RETINAL PHARMACOLOGY OF DIRECTIONAL GANGLION CELLS

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Directionally sensitive (DS) retinal ganglion cells exist in most, if not all, vertebrate retinas. Yet little direct information is known about the retinal mechanism which generate directional sensitivity. This project proposes to study the DS cell and its amacrine cell inputs by use of intracellular and extracellular recording techniques and pharmacological manipulations. Using a superfused retinal eyecup of turtle and rabbit, the effects of synaptic transmitters/modulators and their antagonists can be tested on specific response properties of the DS cell. These results, coupled with the effects of the same agents in low Ca++/high Mg++ perfusate which blocks synaptic transmission, will determine whether certain synaptic interactions occur on the DS ganglion cell membrane. Information based on extracellular recordings and synaptic pharmacology indirectly suggests that several amacrine cell inputs to specialized regions of the ganglion cell membrane are responsible for directional sensitivity. In order to confirm the underlying wiring pattern of these DS cells, they will be stained by injection of intracellular dyes. Subsequent staining with histochemical markers for various amacrine cell naurotransmitters will visualize the interactions between these cells. Knowledge of the neural circuitry for DS cells in the mammalian retina may further the diagnostic usefulness of human optokinetic nystagmus since DS cells provide a major input to the accessory optic system which is responsible for such eye movements.