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PubMed1990

The vestibular nuclei of the cat receive a primary afferent projection from receptors in extraocular muscles.

The vestibular nuclei of adult cat were injected with retrogradely transported tracers, WGA-HRP or fluorescent Diamidino-Yellow. Labelled cells were found in the caudal half of the ipsilateral mesencephalic trigeminal nucleus, in the area where ganglionic cells of the sensory receptors in the extraocular muscles have previously been described. Double labelling experiments were carried out with Diamidino Yellow injected in vestibular nuclei and Fast Blue in extraocular muscles. Some cells in the mesencephalic trigeminal nucleus were found to contain both tracers, providing evidence that vestibular neurons do receive direct afferent signals from extraocular muscles. Therefore, this anatomical demonstration suggests a direct feed-back control between the extraocular muscle receptors and the vestibular nuclei.

Amidines↗
PubMed1985

The vestibuloocular reflex of the adult flatfish. II. Vestibulooculomotor connectivity.

The peripheral and central oculomotor organization of the adult flatfish presents no morphological substrates that suffice to explain adaptive changes in its vestibuloocular reflex system. The necessity for an adaptation occurs because of a 90 degrees displacement of the vestibular with respect to the extraocular coordinate axes during metamorphosis. Since a reorganization of vestibuloocular pathways must be hypothesized (12), the location and termination of electrophysiologically identified secondary vestibular neurons with focus on the horizontal canal system was studied with the intracellular horseradish peroxidase method in adult winter flounders. Pseudopleuronectes americanus. The oculomotor target sites of vertical canal related neurons were similar to those described in mammals. Presumed excitatory anterior canal neurons bifurcated after the main axon had crossed the midline. The descending branch headed toward the spinal cord. The ascending branch reached the oculomotor nucleus via the contralateral medial longitudinal fasciculus and terminated in the superior rectus and inferior oblique subdivisions. Presumed inhibitory posterior canal neurons ascended ipsilaterally in the medial longitudinal fasciculus and terminated mainly in the superior rectus and inferior oblique subdivisions. Horizontal canal neurons exhibited characteristics distinctly different from mammalian ones. Two types of second-order neurons were observed. In the first case, cell bodies were located in the anterior portion of the vestibular nuclear complex. After crossing the midline, the axon ascended in the contralateral medial longitudinal fasciculus. Major termination sites were found in the inferior oblique and superior rectus subdivisions of the oculomotor nucleus. Axonal branches then recrossed the midline and terminated in identical locations on the ipsilateral side. In the second case, cell bodies were located in the descending vestibular nucleus. Their axons crossed the midline and also ascended in the contralateral medial longitudinal fasciculus. Major termination sites were in the trochlear nucleus and in the inferior rectus subdivision of the oculomotor nucleus. As in the first case, axonal branches also recrossed the midline and terminated in identical motoneuron pools on the ipsilateral side. The above target sites were exactly those expected to be used in a reciprocal excitatory-inhibitory fashion during compensatory eye movements. Head-down movement would be excitatory for the lower horizontal canal producing contractions of both superior recti and inferior obliques as well as relaxation of the antagonistic inferior recti and superior obliques.(ABSTRACT TRUNCATED AT 400 WORDS)

Adaptation, Biological↗
PubMed1987

Responses of rat lateral hypothalamic neuron activity to vestibular nuclei stimulation.

Effects of lateral vestibular nucleus (LVN) stimulation on neuronal activity in the rat lateral hypothalamic area (LHA), including specific glucose-sensitive neurons, were investigated by extracellular and intracellular recordings in vivo. Stimulation of the contralateral LVN evoked 3 types of response in 46% (111/240) of the neurons recorded extracellularly: long latency (38.1 +/- 23.6 ms) excitation (62/111, 56%), short latency (6.9 +/- 3.1 ms) excitation-inhibition (33/111, 30%), and inhibition with 20.1 +/- 11.1 ms latency (16/111, 14%). Glucose-sensitive neurons, which were identified by electrophoretic application of glucose, did not respond specifically to such stimulation. Neuronal activity was recorded intracellularly from 31 LHA neurons, of which 13 responded to LVN stimulation. Seven of the 13 neurons showed a long latency EPSP (10.4 +/- 5.5 ms) and the remaining 6 exhibited an EPSP-IPSP sequence with shorter latency (4.5 +/- 3.0 ms). The amplitude of these responses was graded with a change in stimulus intensity. The EPSPs of both types of response were considered to be polysynaptic because of shortening of latencies by higher current stimulation. Since the LHA is implicated in the regulation of autonomic nerve activity, the present results showing polysynaptic pathways from the LVN to the LHA suggest functional involvement of the LHA in vestibulo-autonomic responses.

