Tag Archives: connectomics

The AII Amacrine Cell Connectome: A Dense Network Hub

AII-connectome

We have a new publication in Frontiers in Neuroscience, The AII Amacrine Cell Connectome: A Dense Network Hub.  Authors are Robert E. MarcJames R. Anderson, Bryan W. Jones, Crystal Sigulinsky and J. Scott Lauritzen.

Abstract:  The mammalian AII retinal amacrine cell is a narrow-field, multistratified glycinergic neuron best known for its role in collecting scotopic signals from rod bipolar cells and distributing them to ON and OFF cone pathways in a crossover network via a combination of inhibitory synapses and heterocellular AII::ON cone bipolar cell gap junctions. Long considered a simple cell, a full connectomics analysis shows that AII cells possess the most complex interaction repertoire of any known vertebrate neuron, contacting at least 28 different cell classes, including every class of retinal bipolar cell. Beyond its basic role in distributing rod signals to cone pathways, the AII cell may also mediate narrow-field feedback and feedforward inhibition for the photopic OFF channel, photopic ON-OFF inhibitory crossover signaling, and serves as a nexus for a collection of inhibitory networks arising from cone pathways that likely negotiate fast switching between cone and rod vision. Further analysis of the complete synaptic counts for five AII cells shows that (1) synaptic sampling is normalized for anatomic target encounter rates; (2) qualitative targeting is specific and apparently errorless; and (3) that AII cells strongly differentiate partner cohorts by synaptic and/or coupling weights. The AII network is a dense hub connecting all primary retinal excitatory channels via precisely weighted drive and specific polarities. Homologs of AII amacrine cells have yet to be identified in non-mammalians, but we propose that such homologs should be narrow-field glycinergic amacrine cells driving photopic ON-OFF crossover via heterocellular coupling with ON cone bipolar cells and glycinergic synapses on OFF cone bipolar cells. The specific evolutionary event creating the mammalian AII scotopic-photopic hub would then simply be the emergence of large numbers of pure rod bipolar cells.

 

Ultrastructural Reconstruction of ON Cone Bipolar Cell Projective Fields In The Innter Plexiform Layer of The Rabbit Retina

retina reconstruction

This abstract was presented at the 2014 FASEB Summer Research Conference in Saxtons River, Vermont by J. Scott Lauritzen, Crystal L. Sigulinsky, Noah T. Nelson, Nathan R. Sherbotie, Danny P. Emrich, Rebecca L. Pfeiffer, Jefferson R. Brown, John V. Hoang, Joshua M. Dudleston, Carl B. Watt, Kevin Rapp, Marguerite V. Shaw, Jia-Hui Yang, James R. Anderson, Bryan W. Jones and Robert E. Marc.

Purpose: Functional mapping in tiger salamander shows that bipolar cell (BC) projective fields far exceed their axonal fields, and directly implicates wide-field GABAergic amacrine cells (wf γACs) and gap junctions (Asari & Meister, 2014). Strikingly, single BCs exert differential effects on functionally distinct ganglion cells (GCs), likely achieved by privatized amacrine cell (AC) presynaptic inhibition to specific BC-GC synaptic pairs (Asari & Meister, 2012). To address whether BC projective fields in the mammal are equally broad, wf γAC- and gap junction-dependent, and GC type unselective, we reconstructed all electrical and chemical synaptic partners of a single ON cone BC in the inner plexiform layer of the rabbit retina, and searched BC-GC synaptic pairs for differential synaptic inhibition.

Methods: Cells in retinal connectome 1 (RC1) were annotated with Viking viewer, and explored via connectivity visualizations and 3D rendering (Anderson et al., 2011). Small molecule signals embedded in RC1, e.g. GABA, glycine, and L-glutamate, combined with morphological reconstruction and connectivity analysis allow robust cell classification. We used the MacNeil et al. (2004) rabbit BC classification scheme.

Results: CBb5w 593 is one of 20 ON cone BCs of this class in RC1. This CBb5w is presynaptic to 17 distinct GCs and 262 AC processes, and postsynaptic to 228 AC processes. The majority of these ACs are wf γACs. We estimate this BC forms synapses with 50 unique ACs. Asari & Meister (2014) found that single bipolar cell projective fields range up to 1 mm, far beyond a BC axonal field, and differentially drive multiple classes of GC. We discovered BC-BC within- and cross-class coupling and lateral inhibition that construct sign-conserving and sign-inverting projective fields to many distinct ganglion cell classes across the entire 0.25 mm diameter of RC1, much greater than a 60 µm BC axonal field. Cross-class projections access a broader set of GCs than expected from in-class projections alone. The BC-BC coupling is independent of BC-AII AC coupling. 94% of the CBb5w 593 BC-GC synaptic pairs receive feedback inhibition within the varicosity of the ribbon, but the number of feedback synapses is highly variable (coefficient of variation = 0.81). 35% of the BC-GC pairs receive feedforward inhibition within 2 microns of the postsynaptic density.

Conclusions: Mammalian BCs use novel cross-class topologies to distribute signals to a wide range of GCs and establish projective fields similar to those discovered in non-mammalian species. BC-BC within- and cross-class coupling and lateral inhibition via wf γACs establish sign-conserving and sign-inverting projective fields, respectively, up to 1 mm diameters. BC-GC synaptic pairs overwhelmingly employ feedback vs. feedforward inhibition to modulate signaling, and the numbers of feedback synapses are highly variable across these pairs, accounting for privatized and differential GC responses to the same BC drive.

A Synaptic Basis for Small World Network Design in the ON Inner Plexiform Layer of the Rabbit Retina

Bipolar cells_

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. PfeifferJames 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).

Retinal connectomics: A New Era For Connectivity Analysis in The New Visual Neurosciences

New-Visual-Neurosciences

We have a new publication, this one a chapter titled: Retinal connectomics: A New Era For Connectivity Analysis in The New Visual Neurosciences (A little cheaper on Amazon here) textbook.  Authors are Robert E. Marc, Bryan W. Jones, James S. Lauritzen, Carl B. Watt and James R. Anderson.

Retinal Connectomics: Toward Complete, Accurate Networks

Retinal Connectomics_600

We have a new publication, Retinal connectomics: Toward complete, accurate networks in Progress in Retinal and Eye Research.  Authors are:  Robert E. Marc, Bryan W. JonesCarl B. Watt, Crystal Sigulinsky, James R. Anderson and J. Scott Lauritzen.

Abstract:
Connectomics is a strategy for mapping complex neural networks based on high-speed automated electron optical imaging, computational assembly of neural data volumes, web-based navigational tools to explore 1012-1015 byte (terabyte to petabyte) image volumes, and annotation and markup tools to convert images into rich networks with cellular metadata. These collections of network data and associated metadata, analyzed using tools from graph theory and classification theory, can be merged with classical systems theory, giving a more completely parameterized view of how biologic information processing systems are implemented in retina and brain. Networks have two separable features: topology and connection attributes. The first findings from connectomics strongly validate the idea that the topologies complete retinal networks are far more complex than the simple schematics that emerged from classical anatomy. In particular, connectomics has permitted an aggressive refactoring of the retinal inner plexiform layer, demonstrating that network function cannot be simply inferred from stratification; exposing the complex geometric rules for inserting different cells into a shared network; revealing unexpected bidirectional signaling pathways between mammalian rod and cone systems; documenting selective feedforward systems, novel candidate signaling architectures, new coupling motifs, and the highly complex architecture of the mammalian AII amacrine cell. This is but the beginning, as the underlying principles of connectomics are readily transferrable to non-neural cell complexes and provide new contexts for assessing intercellular communication.