. A greater reduction in response gain was noted in cells contralateral to the lesion. The gain of the contralateral type II responses increased with time such that in the compensated animal bilaterally symmetric gains were recorded. While the significant changes which occur in the gain of type II neurons with recovery from peripheral vestibular lesions can largely be attributed to type I neurons on the other side of the midline, changes in type I neurons were not entirely reflected in the type II population. The spontaneous activity of type II neurons did not undergo any significant changes following the labyrinthine lesion. We present a model utilizing the dynamic responses to estimate the functional recovery of commissural connections in compensated animals. The overall gain of the contralateral type I to ipsilateral type I commissural polysynaptic pathway appears to improve, while the efficacy in the reverse direction remains depressed, suggesting that modifications in commissural connections, particularly involving the type II to type I connections within the MVN on the injured side, mediate aspects of behavioral recovery.

Animals↗
PubMed2001

Cellular basis of vestibular compensation: analysis and modelling of the role of the commissural inhibitory system.

In this study we used a cellular network model of the brainstem vestibulo-ocular reflex (VOR) pathways to investigate the role of the vestibular commissural system in "vestibular compensation", the behavioural recovery that takes place after unilateral labyrinthectomy (UL). The network was initialized on the basis of mathematical analysis and trial simulations to generate a VOR response with a physiologically realistic gain and time constant. The effects of a selective decrease in the strength of commissural inhibitory input to the ipsi-lesional medial vestibular nucleus (MVN) neurones, without changes in other parts of the network, were investigated. Thus we simulated the marked down-regulation of GABA receptor efficacy that our recent experimental results have demonstrated in these cells after UL. The main outcome of this study is the delineation, for the first time, of a specific region of parameter space within which an adaptive change in commissural inhibitory gain is appropriate and sufficient to bring about a re-balancing of bilateral vestibular nucleus activity after UL. For this to be achieved, the relative contribution of the intrinsic, pacemaker-like membrane properties of the ipsi-lesional MVN cells must be equal to or greater than the synaptic input from the primary vestibular afferents in determining the in vivo resting discharge rate of these cells. Recent experimental evidence supports the view that the intrinsic properties of the MVN cells do contribute substantially to their resting discharge in vivo. Previous modelling studies that have excluded a role for the commissural system in vestibular compensation have arrived at this conclusion, because their models operated outside this region of parameter space. A second finding of this study is that, in a network that compensates through a selective change in commissural gain, the time constant of the VOR response is significantly reduced, mimicking the loss of velocity storage after UL in vivo. By contrast, the time constant is unchanged in a network that compensates through changes involving other nonvestibular inputs. These findings indicate that adaptive changes in commissural gain, through the dynamic regulation of GABA receptor efficacy in the vestibular nucleus neurones, may play an important role in vestibular plasticity.

Algorithms↗
PubMed1980

The dynamic discharge properties of oculomotor neurons in rabbits with intact and canal-plugged labyrinths during sinusoidal lateral tilt.

The characteristics of the control exerted by macular and ampullar vestibular receptors on oculomotor neurons (OMN) have been investigated by submitting unanesthetized, encéphale isolé rabbits, with intact and canal-plugged labyrinths, to sinusoidal lateral tilts of varying frequencies (0.013-0.2 Hz). For frequencies of tilt above 0.025 Hz, corresponding to peak angular accelerations suprathreshold for canal related vestibular neurons, both phase and sensitivity of the OMN response differ significantly in the two types of preparation. At lower frequencies of tilt the characteristics of the OMN response are, on the contrary, very similar, thus indicating that also in the intact animals the control of the vertical vestibulo-ocular reflex, in this frequency range, is exerted almost exclusively by the otoliths.

Animals↗
PubMed2001

Role of cholinergic mossy fibers in medial vestibular and prepositus hypoglossal nuclei in vestibular compensation.

Several lines of evidence have suggested that acetylcholine is a possible neurotransmitter/neuromodulator involved in vestibular compensation. Further, the central vestibular system, oculo- and spino-motor neurons and peripheral vestibular efferents contain abundant cholinergic neurons. However, details of cholinergic effective sites during vestibular compensation remain to be clarified. In the present study, we selectively damaged rat vestibulo-floccular and vestibulo-uvulonodular cholinergic mossy fibers using ethylcholine mustard aziridinium ions. In these treated animals, unilateral labyrinthectomy caused more severe vestibulo-ocular deficits especially during the initial stage. From these findings we suggest that vestibulo-floccular and vestibulo-uvulonodular cholinergic mossy fibers contribute to the restoration of a balance between intervestibular nuclear activities for the induction of vestibular compensation during the initial stage.

Acetylcholine↗
PubMed2002

Molecular probes of the vestibular nerve. II. Characterization of neurons in Scarpa's ganglion to determine separate populations within the nerve.

An unambiguous delineation of the exact numbers and/or proportions of calyx-only, dimorph, and bouton-only vestibular afferents is needed to continue studies concerning vestibular integration in the nervous system. Here, we take advantage of immunocytochemical properties of three groups of vestibular afferents. We utilize calretinin to delineate the calyx-only population, and peripherin to stain the bouton-only afferents. An additional subgroup of afferents that stain with calbindin, but not calretinin is also introduced. The size of the cells that stain with these markers was determined. Cells that are calbindin-positive overlap the sizes of Nissl-stained somata. Cells that stain with peripherin or calretinin are non-overlapping with calretinin cells being the largest and peripherin-positive cells the smallest. Twenty percent of the ganglion cells were peripherin positive, another 20% stained with calretinin antibodies, 30% stained with calbindin, and all cells in Scarpa's ganglion stained with parvalbumin. Most of the calretinin-positive cells also stained with calbindin. One-third of the calbindin-positive population stained only with calbindin. These studies indicate that the calyx- and bouton-only populations of vestibular afferents in gerbil comprise at least 40% of the nerve. In addition, at least 10% of the nerve also stains with calbindin and neither calretinin nor peripherin. Based on indirect evidence, we hypothesize that these are a subpopulation of dimorph afferents. This study has provided an anatomical instrument (in addition to intracellular physiological methods) to study separate populations of vestibular afferents.

Action Potentials↗
PubMedDate not supplied

Myelination of the mouse vestibular ganglion.

Myelination of mouse vestibular ganglion cells and preganglionic fibres was examined by light and electron microscopy from gestation day 16 to postnatal day 23. Myelination of the preganglionic fibres occurred essentially during the first 2 days after birth and was almost complete by postnatal day 7. Myelination of the ganglion cells occurred later and lasted longer than that of the fibres. Its onset was observed on postnatal day 9 and the myelin sheaths had fully developed structures 2 weeks later. Thus, myelination of vestibular ganglion neurons appeared to be the latest event to take place in the maturation of the peripheral vestibular system. The sequences of myelination are discussed with respect to those of electrophysiological maturation.

Animals↗
PubMed1992

Plastic properties of the vestibulo-ocular reflex in olivo-ponto-cerebellar atrophy.

Disorders in vestibulo-ocular functions were studied in 4 patients with olivo-ponto-cerebellar atrophy (OPCA). The phenomenon of habituation, considered as a plastic property of the vestibulo-ocular reflex (VOR), was explored with a behavioural paradigm in these patients. When subjected to the habituation paradigm all patients presented a modified response opposite to that observed in normal subjects. The role played by the cerebellum in relation to VOR plasticity--well known in different experimental models--is analyzed. The hypothesis of a modification of the cerebellum's inhibitory action on vestibular nuclei neurons is put forward to explain the inversion of the VOR habituation phenomenon in these patients.

Adult↗