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PubMed2003

Pediatric neurotology.

Pediatric neurotology is a subspecialty encompassing the medical and surgical treatment of conditions involving the middle ear, inner ear and lateral skull base. Multiple otologic and neurotologic diseases exist. In the pediatric patient the most common neurotologic conditions are vertigo, complications of otitis media, cholesteatoma, hearing loss and facial paralysis. Vertigo is differentiated into peripheral and central vestibular abnormalities. Peripheral vestibular causes include Meniere's disease, benign paroxysmal positional vertigo, vestibular neuronitis, otitis media and labyrinthitis. The predominant lesions in our field causing central vestibular disorders are brainstem and posterior fossa tumors. Mastoiditis, meningitis, petrositis, sigmoid sinus thrombosis, extradural abscess, brain abscess, otitic hydrocephalus, cholesteatoma and cholesterol granuloma are complications of otitis media and middle ear disease. Sensorineural hearing loss is now readily treated with cochlear implantation. Facial nerve paralysis may result from infectious and other etiologies.

Child↗

PubMed1979

Organization of vestibular afferents to the vestibular nuclei of the dogfish.

Electrophysiological and light microscopical studies were made on the vestibular area of the dogfish hindbrain. Three vestibular nuclei were distinguished: the superior nucleus (VES), the magnocellularis nucleus (VEM), and the ventral nucleus (VEV). The distribution of field potentials evoked in the hindbrain by stimulation of nerve VIII confirms the location and extent of the vestibular nuclei. It also raises the possibility of a direct contralateral projection of vestibular nerve fibres. Unit studies confirm the interpretation of the field potentials and provide evidence of mono- and polysynaptic activation of vestibular nuclear neurons by vestibular afferents.

Animals↗

PubMedDate not supplied

Action of glutamate in the cat labyrinth.

Glutamate solutions of either 50 mM applied on the membranous labyrinth or 1 mM perfused into the lateral canal in cats increased spontaneous and stimulus-evoked activity of vestibular neurons. Kainic acid (10(-4) M) perfused into the labyrinth produced a depolarizing action on vestibular afferents. These results indicate that glutamate could be an excitatory neurotransmitter at the synapse between vestibular hair cells and afferent nerve fibers in the cat.

Action Potentials↗

PubMed1998

Contribution of vestibular nerve irregular afferents to viewing distance-related changes in the vestibulo-ocular reflex.

The contribution of irregular vestibular afferents to viewing distance-related changes in the angular vestibulo-ocular reflex (AVOR) and combined angular and linear VOR (CVOR) was studied in squirrel monkeys trained to fixate earth-stationary targets that were near (10 cm) and distant (90-170 cm) from their eyes. Perilymphatic anodal galvanic currents were used to reversibly silence irregular vestibular afferents for periods of 4-5 s during the AVOR and CVOR evoked by 0.5- to 4-Hz sinusoidal rotations (6-20 degrees/s peak velocity) or 250-400 degrees/s2 acceleration steps. The direction and magnitude of linear translation were changed by positioning the monkeys at different distances off the axis of turntable rotation. The effects of irregular afferent galvanic ablation (GA) on viewing distance-related changes in the AVOR were studied in four animals. Viewing distance-related changes in the AVOR could not always be evoked and were frequently small in amplitude. GA reduced viewing distance-related change in the AVOR by an average of 64% when it was present. Thus vestibular irregular afferents appear to play an important and necessary role in viewing distance-related changes in the AVOR - on those occasions when the changes occur. Viewing distance-related changes in the CVOR were large and reliably evoked. GA had very little effect on the gain or phase of viewing distance-related changes in the CVOR, although the viewing distance-related CVOR responses of individual central vestibular neurons were affected. We conclude that irregular afferents probably contribute to central signal processing related to both the AVOR and the CVOR, but the signals carried by these afferents are only essential for viewing distance-related changes in AVOR.

Animals↗

PubMed2001

Vestibular histopathology of the human temporal bone. What can we learn?

