Showing 451 - 460 of 681 Items
Effects of Picrotoxin Application on the Cardiac Ganglion of the American Lobster, Homarus americanus
Date: 2023-01-01
Creator: John T Woolley
Access: Open access
- Picrotoxin (PTX) has been employed extensively as a tool within the crustacean stomatogastric nervous system (STNS) for its efficacy in blocking K+ and Cl+ currents gated by both GABA and glutamate. Through blocking some currents in the STNS, PTX allows for examination of other components without their presence. However, effects of PTX are relatively unknown within the lobster’s cardiac ganglion (CG). As an incredibly small nervous system of only nine neurons, the lobster CG presents an excellent model system for studying neural circuits. Given that the chemical synapses in the CG are mediated by glutamate, the present study aimed to investigate the action of PTX in the lobster CG with the intent of better understanding its pharmacological impacts as a potential tool for studying the system. Therefore, this study aimed to establish the effects of PTX on CG responses to the application of exogenous GABA or glutamate. When data from both modulators were pooled, PTX applied at a concentration of 10-5M had significant effects on burst duration but not duty cycle or burst frequency of the CG. PTX did suppress GABA (5x10-5M) mediated inhibition of burst duration and duty cycle. PTX did not have any significant effects on burst duration, duty cycle, or frequency compared to exogenous glutamate application. These results indicate that glutamatergic inhibitory synapses are not present in the CG and PTX partially suppresses only GABAergic responses in this system.
Effects of myosuppressin, a peptide neuromodulator, on membrane currents in the crustacean cardiac ganglion
Date: 2022-01-01
Creator: Anthony Yanez
Access: Open access
- Central pattern generators are neural circuits that can independently produce rhythmic patterns of electrical activity without central or periphery inputs. They control rhythmic behaviors like breathing in humans and cardiac activity in crustaceans. Rhythmic behaviors must be flexible to respond appropriately to a changing environment; this flexibility is achieved through the action of neuromodulators. The cardiac ganglion of Homarus americanus, the American lobster, is a central pattern generator made up of four premotor neurons and five motor neurons. Membrane currents in each cell type, which can be targeted for modulation by various molecules, generate rhythmic bursts of action potentials. Myosuppressin, a FMRFamide-like peptide, is one such neuromodulator. The currents targeted for neuromodulation by myosuppressin are unknown. I investigated the molecular and physiological underpinnings of the modulatory effect of myosuppressin on motor neurons in the cardiac ganglion. First, using single cell RT-qPCR, I determined that across animals, motor neurons express myosuppressin receptor subtype II at equal levels relative to each other. Using sharp intracellular recordings, I showed that myosuppressin decreased burst frequency and the rate of depolarization during the inter-burst interval. I predicted that this effect resulted from the modulation of either A-type potassium current or calcium-dependent potassium current. Using two-electrode voltage clamp, I found that total outward current did not substantially change after treatment with myosuppressin. This result was surprising and provides grounds for explorations of subtle forms of neuromodulation in simple neural circuits.
Genetic Analysis of Adhesion Protein ELMO3 in Arabidopsis thaliana
Date: 2022-01-01
Creator: Garrison Asper
Access: Open access
- The Extracellular Matrix (ECM) between plant cells is vital for structure, development, and intercellular adhesion. A pectin rich layer in between cells, the middle lamella, is largely responsible for regulating the adhesive properties of adjacent plant cells. Homogalacturonan (HG) pectin, the most common, is synthesized in the Golgi and secreted into the ECM where it undergoes calcium crosslinking, increasing its adhesive properties. Mutations in proteins essential for HG synthesis can reveal a severe adhesion defective phenotype, where the hypocotyls of dark grown Arabidopsis exhibit cell sloughing, curling, and general disorganization. A family of five ELMO proteins are suspected to act as scaffolds for pectin biosynthesis enzymes. ELMO1 and ELMO4 mutants exhibit an adhesion deficient phenotype, and a double mutant provides evidence of redundancy in function between ELMO1 and ELMO2. ELMO1-GFP co-immunoprecipitated with enzymes required for HG synthesis indicating its role as a scaffold protein. Double mutants of the other ELMO homologues were created to determine if they exhibit functional redundancy, and ELMO1 and ELMO3 appear partially redundant. A gene deletion of ELMO3 was also created using the CRSPR/Cas9 system, resulting in two distinct elmo3 deletion alleles, which were phenotypically identical to the original elmo3-/- mutant. All adhesion defective phenotypes can be partially suppressed by altering the osmoticum and hence turgor that provides pressure on adhesive cells. Lastly, ELMO3-GFP was localized to the Golgi, the site of pectin biosynthesis, further supporting a common role of the ELMOs in pectin biosynthesis.
Reactions Responsible for Aging in Wood-Based Pyrolysis Oil: Synthesis and Characterization of a Coniferyl Alcohol Dimer
Date: 2021-01-01
Creator: Alejandro Garcia
Access: Open access
- The negative environmental impact and the diminishing supply of fossil fuels demand a renewable alternative. Pyrolysis oils produced from the decomposition of biomass, like wood, are a potential fuel substitute for energy production and a feedstock alternative for manufacturing value-added chemicals. The possibilities offered by pyrolysis oils are offset by oil instability. The oils contain reactive compounds, such as small aldehydes, conjugated aromatics, and acids that over time react and produce higher molecular mass products. This instability manifests as an increase in viscosity by a process referred to as aging. One chemical component, coniferyl alcohol, is proposed to react with formaldehyde under the acidic oil conditions to produce a dimer. In our lab, researchers have detected the coniferyl alcohol dimer in authentic oil samples and have simulated the reaction under conditions that removes the complexity of the pyrolysis oil matrix. This study focused on the synthesis, isolation, and characterization of the dimer structure by employing NMR analysis. GC/MS analysis of a successful synthesis of the dimer showed multiple dimers were produced, but there was one principal product. The NMR analysis of this dimer was used to elucidate the geometry, providing evidence that the product has E stereochemistry for the double bond and trans stereochemistry in the acetal ring. Confirmation of the principal structure provides support for the dimerization mechanism and will allow for future research to address instability of pyrolysis oils.