Animals↗
PubMed2001

Postlesional vestibular reorganization in frogs: evidence for a basic reaction pattern after nerve injury.

Nerve injury induces a reorganization of subcortical and cortical sensory or motor maps in mammals. A similar process, vestibular plasticity 2 mo after unilateral section of the ramus anterior of N. VIII was examined in this study in adult frogs. The brain was isolated with the branches of both N. VIII attached. Monosynaptic afferent responses were recorded in the vestibular nuclei on the operated side following ipsilateral electric stimulation either of the sectioned ramus anterior of N. VIII or of the intact posterior vertical canal nerve. Excitatory and inhibitory commissural responses were evoked by separate stimulation of each of the contralateral canal nerves in second-order vestibular neurons. The afferent and commissural responses of posterior vertical canal neurons recorded on the operated side were not altered. However, posterior canal-related afferent inputs had expanded onto part of the deprived ramus anterior neurons. Inhibitory commissural responses evoked from canal nerves on the intact side were detected in significantly fewer deprived ramus anterior neurons than in controls, but excitatory commissural inputs from the three contralateral canal nerves had expanded. This reactivation might facilitate the survival of deprived neurons and reduce the asymmetry in bilateral resting activities but implies a deterioration of the original spatial response tuning. Extensive similarities at the synaptic and network level were noted between this vestibular reorganization and the postlesional cortical and subcortical reorganization of sensory representations in mammals. We therefore suggest that nerve injury activates a fundamental neural reaction pattern that is common between sensory modalities and vertebrate species.

Animals↗
PubMed1989

Depression of the vestibulo-ocular and optokinetic responses by intrafloccular microinjection of GABA-A and GABA-B agonists in the rabbit.

The functional implication of the cerebellar flocculus in regulation of the VOR and OKR gain has mostly been studied by lesion experiments, and the hypotheses derived from these experiments are not always in line with one another. In the present study, a reversible method was used to inhibit floccular Purkinje cells. The GABA-A agonist muscimol or the GABA-B agonist baclofen were bilaterally injected into the flocculus of rabbits, and the effects of these injections on the gain of the VOR and OKR were studied. Both drugs induced a reduction by at least 50% of the gain of the VOR in light and darkness, and of the OKR. Although GABA-A and GABA-B receptors are known to have different cerebellar localizations, muscimol and baclofen injections resulted in quantitatively similar effects. It is suggested that these GABA-agonists cause either direct or indirect inhibition of floccular Purkinje cells, thus reducing modulation of the firing rate of these neurons by afferent mossy and climbing fibers. Because the flocular Purkinje cells act out of phase with the vestibular neurons which drive the oculomotor neurons, a reduced output of floccular Purkinje cells would result in a reduction of the VOR and OKR gain. These experiments provide strong evidence that the cerebellar flocculus has a positive influence on the basic VOR and OKR gain.

Animals↗
PubMed1975

Neural pathways from the vestibular labyrinths to the flocculus in the cat.

In decerebrate, unanesthetized cats, responses in the flocculus were evoked by electric stimulation of the vestibular nerves and by natural stimulation of horizontal head angular acceleration. Field potentials in the flocculus and intracellular recording from Purkinje cells following vestibular nerve stimulation indicated that the responses were produced by mossy fiber inputs. Field potentials evoked from the contralateral labyrinth were as large as those from the ipsilateral one. There was considerable convergence of bilateral labyrinthine mossy fiber inputs to a Purkinje cell. In view of the effects of incision at the midline of the cerebellum and the brain stem, inputs from the contralateral labyrinth were mainly conveyed through the midline of the brain stem and partly through the midline of the cerebellum. Primary vestibular afferents were involved in the transcerebellar crossed pathway. Fibers of the secondary vestibular neurons projecting to the contralateral flocculus were implicated in the brain stem-mediated pathway and, in part, presumably in the transcerebellar crossed pathway. About one-third of the axon spikes examined in the flocculus responded to horizontal head angular acceleration. Commissural inhibition was observed in more than half of the axon spikes in the flocculus which were presumed to be mono- or polysynaptically activated from the vestibular nerve.

