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At least 685 records · Page 38Linked to original sources
PubMed1992

Vestibularly induced slow oscillations in climbing fiber responses of Purkinje cells in the cerebellar nodulus of the rabbit.

In this report we describe an interesting form of plasticity in climbing fiber responses evoked in Purkinje cells of the rabbit cerebellum by periodic vestibular stimulation. The cerebellar nodulus receives a vestibular as well as a visual climbing fiber afferent input from the contralateral inferior olive. The vestibular input to the inferior olive originates from the ipsilateral medial and descending vestibular nuclei and terminates within the beta-nucleus. This projection to the beta-nucleus from secondary vestibular neurons is GABAergic. This means that vestibularly evoked activity of neurons in the beta-nucleus is controlled by modulation of an inhibitory input, rather than by modification of an excitatory input. We have recorded the climbing fiber responses of single Purkinje cells in the uvula-nodulus (lobules 9c, 9d and 10) of rabbits and we have characterized the climbing fiber response of each Purkinje cell from which we recorded by testing its sensitivity to otolithic stimulation, semicircular canal stimulation and optokinetic stimulation. Vestibularly evoked climbing fiber responses recorded from the left nodulus were stationary. They were repeatedly evoked, for tens of minutes, by sinusoidally rotating the rabbit about the longitudinal axis onto its left side (Fig. 1B). When the vestibular stimulus was stopped the discharge of these climbing fiber responses returned to non-periodic spontaneous levels. However, the vestibularly evoked climbing fiber discharge of approximately 5% of Purkinje cells was not stationary.(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗
PubMed2001

Vestibuloocular reflex of the adult flatfish. III. A species-specific reciprocal pattern of excitation and inhibition.

In juvenile flatfish the vestibuloocular reflex (VOR) circuitry that underlies compensatory eye movements adapts to a 90 degrees relative displacement of vestibular and oculomotor reference frames during metamorphosis. VOR pathways are rearranged to allow horizontal canal-activated second-order vestibular neurons in adult flatfish to control extraocular motoneurons innervating vertical eye muscles. This study describes the anatomy and physiology of identified flatfish-specific excitatory and inhibitory vestibular pathways. In antidromically identified oculomotor and trochlear motoneurons, excitatory postsynaptic potentials (EPSPs) were elicited after electrical stimulation of the horizontal canal nerve expected to provide excitatory input. Electrotonic depolarizations (0.8-0.9 ms) preceded small amplitude (<0.5 mV) chemical EPSPs at 1.2-1.6 ms with much larger EPSPs (>1 mV) recorded around 2.5 ms. Stimulation of the opposite horizontal canal nerve produced inhibitory postsynaptic potentials (IPSPs) at a disynaptic latency of 1.6-1.8 ms that were depolarizing at membrane resting potentials around -60 mV. Injection of chloride ions increased IPSP amplitude, and current-clamp analysis showed the IPSP equilibrium potential to be near the membrane resting potential. Repeated electrical stimulation of either the excitatory or inhibitory horizontal canal vestibular nerve greatly increased the amplitude of the respective synaptic responses. These observations suggest that the large terminal arborizations of each VOR neuron imposes an electrotonic load requiring multiple action potentials to maximize synaptic efficacy. GABA antibodies labeled axons in the medial longitudinal fasciculus (MLF) some of which were hypothesized to originate from horizontal canal-activated inhibitory vestibular neurons. GABAergic terminal arborizations were distributed largely on the somata and proximal dendrites of oculomotor and trochlear motoneurons. These findings suggest that the species-specific horizontal canal inhibitory pathway exhibits similar electrophysiological and synaptic transmitter profiles as the anterior and posterior canal inhibitory projections to oculomotor and trochlear motoneurons. Electron microscopy showed axosomatic and axodendritic synaptic endings containing spheroidal synaptic vesicles to establish chemical excitatory synaptic contacts characterized by asymmetrical pre/postsynaptic membrane specializations as well as gap junctional contacts consistent with electrotonic coupling. Another type of axosomatic synaptic ending contained pleiomorphic synaptic vesicles forming chemical, presumed inhibitory, synaptic contacts on motoneurons that never included gap junctions. Altogether these data provide electrophysiological, immunohistochemical, and ultrastructural evidence for reciprocal excitatory/inhibitory organization of the novel vestibulooculomotor projections in adult flatfish. The appearance of unique second-order vestibular neurons linking the horizontal canal to vertical oculomotor neurons suggests that reciprocal excitation and inhibition are a fundamental, developmentally linked trait of compensatory eye movement circuits in vertebrates.

