Long-term injury induced plasticity in {\it Aplysia\/} neurons: Behavioral, electrophysiological, and morphological studies

Nerve injury is known to produce a variety of electrophysiological and morphological neuronal alterations (reviewed by Titmus and Faber, 1990; Bulloch and Ridgeway, 1989; Walters, 1994). Determining if these alterations are adaptive and how they are activated and maintained could provide important insight into basic cellular mechanisms of injury-induced plasticity. Furthermore, characterization of injury-induced plasticity provides a useful assay system for the identification of possible induction signals underlying these neuronal changes. Understanding fundamental mechanisms and underlying induction signals of injury-induced neuronal plasticity could facilitate development of treatment strategies for neural injury and neuropathic pain in humans.^ This dissertation characterizes long-lasting, injury-induced neuronal alterations using the nervous system of Aplysia californica as a model. These changes are examined at the behavioral, electrophysiological, and morphological levels. Injury-induced changes in the electrophysiological properties of neurons were found that increased the signaling effectiveness of the injured neurons. This increase in signalling effectiveness could act to compensate for partial destruction of the injured neuron's peripheral processes. Recovery of a defensive behavioral response which serves to protect the animal from further injury was found within 2 weeks of injury. For the behavioral recovery to occur, new neural pathways must have been formed between the denervated area and the CNS. This was found to be mediated at least in part by new axonal growth which extended from the injured cell back along the original pathway (i.e. into the injured nerve). In addition, injury produced central axonal sprouting into different nerves that do not usually contain the injured neuron's axons. This could be important for (i) finding alternative pathways to the periphery when the original pathways are impassable and (ii) the formation of additional synaptic connections with post-synaptic targets which would further enhance the signalling effectiveness of the injured cell. ^

Neuromuscular disuse and atrophy: {\it In vivo\/} magnetic resonance studies of intramuscular lipid metabolism and fluid shift changes

We postulated that neuromuscular disuse results in deleteriously affected tissue-vascular fluid exchange processes and subsequently damages the important oxidative bioenergetic process of intramuscular lipid metabolism. The in-depth research reported in the literature is somewhat limited by the ex vivo nature and sporadic time-course characterization of disuse atrophy and recovery. Thus, an in vivo controlled, localized animal model of disuse atrophy was developed in one of the hindlimbs of laboratory rabbits (employing surgically implanted tetrodotoxin (TTX)-filled mini-osmotic pump-sciatic nerve superfusion system) and tested repeatedly with magnetic resonance (MR) throughout the 2-week period of temporarily induced disuse and during the recovery period (following explantation of the TTX-filled pump) for a period of 3 weeks. Controls consisted of saline/"sham"-implanted rabbit hindlimbs. The validity of this model was established with repeated electrophysiologic nerve conduction testing using a clinically appropriate protocol and percutaneously inserted small needle stimulating and recording electrodes. Evoked responses recorded from proximal (P) and distal (D) sites to the sciatic nerve cuff in the TTX-implanted group revealed significantly decreased (p $<$ 0.001) proximal-to-distal (P/D) amplitude ratios (as much as 50-70% below Baseline/pre-implanted and sham-implanted group values) and significantly increased (p $<$ 0.01) differential latency (PL-DL) values (as much as 1.5 times the pre- and sham-implanted groups). By Day 21 of recovery, observed P/D and PL-DL levels matched Baseline/sham-implemented levels. MRI-determined cross-sectional area (CSA) values of Baseline/pre-implanted, sham- or TTX-implanted, and recovering/explanted and the corresponding contralateral hindlimb tibialis anterior (TA) muscles normalized to tibial bone (TB) CSA (in TA/TB ratios) revealed that there was a significant decline (indicative of atrophic response) from pre- and sham-implanted controls by as much as 20% (p $<$ 0.01) at Day 7 and 50-55% (p $<$ 0.001) at Day 13 of TTX-implantation. In the non-implanted contralaterals, a significant increase (indicative of hypertrophic response) by as much as 10% (p $<$ 0.025) at Day 7 and 27% (p $<$ 0.001) at Day 13 + TTX was found. The induced atrophic/hypertrophic TA muscles were observed to be fully recovered by Day 21 post-explantation as evidenced by image TA/TB ratios. End-point biopsy results from a small group of rabbits revealed comprehensive atrophy of both Type I and Type II fibers, although the heterogeneity of the response supports the use of image-guided, volume-localized proton magnetic resonance spectroscopy (MRS) to noninvasively assess tissue-level metabolic changes. MRS-determined results of a 0.25cc volume of tissue within implanted limb TA muscles under resting/pre-ischemic, ischemic-stressed, and post-ischemic conditions at timepoints during and following disuse atrophy/recovery revealed significantly increased intramuscular spectral lipid levels, as much as 2-3 times (p $<$ 0.01) the Baseline/pre-implanted values at Day 7 and 6-7 times (p $<$ 0.001) at Day 13 + TTX, which approached normal levels (compared to pre- and sham-implanted groups) by Day 21 of post-explanation recovery. (Abstract shortened by UMI.) ^

