Theses and Dissertations from UMD
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New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a give thesis/dissertation in DRUM
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Item LOCAL AND TOP-DOWN REGULATION OF OLFACTORY BULB CIRCUITS(2020) Hu, Ruilong; Araneda, Ricardo C; Neuroscience and Cognitive Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The olfactory bulb (OB) is the first place in the brain where chemosensory processing occurs. The neurophysiological mechanisms underlying these processes are mostly driven by inhibition, which is implemented by a large population of local inhibitory neurons, and among them, the granule cell (GCs) is the most prominent type. Local inhibitory interneurons sculpt the coding of output neurons, affecting odor detection, discrimination, and learning. Therefore, the regulation of inhibitory circuits is critical to OB function and fine-tuning OB output. Specifically, inhibitory tone in the OB can be regulated by the dynamic interactions between cell-intrinsic factors affecting neuronal excitability and extrinsic top-down modulation associated with an animal’s behavioral state. Here, I provide new evidence for intrinsic mechanisms governing inhibitory interneuron excitability in the OB and how modulation by noradrenaline works in concert with these intrinsic mechanisms to affect circuit function. This work highlights circuit- and cell-specific differences in noradrenergic modulation with regards to short- and long-term plasticity within OB circuits.Item Role of BK channels in cardiac function(2015) Lai, Michael; Meredith, Andrea L; Bioengineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Large-conductance voltage- and Ca2+-activated potassium (BK) channels are critical modulators of cellular excitability throughout the cardiovascular and nervous systems. The first aim of this work focuses on a novel role for BK channels in regulating cardiac pacing. Recently, BK channels were implicated in heart rate regulation, but the underlying mechanism was unclear. We hypothesized that BK channels regulate heart rate by modulating the intrinsic excitability of sinoatrial node cells (SANCs), the predominant cardiac pacemaking cells. We found that BK channel protein was expressed in SANCs, and that elimination of BK currents via pharmacological inhibition and genetic ablation reduces SANC excitability. Additionally, we characterized the properties of BK currents from SANCs. Our results indicate that BK channels are novel regulators of SANC function, and suggest that BK channels can serve as a novel therapeutic target for treating heart rate disorders. The second aim of this work focuses on the effect of single-nucleotide polymorphisms (SNPs) on BK current properties. There are approximately 100 known non-synonymous SNPs in human KCNMA1, the gene that encodes BK channels, but few have been characterized or linked with disease. We hypothesized that SNPs in KCNMA1 associated with disease, or located in domains of the BK channel gating ring that mediate Ca2+-dependent activation would alter BK current properties. We determined that the effects of SNPs on BK current properties were Ca2+ concentration-dependent. Also, we found that SNP-induced alterations in current kinetics influenced the amplitude of BK currents evoked by action potential waveforms. These results indicate that SNPs in KCNMA1 can modulate BK current properties and could contribute to the diversity of BK currents evoked by physiological stimuli.Item Microfluidic Planar Phospholipids Membrane System Advancing Dynamics Studies of Ion Channels and Membrane Physics(2012) Shao, Chenren; DeVoe, Donald L; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The interrogation of lipid membrane and biological ion channels supported within bilayer phospholipid membranes has greatly expanded our understanding of the roles membrane and ion channels play in a host of biological functions. Several key drawbacks of traditional electrophysiology systems used in these studies have long limited our effort to study the ion channels. Firstly, the large volume buffer in this system typically only allows single or multiple additions of reagents, while complete removal either is impossible or requires tedious effort to ensure the stability of membrane. Thus, it has been highly desirable to be able to rapidly and dynamically modulate the (bio)chemical conditions at the membrane site. Second, it is difficult to change temperature effectively with large thermal mass in macro device. Third, traditional PPM device host vertical membranes, therefore incompatible with confocal microscopy techniques. The miniaturization of bilayer phospholipid membrane has shown potential solution to the drawbacks stated above. A simple microfluidic design is developed to enable effective and robust dynamic perfusion of reagents directly to an on-chip planar phospholipid membrane (PPM). It allows ion channel conductance to be readily monitored under different dynamic reagent conditions, with perfusion rates up to 20 µL/min feasible without compromising the membrane integrity. It is estimated that the lower limit of time constant of kinetics that can be resolved by our system is 1 minute. Using this platform, the time-dependent responses of membrane-bound ceramide ion channels to treatments with La3+ and a Bcl-xL mutant were studied and the results were interpreted with a novel elastic biconcave distortion model. Another engineering challenge this dissertation takes on is the integration of fluorescence studies to micro-PPM system. The resulting novel microfluidic system enables high resolution, high magnification and real-time confocal microscope imaging with precise top and bottom (bio)chemical boundary conditions defined by perfusion, by integrating in situ PPM formation method, perfusion capability and microscopy compatibility. To demonstrate such electro-optical chip, lipid micro domains were imaged and quantitatively studied for their movements and responses to different physical parameters. As an extension to this platform, a double PPM system has been developed with the aim to study interactions between two membranes. Potential application in biophysics and biochemistry using those two platforms were discussed. Another important advantage of microfluidics is its lower thermal mass and compatibility with various microfabrication methods which enables potential integration of local temperature controller and sensor. A prototype thermal PPM chip is also discussed together with some preliminary results and their implication on ceramide channel assembly and disassembly mechanism.Item Catechols as Membrane Anion Transporters(2009) Berezin, Sofya; Davis, Jeffery T.; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)ABSTRACT Title of Document: CATECHOLS AS MEMBRANE ANION TRANSPORTERS Sofya Berezin, Doctor of Philosophy, 2009 Directed By: Professor, Jeffery T. Davis, Department of Chemistry and Biochemistry Synthetic anion transporters have potential as antimicrobials, extractants, sensors, etc. Anionophores may also help us understand how natural systems move ions across hydrophobic barriers. While bacterial siderophores and synthetic analogues use catecholates for Fe3+ uptake, this work reports of catechols facilitating biomembrane transport of anions. We demonstrate that simple bis-catechol III-25 is an anion transporter whose activity depends on catechol's substitution and amphiphilicity. We also describe liposomal assays and devised quantitative description that allows one to study facilitated anion transport. These assays indicate that selectivity of III-25 follows the Hofmeister bias: anions which are easier to dehydrate are made more permeable to the membrane by this bis-catechol. We believe that our description of the ion selectivity and mechanism for III-25 opens an outstanding opportunity for those interested in determining the selectivity and mechanism for other synthetic and natural biomembrane ion transporters. In the beginning of this project we investigated number of simple amides and phenols to evaluate their relative affinity and stoichiometry of interaction with Cl- anion. ESI-MS and 1H NMR analysis showed that a dimer, catechol2*Cl-, was the major complex formed when TBA+Cl- was mixed with excess catechol. Based on this finding we attached two catechols to a TREN scaffold. A hydrophobic alkyl amide groups were linked to TREN's third position. Surprisingly, this simple design led to the active analogs III-23 - III-26. A medium-length, III-25, was the most active compound, indicating that ion transport ability depends on the ability to partition into the biomembrane. Finally, we noticed that the experimentally observed weak dependence of the transport rates on the anion's hydration energy, namely, kAnion decreasing in the order ClO4- > I- > NO3- > Br- > Cl-, is also seen for some of Nature's anion transporters. Thus, anion permeation into the CFTR chloride channel shows a similar trend. We also observed a nonlinear dependence of kAnion on the concentration of bis-catechol. These findings led us to believe that self-association of III-25 provides transient pores that allow permeation without requiring complete dehydration of the inorganic anions. Future efforts will include incorporating selectivity filters into these bis-catechols to help overcome the Hofmeister bias.