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PubMed1984

A neural theory of circadian rhythms: Aschoff's rule in diurnal and nocturnal mammals.

A neural model of the suprachiasmatic nuclei suggests how behavioral activity, rest, and circadian period depend on light intensity in diurnal and nocturnal mammals. These properties are traced to the action of light input (external zeitgeber) and an activity-mediated fatigue signal (internal zeitgeber) on the circadian pacemaker. Light enhances activity of the diurnal model and suppresses activity of the nocturnal model. Fatigue suppresses activity in both diurnal and nocturnal models. The asymmetrical action of light and fatigue in diurnal vs. nocturnal models explains the more consistent adherence of nocturnal mammals to Aschoff's rule, the consistent adherence of both diurnal and nocturnal mammals to the circadian rule, and the tendency of nocturnal mammals to lose circadian rhythmicity at lower light levels than diurnal mammals. The fatigue signal is related to the sleep process S of Borbély (Hum. Neurobiol. 1: 195-204, 1982.) and contributes to the stability of circadian period. Two predictions follow: diurnal mammals obey Aschoff's rule less consistently during a self-selected light-dark cycle than in constant light, and if light level is increased enough during sleep in diurnal mammals to compensate for eye closure, then Aschoff's rule will hold more consistently. The results are compared with those of Enright's model.

Animals↗

PubMed2001

Predictors of airborne endotoxin in the home.

We identified home characteristics associated with the level of airborne endotoxin in 111 Boston-area homes enrolled in a cohort study of home exposures and childhood asthma, and we developed a predictive model to estimate airborne endotoxin. We measured endotoxin in family-room air and in dust from the baby's bed, family room, bedroom, and kitchen floor. Level of airborne endotoxin was weakly correlated (r < 0.3) with level of endotoxin in each of the four types of dust samples and was significantly correlated with endotoxin in family-room dust (p < 0.05). Endotoxin in family-room dust accounted for < 6% of the variability of airborne endotoxin. In a multivariate model, certain home characteristics were positively (p < 0.05) associated with airborne endotoxin. These included current presence of dog (difference in level, dog vs. no dog = 72%, partial R(2 )= 12.8%), past presence of dog (partial R(2) = 5.5%), and endotoxin level in family-room dust (partial R(2) = 5.3%). Use of a dehumidifier (partial R(2) = 6.4%) was negatively associated (p = 0.02; difference = -31%) with airborne endotoxin. Other home characteristics were identified as important determinants of increased airborne endotoxin in this model, but individual coefficients were not statistically significant (alpha = 0.05): total amount of fine dust collected in the home (partial R(2 )= 3.8%), concrete floor in family room (3.7%), water damage (3.6%), and use of cool-mist humidifier in past year (2.7%). This multivariate model explained 42% of the variability of airborne endotoxin levels, a substantial improvement over that with dust endotoxin alone. Airborne endotoxin in Boston-area homes appears to be determined by the presence of dogs, moisture sources, and increased amounts of settled dust.

Air Pollutants↗

PubMed2001

Chloroplast DNA phylogeography of Cunninghamia konishii (Cupressaceae), an endemic conifer of Taiwan.

In this study, we investigated the genetic structure and phylogeographic pattern of the genus Cunninghamia, a member of the Cupressaceae restricted to mainland China and Taiwan, based on sequences of the trnD-trnT noncoding spacer of the chloroplast DNA. Maternal inheritance of chloroplasts was determined experimentally. No paternal leakage was detected. Both parsimony and neighbor-joining analyses revealed the polyphyly of Cunninghamia konishii, populations of which were nested in clades of C. lanceolata from mainland China. The nucleotide diversity of chloroplast DNA sequences within C. konishii (0.0118) was higher than that between species (0.0104), which agrees with a previous allozyme investigation. Based on mutational differences between sequences, a minimum spanning network consisting of five clades was constructed. Significant genetic differentiation (phiST = 0.130, P < 0.001) was detected between the clades based on AMOVA analyses. We infer several possible refugia in the Yunnan, Zhejiang, and Guangdong provinces of south China, all located in the minimum network as interior nodes. We also infer possible migration routes of Cunninghamia populations. The phylogeographic pattern shown in the reconstructed network suggests that the present-day Cunninghamia populations in Taiwan were derived from six different sources in continental Asia via long-distance seed dispersal. A migrant-pool model explains the heterogeneous composition of the organelle DNA in Taiwan's populations and the low differentiation between populations of Taiwan and China (phiCT = 0.012, P = 0.454). In contrast with the genetic heterogeneity within geographic populations, many local populations have attained coalescence at the trnD-trnT alleles, which has led to significant differentiation at the population level.

