abstract: Space exploration is a large field that requires high performing circuitry due to the harsh environment. Within a space environment one of the biggest factors leading to circuit failure is radiation. Circuits must be robust enough to continue operation after being exposed to the high doses of radiation. Bandgap reference (BGR) circuits are designed to be voltage references that stay stable across a wide range of supply voltages and temperatures. A bandgap reference is a piece of a large circuit that supplies critical elements of the large circuit with a constant voltage. When used in a space environment with large amounts of radiation a BGR needs to maintain its output voltage to enable the rest of the circuit to operate under proper conditions. Since a BGR is not a standalone circuit it is difficult and expensive to test if a BGR is maintaining its reference voltage. This thesis describes a methodology of isolating and simulating bandgap references. Both NPN and PNP bandgap references are simulated over a variety of radiation doses and dose rates. This methodology will allow the degradation due to radiation of a BGR to be modeled easily and affordably. It can be observed that many circuits experience enhanced low dose rate sensitivity (ELDRS) which can lead to failure at low total ionizing doses (TID) of radiation. A compact model library demonstrating degradation of transistors at both high and low dose rates (HDR and LDR) will be used to show bandgap references reliability. Specifically, two bandgap references being utilized in commercial off the shelf low dropout regulators (LDO) will be evaluated. The LDOs are reverse engineered in a simulation program with integrated circuit emphasis (SPICE). Within the two LDOs the bandgaps will be the points of interest. Of the LDOs one has a positive regulated voltage and one has a negative regulated voltage. This requires an NPN and a PNP based BGR respectively. This simulation methodology will draw conclusions about the above bandgap references, and how they operate under radiation at different doses and dose rates. / Dissertation/Thesis / Masters Thesis Electrical Engineering 2019

The prevailing view is that enhancement of dopamine (DA) transmission in the mesolimbic system leads to the rewarding properties of alcohol. The mesolimbic DA system, which plays an important role in regulating reward and addiction, consists of DA neurons in the midbrain ventral tegmental area (VTA) that innervate the nucleus accumbens (NAc). It is believed that VTA DA neurons are inhibited by local gamma-aminobutyric acid (GABA) interneurons that express connexin-36 (Cx36) gap junctions (GJs). We have previously demonstrated that blocking Cx36 GJs suppresses electrical coupling between VTA GABA neurons and reduces ethanol intoxication and consumption suggesting that electrical coupling between mature VTA GABA neurons underlies the rewarding properties of ethanol. The aim of this study was to further investigate the role of VTA GABA neurons expressing Cx36 GJs in regulating DA neuron activity and release and mediating ethanol effects on VTA GABA neurons. To this end, we customized a Designer Receptor Exclusively Activated by Designer Drugs (DREADDs) viral vector to target VTA GABA neurons expressing Cx36 GJs in order to chemogenetically modulate their activity. In order to more conclusively demonstrate the role of this sub population of VTA GABA neurons in regulating DA neural activity and release we used electrophysiology to characterize the electrical changes that occur in VTA DA and GABA neurons when Cx36-expressing VTA GABA cells were selectively activated. In addition, we evaluated the effects of activation of VTA GABA neurons on brain stimulation reward and alcohol consumption in ethanol naive and dependent mice. Results indicate that there are two populations of GABA neurons in the VTA, one that is GAD65+/Cx36+ and one that is GAD67+/Cx36-. Activation of Cx36+ VTA GABA neurons by clozapine-n-oxide (CNO) in mice injected with Gq DREADD activated VTA DA neurons and subsequent DA release in the NAc, suggesting that Cx36-containing GABA neurons are inhibiting non-Cx36 GABA neurons to disinhibit DA neurons. In hM3Dq animals, CNO administration provided a rewarding stimulus in the conditioned pace preference paradigm, and reduced consumption in the drink-in-the-dark ethanol consumption paradigm in dependent and naïve mice. A better understanding of the circuitry of the mesolimbic DA system is key to understanding the mechanisms that lead to addiction and may ultimately lead to improved therapies for substance abuse.

