Evo Devo Connectomics Of Sensory Circuit For Visual Navigation

EvoDevo vision

There is an interesting paper from an evo devo perspective out of the Jékely laboratory, looking at the connectomics of some of the earliest of organized visual systems in the Platynereis dumerilii larva.  They have described a visual circuit consisting of 71 neurons and 1,106 “connections”.  The cool thing about this study was that they were also able to combine behavioral experiments with ablations revealing the ability to detect spatial light, directing movement or taxis in the direction of the light.

Its too bad I did not visit with them last time I was in Tübingen as it would have been good to talk connectomics and techniques with them.  I am encouraged that they used serial section transmission electron microscopy to perform circuit level analysis as we think its the right approach for circuit level analysis, though I worry that the resolution was too low to image gap junctions, though they did mention looking for them.  Regardless, I would have loved to see their setup and talked with them.



Notable Paper: On Cone Bipolar Cell Axonal Synapses In The OFF Inner Plexiform Layer Of The Rabbit Retina

JCN cover 2013

This paper in the Journal of Comparative Neurology by  J. Scott Lauritzen, James R. Anderson, Bryan W. Jones, Carl B. Watt, Shoeb Mohammed, John V. Hoang and Robert E. Marc is another effort out of the Marc Laboratory For Connectomics that continues to define complete neural circuits to completeness.

This paper is another elucidation of data from the first Rabbit Retinal Connectome volume (RC1) that reveals that the division between the ON and the OFF inner plexiform layer (IPL) is not structurally absolute. ON cone bipolar cells make noncanonical axonal synapses onto specific targets and receive amacrine cell synapses in the nominal OFF layer, creating novel motifs, including inhibitory crossover networks. Automated transmission electron microscopic imaging, molecular tagging, tracing, and rendering of ∼400 bipolar cells reveals axonal ribbons in 36% of ON cone bipolar cells, throughout the OFF IPL. The targets include γ-aminobutyrate (GABA)-positive amacrine cells (γACs), glycine-positive amacrine cells (GACs), and ganglion cells. Most ON cone bipolar cell axonal contacts target GACs driven by OFF cone bipolar cells, forming new architectures for generating ON–OFF amacrine cells. Many of these ON–OFF GACs target ON cone bipolar cell axons, ON γACs, and/or ON–OFF ganglion cells, representing widespread mechanisms for OFF to ON crossover inhibition. Other targets include OFF γACs presynaptic to OFF bipolar cells, forming γAC-mediated crossover motifs. ON cone bipolar cell axonal ribbons drive bistratified ON–OFF ganglion cells in the OFF layer and provide ON drive to polarity-appropriate targets such as bistratified diving ganglion cells (bsdGCs). The targeting precision of ON cone bipolar cell axonal synapses shows that this drive incidence is necessarily a joint distribution of cone bipolar cell axonal frequency and target cell trajectories through a given volume of the OFF layer. Such joint distribution sampling is likely common when targets are sparser than sources and when sources are coupled, as are ON cone bipolar cells.

Figure Above: The first Rabbit Retinal Connectome volume (RC1), constructed via automated transmission electron microscopy (ATEM) and computational molecular phenotyping (CMP), spans the mid-inner nuclear layer (INL) at section 001 to the ganglion cell layer (GCL) at section 371, shown in a mirror image below. RC1 is a short cylinder ≈ 250 μm in diameter and ≈ 30 μm high containing 341 ATEM sections and 11 intercalated CMP sections. The cylinder is capped at top and bottom with 10-section CMP series allowing molecular segmentation of cells, and an activity marker, 1-amino-4-guanidobutane (AGB), to mark cells differentially stimulated via glutamatergic synapses. ATEM section 001 is a horizontal plane section through the INL visualized with GABA.glycine.glutamate → red.green.blue transparency mapping and a dark gold alpha channel (ANDed taurine + glutamine channels). ATEM section 371 is a horizontal plane section through the GCL visualized with GABA.AGB.glutamate → red.green.blue transparency mapping.

Merry Christmas and Happy New Year, 2011

Merry Christmas and Happy New Year to you from all of us at Webvision.  This image, a Christmas wreath created by Robert E. Marc is composed of 104 rod bipolar cell axonal fields from the world’s first complete connectome with synaptic level resolution.  Each bipolar cell in this field has been annotated from ultrastructural data revealing its extent and connectivities to other cell classes.  The rod bipolar cells have been rendered out in 3D and is viewed from the top, or photoreceptor side, looking down towards the ganglion cell layer.