Current Search: Synapses (x)
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Title
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Frazzled and netrin: a story of neuronal confusion and competition in the drosophila giant fiber system.
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Creator
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Orr, Brian, Murphey, Rodney K., Graduate College
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Date Issued
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2011-04-08
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PURL
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http://purl.flvc.org/fcla/dt/3164669
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Subject Headings
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Neural circuitry, Drosophila, Synapses
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Format
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Document (PDF)
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Title
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ESTABLISHMENT AND APPLICATION OF WORKFLOWS FOR STRUCTURE-FUNCTION ANALYSIS OF SYNAPTIC COMPONENTS.
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Creator
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Thomas, Connon I., Kamasawa, Naomi, Murphey, Rodney, Florida Atlantic University, Department of Biological Sciences, Charles E. Schmidt College of Science
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Abstract/Description
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At the site of neuronal communication, multiple interacting components drive synapse structure and function. Synaptic vesicle pools, membrane proteins, mitochondria, and perisynaptic astrocyte processes (PAPs) are all structures that can be altered through naturally occurring plasticity mechanisms to modulate neurotransmission, and disruption of these structures can result in synapse dysfunction and disease. Due to the minute size of the synapse, electron microscopy (EM) remains the gold...
Show moreAt the site of neuronal communication, multiple interacting components drive synapse structure and function. Synaptic vesicle pools, membrane proteins, mitochondria, and perisynaptic astrocyte processes (PAPs) are all structures that can be altered through naturally occurring plasticity mechanisms to modulate neurotransmission, and disruption of these structures can result in synapse dysfunction and disease. Due to the minute size of the synapse, electron microscopy (EM) remains the gold standard for ultrastructural characterization; however, due to the complexity of EM datasets, extraction of information has become a bottleneck which places limits on the amount of data that can be collected and analyzed. A need exists for easy-to-use workflows that automate and enhance analysis throughput, to keep up with the streams of image data that are able to be produced. Here, I develop the use of AI algorithms, correlative microscopy techniques, and novel structural analysis methods to characterize postsynaptic mitochondria, PAPs, synaptic vesicles, and integral membrane proteins and their impact on synapse structure and function. I show that both postsynaptic mitochondria and PAPs in the visual cortex are positioned to support synapse structure and function; cleavage of a synaptic adhesion molecule affects synaptic vesicle accumulation in the amygdala; and presynaptic voltage gated calcium channels aggregate near active zone machinery in the brainstem. In addition, I highlight the use of virtual reality as a fast and intuitive tool for the identification and isolation of individual neurites in 3D EM. Thus, my work establishes novel technical approaches for EM and advances our understanding of neuronal communication through original research of several synaptic components.
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Date Issued
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2023
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PURL
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http://purl.flvc.org/fau/fd/FA00014315
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Subject Headings
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Synapses, Artificial intelligence, Astrocytes
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Format
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Document (PDF)
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Title
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Localization of chemical and electrical synapses in the retina.
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Creator
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Liu, Yufei., Charles E. Schmidt College of Medicine, Department of Biomedical Science
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Abstract/Description
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The amphibian retina is commonly used as a model system for studying function and mechanism of the visual system in electrophysiology, since the neural structure and synaptic mechanism of the amphibian retina are similar to higher vertebrate retinas. I determined the specific subtypes of receptors and channels that are involved in chemical and electrical synapses in the amphibian retina. My study indicates that glycine receptor subunits of GlyRº1, 3 and 4 and glutamate receptor subunit of...
Show moreThe amphibian retina is commonly used as a model system for studying function and mechanism of the visual system in electrophysiology, since the neural structure and synaptic mechanism of the amphibian retina are similar to higher vertebrate retinas. I determined the specific subtypes of receptors and channels that are involved in chemical and electrical synapses in the amphibian retina. My study indicates that glycine receptor subunits of GlyRº1, 3 and 4 and glutamate receptor subunit of GluR4 are present in bipolar and amacrine dendrites and axons to conduct chemical synapses in the retinal circuit. I also found that the gap junction channel, pannexin 1a (panx1a), is present in cone-dominated On-bipolar cells and rod-dominated amacrine processes possibly to connect rod-and cone-pathway in the inner retina. In addition, panx1a may form hemi-channels that pass ATP and Ca2+ signals. The findings of my study fill the gap of our knowledge about the subtypes of neurotransmitter receptors and gap junction channels conducting visual information in particular cell types and synaptic areas.