STUDIES ON THE CLASS I GLYCOPROTEINS OF THE MURINE MAJOR HISTOCOMPATIBILITY COMPLEX (TRANSPLANTATION ANTIGEN, LYMPHOCYTE, CELL SURFACE MOLECULE)

A series of studies were undertaken to analyze and compare various aspects of murine class I glycoproteins. An initial area of investigation characterized the Qa-1 alloantigens using two-dimensional gel electrophoresis. Analysis of the products of the Qa-1('b), Qa-1('c) and Qa-1('d) alleles indicated that these were distinct molecules as determined by their lack of comigration upon comparative two-dimensional gel analysis. The importance of asparagine-linked glycosylation in the cell surface expression of class I molecules was also examined. These studies employed tunicamycin, an inhibitor of N-linked glycosylation. Tunicamycin treatment of activated T lymphocytes diminished the surface expression of Qa-1 to undetectable levels; the levels of other class I molecules exhibited little or no decrease. These results indicated that N-linked glycosylation has a differential importance in the cell surface expression of various class I molecules. The molecular weight diversity of class I molecules was also investigated. Molecular weight determination of both the fully glycosylated and unglycosylated forms of H-2 and Qa/Tla region encoded molecules established that there is a significant variation in the sizes of these forms of various class I molecules. The most significant difference ((TURN)9,000 daltons) exists between the unglycosylated forms of H-2K('b) and Qa-2, suggesting that the structural organization of these two molecules may be very different. A comparative two-dimensional gel analysis of various class I glycoproteins isolated from resting and activated T and B lymphocytes indicated that class I molecules expressed on activated T cells exhibited an isoelectrophoretic pattern that was distinct from the isoelectrophoretic pattern of class I molecules expessed on the other cell populations. This difference was attributed to a lower sialic acid content of the molecules expressed on activated T cells. Analysis of cell homogenates determined that activated T cells contained a higher level of endogenous neuraminidase activity than was detected in the other populations, suggesting that this may be the basis of the lower sialic acid content. The relationship of the Qa-4 and Qa-2 alloantigens was also examined. It was established that upon mitogen activation, the expression of Qa-4 was greatly decreased, whereas Qa-2 expression was not decreased. However, an anti-Qa-2 monoclonal antibody blocked the binding of an anti-Qa-4 monoclonal antibody to resting cells. These studies established that Qa-4 is a determinant restricted to resting cells, which is closely associated on the surface with the Qa-2 molecule. ^

Prevalence and determinants of type 2 diabetes among Filipino Americans in Houston metropolitan statistical area, Texas

