ANATOMICAL CONNECTIONS OF THE PRIMATE PRETECTAL NUCLEUS OF THE OPTIC TRACT

The pretectal nucleus of the optic tract (NOT) plays an essential role in optokinetic nystagmus, the reflexive movements of the eyes to moti on of the entire visual scene. To determine how the NOT can influence structures that move the eyes, we injected it with lectin-conjugated h orseradish peroxidase and characterized its afferent and efferent conn ections. The NOT sent its heaviest projection to the caudal half of th e ipsilateral dorsal cap of Kooy in the inferior olive. The rostral do rsal cap was free of labeling. The NOT sent lighter, but consistent, p rojections to other visual and oculomotor-related areas including, fro m rostral to caudal, the ipsilateral pregeniculate nucleus, the contra lateral NOT,the lateral and medial terminal nuclei of the accessory op tic system bilaterally, the ipsilateral dorsolateral pontine nucleus, the ipsilateral nucleus prepositus hypoglossi, and the ipsilateral med ial vestibular nucleus. The NOT received input from the contralateral NOT, the lateral terminal nuclei bilaterally, and the ipsilateral preg eniculate nucleus. Although our injections involved the pretectal oliv ary nucleus (PON), there was neither orthograde nor retrograde labelin g in the contralateral PON. Our results indicate that the NOT can infl uence brainstem preoculomotor pathways both directly through the media l vestibular nucleus and nucleus prepositus hypoglossi and indirectly through both climbing and messy fiber pathways to the cerebellar flocc ulus. In addition, the NOT communicates strongly with other retino-rec ipient zones, whose neurons are driven by either horizontal (contralat eral NOT) or vertical (medial and lateral terminal nuclei) fullfield i mage motion. (C) 1994 Wiley-Liss, Inc.