Histologic sections of the human temporal bone display snapshots of the entire lifetime integrated into the moment the bone enters fixative. The bulk of the literature on vestibular histopathology is anecdotal and descriptive in nature, rather than quantitative. This is because the means of describing and measuring patients' vestibular symptoms are poorly developed, and the complex geometry of the vestibular labyrinth complicates efforts to study it in serial histologic sections. Histopathologic findings in the common peripheral vestibulopathies, including Meniere's syndrome, benign paroxysmal positional vertigo, viral labyrinthitis, vestibular neuronitis, and ototoxicity, have all been described. A new quantitative method for assessment of vestibular otopathology using Nomarski optics has recently been reported. It has been successfully applied to create a normative database of age-related changes in the vestibular hair cell populations which, in turn, has been used to study the effects of aminoglycoside ototoxicity and Meniere's syndrome. These data provide the first meaningful opportunity to make structure-function correlations between vestibular function testing and temporal bone pathology in humans. Wider clinical application of vestibular function testing and postmortem temporal bone donation should be promoted by all investigators interested in accumulating the resources necessary to gain a deeper understanding of the human vestibular system in health and disease.

Aged↗

PubMed1981

Meniere's disease: terminology and data bank acquisition.

It is proposed that the term Meniere's disease be restricted to patients with the classic symptom and sign complex in whom the etiologic factor is unknown (idiopathic). The term Meniere's syndrome is restricted to patients whose etiologic factor is known, who have an incomplete form of the disease, or who are in the process of being evaluated. Vestibular neuronitis and cochlear hydrops are terms that should be retained until the concepts of vestibular and cochlear Meniere's disease are better understood and can be identified prospectively. The classic symptoms and signs, both positive and negative, are outlined and a standard evaluation format is suggested. This must submit to mathematical reduction for pre- and post-treatment comparisons. Until this basic problem has been solved to the satisfaction of the profession, the inferences that may be drawn from otherwise excellent studies will continue to be of very limited clinical value.

Electronic Data Processing↗

PubMed2005

Expression of Trk receptors in otolith-related neurons in the vestibular nucleus of rats.

The expression of the three Trk receptors (TrkA, TrkB, and TrkC) in otolith-related neurons within the vestibular nuclei of adult Sprague-Dawley rats was examined immunohistochemically. Conscious animals were subjected to sinusoidal linear acceleration along either the anterior-posterior (AP) or interaural (IA) axis on the horizontal plane. Neuronal activation was defined by Fos expression in cell nuclei. Control animals, viz labyrinthectomized rats subjected to stimulation and normal rats that remained stationary, showed only a few sporadically scattered Fos-labeled neurons. Among experimental rats, the number of Fos-labeled neurons and their distribution pattern in each vestibular subnucleus in animals stimulated along the antero-posterior axis were similar to those along the interaural axis. No apparent topography was observed among neurons activated along these two directions. Only about one-third of the Trk-immunoreactive neurons in the vestibular nucleus expressed Fos. Double-labeled Fos/TrkA, Fos/TrkB and Fos/TrkC neurons constituted 85-98% of the total number of Fos-labeled neurons in vestibular nuclear complex and its subgroups x and y. Our findings suggest that Trk receptors and their cognate neurotrophins in central otolith neurons may contribute to the modulation of gravity-related spatial information during horizontal head movements.

Analysis of Variance↗

PubMed1982

Inhibitory effect of betahistine on polysynaptic neurons in the lateral vestibular nucleus.

Effects of betahistine, an antivertigo drug, were examined on the lateral vestibular nucleus (LVN) neurons of cats anesthetized with alpha-chloralose. Spike generation of monosynaptic LVN neurons elicited by vestibular nerve stimulation remained unaffected with intravenous administration of betahistine up to 5 mg/kg and with iontophoretic application of the drug up to 200 nA. In contrast, the spike generation of polysynaptic I neurons in the LVN was dose-dependently inhibited by intravenous as well as iontophoretic application of betahistine. These results suggest that small doses of betahistine more selectively interfere with synaptic transmission in the polysynaptic I neurons than in the monosynaptic neurons.