The prevailing view is that enhancement of dopamine (DA) transmission in the mesolimbic system leads to the rewarding properties of alcohol. The mesolimbic DA system, which plays an important role in regulating reward and addiction, consists of DA neurons in the midbrain ventral tegmental area (VTA) that innervate the nucleus accumbens (NAc). It is believed that VTA DA neurons are inhibited by local gamma-aminobutyric acid (GABA) interneurons that express connexin-36 (Cx36) gap junctions (GJs). We have previously demonstrated that blocking Cx36 GJs suppresses electrical coupling between VTA GABA neurons and reduces ethanol intoxication and consumption suggesting that electrical coupling between mature VTA GABA neurons underlies the rewarding properties of ethanol. The aim of this study was to further investigate the role of VTA GABA neurons expressing Cx36 GJs in regulating DA neuron activity and release and mediating ethanol effects on VTA GABA neurons. To this end, we customized a Designer Receptor Exclusively Activated by Designer Drugs (DREADDs) viral vector to target VTA GABA neurons expressing Cx36 GJs in order to chemogenetically modulate their activity. In order to more conclusively demonstrate the role of this sub population of VTA GABA neurons in regulating DA neural activity and release we used electrophysiology to characterize the electrical changes that occur in VTA DA and GABA neurons when Cx36-expressing VTA GABA cells were selectively activated. In addition, we evaluated the effects of activation of VTA GABA neurons on brain stimulation reward and alcohol consumption in ethanol naive and dependent mice. Results indicate that there are two populations of GABA neurons in the VTA, one that is GAD65+/Cx36+ and one that is GAD67+/Cx36-. Activation of Cx36+ VTA GABA neurons by clozapine-n-oxide (CNO) in mice injected with Gq DREADD activated VTA DA neurons and subsequent DA release in the NAc, suggesting that Cx36-containing GABA neurons are inhibiting non-Cx36 GABA neurons to disinhibit DA neurons. In hM3Dq animals, CNO administration provided a rewarding stimulus in the conditioned pace preference paradigm, and reduced consumption in the drink-in-the-dark ethanol consumption paradigm in dependent and naïve mice. A better understanding of the circuitry of the mesolimbic DA system is key to understanding the mechanisms that lead to addiction and may ultimately lead to improved therapies for substance abuse.

Numerous events during development require the tightly controlled and regulated interaction of cells - from gastrulation in the early embryo to axonal pathfinding and remodeling of synaptic networks. Each of these events is dependent upon signals generated by cell-cell interactions, which are in turn specified by a diverse number of cell adhesion molecules. Many families of cell adhesion molecules have been described, and these fall into the broad categories of cadherins, immunoglobulin superfamily (IgSF) members, selectins, and integrins. Activated Leukocyte Cell Adhesion Molecule (ALCAM) is a member of the IgSF, and controls numerous developmental processes, ranging from hematopoiesis to neuronal targeting. Furthermore, this protein has been implicated in the progression of numerous cancers of diverse origins. Despite the variety of developmental and pathological processes in which ALCAM has been implicated, little is known about how it signals in the cell - few extracellular binding partners have been isolated, and, as of this writing, no cytoplasmic interactors have been identified. The purpose of the work presented in this thesis was to elucidate the mechanisms by which ALCAM influences cell behavior, specifically in uveal melanoma cells, and to determine novel extra- and intracellular ligands. Here, I report the regulation of cadherin-based junctions by ALCAM in uveal melanoma cells, as well as provide evidence for a novel extracellular interaction with L1 cell adhesion molecule, and identify three novel intracellular binding partners.

To experience the world, we depend on the ability of our brains to process information. Problems can occur when communication between neurons is not regulated, and a significant enough loss of stability could lead to conditions such as migraine and epilepsy. Homeostatic plasticity is thought to constrain activity within physiologically useful ranges. Our lab uses the fruit fly neuromuscular junction as a model synapse to study homeostatic plasticity. Homeostatic potentiation and homeostatic depression are two forms of homeostatic synaptic plasticity. Expression of a dominant negative glutamate receptor subunit in the muscle impairs its sensitivity to glutamate and triggers an increase in the number of vesicles released per evoked potential, or quantal content. This increase in quantal content is called homeostatic potentiation. We found that homeostatic potentiation is a reversible process: quantal content returns to normal levels when expression of the dominant negative ceases. We additionally found that homeostatic potentiation can be ablated at high temperature. Overexpression of the Vesicular Glutamate transporter (VGlut) causes an increase in the amplitude of spontaneous events, leading to a corresponding decrease in quantal content, called homeostatic depression. It is unknown to what degree homeostatic potentiation and homeostatic depression may share regulatory machinery. We screened genes required for homeostatic potentiation in the neuron for additional roles in homeostatic depression. We found that certain genes involved in calcium regulation, such as the IP3 receptor and ryanodine receptor, showed a substantial decrease in evoked potential amplitude in a VGlut overexpression background.

