UTRICULAR INPUT TO CAT EXTRAOCULAR MOTONEURONS

Intracellular recordings from 200 identified extraocular motoneurons i n the bilateral III, IV and VI cranial nuclei were studied to determin e the connectivities between the utricular nerve and the extraocular m otoneurons in cats. Stimulating electrodes were placed within the left utricular nerve, while other branches of the vestibular nerve were re moved. Monosynaptic and disynaptic connections between the utricular n erve and the ipsilateral abducens motoneurons and interneurons were re corded as described previously. Stimulation of the utricular nerve evo ked longer latency depolarizing and hyperpolarizing potentials in cont ra- and ipsilateral medial rectus motoneurons, respectively. Depolariz ing and hyperpolarizing potentials with longer latencies were also rec orded in the ipsilateral inferior oblique and contralateral trochlear motoneurons. The short and longer latency circuits between the utricul ar nerve and extraocular motoneurons may play a role in stabilizing th e retinal image during head tilt and horizontal linear acceleration.