Three sets of studies are proposed to continue the investigator's research program on the prenatal development of the mammalian visual system. In the next 5-year period he will focus on the normal ontogeny of retinal ganglion cells and their projection patterns. In the first set of studies, he will employ immunocytochemical 1methods to identify the cytochemical properties of retinal ganglion cells in the adult retina and to determine how these properties develop in the prenatal 1and postnatal retina. In particular, he will focus on two neuropeptides (somatostatin and neuropeptide Y) that he has found to be contained in distinct subgroups of ganglion cells in the mature retina. The terminal labeling patterns of these immunoreactive neurons within retinorecipient nuclei will also be examined at maturity and during development. His preliminary results indicate that the use of specific antibodies to study cytochemically identified groups of ganglion cells may reveal developmental patterns that could not be discerned by relying solely on anatomical methods. In another set of studies he will investigate the establishment of excitable membrane properties in fetal ganglion cells. The whole-cell patch clamp recording technique will be used to determine how the development of functional properties in retinal ganglion cells relates to the spatiotemporal development of the retina and to the refinements of retinal projection patterns documented by anatomical studies. These studies will be carried out using the isolated cell preparation. He will also set up a retinal slice preparation to examine the relationship between the structural and physiological development of the main classes of retinal ganglion cells. The third set of studies deals with topographic organization of the early crossed and uncrossed retinocollicular pathways. Based on his previous work on this system in the prenatal cat, he has delineated three alternative models that could characterize early topography. Focal retinal injections of the axon tracer DiI will be used to assess which of these models is valid. The results of this research program would increase the understanding of the events underlying the organization and the normal development of the mammalian visual system.