Ultrastructure of vestibular commissural neurons related to velocity storage in the monkey
Section snippets
Experimental animals
Brainstem tissue from one rhesus (M. mulatta; M9316) and two cynomolgus (M. fasicularis; M1190 and M1194) monkeys was used to characterize the ultrastructural anatomy of the monkey MVN under the tissue fixation and processing protocols used in our laboratory. In addition, one cynomolgus (M9210) and two rhesus (M502 and M613) monkeys received midline brainstem lesions and had oculomotor and vestibular testing after the midline medullary section. Animals were obtained from the Charles River
Velocity storage
Velocity storage was affected in both M502 and M613. Divergent strabismus due to bilateral paresis of adduction and gaze paresis precluded further testing of M9210. In both M502 and M613, the pre-operative velocity storage time-constants were initially asymmetric. They were 78 s for rightward and 22 s for leftward slow phases during steps of velocity in M502 (Fig. 1A), and 8 and 19 s for rightward and leftward eye velocities in M613. After the lesion, these values fell to approximately 4 and 6 s,
Discussion
Following the midline medullary section in M613, all oculomotor and vestibular functions attributable to velocity storage were abolished, while the direct aVOR pathway remained unaltered. OCR was also intact, indicating that pathways responsible for this otolith-ocular tilt reflex do not course in the region of the midline lesion. These observations suggest that the lesion-induced vestibular and oculomotor damage was functionally discrete, localized to the production of velocity storage. On the
Conclusions
The behavioral results of this study indicate that vestibular commissural axons related to velocity storage cross the midline of the brainstem in the rostral medulla, just caudal to the abducens nuclei. The anatomical findings suggest that such axons originate from clusters of small and medium-sized neurons located in the lateral crescents of the rostral MVN. The ultrastructural observations support the contentions that two types of indirect pathway commissural cells, and two types of axon
Acknowledgements
Supported by National Institutes of Health research grants DC01705 (G.R.H.) from the National Institute on Deafness and Other Communication Disorders, NS00294 (B.C.) from the National Institute of Neurological Diseases and Stroke, EY11812 (B.C.) and EY1867 (B.C.) from the National Eye Institute. The authors thank Ms Rosemary Lang and Mr Victor Rodriguez for their invaluable assistance with various aspects of this work.
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6.05 - Neuroanatomy of Central Vestibular Connections
2020, The Senses: A Comprehensive Reference: Volume 1-7, Second Edition6.25 - Functional Organization of Vestibular Commissural Pathways
2020, The Senses: A Comprehensive Reference: Volume 1-7, Second EditionThe role of GABA<inf>B</inf> receptors in the vestibular oculomotor system in mice
2016, Behavioural Brain ResearchCitation Excerpt :To verify the involvement of GABA transmission in the mouse VSM, we shed light on the profile of horizontal nystagmus during pseudo-OVAR after baclofen administration. In primates, the horizontal nystagmus of OVAR and the prolonged time constant of the aVOR both disappear without affecting the direct aVOR pathways when the VSM is inactivated by midline section between the vestibular nuclei or systemic administration of baclofen [14,57–60]. In addition, ablation of nodulus/uvula is also known to decrease the horizontal nystagmus during OVAR [44].
The Vestibular System
2012, The Human Nervous System, Third EditionSpatio-temporal pattern of vestibular information processing after brief caloric stimulation
2009, European Journal of RadiologyCitation Excerpt :This mechanism is well known in the clinical practice as the velocity storage mechanism [18] that extends or perseverates the vestibular response over time when the stimulus has ceased, thus improving the ability of vestibulo-ocular reflex. In the brainstem, the central portion of both medial vestibular nucleus and commissure are considered crucial for the velocity storage mechanism [19,20]. This mechanism is also controlled by cerebellar nodulus and uvula [21–23] and by cervical input [24].
The systemic application of diazepam facilitates the reacquisition of a well-balanced vestibular function in a unilateral vestibular re-input model with intracochlear tetrodotoxin infusion using an osmotic pump
2006, Brain ResearchCitation Excerpt :We often clinically use the head-shaking test to observe the presence of any after shaking nystagmus as semicircular canal stimulus was done as one of the vestibular function tests (Takahashi et al., 1990; Katsarkas et al., 2000; Guidetti et al., 2002; Pérez Vazquez et al., 2004). When vestibular function asymmetry existed, semicircular canal stimulus by shaking the head accumulated on the vestibular commissure (Holstein et al., 1999). Head-shaking nystagmus, namely nystagmus toward the contralesional side, was observed after shaking the head by discharging the accumulated velocity that is known to be a velocity storage mechanism (Raphan et al., 1979; Hain et al., 1987).