Animals↗

PubMed1989

Oculomotor functions of the flocculus and the vestibular nuclei after bilateral vestibular neurectomy.

Ito's hypothesis of an important role of the flocculus of the vestibulocerebellum in the immediate visual control of the VOR during visual-vestibular interaction has received substantial support. Nevertheless, several parts in this hypothesis are unclear, at least in primates. In normal monkey, vestibularly driven neurones in the vestibular nuclei do not carry signals which are adequate to account for the full range of eye movement responses during optokinetic tracking (OKN) and different situations of visual-vestibular interaction (especially VOR-suppression). Thus these neurones seem not to be located at the final stage where floccular "gaze-velocity" Purkinje cells (PCs) exert their control function on the three-neurone-reflex arc. The signals of these "central" vestibular neurones (if relevant for the oculomotor output) must further be processed. After bilateral vestibular neurectomy (BVN) only a small number of vestibular nuclei neurones were found with eye velocity sensitivities during smooth pursuit tracking (SP) and OKN in the range of those of floccular PCs (also after BVN), and with the appropriate polarity of modulation. Our difficulties in finding neurones in the vestibular nuclei which, according to their neurophysiological behaviour, could be main target cells of floccular PCs, either in normal or in BVN monkeys, are discussed.

Action Potentials↗

PubMed1999

Neuronal correlates of vestibulo-ocular reflex adaptation in the alert guinea-pig.

The spiking behaviour of 66 second-order vestibular neurons was studied in alert, chronically prepared guinea-pigs during the horizontal vestibulo-ocular reflex (VOR). Among the 66 studied neurons, seven were held long enough (> 1 h) to compare their spiking behaviour before and after a training procedure inducing a decrease in the gain of the VOR. When tested in darkness following adaptation, five of them showed a significant decrease of their sensitivity to head rotation. However, the resting discharge of these five neurons remained unchanged. This suggests that VOR adaptation is mediated not only by changes in synaptic efficacities but also by modifications in the spike generator which transforms synaptic inputs into a pattern of action potentials.

Action Potentials↗

PubMed1992

A physiological study of vestibular and prepositus hypoglossi neurones projecting to the abducens nucleus in the alert cat.

1. Vestibular and prepositus hypoglossi (PH) neurones projecting to the abducens (ABD) nucleus were recorded in the alert cat. Their discharge characteristics were analysed to ascertain the origin of the horizontal eye position signal present in ABD neurones. 2. Neurones were classified according to: their location with respect to the ABD nucleus; their antidromic activation from the ABD nucleus; the synaptic field potential they induced in the ABD nucleus with the spike-triggered averaging technique; and their activity during spontaneous and vestibularly induced eye movements. 3. Vestibular neurones projecting to the ABD nucleus were located in the rostral medial vestibular nucleus. They were excitatory on the contralateral and inhibitory on the ipsilateral ABD neurones. Both types of premotor vestibular neurone showed a firing rate weakly related to eye position, increasing for eye fixations in the contralateral on-direction, and decreasing with ipsilateral fixation. Position sensitivity during eye fixations was (means +/- S.D.) 1.8 +/- 0.9 spikes s-1 deg-1 for excitatory neurones and 2.2 +/- 1.3 spikes s-1 deg-1 for inhibitory neurones. Firing rate exhibited a high variability during eye fixations. Their responses during saccades in the off-direction were characterized by a pause that, although less defined, was occasionally present during saccades in the on-direction. Eye velocity sensitivity during spontaneous saccades in the on-direction was 0.17 +/- 0.15 spikes s-1 deg-1 s-1 for excitatory neurones and 0.15 +/- 0.07 spikes s-1 deg-1 s-1 for inhibitory vestibular neurones. During sinusoidal head stimulation at 0.2 Hz, vestibular neurones showed a type I discharge rate with a phase lead over eye position of 86.0 +/- 14.1 deg for excitatory and 80.2 +/- 12.5 deg for inhibitory neurones. Position sensitivity during vestibular stimulation did not differ significantly from values obtained for spontaneous eye movements. However, the velocity sensitivity of premotor vestibular neurones during head rotation was significantly higher (1.6 +/- 0.2 spikes s-1 deg-1 s-1 for excitatory and 1.5 +/- 0.3 spikes s-1 deg-1 s-1 for inhibitory neurones) than during spontaneous eye movements. 4. PH neurones projecting to the ABD nucleus were located in the rostral one-third of the nucleus. These neurones were excitatory on the ipsilateral and inhibitory on the contralateral ABD nucleus. Their firing rates were correlated mainly with eye position, increasing for abducting eye positions of the ipsilateral eye and decreasing with adduction movements.(ABSTRACT TRUNCATED AT 400 WORDS)

