VIIIth Nerve Research Articles

Velocity storage mechanism in zebrafish larvae

The optokinetic reflex (OKR) and the angular vestibulo-ocular reflex (aVOR) complement each other to stabilize images on the retina despite self- or world motion, a joint mechanism that is critical for effective vision. It is currently hypothesized that signals from both systems integrate, in a mathematical sense, in a network of neurons operating as a velocity storage mechanism (VSM). When exposed to a rotating visual surround, subjects display the OKR, slow following eye movements frequently interrupted by fast resetting eye movements. Subsequent to light-off during optokinetic stimulation, eye movements do not stop abruptly, but decay slowly, a phenomenon referred to as the optokinetic after-response (OKAR). The OKAR is most likely generated by the VSM. In this study, we observed the OKAR in developing larval zebrafish before the horizontal aVOR emerged. Our results suggest that the VSM develops prior to and without the need for a functional aVOR. It may be critical to ocular motor control in early development as it increases the efficiency of the OKR.

Differential Roles for EphA and EphB Signaling in Segregation and Patterning of Central Vestibulocochlear Nerve Projections

Auditory and vestibular afferents enter the brainstem through the VIIIth cranial nerve and find targets in distinct brain regions. We previously reported that the axon guidance molecules EphA4 and EphB2 have largely complementary expression patterns in the developing avian VIIIth nerve. Here, we tested whether inhibition of Eph signaling alters central targeting of VIIIth nerve axons. We first identified the central compartments through which auditory and vestibular axons travel. We then manipulated Eph-ephrin signaling using pharmacological inhibition of Eph receptors and in ovo electroporation to misexpress EphA4 and EphB2. Anterograde labeling of auditory afferents showed that inhibition of Eph signaling did not misroute axons to non-auditory target regions. Similarly, we did not find vestibular axons within auditory projection regions. However, we found that pharmacologic inhibition of Eph receptors reduced the volume of the vestibular projection compartment. Inhibition of EphB signaling alone did not affect auditory or vestibular central projection volumes, but it significantly increased the area of the auditory sensory epithelium. Misexpression of EphA4 and EphB2 in VIIIth nerve axons resulted in a significant shift of dorsoventral spacing between the axon tracts, suggesting a cell-autonomous role for the partitioning of projection areas along this axis. Cochlear ganglion volumes did not differ among treatment groups, indicating the changes seen were not due to a gain or loss of cochlear ganglion cells. These results suggest that Eph-ephrin signaling does not specify auditory versus vestibular targets but rather contributes to formation of boundaries for patterning of inner ear projections in the hindbrain.

Selective Tracing of Auditory Fibers in the Avian Embryonic Vestibulocochlear Nerve

The embryonic chick is a widely used model for the study of peripheral and central ganglion cell projections. In the auditory system, selective labeling of auditory axons within the VIIIth cranial nerve would enhance the study of central auditory circuit development. This approach is challenging because multiple sensory organs of the inner ear contribute to the VIIIth nerve (1). Moreover, markers that reliably distinguish auditory versus vestibular groups of axons within the avian VIIIth nerve have yet to be identified. Auditory and vestibular pathways cannot be distinguished functionally in early embryos, as sensory-evoked responses are not present before the circuits are formed. Centrally projecting VIIIth nerve axons have been traced in some studies, but auditory axon labeling was accompanied by labeling from other VIIIth nerve components (2,3). Here, we describe a method for anterograde tracing from the acoustic ganglion to selectively label auditory axons within the developing VIIIth nerve. First, after partial dissection of the anterior cephalic region of an 8-day chick embryo immersed in oxygenated artificial cerebrospinal fluid, the cochlear duct is identified by anatomical landmarks. Next, a fine pulled glass micropipette is positioned to inject a small amount of rhodamine dextran amine into the duct and adjacent deep region where the acoustic ganglion cells are located. Within thirty minutes following the injection, auditory axons are traced centrally into the hindbrain and can later be visualized following histologic preparation. This method provides a useful tool for developmental studies of peripheral to central auditory circuit formation.

Vestibular-mediated synaptic inputs and pathways to sympathetic preganglionic neurons in the neonatal mouse.

