Superior Vestibular Nucleus Research Articles

Commissural and monosynaptic inputs to medial vestibular nucleus GABAergic neurons in mice.

MVN GABAergic neurons is involved in the rebalance of commissural system contributing to alleviating acute peripheral vestibular dysfunction syndrome. This study aims to depict monosynaptic inputs to MVN GABAergic neurons. The modified rabies virus-based retrogradation method combined with the VGAT-IRES-Cre mice was used in this study. Moreover, the commissural connections with MVN GABAergic neurons were analyzed. We identified 60 nuclei projecting to MVN GABAergic neurons primarily distributed in the cerebellum and the medulla. The uvula-nodulus, gigantocellular reticular nucleus, prepositus nucleus, intermediate reticular nucleus, and three other nuclei sent dense inputs to MVN GABAergic neurons. The medial (fastigial) cerebellar nucleus, dorsal paragigantocellular nucleus, lateral paragigantocellular nucleus and 10 other nuclei sent moderate inputs to MVN GABAergic neurons. Sparse inputs to MVN GABAergic neurons originated from the nucleus of the solitary tract, lateral reticular nucleus, pedunculopontine tegmental nucleus and 37 other nuclei. The MVN GABAergic neurons were regulated by the contralateral MVN, lateral vestibular nucleus, superior vestibular nucleus, and inferior vestibular nucleus. Our study contributes to further understanding of the vestibular dysfunction in terms of neural circuits and search for new strategies to facilitate vestibular compensation.

Use of a tissue clearing technique combined with retrograde trans-synaptic viral tracing to evaluate changes in mouse retinorecipient brain regions following optic nerve crush.

Successful establishment of reconnection between retinal ganglion cells and retinorecipient regions in the brain is critical to optic nerve regeneration. However, morphological assessments of retinorecipient regions are limited by the opacity of brain tissue. In this study, we used an innovative tissue cleaning technique combined with retrograde trans-synaptic viral tracing to observe changes in retinorecipient regions connected to retinal ganglion cells in mice after optic nerve injury. Specifically, we performed light-sheet imaging of whole brain tissue after a clearing process. We found that pseudorabies virus 724 (PRV724) mostly infected retinal ganglion cells, and that we could use it to retrogradely trace the retinorecipient regions in whole tissue-cleared brains. Unexpectedly, PRV724-traced neurons were more widely distributed compared with data from previous studies. We found that optic nerve injury could selectively modify projections from retinal ganglion cells in the hypothalamic paraventricular nucleus, intergeniculate leaflet, ventral lateral geniculate nucleus, central amygdala, basolateral amygdala, Edinger-Westphal nucleus, and oculomotor nucleus, but not the superior vestibular nucleus, red nucleus, locus coeruleus, gigantocellular reticular nucleus, or facial nerve nucleus. Our findings demonstrate that the tissue clearing technique, combined with retrograde trans-synaptic viral tracing, can be used to objectively and comprehensively evaluate changes in mouse retinorecipient regions that receive projections from retinal ganglion cells after optic nerve injury. Thus, our approach may be useful for future estimations of optic nerve injury and regeneration.

In Vivo Localization of the Human Velocity Storage Mechanism and Its Core Cerebellar Networks by Means of Galvanic-Vestibular Afternystagmus and fMRI

Humans are able to estimate head movements accurately despite the short half-life of information coming from our inner ear motion sensors. The observation that the central angular velocity estimate outlives the decaying signal of the semicircular canal afferents led to the concept of a velocity storage mechanism (VSM). The VSM can be activated via visual and vestibular modalities and becomes manifest in ocular motor responses after sustained stimulation like whole-body rotations, optokinetic or galvanic vestibular stimulation (GVS). The VSM has been the focus of many computational modelling approaches; little attention though has been paid to discover its actual structural correlates. Animal studies localized the VSM in the medial and superior vestibular nuclei. A significant modulation by cerebellar circuitries including the uvula and nodulus has been proposed. Nevertheless, the corresponding neuroanatomical structures in humans have not been identified so far. The aim of the present study was to delineate the neural substrates of the VSM using high-resolution infratentorial fMRI with a fast T2* sequence optimized for infratentorial neuroimaging and via video-oculography (VOG). The neuroimaging experiment (n=20) gave first in vivo evidence for an involvement of the vestibular nuclei in the VSM and substantiate a crucial role for cerebellar circuitries. Our results emphasize the importance of cerebellar feedback loops in VSM most likely represented by signal increases in vestibulo-cerebellar hubs like the uvula and nodulus and lobule VIIIA. The delineated activation maps give new insights regarding the function and embedment of Crus I, Crus II, and lobule VII and VIII in the human vestibular system.

