Synaptic inputs from superior colliculus to vertical eye movement motoneurons in the cat.

The superior colliculus (SC) plays an important role in the transformation of visual and auditory signals into motor commands to generate saccadic eye movements toward the targets. This study investigated the synaptic input patterns from the SC, into vertical eye movement-related superior and inferior rectus motoneurons, using intracellular recording and SC stimulating techniques in anesthetized adult cats. It was found that the responses obtained from these motoneurons consisted of complex components: a sequence of monosynaptic excitatory postsynaptic potentials (EPSPs), di- or trisynaptic EPSPs or inhibitory postsynaptic potentials (IPSPs) and polysynaptic EPSPs. The amplitudes of the latter two components almost coincided with the motor map of the SC, which represented the correlation between the sites of SC stimulation and the directions and amplitudes of evoked saccades. It was concluded that the SC elicits vertical eye movements through these di- or trisynaptic and polysynaptic pathways in the cat.