NEURITIC SPECIFICITY IN RETINOTECTAL CO-CULTURES
SMALHEISER, NEIL RAYMOND
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Explants of fetal mouse retina and superior colliculus (tectum), alone or in co-culture, were characterized with extra-cellular electrophysiologic recordings, light microscopic examination of living culture arrays, and extracellular anterograde Golgi-like HRP injections. The in vitro retinotectal projections that formed were shown to possess four kinds of specificity characteristics of the projection in situ: (1) Longterm retinal ganglion-cell axon maintenance was dependent upon invasion of tectal explants. (2) Complex ramifications and functional terminal arborizations developed over the course of a month in vitro (3) Ingrowing retinal fibers preferred the superficial regions of the tectal explant. (4) An inappropriate source of neurites (from dorsal root ganglia) did not show extensive invasion, ramification, or terminal arborization within tectal explants; conversely, retinal fibers did not readily innervate an inappropriate target (the spinal cord). Initial tests to see if fibers from a nasal or temporal half-retina preferred specific anterior or posterior regions within a co-cultured whole tectum were encouraging. Retinotectal co-cultures offer a promising model system for exploring the cellular and molecular basis of specific neural connections in the developing CNS.