Utricular input to cat extraocular motoneurons

Intracellular recordings from 200 identified extraocular motoneurons in the bilateral III, IV and VI cranial nuclei were studied to determine the connectivities between the utricular nerve and the extraocular motoneurons in cats. Stimulating electrodes were placed within the left utricular nerve, while other branches of the vestibular nerve were removed. Monosynaptic and disynaptic connections between the utricular nerve and the ipsilateral abducens motoneurons and interneurons were recorded as described previously. Stimulation of the utricular nerve evoked longer latency depolarizing and hyperpolarizing potentials in contra- and ipsilateral medial rectus motoneurons, respectively. Depolarizing and hyperpolarizing potentials with longer latencies were also recorded in the ipsilateral inferior oblique and contralateral trochlear motoneurons. The short and longer latency circuits between the utricular nerve and extraocular motoneurons may play a role in stabilizing the retinal image during head tilt and horizontal linear acceleration.