Undergraduate Research Scholars Capstone (2006–present)

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Bcep176 and Bglu421 - two novel phages contributing to the understanding of pathogenicity and diversity in Burkholderiacae
(2006-07-11) Mera, Linet
Phage, although but a fraction of the size of bacteria, can, by lysogenic conversion, transform a harmless bacterium into a ruthless pathogen (3). This paper will discuss two new lysogenic dsDNA tailed phages of Burkholderia. Bcep176 was induced from Burkholderia multivorans ATCC17616, thought to be found in pulmonary infections (9), and Bglu421, from a rice seed isolate of B. glumae BG 10421, known to be the causative agent for rice seed rot (19). The capsid-to-tail proteins and tail assembly cassette of Bcep176 demonstrated significant modular mosaicism to homologs in lambdoid phages phiE125 and phi1026b – phages involved in the study of bacterial bioweapons (13, 26). Bglu421 exhibited modular mosaicism in tail assembly cassette and putative morons to homolog counterparts in a previously unannotated prophage of Burkholderia pseudomallei Pasteur - causative agent of melioidosis in a variety of animals (12). Further analysis of both phages indicates siphophage morphology and lambda-like proteins in Bcep176 and a putative pathogenicity factor in Bglu421. The importance of genomic sequencing and analysis of bacteriophages lies in their role of influencing the pathogenicity of their host (5), and their potential for use as cures of bacterial disease (1).
Austism and the Potential Role of Immune Function and Prenatal Methymercury Exposure
(2006-07-11) Bustamante, Nirma Dora
Methylmercury (MeHg) remains to be a major public health concern because of the presence of widespread contamination of our environment and the severe neuropathological changes that can occur with exposure to the developing central nervous system (CNS). The blood-brain barrier (BBB) represents an important target for MeHg. However, before the BBB is fully formed or if the BBB is compromised once it is formed, it can not effectively isolate the brain from circulating toxins and foreign compounds. The current project examines the hypothesis that there is a correlation between childhood vaccination and the neurotoxic effects of mercury in the form of MeHg in the pathogenesis of autism. The effects from exposure to MeHg and activation of the immune system can affect neuronal survival and development and could result in the faulty wiring that appears to occur in the CNS of autistic children. Mice were exposed to low dose (0.03 µg/kg of body weight of the pregnant mouse) MeHg during prenatal development. Lipopolysaccharide (LPS) was administered during early iv postnatal development as an immunostimulant. In order to determine the optimal time in which the injection of LPS would be the most effective, mice were injected with LPS then euthanized and injected with Evans Blue dye at 4, 6, 22, and 48 hours. The brain was separated into forebrain, cerebellum, and brainstem. Using a fluorescence micro plate reader, the quantity of Evans Blue leaking into the brain through the BBB was calculated. It was determined the mice should be euthanized 6 hours after administration of LPS. LPS or the control solution, phosphate buffered saline (PBS), was administered at postnatal day 18 into mouse pups that received MeHg prenatally and then the integrity of the BBB was checked 6 hours later. No difference was observed between mice given LPS compared to the mice given PBS most likely due to too much variability. There may be an effect of LPS but it is masked by the variability that occurs when using this assay in such young mice. A radioactive assay using 14C-labeled sucrose is going to be used in order to acquire better results.
Isolation and Characterization of an Anti-viral RISC in Plants
(2006-07-11) Ciomperlik, Jessica
As a defense against viral infection, plants are only very recently thought to use an RNA-induced silencing complex (RISC) as part of the RNA interference (RNAi) pathway to target and cleave viral RNA. To counteract this, some viruses have evolved proteins to inhibit RISC-mediated activity, thus ensuring their continued virulence. This research focused on the elucidation and analysis of anti-viral RISC in plants, to gain an understanding of how both the plant defense and countering viral mechanisms operate at the molecular level. A virus-host model system was used to examine this; Nicotiana benthamiana plants were infected with Tomato bushy stunt virus (TBSV) and time was allowed for RISC to target and cleave the viral RNA. If the TBSV defense protein, called P19, was present, the virus was not degraded by RISC and infection culminated in the death of the plant. When the plants were instead inoculated with a mutant of the virus, in which P19 was not expressed, RISC cleared the viral RNA and the plant survived the infection. This agrees with the model that RISC can (be programmed to) act as an anti-TBSV complex. To examine the composition of the anti-TBSV RISC, plant proteins from both scenarios (with the presence or absence of P19) were subjected to various biochemical analyses and purification techniques. Proteins most closely associated with RISC activity in vitro (degradation of viral RNA in the test tube) were purified toward determining their identity. Future experiments are planned to examine if the antiviral RISC proteins are unique to TBSV infected plants or whether they are also associated with other virus infections.
