INPUT TO THE PRIMATE FRONTAL EYE FIELD FROM THE SUBSTANTIA-NIGRA, SUPERIOR COLLICULUS, AND DENTATE NUCLEUS DEMONSTRATED BY TRANSNEURONAL TRANSPORT

The purpose of these experiments was to study the subcortical input to the frontal eye field (FEF) and to determine which subcortical struct ures might project to the FEF via pathways that contain only a single intervening synapse. We used retrograde transneuronal transport of her pes simplex virus type 1 (HSV-1) to label second-order neurons that se nd information to the FEF of cebus monkeys. The saccade region of the FEF was identified physiologically using intracortical stimulation and then injected with a strain of HSV-1 known to be transported transneu ronally in the retrograde direction. Retrograde transport of virus lab eled neurons was observed in all the thalamic sites known to innervate the FEF. In addition, we found neurons labeled by transneuronal trans port in three subcortical sites: the pars reticulata of the substantia nigra, the optic and intermediate gray layers of the superior collicu lus, and a posterior portion of the dentate nucleus of the cerebellum. Each of these sites has been shown in prior studies to project to tha lamic regions that innervate the FEF. Moreover, the neurons labeled th rough transneuronal transport were located in a subregion of each subc ortical site that is known to be involved in oculomotor control. These observations demonstrate that signals from the substantia nigra, supe rior colliculus and dentate nucleus can have a significant influence o n the output of the FEF.