Modeling Coupled Disease-Behavior Dynamics of SARS-CoV-2 Using Influence Networks
Date: 2021-01-01
Creator: Juliana C. Taube
Access: Open access
- SARS-CoV-2, the virus that causes COVID-19, has caused significant human morbidity and mortality since its emergence in late 2019. Not only have over three million people died, but humans have been forced to change their behavior in a variety of ways, including limiting their contacts, social distancing, and wearing masks. Early infectious disease models, like the classical SIR model by Kermack and McKendrick, do not account for differing contact structures and behavior. More recent work has demonstrated that contact structures and behavior can considerably impact disease dynamics. We construct a coupled disease-behavior dynamical model for SARS-CoV-2 by incorporating heterogeneous contact structures and decisions about masking. We use a contact network with household, work, and friend interactions to capture the variation in contact patterns. We allow decisions about masking to occur at a different time scale from disease spread which dramatically changes the masking dynamics. Drawing from the field of game theory, we construct an individual decision-making process that relies on perceived risk of infection, social influence, and individual resistance to masking. Through simulation, we find that social influence prevents masking, while perceived risk largely drives individuals to mask. Underlying contact structure also affects the number of people who mask. This model serves as a starting point for future work which could explore the relative importance of social influence and perceived risk in human decision-making.
The Congressional Database: Designing a Web Application Using an HCI Approach
Date: 2021-01-01
Creator: Liam R. Juskevice
Access: Open access
- The activities of the United States Senate are a topic of interest for researchers and concerned members of the public alike. Websites such as GovTrack and Congress.gov allow people to research specific bills among many other offerings. However, they have significant weaknesses regarding their ease of use and the way they organize and store data. The Congressional Database Project aims to provide an intuitive user experience navigating government data while storing the data in a consistent database. We approach this project from an HCI perspective in order to determine the best ways to improve the user experience. We have conducted a qualitative user study to test the effectiveness of our design and identify potential areas of improvement. This paper provides an in-depth overview of the design of the Congressional Database on the front end and back end. It then explains the methodology of our user study and discusses the implications of its findings.
"Italianos por todos lados (Italians Everywhere)": Italian Immigrants and Argentine Exceptionalism Access to this record is restricted to members of the Bowdoin community. Log in here to view.
Date: 2022-01-01
Creator: Julia Elisabeth Perillo
Access: Access restricted to the Bowdoin Community
The Roles of ROG1, REM1, and REM2 in a WAK Mediated Pectin Response Access to this record is restricted to members of the Bowdoin community. Log in here to view.
Date: 2015-05-01
Creator: Joshua A Benton
Access: Access restricted to the Bowdoin Community
Digital Market Concentration: An Institutional and Social Cost Analysis
Date: 2022-01-01
Creator: Jack Shane
Access: Open access
- In this thesis, I develop an analysis of the industry concentration seen in digital markets today. I begin with a description and argument for the use of institutional economics. This framework allows for the integration of an interdisciplinary approach to economics. My analysis details the socioeconomic and political impacts, as well as the underlying market dynamics that have pushed digital markets towards concentration. I offer novel explanations for the lack of firm behavior that should theoretically increase profit, the existence of barriers to competition, and consumer behavior that focus on the role of social institutions. I also detail many of the social costs of these concentrated markets, such as their impact on democracy, power to influence social institutions, and the impact they have on concentration in other markets. This is done to show that the fears surrounding monopolies do not end with prices. Even in digital markets, where many times prices are very low, if not zero, there are reasons that monopoly is economically inefficient and socially sub-optimal. However, due to the path-dependent nature of the extreme benefits associated with digital markets, policymakers cannot reasonably propose breaking up these companies. Instead, they must use the power of the government to counteract the conglomerations of social power seen in these private companies in search of an optimal outcome.
From “a Journey for Peace” to the “Butchers of Beijing”: How Presidents have Used Rhetoric about China to Win the Two-Level Game
Date: 2021-01-01
Creator: Juliet Halvorson-Taylor
Access: Open access
- This thesis is an exploration of how American presidents have used rhetoric for strategic ends in the US-China relationship. Whenever a president speaks, he is speaking to multiple audiences at the same time, yet he also must balance a number of important considerations. I used Robert Putnam’s “Two-Level Game Theory” as a framework for understanding the conditions surrounding a moment of significance in US-China relations in order to decipher a president’s rhetorical choices. The project is divided into five main parts. First, I used the UCSB American Presidency Project to identify broad trends in rhetoric towards China across presidencies. I found that every president has spoken more about China than his predecessor since the 1980s and that presidents are increasingly using negative rhetoric when talking about China. Then, I conducted three case studies, within the Putnam framework, on important points in three presidencies: Truman’s decision to withdraw aid from the KMT, Nixon’s visit to China, and Clinton’s reversal on the issue of MFN status for China. Lastly, I concluded that when “win-sets” on both sides (in these examples: on both the American and Chinese sides) are either large or small, a president should speak about China more frequently. I also looked at Trump’s presidency and the beginnings of Biden’s in order to see how these trends are playing out currently.