Effect and mechanism of BDNF/TrkB signaling on vestibular compensation

ABSTRACT Brain-derived neurotrophic factor (BDNF) regulates neuronal plasticity by targeting the tyrosine kinase B receptor (TrkB) receptor, but limited researches concentrate on the role of BDNF/TrkB signaling in vestibular compensation. In this study, rats with unilateral vestibular dysfunction were established by unilateral labyrinthectomy (UL) and infusion with siBDNF or 7, 8-Dihydroxyflavone (7,8-DHF, a TrkB receptor agonist). The behavioral scores of rats with vestibular deficits were determined and the rotarod test was performed after UL. BDNF and TrkB levels after UL were determined by western blot and quantitative reverse transcription PCR (qRT-PCR). 5-bromo-2ʹ-deoxyuridine (BrdU)-positive cells (newly generated cells) and GAD67-positive cells (GABAergic neurons) were identified by immunohistochemistry. Glial fibrillary acidic protein (GFAP) (astrocyte marker)-positive cells were identified and GABA type A receptor (GABAAR) expression was detected by immunofluorescence. We found that after UL, BDNF and TrkB levels were up-regulated with a maximum value at 4 h, and then progressively down-regulated during 4 h ~ 7 d. Blocking BDNF/TrkB signaling inhibited the recovery from vestibular deficits, decreased the numbers of newly generated cells and astrocytes in medial vestibular nucleus (MVN), inferior vestibular nerve (IVN), superior vestibular nerve (SVN) and lateral vestibular nucleus (LVN), and disrupted the balances of GABAergic neurons and GABAAR expressions in the left (lesioned) side and right (intact) side of MVN, whereas activation of BDNF/TrkB signaling caused opposite results. The current study indicated that BDNF/TrkB signaling avails vestibular compensation, depending on the number of newly generated cells and astrocytes, the rebalance of GABAergic neurons, and GABAAR expression in bilateral MVN.

Lesion-induced changes of brevican expression in the perineuronal net of the superior vestibular nucleus.

Damage to the vestibular sense organs evokes static and dynamic deficits in the eye movements, posture and vegetative functions. After a shorter or longer period of time, the vestibular function is partially or completely restored via a series of processes such as modification in the efficacy of synaptic inputs. As the plasticity of adult central nervous system is associated with the alteration of extracellular matrix, including its condensed form, the perineuronal net, we studied the changes of brevican expression in the perineuronal nets of the superior vestibular nucleus after unilateral labyrinth lesion. Our results demonstrated that the unilateral labyrinth lesion and subsequent compensation are accompanied by the changing of brevican staining pattern in the perineuronal nets of superior vestibular nucleus of the rat. The reduction of brevican in the perineuronal nets of superior vestibular nucleus may contribute to the vestibular plasticity by suspending the non-permissive role of brevican in the restoration of perineuronal net assembly. After a transitory decrease, the brevican expression restored to the control level parallel to the partial restoration of impaired vestibular function. The bilateral changing in the brevican expression supports the involvement of commissural vestibular fibers in the vestibular compensation. All experimental procedures were approved by the 'University of Debrecen - Committee of Animal Welfare' (approval No. 6/2017/DEMAB) and the 'Scientific Ethics Committee of Animal Experimentation' (approval No. HB/06/ÉLB/2270-10/2017; approved on June 6, 2017).

Vestibular Brainstem Dysmorphology in an Animal Model of Autism Spectrum Disorder

