Retinal ganglion cells (GCs) integrate excitatory and inhibitory inputs and perform computations that encode diverse features of the visual scene. The output of these functionally and morphologically diverse GCs establish visual signaling streams, maintained throughout the visual pathway. Ultimately, they create our perception of the size, shape and color of objects and their relationships in space. They establish relationships of objects in time, so that we know when it is stationary or moving, and when moving, its direction and velocity. To this end, there is a general division of labor between the retina's inhibitory neurotransmitter systems. GABA, and its receptors, modulate spatial vision, whereas glycine, and its receptors, modulate temporal vision. There are five glycine receptor subunits (one ? and 4?s). The GlyR? subunits combine with a single ? subunit to make functional receptors with diverse biophysical properties. Our work shows that all GCs expresses one or more GlyR??s and the composition differs across GC type. We hypothesize that variety enhances the diversity of inhibitory functions across and within GC types and are used to encode the visual scene. However, the specific function of GlyR? subunits is almost completely unknown. We know that the responses (and transmitter release) of the GABA and glycinergic amacrine cells presynaptic to GCs are modulated by other glycinergic amacrine cell input. This means that until GlyRs can be selectively eliminated in GCs or ACs, we cannot disambiguate the role of direct GlyR? inhibition to GCs from GlyR? modulation in the upstream circuit that provides input to the GCs. We developed a novel AAV-shRNA knockdown (KD) approach that eliminates expression of individual G lyR? subunits in GCs, while leaving their upstream expression intact. We propose to use this approach to define the role of GlyR? direct inhibition in 7 identified GC types and by extension the role of isolated GABA inputs in those same GCs.
In Aim 1 we ask if a single GlyR?, GlyR?1 expressed by the 4 functionally diverse ?GCs modulates the same or different aspects of their visual responses.
In aim 2 we ask if two different GlyR? subunits, expressed in the same GC, increase the diversity of inhibition to modulate different aspects of the visual response in a single GC type. We use electrophysiological assays to characterize the spiking responses of the GCs, underlying currents and the relationships between the kinetics of excitatory and inhibitory input with the postsynaptic response. This proposal addresses the novel concept: that diverse glycine subunit specific inhibition interacts with presynaptic inputs to controls visual computation.
The visual scene contains multiple streams of information that are efficiently processed and categorized by the retina. The spatio-temporal responses of GCs require the correct integration of bipolar cell excitatory and amacrine cell inhibitory inputs to GC. This project will define how diverse inhibitory inputs are shaped and how they are matched with excitation, which results in the accurate representation of the visual scene that is proved by the retina to the rest of the central nervous system.
