Global ETD Search

1	Identification of Moving Conspecifics in the Weakly Electric Fish Eigenmannia virescens Peters, Kathleen 21 August 2018 (has links) Eigenmannia virescens is a gymnotiform weakly electric fish which uses a quasi-sinusoidal electric organ discharge (EOD) to sense their environment. EOD frequency (EODF) is individual-specific. In conspecific interactions, each fish perceives the EODF of the conspecific as a periodic amplitude modulation (AM) of their own discharge. When both fish are stationary, the depth of this AM is constant, but it varies when fish are swimming. We hypothesized that AM variations during swimming act as a noise source that could have no effect on, hinder, or enhance EODF identification. To test this, we quantified the jamming avoidance response (JAR) (a natural behaviour wherein fish are required to accurately determine one another’s EODF) in response to stimuli of varying depths of noise. These experiments demonstrated that swimming noise does not impair the ability of E. virescens to identify conspecific EODF, and actually improves its ability to detect the presence of a neighbouring fish. Weakly electric fish Envelope Amplitude modulation Electric organ discharge
2	Role of N- and C- termini in inactivation of sodium channel in weakly electric fish Wu, Mingming 22 October 2009 (has links) The weakly electric fish Sternopygus macrurus emits an electric organ discharge (EOD) composed of a series of pulses. The EOD pulse is mainly shaped by sodium currents. There are two sodium channel α subunits orthologs of the mammalian Nav1.4 expressed in the EO of Sternopygus. Previous studies identified a novel splice variant of the Nav1.4b (Nav1.4bL), in which an extra 51-amino acid occurs in the N terminal end. Nav1.4bL currents inactivate and recover from inactivation significantly faster than Nav1.4bS. The voltage-dependence of steady-state inactivation of smNav1.4bL shifts to hyperpolarized potential. Structural analysis predicts an α-helix in the middle of the extended N terminus. Removal of a proline right after the α-helix significantly slows down current decay but has no effect on channel recovery from inactivation, suggesting inactivation and recovery have independent mechanism. Mutagenesis analysis of the extended N terminus showed that the short helical region, especially the positive charges in the helix, is an important determinant for channel voltage-dependence of steady-state inactivation. However, other residues outside the helical region are required for regulation of fast inactivation and recovery form inactivation. Functional and structural analysis provides evidence for the importance of the C terminus in fish Nav1.4b channel properties. Chimera in which the C terminus of smNav1.4bS was substituted by the human Nav1.4 C terminus, shows an 11 mV positive shift in voltage-dependence of activation and a -16 mV negative shift in inactivation. Deletion of the distal half of smNav1.4bS negatively shifted voltage-dependence of inactivation and significantly accelerated channel recovery from inactivation. In the deletion mutant, the regulation by the N segment is missing. Substitution of the C terminus mutant retains wild type channel inactivation and recovery properties and can be regulated by N segment again. My study provides evidence that the extended N terminus of smNav1.4bL binds the distal part of C terminal tail to modulate channel inactivation properties. This is the first time to show the distal C terminus is involved in channel recovery from inactivation. Studies in the fish sodium channel properties provide useful information to understand function and structure of voltage-gated sodium channels. / text Weakly electric fish Sternopygus macrurus Electric organ discharge Sodium channels N terminus C terminus Channel inactivation
3	Developing Tools towards Ion Homeostasis in Spatially Polarized Excitable Cells Liu, Ziyi 16 January 2024 (has links) In 1800, Volta, inspired by the electric organs of a genus of electric fish, the Electrophorus, invented the first electric batteries, which were termed "artificial electric organs." Since then, the far-reaching implications of the fishes’ electrogenesis have come under greater attention and interest. In these fishes, the electric organ resembles a series of batteries. The electric organs are formed by electrocytes (the "batteries") with a distinct cytomorphology for discharging and charging. Although the arrangements of electrocytes in the electric organ are