Introduction - Prenatal exposure to the antiepileptic drug valproic acid (VPA) is associated with an elevated risk of a diagnosis of autism spectrum disorder (ASD) in humans. Accordingly, in utero exposure to VPA is a clinically relevant and validated animal model of ASD. Previous work from our lab on VPA-exposed animals revealed significant changes in the auditory brainstem and cerebellum. Specifically, we have shown fewer neurons in the auditory brainstem, reduced expression of calcium binding proteins, reduced connectivity and hyperactivation in response to pure tone stimuli. In the cerebellum, we have found smaller Purkinje cells, reduced expression of calbindin (CB) and significant gait ataxia. Based on these findings, we rationalized that brainstem vestibular pathways might similarly be affected in VPA-exposed animals. We therefore hypothesized that in utero VPA exposure will result in fewer neurons in the vestibular nuclei, reduced CB+ immunolabeling, postural instability and poor gait performance after vestibular challenge. Methods - After timed mating, pregnant rats were fed peanut butter meals from embryonic days 7 through 12. Dams in the VPA groups were fed peanut butter with 800mg/kg VPA on E10 and 12. Pups were delivered without interference and were handled by experimenters from postnatal day (P) 15-20. Starting on P21, control and VPA-exposed animals underwent a battery of motor tests and vestibular challenges from P21-28. All morphological studies were done using brain tissue from P28 animals. Results - Compared to control animals, we found significantly fewer neurons in the spinal, lateral and superior vestibular nuclei and larger neuronal cell bodies in the spinal and lateral vestibular nuclei in VPA-exposed animals. In the lateral nucleus we also found significantly more stellate and fusiform neurons but fewer round/oval neurons. Preliminary examination of the number of CB+ terminals in the vestibular nuclei suggests that afferent inputs to these neurons may have reduced CB expression. Behavioral tests suggest that VPA-exposed animals are more severely impacted by vestibular challenge than control animals. Conclusion and Significance - Our results are consistent with both structural and functional changes in animals exposed to VPA in utero. Together, our research provides evidence for significant brainstem dysfunction and we propose these alterations extend to human cases of ASD. This work will clarify the brainstem centers impacted in ASD and may lead to the development of simple, non-invasive tests of vestibular function to screen for ASD.

Angular vestibulo ocular reflex loss with preserved saccular function in Machado-Joseph disease

ObjectiveTo provide a comprehensive evaluation of the vestibular function in Machado-Joseph Disease (MJD). Methods21 MJD patients and 19 healthy Controls underwent a detailed clinical neuro-otological evaluation including VOR gain of all six semicircular canals by video Head Impulse Test (vHIT), remaining horizontal VOR function by Suppression Head Impulse test (SHIMP), and saccular function by cervical Vestibular Evoked Myogenic Potentials (cVEMP). ResultsAll MJD had significantly lower VOR gain in all six semicircular canals (p < 0.001) with a mean ± SEM of horizontal gain of 0.52 ± 0.04 and vertical gain of 0.57 ± 0.03 versus Controls' gain of 0.95 ± 0.01 and 0.81 ± 0.02, respectively (p < 0.001). MJD showed also a significantly lower VOR gain on the SHIMP test with left gain of 0.51 ± 0.04 and right gain of 0.46 ± 0.03 versus Controls' gain of 0.79 ± 0.01 and 0.83 ± 0.03, respectively (p < 0.001). In contrast, MJD had normal saccular function reflected by the presence of cVEMP response in 18/20 patients and in 12/17 of Controls, with a non-significant difference between MJD and Controls of P13 and N23 peaks latency and normalized peak-to-peak amplitude. ROC analysis of horizontal VOR gain resulted in an area under the curve of 0.993 making the average lateral canals' VOR gain an excellent classifier of MJD vs Controls. ConclusionsHorizontal and vertical VOR impairment with preserved sacculo-collic function seems to be a distinctive feature of MJD and could be explained by selective, mostly medial and superior vestibular nuclei degeneration. This study further supports the idea that horizontal VOR gain measured by vHIT could be a potential neurophysiological biomarker of MJD.

Anatomical Location of the Vestibulocerebellar Tract in the Healthy Human Brain: A Diffusion Tensor Imaging Study

The vestibulocerebellar tract (VCT) is regarded as an important pathway of the central vestibular system. We identified the anatomical characteristics of the primary and secondary VCTs in a normal human brain using diffusion tensor imaging (DTI) tractography. Thirty-one healthy adults were recruited. A 1.5 T scanner was used for DTI tractography. A seed region of interest (ROI) was placed on the superior and medial vestibular nuclei at the pons level and a target ROI was placed on the uvula–nodulus of the cerebellum for reconstructing the primary VCT. In the secondary VCTs, the seed ROI was placed on the inferior and medial vestibular nuclei at the medulla oblongata level, and target ROIs were placed on the bilateral uvula–nodulus of the cerebellum. The primary VCT originated from the superior and medial vestibular nuclei at the pons level and terminated at the ipsilateral uvula–nodulus of the cerebellum. The component of the secondary VCTs originated from the inferior and medial vestibular nuclei at the level of the medulla oblongata and terminated at the bilateral uvula–nodulus of the cerebellum. Among them, 70.97% in the contralateral secondary VCT crossed at the vermis of the cerebellum. In addition, the fractional anisotropies (FAs) and mean diffusivity (MD) values of the primary VCT were significantly higher and lower, respectively, compared to those of the secondary VCTs (p < 0.05). The contralateral secondary VCT was significantly higher and lower in the MD and tract volume, respectively (p < 0.05), compared to the ipsilateral VCT. Therefore, we believe that the results will be useful for future studies of the vestibular projection pathway in the human brain injury aspect of central vestibular syndrome.

