It is proposed to study the neurocircuitry of the outer and inner plexiform layers of the retina of the turtle by various light and electron microscope techniques. We wish to understand the morphological basis for functional pathways being described from intracellular physiological experiments. The turtle retina has advantages over other vertebrate retinas in that the spectral types of photoreceptors are morphologically identifiable and these and second order neurons have yielded nice intracellular recordings. Thus it is more feasible to unravel color coded pathways, ON and OFF center pathways, orientation and directionally selective pathways in the turtle retina than in any other vertebrate retina at present. Specifically we plan to a) characterize the cone photoreceptor type with the large clear, fluorescent oil droplet and determine its connections with other spectral types of cone in the OPL, b) determine which cone or rod photoreceptors are involved in the large gap junctions seen between telodendria in the neuropil of the OPL, c) determine the connectivity of H2, H3 and H4 horizontal cells with specific cone types, d) determine the spectral connections and exact morphology of the synapses of bipolars B1, B2 and B9 (the latter may be serotonergic and is of particular interest), e) begin a serial section EM study of the neuropil of the IPL in the visual streak with particular concentration on bipolar cell connectivity and f) study the type and distribution of synaptic inputs upon directionally selective and orientation selective ganglion cells.
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