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.
This abstract was presented today at the 2014 Association for Research in Vision and Opthalmology (ARVO) meetings in Orlando, Florida by J Scott Lauritzen, Noah T. Nelson, Crystal L. Sigulinsky, Nathan Sherbotie, John Hoang, Rebecca L. Pfeiffer, James R. Anderson, Carl B. Watt, Bryan W. Jones and Robert E. Marc.
Purpose: Converging evidence suggests that large- and intermediate-scale neural networks throughout the nervous system exhibit small world’ design characterized by high local clustering of connections yet short path length between neuronal modules (Watts & Strogatz 1998 Nature; Sporns et al.2004 Trends in Cog Sci). It is suspected that this organizing principle scales to local networks (Ganmor et al. 2011 J Neurosci; Sporns 2006 BioSystems) but direct observation of synapses and local network topologies mediating small world design has not been achieved in any neuronal tissue. We sought direct evidence for synaptic and topological substrates that instantiate small world network architectures in the ON inner plexiform layer (IPL) of the rabbit retina. To test this we mined ≈ 200 ON cone bipolar cells (BCs) and ≈ 500 inhibitory amacrine cell (AC) processes in the ultrastructural rabbit retinal connectome (RC1).
Methods: BC networks in RC1 were annotated with the Viking viewer and explored via graph visualization of connectivity and 3D rendering (Anderson et al. 2011 J Microscopy). Small molecule signals embedded in RC1 e.g. GABA glycine and L-glutamate combined with morphological reconstruction and connectivity analysis allow for robust cell classification. MacNeil et al. (2004 J Comp Neurol) BC classification scheme used for clarity.
Results: Homocellular BC coupling (CBb3::CBb3 CBb4::CBb4 CBb5::CBb5) and within-class BC inhibitory networks (CBb3 → AC –| CBb3 CBb4 → AC –| CBb4 CBb5 → AC –| CBb5) in each ON IPL strata form laminar-specific functional sheets with high clustering coefficients. Heterocellular BC coupling (CBb3::CBb4 CBb4::CBb5 CBb3::CBb5) and cross-class BC inhibitory networks (CBb3 → AC –| CBb4 CBb4 → AC –| CBb3 CBb4 → AC –| CBb5 CBb5 → AC –| CBb4 CBb3 → AC –| CBb5 CBb5 → AC –| CBb3) establish short synaptic path lengths across all ON IPL laminae.
Conclusions: The retina contains a greater than expected number of synaptic hubs that multiplex parallel channels presynaptic to ganglion cells. The results validate a synaptic basis (ie. direct synaptic connectivity) and local network topology for the small world architecture indicated at larger scales providing neuroanatomical plausibility of this organization for local networks and are consistent with small world design as a fundamental organizing principle of neural networks on multiple spatial scales.
Support: NIH EY02576 (RM), NIH EY015128 (RM), NSF 0941717 (RM), NIH EY014800 Vision Core (RM), RPB CDA (BWJ), Thome AMD Grant (BWJ).
This image of ganglion cells, Müller cells and starburst amacrine cells in the human retina is from a patient suffering from retinitis pigmentosa (RP). This disease this patient suffered from slowly causes people affected with this disease to go blind and is a constant reminder to me of why we engage in our research.
For some, this is a pretty, though abstract image created through a set of technologies called computational molecular phenotyping (CMP). The colors in this image come from antibodies labeling taurine, glutamine and glutamate, all small molecular species that reveal metabolic states in these tissues.
For us, these images reveal variation in cell types as well as abnormalities in other kinds of cells that presage retinal stress and the cellular responses that alter the retina in ways that both cause blindness and make it difficult to rescue vision loss. We also see the beginnings of changes in the circuitry of the retina that forever will alter the way that diseased retinas process information.
Image courtesy of Bryan William Jones, Ph.D. and originally appeared here.
There has been quite a bit of discussion of connectomes in the last while with President Obama’s new BRAIN initiative. It is important to consider some of the requirements of obtaining a true synapse level wiring map in the brain as many are articulating from this initiative. While there are new technologies that will be required to undertake this initiative for mapping the entire brain, the NIH NEI has been funding an ongoing project to study retinal circuitry which guides the community in how to approach a true synapse level map of the nervous system.
An example of this work in Current Opinion in Neurobiology titled Building Retinal Connectomes is a review that illustrates the importance of having a complete network graph of connectivities in the retina and by extension other neural systems. Complete network graphs are what will be required to understand how retinal systems (and any neural system) is constructed. Even though the retinal community understands how retinas are wired in broad strokes, the precise, fine details are critical and elucidating them requires a new level of complete annotation derived from advances in light and ultrastructural imaging, data management, navigation and validation.
Authors are Robert E. Marc, Bryan W. Jones, J. Scott Lauritzen, Carl B. Watt and James R. Anderson.
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.
We at Webvision would like to wish you all a very happy holiday season and a happy New Year in 2013. Continuing on the theme from last years holiday season wishes, we have for you a colorful holiday image titled “Connectomics, First Light” from Robert E. Marc utilizing data generated by Scott Lauritzen, Crystal Sigulinsky and John Vo Hoang.
What we are seeing is a necklace of coupled retinal bipolar cells linked by sparse suboptical gap junctions, fundamentally new circuitry for retinal processing. There is much more to this story, but we’ll wait until the publication. For now, consider these data generated from the Connectomics project in the Marclab at the Moran Eye Center to be a colorful holiday image that represents our best wishes to you.