Microstructure and Cerebral Blood Flow within White Matter of the Human Brain: A TBSS Analysis.

BACKGROUND White matter (WM) fibers connect different brain regions and are critical for proper brain function. However, little is known about the cerebral blood flow in WM and its relation to WM microstructure. Recent improvements in measuring cerebral blood flow (CBF) by means of arterial spin labeling (ASL) suggest that the signal in white matter may be detected. Its implications for physiology needs to be extensively explored. For this purpose, CBF and its relation to anisotropic diffusion was analyzed across subjects on a voxel-wise basis with tract-based spatial statistics (TBSS) and also across white matter tracts within subjects. METHODS Diffusion tensor imaging and ASL were acquired in 43 healthy subjects (mean age = 26.3 years). RESULTS CBF in WM was observed to correlate positively with fractional anisotropy across subjects in parts of the splenium of corpus callosum, the right posterior thalamic radiation (including the optic radiation), the forceps major, the right inferior fronto-occipital fasciculus, the right inferior longitudinal fasciculus and the right superior longitudinal fasciculus. Furthermore, radial diffusivity correlated negatively with CBF across subjects in similar regions. Moreover, CBF and FA correlated positively across white matter tracts within subjects. CONCLUSION The currently observed findings on a macroscopic level might reflect the metabolic demand of white matter on a microscopic level involving myelination processes or axonal function. However, the exact underlying physiological mechanism of this relationship needs further evaluation.

Transcranial magnetic stimulation (TMS) inhibits cortical dendrites

One of the leading approaches to non-invasively treat a variety of brain disorders is transcranial magnetic stimulation (TMS). However, despite its clinical prevalence, very little is known about the action of TMS at the cellular level let alone what effect it might have at the subcellular level (e.g. dendrites). Here, we examine the effect of single-pulse TMS on dendritic activity in layer 5 pyramidal neurons of the somatosensory cortex using an optical fiber imaging approach. We find that TMS causes GABAB-mediated inhibition of sensory-evoked dendritic Ca(2+) activity. We conclude that TMS directly activates fibers within the upper cortical layers that leads to the activation of dendrite-targeting inhibitory neurons which in turn suppress dendritic Ca(2+) activity. This result implies a specificity of TMS at the dendritic level that could in principle be exploited for investigating these structures non-invasively.

Magnetic Resonance Imaging Finding in Small Ruminants with Brain

Brain disease is an important cause of neurologic deficits in small ruminants, however few MRI features have been described. The aim of this retrospective, case series study was to describe MRI characteristics in a group of small ruminants with confirmed brain disease. A total of nine small ruminants (six sheep and three goats) met inclusion criteria. All had neurologic disorders localized to the brain and histopathologic confirmation. In animals with toxic-metabolic diseases, there were bilaterally symmetric MRI lesions affecting either the gray matter (one animal with polioencephalomalacia) or the white matter (two animals with enterotoxemia). In animals with suppurative inflammation, asymmetric focal brainstem lesions were present (two animals with listeric encephalitis), or lesions typical of an intra-axial (one animal) or dural abscess (one animal), respectively. No MRI lesions were detected in one animal with suspected viral cerebellitis and one animal with parasitic migration tracts. No neoplastic or vascular lesions were identified in this case series. Findings from the current study supported the use of MRI for diagnosing brain diseases in small ruminants.