To assess when vestibulosympathetic projections become functional postnatally, and to establish a preparation in which vestibulosympathetic circuitry can be characterized more precisely, we used an optical approach to record VIIIth nerve-evoked synaptic inputs to thoracic sympathetic preganglionic neurons (SPNs) in newborn mice. Stimulation of the VIIIth nerve was performed in an isolated brainstem-spinal cord preparation after retrogradely labelling with the fluorescent calcium indicator Calcium Green 1-conjugated dextran amine, the SPNs and the somatic motoneurons (MNs) in the thoracic (T) segments T2, 4, 6, 8, 10 and 12. Synaptically mediated calcium responses could be visualized and recorded in individual SPNs and MNs, and analysed with respect to latency, temporal pattern, magnitude and synaptic pharmacology. VIIIth nerve stimulation evoked responses in all SPNs and MNs investigated. The SPN responses had onset latencies from 90 to 200 ms, compared with much shorter latencies in MNs, and were completely abolished by mephenesin, a drug that preferentially reduces polysynaptic over monosynaptic transmission. Bicuculline and picrotoxin, but not strychnine, increased the magnitudes of the SPN responses without changing the onset latencies, suggesting a convergence of concomitant excitatory and inhibitory synaptic inputs. Lesions strategically placed to test the involvement of direct vestibulospinal pathways versus indirect pathways within the brainstem showed that vestibulosympathetic inputs in the neonate are mediated predominantly, if not exclusively, by the latter. Thus, already at birth, synaptic connections in the vestibulosympathetic reflex are functional and require the involvement of the ventrolateral medulla as in adult mammals.

The anatomical and physiological framework for vestibular prostheses.

This article reviews the structure function of the vestibular system and its pathology with respect to requirements for the design and construction of a functional vestibular prosthesis. The ultimate goal of a vestibular prosthesis is to restore balance and equilibrium through direct activation of vestibular nerve fibers. An overview of the peripheral and central vestibular systems that highlights their most important functional aspects re: the design of a prosthesis is provided. Namely, the peripheral labyrinth faithfully transduces head motion and gravity in both the time and frequency domains. These signals are described in hopes that they may be prosthetically replicated. The peripheral and central connections of the vestibular nerve are also discussed in detail, as are the vestibular nuclei in the brainstem that receive VIIIth nerve innervation. Lastly, the functional effector pathways of the vestibular system, including the vestibulo-ocular, vestibulo-spinal, vestibulo-colic, vestibulo-autonomic, and vestibular efferent innervation of the labyrinth are reviewed.

The Vestibular System Implements a Linear–Nonlinear Transformation In Order to Encode Self-Motion

Author SummaryUnderstanding how the coding of sensory information changes at different stages of sensory processing remains a fundamental challenge in systems neuroscience. Here we address this question by studying early sensory processing in vestibular pathways of monkeys, a system for which sensory stimuli are relatively easy to describe. Peripheral vestibular afferents detect and encode head motion in space to ensure posture and gaze is accurate and stable during everyday life. In this study, we show that central vestibular neurons nonlinearly integrate their afferent inputs, which helps explain the mechanisms that generate enhanced feature detection in sensory pathways. In addition, our results overturn conventional wisdom that early vestibular processing is linear, revealing a striking boosting nonlinearity that is a hallmark of the first central stage of vestibular processing. Studies from other sensory systems have shown that higher-order neurons can more efficiently detect specific features of sensory input, and that nonlinear transformations can increase this efficiency. We suggest that nonlinear integration of afferent input by central vestibular neurons extends their coding range and facilitates the detection of natural vestibular stimuli.

