Study on output mechanism from the superior colliculus concerning vertical saccadic eye movement.

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(1) Anatomical identification of supranuclear gaze center of vertical eye movement.Distribution of premotor neurons projecting to motoneurons concerning vertical eye movements was investigated. In anesthetized cats with Nembutal, wheat germ agglutinin conjutated to horseradish peroxidase (WGA-HRP) was injected into the nerves of the eye muscles which concern vertical eye movements. WGA-HRP was taken up by motor axons and retorogradely transported to their cell bodies. It was further taken up by synaptic terminals of premotor neurons terminating on those motoneurons and their cell bodies were transsynaptically labeled. This study revealed that the last-order premotor neurons were located in the field of Forel, the interstitial nucleus of Cajal, and the vestibular nuclei, and the distribution of such neurons were analyzed.(2) Identification of location of output neurons of the superior colliculus which produce upward and downward eye movements.After identifiying the location in the superior colliculus from which evoke upward or downward eye movement was evoked by electrical stimulation, biocytin (anterograde tracer) was injected into the superior colliculus and projections from the superior colliculus to the brain stem structure were investigated.(3) Identification of projection from the superior colliculus to supuranuclear neurons using a double labeling technique.Injection of biocytin into the superior colliculus using the mothod mentioned in (2) and injection of WGA-HRP into the muscle nerves using the method mentioned in (1) were performed in the same animal. This study enabled us to identify the last order premotor neurons receiving input from the superior colliculus and terminating on ocular motoneurons.