EFFERENT PATHWAYS OF THE NUCLEUS OF THE OPTIC TRACT IN MONKEY AND THEIR ROLE IN EYE-MOVEMENTS

To clarify the role of the pretectal nucleus of the optic tract (NOT) in ocular following, we traced NOT efferents with tritiated leucine in the monkey and identified the cell groups they targeted. Strong local projections from the NOT were demonstrated to the superior colliculus and the dorsal terminal nucleus bilaterally and to the contralateral NOT. The contralateral oculomotor complex, including motoneurons (C-gr oup) and subdivisions of the Edinger-Westphal complex, also received i nputs. NOT efferents terminated in all accessory optic nuclei (AON) ip silaterally; contralateral AON projections arose from the pretectal ol ivary nucleus embedded in the NOT. Descending pathways contacted prece rebellar nuclei: the dorsolateral and dorsomedial pontine nuclei, the nucleus reticularis tegmenti pontis, and the inferior olive. Direct pr ojections from NOT to the ipsilateral nucleus prepositus hypoglossi (p pH) appeared to be weak, but retrograde tracer injections into rostral ppH verified this projection; furthermore, the injections demonstrate d that AON efferents also enter this area. Efferents from the NOT also targeted ascending reticular networks from the pedunculopontine tegme ntal nucleus and the locus coeruleus. Rostrally, NOT projections inclu ded the magnocellular layers of the lateral geniculate nucleus (Ign); the pregeniculate, peripeduncular, and thalamic reticular nuclei; and the pulvinar, the zona incerta, the mesencephalic reticular formation, the intralaminar thalamic nuclei, and the hypothalamus. The NOT could generate optokinetic nystagmus through projections to the AON, the pp H, and the precerebellar nuclei. However, NOT also projects to structu res controlling saccades, ocular pursuit, the near response, Ign motio n sensitivity, visual attention, vigilance, and gain modification of t he vestibule-ocular reflex. Any hypothesis on the function of NOT must take into account its connectivity to all of these visuomotor structu res. (C) 1996 Wiley-Liss, Inc.