Abducens Nerve↗

PubMed2006

On the role of the central nervous system in regulating the mineralisation of inner-ear otoliths of fish.

Stato- or otoliths are calcified structures in the organ of balance and equilibrium of vertebrates, the inner ear, where they enhance its sensitivity to gravity. The compact otoliths of fish are composed of the calcium carbonate polymorph aragonite and a small fraction of organic molecules. The latter form a protein skeleton which determines the morphology of an otolith as well as its crystal lattice structure. This short review addresses findings according to which the brain obviously plays a prominent role in regulating the mineralisation of fish otoliths and depends on the gravity vector. Overall, otolith mineralisation has thus been identified to be a unique, neuronally guided biomineralisation process. The following is a hypothetical model for regulation of calcification by efferent vestibular neurons: (1) release of calcium at tight junctions in the macular epithelia, (2) macular carbonic anhydrase activity (which in turn is responsible for carbonate deposition), (3) chemical composition of matrix proteins. The rationale and evidence that support this model are discussed.

Adaptation, Physiological↗

PubMed1979

Retrograde axon reaction in the lateral vestibular nucleus of neonatal and adult rats.

Upper cervical cord lesions were performed in neonatal and adult rats (neonates survived for 10-20 days, adults 7-30 days). Retrograde axonal reaction was examined in the lateral vestibular nucleus. Nuclear eccentricity, which is a normal feature in neonatal lateral vestibular neurons, is not peculiar to adult neurons. As early as 7 days after cordotomy, neonatal neurons reacted severely, to the extent of atrophy and cell loss. Seven days after cordotomy, adult neurons were swollen, with eccentrically placed nuclei and Nissl granules which had undergone dissolution. The latter feature is regarded as the diagnostic feature in identifying reacting chromatolytic cells.

Animals↗

PubMed2006

The anatomy of the vestibular nuclei.

The vestibular portion of the eighth cranial nerve informs the brain about the linear and angular movements of the head in space and the position of the head with respect to gravity. The termination sites of these eighth nerve afferents define the territory of the vestibular nuclei in the brainstem. (There is also a subset of afferents that project directly to the cerebellum.) This chapter reviews the anatomical organization of the vestibular nuclei, and the anatomy of the pathways from the nuclei to various target areas in the brain. The cytoarchitectonics of the vestibular brainstem are discussed, since these features have been used to distinguish the individual nuclei. The neurochemical phenotype of vestibular neurons and pathways are also summarized because the chemical anatomy of the system contributes to its signal-processing capabilities. Similarly, the morphologic features of short-axon local circuit neurons and long-axon cells with extrinsic projections are described in detail, since these structural attributes of the neurons are critical to their functional potential. Finally, the composition and hodology of the afferent and efferent pathways of the vestibular nuclei are discussed. In sum, this chapter reviews the morphology, chemoanatomy, connectivity, and synaptology of the vestibular nuclei.

Animals↗

PubMed1988

Behavior of reticular, vestibular and prepositus neurons terminating in the abducens nucleus of the alert cat.