Distributive characteristics of projection from vestibular nuclei to nucleus raphe magnus in rats**

BACKGROUNDMorphological studies have confirmed that vestibular nuclei accepts serotoninergic projections from nucleus raphe magnus, nucleus raphes pallidus, etc. But it is still unclear whether there is bi-directional association between vestibular nuclei and nucleus raphe magnus. OBJECTIVETo observe the characteristics of projective fibers from vestibular nuclei to nucleus raphe magnus using tetramethyl rhodamine (TMR) in rats, so as to provide more sufficient morphological evidence of neural association from vestibular nuclei. DESIGNAn observational experiment. SETTINGDepartment of Anatomy (K.K. Leung Brain Research Center), the Fourth Military Medical University of Chinese PLA. MATERIALSEighteen male SD rats of clean degree, weighing 250–280 g, were provided by the Experimental Animal Center of the Fourth Military Medical University of Chinese PLA. METHODSThe experiments were carried out in the laboratory of Department of Anatomy (K.K. Leung Brain Research Center), the Fourth Military Medical University of Chinese PLA from September 2006 to January 2007. All the rats were anesthetized with intraperitoneal injection of pentobarbital sodium, then according to the coordinates on the rat brain atlas, 0.1 µ L TMR (100 g/L) was injected into nucleus raphes magnus via the tip of glass microtubule by means of microinjection. Seven days later, the rats were anesthetized, then perfused and fixed to remove brain, and then frozen coronal brain sections were prepared. The retrogradely labeled neurons in the injected and projected sites were observed under fluorescence microscope. Light filters with evoked wave length of 540–553 nm and emission wave length ≥ 1 580 nm were selected to observe the orange TMR-labeled neurons. All the sections were observed and counted under the fluorescence microscope. MAIN OUTCOME MEASURESCharacteristics and number of retrogradely labeled neurons at different sites of nuclei. RESULTSTotally 18 SD rats were enrolled, 9 of them were excluded due to the deviation of injected site, and the other 9 were involved in the final analysis of results. The concentrated region of TMR injection was mainly restricted to nucleus raphes magnus, and diffused to the surrounding area to different extents. There were obvious differences in the distributions of the labeled neurons among the subdivisions in vestibular nuclei, as well as the distributions of the labeled neurons at different sites in the same subdivision. The majority of the labeled neurons distributed in the rostral levels of medial vestibular nucleus and the lateral vestibular nucleus, while fewer labeled neurons were observed in superior vestibular nucleus. CONCLUSION(1) There might be bi-directional association between vestibular nucli and nucleus raphe magnus, suggesting that nucleus raphe magnus played a role in the transmission and processing of vestibular information. (2) The projection from nucleus raphe magnus to vestibular nucleus has certain distributive characteristics in the region.

Lowering barometric pressure induces neuronal activation in the superior vestibular nucleus in mice.

Weather changes accompanied by decreases in barometric pressure are suggested to trigger meteoropathy, i.e., weather-related pain. We previously reported that neuropathic pain-related behavior in rats is aggravated by lowering barometric pressure, and that this effect is abolished by inner ear lesions. These results suggest that mechanisms that increase vestibular neuronal activity may parallel those that contribute to meteoropathy generation. However, it remains unknown whether changes in barometric pressure activate vestibular neuronal activity. To address this issue, we used expression of c-Fos protein as a marker for neural activation. Male and female mice were placed in a climatic chamber, and the barometric pressure was lowered by 40 hPa, from 1013 hPa, for 50 min (LP stimulation). The total number of c-Fos-positive cells in the vestibular nuclei was counted bilaterally after LP stimulation. We also video-recorded mouse behaviors and calculated the total activity score during the LP stimulation. LP stimulation resulted in significant c-Fos expression in the superior vestibular nucleus (SuVe) of male and female mice. There was no effect of LP stimulation on the total activity score. These data show that distinct neurons in the SuVe respond to LP stimulation. Similar mechanisms may contribute to the generation of meteoropathy in humans.

