Properties of a new vestibulospinal projection, the caudal vestibulospinal tract

Abstract

Neurons in the caudal portions of the medial and descending vestibular nuclei and in vestibular cell group f that project to the cervical or lumbar spinal cord were located by antidromic spinal stimulation. These caudal vestibulospinal tract (CVST) neurons have a median conduction velocity of 12 m/sec, which is well below the conduction velocities of typical lateral or medial vestibulospinal tract (LVST, MVST) axons. The descending fiber trajectories of CVST neurons, determined by comparing thresholds for activation of each neuron from six points in the spinal white matter, were remarkably diverse. Unlike LVST and MVST axons, which are located in the ipsilateral ventral funiculi, CVST axons can be found in both the ventral and dorsolateral funiculi on both sides of the spinal cord. The CVST system is thus both anatomically and physiologically different from the LVST and MVST.

Responses of caudal vestibular nucleus neurons of conscious cats to rotations in vertical planes, before and after a bilateral vestibular neurectomy

“…The CVN have functions in addition to autonomic regulation, as this region projects to the cerebellar nodulus and uvula (Epema et al 1985;Sato et al 1989;Thunnissen et al 1989;Barmack et al 1992) as well as to the dorsal horn of the upper cervical spinal cord (Peterson et al 1978;Bankoul et al 1995). The present data indicate that these areas mainly receive from the CVN relatively simple signals regarding head position or head velocity, at least during rotations in vertical planes.…”

“…Although the CVN do not play an appreciable direct role in mediating vestibulo-ocular reflexes (Wilson and Melvill Jones 1979), this region has been associated with several other functions. For example, a specialized projection to the upper cervical spinal cord arises from the CVN (Peterson et al 1978); this projection differs from the classical vestibulospinal tracts in that it terminates mainly in the dorsal horn (Bankoul et al 1995), and is presumably involved in modulating the processing of sensory signals from neck receptors. The CVN also provide considerable inputs to the cerebellar nodulus and uvula (Epema et al 1985;Sato et al 1989;Thunnissen et al 1989;Barmack et al 1992).…”

Development of the Vestibular System

“…The semicircular canal nerve makes inhibitory trisynaptic connections with some neck motoneurons through the LVST [114,115]. In addition, the caudal parts of the medial and spinal vestibular nuclei give rise to a third vestibulospinal projection, the caudal vestibulospinal tract [116]. The function of this pathway, which appears to project bilaterally to all levels of the spinal cord, is still unclear.…”

Neuronal loss in human medial vestibular nucleus

“…The main projections from the caudal part of the MVN innervate the cervical and thoracic spinal cord (Peterson et al, 1978), while those from the rostral part project to the oculomotor nuclei (McCrea et al, 1987). The MVN is also the origin of commissural fibers.…”