Determining the role of pre-synaptic NMDA Receptors in topographic map formation

Efficient processing of sensory information is a critical function of the nervous system. Deficits in sensory processing and integration are commonly seen in neurodevelopmental disorders such as autism. In the visual system, neurons are often organized topographically, such that neighboring neurons monitor adjacent regions of space. Retinal ganglion cells (RGCs) project topographically to the superior colliculus (SC) and dorsal lateral geniculate nucleus (dLGN). During development, spontaneous correlated activity is critical for the establishment of topography in both the SC and dLGN. However, the mechanisms by which activity mediates topographic map formation remain unclear. Previous studies suggest that N-methyl-D-aspartate receptors (NMDARs) play a critical role in the establishment of topography by RGCs, however, it remains unclear if they are required both pre- and post-synaptically. To determine the role of pre-synaptic NMDARs in the development of topography, we used a conditional genetic strategy to specifically ablate NMDAR function in RGCs. We focally labeled RGCs and visualized the termination zone (TZ) of their projections in the SC and dLGN. Our preliminary data suggests that there was no change in TZ size in the SC, but TZs appeared to be larger in the dLGN. Bulk labeling of all RGCs in both eyes showed that eye-specific lamination was similar to controls, suggesting this activity-dependent process is unaffected in the absence of pre-synaptic NMDARs. Together, these data suggest that pre-synaptic NMDARs may play a critical role in retinogeniculate map formation but not in retinocollicular map formation