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Highlights • Brainstem neural circuits for horizontal and vertical saccades. • Reciprocity between upward and its contralateral downward saccade systems. • Similarity of well-known vestibuloocular and saccade generating pathways. • The saccade system and the VOR system share common semicircular canal coordinate. • Commissural inhibition of two superior colliculi supports canal coordinate hypothesis. Abstract Sensory signals for eye movements (visual and vestibular) are initially coded in different frames of reference but finally translated into common coordinates, and share the same final common pathway, namely the same population of extraocular motoneurons. From clinical studies in humans and lesion studies in animals, it is generally accepted that voluntary saccadic eye movements are organized in horizontal and vertical Cartesian coordinates. However, this issue is not settled yet, because neural circuits for vertical saccades remain unidentified. We recently determined brainstem neural circuits from the superior colliculus to ocular motoneurons for horizontal and vertical saccades with combined electrophysiological and neuroanatomical techniques. Comparing well-known vestibuloocular pathways with our findings of commissural excitation and inhibition between both superior colliculi, we proposed that the saccade system uses the same frame of reference as the vestibuloocular system, common semicircular canal coordinate. This proposal is mainly based on marked similarities (1) between output neural circuitry from one superior colliculus to extraocular motoneurons and that from a respective canal to its innervating extraocular motoneurons, (2) of patterns of commissural reciprocal inhibitions between upward saccade system on one side and downward system on the other, and between anterior canal system on one side and posterior canal system on the other, and (3) between the neural circuits of saccade and quick phase of vestibular nystagmus sharing brainstem burst neurons. In support of the proposal, commissural excitation of the superior colliculi may help to maintain Listing's law in saccades in spite of using semicircular canal coordinate. [ABSTRACT FROM AUTHOR]

Zusammenfassung Neurophysiologische Untersuchungen des Hirnstamms stellen auch in Zeiten der hochauflösenden Magnetresonanztomographie weiterhin einen wichtigen Bestandteil in der topographischen Diagnostik von Hirnstammläsionen dar. Während die vestibulär evozierten myogenen Potenziale (VEMP) in der Hals-Nasen-Ohren-Heilkunde einen festen Bestandteil in der neuro-otologischen Diagnostik des Gleichgewichtsorgans eingenommen haben, sind sie in der Neurologie bisher wenig verbreitet. Mit Hilfe der VEMP können unterschiedliche Reflexbögen des Hirnstamms, der vestibulocollische sowie der vestibulookuläre Reflex differenziert neurophysiologisch untersucht werden. Die aktuelle Arbeit soll einen Überblick über die Anatomie und Physiologie sowie die Methodik der VEMP geben. Darüber hinaus sollen die Einsatzmöglichkeiten und Bedeutung der VEMP in der Neurologie dargestellt werden. Summary Even in times of high-resolution magnetic resonance imaging, neurophysiological studies of the brainstem do still play a crucial role in the topographic diagnostic of brainstem pathology. Vestibular evoked myogenic potentials (VEMP) form an integral part of the neurootological examinations in order to establish the functional status of the otolith organs in otorhinolaryngology, whereas they are less established in neurology. By means of VEMP different reflex circuits of the brainstem, the vestibulocollic reflex and the vestibuloocular reflex can be investigated. The recent article gives an overview of the anatomy and physiology of the VEMP and its methodological approach. Furthermore, the characteristics and capabilities of the VEMP in neurological disorders are presented. [ABSTRACT FROM AUTHOR]