Coding of Velocity Storage in the Vestibular Nuclei.

Semicircular canal afferents sense angular acceleration and output angular velocity with a short time constant of ≈4.5 s. This output is prolonged by a central integrative network, velocity storage that lengthens the time constants of eye velocity. This mechanism utilizes canal, otolith, and visual (optokinetic) information to align the axis of eye velocity toward the spatial vertical when head orientation is off-vertical axis. Previous studies indicated that vestibular-only (VO) and vestibular-pause-saccade (VPS) neurons located in the medial and superior vestibular nucleus could code all aspects of velocity storage. A recently developed technique enabled prolonged recording while animals were rotated and received optokinetic stimulation about a spatial vertical axis while upright, side-down, prone, and supine. Firing rates of 33 VO and 8 VPS neurons were studied in alert cynomolgus monkeys. Majority VO neurons were closely correlated with the horizontal component of velocity storage in head coordinates, regardless of head orientation in space. Approximately, half of all tested neurons (46%) code horizontal component of velocity in head coordinates, while the other half (54%) changed their firing rates as the head was oriented relative to the spatial vertical, coding the horizontal component of eye velocity in spatial coordinates. Some VO neurons only coded the cross-coupled pitch or roll components that move the axis of eye rotation toward the spatial vertical. Sixty-five percent of these VO and VPS neurons were more sensitive to rotation in one direction (predominantly contralateral), providing directional orientation for the subset of VO neurons on either side of the brainstem. This indicates that the three-dimensional velocity storage integrator is composed of directional subsets of neurons that are likely to be the bases for the spatial characteristics of velocity storage. Most VPS neurons ceased firing during drowsiness, but the firing rates of VO neurons were unaffected by states of alertness and declined with the time constant of velocity storage. Thus, the VO neurons are the prime components of the mechanism of coding for velocity storage, whereas the VPS neurons are likely to provide the path from the vestibular to the oculomotor system for the VO neurons.

Role of the vestibular nuclear complex in facilitating the jaw-opening reflex following stimulation of the red nucleus

According to our previous studies, stimulation of the red nucleus (RN) facilitates the low-threshold afferent-evoked jaw-opening reflex (L-JOR). It has been reported that the RN projects to the superior (SVN), lateral (LVN) and inferior vestibular (IVN) nuclei. The SVN and the LVN have reciprocal intrinsic connections with the medial vestibular nucleus (MVN). Our previous study demonstrated that stimulation of the vestibular nuclear complex (VN) modulates the L-JOR. These facts suggest that RN-induced facilitation of the L-JOR is mediated via the VN. In the present work we investigated whether electrically induced lesions of the VN, or microinjection of muscimol into the VN, affects RN-induced facilitation of the L-JOR. The L-JOR was evoked by electrical stimulation of the inferior alveolar nerve. The stimulus intensity was 1.2 times the evocation threshold. Lesions of the MVN or the LVN or the SVN, and the muscimol injection into the MVN or the LVN or the SVN, reduced the RN-induced facilitation of the L-JOR. Conversely, lesions of the IVN, and the muscimol injection into the IVN, increased the RN-induced facilitation of the L-JOR. These results suggest that the RN-induced facilitation of the L-JOR is mediated by a relay in the VN.

Hypothalamic orexin-A (hypocretin-1) neuronal projections to the vestibular complex and cerebellum in the rat

Immunohistochemistry combined with retrograde tract-tracing techniques were used to investigate the distribution of orexin-A (OX-A)- and OX-A receptor-like (OX1) immunoreactivity within the vestibular complex and cerebellum, and the location of hypothalamic OX-A neurons sending axonal projections to these regions in the Wistar rat. OX-A immunoreactive fibers and presumptive terminals were found throughout the medial (MVe) and lateral (LVe) vestibular nuclei. Light fiber labeling was also observed in the spinal and superior vestibular nuclei. Within the cerebellum, dense fiber and presumptive terminal labeling was observed in the medial cerebellar nucleus (Med; fastigial nucleus), with less dense labeling in the interposed (Int) and lateral cerebellar nuclei (Lat; dentate nucleus). A few scattered OX-A immunoreactive fibers were also observed throughout the cortex of the paraflocculus. OX1-like immunoreactivity was found densely concentrated within LVe, moderate in MVe, and scattered within the spinal and superior vestibular nuclei. Within the cerebellum, OX1-like immunoreactivity was also observed densely within Med and in the dorsolateral aspects of Int. Additionally, OX1 like-labeling was found in Lat, and within the granular layer of the caudal paraflocculus cerebellar cortex. Fluorogold (FG) microinjected into these vestibular and cerebellar regions resulted in retrogradely labeled neurons throughout the ipsilateral hypothalamus. Retrogradely labeled neurons containing OX-A like immunoreactivity were observed dorsal and caudal to the anterior hypothalamic nucleus and extending laterally into the lateral hypothalamic area, with the largest number clustered around the dorsal aspects of the fornix in the perifornical area. A few FG OX-A like-immunoreactive neurons were also observed scattered throughout the dorsomedial, and posterior hypothalamic nuclei. These data indicate that axons from OX-A neurons terminate within the vestibular complex and deep cerebellar nuclei of the cerebellum and although the function of these pathways is unknown, they likely represent pathways by which hypothalamic OX-A containing neurons co-ordinate vestibulo-cerebellar motor and autonomic functions associated with ingestive behaviors.

