TY - JOUR T1 - Connectivity map of bipolar cells and photoreceptors in the mouse retina JF - bioRxiv DO - 10.1101/065722 SP - 065722 AU - Christian Behrens AU - Timm Schubert AU - Silke Haverkamp AU - Thomas Euler AU - Philipp Berens Y1 - 2016/01/01 UR - http://biorxiv.org/content/early/2016/07/25/065722.abstract N2 - Visual processing already starts at the very first synapse of the visual system. In the mouse retina, three different kinds of photoreceptors (M-cones, S-cones and rods) provide input to 14 parallel bipolar cell types. The precise pattern of connectivity between them determines which signals are available to downstream circuits and therefore the entire visual system. While it has been shown that cone bipolar cell types 1 contact M-cones and type 9 contacts S-cones selectively, most bipolar cell types are thought to contact all cones within their dendritic field. Also, ON bipolar cells are thought to contact cones exclusively via so-called invaginating synapses, while OFF bipolar cells are thought to form basal synapses. By mining publically available electron microscopy data, we confirm that there are no additional M-or S-cone selective bipolar cell types in the mouse retina; however, we found interesting violations of the established rules of outer retinal connectivity: Cone bipolar cell type X contacted only ~20% of the cones in its dendritic field and made mostly atypical non-invaginating contacts with cones. Types 5T, 5O and 8 also contacted fewer cones than expected from the extent of their dendritic field. In addition, we provide anatomical evidence that rod and cone pathways are interconnected in both directions: Not only OFF-types 3A, 3B and 4 get direct input from rods but also rod bipolar cells from cones. Together, this suggests that the organization of the outer plexiform layer is less straightforward than classically thought. ER -