Synaptic Convergence Patterns onto Retinal Ganglion Cells Are Preserved despite Topographic Variation in Pre- and Postsynaptic Territories.

Summary Sensory processing can be tuned by a neuron's integration area, the types of inputs, and the proportion and number of connections with those inputs. Integration areas often vary topographically to sample space differentially across regions. Here, we highlight two visual circuits in which topographic changes in the postsynaptic retinal ganglion cell (RGC) dendritic territories and their presynaptic bipolar cell (BC) axonal territories are either matched or unmatched. Despite this difference, in both circuits, the proportion of inputs from each BC type, i.e., synaptic convergence between specific BCs and RGCs, remained constant across varying dendritic territory sizes. Furthermore, synapse density between BCs and RGCs was invariant across topography. Our results demonstrate a wiring design, likely engaging homotypic axonal tiling of BCs, that ensures consistency in synaptic convergence between specific BC types onto their target RGCs while enabling independent regulation of pre- and postsynaptic territory sizes and synapse number between cell pairs. Graphical Abstract Highlights • Bipolar cells (BCs) and ganglion cells (GCs) can vary topographically in size • Changes in BC size do not always scale with that of their postsynaptic GCs • Proportion of synapses from each BC type with partner GC is invariant of location • BC axonal tiling promotes maintenance of stereotypic BC-GC connectivity patterns Yu et al. show that the density of excitatory synapses on retinal output neurons is invariant of retinal location, even though connectivity between pre- and postsynaptic cell pairs can vary. These results have implications for understanding topographic variations in processing of visual stimuli and for understanding consistency of CNS wiring diagrams. [ABSTRACT FROM AUTHOR]