Maureen A. McCall, Professor and Kentucky Lions Eye Research Endowed Chair, at University of Louisville will be delivering a seminar on “Diverse Glycinergic Receptor Subunits & Retinal Ganglion Cell Visual Function” on Wednesday, March 21st at 12:00 Noon in the Moran Eye Center auditorium.
Abstract: In the retina excitatory signaling lays down the basic foundation of visual processing and inhibition shapes excitation to produce the diverse visual responses of its almost 40 different ganglion cell types. Much of inhibition occurs from the inputs of the ~50 amacrine cells (ACs). Approximately half of these amacrine cells are GABAergic and the others are glycinergic. This is unlike the rest of the CNS, where either GABA or glycine is the primary inhibitory neurotransmitter and there are fewer interneurons. AC inputs mediate feedforward, feedback, crossover and serial inhibition that ultimately shape the excitatory output of bipolar cells (BCs), as well as the responses of GCs. In general, GABA inhibition refines spatial responses (object size, shape and location in space and direction of object motion and glycine inhibition shapes temporal responses (object motion and velocity, and the timing of responses to standing contrast. This is a simplistic view, belied by recent studies suggesting that each AC type may uniquely shape visual function and by extension must be crucial to mechanisms that control the diversity of visual responses of the ~40 GC types that form parallel processing channels and establish the framework for all subsequent vision. We know from BCs that inhibitory diversity is enhanced by expression of different inhibitory subunits with different deactivation kinetics, e.g., GABAA, GABAC and. A role for GlyRα subunit diversity is clear in both spinal cord and brainstem, where individual.
GlyRαs create a variety of synaptic interactions to tune the postsynaptic response and modulate different functions15-17. Because the retina has a wider diversity of interneurons (ACs), and it is the only structure that expresses all 4 GlyRα subunits, in addition to GABARs, we hypothesize that this variety contributes substantially to GC visual function. I will discuss the distribution and function of glycinergic receptor isoforms across the retina and retinal ganglion cells. I will describe what we have found about the roles of glycine subunit specific inhibition in shaping the visual responses of retinal ganglion cells.