IDIOPATHIC SUDDEN SENSORINEURAL HEARING LOSS AND COMORBID BENIGN PAROXYSMAL POSITIONAL VERTIGO

In Reply First, we thank Dr. Pirodda for the interest in our article and the intriguing comments and suggestions. As Dr. Pirodda indicated, there is a striking contrast between our study (1) and the recently published study by Kim et al. (2). Dr. Pirodda raised concerns about the heterogeneity of age in our study as a result of including both patients with compromised vascular conditions and patients free from vascular risks. As described in our study, however, the age range from 9 to 90 years applied to all of the patients with idiopathic sudden sensorineural hearing loss (ISSNHL) initially found in a chart review and not to the patients with ISSNHL with benign paroxysmal positional vertigo (BPPV) who were ultimately included in this study. Indeed, the age of the patients with ISSNHL and BPPV (n = 32) ranged from 14 to 68 years (Fig. 1). Because the control group (ISSNHL without BPPV) was near-perfect age-matched with the BPPV group, the difference in the hearing outcome between the 2 groups cannot be ascribed to the age distribution. Moreover, not only age but also almost all of the hitherto-alleged prognostic factors were controlled by excluding patients with diabetes or treatment delay. Therefore, we believe that BPPV itself is an indicator of severe disease and a poor prognosis (1).FIG. 1: Age distribution of the patient and control groups in our study.It is mandatory to select treatment options that consider an individual patient’s risk factors. Needless to say the addition of anti-platelet agents in patients with more vascular risks or the precaution of using a volume expander in patients with heart problems or renal failure, treatment for ISSNHL should follow standard protocols based on evidence-based medicine. Previously, several treatment options aimed to increase inner ear perfusion have been tried in an attempt to restore hearing loss. Because only high-dose steroid therapy is accepted as beneficial (3), we use systemic steroid as a mainstay for treating ISSNHL. In line with a previous study (4), ISSNHL patients with simultaneous onset of BPPV had worse initial hearing than those without BPPV, and the improvement was less in the BPPV group than in the control group in our study. The involvement of multiple semicircular canals (19%) and a substantial proportion of recurrences of BPPV (41%) also were remarkable findings of comorbid BPPV in ISSNHL patients. Delayed BPPV can follow acute-onset paralytic vestibulopathy in neurolabyrinthitis or vestibular neuritis, in which the most plausible pathogenic mechanism is secondary degeneration of the utricle after viral or vascular insults to the inner ear or VIIIth cranial nerve territory. By contrast, in simultaneous-onset BPPV and ISSNHL, the initial insult is more likely to be focused on the inner ear, or if the lesion is on the VIIIth nerve, the insult may be severe enough to produce mechanical dislodgement of the otolith particles from the macula utriculi without delay. We speculated that these different pathogenetic mechanisms may be responsible for the poor prognosis and different steroid responsiveness in ISSNHL patients with comorbid BPPV. We hope that this letter is helpful for clarifying the issues raised and prompts further studies to elucidate the mechanisms involved in and prognosis of simultaneous BPPV in ISSNHL. Jae-Jin Song, M.D., Ph.D. Department of Otorhinolaryngology–Head and Neck Surgery, Seoul National University Bundang Hospital, Seongnam, Korea Ji Soo Kim, M.D., Ph.D. Department of Neurology Surgery, Seoul National University Bundang Hospital, Seongnam, Korea Ja-Won Koo, M.D., Ph.D. Department of Otorhinolaryngology–Head and Neck Surgery, Seoul National University Bundang Hospital Seongnam, Korea and Sensory Organ Research Institute Seoul National University Medical Research Center Seoul, Korea [email protected]

Vestibular Migraine

To compare the attitudes and opinions of otologists and neurologists regarding the cause, diagnosis, and management of vestibular migraine. Survey questionnaire. An 18-question survey designed to elicit opinions about the cause, diagnosis, pathophysiology, and management of migraine and dizziness was mailed to the entire memberships of the American Neurotology Society (ANS) and the International Headache Society (IHS). Survey participant responses were recorded for physician practice characteristics and for opinions on various clinical features of vestibular migraine. Of the 917 surveys mailed, 146 were completed by ANS members and 110 by IHS members. The frequency of respondents listing symptom origin as central to a diagnosis of migraine was 43% for ANS members versus 62% of IHS members. Only 31% of ANS respondents thought that a sensory trigger was a major etiologic factor. Of the IHS respondents, 60% thought a triggering event was mediated by the Vth nerve and 28% by the VIIIth nerve. Opinions varied on the character of dizziness and cochlear symptoms associated with migraine. Compared with 26% of IHS members, 55% of ANS members were more likely to view hearing loss as a migraine symptom. IHS members expressed a greater tendency to use triptans and anticonvulsants when compared with ANS members. The results suggested that ANS and IHS members have different perspectives on the clinical presentation, pathophysiology, and management of vestibular migraine. These differences can result in patient confusion and inadvertently have an adverse effect on patient care, thereby potentially affecting patient outcomes.

