Abstract
Excitatory glutamatergic inputs from bipolar cells in part define the physiological properties of retinal ganglion cells. In this study, we investigate the distribution of excitatory synapses on various types of mouse retinal ganglion cells, by randomly transfecting cells with PSD95-GFP plasmids. Despite wide variation in the size and morphology of retinal ganglion cells, the expression of PSD95 puncta follows two general rules: (1) The PSD95 puncta are regularly spaced, in 1-2 μm interval, on local dendritic segments. Thus, the presence of an excitatory synapse creates an exclusion zone that rules out the presence of other synaptic inputs. (2) The spatial distribution of PSD95 puncta in a two-dimensional space is similar for most cell types. The excitatory synapses on primary dendrites are much less, and the density of excitatory inputs peaks at the edge of cell’s dendritic field. Mapping the distribution of synapses on retinal ganglion cells provides explicit structure information that facilitates the understanding of how distribution and localization of excitatory inhibitory inputs shape neuron’s responses.