Abducens Nerve↗
PubMed1992

Inputs from regularly and irregularly discharging vestibular nerve afferents to secondary neurons in squirrel monkey vestibular nuclei. III. Correlation with vestibulospinal and vestibuloocular output pathways.

1. A previous study measured the relative contributions made by regularly and irregularly discharging afferents to the monosynaptic vestibular nerve (Vi) input of individual secondary neurons located in and around the superior vestibular nucleus of barbiturate-anesthetized squirrel monkeys. Here, the analysis is extended to more caudal regions of the vestibular nuclei, which are a major source of both vestibuloocular and vestibulospinal pathways. As in the previous study, antidromic stimulation techniques are used to classify secondary neurons as oculomotor or spinal projecting. In addition, spinal-projecting neurons are distinguished by their descending pathways, their termination levels in the spinal cord, and their collateral projections to the IIIrd nucleus. 2. Monosynaptic excitatory postsynaptic potentials (EPSPs) were recorded intracellularly from secondary neurons as shocks of increasing strength were applied to Vi. Shocks were normalized in terms of the threshold (T) required to evoke field potentials in the vestibular nuclei. As shown previously, the relative contribution of irregular afferents to the total monosynaptic Vi input of each secondary neuron can be expressed as a %I index, the ratio (x100) of the relative sizes of the EPSPs evoked by shocks of 4 x T and 16 x T. 3. Antidromic stimulation was used to type secondary neurons as 1) medial vestibulospinal tract (MVST) cells projecting to spinal segments C1 or C6; 2) lateral vestibulospinal tract (LVST) cells projecting to C1, C6; or L1; 3) vestibulooculo-collic (VOC) cells projecting both to the IIIrd nucleus and by way of the MVST to C1 or C6; and 4) vestibuloocular (VOR) neurons projecting to the IIIrd nucleus but not to the spinal cord. Most of the neurons were located in the lateral vestibular nucleus (LV), including its dorsal (dLV) and ventral (vLV) divisions, and adjacent parts of the medial (MV) and descending nuclei (DV). Cells receiving quite different proportions of their direct inputs from regular and irregular afferents were intermingled in all regions explored. 4. LVST neurons are restricted to LV and DV and show a somatotopic organization. Those destined for the cervical and thoracic cord come from vLV, from a transition zone between vLV and DV, and to a lesser extent from dLV. Lumbar-projecting neurons are located more dorsally in dLV and more caudally in DV. MVST neurons reside in MV and in the vLV-DV transition zone.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1984

The sleep-wake transition in the oculomotor system.

Eye and head position, EEG, and activity of oculomotor and vestibular neurons in the brainstem were recorded during alertness and at the transition to light sleep. Characteristic changes of firing patterns were found in many neuronal populations at the sleep-wake transition and could be related to disruption of fixation and rapid and compensatory eye movement generation. Motoneurons decreased their firing rate by 20 to 50%, and their eye velocity coding deteriorated. Burst neurons had a significant drop in maximum firing rates and often showed continuous activity unrelated to rapid eye movements, but responded to vestibular stimuli. Pause neurons went completely silent. Neurons in the vestibular nuclei often reduced their level of activity, but still responded qualitatively unchanged to semicircular canal stimulation. In the framework of current models of oculomotor organization, the sleep-wake transition can be interpreted as a non-equilibrium phase transition which is driven by specific inputs and nonspecific activating systems.

Animals↗
PubMed1975

Properties of projections from vestibular nuclei to medial reticular formation in the cat.