Segmental patterns of vestibular-mediated synaptic inputs to axial and limb motoneurons in the neonatal mouse assessed by optical recording

Proper control of movement and posture occurs partly via descending projections from the vestibular nuclei to spinal motor circuits. Days before birth in rodents, vestibulospinal neurons develop axonal projections that extend to the spinal cord. How functional these projections are just after birth is unknown. Our goal was to assess the overall functional organization of vestibulospinal inputs to spinal motoneurons in a brainstem-spinal cord preparation of the neonatal mouse (postnatal day (P) 0-5). Using calcium imaging, we recorded responses evoked by electrical stimulation of the VIIIth nerve, in many motoneurons simultaneously throughout the spinal cord (C2, C6, T7, L2 and L5 segments), in the medial and lateral motor columns. Selective lesions in the brainstem and/or spinal cord distinguished which tracts contributed to the responses: those in the cervical cord originated primarily from the medial vestibulospinal tracts but with a substantial contribution from the lateral vestibulospinal tract; those in the thoracolumbar cord originated exclusively from the lateral vestibulospinal tract. In the thoracolumbar but not the cervical cord, excitatory commissural connections mediated vestibular responses in contralateral motoneurons. Pharmacological blockade of GABA(A) receptors showed that responses involved a convergence of excitatory and inhibitory inputs which in combination produced temporal response patterns specific for different segmental levels. Our results show that by birth vestibulospinal projections in rodents have already established functional synapses and are organized to differentially regulate activity in neck and limb motoneurons in a tract- and segment-specific pattern similar to that in adult mammals. Thus, this particular set of descending projections develops several key features of connectivity appropriately at prenatal stages. We also present novel information about vestibulospinal inputs to axial motoneurons in mammals, providing a more comprehensive platform for future studies into the overall organization of vestibulospinal inputs and their role in regulating postural stability.

Facial and Vestibulocochlear Nerve Avulsion at the Fundus of the Internal Auditory Canal in a Child Without a Temporal Bone Fracture

To describe a case of facial, vestibular, and cochlear nerve avulsion secondary to blunt trauma without an associated temporal bone fracture. Clinical capsule report. University hospital. A 3.5-year-old girl presented with immediate facial nerve paralysis and complete deafness after being struck by an automobile. High-resolution computed tomography demonstrated a depressed occipital bone fracture with no visible fracture of the temporal bone. Magnetic resonance imaging sequence raised the question of VIIth nerve bundle discontinuity at the distal end of the internal auditory canal. The patient underwent a posterior fossa craniotomy via a translabyrinthine approach 9 months after the initial injury, and facial and auditory nerve avulsion at the fundus was confirmed at the time of surgery. The proximal segment of the facial nerve had formed a traumatic neuroma, which was resected, and primarily anastomosed to the rerouted distal segment. Facial nerve function. Patient has regained facial function to Grade III/VI House-Brackmann with no asymmetry at rest. An unusual pattern of injury is described. We suggest that in patients presenting with facial nerve paralysis secondary to blunt trauma, without an associated temporal bone fracture, high-resolution magnetic resonance imaging is recommended to evaluate internal auditory canal discontinuity of the VIIth and VIIIth nerve complexes. A potential mechanism of avulsion is explained.

Déficit funcional en la capacidad auditiva de oyentes con trastorno de neuropatía auditiva

Auditory neuropathy spectrum disorder (ANSD) is a form of auditory dysfunction in which peripheral processes can be normal, but neural transmission through the VIIIth nerve and auditory brainstem is disrupted. The perceptual consequences of ANSD are distinct from those of cochlear hearing loss and most commonly include distortion of temporal (timing) cues and altered frequency discrimination. These basic processing deficits can, in turn, affect functional hearing, resulting in severe impairment of speech perception particularly in the presence of background noise. This article will address the mechanisms underlying ANSD, illustrate it’s effects in a detailed case study and show evidence for the use of personal FM devices in affected listeners.

