Seminar: Molecular Organization of the First Visual Synapse

Seminar Flyer-Martemyanov

Kirill Martemyanov, Associate Professor at the Scripps Institute will be delivering a seminar on Molecular Organization of the First Visual Synapse, on Wednesday, February 10th at 12pm in the Moran Eye Center auditorium.

Abstract: Signaling in the retina plays an essential role in our vision. Light is detected by rod and cone photoreceptors that convert it to the electrical response further propagated through the retina circuitry by means of synaptic communication between neurons. To be able to see at low light levels, highly sensitive rods must faithfully transmit the signal that they generate to downstream bipolar neurons. The efforts in my laboratory are focused on studying molecular players and signaling events at the first visual synapse between formed by rod photoreceptors. I will describe how multiple elements of the synaptic signaling machinery are organized and scaffolded together to ensure proper transmission of signal generated by rods enabling vision at low light.

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).

Seminar: Beth Stevens, To Prune Or Not To Prune? Mechanisms That Control Microglia-Mediated Synaptic Pruning During Development

Beth Stevens seminar

The University of Utah Program in Neuroscience presents Dr. Beth Stevens who will deliver a seminar in the Eccles Institute of Human Genetics auditorium, Tuesday April 15th, 2013 at 4:00pm.  Dr. Stevens will discuss “Mechanisms that control microglia-mediated synaptic pruning during development”.

Faculty host is Karen Wilcox.  Questions: Contact Tracy Marble at 801 581-4820.