Selective elimination of specific classes of retinal ganglion cells can provide a new way to study the function and central organization of the information processing channels that begin with the X, Y and W ganglion cells in the retina. The proposed pilot studies are designed to achieve this by developing a new technique based on the selectivity of the central projections of these ganglion cell classes, and the potolytic potential of fluorescent dyes. A two stage process is proposed in which a retrogradely transported fluorescent dye is injected into the superior colliculus, and labeled cells in the retina are selectively destroyed by subsequent irradiation of the eye with ultra violet (UV) light. Photolysis has been used successfully in the past to destroy single cells by UV irradiation of paramecia that contain photodynamic substances. The effectiveness of this method depends on the production of free oxygen radicals during fluorescence that disrupt the genetic machinery of the cell. The first aim of the proposed research is to identify (or develop) a retrogradely transported fluorescent dye that has such photodynamic qualities. The second is to determine whether the use of such a dye can eliminate specific classes of retinal ganglion cells. The photodynamic potential of a variety of fluorescent dyes will be tested in the mouse retino-tectal system. Once the optimal tracer and basic parameters for this method have been determined, it selectivity will be tested in the retino-tectal system of the cat by previously established electrophysiological and morphological criteria.