Retinal ganglion cells projecting to the nucleus of the optic tract in the rat.

The nucleus of the optic tract (NOT) has been identified as the link between the retina and the premotor nuclei in the pathway mediating the optokinetic nystagmus (OKN). However, it is still unclear from what parts of the retina and what kinds of retinal ganglion cells the NOT receives visual inputs related to OKN. In the present study, horseradish peroxidase conjugated with wheatgerm agglutinin (WGA-HRP) was injected into the NOT of hooded rats to investigate retrogradely labeled cells in the retina. A solution of WGA-HRP was injected into the NOT through a glass micropipette. Injection sites of the brain and the retina were processed by tetramethyl benzidine protocol and Hanker-Yates method. The labeled cells were observed in the whole area of the retina contralateral to the injection site, while located only in the ventral region of the retina ipsilateral to the injection site. In the retina contralateral to the injection site, a large number of small-sized cells and a few medium-sized cells were labeled diffusely except for surroundings of the optic disc, whereas in the ipsilateral retina there were small and medium-sized cells in the ventral part, being about 8 times greater than those in the contralateral retina. The present study indicates that visual signals responsible for OKN are conducted through the retinal ganglion cells mainly contralaterally, and only from the ventral area of the retina ipsilateral to the injection site.