The goal of the research is to understand inhibitory synaptic circuitry in the retina that is mediated by a bipolar cell subtype which may be GABAergic. The hypothesis to be addressed is that the four subtypes of GABAergic bipolar cells comprise a single functional unit that synapses upon one type of ganglion cell, the small-simple/ON-OFF type, that is stratified throughout the full thickness of the IPL. Post-embedding electron microscopic immunocytochemistry and whole-cell patch-clamp recording techniques will be used to explore the synaptic circuitry and function of these GABAergic bipolar cells. To this means the study will: (1) characterize the morphology of ganglion cells that demonstrate IPSCs elicited directly by the bipolar cells, followed by labeling with horseradish peroxidase (HRP)/rhodamine for light microscopy and post-embedding immunocytochemical electron microscopy; (2) determine the temporal response properties of the cells by current injection and the polarity of the response type of the filled cells by its dendritic stratification within the IPL; and (3) determine the synaptic organization of the HRP-filled ganglion cells with respect to input from GABA-immunoreactive and non-GABA-immunoreactive bipolar cells, as well as the GABAergic and non-GABAergic amacrine cells.