The inner retina is a major site of neuronal processing in the visual system. Here, among a host of amacrine cells, ganglion cell receptive fields are formed, rod and cone pathways merge into one output, and other neurons respond selectively to directional stimuli. Bipolar cells are the principle elements which transmit visual activity from photoreceptors to the inner retina, but neither the identify of the bipolar cell transmitter, nor the output sign have been established. The PI proposes to investigate neuronal circuits in the inner retina using an integrated approach which includes: i) a study of ACh and glycine release to investigate the inputs to cholinergic and glycinergic amacrine cells. ii) extracellular and intracellular recording from the rabbit retina to investigate the function of post-synaptic glutamate recetors. iii) extracellular recording in the primate (monkey or baboon) retina to investigate colour vision and iv) intracellular staining and recording under microscope control. The last technique provides a method to record and stain identified neurons in the living retina, such as the cholinergic amacrine cells. This will simplify the analysis of the mechanism underlying directional selectivity. Glycine, an inhibitory transmitter is found in some bipolar cell which are thought to be excitatory. This anomaly may be explained by the study of dye coupling between glycinergic AII amacrine cells and bipolar cells. Since the gap junctions between these cells are a major site of rod input to cone pathways, the control of gap junction conductance by the dopaminergic cell A18 may act as a switch between rod and cone vision. By dual recordings, the PI will test to see if bipolar cells are inhibitory or excitatory and a pharmacological analysis will be performed to identify the bipolar cell transmitter. The goal of this proposal is to identify the neurons and transmitters of major circuits in the inner retina.
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