Diabetes in adults (type 2) has emerged as a world health problem. Prevalence and risk factors have been found to vary in different populations. The wide range of prevalence rates worldwide indicates the importance of genetic and environmental factors in the etiology of the disease. The few available studies suggest that Filipinos are among the higher-risk groups for developing diabetes. This cross-sectional study estimated the overall prevalence rate of type 2 diabetes among Filipino Americans, ages 20–74 years and residents of Houston Metropolitan Statistical Area, Texas, to be 16.1%. The observed high prevalence was associated with age, sex, family history of diabetes, obesity, region of birth; and, in women, gestational diabetes and income. The diabetic Filipino Americans had a higher proportion of parental history of diabetes, medical history of hypertension, and history of smoking; were physically less active, but generally non-obese, compared with the United States diabetic population. ^

Delineating the molecular basis of human genetic diseases: Epigenetic and functional studies

Identifying and characterizing the genes responsible for inherited human diseases will ultimately lead to a more holistic understanding of disease pathogenesis, catalyze new diagnostic and treatment modalities, and provide insights into basic biological processes. This dissertation presents research aimed at delineating the genetic and molecular basis of human diseases through epigenetic and functional studies and can be divided into two independent areas of research. The first area of research describes the development of two high-throughput melting curve based methods to assay DNA methylation, referred to as McMSP and McCOBRA. The goal of this project was to develop DNA methylation methods that can be used to rapidly determine the DNA methylation status at a specific locus in a large number of samples. McMSP and McCOBRA provide several advantages over existing methods, as they are simple, accurate, robust, and high-throughput making them applicable to large-scale DNA methylation studies. McMSP and McCOBRA were then used in an epigenetic study of the complex disease Ankylosing spondylitis (AS). Specifically, I tested the hypothesis that aberrant patterns of DNA methylation in five AS candidate genes contribute to disease susceptibility. While no statistically significant methylation differences were observed between cases and controls, this is the first study to investigate the hypothesis that epigenetic variation contributes to AS susceptibility and therefore provides the conceptual framework for future studies. ^ In the second area of research, I performed experiments to better delimit the function of aryl hydrocarbon receptor-interacting protein-like 1 (AIPL1), which when mutated causes various forms of inherited blindness such as Leber congenital amaurosis. A yeast two-hybrid screen was performed to identify putative AIPL1-interacting proteins. After screening 2 × 106 bovine retinal cDNA library clones, 6 unique putative AIPL1-interacting proteins were identified. While these 6 AIPL1 protein-protein interactions must be confirmed, their identification is an important step in understanding the functional role of AIPL1 within the retina and will provide insight into the molecular mechanisms underlying inherited blindness. ^

The effect of the shift from HMO to PPO plans on the prevalence of hospital bad debt in the insured population: A case study in two Houston-area hospitals

In spite of the dramatic increase and general concern with U.S. hospital bad debt expense (AMNews, January 12, 2004; Philadelphia Business Journal, April 30, 2004; WSJ, July 23, 2004), there appears to be little available analysis of the precise sources and causes of its growth. This is particularly true in terms of the potential contribution of insured patients to bad debt expense in light of the recent shift in managed care from health maintenance organization (HMO) plans to preferred provider organization (PPO) plans (Kaiser Annual Survey Report, 2003). This study examines and attempts to explain the recent dramatic growth in bad debt expense by focusing on and analyzing data from two Houston-area hospital providers within one healthcare system. In contrast to prior studies in which self-pay was found to be the primary source of hospital bad debt expense (Saywell, R. M., et al., 1989; Zollinger, T. W., 1991; Weissman, Joel S., et al., 1999), this study hypothesizes that the growing hospital bad debt expense is mainly due to the shifting trend away from HMOs to PPOs as a conscious decision by employers to share costs with employees. Compared to HMO plans, the structure of PPOs includes higher co-pays, coinsurance, and deductibles for the patient-pay portion of medical bills, creating the potential for an increase in bad debt for hospital providers (from a case study). This bad debt expense has a greater impact in the community hospital than in the Texas Medical Center hospital. ^

The association of area socioeconomic status and cancer screening: A systematic review and multilevel study