Disruption of the Head Direction Cell Signal after Occlusion of the Semicircular Canals in the Freely Moving Chinchilla

Head direction (HD) cells in the rat anterodorsal thalamic nucleus (ADN) fire relative to the animal's directional heading. Lesions of the entire vestibular labyrinth have been shown to severely alter VIIIth nerve input and disrupt these HD signals. To assess the specific contributions of the semicircular canals without altering tonic VIIIth nerve input, ADN cells were recorded from chinchillas after bilateral semicircular canal occlusion. Although ADN HD cells (and also hippocampal place cells and theta cells) were identified in intact chinchillas, no direction-specific activity was seen after canal occlusions. Instead, "bursty" cells were observed that exhibited burst-firing patterns similar to normal HD cells but with firing unrelated to the animal's actual head direction. Importantly, when pairs of bursty cells were recorded, the temporal order of their firing was dependent on the animal's turning direction, as is the case for pairs of normal HD cells. These results suggest that bursty cells are actually disrupted HD cells. The present findings further suggest that the HD cell network is still able to generate spiking activity after canal occlusions, but the semicircular canal input is critical for updating the network activity in register with changes in the animal's HD.

Development of multisensory convergence in the Xenopus optic tectum.

The adult Xenopus optic tectum receives and integrates visual and nonvisual sensory information. Nonvisual inputs include mechanosensory inputs from the lateral line, auditory, somatosensory, and vestibular systems. While much is known about the development of visual inputs in this species, almost nothing is known about the development of mechanosensory inputs to the tectum. In this study, we investigated mechanosensory inputs to the tectum during critical developmental stages (stages 42-49) in which the retinotectal map is being established. Tract-tracing studies using lipophilic dyes revealed a large projection between the hindbrain and the tectum as early as stage 42; this projection carries information from the Vth, VIIth, and VIIIth nerves. By directly stimulating hindbrain and visual inputs using an isolated whole-brain preparation, we found that all tectal cells studied received both visual and hindbrain input during these early developmental stages. Pharmacological data indicated that the hindbrain-tectal projection is glutamatergic and that there are no direct inhibitory hindbrain-tectal ascending projections. We found that unlike visual inputs, hindbrain inputs do not show a decrease in paired-pulse facilitation over this developmental period. Interestingly, over this developmental period, hindbrain inputs show a transient increase followed by a significant decrease in the alpha-amino-3-hydroxyl-5-methyl-4-isoxazolepropionate (AMPA)/N-methyl-D-aspartate (NMDA) ratio and show no change in quantal size, both in contrast to visual inputs. Our data support a model by which fibers are added to the hindbrain-tectal projection across development. Nascent fibers form new synapses with tectal neurons and primarily activate NMDA receptors. At a time when retinal ganglion cells and their tectal synapses mature, hindbrain-tectal synapses are still undergoing a period of rapid synaptogenesis. This study supports the idea that immature tectal cells receive converging visual and mechanosensory information and indicates that the Xenopus tectum might be an ideal preparation to study the early development of potential multisensory interactions at the cellular level.

Mauthner cells

Mauthner cells

Traitement des vertiges selon leurs mécanismes

Vertigo is an illusion of rotatory or linear movement that demonstrates a functional or lesional disturbance of the vestibular system, from periphery to central connections. According to the ANAES report (1997), benign paroxysmal positional vertical vertigo, vestibular neuronitis and Ménière's disease account for 40-50% of all mixed vertigo etiologies. Central etiologies may account for 20-40% of causes and 10-40% remain more difficult to classify, and are usually classified under the term of "peripheral vestibulopathy." These include vertigo due to neurovascular compression syndrome of the VIIIth nerve. Clinical manifestations, differential diagnosis, and treatment of the main etiologies of vertigo will be developed in this chapter. A specific section will discuss the subject of neurovascular compression syndrome of the VIIIth nerve. Even though some publications should be challenged, it appears that neurovascular compression syndrome of the VIIIth nerve might explain some cases of vertigo or chronic instability, with or without cochlear signs. The diagnosis is difficult and must be established on multiple clinical, electrophysiological and radiological arguments. A therapeutic test with antiepileptic drugs is helpful. The treatment includes these drugs as a first option but may require a neurosurgical approach if medical treatment fails.

