Properties of utricular and saccular nerve-activated vestibulocerebellar neurons in cats

Properties of otolith inputs to vestibulocerebellar neurons were investigat ed in 14 adult cats. In the vestibular nuclei, we recorded single-unit acti vities that responded orthodromically after stimulation of the utricular an d/or saccular nerves and antidromically after stimulation of the cerebellum (uvula-nodulus and anterior vermis). Descending axonal projections to the spinal cord were also examined by antidromic stimulation of the caudal end of the C1 segment. Forty-seven otolith-activated neurons that projected to the uvula-nodulus were recorded. Thirteen (28%) of the 47 neurons received convergent inputs from the utriculus and sacculus. The remaining 34 (72%) v estibular neurons were non-convergent neurons: 18 (38%) received utricular input alone, and 16 (34%) received saccular input alone. Most (35/47) vesti bulocerebellar neurons were located in the descending vestibular nucleus an d only one of these projected to the spinal cord. Seven of the 47 vestibulo cerebellar neurons were located in the lateral vestibular nucleus and most of these neurons projected to the spinal cord. The remaining neurons were l ocated in group X (two neurons) and the superior vestibular nucleus (three neurons). In a different series of experiments, 37 otolith-activated vestib ular neurons were tested to determine whether they projected to the uvula-n odulus and/or the anterior vermis. Nineteen of the 37 neurons projected to the anterior vermis, 13/37 projected to the uvula-nodulus, and 5/37 project ed to both. The utricular and/or saccular nerve-activated vestibulocerebell ar neurons projected to not only the uvula-nodulus, but also to the anterio r vermis. In summary, the results of this study showed that vestibular neur ons receiving inputs from the utriculus and/or sacculus projected to the ce rebellar cortex. This indirect otolith-cerebellar pathway terminated both i n the anterior lobe and in the uvula/nodulus.