Developmental patterning of glutamatergic synapses onto retinal ganglion cells

Additional file 1:

Connectivity with bipolar cells shapes excitatory center of RGC receptive fields. (a) The lateral extent of the RGC dendritic arbor and its connectivity with bipolar cell axon terminals largely determines the region of visual space sampled by the RGC. Blue rectangle indicates the lateral extent of the receptive field center for RGC in white (G). P, cone photoreceptors; B, bipolar cells. IPL, inner plexiform layer. (b) The number of synapses (red dots) per unit area of retinal surface between a RGC and the mosaic of bipolar cell axons (shaded polygons) varies across the dendritic field of large-field RGCs. Blue outline denotes the extent of the receptive field center of this RGC. (c-f) Centro-peripheral gradients in the density of connections between a RGC and the mosiac of bipolar cell axon terminals contributes to RGC receptive fields that are more sensitive to a visual stimulus at their centers. (c) Representation of the gaussian-like receptive fields of individual BCs (red and green) in the background of the receptive fields of the population of BCs of the same subtype. Each receptive field reflects the sensitivity of a given BC to the region of visual space represented along the x-axis. (d) The number of BC inputs (y-axis) onto a single RGC at different regions of its dendritic field (x-axis). Synaptic density is highest at the center of the RGC dendritic field. Alternating gray and white bars indicate the axonal territories of adjacent bipolar cells. (e) The relative weighting of bipolar cell receptive fields by a RGC with the connectivity pattern shown in (d). (f) Excitatory receptive field of the RGC calculated by summing the weighted receptive fields in (e). (c-f) Adapted from [12].

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Additional file 2:

RGC rotation. Rotation of the P7 bistratified RGC shown in Figure 1.

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Additional file 3:

PSD95-YFP puncta on primary dendrites of RGCs. PSD95-YFP puncta are found on primary dendrites of (a, b) some, but (c) not all OFF RGCs. This is particularly apparent in the orthogonal rotations of the image stack (right panels).

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Additional file 4:

P22 RGC with a large dendritic arbor in the ON sublamina and a small dendritic arbor stratifying within the OFF sublamina. PSD95-YFP puncta are restricted to the two sublaminae within the IPL at which dendrites stratify. Note the absence of PSD95-YFP puncta within the dendritic segment traversing the two sublaminae.

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Additional file 5:

Comparison of ON and OFF monostratified cells across development. (a-c) Average dendritic and puncta densities for monostratified RGCs. ON cells are shown in green. OFF cells are shown in red. Error bars = standard error of mean. An asterisk indicates a significant difference between ON and OFF cells. (d-f) Ratio of dendritic and puncta densities of the inner half of the dendritic arbor divided by the outer half.

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Additional file 6:

Potential relationship between RGC tiling and centro-peripheral gradient in BC synaptic distribution across the RGC arbor. (a) Schematic of the cellular mosaic formed by a single type of RGC in which dendritic territories overlap in the periphery but not the center of each dendritic field. (b) Illustration of how lower areal densities of synapses (red dots) in the periphery of the RGC dendritic arbor might be the result of dendritic competition for presynaptic contacts. Blue circles represent the lateral spread of an individual BC axonal arbor. BCs in the periphery of an RGC dendritic arbor are more likely to divide their inputs between dendrites of neighboring RGCs of the same subtype. Asterisk indicates soma.

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Additional file 7:

Two dimensional representation of the skeletonization algorithm used to measure the length of dendrites. The red fields represent dendritic segments. A seed pixel (first blue dot) is chosen at an extreme edge of the object. This pixel initiates a wave of activated pixels (green bar) that spreads throughout the object. The mean positions of the wave at each step are connected to generate a skeleton. The number of nodes in the skeleton is subsequently reduced to reduce noise.

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