Descending pathways of the nucleus of the optic tract in the rat.

The descending pathways of the nucleus of the optic tract (pars lateralis) (NOTL) in the rat were examined in Nauta-Gygax impregnated sections and further confirmed by the horseradish peroxidase labeling technique. Following stereotactic lesions in the NOTL, visual cortex, and superior colliculus, projections which orginate in the NOTL were identified by elimination of the tectofugal and tectopetal fibers of the superior colliculus. The descending fibers from the NOTL appeared to be organized into three bundles. (1) The NOTL-contralateral NOTL fibers, which connect bilateral NOTLs through a part of the posterior commissure. (2) The NOTL-nucleus tegmenti pontis and inferior olivary nucleus fibers, which project to the ventromedial part of the nucleus tegmenti pontis and the dorsal cap of the inferior olivary nucleus, ipsilaterally to the NOTL. (3) The NOTL-pontine nuclei fibers, which terminate within the medial one-third of the pars lateralis of the ipsilateral pontine nuclei with topical relations.