Micropolis: A Virtual City for Water Distribution System Research Applications
(2006-07-11) Torres, Jacob
For security reasons, cities keep their water distribution system data confidential. This data includes geographic layout of pipes, tanks, pumps, wells, buildings, and demands. While the secrecy of water system data is crucial, it poses a difficulty for research on water distribution systems as results can not be publicized. Therefore, a library of virtual water distribution systems can be an important research tool for comparative development of many analytical methods. A “virtual city” has been developed, including a comprehensive water distribution system, as a first entry into such a library. “Micropolis” is a virtual city of 5000 residents fully described in both geographic information systems (GIS) and EPANet hydraulic model frameworks. To simulate realism of infrastructure, a developmental timeline spanning 130 years was described, and this timeline is manifested in items such as pipe material, diameter, and topology. Examples of using the virtual city for simulations of contaminant spread are presented, and future applications will include fire flow and water auditing. The data digital files describing Micropolis are available from the authors for others’ use. It is hoped that other virtual cities will follow for the use of the research community.
SNAKE SPECIES RICHNESS IN RELATION TO HABITAT IN THE POST OAK SAVANNAH OF EAST CENTRAL TEXAS
(2006-07-11) Putegnat, John
This project examined snake species richness and relative abundances in a heterogeneous landscape within the post oak savannah of East Central Texas. Snakes were sampled using funnel traps (with drift fences for terrestrial species) and hand capture from April to August of 2005 at a 1295 hectare ranch managed for wildlife habitat. Ten sites were sampled within the following habitat categories: upland woodland, prairie, riparian forest, and ponds. A total of 184 individuals of 15 species were observed or captured. The most abundant species were the plain-bellied water snake (Nerodia erythrogaster), western ribbon snake (Thamnophis proximus), and eastern coachwhip (Masticophis flagellum). The least abundant species were the brown snake (Storeria dekayi), speckled kingsnake (Lampropeltis getula), and eastern coral snake (Micrurus fulvius). The timber rattlesnake (Crotalus horridus), a threatened species, appears to have a viable population within the study area. Abundance and species richness varied according to each habitat, with riparian forest having highest collective abundance and species richness, and pond habitats yielding fewest individuals and species.
IDENTIFICATION OF EROSIONAL HOTSPOTS AND SHORELINE POSITION UTILIZING AN ALONGSHORE SHORELINE MONITORING SYSTEM: GALVESTON ISLAND’S WEST END
(2006-07-11) McInnes, Andrew J.
A continuous synoptic alongshore method of beach surveying was developed to identify shoreline position, erosional hotspots, and to examine the morphological variation of the Gulf beaches of Galveston Island’s west end. Near-weekly (average 3 per month) surveys were conducted over 15 consecutive months for the approximately 30 km section of the west end of Galveston Island beginning April 2004 through September 2005. Erosional or accretional hotspots are operationally defined here as areas which can be statistically determined to have significantly greater migration than the mean migration for the entire beach, and are often, but not necessarily, ephemeral. The shoreline, by definition, is the wetline - the wet/dry interface on the beach, the furthest point of wave run-up - and was recorded by tracing the wetline immediately after the turn of the high tide utilizing an all Terrain Vehicle (ATV) equipped with a post-processed kinematic Global Positioning System (GPS). This system provides high-resolution topographical surveying with sub-decimeter accuracy in the both the horizontal and vertical dimensions. The data were assembled in order to determine mean wetlines – monthly, quarterly, or annually; repeated localized statistically significant landward advance of the shoreline is indicative of potential erosional hotspots while an annual net landward migration of the wetline indicates a retreating shoreline - erosion. This work demonstrates that by using this economically feasible surveying method, highly accurate shoreline positions can be used to monitor the morphological changes of the shoreline and to identify erosional hotspots. Over the study period the area exhibited a mean annual erosion rate of 4.95m -1 with a range of 59.83m (-23.86m to 36.04m); the median offset was 4.73m; and mean elevation of the wetline was 1.15m (elevation lacks uniformity both spatially or temporally). This project shows that frequent synoptic surveys enable the identification of erosional hotspots and enables the establishing of an accurate, non-datum corrected shoreline position. Regular monitoring enables determination of erosional hotspots and shoreline migration due to storm events and annual cycles. Archiving and analysis of these short-term vacillations provides a long time-series of shoreline position and is of utility to coastal management and numerous stakeholders.