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Date Issued
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2011
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PURL
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http://purl.flvc.org/FAU/3332725
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Subject Headings
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Synapses, Neurotransmitters, Neural receptors, Cellular signal transduction
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Format
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Document (PDF)
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Title
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Molecular Mechanisms Of CaV2.1 Expression and Functional Organization at the Presynaptic Terminal.
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Creator
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Das, Brati, Young, Samuel M., Florida Atlantic University, Charles E. Schmidt College of Science, Department of Biological Sciences
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Abstract/Description
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Neuronal circuit output is dependent on the embedded synapses’ precise regulation of Ca2+ mediated release of neurotransmitter filled synaptic vesicles (SVs) in response to action potential (AP) depolarizations. A key determinant of SV release is the specific expression, organization, and abundance of voltage gated calcium channel (VGCC) subtypes at presynaptic active zones (AZs). In particular, the relative distance that SVs are coupled to VGCCs at AZs results in two different modes of SV...
Show moreNeuronal circuit output is dependent on the embedded synapses’ precise regulation of Ca2+ mediated release of neurotransmitter filled synaptic vesicles (SVs) in response to action potential (AP) depolarizations. A key determinant of SV release is the specific expression, organization, and abundance of voltage gated calcium channel (VGCC) subtypes at presynaptic active zones (AZs). In particular, the relative distance that SVs are coupled to VGCCs at AZs results in two different modes of SV release that dramatically impacts synapse release probability and ultimately the neuronal circuit output. They are: “Ca2+ microdomain,” SV release due to cooperative action of many loosely coupled VGCCs to SVs, or “Ca2+ nanodomain,” SV release due to fewer more tightly coupled VGCCs to SVs. VGCCs are multi-subunit complexes with the pore forming a1 subunit (Cav2.1), the critical determinant of the VGCC subtype kinetics, abundance, and organization at the AZ. Although in central synapses Cav2.2 and Cav2.1 mediate synchronous transmitter release, neurons express multiple VGCC subtypes with differential expression patterns between the cell body and the pre-synapse. The calyx of Held, a giant axosomatic glutamatergic presynaptic terminal that arises from the globular bushy cells (GBC) in the cochlear nucleus, exclusively uses Cav2.1 VGCCs to support the early stages of auditory processing. Due to its experimental accessibility the calyx provides unparalleled opportunities to gain mechanistic insights into Cav2.1 expression, organization, and SV release modes at the presynaptic terminal. Although many molecules are implicated in mediating Cav2.1 expression and SV to VGCC coupling through multiple binding domains on the C-terminus of the Cav2.1 a1 subunit, the underlying fundamental molecular mechanisms remain poorly defined. Here, using viral vector mediated approaches in combination with Cav2.1 conditional knock out transgenic mice, we demonstrate that that there a two independent pathways that control Cav2.1 expression and SV to VGCC coupling at the calyx of Held. These implications for the regulation of synaptic transmission in CNS synapses are discussed.
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Date Issued
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2016
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PURL
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http://purl.flvc.org/fau/fd/FA00004584
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Subject Headings
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Synapses., Neural transmission., Cellular signal transduction.
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Format
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Document (PDF)
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Title
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FRAZZLED/DCC REGULATES SYNAPTOGENESIS AT A DROSOPHILA GIANT SYNAPSE.
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Creator
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Lopez, Juan, Murphey, Rodney, Florida Atlantic University, Department of Biological Sciences, Charles E. Schmidt College of Science
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Abstract/Description
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Synaptogenesis is a requirement for cellular communication, but the specific molecular mechanisms underlying synaptogenesis are unclear. Here, we investigate and show the role of the protein Frazzled in synaptogenesis using the transheterozygous Frazzled loss-of-function (LOF) mutant in Drosophila. Leveraging the UAS-GAL4 expression system, we drove expression of various Frazzled/DCC gene constructs in the Giant Fibers (GF) of flies and found changes to synaptogenesis and axon pathfinding. We...
