Convergence of posterior semicircular canal and saccular inputs in single vestibular nuclei neurons in cats

Convegnence between posterior canal (PC) and saccular (SAC) inputs in singl e vestibular nuclei neurons was investigated in decerebrated cats. Postsyn aptic potentials were recorded intracellularly after selective stimulation of the SAC and PC nerves. Stimulation of either the SAC or PC nerve orthodr omically activated 143 vestibular nuclei neurons. Of these, 61 (43%) were a ntidromically activated by stimulation of the C1-C2 junction, 14 (10%) were antidromically activated by stimulation of the oculomotor or trochlear nuc leus, and 14 (10%) were antidromically activated by stimulation of both the oculomotor or trochlear nucleus and the spinal cord. Fifty-four (38%) neur ons were not activated by stimulation of either or both. We named these neu rons vestibulospinal (VS), vestibulo-ocular (VO), vestibulo-oculo-spinal (V OS) and vestibular (V) neurons, respectively. Both PC and SAC inputs conver ged in 47 vestibular nuclei neurons (26 VS, 2 VO, 6 VOS and 13 V neurons). Of these, 19 received monosynaptic excitatory inputs from both nerves. This input pattern was frequently seen in VS neurons. Approximately half of the convergent VS neurons descended to the spinal cord through the lateral ves tibulospinal tract. The remaining half and all the convergent VOS neurons d escended to the spinal cord through the medial vestibulospinal tract. Most of the convergent neurons were located in the lateral nucleus or descending nucleus. (C) Springer-Verlag 2000.