Background. The gap between actual and ideal rates of routine cancer screening in the U.S., particularly for colorectal cancer screening (CRCS) (1;2), is responsible for an unnecessary burden of morbidity and mortality, particularly for disadvantaged groups. Knowledge about the effects of individual and area influences is being advanced by a growing body of research that has examined the association of area socioeconomic status (SES) and cancer screening after controlling for individual SES. The findings from this emerging and heterogeneous research in the cancer screening literature have been mixed. Moreover, multilevel studies in this area have not yet adequately explored the possibility of differential associations by population subgroup, despite some evidence suggesting gender-specific effects. ^ Objectives and methods. This dissertation reports on a systematic review of studies on the association of area SES and cancer screening and a multilevel study of the association between area SES and CRCS. The specific aims of the systematic review are to: (1) describe the study designs, constructs, methods, and measures; (2) describe the association of area SES and cancer screening; and (3) identify neglected areas of research. ^ The empiric study linked a pooled sample of respondents aged ≥50 years without a personal history of colorectal cancer from the 2003 and 2005 California Health Interview Surveys with a comprehensive set of census-tract level area SES measures from the 2000 U.S. Census. Two-level random intercept models were used to test 2 hypotheses: (1) area SES will be associated with adherence to two modalities of CRCS after controlling for individual SES; and (2) gender will moderate the relationship between area socioeconomic status and adherence to both modalities of CRCS. ^ Results. The systematic review identified 19 eligible studies that demonstrated variability in study designs, methods, constructs, and measures. The majority of tested associations were either not statistically significant or significant and in the positive direction, indicating that as area SES increased, the odds of CRCS increased. The multilevel study demonstrated that while multiple aspects of area SES were associated with CRCS after controlling for individual SES, associations differed by screening modality and in the case of endoscopy, they also differed by gender. ^ Conclusions. Conceptual and methodologic heterogeneity and weaknesses in the literature to date limit definitive conclusions about the underlying relationships between area SES and cancer screening. The multilevel study provided partial support for both hypotheses. Future research should continue to explore the role of gender as a moderating influence with the aim of identifying the mechanisms linking area SES and cancer prevention behaviors. ^

Incident hypertension among pre-hypertensive adolescents: Evaluation of pre-hypertension as an independent risk factor among secondary school students in the Houston area

Cardiovascular disease has been the leading cause of death in the United States for over fifty years. While multiple risk factors for cardiovascular disease have been identified, hypertension is one of the most commonly recognized and treatable. Recent studies indicate that the prevalence of hypertension among children and adolescents is between 3-5%, much higher than originally estimated and likely rising due to the epidemic of obesity in the U.S. In 2004, the National High Blood Pressure Education Program Working Group on High Blood Pressure in Children and Adolescents published new guidelines for the diagnosis and treatment of hypertension in this population. Included in these recommendations was the creation of a new diagnosis, pre-hypertension, aimed at identifying children at-risk for hypertension to provide early lifestyle interventions in an effort to prevent its ultimate development. In order to determine the risk associated with pre-hypertension for the development of incident HTN, a secondary analysis of a repeated cross-sectional study measuring blood pressure in Houston area adolescents from 2000 to 2007 was performed. Of 1006 students participating in the blood pressure screening on more than one occasion not diagnosed with hypertension at initial encounter, eleven were later found to have hypertension providing an overall incident rate of 0.5% per year. Incidence rates were higher among overweight adolescents–1.9% per year [IRR 8.6 (1.97, 51.63)]; students “at-risk for hypertension” (pre-hypertensive or initial blood pressure in the hypertensive range but falling on subsequent measures)–1.4% per year [IRR 4.77 (1.21, 19.78)]; and those with blood pressure ≥90th percentile on three occasions–6.6% per year [IRR 21.87 (3.40, 112.40)]. Students with pre-hypertension as currently defined by the Task Force did have an increased rate of hypertension (1.1% per year) but it did not reach statistical significance [IRR 2.44 (0.42, 10.18)]. Further research is needed to determine the morbidity and mortality associated with pre-hypertension in this age group as well as the effectiveness of various interventions for preventing the development of hypertensive disease among these at-risk individuals. ^

