Synaptic Input Patterns from the Superior Colliculus to Vertical Eye Movement-Motoneurons in the Cat

Yuji Sasaki, Hiromi Matsui and Akihiko Tamai

Department of Ophthalmology, Faculty of Medicine, Tottori University, Yonago 683, Japan

The superior colliculus (SC) is known to play an important role in the transformation from visual and auditory signals to motor commands to generate saccadic eye movements toward the targets. This study investigated the synaptic input patterns into vertical eye movement-related superior and inferior rectus motoneurons from the SC, using the 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 potential (EPSP), di- or trisynaptic EPSP or inhibitory postsynaptic potential (IPSP) and polysynaptic EPSP. Amplitudes of the latter 2 components nearly 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. Therefore, it is concluded that the SC elicits vertical eye movements through these di- or trisynaptic and polysynaptic pathways in the cat.

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