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J Comp Neurol. 2016 Jul 22. doi: 10.1002/cne.24084. [Epub ahead of print]

Rod-cone crossover connectome of mammalian bipolar cells.

Author information

1
HHMI Janelia Research Campus, Ashburn, Virginia, USA.
2
Department of Ophthalmology, John A. Moran Vision Institute, University of Utah School of Medicine, Salt Lake City, Utah, USA.
3
Department of Optometry and Vision Science and Centre for Eye Health, University of New South Wales, Sydney, Australia.
4
Scientific Computing and Imaging Institute, University of Utah School of Computing, Salt Lake City Utah, USA.

Abstract

The basis of cross-suppression between rod and cone channels has long been an enigma. Using rabbit retinal connectome RC1, we show that all cone bipolar cell (BC) classes inhibit rod BCs via amacrine cell (AC) motifs (C1-6); that all cone BC classes are themselves inhibited by AC motifs (R1-5, R25) driven by rod BCs. A sparse symmetric AC motif (CR) is presynaptic and postsynaptic to both rod and cone BCs. ON cone BCs of all classes drive inhibition of rod BCs via motif C1 wide-field GABAergic ACs (γACs) and motif C2 narrow field glycinergic ON ACs (GACs). Each rod BC receives ≈10 crossover AC synapses and each ON cone BC can target ≈10 or more rod BCs via separate AC processes. OFF cone BCs mediate monosynaptic inhibition of rod BCs via motif C3 driven by OFF γACs and GACs and disynaptic inhibition via motifs C4 and C5 driven by OFF wide-field γACs and narrow-field GACs, respectively. Motifs C4 and C5 form halos of 60-100 inhibitory synapses on proximal dendrites of AI γACs. Rod BCs inhibit surrounding arrays of cone BCs through AII GAC networks that access ON and OFF cone BC patches via motifs R1, R2, R4, R5 and a unique ON AC motif R3 that collects rod BC inputs and targets ON cone BCs. Crossover synapses for motifs C1, C4, C5, and R3 are 3-4× larger than typical feedback synapses, which may be a signature for synaptic winner-take-all switches. J. Comp. Neurol., 2016.

KEYWORDS:

RRID AB_2341093; RRID AB_2532053; RRID AB_2532055; RRID AB_2532057; RRID AB_2532059; RRID AB_2532060; RRID AB_2532061; RRID SCR-002937; RRID SCR-008606; RRID SCR_001622; RRID SCR_005986; RRID SCR_008394; amacrine cells; cone vision; connectomics; networks; retina; rod vision; synapses; transmission electron microscopy

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