In one series of experiments, vestibular neurons that could be activated antidromically by stimulation of the contralateral medial reticular formation were studied with extracellular recording in cats under pentobarbital anesthesia. These neurons were found in all of the four main vestibular nuclei, but were less prevalent in dorsal Deiters' nucleus and in the central region of the superior vestibular nucleus than elsewhere. Regions of the pontine and medullary reticular formation from which neurons in different vestibular nuclei were activated corresponded to the pattern of vestibuloreticular projections described by neuroanatomists. 2. Latencies of antidromic responses to stimulation of the contralateral reticular formation ranged from 0.6 to over 3 ms, indicating a relatively slow transfer of activity from vestibular nuclei to reticular formation.

Animals↗
PubMed1983

The superior vestibular nucleus: an intracellular HRP study in the cat. II. Non-vestibulo-ocular neurons.

Superior vestibular neurons were penetrated with horseradish peroxidase (HRP)-loaded glass microelectrodes in anesthetized cats and identified electrophysiologically following electrical stimulation of the vestibular nerves and oculomotor complex. Neurons that were not antidromically activated from the oculomotor complex were stained by intracellular injection of horseradish peroxidase. Three types of neurons are identified according to their initial axonal trajectories into the cerebellum, the dorsal pontine reticular formation, or the brachium conjunctivum. Ipsilateral vestibular nerve input to all neurons is primarily monosynaptic and excitatory, whereas the contralateral is inhibitory. The neurons are located in the periphery of the superior vestibular nucleus. Soma diameters range from 20.5 micrometers to 44 micrometers. Most neurons exhibit globular and ovoid cell bodies. The dendritic arbors are intermediate between iso- and allodendritic branching patterns. The few spines and dendritic appendages present are distributed mainly distally on the dendrites. Soma size does not correlate with axon diameter, number of dendrites, or dendritic territories.

Animals↗
PubMed1996

[Detection of latent herpes simplex virus in human vestibular ganglia].

Viral infections are considered to be one of the possible etiologies of vestibular neuronitis. Herpes simplex virus type 1 (HSV-1) is a likely candidate agent as this virus has a strong neurotropism, and can establish latent infections in the nervous system. However the existence of infections in the vestibular ganglia has not been established. In this study, 31 vestibular ganglia from autopsied adults were investigated. Polymerase chain reaction (PCR) was used to detect HSV-1 viral genomes, and reverse transcription-PCR (RT-PCR) and in situ hybridization (ISH) methods were employed to demonstrate latency associated transcripts (LAT) of HSV-1, which has been known to be latency specific. HSV-1 DNA was detected in 6 of 10 (60%) vestibular ganglia using the PCR method, and HSV-1 LAT was detected in 5 of 8 (63%) vestibular ganglia using the RT-PCR method. However, ISH showed that only 1 of 13 (7.7%) vestibular ganglia was HSV-1 LAT positive. In total only 1 of 3,830 (0.03%) neurons from 13 vestibular ganglia was found to be positive. The results indicate with certainty that HSV-1 does produce latent infections in human vestibular ganglia, and that the percentage of HSV-1 infected neurons is less than that of trigeminal ganglia. The results of this study also suggest that the rare presence of HSV-1 LAT in the ganglia may possibly correspond to the less frequent occurrence of vestibular neuronitis resulting from reactivation of HSV-1.

Adult↗
PubMed1998

Gastric related neurons in the rat medial vestibular nucleus.

Some structural and functional peculiarities of the rat vestibular nuclei neurones involved in realisation of vestibular-gastrointestinal reflectory reactions were studied. After microinjection of a horseradish peroxidase solution in the 'gastric' area of the nucleus tractus solitarius, retrogradely-labelled cell bodies were found in caudal part of the medial vestibular nucleus. Electrical stimulation of these neurons resulted in the decrease of gastric tone. The respiratory arrest was registered simultaneously. The results suggest that activation of the identified vestibular neurons can induce coordinated changes in visceral systems which are peculiar to a vomiting reaction.

Animals↗
PubMed1988

Properties and localization of the anterior semicircular canal-activated vestibulocollic neurons in the cat.