MOUSE MAMMARY TUMOR VIRUS-RELATED PROTEINS: ISOLATION AND CHARACTERIZATION OF A UNIQUE GLYCOPROTEIN

Mouse mammary tumor virus (MMTV) contained six major proteins, identified as gp55, gp33, p25, pp20, p12, and p10. Immunoprecipitation of cytoplasmic extracts from MMTV-infected, pulse-labeled cells identified three MMTV core-specific precursor proteins, termed Pr78('gag), Pr110('gag), Pr110('gag), and Pr180('gag+). The major intracellular core-specific precursor polyprotein, Pr78('gag), contained antigenic determinants and tryptic peptides characteristic of p25, p12, and p10. Pr110('gag) contained all but one of the leucine-containing tryptic peptides of Pr78('gag), plus several additional peptides. In addition to Pr78('gag) and Pr110('gag), monospecific antisera to virion p12 and p25 also precipitated from pulse-labeled cells a small amount of Pr180('gag+). This large polyprotein contained nearly all of the leucine-containing tryptic peptides of Pr78('gag) and Pr110('gag) plus several additional peptides. By analogy to type-C viral systems, Pr180('gag+) is presumed to represent a gag-pol-specific common precursor which is the major translation product in the synthesis of MMTV RNA-dependent-DNA polymerase. Immunoprecipitation of cytoplasmic extracts from pulse-labeled cells with antisera to gp55 identified two envelope-specific proteins, designated gPr76('env) and gP79('env). The major envelope-specific precursor, gPr76('env), could be labeled with radioactive glucosamine and contained antigenic determinants and tryptic peptides characteristic of gp55 and gp33. A quantitatively minor glycoprotein, gP79('env), contained both fucose and glucosamine and was precipitable from cytoplasmic extracts with monospecific serum to gp55. It is suggested that gP79('env) represents fucosylated gPr76('env) which is transiently synthesized and cleaved rapidly into gp55 and gp33.^ A glycoprotein of 130,00 molecular weight (gP130) was precipitable from the cytoplasm of GR-strain mouse mammary tumor cells by a rabbit antiserum (anti-MMTV) to Gr-strain mouse mammary tumors virus (GR-MMTV). Two dimensional thin layer analysis of ('35)S-methionine-containing peptides revealed that five of nine gp33 peptides and one of seven gp55 peptides were shared by gP130 and gPr76('env). Six of ten p25 peptides and four more core-related peptides were shared by Pr78('gag) and gP130. Protein gP130 also contained several tryptic peptides not found in gPr76('env), or in the core protein precursors Pr78('gag), Pr110('gag), or Pr180('gag+). both gP130 and a second protein, p30, were found in immunoprecipitates of detergent disrupted, isotopically labeled GR-MMTV treated with anti-MMTV serum. Results suggest that antibodies to gP130 in the anti-MMTV serum are capable of recognizing those protein sequences which are not related to viral structural proteins. These gP130-unique peptides are evidently host specific. Polyproteins consisting of juxtaposed host- and virus-related protein tracts have been implicated in the process of cell transformation in other mammalian systems. Therefore, gP130 may be instrinsic to the oncogenic potential of MMTV. ^

THE SITE AND MECHANISM OF ACTION OF BENZODIAZEPINE IN RABBIT HIPPOCAMPUS

The purpose of this study was to determine the effects of benzodiazepine in area CA1 of the hippocampus, and to explore possible mechanisms of action for these agents in this brain area. Two distinctly different benzodiazepine-induced changes in hippocampal physiology have been identified. First, benzodiazepine depresses the population spike recorded in stratum pyramidale, indicating a decrease in action potential generation. Second, benzodiazepine decreases the magnitude of post-tetanic potentiation of the population EPSP recorded in stratum radiatum, and shortens the duration. The effect of benzodiazepine on pyramidal cell excitation was reversed by the GABA antagonis bicuculline, and mimicked by GABA itself. Thus the available evidence is consistent with the hypothesis that benzodiazepine acts by enhancing the effect of GABA in this area. In stratum radiatum, on the other hand, the effect of benzodiazepine on post tetanic potentiation of the population EPSP was not altered by bicuculline although bicuculline did antagonize GABA in this area. In addition, application of GABA, while it caused profound changes in the population EPSP,p, did not cause the same changes that were induced by benzodiazepine. Thus the evidence does not support the hypothesis that benzodiazepine is acting in stratum radiatum by enhancing the effects of GABA. ^

Investigating the Diversity of Radial Glia Fates in the Rat Neocortex

Radial Glia (RG) are a mitotically active population of cells which reside within the ventricular zone at the lateral ventricle and give rise to the pyramidal neurons and astrocytes of the neocortex. Through cellular divisions, RG produce two daughter cells, one which resides in the ventricular zone and becomes another RG while the other is an immature progenitor which migrates away from the ventricle and populates the growing cortex. RG have been found to be a heterogeneous population of cells which express different surface antigens and genetic promoters which may influence the cellular fate of their progeny. In this study we have investigated the progenitor profiles of two promoters, nestin (a neural intermediate filament) and GLAST (astrocyte specific glutamate transporter) within the RG. In-utero electroporation was used to transfect reporter plasmids under the control of promoter driven Cre-Recombinase into the RG lining the lateral ventricle during mid-neurogensesis (E14). It was found that there was a large amount of overlap between the nestin and GLAST expressing populations of RG, however, there was still a small subset of cells which exclusively expressed GLAST. This prompted us to investigate the lineage of these two promoters using the PiggyBac transposon system which uses promoter driven episomal plasmids to incorporate a reporter gene into the genome of the transfected cells, allowing use to trace their full progeny. Our data shows that nestin expressing RG generate mostly neurons and few astrocytes while the GLAST expressing RG generate a greater proportion of astrocytes to neurons.