Alleles↗

PubMed2006

Can we predict uranium bioavailability based on soil parameters? Part 2: soil solution uranium concentration is not a good bioavailability index.

The present study aimed to quantify the influence of soil parameters on uranium uptake by ryegrass. Ryegrass was established on eighteen distinct soils, spiked with (238)U. Uranium soil-to-plant transfer factors (TF) ranged from 0.0003 to 0.0340kgkg(-1). There was no significant relation between the U soil-to-plant transfer (or total U uptake or flux) and the uranium concentration in the soil solution or any other soil factor measured, nor with the U recovered following selective soil extractions. Multiple linear regression analysis resulted in a significant though complex model explaining up to 99% of variation in TF. The influence of uranium speciation on uranium uptake observed was featured: UO(2)(+2), uranyl carbonate complexes and UO(2)PO(4)(-) seem the U species being preferentially taken up by the roots and transferred to the shoots. Improved correlations were obtained when relating the uranium TF with the summed soil solution concentrations of mentioned uranium species.

Biological Availability↗

PubMed1993

Solution structure of the exocyclic 1,N2-propanodeoxyguanosine adduct opposite deoxyadenosine in a DNA nonamer duplex at pH 8.9. model of pH-dependent conformational transition.

The solution structure of the complementary d(C1-A2-T3-G4-X5-G6-T7-A8-C9).d(G10-T11-A12-C13-A14-C15-A16-T17-G18) DNA duplex (designated X.A 9-mer), which contains a 1,N2-propanodeoxyguanosine exocyclic adduct X5 opposite deoxyadenosine A14 at the center, is pH dependent [Kouchakdjian, M., Eisenberg, M., Live, D., Marinelli, E., Grollman, A., & Patel, D.J. (1990) Biochemistry 29, 4456-4465]. In our previous paper [Huang, P., & Eisenberg, M. (1992) Biochemistry 31, 6518-6532] we established the three-dimensional structure of this X.A 9-mer duplex at pH 5.8 by use of restrained molecular dynamics followed by NOE-based back-calculation refinement. The present paper discusses the structure at pH 8.9 and the pH-dependent conformational transition between the structures at pH 5.8 and at pH 8.9. The structure at pH 8.9 is calculated starting from five different conformations. The final structures converge and agree well with the experimental NOE intensities. These structures are essentially B-type DNA (with X5 and A14 in the BII conformation while the other residues are in the most commonly described BI conformation) and display an approximate 27 degrees kink at the center of the helix. At the kink site, X5 is positioned in the major groove with the exocyclic ring directed toward the G6.C13 base pair, unstacked from the flanking base G6 and exposed to the solvent. A14, opposite the lesion, remains stacked with its neighbor C15, but not with C13. The kinked helix can accommodate the rotation of the bulky X5 about its glycosidic bond. We propose here a model for the pH-dependent transition. Our model explains the conformational change, which includes the anti and syn rotation of the bulky adduct around its glycosidic bond, with a minimal energy barrier and with an overall kink of the DNA helix. These new findings, fully consistent with the NMR experimental data, were revealed only after restrained dynamics refinement. Distance-restrained energy minimization by itself was insufficient, as shown by the previous NMR study.

Base Sequence↗

PubMed2001

Family survivorship and quality of life following a cancer diagnosis.

The objectives of this study were: (a) to examine the quality of life of the family as a unit during the long-term survivor phase of illness and (b) to test a family model of factors that may influence family quality of life. The family survivorship model, which includes illness survival stressors (family stressors, fear of recurrence, and patient somatic concerns), resources (family hardiness and family social support), appraisal (family meaning of the illness), and the outcome, family quality of life, was used to guide this exploratory cross-sectional study. A random, stratified sample of 123 families (N = 246 individuals) was interviewed 1-5 years after treatment ended. The model explained 63% of the variance in family quality of life, with the strongest predictors being concurrent family stressors, family social support, family member fear of recurrence, family meaning of the illness, and patient employment status. The study findings suggest the importance of addressing cancer-related stressors, family resources, and family meaning as key factors related to family quality of life.

Adult↗

PubMed2001

Projective identification in common couple dances.

This paper integrates the object relations concept of projective identification and the systemic concept of marital dances to develop a more powerful model for working with more difficult and distressed couples. This integrated model explains how some couples use the defenses of splitting and projective identification to externalize and transpose internal conflicts into interpersonal conflicts in five common marital dances. The author suggests how object relations techniques can be used to interrupt the projective identifications, help clients to reown their disowned and projected affects and resolve the conflict on the intrapsychic level so that the marital dance is no longer necessary to resolve the intrapsychic issues.

Conflict, Psychological↗

PubMed1994

Education and the health professions: explaining policy choices among the states.