Unit activities of secondary vestibular neurons that selectively responded to stimulation of the anterior semicircular canal nerve (ACN) were recorded extracellularly in the anesthetized cat. Axonal pathways and projections in the spinal cord of the ACN-activated neurons were examined by recording their antidromic responses to stimulation of the lateral and medial vestibulospinal tracts (LVST and MVST), and the bilateral neck extensor motoneuron pools in the C1 segment (C1 dorsal rami [DR] motoneuron pools). In order to determine whether the neurons had ascending axon collaterals to the extraocular motoneurons, the contralateral (c-) inferior oblique (IO) motoneuron pool was also stimulated. Twenty-seven neurons sent their axons to the ipsilateral (i-) C1DR motoneuron pool via the LVST without any projection to the extraocular motoneuron pool. All the cells except one were located in the ventral part of the lateral vestibular nucleus. This pathway produced monosynaptic EPSPs with short time-to-peak and short half-width in C1DR motoneurons (16/16 motoneurons). Eight neurons sent axons to the i-C1DR motoneuron pool via the MVST without any to the extraocular motoneuron pool. Cell somata were located in the descending nucleus or in the ventral part of the lateral nucleus. These neurons did not produce postsynaptic potentials (PSPs) in any C1DR motoneurons. All thirty-five neurons sending axons to the c-C1DR motoneuron pool have ascending axon collaterals to the c-IO motoneuron pool.

Action Potentials↗
PubMed1983

The superior vestibular nucleus: an intracellular HRP study in the cat. I. Vestibulo-ocular neurons.

Superior vestibular neurons were penetrated with horseradish peroxidase (HRP)-loaded glass microelectrodes in anesthetized cats. Responses to electrical stimulation of the oculomotor complex and the vestibular nerves were characterized and selected neurons were injected with HRP. Neurons antidromically activated by oculomotor complex stimulation were generally monosynaptically excited by the ipsilateral vestibular nerve. Notable was the absence of strong commissural inhibition by stimulation of the contralateral vestibular nerve. Light microscopy of antidromically identified injected cells demonstrated that these cells are predominantly located at the central levels of the superior vestibular nucleus along the incoming vestibular nerve fibers but a few are found at more caudal levels. Cell bodies, elongated or pyramidal, are mainly medium-sized to large (30-50 micrometers). Dendritic trees extend in a plane at an acute to the collaterals of the vestibular nerve fibers. Dendrites remain within the nuclear territory and generally display an isodendritic branching pattern. Dendritic spines and appendages are mainly distributed on secondary and distal dendrites. A few terminal enlargements similar to growth cones are observed in these neurons. Axons of these neurons project rostrally via the medial longitudinal fasciculus, while a minor projection via the brachium conjunctivum is also found. Axon collaterals, when present, originate in the nucleus itself and in the pontine reticular formation.

Animals↗
PubMed2001

Synaptic plasticity in the medial vestibular nuclei: role of glutamate receptors and retrograde messengers in rat brainstem slices.

The analysis of cellular-molecular events mediating synaptic plasticity within vestibular nuclei is an attempt to explain the mechanisms underlying vestibular plasticity phenomena. The present review is meant to illustrate the main results, obtained in vitro, on the mechanisms underlying long-term changes in synaptic strength within the medial vestibular nuclei. The synaptic plasticity phenomena taking place at the level of vestibular nuclei could be useful for adapting and consolidating the efficacy of vestibular neuron responsiveness to environmental requirements, as during visuo-vestibular recalibration and vestibular compensation. Following a general introduction on the most salient features of vestibular compensation and visuo-vestibular adaptation, which are two plastic events involving neuronal circuitry within the medial vestibular nuclei, the second and third sections describe the results from rat brainstem slice studies, demonstrating the possibility to induce long-term potentiation and depression in the medial vestibular nuclei, following high frequency stimulation of the primary vestibular afferents. In particular the mechanisms sustaining the induction and expression of vestibular long-term potentiation and depression, such as the role of various glutamate receptors and retrograde messengers have been described. The relevant role of the interaction between the platelet-activating factor, acting as a retrograde messenger, and the presynaptic metabotropic glutamate receptors, in determining the full expression of vestibular long-term potentiation is also underlined. In addition, the mechanisms involved in vestibular long-term potentiation have been compared with those leading to long-term potentiation in the hippocampus to emphasize the most significant differences emerging from vestibular studies. The fourth part, describes recent results demonstrating the essential role of nitric oxide, another retrograde messenger, in the induction of vestibular potentiation. Finally the fifth part suggests the possible functional significance of different action times of the two retrograde messengers and metabotropic glutamate receptors, which are involved in mediating the presynaptic mechanism sustaining vestibular long-term potentiation.