Show moreSynaptogenesis is a requirement for cellular communication, but the specific molecular mechanisms underlying synaptogenesis are unclear. Here, we investigate and show the role of the protein Frazzled in synaptogenesis using the transheterozygous Frazzled loss-of-function (LOF) mutant in Drosophila. Leveraging the UAS-GAL4 expression system, we drove expression of various Frazzled/DCC gene constructs in the Giant Fibers (GF) of flies and found changes to synaptogenesis and axon pathfinding. We identified decreases in electrical synaptogenesis and distinct axon pathfinding errors in Frazzled LOF mutants. Strikingly, the expression of Frazzled intracellular domain (ICD) significantly rescues both phenotypes, while full-length Frazzled protein only partially rescues these phenotypes, prompting us to explore the role of different domains within the protein. Deleting the P1 and P2 domains of Frazzled does not rescue axon pathfinding but did partially rescue synaptogenesis while deleting the P3 domain failed to rescue either phenotype. Moreover, when we drive expression Frazzled with a point-mutated P3 domain, silencing its transcriptional activation domain, it fails to rescue both synaptogenesis and axon pathfinding. These results strongly suggest that Frazzled regulates both synaptogenesis and axon pathfinding in the GFs and is necessary for synaptogenesis of the mixed electrochemical GF synapse. Our results provide novel insights into the molecular mechanisms governing neural circuit assembly and highlight Frazzled as a key player in axon guidance and synaptic development.
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Date Issued
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2023
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PURL
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http://purl.flvc.org/fau/fd/FA00014310
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Subject Headings
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Drosophila, Synapses, Gap Junctions, Receptors, Cell Surface
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Format
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Document (PDF)
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Title
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Dscam1 Regulates Synapse Formation and Function in the Giant Fiber System of Drosophila.
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Creator
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Spencer, Casey L., Murphey, Rodney, Florida Atlantic University, Department of Biological Sciences, Charles E. Schmidt College of Science
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Abstract/Description
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Proper formation of synapses in the developing nervous system is critical to the expected function and behavior of an adult organism. Neurons must project neurites, in the form of axons or dendrites, to target areas to complete synaptic circuits. The biochemical tool that cells use to interact with the external environment and direct the guidance of developing neurites are guidance receptors. One such guidance receptor that is extensively studied to uncover its roles in developmental...
Show moreProper formation of synapses in the developing nervous system is critical to the expected function and behavior of an adult organism. Neurons must project neurites, in the form of axons or dendrites, to target areas to complete synaptic circuits. The biochemical tool that cells use to interact with the external environment and direct the guidance of developing neurites are guidance receptors. One such guidance receptor that is extensively studied to uncover its roles in developmental disorders and disease is DSCAM (Down-Syndrome Cell Adhesion Molecule). To better understand the role of DSCAM in humans, a fly homolog Dscam1 was extensively characterized in the giant fiber system (GFS) of Drosophila to further explore its roles in axon guidance, synapse formation, and synapse function. The UAS-Gal4 system was used to alter the protein levels of Dscam1 within the giant fiber interneurons (GFs). A UAS-RNAi construct against Dscam1 was used to knockdown translation of all possible isoforms within the GFs. A UAS-Dscam1(TM2) construct was used to overexpress a single isoform of Dscam1 that is specifically trafficked to the axons. Confocal microscopy was used to determine the morphological changes associated with dysregulated Dscam1 levels. Visualization via fluorescent markers was accomplished of both pre- and post-synaptic cells, the GFs and tergotrochanteral motorneurons (TTMns), respectively, and synapse interface was determined as colocalization of the two cells. Additionally, the functional components of the GF-TTMn synapse, both gap-junctions, and presynaptic chemical active zones were tagged via fluorescent antibodies and quantified.
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Date Issued
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2023
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PURL
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http://purl.flvc.org/fau/fd/FA00014364
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Subject Headings
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Drosophila, Cell Adhesion Molecules, Nervous System, Synapses
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Format
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Document (PDF)
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Title
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A Framework for Understanding Power Supply and Demand in Presynaptic Nerve Terminals.