HPV vaccine coverage in Texas counties: An application of multilevel, small area estimation

Health departments, research institutions, policy-makers, and healthcare providers are often interested in knowing the health status of their clients/constituents. Without the resources, financially or administratively, to go out into the community and conduct health assessments directly, these entities frequently rely on data from population-based surveys to supply the information they need. Unfortunately, these surveys are ill-equipped for the job due to sample size and privacy concerns. Small area estimation (SAE) techniques have excellent potential in such circumstances, but have been underutilized in public health due to lack of awareness and confidence in applying its methods. The goal of this research is to make model-based SAE accessible to a broad readership using clear, example-based learning. Specifically, we applied the principles of multilevel, unit-level SAE to describe the geographic distribution of HPV vaccine coverage among females aged 11-26 in Texas.^ Multilevel (3 level: individual, county, public health region) random-intercept logit models of HPV vaccination (receipt of ≥ 1 dose Gardasil® ) were fit to data from the 2008 Behavioral Risk Factor Surveillance System (outcome and level 1 covariates) and a number of secondary sources (group-level covariates). Sampling weights were scaled (level 1) or constructed (levels 2 & 3), and incorporated at every level. Using the regression coefficients (and standard errors) from the final models, I simulated 10,000 datasets for each regression coefficient from the normal distribution and applied them to the logit model to estimate HPV vaccine coverage in each county and respective demographic subgroup. For simplicity, I only provide coverage estimates (and 95% confidence intervals) for counties.^ County-level coverage among females aged 11-17 varied from 6.8-29.0%. For females aged 18-26, coverage varied from 1.9%-23.8%. Aggregated to the state level, these values translate to indirect state estimates of 15.5% and 11.4%, respectively; both of which fall within the confidence intervals for the direct estimates of HPV vaccine coverage in Texas (Females 11-17: 17.7%, 95% CI: 13.6, 21.9; Females 18-26: 12.0%, 95% CI: 6.2, 17.7).^ Small area estimation has great potential for informing policy, program development and evaluation, and the provision of health services. Harnessing the flexibility of multilevel, unit-level SAE to estimate HPV vaccine coverage among females aged 11-26 in Texas counties, I have provided (1) practical guidance on how to conceptualize and conduct modelbased SAE, (2) a robust framework that can be applied to other health outcomes or geographic levels of aggregation, and (3) HPV vaccine coverage data that may inform the development of health education programs, the provision of health services, the planning of additional research studies, and the creation of local health policies.^

A geographic information science (GIS) approach to conducting comparative area-level community assessments in the Texas CORD Study

This study assessed and compared sociodemographic and income characteristics along with food and physical activity assets (i.e. grocery stores, fast food restaurants, and park areas) in the Texas Childhood Obesity Research Demonstration (CORD) Study intervention and comparison catchment areas in Houston and Austin, Texas. The Texas CORD Study used a quasi-experimental study design, so it is necessary to establish the interval validity of the study characteristics by confirming that the intervention and comparison catchment areas are statistically comparable. In this ecological study, ArcGIS and Esri Business Analyst were used to spatially relate U.S. Census Bureau and other business listing data to the specific school attendance zones within the catchment areas. T-tests were used to compare percentages of sociodemographic and income characteristics and densities of food and physical activity assets between the intervention and comparison catchment areas.^ Only five variables were found to have significant differences between the intervention and comparison catchment areas: Age groups 0-4 and 35-64, the percentage of owner-occupied and renter-occupied households, and the percentage of Asian and Pacific Islander residents. All other variables showed no significant differences between the two groups. This study shows that the methodology used to select intervention and comparison catchment areas for the Texas CORD Study was effective and can be used in future studies. The results of this study can be used in future Texas CORD studies to confirm the comparability of the intervention and comparison catchment areas. In addition, this study demonstrates a methodology for describing detailed characteristics about a geographic area that practitioners, researchers, and educators can use.^