Effects of Pinealectomy on Hypothalamic Metabolic and Clock Gene Rhythms
(2006-07-11) Clauson, Amanda
A neuroendocrine loop model has been proposed for explaining the generation of avian circadian rhythms. The basis of this model is that the circadian system is composed of interconnected circadian pacemakers residing within the suprachiasmatic nucleus (SCN) complex, retina and pineal gland, which control the phase of rhythmicity of peripheral oscillators in the absence of photic or neuroendocrine input from the rest of the system (Cassone and Menaker, 1984). However, recent data question the validity of the neuroendocrine loop model by suggesting that although melatonin administration affects overt clock function, (Lu and Cassone, 1993) it has no effect on the transcription of clock genes (Yasuo et al., 2002). Thus, expression of these genes could be independent of pineal function. My research attempts to elucidate whether metabolic rhythms in the vSCN and clock gene expression in the vSCN and mSCN are coupled and to reveal the effects of pineal melatonin on these rhythms. This is done by comparing the affects of pinealectomy on 2DG uptake and canonical "clock" gene expression in the hypothalamus of house sparrows, Passer domesticus. Since other brain structures exhibit metabolic and clock gene rhythms, investigation of clock gene expression and 2DG uptake will also be undertaken in peripheral structures, e.g. the habenula and optic tectum. Currently, analysis of 2DG uptake at Day 0 has been completed and the process of analysis for Day 10 has begun. Using in situ hybridization techniques, I will quantify clock gene expression in both the vSCN and mSCN to determine if clock gene rhythms persist despite the absence of the pineal gland, the source of rhythmic melatonin for passerine birds. Because in situ analysis must be done from all timepoints and conditions simultaneously, and given the breadth of this experiment, these analyses are still being undertaken.
Annexation of Interchromosomal Space During Viral Infection of 3D Tissue Matrix
(2006-07-11) Crannell, Zachary
The process of viral infection has been shown to be a tightly structured process that exerts precise control over the nucleus. By quantitatively documenting the dynamic nuclear changes in response to nuclear infection of cells suspended in a three-dimensional collagen matrix, an understanding of nuclear reorganization can be elucidated from the tissue. Tissues were cultured in vitro in three dimensional collagen matrices which act as scaffolding that mimics the native environment. The cells were then infected with cytomegalo virus (CMV) which was labeled with green fluorescent protein to allow identification of the virus. During viral infection, nonlinear optical microscopy (NLOM) was employed to nondestructively image the nuclear volume over time. Comparing changes in the nuclear volume with control values, we expected to identify several stages of nuclear reorganization that have previously been identified during infection of 2D tissue cultures. Once it has been demonstrated that NLOM can be successfully used to track dynamics of infection, multiple mutant fluorescent proteins can be used to track host, virus and immune response to viral infection.
THE USE OF GROUND-PENETRATING RADAR FOR ARCHAEOLOGY: DETERMINING SITE FORMATION PROCESSES AND SUBSURFACE FEATURES ON TUTUILA ISLAND, AMERICAN SAMOA
(2006-07-11) Welch, Daniel
The use of geophysical remote sensing techniques has been increasing for several decades. As this technology becomes increasingly affordable and accurate, more and more archaeologists are beginning to wonder how this emerging technology can complement traditional archaeological techniques. This thesis presents the results of a study using ground-penetrating radar in the mountain settings of American Samoa, a chain of volcanic islands in the South Pacific. Our results show that in American Samoa, ceremonial mound (i.e. star mound) construction details were easily seen in radar profiles. Ground penetrating radar has the potential to yield significant details about such mounds, with no physical impact to the site.