Animals↗
PubMed1985

Transneuronal transport in the vestibular and auditory systems of the squirrel monkey and the arctic ground squirrel. I. Vestibular system.

Transneuronal transport of [3H]proline, [3H]fucose, and [3H]leucine in various combinations from pledgets implanted in the ampulla of a single semicircular duct was studied in the squirrel monkey and arctic ground squirrel after long survival periods. Tritiated amino acids implanted in any single ampulla resulted in labeling of nearly all vestibular and auditory receptors, nearly all cells of the vestibular and spiral ganglia and central transport via nearly all root fibers of both nerves. Primary vestibular fibers were distributed to the vestibular nuclei (VN) and specific parts of the cerebellum in the pattern previously described. Transneuronal transport of [3H]proline by vestibular neurons was present in all known secondary pathways, except those projecting to thalamic nuclei. Observations were similar in both species, except for small differences in commissural vestibular projections. Major commissural transport was to all parts of the opposite medial vestibular nucleus (MVN) and to peripheral parts of the superior vestibular nucleus (SVN), but some transport was present in all contralateral VN, including ventral cell group y. Descending transneuronal transport was evident in vestibulospinal tract (VST) ipsilaterally and in the medial longitudinal fasciculus (MLF) bilaterally. Both [3H]proline and [3]fucose were transported transneuronally to the ipsilateral abducens nucleus (AN); with long survivals [3H]proline was transported peripherally via the ipsilateral abducens nerve root. Ascending transport in the MLF was bilateral, asymmetric and greatest contralaterally. Fibers entered the contralateral MLF near the AN and the lateral wing of the ipsilateral MLF rostral to most of the VN. Terminals in the trochlear nuclei (TN) were bilateral and greatest contralaterally. In the monkey terminals in ipsilateral oculomotor complex (OMC) were distributed uniformly in all subdivisions, except for the medial rectus subdivision (MRS), where terminals were more numerous. The greatest density of terminals was present contralaterally in the superior rectus subdivision (SRS) of the OMC; only sparse terminals were present in the MRS on that side. Transport in the ipsilateral abducens nerve roots in the monkey and the virtual absence of transport to the MRS of the contralateral OMC suggested transneuronal transport to abducens motor neurons, but not to internuclear neurons (AIN). The AIN project only to the MRS of the contralateral OMC and do not appear to receive vestibular input. Comparable observations were made in the AN, TN and OMC of the ground squirrel, although the representation of the extraocular muscles in the OMC is unknown.(ABSTRACT TRUNCATED AT 400 WORDS)

Abducens Nerve↗
PubMed1978

[Modulation of the activity of neurons of Deiter's nucleus upon electric stimulation of the hypothalamus and limbic structures of the brain].

In immobilized cats, stimulation of the lateral hypothalamus facilitates the activity of vestibular neurons; stimulation of the hypothalamic ventro-medial nucleus and dorsal hippocampus suppresses the unit activity, mainly. The effects of stimulation of the basolateral amygdalar nucleus were excitatory as well as inhibitory. Prevalence of the long-latency tonic responses indicates that the modulating effects of the hypothalamus and limbic structures are fulfilled through either mesencephalic RF or thalamic nuclei.

Amygdala↗
PubMed1985

[Structure and origin of axonal terminals innervating neurons of the vestibular ganglia].

Structural organization of the frog axonal terminals, realizing the synaptic contact with neurons of the vestibular ganglion have been studied electron microscopically. Two kinds of axonal terminals are revealed. They differ in quantitative and qualitative composition of their synaptic vesicles convergated simultaneously in various combinations to the ganglious neurons. Using the axonal retrograde transport of horseradish peroxidase, the nature of these axonal terminals is analysed. Their source is demonstrated to be neurons of the reticular formation and ventral vestibular nucleus of the medulla oblongata, as well as Purkinje's cells of the cerebellum.

Animals↗
PubMed1979

Vestibular mechanisms.