The activity of pontomedullary reticular, vestibular, and prepositus neurons has been recorded in the alert cat during spontaneous and vestibular-induced eye movements. Neurons were identified by their antidromic activation from the abducens nucleus. Spikes of these neurons were used to trigger the recording of field potentials in the abducens nucleus. The analysis by post-spike averaging of the field potentials showed the presence of a trifold system of reciprocal (excitatory and inhibitory) direct projections that originated in the above nuclei and terminated in the abducens nucleus with a distinctly graded effectiveness. This trifold afferent system is involved in the generation of fast eye movements, slow compensatory movements of vestibular origin, and eye fixation, respectively.

Abducens Nerve↗

PubMed1980

Development of the brain stem in the rat. III. Thymidine-radiographic study of the time of origin of neurons of the vestibular and auditory nuclei of the upper medulla.

Groups of pregnant rats were injected with two successive daily doses of 3H-thymidine from gestational days 12 and 13 (E12 + 13) until the day before parturition (E21 + 22). In adult progeny of the injected rats the proportion of neurons generated on specific embryonic days was determined quantitatively in the vestibular and auditory nuclei of the upper medulla. In the vestibular nuclei, neurons are generated between days E11 and E15 in an overlapping sequential order, yielding a lateral-to-medial and a rostral-to-caudal internuclear gradient. In the lateral vestibular nucleus peak production time is day E12; in the superior nucleus, E13; in the inferior nucleus, E13 and E14; and in the medial nucleus, E14. The early generation of neurons of the lateral vestibular nucleus may reflect the early differentiation of the circuit from the gravity receptors (utricle) to neurons of the spinal cord controlling postural balance. The later production of neurons of the superior vestibular nucleus may reflect the subsequent differentiation of the circuit from the rotational receptors (semicircular canals) to the neurons of the brain stem controlling eye movements. The generation time of neurons of the nucleus prepositus hypoglossi overlaps with that of the medial vestibular nucleus. The neurons of the anteroventral and posteroventral cochlear nuclei are produced from days E13 to E17, with no temporal differences between the two nuclei. The neurons of the dorsal cochlear nucleus are generated over a very long time span, beginning on day E12 and extending into the postnatal period. There is a sequence in the production of neurons forming the different layers of the dorsal cochlear nucleus in the following order: pyramidal cells, cells of the inner layer, cells of the outer layer and, finally, cells of the granular layer. There is also a sequential production of neurons in four nuclei of the superior olivary complex. In the lateral trapezoid nucleus peak production time is day E12; in the medial superior olivary nucleus, day E13; in the medial trapezoid nucleus, day E15; and in the lateral superior olivary nucleus, day E16. This order yields a medial-to-lateral gradient in the dorsal aspect of the superior olivary complex, and a lateral-to-medial gradient ventrally. These mirror-image gradients were also seen intranuclearly in the lateral superior olivary nucleus and the medial trapezoid nucleus. The cytogenetic gradients could not be related to tonotopic representation; however, they could be related to the lateral location of ipsilateral cochlear nucleus input to the lateral superior olivary nucleus and the medial location of the contralateral cochlear nucleus input to the medial trapezoid nucleus.

Animals↗

PubMed1993

Responses of caudal medullary raphe neurons to natural vestibular stimulation.

1. Over two thirds of caudal medullary raphespinal neurons respond to electrical stimulation of the vestibular nerve, and it has been suggested that these neurons may participate in the generation of vestibulospinal and vestibulosympathetic reflexes. The objective of the present study was to determine which vestibular endorgans (semicircular canals or otolith organs) provide inputs to these cells. 2. Experiments were conducted on decerebrate cats that were baroreceptor denervated and vagotomized, and that had a cervical spinal cord transection so that inputs from tilt-sensitive receptors outside of the labyrinth did not influence the units we recorded. 3. In most experiments, vertical vestibular stimulation was used to stimulate the anterior and posterior semicircular canals and the otolith organs. The plane of whole body rotation that produced maximal modulation of a neuron's firing rate (response vector orientation) was measured at one or more frequencies between 0.1 and 0.5 Hz. Neuron dynamics were then studied with sinusoidal (0.02-1 Hz) stimuli aligned with this orientation. Alternatively, in two animals horizontal rotations at 0.5 and 1.0 Hz were employed to stimulate the horizontal semicircular canals. 4. The properties of raphespinal neurons were similar to those of a larger sample of raphe neurons studied that either could not be antidromically activated from the cervical spinal cord or were not tested for a spinal projection. In response to vertical vestibular stimulation, > 85% of caudal medullary raphe neurons had response gains that remained relatively constant across stimulus frequencies, like regularly firing otolith afferents.(ABSTRACT TRUNCATED AT 250 WORDS)