Afferent Pathways↗
PubMed1995

Small neurons in the vestibular nerve root project to the marginal shell of the anteroventral cochlear nucleus in the cat.

We injected biotinylated dextran amine (BDA) into marginal shell regions of the anteroventral cochlear nucleus (AVCN) of the cat. These injections led to retrograde labeling of cells including small cells (median some area = 111 micron2, equivalent diameter = 11.9 microns) in the vestibular nerve root (VNR), just ventral to an anterior part of the AVCN. This is an unexpected new finding. The cells were scattered among BDA-labeled fibers and were oriented parallel to the course of the VNR fibers. We suggest that the small neurons of the VNR might serve as second-order vestibular neurons conveying information from vestibular end organs to the cochlear nucleus (CN) and/or act as interneurons between the olivocochlear fibers in the VNR and the CN.

Animals↗
PubMed1999

Neurotrophins, NMDA receptors, and nitric oxide in development and protection of the auditory system.

Neurotrophic factors are secreted peptides that when interacting with specific classes of membrane receptors activate intracellular signaling cascades that prevents neuronal death during embryonic development. The establishment of gene-targeted null mutant mice for the neurotrophic factors, brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT3) has led to the discovery that they are crucial trophic factors for the survival of auditory and vestibular neurons during development. BDNF is the major survival factor for vestibular ganglion neurons, while NT-3 only support a small number of these neurons. In the cochlea, auditory type I neurons require NT3 for their survival, whereas type II neurons depend on BDNF. With this information at hand recent progress has been made regarding the prevention of aminoglycoside-induced hearing loss in the adult guinea pig. These results and the mechanisms leading to hair cell damage are discussed in this paper.

Aminoglycosides↗
PubMed1986

Evidence for an alteration in brainstem cholinergic pathways following unilateral labyrinthectomy in the frog.

Following VIIIth nerve stimulation, field potentials recorded in the contralateral vestibular nuclei of isolated medullae are larger in amplitude and more sensitive to atropine in chronically hemilabyrinthectomized frogs than those of controls. The atropine-sensitive component occurs at a latency which precludes involvement of the monosynaptic commissural projection between second order vestibular neurons. Therefore, in addition to this commissural projection, the contributions of more indirect pathways have to be considered in an attempt to understand the neuronal basis of behavioral improvement following vestibular lesions.

Animals↗
PubMed1981

Role of vestibular nuclei in 'optic' nystagmus.

Horizontal eye nystagmus beating towards the stimulated side ('optic' nystagmus) was evoked in 25 guinea pigs by stimulating an optic nerve. The complete ablation of the vestibular nuclear complex abolished this nystagmus. In a second group of 15 animals, the behavior of 63 vestibular neurons identified electrophysiologically was analyzed during eye nystagmus; most of these neurons responded with a tonic increase in discharge rate to stimulation of the optic nerves. Units sensitive to the direction of optic and labyrinthine nystagmus were also identified.

Animals↗
PubMed1986

Delayed swayback in goat kids, a study of 23 cases.