It is apparent from this and other reviews of the subject that our knowledge of vestibular function is most complete for the primary canal and otolithic afferents. Relatively little progress has been made in the understanding of receptor mechanisms and the functional importance of the efferent vestibular system. Since most of it has been summarized previously the latter were not considered here. Considerably more knowledge has accumulated in the field of central vestibular mechanisms, particularly those related to eye movements. Recent advances in functional synaptology of direct and indirect vestibuloocular pathways are described. It appears that the indirect pathways are essential for the central integration of the peripheral head velocity into a central eye position signal. Candidates for the neural integrator are presented and discussed and their connectivity described both for the horizontal and the relatively poorly studied vertical eye movement system. This field will certainly be studied extensively during the next years. Another interesting field is the role of the cerebellum in the control the vestibuloocular reflex. Recent data and hypotheses, including the problem of cerebellar plasticity, are summarized and evaluated. That the vestibular nuclei are by no means a simple relay system for specific vestibular signals destined for other sensory or motor centers is evidenced in this review by the description of multiple canal-canal, canalotolith, and visual-vestibular convergence at the nuclear level. Canal-otolith and polysensory convergence in vestibular neurons enables them to correct for the inherent inadequacies of the peripheral canal system in the low frequency range. The mechanisms of polysensory interaction in the central vestibular system will undoubtedly be an important and interesting field for future research.

Abducens Nerve↗
PubMed1988

Epidemiological studies on benign paroxysmal positional vertigo in Japan.

In 1980, the Research Committee of Peripheral Vestibular Disorders in Japan, which is supported by the Ministry of Health and Welfare, was founded by 24 members, from several districts in Japan. The Committee's first task was to draft the diagnostic criteria for several peripheral vestibular disorders, such as benign paroxysmal positional vertigo (BPPV), and vestibular neuronitis. For the national epidemiological survey, they then collected the data on 101 cases of BPPV out of some 783 vestibular disorder patients. In addition, data on 103 patients of BPPV out of 559 vestibular disorder patients were also collected from the Neuro-otological Clinic of the Toyama Medical and Pharmaceutical University Hospital. From these epidemiological surveys, the incidence of BPPV in Japan was estimated at 10.7 per 100,000 population, while that of BPPV in Toyama was estimated at 17.3 per 100,000 population. The ratio of BPPV was higher in female than male patients in both surveys. The age at the onset of BPPV peaked in the fourth decade in both males and females. Compared with the other epidemiological features of Meniere's disease and sudden deafness with vertigo in the same surveys, it appeared that the characteristic features of BPPV are epidemiologically similar to those of Meniere's disease, but different from those of sudden deafness.

Female↗
PubMed2004

Properties of horizontal semicircular canal nerve-activated vestibulospinal neurons in cats.

Axonal pathways, projection levels, and locations of horizontal semicircular canal (HC) nerve-activated vestibulospinal neurons were studied. The HC nerve was selectively stimulated. Vestibulospinal neurons were activated antidromically with four stimulating electrodes, inserted bilaterally into the lateral vestibulospinal tracts (LVST) and medial vestibulospinal tracts (MVST) at the C1/C2 junction. Stimulating electrodes were also positioned in the C3, T1, and L3 segments and in the oculomotor nuclei. Most HC nerve-activated vestibulospinal neurons were located in the ventral portion of the medial, lateral, and the descending nuclei. Among the 157 HC nerve-activated vestibular neurons, 83 were antidromically activated by stimulation at the C1/C2 junction. Of these 83 neurons, axonal pathways of 56 HC nerve-activated vestibulospinal neurons were determined. Most (48/56) of these had axons that descended through the MVST, with the remainder (8 neurons) having axons that descended through the ipsilateral (i-) LVST. Laterality of the axons' trajectories through the MVST was investigated. The majority of vestibulospinal neurons (24/28) with axons descending through the contralateral MVST were also antidromically activated from the oculomotor nucleus, whereas almost all vestibulospinal neurons (19/20) with axons descending through the i-MVST were not. Most HC nerve-activated vestibulospinal neurons were activated antidromically only from the C1/C2 or C3 segments. Only one neuron that was antidromically activated from the T1 segment had an axon that descended through the i-LVST. None of the HC nerve-activated vestibulospinal neurons were antidromically activated from the L3 segment. It is likely that the majority of HC nerve-activated vestibulospinal neurons terminate in the cervical cord and have strong connections with neck motoneurons.