Neisseria meningitidis ist mit jahrlich etwa 700.000 Erkrankungsfallen weltweit und einer Mortalitat von circa 7% einer der häufigsten Ausloser der bakteriellen Hirnhautentzündung. Der entscheidende Schritt zur Auslosung einer Meningitis ist die Uberwindung der Blut-Hirn-Schranke. Diese im menschlichen Korper einmalig dichte Barriere wird maßgeblich durch Tight-Junctions spezialisierter Endothelzellen der Hirnkapillaren aufrecht erhalten. Ob N. Meningitidis diese Barriere auf einem parazellulären oder transzellulärem Weg uberwindet, ist nicht vollstandig geklart. In dieser Arbeit wurde der Einfluss von N. meningitidis auf die Tight-Junction Proteine Occludin und ZO-1 unter Nutzung des HBMEC Zellkulurmodelles untersucht. Neben einer verminderten Genexpression von Occludin zeigte sich dabei eine Abspaltung eines 50 kDa Fragmentes von Occludin. Gleichzeitig konnte eine Umverteilung von Occludin von den Zellgrenzen in das Zytoplasma beobachtet werden. ZO-1 hingegen wurde weder in seiner Exprimierung, noch in seiner intrazellularen Verteilung beeinflusst. Mittels eines in dieser Arbeit etablierten Assays zur Bestimmung der Permeabilitat eines HBMEC-Monolayer als vereinfachtes in-vitro Modell der Blut-Hirn-Schranke konnte bestatigt werden, dass durch die Beeinflussung von Tight-Junction Proteinen die parazellulare Permeabilitat steigt. In weiteren Analysen konnten diese Prozesse auf eine gesteigerte Aktivitat von Matrixmetalloproteinase 8 zurückgefuhrt werden. Die Ergebnisse dieser Arbeit zeigen einen neuen Mechanismus auf, durch den N. meningitidis im Stande ist, die-Hinr-Schranke auf einem parazellulärem Weg zu überwinden. / Neisseria meningitidis is a leading cause of bacterial meningitis with about 700.000 cases per year and a mortality of approximately 7%. A crucial step in the pathogenesis of meningococcal meningitis is the crossing of the blood-brain barrier (BBB). This barrier mainly consists of tight junctions of the microvascular endothelial cells. It remains unclear whether N. meningitidis passes the BBB by a paracellular or transcellular route. In this work the influence of N. meningitidis on the tight junction proteins occludin and ZO-1 was investigated by using the HBMEC cell-culture model. Using QRT-PCR a reduced expression of occludin was seen, western-blot analyses showed a cleavage of occludin into a fragment of 50 kDA. Immonulourescence further showed a complete dissociation of occludin from the cell membrane, whereas ZO-1 was not influenced. By establishing a permeability-assay an increased permeability of the HBMEC monolayer after infection with N. meningitidis was demonstrated. Further work showed, that these effects are dependent of an increased activity of matrix metalloproteinase-8. These results reveal a new mechanism that could enable N. meningitidis to cross the BBB by a paracellular route.