Anatomie fonctionnelle du nerf vestibulaire

The vestibular system detects head movements such as angular rotation, translation, and head position relative to gravity. It acts to stabilize the eyes and posture through subcortical reflexes. Its signals are also integrated at the cortical level to participate in the elaboration of a body scheme, used for different functions such as spatial orientation and motor control. The vestibular nerve shows a resting discharge rate that is modulated up or down according to head motion or position. Central functioning depends on the detection of an asymmetry between signals coming from a pair of peripheral sensors, one on either side. In pathological cases, unilateral peripheral dysfunction is interpreted by the central system as an asymmetry resulting from a change in head position leading to nystagmus, postural disturbances, and vertigo. The dysfunction can be either a deficit, such as observed in vestibular neuronitis, or hyperactivity such as observed in neurovascular compression syndrome of the VIIIth nerve. Anatomically, the VIIIth nerve has a long Root Entry Zone (REZ) that extends over 10mm before entering the brainstem. The VIIIth nerve is also physiologically close to numerous vessels at the pontocerebellar angle and internal auditory meatus. Therefore, vestibular syndrome resulting from neurovascular compression syndrome of the VIIIth nerve may exist, but it is very difficult to prove using radiological imagery.

Auditory Input to CNS Is Acquired Coincidentally with Development of Inner Ear after Formation of Functional Afferent Pathway in Zebrafish

Auditory perception in vertebrates depends on transduction of sound into neural signals in the inner ear hair cells (HCs) and on transmission of these signals to the brain through auditory (VIIIth) nerve afferents. To investigate the developmental acquisition of auditory inputs by the CNS, we have electrophysiologically and morphologically examined the process of acquisition of auditory responsiveness by zebrafish macular HCs and the Mauthner cells (M-cells) in vivo. The M-cells are a paired large reticulospinal neurons in the hindbrain; they receive direct inputs from the VIIIth nerve afferents and initiate an acoustic startle response. Whole-cell recordings from the M-cells showed that sound-evoked postsynaptic currents were first observed around 40 h postfertilization (hpf); during subsequent development, onset latency decreased and amplitude increased. The appearance and development of microphonic potentials in the inner ear coincided with those of the acoustic responses of the M-cell, whereas the functional auditory circuits from the macular HCs to the M-cell were already formed at 27 hpf. These results suggest that the functional maturation of inner ear after formation of the auditory pathway is a critical process in the acquisition of auditory inputs by CNS neurons.

The role of magnetic resonance imaging in the identification of suspected acoustic neuroma: a systematic review of clinical and cost effectiveness and natural history