Identification of Neural Networks That Contribute to Motion Sickness through Principal Components Analysis of Fos Labeling Induced by Galvanic Vestibular Stimulation

Motion sickness is a complex condition that includes both overt signs (e.g., vomiting) and more covert symptoms (e.g., anxiety and foreboding). The neural pathways that mediate these signs and symptoms are yet to identified. This study mapped the distribution of c-fos protein (Fos)-like immunoreactivity elicited during a galvanic vestibular stimulation paradigm that is known to induce motion sickness in felines. A principal components analysis was used to identify networks of neurons activated during this stimulus paradigm from functional correlations between Fos labeling in different nuclei. This analysis identified five principal components (neural networks) that accounted for greater than 95% of the variance in Fos labeling. Two of the components were correlated with the severity of motion sickness symptoms, and likely participated in generating the overt signs of the condition. One of these networks included neurons in locus coeruleus, medial, inferior and lateral vestibular nuclei, lateral nucleus tractus solitarius, medial parabrachial nucleus and periaqueductal gray. The second included neurons in the superior vestibular nucleus, precerebellar nuclei, periaqueductal gray, and parabrachial nuclei, with weaker associations of raphe nuclei. Three additional components (networks) were also identified that were not correlated with the severity of motion sickness symptoms. These networks likely mediated the covert aspects of motion sickness, such as affective components. The identification of five statistically independent component networks associated with the development of motion sickness provides an opportunity to consider, in network activation dimensions, the complex progression of signs and symptoms that are precipitated in provocative environments. Similar methodology can be used to parse the neural networks that mediate other complex responses to environmental stimuli.

Vulnerability of the vestibular organs to transient ischemia: Implications for isolated vascular vertigo

The aim of this study was to elucidate the mechanism of isolated vascular vertigo by determining selective and relative ischemic vulnerability of the vestibular structures using a global hypoperfusion model in rats. Sprague-Dawley male rats weighing 330–350g were subjected to transient global ischemia of the brain using a 4-vessel-occlusion (4VO) model. After permanent occlusion of both vertebral arteries (VA) using electrocauterization, both common carotid arteries (CCAs) were occluded for 5–20min with ligation. One hour after reperfusion of the CCAs, the animals were sacrificed and subjected to c-Fos staining of the entire cerebellum, brainstem, and vestibular ganglion. The rats in the sham group received the same surgical procedures except the vessel ligation. With 4VO for 5–15min, both the sham and experimental groups showed a weak and scarce c-Fos expression in the medial vestibular nucleus (MVN), neuron Y, and cochlear nucleus. After 4VO for 20min, only the MVN began to show a significant difference in the number of c-Fos positive neurons between the experimental and sham groups (33.7±17.7 vs.7.1±5.1, Wilcoxon rank test, p=0.005). With 4VO for up to 20min, c-Fos positive neurons were not found in other areas of the brainstem and cerebellum, including the superior, lateral, and spinal vestibular nuclei, the vestibular ganglion, the cerebellar cortex, and the deep cerebellar nuclei. The vestibular structures appear to be vulnerable to ischemia more than any other structures in the brainstem and cerebellum. Of the vestibular structures, the MVN is most vulnerable to ischemic insults in rats. These findings are consistent with the common findings of vertigo as an initial and isolated symptom of posterior circulation ischemia in human.