Animals↗
PubMed2000

Lack of growth-associated protein-43 reemergence or of growth-associated protein-43 mRNA modulation in deafferented vestibular nuclei during the first 6 weeks after unilateral inner ear lesion.

We investigated whether a unilateral inner ear lesion that destroyed the labyrinthine receptors, the cochlear receptors, and the spiral ganglion induced collateral sprouting in rat vestibular and auditory brainstem nuclei, using growth-associated protein-43 (GAP-43) as an indicator of synaptic remodeling. Both immunocytochemistry and in situ hybridization were performed to detect a potential modulation of GAP-43 and of its messenger RNA (mRNA) at different times after surgery. We failed to observe a reemergence of GAP-43 or a modulation of its mRNA in the deafferented vestibular nuclei at all survival times tested. In contrast, a substantial increase in the expression of GAP-43 was observed in the neuropil of the ipsilateral deafferented cochlear nuclei and in cell bodies of the ipsilateral superior olive. This increase was associated with an up- and downregulation of the mRNA coding for GAP-43 in the ipsilateral ventral cochlear nucleus and in the ipsilateral superior olive, respectively. These data indicate that synaptic remodeling, as assessed by GAP-43 expression, does not seem to occur in the deafferented vestibular complex during the first 6 weeks after labyrinthectomy, whereas it occurs within the first deafferented auditory relays at times as early as 4 days following spiral ganglion and cochlear receptors removal. We conclude that recovery of a normal resting discharge of the deafferented central vestibular neurons and consequently recovery of a normal resting posture and eye position may not depend on collateral sprouting of the remaining vestibular afferents. In contrast, we confirmed that a reactive synaptogenesis occurs in the brainstem auditory nuclei following cochlea and spiral ganglion removal. Its functional significance remains an open question.

Afferent Pathways↗
PubMedDate not supplied

Commissural projections of the superior vestibular nucleus in the rat.

Wheatgerm agglutinin horseradish peroxidase (WGA-HRP) injections confined to the superior vesicular nucleus (SVN) of six Fischer 344 rats labeled commissural vestibular neurons (CVN) in central and ventral portions of contralateral SVN and Group Y nucleus (Grp Y). When the injection included medial vestibular nucleus (MVN) and Grp Y, labeling was similar with additional labeling in contralateral ventrolateral MVN. A dried pledget of WGA-HRP placed in a midline IV ventricle lesion (N = 4), bilaterally labeled SVN and Grp Y (MVN could not be assessed) CVN. While Grp Y CVN are significantly smaller (138.8 +/- 64.7 microns2) than the CVN in the SVN (177.9 +/- 73.9 microns2) or MVN (196.2 +/- 61.9 microns2), cellular eccentricity (shape) is similar in all three nuclei (0.80, 0.77, SVN, MVN, Grp Y).

Analysis of Variance↗
PubMed1976

[Unilateral caloric hyporeflexis].

Seventy-one patients with an unilateral caloric hypofunction were examined in order to establish the correlation with cochlear function. We divised our cases following the subjective clinical syndromes. Groupe A (12 patients) with a history of only one crise of vertigo. Groupe B (13 patients) with repeated vertiginous attacks. Groupe C (21 patients) with a positional vertigo only. Groupe D (15 patients) with rather undefinite complaints. Groupe E (7 patients) with no vertigo at all. We believe to discern the following syndromes in our cases of unilateral vestibular hypofunction: 9 cases with a history of a unique vertiginous crises could be considered as a vestibular "neuronitis" in the narrow sense of the word. One case with recidiving attacks could be considered as a neuronitis, or as a Menière without cochlear disturbances. Some cases with a positional vertigo only or with very vague complaints could be considered as a neuronitis in a large sense.

Electronystagmography↗
PubMed1992

[Vertigo in children].

The main difference between childhood and adulthood vertigo is that the evaluation of symptoms and examination pose special challenges in pediatric patients, depending on age. Vertigo in pre-teenage children is similar to vertigo in adults. In contrast, although benign paroxysmal vertigo, vestibular neuronitis, and Ménière's vertigo occur in children, the distribution of these conditions is different from that seen in adults. After vestibular and cochlear investigations as well as a CT scan or MRI study to outrule a tumor of the posterior cerebral fossa, the diagnosis of vestibular vertigo is established. Often, the diagnosis proposed cannot be considered as final and requires reappraisal according to the long-term course. Collation of case-reports with highly accurate documents is essential in order to strive to develop more satisfactory approaches.

