Our major long-term objective is to understand the synaptic connections of the neurons that underly complex visual functions such as color vision, directional selectivity and orientation specificity in the vertebrate retina. For this purpose the turtle retina is particularly advantageous because a) the spectral types of cone can be recognized on morphological criteria so that chromatic wiring to second order neurons can be readily studied, and 2) the retina with its linear visual streak organization is particularly specialized for motion and orientation detection. Moreover, the turtle retina has been a favorite experimental retina for electrophysiologists because stable long-term intracellular recordings are possible from all the retinal neurons with subsequent marking of the neurons with HRP for anatomical investigations. Using anatomical techniques of studying serial semi-thin and ultrathin sections for electron microscopy (EM) and reconstructing neurons and portions of the neuropil we intend to: 1) determine the arrangement and ultrastructural characteristics of the various spectral types of cone pedicle in the outer plexiform layer with particular emphasis on the blue and ultraviolet sensitive cone pedicles. 2) Subsequently we will determine the chromatic input to C-type horizontal cells and the unknown H4 type of the turtle retina and various bipolar cell types. 4) In addition we will determine the connections of the Golgi-- stained centrifugal bipolar in the OPL to see whether this cell might be an interplexiform cell. 5) Using immunocytochemical staining of bipolar cells we will study which chromatic type they might be and study their output to amacrine and ganglion cells in the inner plexifonil layer. Simultaneously we will continue examining HRP-marked and physiologically -identified 6) amacrine and 7) ganglion cells for synaptology of their inputs and outputs. We will concentrate particularly on color-coded and directionally-selective and motion-sensitive amacrine and ganglion cells. We will use EM immunocytochemistry in combination with serial section EM to determine what the neurotransmitter specific input and output neurons might be that are involved with these HRP-marked amacrine and ganglion cells. Finally we will determine the synaptic circuitry of substance P amacrine and ganglion cells as well as attempt to discover which ganglion cell types these might be, by double labeling of retrogradely rhodamine-bead labeled ganglion cells.
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