The glycine receptor is a key inhibitory receptor in the retinal inner plexiform layer. It is found in ~ 40% of amacrine cells. Almost all retinal neurons express glycine receptors. Although glycine performs a number of roles in retina, there has not been a description of the different glycine receptors that may exist. This is in contrast to the two other main fast transmitters in retina, GABA and glutamate. Receptor subtypes for both of these neurotransmitters have been identified, extensively described, and shown to play key, distinct roles in retinal physiology. It is evident that the complexity of synaptic communication in retina is largely due to the diversity of GABA and glutamate receptor subtypes. The same level of complexity is not evident at the glycinergic synapse. A major limitation is that there is very little information about glycine receptor subtypes and poor tools to investigate it. The governing hypothesis of this proposal is that there are multiple glycine receptors in retina. The research plan will be to address the functional and pharmacological differences between glycine receptors in retina, correlating this with the properties of glycine subunits. It is known that at least three types of glycine receptor alpha subunit are expressed in retina and they have different distributions. This implies that there are functional differences between the subunits, warranting the anatomical segregation. This study's long term goal is to define the properties of glycine receptor subtypes as they relate to the function of the synapse and the physiology of vision. One motivation for this study is our finding that there are fast and slow glycine currents in ganglion cells, that these currents have different pharmacological properties, and that they are differentially regulated by second messenger pathways. This suggests that glycine receptor subtypes exist and that their properties are important in specific retinal functions. A first step in understanding glycine receptor diversity is to develop the tools to identify and characterize glycine receptor subtypes. This proposal will use biophysical, pharmacological, and molecular approaches to develop these tools. Two specific aims are to find agonists and antagonists that can distinguish between glycine receptor subtypes. Another is to characterize GABA receptor antagonists which interact with the glycine receptor. These specific aims are a necessary first step in unraveling inhibitory synapses in retina.