Identification of Synaptic Patterns of NMDA Receptor Subtypes Upon Direction-Selective Rabbit Retinal Ganglion Cells

Purpose: The objective of this study was to identify anisotropies that contribute to the directional preference of direction-selective retinal ganglion cells (DS RGCs) in the rabbit retina. We investigated the distributions of N-methyl-d-aspartate receptor 1 (NMDAR1), NMDAR2A and NMDAR2B receptor subunits in the dendritic arbors of rabbit DS RGCs. Methods: The distributions of the NMDAR subunits on the DS RGCs were determined using immunocytochemistry. DS RGCs were injected with Lucifer yellow, and the cells were identified by their characteristic morphology. The triple-labeled images of dendrites, kinesin II and NMDARs were visualized using confocal microscopy and were reconstructed from high-resolution confocal images. Results: We found no evidence of asymmetry in any of the NMDAR subunits examined on the dendritic arbors of both the ON and OFF layers of DS RGCs. Conclusions: Our results indicate that direction selectivity appears to lie in the neuronal circuitry afferent to the DS RGCs.