Abstract: Vestibular information is essential for the control of posture, balance, and eye movements. The vestibular nerve projects to the four nuclei of the vestibular nuclear complex (VNC), as well as to several additional brainstem nuclei and the cerebellum. We have found that expression of the calcium-binding proteins calretinin (CR) and calbindin (CB), and the synthetic enzyme for nitric oxide synthase (nNOS) define subdivisions of the medial vestibular nucleus (MVe) and the nucleus prepositus (PrH), in cat, monkey, and human. We have asked if the pattern of expression of nonphosphorylated neurofilament protein (NPNFP) might define additional subdivisions of these or other nuclei that participate in vestibular function. We studied the distribution of cells immunoreactive to NPNFP in the brainstems of 5 cats and one squirrel monkey. Labeled cells were scattered throughout the four nuclei of the VNC, as well as in PrH, the reticular formation (RF) and the external cuneate nucleus. We used double-label immunofluorescence to visualize the distribution of these cells relative to other neurochemically defined subdivisions. NPNFP cells were excluded from the CR and CB regions of the MVe. In PrH, NPNFP and nNOS were not colocalized. Cells in the lateral vestibular nucleus and RF colocalized NPNFP and a marker for glutamatergic neurons. We also found that the cholinergic cells and axons of cranial nerve nuclei 3, 4, 6, 7,10 and 12 colocalize NPNFP. The data suggest that NPNFP is expressed by a subset of glutamatergic projection neurons of the vestibular brainstem. NPNFP may be a marker for those cells that are especially vulnerable to the effects of normal aging, neurological disease or disruption of sensory input. [Copyright &y& Elsevier]

Abstract: In Xenopus laevis tadpoles, effects of asymmetrical light conditions on the roll-induced vestibuloocular reflex (rVOR) were tested for the developmental period between stage 47 and 49. For comparison, the rVOR was tested in dim- and high-symmetrical light environments. Test parameters were the rVOR gain and rVOR amplitude. Under all light conditions, the rVOR increased from tadpole stage 47 to 49. For all stages, the asymmetrical light field induced the strongest response, the dim light field the weakest one. The response for the left and right eye was identical, even if the tadpoles were tested under asymmetrical light conditions. The experiments can be considered as hints (1) for an age-dependent light sensitivity of vestibular neurons, and (2) for the existence of control systems for coordinated eye movements that has its origin in the proprioceptors of the extraocular eye muscles. [Copyright &y& Elsevier]

Abstract: Objective: Recent work has demonstrated the existence of ocular vestibular evoked myogenic potentials (OVEMPs), which likely reflect projections underlying the translational vestibular ocular reflex (TVOR). We examined extraocular muscle activity associated with impulsive acceleration of the head in the transmastoid plane. Methods: Accelerometry was measured in 4 subjects in response to acceleration impulses produced by a gamma function delivered with a Minishaker (4810, Bruel & Kjaer). This stimulus produced peak head accelerations of 0.13–0.14g occurring at between 3.1 and 4.0ms at the mastoids for both right and left head movement. OVEMPs were recorded in 10 normal subjects with 5 directions of gaze, using electrode pairs placed lateral to, above and below the eyes. Results: OVEMPs occurred at short latency, with initial peaks between 10.3ms (p10) and 15.3ms (n15). For a given recording site and gaze direction, the responses were determined solely by the direction of imposed acceleration. Conclusions: We propose that, given the transtemporal nature of the stimuli, utricular afferents are likely to be powerfully activated. The OVEMPs evoked may be generated by the lateral recti and oblique muscles. Significance: Sudden lateral accelerations of the head evoke the translational VOR and ocular counter rolling reflex and the pattern of muscle activations indicated by the OVEMPs appear to be a manifestation of these reflexes. [Copyright &y& Elsevier]

Abstract: Using collision tests of orthodromically and antidromically generated spikes, we studied the axonal pathways, axonal projection levels, and soma location of anterior semicircular canal (AC) nerve-activated vestibulospinal neurons in decerebrate cats. AC nerve-activated vestibulospinal neurons (n =74) were mainly located in the ventral portion of the lateral vestibular nuclei and the rostral portion of the descending vestibular nucleus, which is consistent with previous studies. Of these neurons, 15% projected through the ipsilateral (i-) lateral vestibulospinal tract (LVST), 74% projected through the medial vestibulospinal tract (MVST), and 11% projected through the contralateral (c-) LVST. The vast majority (78%) of AC nerve-activated vestibulospinal neurons were activated antidromically only from the cervical segment of the spinal cord; 15% of neurons were activated from the T1 segment and only one neuron was activated from the L3 segment. AC nerve-activated vestibulospinal neurons may primarily target the neck muscles and thus contribute to the vestibulocollic reflex. Most of the c-LVST neurons were also activated antidromically from the oculomotor nucleus, suggesting that they are closely related to the control of combined eye-head movements. [Copyright &y& Elsevier]