well-understood, the mechanisms involved in generating electric discharges within equivalent circuits remain unclear. In this thesis, the first element consists of adapting spatially defined models that we use to investigate the process of electrocyte charging and recharging under the added assumption of ion homeostasis, the process by which a cell restores its internal milieu. The study focuses on Eigenmannia and Electrophorus, two genera of electric fish. Eigenmannia's steady high-frequency dipole oscillator-like electric organ discharges enables electro-sensing and electro-communication, whilst Electrophorus's brief taser-like electric bursts serve as tetanizing predatory assaults. In addition, the second section of this study proposes a one-dimensional charge difference model that focuses on the modification of endogenous electric fields resulting from the uneven distribution of ions in a homeostatic apparatus. Electric Organ Discharge Electric Fish Eigenmannia Electrophorus Ion Homeostasis Endogenous Electric Field Polarized Excitable Cell
4	Phylogeny and Molecular Evolution of the Voltage-gated Sodium Channel Gene scn4aa in the Electric Fish Genus Gymnotus Xiao, Dawn Dong-yi 19 March 2014 (has links) Analyses of the evolution and function of voltage-gated sodium channel proteins (Navs) have largely been limited to mutations from individual people with diagnosed neuromuscular disease. This project investigates the carboxyl-terminus of the Nav paralog (locus scn4aa 3’) that is preferentially expressed in electric organs of Neotropical weakly-electric fishes (Order Gymnotiformes). As a model system, I used the genus Gymnotus, a diverse clade of fishes that produce species-specific electric organ discharges (EODs). I clarified evolutionary relationships among Gymnotus species using mitochondrial (cytochrome b, and 16S ribosome) and nuclear (rag2, and scn4aa) gene sequences (3739 nucleotide positions from 28 Gymnotus species). I analyzed the molecular evolution of scn4aa 3’, and detected evidence for positive selection at eight amino acid sites in seven Gymnotus lineages. These eight amino acid sites are located in motifs that may be important for modulation of EOD frequencies. phylogeny systematics molecular evolution evolution voltage-gated sodium channel scn4a Nav1.4 sodium channel gene protein fish electric fish knifefish Neotropical fish Gymnotiform Gymnotus electric organ discharge electric field electric organ electric signal cytochrome b 16S ribosome phylogenetic reconstruction phylogenetic tree evolutionary history positive selection patterns of selection neuromuscular disease gene duplication differential expression maximum parsimony parsimony PAUP* Bayesian inference MrBayes Bayesian maximum likelihood PAML 0307
5	Phylogeny and Molecular Evolution of the Voltage-gated Sodium Channel Gene scn4aa in the Electric Fish Genus Gymnotus Xiao, Dawn Dong-yi 19 March 2014 (has links) Analyses of the evolution and function of voltage-gated sodium channel proteins (Navs) have largely been limited to mutations from individual people with diagnosed neuromuscular disease. This project investigates the carboxyl-terminus of the Nav paralog (locus scn4aa 3’) that is preferentially expressed in electric organs of Neotropical weakly-electric fishes (Order Gymnotiformes). As a model system, I used the genus Gymnotus, a diverse clade of fishes that produce species-specific electric organ discharges (EODs). I clarified evolutionary relationships among Gymnotus species using mitochondrial (cytochrome b, and 16S ribosome) and nuclear (rag2, and scn4aa) gene sequences (3739 nucleotide positions from 28 Gymnotus species). I analyzed the molecular evolution of scn4aa 3’, and detected evidence for positive selection at eight amino acid sites in seven Gymnotus lineages. These eight amino acid sites are located in motifs that may be important for modulation of EOD frequencies. phylogeny systematics molecular evolution evolution voltage-gated sodium channel scn4a Nav1.4 sodium channel gene protein fish electric fish knifefish Neotropical fish Gymnotiform Gymnotus electric organ discharge electric field electric organ electric signal cytochrome b 16S ribosome phylogenetic reconstruction phylogenetic tree evolutionary history positive selection patterns of selection neuromuscular disease gene duplication differential expression maximum parsimony parsimony PAUP* Bayesian inference MrBayes Bayesian maximum likelihood PAML 0307

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