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Creator
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Justs, Karlis Anthony, Macleod, Gregory T., Florida Atlantic University, Charles E. Schmidt College of Science, Department of Biological Sciences
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Abstract/Description
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The molecular mechanisms of synaptic function and development have been studied extensively, but little is known about the energy requirements of synapses, or the mechanisms that coordinate their energy production with their metabolic demands. These are oversights, as synapses with high energy demands are more susceptible to degeneration and degrade in the early stages of diseases such as amyotrophic lateral sclerosis, spinal muscle atrophy and Parkinson’s disease. Here, in a structure...
Show moreThe molecular mechanisms of synaptic function and development have been studied extensively, but little is known about the energy requirements of synapses, or the mechanisms that coordinate their energy production with their metabolic demands. These are oversights, as synapses with high energy demands are more susceptible to degeneration and degrade in the early stages of diseases such as amyotrophic lateral sclerosis, spinal muscle atrophy and Parkinson’s disease. Here, in a structure-function study at Drosophila motor neuron terminals, a neurophysiological model was generated to investigate how power (ATP/s) supply is integrated to satisfy the power demand of presynaptic terminals. Power demands were estimated from six nerve terminals through direct measurements of neurotransmitter release and Ca2+ entry, as well as theoretical estimation of Na+ entry and power demands at rest (cost of housekeeping). The data was leveraged with a computational model that simulated the power demands of the terminals during their physiological activity, revealing high volatility in which power demands can increase 15-fold within milliseconds as neurons transition from rest to activity. Another computational model was generated that simulated ATP production scenarios regarding feedback to the power supply machinery (Oxphos and glycolysis) through changes in nucleotide concentrations, showing that feedback from nucleotides alone fail to stimulate power supply to match the power demands of each terminal. Failure of feedback models invokes the need for feed forward mechanisms (such as Ca2+) to stimulate power supply machinery to match power demands. We also quantified mitochondrial volume, density, number and size in each nerve terminal, revealing all four features positively correlate with the terminals power demands. This suggests the terminals enhance their oxidative capacity by increasing mitochondrial content to satisfy their power demands. And lastly, we demonstrate that abolishing an ATP buffering system (the phosphagen system) does not impair neurotransmission in the nerve terminals, suggesting motor nerve terminals are capable of satisfying their power demands without the ATP buffering system.
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Date Issued
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2019
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PURL
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http://purl.flvc.org/fau/fd/FA00013323
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Subject Headings
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Presynaptic Terminals, Adenosine triphosphate, Synapses--metabolism, Bioenergetics
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Format
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Document (PDF)
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Title
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Frazzled’s Role in Synapse Formation at a Drosophila Giant Synapse.
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Creator
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Lopez, Juan, Murphey, Rodney K., Florida Atlantic University, Charles E. Schmidt College of Science, Department of Biological Sciences
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Abstract/Description
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In Drosophila melanogaster, the GFS is synaptically coupled to the Tergotrochanteral motoneurons; these neurons form a signaling pathway from the brain to the jump muscles (Thomas and Wyman, 1983). Part of this signaling is done through gap junctions, and placement of these gap junctions was partially shown to be regulated by the binding of Netrin, a class of guidance molecule (Orr et al., 2014). In the present study we investigate the role of Netrin's receptor Frazzled in the placement of...
Show moreIn Drosophila melanogaster, the GFS is synaptically coupled to the Tergotrochanteral motoneurons; these neurons form a signaling pathway from the brain to the jump muscles (Thomas and Wyman, 1983). Part of this signaling is done through gap junctions, and placement of these gap junctions was partially shown to be regulated by the binding of Netrin, a class of guidance molecule (Orr et al., 2014). In the present study we investigate the role of Netrin's receptor Frazzled in the placement of gap junctions in Drosophila at: 1) Presynaptic neurons (Giant Fibers [GF]), 2) Postsynaptic neurons (Tergotrochanteral motoneurons [TTMn]), and 3) Presynaptic + Postsynaptic neurons simultaneously. Effects of Frazzled were tested using Frazzled RNAi and a combination of electrophysiological recordings and imaging of the GF-TTMn synapse. The results from this study show that presynaptic and postsynaptic knockdown of Frazzled delayed muscular responses and altered the anatomy of both the GF's and TTMn's.