Afferent Pathways↗

PubMed1997

Central vestibular networks in the guinea-pig: functional characterization in the isolated whole brain in vitro.

The isolated, in vitro whole brain of guinea-pig was used to assess some of the main physiological and pharmacological properties of the vestibulo-ocular pathways in this species. Extracellular and intracellular recordings were obtained from the vestibular, abducens and oculomotor nuclei, as well as from the abducens and oculomotor nerves, while inputs from the vestibular afferents, the visual pathways and the spinal cord were activated. The three main types of medial vestibular nucleus neurons (A, B and B+LTS), previously described on slices, were also identified in the isolated brain. They had similar membrane properties in both preparations. Eighty-five per cent of cells recorded in the vestibular nucleus responded with monosynaptic, excitatory postsynaptic potentials (latency 1.05-1.9 ms) to stimulation of the ipsilateral vestibular nerve, and were thus identified as second-order vestibular neurons. In addition, stimulation of the contralateral vestibular afferents revealed in most cases a disynaptic or trisynaptic, commissural inhibition. Second-order vestibular neurons displayed in the isolated brain a high degree of variability of their spontaneous activity, as in alert guinea-pigs. Type A neurons always exhibited a regular firing, while type B and B+LTS cells could have very irregular patterns of spontaneous discharge. Thus, type A and type B neurons might correspond, respectively, to the tonic and phasic vestibular neurons described in vivo. The regularity of spontaneous discharge was positively correlated with the amplitude of spike after hyperpolarization, and there was a trend for irregular neurons to be excited from ipsilateral vestibular afferents at shorter latencies than regular units. Synaptic activation could trigger subthreshold plateau potentials and low-threshold spikes in some of the second-order vestibular neurons. As a second step, the pharmacology of the synaptic transmission between primary vestibular afferents and second-order neurons was assessed using specific antagonists of the glutamatergic receptors. Both the synaptic field potentials and excitatory postsynaptic potentials elicited in the medial vestibular nucleus by single shock stimulation of the ipsilateral vestibular nerve were largely or, sometimes, totally blocked by 6-cyano-7-nitroquinoxaline-2,3-dione, indicating a dominating role of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor-mediated glutamatergic transmission. The remaining component of the responses was completely or partially suppressed by DL-2-amino-5-phosphonovaleric acid in 35% of the cases, suggesting a concomitant, moderate involvement of N-methyl-D-asparate receptors. In addition, a synaptic response resistant to both antagonists, but sensitive to a zero Ca2+/high Mg(2+)-containing solution, was often observed. Finally, recordings from abducens and oculomotor complexes confirmed the existence in the guinea-pig of strong bilateral, disynaptic excitatory and inhibitory inputs from vestibular afferents to motoneurons of extraocular muscles, which contribute to generation of the vestibulo-ocular reflex. The functional integrity of vestibular-related pathways in the isolated brain was additionally checked by stimulation of the spinal cord and optic tract. Stimulation of the spinal cord evoked, in addition to antidromic responses in the vestibular nucleus, short-latency synaptic responses in both the vestibular nucleus and abducens motoneurons, suggesting possible recruitment of spinal afferents. Activation of visual pathways at the level of the optic chiasm often induced long latency responses in the various structures under study. These results demonstrate that the in vitro isolated brain can be readily used for detailed, functional studies of the neuronal networks underlying gaze and posture control.

Animals↗