The broad goal of our research program is to understand how neural circuit function depends on the intrinsic properties of component cells and synapses. The specific goal of this proposal is to determine how rod-mediated visual processing in the retina depends on the timing of signaling at rod bipolar (RB) cell synapses with postsynaptic AII amacrine cells. Transmission at the RB?AII synapse is shaped by intrinsic (e.g. synapse-specific dynamics of vesicle release and recycling) and extrinsic (e.g. inhibition of RBs by interneuron circuits) factors. This application comprises two specific aims that integrate synapse- and circuit-level analyses of RB?AII transmission.
Specific Aim 1 tests the novel hypothesis that Ca2+ influx into the RB terminal regulates the strength and timing of transmission at the synapse by two calmodulin (CaM)-dependent mechanisms: one modulates membrane lipid composition by regulating a Ca2+-independent phospholipase A2 (iPLA2); the second affects a constitutively active brake on spontaneous release. Modulation of transmission is studied by electrophysiological experimentation, and temporal coding is examined in a retina in which RBs lack a fast mode of exocytosis: the complexin (clpx) 3 knockout.
Specific Aim 2 determines the organization and physiological function of parallel inhibitory pathways converging on the RB. Scanning block face electron micrographic (SBEM) reconstruction identifies inhibitory amacrine cells (ACs) presynaptic to RBs. AC?RB synapses are studied functionally using various electrophysiological techniques: paired AC-RB recording, optogenetic stimulation of ACs, and optogenetic stimulation of bipolar cells-BCs-presynaptic to the ACs. Relevance to Public Health: Understanding how temporal coding is implemented by retinal synapses informs the design of retinal prosthetics and the study of animal models of human retinal diseases. A goal of vision research is the development of gene-based therapies for treating blindness caused by photoreceptor degeneration, and a promising therapy is the generation of light sensitivity in retinal interneurons by virally-mediated expression of channelrhodopsin-2 (ChR2), a light-gated cation channel. We will express ChR2 in interneurons to study synaptic interactions in retinal circuits and thereby generate critical information about the operating range of a retina in which ChR2 is the only light sensor. We address three goals of the Retinal Diseases Program in the National Plan for Eye and Vision Research: 1) determining potential therapeutic strategies for treatment of retinitis pigmentosa, 2) increasing understanding of post-photoreceptor adaptation (i.e. interactions between excitatory and inhibitory synapses), and 3) increasing understanding of how inter-cellular interactions in neural networks generate signals that are interpretable as visual images.
The proposed studies concerning the mechanisms governing visual stimulus coding by synaptic interactions in the mammalian retina will generate fundamental information about the neural basis of vision. This will facilitate the evaluation of retinal circuits in mouse models of human retinal diseases and the assessment of treatment strategies in these models. Additionally, our proposed studies using the light- gated cation channel, channelrhodopsin-2, could contribute to the development of gene-based therapies for treating human blindness arising from pathologies, like retinitis pigmentosa, that cause photoreceptor degeneration
|Park, Silvia J H; Pottackal, Joseph; Ke, Jiang-Bin et al. (2018) Convergence and Divergence of CRH Amacrine Cells in Mouse Retinal Circuitry. J Neurosci 38:3753-3766|
|Graydon, Cole W; Lieberman, Evan E; Rho, Nao et al. (2018) Synaptic Transfer between Rod and Cone Pathways Mediated by AII Amacrine Cells in the Mouse Retina. Curr Biol 28:2739-2751.e3|
|Demb, Jonathan B; Singer, Joshua H (2016) Mind the Gap Junctions: The Importance of Electrical Synapses to Visual Processing. Neuron 90:207-9|
|Mortensen, Lena S; Park, Silvia J H; Ke, Jiang-Bin et al. (2016) Complexin 3 Increases the Fidelity of Signaling in a Retinal Circuit by Regulating Exocytosis at Ribbon Synapses. Cell Rep 15:2239-2250|
|Pallotto, Marta; Watkins, Paul V; Fubara, Boma et al. (2015) Extracellular space preservation aids the connectomic analysis of neural circuits. Elife 4:|
|Firl, Alana; Ke, Jiang-Bin; Zhang, Lei et al. (2015) Elucidating the role of AII amacrine cells in glutamatergic retinal waves. J Neurosci 35:1675-86|
|Demb, Jonathan B; Singer, Joshua H (2015) Functional Circuitry of the Retina. Annu Rev Vis Sci 1:263-289|
|Choi, Hannah; Zhang, Lei; Cembrowski, Mark S et al. (2014) Intrinsic bursting of AII amacrine cells underlies oscillations in the rd1 mouse retina. J Neurophysiol 112:1491-504|
|Margolis, David J; Gartland, Andrew J; Singer, Joshua H et al. (2014) Network oscillations drive correlated spiking of ON and OFF ganglion cells in the rd1 mouse model of retinal degeneration. PLoS One 9:e86253|
|Stafford, Benjamin K; Manookin, Michael B; Singer, Joshua H et al. (2014) NMDA and AMPA receptors contribute similarly to temporal processing in mammalian retinal ganglion cells. J Physiol 592:4877-89|
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