The results of a retrospective study of 23 goat kids with delayed swayback are reported. Principal clinical signs were ataxia, loss of postural control, spasticity of the hindlimbs, and muscular weakness, often progressing to permanent recumbency. Denervation of skeletal muscles was demonstrated by electromyography in 2 kids. Three kids slowly recovered during hospitalisation. Histopathological changes were characterized by degeneration of selected neuronal populations with their processes within the central and the peripheral nervous system. Affected systems included upper motor neuron, vestibular, general proprioceptive, and lower motor neuron pathways, with additional involvement of the cerebellar cortex in some animals. Our findings, including limited ultrastructural observations, support the notion that the neuraxon rather than the myelin sheath is the prime target of disease in delayed swayback. The available copper values of affected kids and their unaffected herd mates were significantly lower than those of random control goats, which provides further support for a role of copper deficiency in the aetiology of this disease in the goat.

Animals↗
PubMed1988

Yaw direction neurons in the cat inferior olive.

1. Single units that responded to yaw rotation were recorded extracellularly in the caudal inferior olive (IO) of barbiturate-anesthetized cats. Of 276 neurons, 55 responded reliably to yaw, and extensive quantitative data were recorded from 25. 2. No yaw-sensitive IO neuron responded to somatosensory or auditory stimuli but two responded, though unreliably, to flash. 3. Yaw-sensitive IO cells fired at low (1-4 spikes/s), irregular rates during one direction of rotation. Though cells responded reliably during yaw, firing rates varied considerably from cycle to cycle. Rotation speed and acceleration were not represented in any cell's firing rate. 4. Eighty five percent (47/55) of yaw-sensitive cells fired during contralateral rotation, 9% (5/55) during ipsilateral rotation, and 6% (3/55) fired from late in the ipsilateral phase of a sinusoidal oscillation to the middle of the contralateral phase. 5. Responses were tested to 0.1-Hz sinusoidal yaw oscillations with a range of peak angular velocities (1-200 degrees/s). Thresholds were not sharp because of the cycle to cycle variability in response rates but were estimated using averaged responses. The peak rate of the most sensitive cell was driven to criterion (2 SD above spontaneous rate) by an oscillation with a peak velocity of 1 degrees/s. Other cells reached criterion between 5 and 50 degrees/s. 6. Sinusoidal oscillation at all frequencies tested (0.01-0.5 Hz) elicited approximately the same firing rates. Even at 0.01 Hz cells responded well. Responses lagged acceleration by approximately 25 degrees at 0.01 Hz and shifted to later parts of the cycle as frequency increased so that firing lagged acceleration by approximately 200 degrees at 0.5 Hz. 7. Histological reconstruction showed that yaw-sensitive neurons were recorded in olivary subnucleus beta (N beta), the dorsal cap of Kooy (DC), the posterior medial region of the medial accessory division of the inferior olive (MAO), and in the medial-lateral center of the caudal MAO. 8. Yaw-sensitive neurons in the inferior olive provide a signal to the cerebellum that indicates the direction of passive rotation over a wide range of velocity and acceleration. The signal from individual neurons does not reliably encode either rotation velocity or acceleration. Yaw-sensitive IO neurons are therefore unlike other central vestibular neurons but are similar to somatosensory IO cells which signal the presence, but not the intensity of a stimulus.

Action Potentials↗
PubMed1992

[Immunohistochemical studies on the guinea pig's vestibular ganglion cell--with reference to the distribution of substance P and neurofilament].

The immunocytochemical distribution and morphological characteristics of substance P and neurofilament in vestibular end organs and the vestibular ganglion of the guinea pig were investigated. The effect of capsaicin on substance P-like immunoreactivity was also evaluated in this study. Substance P-like immunoreactivity was found in the peripheral region of vestibular end organs and in small or medium size vestibular ganglion cells. Approximately 85% of vestibular ganglion cells showed substance P-like immunoreactivity. Although substance P-like immunoreactivity was depleted in the nasal mucosa and trigeminal ganglion by capsaicin treatment, substance P distributed in the primary vestibular neurons was not affected. In contrast to the distribution of substance P, neurofilament was also found in the primary afferent neurons in the central regions of vestibular end organs. Neurofilament immunoreactive cells, which were larger in size than cells without neurofilament-like immunoreactivity comprised about 34% of vestibular ganglion cells. These immunocytochemical findings suggest that vestibular ganglion cells can be classified on the basis of size and immunocytochemical characteristics.

Animals↗