Gene Expression Profiling of 3T3-L1 Adipocytes Expressing the Mitochondrial Uncoupling Protein 1 (UCP1)
(2006-07-11) Senocak, Fatih
During the past 20 years, there has been a significant increase in the number of individuals developing type II diabetes mellitus (T2DM). Evidence from several studies indicates that obesity and weight gain (increase in white adipose tissue) are associated with an increased risk of developing diabetes. Current treatments to combat this epidemic involve the reduction in white adipose tissue (WAT). Previously we proposed that the forced expression of uncoupling protein 1 (UCP1), normally part of the thermogenic mechanisms found in brown adipose tissue (BAT), can be used to reduce accumulation of triglycerides in white adipocytes, and thereby regulate body fat mass. The aim of this study was to determine the effects of forced UCP1 expression on global changes in energy metabolism in white adipocytes. Specifically, we used DNA microarrays to characterize the changes in white adipocyte gene expression upon UCP1 expression and determine the extent to which UCP1 expressing white adipocytes emulate brown adipocytes. Murine 3T3-L1 preadipocytes, either expressing UCP1 or control (i.e., no UCP1) were cultured to confluence. On day 2 post confluence, the preadipocytes were induced to differentiate using a standard adipogenic cocktail consisting of insulin, isobutylmetyhylxanthine (IBMX), and dexamethasone (DEX). At 10 days post-isolation, total RNA was isolated and the transcript levels profiled using the Codelink microarray system (Agilent, CA).
Seismic Discontinuities in the Mantle Beneath the Western Pacific: Evidence from ScS Reverberations
(2006-07-11) Bagley, Brian
Earthquakes generate seismic waves that travel through the Earth and can be reflected by changes in density and/or seismic velocity that may relate to changes in the phase or chemical composition of the mantle. To study these discontinuities we use the ScS reverberative interval of seismic records. This is accomplished by inverting zeroth order waves for whole mantle properties that are used to create a profile of reflectivity vs. depth through the mantle. This profile includes the expected transition zone discontinuities. We then create a second profile through a process of iterative forward modeling to locate the depth of additional mantle discontinuities. We have selected three source-receiver paths in the western Pacific as our research area because of its high seismic activity, and the widespread coverage of seismometers. We found the expected transition zone discontinuities at 410 km and 660 km in all three paths. We found discontinuities at 83 and 288 km in path A, which samples the oceanic crust between the Marianas trench and Hawaii. In path B, which samples an area between the Izu-Bonin trench and Hawaii, we found discontinuities at 77, 321, and 2645 km. Path C, which samples the Sea of Japan and includes the subducted Pacific plate contains discontinuities at 337, 558, 850, and 2782 km. Many of these discontinuities have been detected in previous studies using different methods [e.g., Zang et al., 2003; Revenaugh and Jordan, 1991]. We believe the discontinuities near 300 km in paths A and B signal the presence of stishovite in eclogitic mid-upper mantle. The negative reflectivity of the feature at 337 km in path C is interpreted as evidence of a partially molten zone above the 410-km discontinuity, as has been indicated in previous studies [e.g., Revenaugh and Sipkin, 1994].