Effects of Study Area Size on Geographic Characterizations of Health Events: Prostate Cancer Incidence in Southern New England, USA, 1994-1998.

ABSTRACT : BACKGROUND : We consider how representations of geographic variation in prostate cancer incidence across Southern New England, USA may be affected by selection of study area and/or properties of the statistical analysis. METHOD : A spatial scan statistic was used to monitor geographic variation among 35,167 incident prostate cancer cases diagnosed in Massachusetts, Connecticut and Rhode Island from 1994 to 1998, in relation to the 1990 populations of men 20+ years of age living in that region. Results from the combined-states analysis were compared to those from single-states. Impact of scanning procedures set to examine up to 50% or no more than10% of at-risk populations also was evaluated. RESULTS : With scanning set to 50%, 5 locations in the combined-states analysis were identified with markedly distinct incidence rates. Fewer than expected cases were estimated for nearly all Connecticut, Rhode Island and West Central Massachusetts, whereas census tracts on and around Cape Cod, and areas of Southwestern Connecticut and adjacent to greater Boston were estimated to have yielded more than expected incidence. Results of single-state analyses exhibited several discrepancies from the combined-states analysis. More conservative scanning found many more locations with varying incidence, but discrepancies between the combined- and single-state analysis were fewer. CONCLUSION : It is important to acknowledge the conditional nature of spatial analyses and carefully consider whether a true cluster of events is identified or artifact stemming from selection of study area size and/or scanning properties.

Knockdown of Kiaa0319 Reduces Dendritic Spine Density

Developmental Dyslexia is a reading disorder that affects individuals that possess otherwise normal intelligence. Until the four candidate dyslexia susceptibility genes were discovered, the cause of cortical malformations found in post mortem dyslexic brains was unclear. Normal brain development is crucial for the proper wiring of the neural circuitry that allow an individual to perform cognitive tasks like reading. For years, familial and twin studies have suggested that there was a genetic basis to the causation of dyslexia. Kiaa0319 was among the candidate dyslexia susceptibility genes that were ascertained. KIAA0319 is located on Chromosome 6p22.2-22.3 and has been found to exhibit differential spatial-temporal expression patterns in the brain throughout development, which suggests that the polycystic kidney disease (PKD) domain encoded by KIAA0319 facilitates cell-cell adhesion to enable neuronal precursors to crawl up the radial glia during neuronal migration. With the knowledge of KIAA0319 involvement in early neurogenesis, we were interested in determining how different KIAA0319 expression may impact cortical neurons in layer II and III during early adulthood. We show that KIAA0319 knockdown in cortical pyramidal neurons significantly reduces the dendritic spine density. Studies have shown that changes in dendritic spine morphology and density affect properties of neural circuitry. Henceforth, this finding may reveal a link between the Kiaa0319 gene and the deficit of the neural processing task of reading due to reduced spines density. Finding a correlation between Kiaa0319 expression and its influence on dendritic spine development may lead to a greater insight of a direct link between the dyslexia susceptibility gene and the biological mechanism that causes dyslexia.

An examination of the relationship between maternal and neighborhood-level characteristics and intrauterine growth retardation in Harris County, Texas, 1999--2001