Recent calls for restructuring of the nation's health care system have highlighted the deficiencies in the current system of education for the health professions. Of particular concern are the dominance of specialization and hospital-based training and the tendency of new health care providers to settle in communities without substantial health needs. The states are the key actors in reforming health professions education, serving as a primary funding source for health professions schools, chief licensors and regulators of health professions, regulators of private health insurance, key providers of Medicaid, and architects of a variety of subsidy and regulatory programs providing incentives for health professionals to choose specialties and locations for practice. This article provides a taxonomy of state policies affecting health professions education reform and classifies the states according to the choices they have made. Findings show that few states take advantage of their policy options across the four policy types and that most tend to concentrate their efforts on a few policies--ignoring potential means of encouraging more primary care providers in underserved areas. Results from regression models explaining state choice of policy adoption highlight the political nature of policy choice and the highly variable nature of state response in health professions education reform.

Education, Medical↗

PubMed2005

Modeling social reintegration in persons with spinal cord injury.

PURPOSE: This study was undertaken to identify and develop a model of the factors related to social reintegration in persons with spinal cord injury (SCI). METHOD: A convenience sample of 145 persons with SCI living in two cities in South Korea anonymously completed a questionnaire that comprised the assessment of social reintegration, a tool developed to measure the degree of adjustment to community living in persons with SCI. Structural equation modeling was used to examine the direct and indirect effects of self-esteem, social barriers, physical function, family support, informational support, perceived stress, emotion-focused coping (EFC), and problem-focused coping (PFC) on social reintegration. RESULTS: The model explained 65% of the variance in social reintegration in persons with SCI. The results indicated that the social integration of persons with SCI was influenced most by EFC. Family support, informational support, perceived stress and social barriers were also significantly related to social reintegration. CONCLUSIONS: These findings suggest implications for developing the interventions at various levels including family and community and specific to individual coping strategies to enhance social reintegration in persons with SCI.

Adaptation, Psychological↗

PubMed1993

Physiologically based modeling of 2-butoxyethanol disposition in rats following different routes of exposure.

2-Butoxyethanol (BE) is widely used as a solvent in coatings and other consumer products and has shown hematotoxicity in laboratory animals. To provide a physiological basis for extrapolating toxicokinetic data observed in rats to humans, a blood flow rate-limited, physiologically based pharmacokinetic model was developed to describe the distribution and metabolism of BE in rats following drinking water, dermal, and inhalation exposures. The major urinary metabolite, butoxyacetic acid, represented 45 to 60% of the absorbed dose in all three routes of exposure. Other identified urinary metabolites in our studies included ethylene glycol and BE-glucuronide. A model formulation of the possible metabolic pathways based on the experimental data was proposed. The amounts of individual urinary metabolites were used to develop the model. Metabolic constants were estimated by fitting the data within the constraints of in vitro measurements. The model explained the change of profiles of urinary metabolites in different exposure routes by taking into account the differences in absorption rate and by incorporating a minor pathway for metabolism by skin. Sensitivity analysis showed that metabolic constants and blood flow rate to liver had a relatively larger influence on the production of urinary metabolites than the organ volume or the partition coefficient for BE.

Administration, Cutaneous↗

PubMed1999

The role of locus coeruleus in the regulation of cognitive performance.

Noradrenergic locus coeruleus (LC) neurons were recorded in monkeys performing a visual discrimination task, and a computational model was developed addressing the role of the LC brain system in cognitive performance. Changes in spontaneous and stimulus-induced patterns of LC activity correlated closely with fluctuations in behavioral performance. The model explains these fluctuations in terms of changes in electrotonic coupling among LC neurons and predicts improved performance during epochs of high coupling and synchronized LC firing. Cross correlations of simultaneously recorded LC neurons confirmed this prediction, indicating that electrotonic coupling in LC may play an important role in attentional modulation and the regulation of goal-directed versus exploratory behaviors.

Action Potentials↗

PubMed1989

Unemployment, socioenvironmental factors, and coronary heart disease in Scotland.

Scotland, which has one of the highest death rates in the world from coronary heart disease, also has considerable regional variation in mortality from this cause. The relation between standardised mortality ratios for coronary deaths (1979-83) for 56 local government districts and a range of socioeconomic factors from the 1981 Census as well as climatic factors and water hardness were investigated. Strong associations were seen with several measures of social disadvantage, the strongest being with percentage of male unemployment. A fitted multiple regression model with mortality from coronary heart disease in men found independent effects of two social variables (percentage male unemployment and percentage social class III-V) and one climatic factor (rainfall). The model explained much (73%) of the geographical variation in mortality from coronary heart disease, but part of the geographical pattern, in particular some of the east-west gradient in mortality, remained unexplained by it. Explanations for the geographical variation and the association with economic factors are currently being sought in terms of individual risk factors in a large screening study, the Scottish Heart Health Study.