Analysis of Pebble-Bed VHTR Spectrum Shifting Capabilities for Advanced Fuel Cycles
(2006-07-11) Pritchard, Megan
Gas-cooled nuclear reactors have been receiving specific attention for Generation IV possibilities due to desired characteristics such as relatively low cost, short construction period, and inherent safety. Attractive inherent characteristics include an inert, single phase helium coolant, refractory coated fuel with high temperature capability and low fission product release, and graphite moderator with high temperature stability and long response times. The passively safe design has a relatively low power density, annular core, large negative temperature coefficient, and passive decay heat removal system. The objective of the U.S. DOE NERI Project is to assess the possibility, advantages and limitations of achieving ultra-long life VHTR (Very High Temperature Reactor) configurations by utilizing minor actinides as a fuel component. The present analysis takes into consideration and compares capabilities of pebble-bed core designs with various core and reflector configuration to allow spectrum shifting for advanced actinide fuels. Whole-core 3D models for pebble-bed design with multi-heterogeneity treatments in SCALE 5.0 are developed to compare computational results with experiments. Obtained results are in agreement with the available HTR-10 data. By altering the moderator to fuel ratio, a shift in the spectrum is observed. The use of minor actinides as fuel components relies on spectrum shifting capabilities. Actinide fueled VHTR configurations reveal promising performance. With an optimized pebble-bed model, the spectrum shifting abilities are apparent and effects of altered moderator to fuel ratio, and Dancoff factor are investigated. This will lead to a facilitated development of new fuel cycles in support of future operation of Generation IV nuclear energy systems.
Dynamic Monte Carlo Simulations of the Oxygen Electroreduction Reaction on a Bimetallic Surface
(2006-07-11) Wood, Adam; Balbuena, Perla
Platinum and platinum alloy surfaces are used as catalysts to promote the reduction of oxygen, one of the reactions used to generate electrical energy in low temperature fuel cells, which are sought as promissory clean power sources. In such devices, the oxygen reduction is the slowest of the two electrode reactions, significantly affecting the performance of the fuel cell. Oxygen reduction is also important for several biological problems, such as oxygen transport in living organisms. In my research, I analyzed the effect of concentrations of a secondary metal on the overall mechanism of oxygen reduction on platinum alloy catalysts. I employed dynamic Monte Carlo, a simulation program that studies the kinetics of reactions, and returns relevant data that can be analyzed. To better understand how to improve the oxygen current density, I studied two different cases involving a bimetallic surface. For the first case I employed an initial secondary metal M at varying concentrations with a 100% increase in activation energy for the adsorption of oxygen, but a 10% decrease in activation energy for the other four electron transfer reactions, while the second case I kept the above values, but reduced the activation energy for the adsorption of oxygen to a 10% increase on metal M. I discovered that between 50 to 70% metal concentration enabled the best sites for reduction for the first case, and 50 to 90% metal concentration enabled the best sites for reduction for the second case. This is particularly important, for if it can be discovered that a secondary metal mixed with platinum can yield the results I discovered, then the reduction of oxygen may become commercially feasible, reducing the cost of the catalyst needed, and by increasing the current density yield resulting in greater reduction performance.
Comparison of Circadian Changes in the Retinas of Migrating and Non-migrating Blackcaps, Sylvia atricapilla
(2006-07-11) Shockley, Ross
The retinas of birds and other vertebrates undergo morphological and physiological changes throughout the day, which help regulate daily changes in visual sensitivity. One particular change is the contraction and elongation of photoreceptor outer segments, which is regulated by an endogenous circadian clock. Normally, Blackcaps (Sylvia atricapilla) are diurnal, but they migrate at night. In the current experiment, outer segment lengths of migrating and non-migrating Blackcaps were measured throughout the day and analyzed, and they show a trend toward circadian rhythmicity across the day. There also appears to be an advance in the phase of the rhythm in retinomotor movements when birds are migrating. These results indicate that circadian-controlled retinomotor movements could be modifications within the retina to accommodate the nocturnal lifestyle of migratory Blackcaps. We hypothesize that a change in retinal physiology and morphology may allow the formation of a migratory “night-vision” to accommodate the migrating Blackcap’s nocturnal lifestyle.
The hunt for CikR: response regulator for CikA in Synechococcus elongatus PCC 7942
(2006-07-11) Malcolm, Hannah R.