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Date Issued
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2018
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PURL
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http://purl.flvc.org/fau/fd/FA00013085
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Subject Headings
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Drosophila melanogaster--Nervous system., Gap Junctions., Synapses., Netrin Receptors.
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Format
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Document (PDF)
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Title
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Function of glycinergic interplexiform cells in rod synaptic transmission.
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Creator
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Jiang, Zheng., Charles E. Schmidt College of Science, Department of Biological Sciences
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Abstract/Description
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The interplexiform cells(IP cells) are the most recently discovered neurons in the retina and their function is to provide centrifugal feedback in retina. The anatomical structure of the IP cells has been well studied, but the function of these neurons is largely unknown. I systematically studied the excitatory and inhibitory inputs from IP cells in salamander retina. I found that L-EPSCs in IP cells are mediated by AMPA and NMDA receptors; in addition, L-IPSCs are mediated by glycine...
Show moreThe interplexiform cells(IP cells) are the most recently discovered neurons in the retina and their function is to provide centrifugal feedback in retina. The anatomical structure of the IP cells has been well studied, but the function of these neurons is largely unknown. I systematically studied the excitatory and inhibitory inputs from IP cells in salamander retina. I found that L-EPSCs in IP cells are mediated by AMPA and NMDA receptors; in addition, L-IPSCs are mediated by glycine receptors and GABAC receptors. In response to light, IP cells reaction potentials transiently at the onset and onset of light stimulation. The major neural transmitter of IP cells in salamander retina is glycine. We also studied the distribution and function of glycine transporters. Our result indicates that GlyT1- and GlyT2-like transporters were present in Muller cells and neurons. The glycine feedback at outer plexiform layer (OPL) has effects on both the bipolar cell dendrites and rod photoreceptor terminals. At bipolar cell dendrites, glycine selectively depolarizes rod-dominant On-bipolar cells, and hyperpolarizes Off- bipolar cells. At rod photoreceptor terminals, 10 M glycine activates voltage-gated Ca2+ channels. These effects facilitated glutamate vesicle release in photoreceptors. It increases the sEPSC in OFF bipolar cells. The combined effect of glycine at rod terminals and bipolar cell dendrites leads to enhanced dim light signal transduction in the rod photoreceptor to ganglion cell pathway. This study provides a model that displays the function of centrifugal feedback through IP cells in the retina.
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Date Issued
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2009
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PURL
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http://purl.flvc.org/FAU/2708369
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Subject Headings
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Cellular signal transduction, Neurochemistry, Neuroplasticity, Synapses, Retina, Cytology, Visual pathways
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Format
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Document (PDF)
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Title
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pH Dynamics within the Drosophila Synaptic Cleft During Activity.
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Creator
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Feghhi, Touhid, Lau, Andy W.C., Macleod, Gregory T., Florida Atlantic University, Department of Physics, Charles E. Schmidt College of Science
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Abstract/Description
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Acute pH sensitivity of many neural mechanisms highlights the vulnerability of neurotransmission to the pH of the extracellular milieu. The dogma is that the synaptic cleft will acidify upon neurotransmission because the synaptic vesicles corelease neurotransmitters and protons to the cleft, and the direct data from sensory ribbon-type synapses support the acidification of the cleft. However, ribbon synapses have a much higher release probability than conventional synapses, and it’s not...
Show moreAcute pH sensitivity of many neural mechanisms highlights the vulnerability of neurotransmission to the pH of the extracellular milieu. The dogma is that the synaptic cleft will acidify upon neurotransmission because the synaptic vesicles corelease neurotransmitters and protons to the cleft, and the direct data from sensory ribbon-type synapses support the acidification of the cleft. However, ribbon synapses have a much higher release probability than conventional synapses, and it’s not established whether conventional synapses acidify as well. To test the acidification of the cleft in the conventional synapse, we used genetically encoded fluorescent pH reporters targeted to the synaptic cleft of Drosophila larvae. We observed alkalinization rather than acidification during activity, and this alkalinization was dependent on the exchange of protons for calcium at the postsynaptic membrane. A reaction-diffusion computational model of the pH dynamics at the Drosophila larval neuromuscular junction was developed to leverage the experimental data. The model incorporates the release of glutamate, ATP, and protons from synaptic vesicles into the cleft, PMCA activity, bicarbonate, and phosphate buffering systems. By means of numerical simulations, we reveal a highly dynamic pH landscape within the synaptic cleft, harboring deep but exceedingly rapid acid transients that give way to a prolonged period of alkalinization.
