The proposed experiments are aimed at morphological, functional and developmental characteristics of specific retinofugal projections, with particular emphasis on the partial crossings of these projections. We will pursue this goal in normal mice and in mice with abnormal bilateral projections--albinos and mice lacking one eye since birth. By injecting horseradish peroxidase (HRP) into the lateral geniculate nucleus, superior colliculus and suprachiasmatic nucleus we will identify the types of ganglion cells projecting to these targets, their distribution across the retina, and how contralaterally projecting cells compare to ipsilaterally projecting ones. Through HRP injections we hope to find out where displaced ganglion cells project to and where in the retina they presumably receive their input. By combining two retrograde markers, HRP and fluorescent dyes, we will search for ganglion cells supplying both the superior colliculus and the lateral geniculate nucleus, and for ganglion cells sending branches into both optic tracts. We wish to learn how common such bilateral branches are in normal mice and whether errors in bilateral branching are involved in the albino defect and in the abnormal projections following early eye removal. By following the course of labeled optic nerve fibers between the retina and optic targets we will examine their topographical arrangement. In albino mice we will search for fiber abnormalities in the optic chiasm. We will inject tritiated thymidine at times during the embryonic period, when ganglion cells are being formed, and later will correlate the time of ontogenetic appearance with the projection pattern of ganglion cells. We wish to learn whether ipsilaterally projecting ganglion cells differ from contralaterally projecting ones, and displaced ganglion cells from normally placed ones in ontogenetic age. From this we hope to obtain indications about the ontogenetic time when the albino defect is expressed. In eyeless mutant mice we will ask whether the map information in the tectum has to be imposed by retinal fibers or whether it will develop in total congential absence of eyes.
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