Circadian rhythms are daily cycles of activity that have been demonstrated in many organisms including bacteria, fungi, insects, plants, and mammals. A clock system is composed of three parts: the input pathway, the central oscillator, and the output pathway. The input pathway takes temporal and environmental signals and transfers that information to the central oscillator, which contains the core components of the clock, to synchronize the endogenous clock with the environment. Temporal cues are then sent through output pathways to control certain cell processes. The CikA (circadian input kinase) protein is an integral part of the input pathway because a cikA mutant cannot reset its circadian rhythm in response to dark pulses. CikA contains a histidine protein kinase (HPK) domain, which suggests that CikA is part of a bacterial two-component signal transduction system in which CikA autophosphorylates in response to a signal and transfers that phosphate to a putative partner response regulator (RR), named CikR. The purpose of this project is to identify CikR. Bioinformatic analysis of the Synechococcus elongatus PCC 7942 genome identified nineteen potential cikR genes. Thirteen of the cikR candidates were eliminated due to their proximity to another HPK, or because their function was known and unrelated to the clock. Five of the remaining six genes were cloned and their protein products were overexpressed in Escherichia coli. Each protein was purified by affinity chromatography and used in trans--phosphorylation experiments to determine if a phosphoryl group can be transferred from radio-labeled, phosphorylated CikA to any CikR candidate. To date, no phosphoryl transfer has been detected; however, the sixth gene is currently being cloned for future tests. In vivo analysis of null alleles and overexpression constructs in the cyanobacterium has shown that at least two of the cikR candidate genes is necessary for normal circadian clock function as measured by luciferase reporters.
The Effect of Deformation on Grain Boundary Wetness in Partially Molten Peridotite
(2006-07-11) Schneider, Stephen E.
The spatial distribution of the melt phase can affect many properties of partially molten rocks, including viscosity and seismic wave velocity. A good way to quantify this distribution is the grain boundary wetness, the fraction of total grain boundaries that are in contact with melt. This goal of this study was to quantify the effect of deformation on grain boundary wetness. We analyzed three prepared samples consisting of olivine and 3%, 7% or 15% of a basalt melt phase, which were equilibrated at 1250°C, 300 MPa of confining stress and <50 MPa of differential stress. We describe a process developed to calculate the grain boundary wetness from prepared SEM images of the samples. We find an expected dependence of wetness on porosity. The effect of deformation was not consistent across all three samples: the two higher melt fraction samples show greater wetness before deformation, while the 3% melt sample showed no effect. This result does not agree with experiments on an organic analog material, which indicated that deformation increases wetness. If viscosity increases with wetness, the results of this study indicate that partially molten peridotite strengthen with deformation, which would have important implications for mantle dynamics. Some researchers have proposed that if you deform a sample of partially molten peridotite it will in fact raise the grain boundary wetness Takei [private communication, 2004]. This statement is bold because if you raise the wetness of the sample then the viscosity goes down thereby making the specimen weaker. Our results show that deformation does not have a consistent discernible effect on grain boundary wetness in partially molten peridotite.
Effects of Sialyltransferase Mutation on Drosophila melanogaster Viability, Fertility, and Longevity
(2006-07-11) Pitts, Jared
Sialyltransferase and other glycosylation enzymes are emerging as important players in crucial regulatory post-translational modifications. These enzymes transfer sugars to glycoproteins and glycolipids, and may aid in activation and suppression of these molecules. Drosophila Sialyltransferase (DSiaT) shows expression during Central Nervous System development in larvae. This leads us to believe it plays an important role in not only this process but also the overall health of the flies. We report that mutations to this gene show significant reductions in fly longevity, fertility, and viability. Immunohistochemical staining experiments revealed DSiaT expression in ovaries, which implies a possible correlation between the sialyltransferase protein and oogenesis. Attempts to rescue this mutant phenotype back to wild type, using mutant flies that also possessed a functional copy of DSiaT downstream of an upstream activating sequence (UAS), were successful in most cases.