Molecular composition of extracellular matrix in the vestibular nuclei of the rat

Previous studies have demonstrated that the molecular and structural composition of the extracellular matrix (ECM) shows regional differences in the central nervous system. By using histochemical and immunohistochemical methods, we provide here a detailed map of the distribution of ECM molecules in the vestibular nuclear complex (VNC) of the rat. We have observed common characteristics of the ECM staining pattern in the VNC and a number of differences among the individual vestibular nuclei and their subdivisions. The perineuronal net (PNN), which is the pericellular condensation of ECM, showed the most intense staining for hyaluronan, aggrecan, brevican and tenascin-R in the superior, lateral and medial vestibular nuclei, whereas the HAPLN1 link protein and the neurocan exhibited moderate staining intensity. The rostral part of the descending vestibular nucleus (DVN) presented a similar staining pattern in the PNN, with the exception of brevican, which was negative. The caudal part of the DVN had the weakest staining for all ECM molecules in the PNN. Throughout the VNC, versican staining in the PNN, when present, was distinctive due to its punctuate appearance. The neuropil also exhibited heterogeneity among the individual vestibular nuclei in ECM staining pattern and intensity. We find that the heterogeneous distribution of ECM molecules is associated in many cases with the variable cytoarchitecture and hodological organization of the vestibular nuclei, and propose that differences in the ECM composition may be related to specific neuronal functions associated with gaze and posture control and vestibular compensation.

Histamine Excites Rat Superior Vestibular Nuclear Neurons via Postsynaptic H1 and H2 Receptors in vitro

The superior vestibular nucleus (SVN), which holds a key position in vestibulo-ocular reflexes and nystagmus, receives direct hypothalamic histaminergic innervations. By using rat brainstem slice preparations and extracellular unitary recordings, we investigated the effect of histamine on SVN neurons and the underlying receptor mechanisms. Bath application of histamine evoked an excitatory response of the SVN neurons, which was not blocked by the low-Ca²⁺/high-Mg²⁺ medium, indicating a direct postsynaptic effect of the amine. Selective histamine H₁ receptor agonist 2-pyridylethylamine and H₂ receptor agonist dimaprit, rather than VUF8430, a selective H₄ receptor agonist, mimicked the excitation of histamine on SVN neurons. In addition, selective H₁ receptor antagonist mepyramine and H₂ receptor antagonist ranitidine, but not JNJ7777120, a selective H₄ receptor antagonist, partially blocked the excitatory response of SVN neurons to histamine. Moreover, mepyramine together with ranitidine nearly totally blocked the histamine-induced excitation. Immunostainings further showed that histamine H₁ and H₂ instead of H₄ receptors existed in the SVN. These results demonstrate that histamine excites the SVN neurons via postsynaptic histamine H₁ and H₂ receptors, and suggest that the central histaminergic innervation from the hypothalamus may actively bias the SVN neuronal activity and subsequently modulate the SVN-mediated vestibular functions and gaze control.

Hypertrophic Degeneration of the Inferior Olive Yields Erroneous Internal Estimates of Direction of Gravity (P02.255)

Objective: To investigate the role of the inferior olive (IO) for estimating direction of gravity. Background Central graviceptive pathways (CGP) connect the vestibular nuclei with cerebellar, brainstem and cortical areas. Acute lesions along the CGP lead to ocular torsion, skew deviation and subjective visual vertical (SVV) tilt. The IO is interconnected with the contralateral dentate nucleus and the ipsilateral red nucleus. Disruption of the central tegmental tract connecting the red nucleus with the IO may interfere with estimating direction of gravity. Design/Methods: We assessed the SVV in a 65yo man with a pontomesencephalic hemorrhage that included the medial vestibular nuclei, the right superior and lateral vestibular nucleus, the right interstitial nucleus of Cajal, the medial longitudinal fasciculus and central tegmental tract bilaterally. SVV was assessed at 16 days and 4 months after hemorrhage. Initially, he presented with gait ataxia, horizontal gaze palsy, impaired upgaze, and left-sided sensorimotor impairment. After four months he developed a vertical pendular nystagmus and increased gait ataxia. MR-imaging revealed a hypertrophic degeneration of the right IO. Results: Whereas SVV adjustments obtained at day 16 deviated 3.7° ipsilesional, large contralesional (-15.2°) deviations were found after four months. Conclusions: A shift from ipsilesional to contralesional SVV deviations in the presence of a hypertrophic degeneration of the IO was observed. We hypothesize that disrupted inhibitory GABA-ergic input from the red nucleus to the IO results in synchronized oscillations of IO neurons. These synchronized oscillations are signaled to the cerebellum, which results in a loss of inhibitory control that is normally provided through this pathway. This loss of inhibition could lead to hyperactivity of the dentate nucleus contralateral to the affected IO and consequently to a SVV tilt to the side of the overactive dentate nucleus. Such a mechanism would be in accordance to previous reports describing SVV tilts contralateral to an inhibited dentate nucleus. Supported by: Swiss National Science Foundation (3200B0-105434 and 32003B_130163/1), the Betty and David Koetser Foundation for Brain Research, Zurich, Switzerland, and the Center of Integrative Human Physiology, University of Zurich, Switzerland. Disclosure: Dr. Tarnutzer has nothing to disclose. Dr. Palla has nothing to disclose. Dr. Marti has nothing to disclose. Dr. Schuknecht has nothing to disclose. Dr. Straumann has nothing to disclose.

