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Timm Schubert, Christian Behrens, Thomas Euler, Philipp Berens; Connectivity map of bipolar cells and photoreceptors in the outer mouse retina. Invest. Ophthalmol. Vis. Sci. 2016;57(12):597.
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© ARVO (1962-2015); The Authors (2016-present)
In the mouse retina, two types of cone photoreceptors (short (S) and medium (M) wavelength-sensitive cones) provide input to 13 types of cone bipolar cells. Type 1 bipolar cells is supposed to predominantly receive input from M-cones, whereas type 9 bipolar cells selectively contact S-cones (reviewed by Euler et al., 2014). Additionally, one type of rod photoreceptors (rods) contacts rod bipolar cells (RBCs). However, how cone and rod pathways are interconnected at the level of individual photoreceptor-bipolar cell synapse is unknown. Additionally, it is unknown to which degree the remaining cone bipolar cell types selectively sample input from S- and/or M-cones.
We exploit the serial block-face scanning electron microscopy dataset of the mouse retina provided by Helmstaedter et al. (2013) to systematically analyze the connectivity between cones, rods and bipolar cells in the outer plexiform layer. Using volume segmentation and contact classification, we reconstruct 163 cone and 2176 rod terminals and identify 13 S-cones based on their specific contacts with type 9 bipolar cells. Using an automated classification approach, we analyzed the contact types between photoreceptors and bipolar cells.
First, in addition to the input from rods, 63% of RBCs (n=141) receive input from cones indicating that two functionally distinct groups of RBC exist. Second, XBC cone bipolar cells contact very few cones (1.0 cones/XBC, 95% CI [0.14,2.14], n=7). Third, type 1 and type 3A OFF CBCs make contacts with both S- and M-cones, but in type 3A cells M-cone input dominates cone input (with type 3A cells on average contacted by 0.31 S-cones (95% CI [0.08,0.54]) and by 0.79 M-cones (95% CI [0.67,0.93]), n= 22) suggesting that this type may form the ’vertical green pathway’ in the mouse retina.
We found that the large scale outer retinal connectivity map can be used for anatomical classification of bipolar cell types and provides important insight in the putative function of bipolar cells.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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