Temporal Changed in the Abundance and Cellular Distribution of GAPDH
(2006-07-11) Carter, Jessica
Glyceraldehyde 3-phosphate dehydrogenase (GAPDH) is a metabolic enzyme originally thought to be only involved in glycolysis. New studies have shown that this protein contains novel functions not previously anticipated. Furthermore, separate circadian oscillations in glycolytic processes and “clock” genes exist. It is hypothesized that GAPDH is a potential link between the glycolytic and clock gene pathways. The changes in the amount and location of GAPDH in chicken retinas, pineal glands, and brain tissues at four time points throughout the day while in constant darkness (DD) were examined. GAPDH was localized using standard immunohistochemical techniques. In the retinal tissue, GAPDH was found in a high abundance in the ganglion cells, outer plexiform layer, outer nuclear layer, inner nuclear and plexiform layer, and the photoreceptor cell layer of the retina. Additionally, a circadian rhythm in GAPDH abundance was observed in the outer plexiform layer, outer nuclear layer, inner nuclear and plexiform layer, and the photoreceptor cell layer, which all had a rhythmic expression and gradual decrease at CT12. The pineal gland and parasympathetic terminals also displayed rhythmic expression. The parasympathetic terminal showed high abundance at CT0 and CT6, with a sharp drop at CT12. The pineal gland contained a similar temporal distribution, but with a gradual decrease to CT12. Data is still being collected on the brain sections. The results indicate that the relative abundance of the “glycolytic” protein, GAPDH, is under the control of an endogenous circadian clock.
Effects of Dioxin on Clock, Melatonin Biosynthetic, and Redox Sensitive Genes on Chick Pinealocytes In Vitro
(2006-07-11) Hunt, Jayme
It has been speculated that dioxin treatment can modulate circadian rhythms. Cytochrome P4501A (CYP1A) is strongly induced by the xenobiotic dioxin via activation of arylhydrocarbon receptors within cells. Furthermore, regulation of CYP1A has been shown to occur via redox dependent activity of nuclear factor 1 X-type (NF1X) and cellular redox potential can regulate the circadian clock. As such we hypothesized that exposure to dioxin could affect circadian rhythmicity. We explored the pharmacological effects of the environmental toxicant dioxin on the expression of canonical clock genes, genes involved in melatonin biosynthesis, and putative redox sensitive genes CYP1A5 (an avian ortholog of human CYP1A) and NF1X using quantitative real-time PCR analysis. Dioxin altered the amplitude and phase of the rhythms of clock genes Brain and Muscle ARNT-Like (BMAL) 1 and BMAL2; melatonin biosynthetic pathway genes, hydroxyindole-O-methyltransferase (HIOMT), arylalkylamine-N-acetyltransferase (AANAT), and tryptophan hydroxylase (TrH); and redox sensitive genes, CYP1A5 and NF1X. These results suggest dioxin treatment may uncouple the melatonin biosynthetic pathway from the pineal circadian clock or that the circadian affects of dioxins may be mediated via its affects directly on melatonin synthesis and not directly at the level of the molecular circadian clock.
The Influence of Context Reinstatement on the Recovery of Blocked Memories
(2006-08-16) Williams, Jennifer
The present study examined the effect of context reinstatement on the recovery of experimentally blocked memories and the possible creation of memory errors. Context refers to every aspect of the environment in which a to-be-remembered event has taken place. Physically returning to a learning context, or creating a mental representation of it, may allow one to use context information as a source of memory cues to enhance memory performance. This is referred to as context reinstatement. Research shows that memory performance is best if learning and testing conditions match, rather than if they are mismatched (Smith, 1979; Thomson & Tulving, 1970). It is unclear if context reinstatement can influence not only the enhancement of continuously accessible memories, but whether it might also help with the recovery of blocked memories. Also, because mentally reinstating context is a form of mental imagery, it is possible that this process of reinstatement would lead to the creation of memories for imagined events or memory errors. To examine these questions the present study manipulated mental and physical reinstatement and examined both accurate and inaccurate memories. The present study included three phases. First, participants performed an incidental learning task with a series of word lists in one context. Next, participants performed either memory interference tasks for three of the learned lists or distracter tasks in a different context. Lastly, participants completed a series of memory tests in either the first or second context, with or without context reinstatement. Results showed strong blocking effects in the forget condition groups. Recovery effects were stronger in the physical reinstatement group, as compared to the other groups. Interestingly, memory errors were similar across experimental groups. Thus, physical, but not mental, context reinstatement aided in the recovery of blocked memories, but the use of mental reinstatement did not lead to memory errors. Results may edify other memory researchers, forensic investigators and clinical psychologists who may use forms of context reinstatement and mental imagery for memory enhancement or recovery purposes.

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