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Date Issued
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2023
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PURL
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http://purl.flvc.org/fau/fd/FA00014221
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Subject Headings
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Synapses, pH (Chemistry), Hydrogen-ion concentration., Synaptic Transmission, Drosophila
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Format
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Document (PDF)
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Title
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Regulation of rapid signaling at the cone ribbon synapse via distinct pre- and postsynaptic mechanisms.
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Creator
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Rowan, Matthew JM., Charles E. Schmidt College of Science, Department of Biological Sciences
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Abstract/Description
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Background: Light-adaptation is a multifaceted process in the retina that helps adjust the visual system to changing illumination levels. Many studies are focused on the photochemical mechanism of light-adaptation. Neural network adaptation mechanisms at the photoreceptor synapse are largely unknown. We find that large, spontaneous Excitatory Amino Acid Transporter (EAATs) activity in cone terminals may contribute to cone synaptic adaptation, specifically with respect to how these signals...
Show moreBackground: Light-adaptation is a multifaceted process in the retina that helps adjust the visual system to changing illumination levels. Many studies are focused on the photochemical mechanism of light-adaptation. Neural network adaptation mechanisms at the photoreceptor synapse are largely unknown. We find that large, spontaneous Excitatory Amino Acid Transporter (EAATs) activity in cone terminals may contribute to cone synaptic adaptation, specifically with respect to how these signals change in differing conditions of light. EAATs in neurons quickly transport glutamate from the synaptic cleft, and also elicit large thermodynamically uncoupled Cl- currents when activated. We recorded synaptic EAAT currents from cones to study glutamate-uptake events elicited by glutamate release from the local cone, and from adjacent photoreceptors. We find that cones are synaptically connected via EAATs in dark ; this synaptic connection is diminished in light-adapted cones. Methods: Whole-cell patch-clamp was performed on dark- and transiently light-adapted tiger salamander cones. Endogenous EAAT currents were recorded in cones with a short depolarization to -10mV/2ms, while spontaneous transporter currents from network cones were observed while a local cone holding at -70mV constantly. DHKA, a specific transporter inhibitor, was used to identify EAAT2 currents in the cone terminals, while TBOA identified other EAAT subtypes. GABAergic and glycinergic network inputs were always blocked with picrotoxin and strychnine. Results: Spontaneous EAAT currents were observed in cones held constantly at -70mV in dark, indicating that the cones received glutamate inputs from adjacent photoreceptors. These spontaneous EAAT currents disappeared in presence of a strong light, possibly because the light suppressed glutamate releases from the adjacent photoreceptors. The spontaneous EAAT currents were blocked with TBOA, but not DHKA, an inhibitor for EAAT2 subtype, suggesting that a, non-EAAT 2 subtype may reside in a basal or perisynaptic area of cones, with a specialized ability to bind exocytosed glutamate from adjacent cones in dark. Furthermore, these results could be artificially replicated by dual-electrode recordings from two adjacent cones. When glutamate release was elicited from one cone, the TBOA-sensitive EAAT currents were observed from the other cone. Conclusions: Cones appear to act like a meshwork, synaptically connected via glutamate transporters. Light attenuates glutamate release and diminishes the cone-cone synaptic connections. This process may act as an important network mechanism for cone light adaptation.
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Date Issued
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2011
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PURL
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http://purl.flvc.org/FAU/3337186
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Subject Headings
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Synapses, Neural transmission, VIsual perception, Presynaptic receptors, Molecular neurobiology, Glutamic acid, Neural receptors, Cellular signal transduction, Retina, Cytology
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Format
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Document (PDF)