The retinopetal system in the rat.

After horseradish peroxidase had been applied to the ends of the optic nerves of Sprague-Dawley rats that had been sectioned at their entry into the eyeball, retrogradely labelled neurons were found in the pretectal region (mostly in the contralateral medial pretectal area) and in the ventrolateral area of the contralateral central grey matter at the level of the mesencephalic-metencephalic junction. In some cases a few weakly labelled neurons were also observed in the oculomotor or trochlear nuclei. These findings confirm the existence of a retinopetal system in this mammal.