The persistence of low birth weight and intrauterine growth retardation (IUGR) in the United States has puzzled researchers for decades. Much of the work that has been conducted on adverse birth outcomes has focused on low birth weight in general and not on IUGR. Studies that have examined IUGR specifically thus far have focused primarily on individual-level maternal risk factors. These risk factors have only been able to explain a small portion of the variance in IUGR. Therefore, recent work has begun to focus on community-level risk factors in addition to the individual-level maternal characteristics. This study uses Social Ecology to examine the relationship of individual and community-level risk factors and IUGR. Logistic regression was used to establish an individual-level model based on 155, 856 births recorded in Harris County, TX during 1999-2001. IUGR was characterized using a fetal growth ratio method with race/ethnic and sex specific mean birth weights calculated from national vital records. The spatial distributions of 114,460 birth records spatially located within the City of Houston were examined using choropleth, probability and density maps. Census tracts with higher than expected rates of IUGR and high levels of neighborhood disadvantage were highlighted. Neighborhood disadvantage was constructed using socioeconomic variables from the 2000 U.S. Census. Factor analysis was used to create a unified single measure. Lastly, a random coefficients model was used to examine the relationship between varying levels of community disadvantage, given the set of individual-level risk factors for 152,997 birth records spatially located within Harris County, TX. Neighborhood disadvantage was measured using three different indices adapted from previous work. The findings show that pregnancy-induced hypertension, previous preterm infant, tobacco use and insufficient weight gain have the highest association with IUGR. Neighborhood disadvantage only slightly further increases the risk of IUGR (OR 1.12 to 1.23). Although community level disadvantage only helped to explain a small proportion of the variance of IUGR, it did have a significant impact. This finding suggests that community level risk factors should be included in future work with IUGR and that more work needs to be conducted. ^

The in vivo and in vitro formation of sticky DNA and the GAA.TTC trinucleotide repeat associated with Friedreich's ataxia

Friedreich's ataxia is caused by the expansion of the GAA•TTC trinucleotide repeat sequence located in intron 1 of the frataxin gene. The long GAA•TTC repeats are known to form several non-B DNA structures including hairpins, triplexes, parallel DNA and sticky DNA. Therefore it is believed that alternative DNA structures play a role in the loss of mRNA transcript and functional frataxin protein in FRDA patients. We wanted to further elucidate the characteristics for formation and stability of sticky DNA by evaluating the structure in a plasmid based system in vitro and in vivo in Escherichia coli. The negative supercoil density of plasmids harboring different lengths of GAA•TTC repeats, as well as either one or two repeat tracts were studied in E. coli to determine if plasmids containing two long tracts (≥60 repeats) in a direct repeat orientation would have a different topological effect in vivo compared to plasmids that harbored only one GAA•TTC tract or two tracts of < 60 repeats. The experiments revealed that, in fact, sticky DNA forming plasmids had a lower average negative supercoil density (-σ) compared to all other control plasmids used that had the potential to form other non-B DNA structures such as triplexes or Z-DNA. Also, the requirements for in vitro dissociation and reconstitution of the DNA•DNA associated region of sticky DNA were evaluated. Results conclude that the two repeat tracts associate in the presence of negative supercoiling and MgCl 2 or MnCl2 in a time and concentration-dependent manner. Interaction of the repeat sequences was not observed in the absence of negative supercoiling and/or MgCl2 or in the presence of other monovalent or divalent cations, indicating that supercoiling and quite specific cations are needed for the association of sticky DNA. These are the first experiments studying a more specific role of supercoiling and cation influence on this DNA conformation. To support our model of the topological effects of sticky DNA in plasmids, changes in sticky DNA band migration was measured with reference to the linear DNA after treatment with increasing concentrations of ethidium bromide (EtBr). The presence of independent negative supercoil domains was confirmed by this method and found to be segregated by the DNA-DNA associated region. Sequence-specific polyamide molecules were used to test the effect of binding of the ligands to the GAA•TTC repeats on the inhibition of sticky DNA. The destabilization of the sticky DNA conformation in vitro through this binding of the polyamides demonstrated the first conceptual therapeutic approach for the treatment of FRDA at the DNA molecular level. ^ Thus, examining the properties of sticky DNA formed by these long repeat tracts is important in the elucidation of the possible role of sticky DNA in Friedreich's ataxia. ^

Non B-DNA structures and genomic instability associated with myotonic dystrophy type 2 (CCTG).(CAGG) repeats