To evaluate the clinical effectiveness and cost-effectiveness of a range of diagnostic strategies for investigating patients with unilateral hearing loss and/or tinnitus, with a view to confirming or eliminating a diagnosis of acoustic neuroma, and to describe the natural history of acoustic neuroma. Major electronic databases were searched from January 1980 to August 2008. Selected studies were assessed and subjected to data extraction and quality assessment using standard methods. Studies comparing auditory brainstem response (ABR) with magnetic resonance (MR) imaging were highly heterogeneous. ABR has high sensitivity compared with MR imaging for acoustic neuromas greater than 1 cm in size but not for smaller neuromas. The sensitivities of T2-weighted (T2W) and T2-star-weighted (T2*W) imaging strategies compared with gadolinium-enhanced T1-weighted (GdT1W) MR imaging (gold standard) were high and relatively homogeneous. The specificity of T2W and T2*W studies ranged from 90% to 100% and from 86% to 99% respectively. The review of cost-effectiveness showed that GdT1W MR imaging immediately or in conjunction with ABR appears to be more cost-effective than 'traditional' protocols; ABR/GdT1W MR imaging protocols were more cost-effective than going directly to GdT1W MR imaging. Non-contrast-enhanced MR imaging was found to be a more cost-effective test for acoustic neuroma than GdT1W MR imaging. The incidence of acoustic neuroma has increased over the last 30 years, with the median age at diagnosis remaining at 55 years. Most patients present with insidious symptoms of unilateral hearing impairment, tinnitus and/or vertigo. The pattern and rate of growth of acoustic neuroma are highly variable and currently unpredictable. At least 50% of tumours do not grow, at least for some years after diagnosis. Some studies have found large initial size to be a determinant of later growth, with the opposite also being reported. The mean growth rate for all tumours varies between 1 and 2 mm/year, with a rate of 2-4 mm/year for only those that grow; however, there are cases with significant regression (5%) or exceptional growth (which may exceed 18 mm/year). The majority of the evidence reviewed was poorly reported and there is therefore an inherent risk of bias. Given the recent improvement in resolution and reduction in cost of MR imaging, ABR can no longer be considered appropriate as the primary test used to screen for acoustic neuroma. T2W or T2*W sequences enable accurate evaluation of the VIIIth and VIIth cranial nerves within the cerebellopontine angle and internal auditory canal as well as evaluation of the cochlea and labyrinth, and inclusion of GdT1W sequences is unlikely to contribute information that would alter patient management in the screening population. The quality of the imaging chain and experience of the reporting radiologist are key factors determining the efficacy of a non-contrast screening strategy. Based on a cost-effectiveness model developed to reflect UK practice it was concluded that a diagnostic algorithm that deploys non-contrast MR imaging as an initial imaging screen in the investigation of acoustic neuroma is less costly than and likely to be as effective as available contrast MR imaging.

Auditory input to CNS is acquired coincidentally with development of inner ear after formation of functional afferent pathway in zebrafish

Auditory perception in vertebrates depends on transduction of sound into neural signals in the inner ear hair cells (HCs) and on transmission of these signals to the brain through auditory (VIIIth) nerve afferents. To investigate the developmental acquisition of auditory inputs by the CNS, we have electrophysiologically and morphologically examined the process of acquisition of auditory responsiveness by zebrafish macular HCs and the Mauthner cells (M-cells) in vivo. The M-cells are a paired large reticulospinal neurons in the hindbrain; they receive direct inputs from the VIIIth nerve afferents and initiate an acoustic startle response. Whole-cell recordings from the M-cells showed that sound-evoked postsynaptic currents were first observed around 40 h postfertilization (hpf); during subsequent development, onset latency decreased and amplitude increased. The appearance and development of microphonic potentials in the inner ear coincided with those of the acoustic responses of the M-cell, whereas the functional auditory circuits from the macular HCs to the M-cell were already formed at 27 hpf. These results suggest that the functional maturation of inner ear after formation of the auditory pathway is a critical process in the acquisition of auditory inputs by CNS neurons.

脳底動脈解離後に生じた高度感音難聴例

A 55-year-old woman suddenly noticed right hearing loss and tinnitus. Several days later, she lost consciousness, and was referred to Ehime Prefectural Central Hospital. Computed tomography (CT) showed subarachnoidal hemorrhage at the right cerebellopontine angle. However, subsequent CT-angiography and four-vessel cerebral angiography could not detect the exact cause of hemorrhage, such as aneurysm and arterial dissection. When she regained consciousness a few days later, she noticed worsening of right hearing loss and dizziness. Pure-tone audiogram showed complete deafness in the right ear. Distortion product otoacoustic emission and auditory brainstem response were not elicited in the right ear. Caloric test demonstrated canal paresis of the right ear with normal response in visual suppression. There were no neurological deficits other than right VIIIth nerve damage. Cerebral infarction and vasospasm were negative in magnetic resonance imaging (MRI) and MR-angiography performed on the 5th day. One month after onset, four-vessel angiogram demonstrated stenosis of the basilar artery near the branching site of AICA. These findings suggested that her deafness and disequilibrium were due to inner ear ischemia caused by dissection of the basilar artery, which also caused subarachnoidal hemorrhage.