The long term goal of this research is to understand the cellular interactions that produce mapped projections and intraocular segregation within the vertebrate visual pathway. When a third eye primordium is implanted in a frog embryo two retinas coinnervate one optic tectum and transform the normal continuous map into a retina-specific striped pattern similar to the occular dominance columns of mammals. This segregation is not maintained when retinal ganglion cell activity is blocked by tetrodotoxin but little is known about the role played by tectal neurons in this activity-dependent segregation process. The first specific aim of this project is to define the relationship of tectal cells or circuits to stripes identified in the fixed or the living tadpole brain using the anterograde transport of tetra-methylrhodamin isothiocyanate (TRITC). Retinal versus tectal cell response properties in relation to TRITC labeled stripes will be studied electrophysiologically. The morphology of tectal cells in relation to labeled stripes will also be studied with intracellular lucifer yellow fills and horseradish peroxidase. These cells will be classified using double-label techniques (retrograde transport of fluorescent beads from projection zones and immunocytochemistry with transmitter-related antibodies). A second specific aim is to develop immunological tags that will allow identification of different classes of tectal cells outside of their normal context (e.g. in striped tecta, in undifferentiated caudal tecta, and ultimately in tissue culture). These studies will also use double-label techniques. In addition they will include a focused effort to make tectal cell-type specific monoclonal antibodies. This research capitalizes on the accessible and malleable amphibian embryo and tadpole. Nevertheless the activity-dependent mechanisms of competition and map fidelity that they address are likely to be conserved across all vertebrates. Therefore, principles established in this model system should generalize to higher vertebrates where they can be used in formulating clinical treatments that minimize the long term effects of such early ocular dysfunctions as aphakia and strabismus in man himself.