Distribution of zebrin‐immunoreactive Purkinje cell terminals in the cerebellar and vestibular nuclei of birds

Zebrin II (aldolase C) is expressed in a subset of Purkinje cells in the mammalian and avian cerebella such that there is a characteristic parasagittal organization of zebrin-immunopositive stripes alternating with zebrin-immunonegative stripes. Zebrin is expressed not only in the soma and dendrites of Purkinje cells but also in their axonal terminals. Here we describe the distribution of zebrin immunoreactivity in both the vestibular and the cerebellar nuclei of pigeons (Columba livia) and hummingbirds (Calypte anna, Selasphorus rufus). In the medial cerebellar nucleus, zebrin-positive labeling was particularly heavy in the “shell,” whereas the “core” was zebrin negative. In the lateral cerebellar nucleus, labeling was not as heavy, but a positive shell and negative core were also observed. In the vestibular nuclear complex, zebrin-positive terminal labeling was heavy in the dorsolateral vestibular nucleus and the lateral margin of the superior vestibular nucleus. The central and medial regions of the superior nucleus were generally zebrin negative. Labeling was moderate to heavy in the medial vestibular nucleus, particulary the rostral half of the parvocellular subnucleus. A moderate amount of zebrin-positive labeling was present in the descending vestibular nucleus: this was heaviest laterally, and the central region was generally zebrin negative. Zebrin-positive terminals were also observed in the the cerebellovestibular process, prepositus hypoglossi, and lateral tangential nucleus. We discuss our findings in light of similar studies in rats and with respect to the corticonuclear projections to the cerebellar nuclei and the functional connections of the vestibulocerebellum with the vestibular nuclei.

Fos expression in neurons of the rat vestibulo-autonomic pathway activated by sinusoidal galvanic vestibular stimulation.

The vestibular system sends projections to brainstem autonomic nuclei that modulate heart rate and blood pressure in response to changes in head and body position with regard to gravity. Consistent with this, binaural sinusoidally modulated galvanic vestibular stimulation (sGVS) in humans causes vasoconstriction in the legs, while low frequency (0.02–0.04 Hz) sGVS causes a rapid drop in heart rate and blood pressure in anesthetized rats. We have hypothesized that these responses occur through activation of vestibulo-sympathetic pathways. In the present study, c-Fos protein expression was examined in neurons of the vestibular nuclei and rostral ventrolateral medullary region (RVLM) that were activated by low frequency sGVS. We found c-Fos-labeled neurons in the spinal, medial, and superior vestibular nuclei (SpVN, MVN, and SVN, respectively) and the parasolitary nucleus. The highest density of c-Fos-positive vestibular nuclear neurons was observed in MVN, where immunolabeled cells were present throughout the rostro-caudal extent of the nucleus. c-Fos expression was concentrated in the parvocellular region and largely absent from magnocellular MVN. c-Fos-labeled cells were scattered throughout caudal SpVN, and the immunostained neurons in SVN were restricted to a discrete wedge-shaped area immediately lateral to the IVth ventricle. Immunofluorescence localization of c-Fos and glutamate revealed that approximately one third of the c-Fos-labeled vestibular neurons showed intense glutamate-like immunofluorescence, far in excess of the stain reflecting the metabolic pool of cytoplasmic glutamate. In the RVLM, which receives a direct projection from the vestibular nuclei and sends efferents to preganglionic sympathetic neurons in the spinal cord, we observed an approximately threefold increase in c-Fos labeling in the sGVS-activated rats. We conclude that localization of c-Fos protein following sGVS is a reliable marker for sGVS-activated neurons of the vestibulo-sympathetic pathway.