There are many diseases associated with the expansion of DNA repeats in humans. Myotonic dystrophy type 2 is one of such diseases, characterized by expansions of a (CCTG)•(CAGG) repeat tract in intron 1 of zinc finger protein 9 (ZNF9) in chromosome 3q21.3. The DM2 repeat tract contains a flanking region 5' to the tract that consists of a polymorphic repetitive sequence (TG)14-25(TCTG)4-11(CCTG) n. The (CCTG)•(CAGG) repeat is typically 11-26 repeats in persons without the disease, but can expand up to 11,000 repeats in affected individuals, which is the largest expansion seen in DNA repeat diseases to date. This DNA tract remains one of the least characterized disease-associated DNA repeats, and mechanisms causing the repeat expansion in humans have yet to be elucidated. Alternative, non B-DNA structures formed by the expanded repeats are typical in DNA repeat expansion diseases. These sequences may promote instability of the repeat tracts. I determined that slipped strand structure formation occurs for (CCTG)•(CAGG) repeats at a length of 42 or more. In addition, Z-DNA structure forms in the flanking human sequence adjacent to the (CCTG)•(CAGG) repeat tract. I have also performed genetic assays in E. coli cells and results indicate that the (CCTG)•(CAGG) repeats are more similar to the highly unstable (CTG)•(CAG) repeat tracts seen in Huntington's disease and myotonic dystrophy type 1, than to those of the more stable (ATTCT)•(AGAAT) repeat tracts of spinocerebellar ataxia type 10. This instability, however, is RecA-independent in the (CCTG)•(CAGG) and (ATTCT)•(AGAAT) repeats, whereas the instability is RecA-dependent in the (CTG)•(CAG) repeats. Structural studies of the (CCTG)•(CAGG) repeat tract and the flanking sequence, as well as genetic selection assays may reveal the mechanisms responsible for the repeat instability in E. coli, and this may lead to a better understanding of the mechanisms contributing to the human disease state. ^

Hazardous air pollutants and childhood lymphohematopoietic cancer in Southeast Texas, 1995--2004

Southeast Texas, including Houston, has a large presence of industrial facilities and has been documented to have poorer air quality and significantly higher cancer rates than the remainder of Texas. Given citizens’ concerns in this 4th largest city in the U.S., Mayor Bill White recently partnered with the UT School of Public Health to determine methods to evaluate the health risks of hazardous air pollutants (HAPs). Sexton et al. (2007) published a report that strongly encouraged analytic studies linking these pollutants with health outcomes. In response, we set out to complete the following aims: 1. determine the optimal exposure assessment strategy to assess the association between childhood cancer rates and increased ambient levels of benzene and 1,3-butadiene (in an ecologic setting) and 2. evaluate whether census tracts with the highest levels of benzene or 1,3-butadiene have higher incidence of childhood lymphohematopoietic cancer compared with census tracts with the lowest levels of benzene or 1,3-butadiene, using Poisson regression. The first aim was achieved by evaluating the usefulness of four data sources: geographic information systems (GIS) to identify proximity to point sources of industrial air pollution, industrial emission data from the U.S. EPA’s Toxic Release Inventory (TRI), routine monitoring data from the U.S. EPA Air Quality System (AQS) from 1999-2000 and modeled ambient air levels from the U.S. EPA’s 1999 National Air Toxic Assessment Project (NATA) ASPEN model. Further, once these four data sources were evaluated, we narrowed them down to two: the routine monitoring data from the AQS for the years 1998-2000 and the 1999 U.S. EPA NATA ASPEN modeled data. We applied kriging (spatial interpolation) methodology to the monitoring data and compared the kriged values to the ASPEN modeled data. Our results indicated poor agreement between the two methods. Relative to the U.S. EPA ASPEN modeled estimates, relying on kriging to classify census tracts into exposure groups would have caused a great deal of misclassification. To address the second aim, we additionally obtained childhood lymphohematopoietic cancer data for 1995-2004 from the Texas Cancer Registry. The U.S. EPA ASPEN modeled data were used to estimate ambient levels of benzene and 1,3-butadiene in separate Poisson regression analyses. All data were analyzed at the census tract level. We found that census tracts with the highest benzene levels had elevated rates of all leukemia (rate ratio (RR) = 1.37; 95% confidence interval (CI), 1.05-1.78). Among census tracts with the highest 1,3-butadiene levels, we observed RRs of 1.40 (95% CI, 1.07-1.81) for all leukemia. We detected no associations between benzene or 1,3-butadiene levels and childhood lymphoma incidence. This study is the first to examine this association in Harris and surrounding counties in Texas and is among the first to correlate monitored levels of HAPs with childhood lymphohematopoietic cancer incidence, evaluating several analytic methods in an effort to determine the most appropriate approach to test this association. Despite recognized weakness of ecologic analyses, our analysis suggests an association between childhood leukemia and hazardous air pollution.^

