Developmental patterning of glutamatergic synapses onto retinal ganglion cells.
BACKGROUND
Neurons receive excitatory synaptic inputs that are distributed across their dendritic arbors at densities and with spatial patterns that influence their output. How specific synaptic distributions are attained during development is not well understood. The distribution of glutamatergic inputs across the dendritic arbors of mammalian retinal ganglion cells (RGCs) has long been correlated to the spatial receptive field profiles of these neurons. Thus, determining how glutamatergic inputs are patterned onto RGC dendritic arbors during development could provide insight into the cellular mechanisms that shape their functional receptive fields.


RESULTS
We transfected developing and mature mouse RGCs with plasmids encoding fluorescent proteins that label their dendrites and glutamatergic postsynaptic sites. We found that as dendritic density (dendritic length per unit area of dendritic field) decreases with maturation, the density of synapses along the dendrites increases. These changes appear coordinated such that RGCs attain the mature average density of postsynaptic sites per unit area (areal density) by the time synaptic function emerges. Furthermore, stereotypic centro-peripheral gradients in the areal density of synapses across the arbor of RGCs are established at an early developmental stage.


CONCLUSIONS
The spatial pattern of glutamatergic inputs onto RGCs arises early in synaptogenesis despite ensuing reorganization of dendritic structure. We raise the possibility that these early patterns of synaptic distributions may arise from constraints placed on the number of contacts presynaptic neurons are able to make with the RGCs.
Morgan
Josh L
JL
Department of Biological Structure, University of Washington, Seattle, WA 98195, USA. j37@u.washington.edu
Schubert
Timm
T
Wong
Rachel O L
RO
D000818:Animals; D015415:Biomarkers; D003712:Dendrites / Q000502:physiology; D000076122:Disks Large Homolog 4 Protein; D019706:Excitatory Postsynaptic Potentials / Q000502:physiology; D018698:Glutamic Acid / Q000502:physiology*; D051528:Guanylate Kinases; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics; D008164:Luminescent Proteins / Q000235:genetics; D008565:Membrane Proteins / Q000235:genetics; D051379:Mice; D008810:Mice, Inbred C57BL; D018408:Patch-Clamp Techniques; D012160:Retina / Q000166:cytology* / Q000196:embryology* / Q000502:physiology; D012165:Retinal Ganglion Cells / Q000502:physiology* / Q000648:ultrastructure; D013569:Synapses / Q000502:physiology*; D009435:Synaptic Transmission / Q000502:physiology; D014162:Transfection
D015415:Biomarkers; D000076122:Disks Large Homolog 4 Protein; C501447:Dlg4 protein, mouse; D047908:Intracellular Signaling Peptides and Proteins; D008164:Luminescent Proteins; D008565:Membrane Proteins; D018698:Glutamic Acid; D051528:Guanylate Kinases