Neuronal organization of the vestibulospinal system in the cat.

In the lateral and descending vestibular nucleus, vestibulospinal neurons were surveyed extra- and intracellularly in cats anesthetized with sodium pentobarbital. The neurons were investigated both by their antidromic activation from the spinal cord (C1, C4, T1, L1 and L5 spinal levels) and from the oculomotor nucleus region, and by orthodromic activation from the vestibular nerve. Axonal courses of vestibulospinal neurons were determined electrophysiologically at C1 level, as medial (MVST) or lateral (LVST). By single and the same electrodes a number of neurons were recorded in wide regions of the lateral and descending vestibular nucleus from single cats. Thus, it became possible to investigate somatotopical localization systematically for the first time with microelectrode techniques. Neurons of origin of the LVST were localized in the lateral vestibular nucleus. Second-order vestibular neurons were localized in the ventral region of the lateral vestibular nucleus, and in the rostral region of the descending vestibular nucleus. Many second-order, double discharge MVST neurons were identified in the descending and lateral vestibular nucleus. Somatotopical localization were recognized, but non-second-order cervical neurons were identified in the dorsal region, although second-order lumbar neurons were identified in the ventral region of the lateral vestibular nucleus. Specific modes of vestibular activation of these vestibulospinal neurons were discussed, and the vestibulospinal systems in the cat and rabbit were discussed.