Using small area estimation and geographic information systems technology to target health services for the uninsured

The three articles that comprise this dissertation describe how small area estimation and geographic information systems (GIS) technologies can be integrated to provide useful information about the number of uninsured and where they are located. Comprehensive data about the numbers and characteristics of the uninsured are typically only available from surveys. Utilization and administrative data are poor proxies from which to develop this information. Those who cannot access services are unlikely to be fully captured, either by health care provider utilization data or by state and local administrative data. In the absence of direct measures, a well-developed estimation of the local uninsured count or rate can prove valuable when assessing the unmet health service needs of this population. However, the fact that these are “estimates” increases the chances that results will be rejected or, at best, treated with suspicion. The visual impact and spatial analysis capabilities afforded by geographic information systems (GIS) technology can strengthen the likelihood of acceptance of area estimates by those most likely to benefit from the information, including health planners and policy makers. ^ The first article describes how uninsured estimates are currently being performed in the Houston metropolitan region. It details the synthetic model used to calculate numbers and percentages of uninsured, and how the resulting estimates are integrated into a GIS. The second article compares the estimation method of the first article with one currently used by the Texas State Data Center to estimate numbers of uninsured for all Texas counties. Estimates are developed for census tracts in Harris County, using both models with the same data sets. The results are statistically compared. The third article describes a new, revised synthetic method that is being tested to provide uninsured estimates at sub-county levels for eight counties in the Houston metropolitan area. It is being designed to replicate the same categorical results provided by a current U.S. Census Bureau estimation method. The estimates calculated by this revised model are compared to the most recent U.S. Census Bureau estimates, using the same areas and population categories. ^

The relationship between supermarket nutrient movements and the mortality rates from fat-associated and non-fat-associated cardiovascular disease: Development of an ecologic method for determining community food patterns

Supermarket nutrient movement, a community food consumption measure, aggregated 1,023 high-fat foods, representing 100% of visible fats and approximately 44% of hidden fats in the food supply (FAO, 1980). Fatty acid and cholesterol content of foods shipped from the warehouse to 47 supermarkets located in the Houston area were calculated over a 6 month period. These stores were located in census tracts with over 50% of a given ethnicity: Hispanic, black non-Hispanic, or white non-Hispanic. Categorizing the supermarket census tracts by predominant ethnicity, significant differences were found by ANOVA in the proportion of specific fatty acids and cholesterol content of the foods examined. Using ecological regression, ethnicity, income, and median age predicted supermarket lipid movements while residential stability did not. No associations were found between lipid movements and cardiovascular disease mortality, making further validation necessary for epidemiological application of this method. However, it has been shown to be a non-reactive and cost-effective method appropriate for tracking target foods in populations of groups, and for assessing the impact of mass media nutrition education, legislation, and fortification on community food and nutrient purchase patterns. ^

Spatial analysis of pertussis cases in Harris County from 2005-2010

Objective: This study examined the recent trends and characteristics of reported pertussis in Harris County from 2005-2010. ^ Methods: The study population included surveillance data from all reported pertussis cases from January 1, 2005 to December 31, 2010 to Harris County Public Health and Environmental Services (HCPHES). We calculated incidence and attack rates for varying age groups, race/ethnicity, and gender. Spatial analyses were conducted of hot spot and cluster of incident cases in Harris County census tracts. Maps were constructed using geographic information system. ^ Results: Age-specific incidence rates of reported cases of pertussis were highest among infants under a year of age and lowest among adults age 20 and older. Hispanics represented the most cases reported compared to any other race or ethnic group (42% of 483 cases). Age-adjusted rates were highest in 2009 at 9.81 cases per 100,000 population. Only 31.2% of people received at least four of the recommended five doses of vaccine. Spatial analyses revealed statistically significant clusters within the northeast region of Harris County. ^ Conclusions: Hispanic infants are the most at risk group for pertussis. Although 70% of cases had a history of immunization, 41.8% of infants were appropriately vaccinated for their age. Increased vaccination coverage may decrease the incidence of pertussis.^