Child↗
PubMed1988

Responses of single neurons in the parietoinsular vestibular cortex of primates.

1. Neurons activated by stimulation of the horizontal and/or vertical vestibular semicircular canals were recorded in the parietoinsular vestibular cortex in four awake Java monkeys (Macaca fascicularis) and three squirrel monkeys (Saimiri sciureus). Steady tilt in darkness or during illumination of a vertically striped cylinder or of the normal laboratory surroundings did not lead to a significant change in PIVC neuron activity. Thus vestibular input to this cortical region seems to be restricted to signals originating in the semicircular canal receptors. 2. Vestibular stimulation in the three main experimental planes (roll, yaw, and pitch) and in planes in between provided clear evidence that optimum activation can be found in planes that do not coincide with the planes of the semicircular canals but are distributed over all possible spatial planes through the head. 3. Definite evidence of clustering in subdivisions of PIVC of neurons responding to the same optimum rotation plane was obtained in squirrel monkeys and is also suggested to exist in PIVC of Java monkeys. 4. Nearly all neurons responding to vestibular stimulation were also activated by visual large-field movement (optokinetic stimulation). Responses to optokinetic stimuli were always at optimum when the direction of the movement pattern corresponded to the optimum vestibular plane. Two classes of visual-vestibular interaction were found: Synergistic neurons were those PIVC cells with the strongest response to visual movement stimulation in the opposite direction to that leading to a maximum response to vestibular stimulation. Antagonistic neurons had a response maximum when the visual stimulus was moved in the direction of optimum vestibular stimulation. 5. Most PIVC neurons responded to stimulation of the deep mechanoreceptors in the neck region. This input from the neck receptors was tested quantitatively only in the horizontal plane (trunk rotation with the head fixed in space or head rotation with the trunk fixed in space). It interacted with vestibular signals at the PIVC neurons either in an antagonistic or a synergistic manner, the latter meaning activation during rotation of the head in the same direction as that leading to activation induced by semicircular canal stimulation. 6. In addition to the direction-specific vestibular, visual, and neck receptor inputs, a rather complex somatosensory input to PIVC neurons exists, including responses to stimulation of mechanoreceptors of the skin, the muscles, and the joint receptors of legs and arms. Total body vibration also led to activation of some of the neurons.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1994

Morphological and electrophysiological consequences of unilateral pre- versus postganglionic vestibular lesions in the frog.

The combined removal of the labyrinthine sense organs and of the ganglion of Scarpa on one side (postganglionic section) resulted in a degeneration of afferent fibres in the eighth nerve of the frog (Rana temporaria) within 2-4 days. If the eighth nerve was sectioned more peripherally (preganglionic section) and its distal part was removed together with the labyrinthine organs degeneration of afferent fibres was absent or restricted to very few fibres. Electrical stimulation of vestibular afferents in vitro evoked monosynaptic field potentials in the ipsilateral and via commissural fibres di- and polysynaptic field potentials in the contralateral vestibular nuclei. Afferent-evoked field potentials recorded on the intact side of chronic frogs (> or = 60 days) with a pre- or postganglionic lesion and afferent-evoked field potentials recorded on the operated side of chronic frogs with a preganglionic lesion had amplitudes that were very similar to those recorded in control frogs. Commissurally evoked field potentials recorded on the operated side of chronic frogs with pre- or postganglionic lesions were significantly increased (by about 90%) with respect to control amplitudes. In both groups the time-course of this increase was very similar, started between 15 and 30 days and saturated for survival periods longer than 60 days. Unilateral inactivation of vestibular afferents, but not degeneration, is the likely common denominator of the central process leading to the reported neural changes. A reactive supersensitivity of central vestibular neurons on the operated side for glutamate as a possible mechanism is unlikely, since converging afferent and commissural inputs are both glutamatergic and only one of them, the commissural input, was potentiated. Comparison of the time-courses of neural changes in the vestibular nuclei and postural recovery in the same individuals excludes a causal relation between both phenomena.

Animals↗