Abstract: The clawed toad Xenopus laevis is a common experimental animal used in many disciplines of life sciences, such as integrative, developmental and molecular biology or experimental medicine. Since 30 years, Xenopus is used in biological research in space. Important milestones were the years 1975, when Xenopus embryos flew for the first time on the Russian space station Salut-4 and 1994, when Xenopus eggs were successfully fertilized for the first time in space during the Japanese Spacelab mission STS-47 and developed in microgravity to vital tadpoles. Most Xenopus studies were related to embryogenesis and development. Observations during and after altered gravity revealed changes such as the thickening of the blastocoel roof, the dorsalization of the tail, and modifications of vestibular reflexes, fictive and freely swimming. Many changes were reversible even during microgravity exposure. Studies about the vestibuloocular reflex or synapse formation revealed an age-related sensitivity to altered gravity. Xenopus offers useful tools for studies about microgravity effects on living systems. Its oocyte is a suitable model to study ion channel function in space; the dorsalization model can be used to analyse growth factor sensibilities. Hardware for life support of adults, tadpoles and embryos (cf. SUPPLY unit in combination with miniaquaria) as well as for controlled experiments in space are prerequisites for an extension of research with Xenopus. The application aspect is based on the fact that fundamental research per se brings benefit to man. [Copyright &y& Elsevier]

Abstract: Diazepam is a popular medicine used in the treatment of acute vertigo. In the past, many studies investigating the effect of diazepam in peripheral vestibular destruction have been reported. However, no previous study has yet investigated the effect of diazepam on a model with a transient and reversible vestibular function similar to recurrent vertigo as seen in Meniere''s disease. We thus made a peripheral vestibular re-input model by the unilateral intracochlear administration of tetrodotoxin (TTX) using an osmotic pump and then examined the influence of diazepam on the vestibular system in this model. Hartley white guinea pigs were intracochlearly administered with TTX on the right side for 3 days by an osmotic pump. Animals were divided into three groups, TTX alone (control group (n = 7)), TTX and an intraperitoneal diazepam injection once a day for 3 days (diazepam group (n = 6)) and vehicle injection (vehicle group (n = 6)). A caloric response and vestibuloocular reflex (VOR) were observed at 7 and 14 days after completing 3 days of TTX administration. Seven days after vestibular re-input, a directional preponderance of the nystagmus (DP) to the TTX-treated side was observed in the control and vehicle groups on VOR examination. DP was not observed in the diazepam group on any examined day. The R/L time ratio of caloric response showed no statistical difference between three groups on any examined day. These results suggest that diazepam may thus be useful for patients in an acute stage of peripheral vestibular vertigo by decreasing their vertiginous symptoms. [Copyright &y& Elsevier]

Objective: The vestibular system is a major pathway to nausea and vomiting, and the vestibuloocular reflex (VOR) is a central component; its function can be studied using the vestibular autorotation test (VAT). We hypothesize that women with hyperemesis gravidarum (HG) may have VOR abnormalities. Study Design: Women with HG were compared with women without HG using the VAT. Horizontal and vertical VOR gains and phases were evaluated at 3 frequency ranges: low (2.0 to 3.5 Hz), medium (greater than 3.5 to 5.0 Hz), and high (greater than 5.0 to 6.0 Hz) during pregnancy and postpartum. Results: Twenty women with HG and 48 unaffected women were evaluated in early pregnancy. Women with HG had higher horizontal gains at all 3 frequency ranges. Horizontal phase differences were also observed at medium frequencies. No VAT differences were noted postpartum. Conclusion: Women experiencing HG had a higher mean VOR horizontal gain and lower horizontal phase when compared with unaffected women. [Copyright &y& Elsevier]