Die Öffnung der Blut-Nerven-Schranke ist ein wichtiger Baustein in der Pathogenese neuropathischer Schmerzen. Die Blut-Nerven-Schranke schützt das periphere Nervensystem vor externen Einflüssen, wahrt die endoneurale Homöostase und trägt zur Aufrechterhaltung der neuronalen Signalweiterleitung bei. Sie wird durch die Pars epitheloidea des Perineuriums und endoneurale Gefäßzellen gebildet. Essentieller Bestandteil der Blut-Nerven-Schranke sind zwischen Perineural- und Gefäßzellen exprimierte Tight Junctions. Im Rahmen dieser Dissertation wurden die Tight Junction Proteine ZO-1, Claudin-1, -5, -19 und Occludin sowohl in einem Tiermodell neuropathischer Schmerzen, der Chronic Constriction Injury, als auch in Nervenbiopsien (N. suralis) von an Polyneuropathien erkrankten Patienten mittels Immunfluoreszenzfärbungen qualitativ und quantitativ untersucht. / The opening of the blood nerve barrier is an important in the pathogenesis of neuropathic pain. The blood nerve barrier protects the peripheral nervous system from external influences, preserves endoneurial homeostasis, and helps maintain neuronal signal transduction. It is formed by the pars epitheloidea of the perineurium and endoneural vascular cells. An essential component of the blood-nerve barrier are tight junctions expressed between perineural and vascular cells. In this thesis, the tight junction poteins ZO-1, claudin-1, -5, -19 and occludin were examined qualitatively and quantitatively in an animal model of neuropathic pain, the Chronic Constriction Injury, as well as in human nerve biopsies (N. suralis) by patients suffering from polyneuropathy using immunofluorescence stainings.

The Sertoli cell tight junction (TJ) of the seminiferous epithelium is important for the developmental process of spermatogenesis as it separates germ cells in the seminiferous tubules from the general circulation in the testicular interstitium. Absence of the TJ leads to spermatogenic arrest and infertility. TJs form at puberty as circulating gonadotrophins luteinising hormone/testosterone and follicle stimulating hormone increase. Several studies have demonstrated hormonal regulation of the two major TJ proteins, claudin-11 and occludin, and also of TJ function in vitro and in vivo. Men with low levels of circulating gonadotrophins exhibit an immature and dysfunctional TJ phenotype, which is reversed upon the exogenous application of gonadotrophins. This thesis hypothesises that claudin-11 and occludin are the major contributors to TJ function, and that gonadotrophins regulate TJ function and structure via these two proteins in several species including humans. This PhD was divided into four separate studies to address these hypotheses. The first study selectively silenced the genetic expression of claudin-11 and occludin with small interfering RNA (siRNA) in cultured immature rat Sertoli cells to determine their contribution to Sertoli cell TJ function in vitro. siRNA treatment against either protein significantly (p less than 0.01) reduced TJ function by ~50% as assessed by transepithelial electrical resistance. Immunocytochemistry displayed marked reductions in the localisation of these proteins to the TJ after siRNA treatment. It was concluded that both proteins significantly contributed to TJ function in vitro. The second and third studies then aimed to study hormonal regulation of the TJ in vivo. Weekly injections of the gonadotrophin releasing hormone antagonist acyline were used to suppress circulating gonadotrophins and spermatogenesis in adult rats. Acyline treatment disrupted i) the localisation of occludin to the TJ and ii) TJ function as shown by permeability to a biotin tracer, which was impermeable to TJs in controls. Short-term hormone replacement partially restored the effects of gonadotrophin suppression. It was concluded that gonadotrophins regulate the maintenance of the TJ in rats in vivo. The third study used the hypogonadal (hpg) mouse, which is a naturally occurring model of gonadotrophin deficiency with inactive spermatogenesis. Claudin-11 in hpg mice was not localised at the TJs, and these were dysfunctional as shown by permeability to biotin. Following hormone treatment, TJs were structurally and functionally competent, demonstrating that gonadotrophins also regulate the formation of TJs in vivo. The fourth study subsequently analysed TJs in gonadotrophin suppressed men, and it was found that claudin-11 staining was reduced from continuous bands in control men, to punctate staining in gonadotrophin-suppressed men, demonstrating that gonadotrophins also regulate the localisation of claudin-11 to the TJ in men in vivo. In summary, it is concluded that the Sertoli cell TJ is hormonally regulated, and that the major contributors to TJ function in vivo and in vitro are claudin-11 and occludin. It is hypothesised that the reduction of claudin-11 localisation to the TJ in men may also result in a loss of human Sertoli cell TJ function, suggesting that the TJ may be a potential target of hormonal contraception in men.

Thesis (M.S.)--State University of New York at Binghamton, Department of Physics, 2006. / Includes bibliographical references.

Thesis (Ph.D.)--Hong Kong University of Science and Technology, 2007. / Includes bibliographical references (leaves 119-134). Also available in electronic version.