The long range objective of this research is to define the cellular interactions that establish the stereotypic patterning of vertebrate sensory pathways. Research during the proposed funding period will concentrate on the development of continuously ordered visual maps and periodic eye-specific afferent segregation within single topographically organized zones. Our work employs embryonic microsurgery to add a third eye primordium to the forebrain region of frog embryos. This forces two retinas to converge on an optic tectum where the normally continuous map from the contralateral eye invariably becomes disrupted into a pattern of eye-specific stripes that are similar to the naturally occurring ocular dominance columns of cat and primate brains. We will use tetrodotoxin silencing of one or both retinas in conjunction with horseradish peroxidase histochemistry, 3H-proline autoradiography and extracellular electrophysiological recordings to determine if neural activity in the afferents is a critical determinant of fine-tuning in normal retinotectal maps and of the eye-specific segregation when two retinas converge on a single tectal lobe. We will employ electromicroscopy to examine regulation of innervation density. Golgi techniques will be used to study the morphology and orientation of tectal neurons in order to determine if post-synaptic cells are aligned relative to the terminal bands produced upon double innervation. Finally, we will study the distribution of cells concentrating 3H gamma aminobutyric acid in normal and striped tectal lobes. We wish to know if inhibitory post-synaptic circuits are related either to orientation or periodicity of induced tectal stripes. The experiments we propose capitalize on the accessible and malleable amphibian embryo. Nevertheless, the mechanisms of intraocular competition and visual map fidelity which we address are likely to be conserved across all vertebrate species. We therefore believe that our results will generalize to higher vertebrates and that they will ultimately be applicable to developing clinical treatments that minimize the long term effects of early ocular dysfunctions such as aphakia and strabismus in man himself.