Adult↗

PubMed2003

Behaviors of older men living in the community. Correlates producing active composure.

The correlates of active composure behaviors for older veteran men living in the community were investigated to identify this aspect of the complex domain of health behavior. Cox's (1982) Interaction Model of Client Health Behavior was used to frame this investigation. The independent variables were age, education, race, marital status, children, siblings, income, spiritual well-being, functional status, motivation, health conceptions, and loneliness. The dependent variable was Schwirian's (1992) active composure, conceptualized as activities producing rest, relaxation, and anxiety and stress reduction. The sample was male veterans (N = 184) older than 65 who were not living in an institution. A multiple regression model explained 49% of the variance in active composure. Race, income, religious aspect of spiritual well-being, instrumental activities of daily living, and loneliness were significant predictors. Results suggest that nurses may find these correlates helpful in facilitating the identification of risk status and developing active composure self-care strategies for older men living in the community.

Activities of Daily Living↗

PubMed1992

Health beliefs: a cultural division?

Uptake of preventive health programmes seems to be related to people's underlying motivations, attitudes and beliefs about health and illness. Current theories used to account for variance in behaviours by social group (such as the health belief model and locus of control model) explain only some of the variance in these motivations and attitudes, and have not been adequately tested on women from different ethnic minority groups. Health beliefs have important implications for nursing given the role of the nurse in health promotion and patient teaching. This paper identifies and compares the health beliefs of women of Asian origin and white indigenous women living in an inner-London borough, through in-depth semi-structured interviews, and considers the findings in relation to health promotion practices and the role of the nurse. The Asian women rated their health as worse than the white women; this requires further study. Comments and views gathered about the causes of various diseases indicated that it may be unrealistic to fit a person's health beliefs into a distinct model. Beliefs about disease appeared to be culturally sensitive; health education, therefore, must also be culturally sensitive.

Asia↗

PubMed2001

Hepatic metallothionein as a biomaker for metal contamination: age effects and seasonal variation in European flounders (Pleuronectes flesus) from the Severn Estuary and Bristol Channel.

Hepatic concentrations of metallothionein [MT] and three metals (Cu, Zn, Cd) were determined in 242 European flounders (Pleuronectes flesus) collected from power stations at Oldbury-upon-Severn and Hinkley Point, located in Severn Estuary and Bristol Channel, UK, respectively, between March 1996 and February 1998. A model involving three-factor analysis of variance (ANOVA) was used to examine variation in MT and metal concentrations with respect to season, year and site; with age-class included as a covariate in the analysis. Hepatic concentrations of MT and Cd (and to some degree, Cu, but not Zn) increased significantly with age. The model explained 38, 25, 17 and 26% of the variation in MT, Cu, Zn and Cd, respectively, with significant effects due to season, and to a lesser extent, to year. Site was only a significant factor for Cd which was higher in fish from Hinkley. Correlation between the individual concentration of MT and each metal alone, or in combination, was poor, and explained only an additional 3.0% of the residual variation in MT, most of which was attributable to Cu (2.7%). Compared to other industrialised estuaries, Cd concentrations were high (>20 micro g-1 in some individuals). The study emphasises the importance of seasonal variation and other factors in biomonitoring programmes and highlights the limitations of using [MT] as a biomarker for metal contamination in flounders from the Severn Estuary.

Age Factors↗

PubMed2006

Parameter stability of the functional-structural plant model GREENLAB as affected by variation within populations, among seasons and among growth stages.

BACKGROUND AND AIMS: It is increasingly accepted that crop models, if they are to simulate genotype-specific behaviour accurately, should simulate the morphogenetic process generating plant architecture. A functional-structural plant model, GREENLAB, was previously presented and validated for maize. The model is based on a recursive mathematical process, with parameters whose values cannot be measured directly and need to be optimized statistically. This study aims at evaluating the stability of GREENLAB parameters in response to three types of phenotype variability: (1) among individuals from a common population; (2) among populations subjected to different environments (seasons); and (3) among different development stages of the same plants. METHODS: Five field experiments were conducted in the course of 4 years on irrigated fields near Beijing, China. Detailed observations were conducted throughout the seasons on the dimensions and fresh biomass of all above-ground plant organs for each metamer. Growth stage-specific target files were assembled from the data for GREENLAB parameter optimization. Optimization was conducted for specific developmental stages or the entire growth cycle, for individual plants (replicates), and for different seasons. Parameter stability was evaluated by comparing their CV with that of phenotype observation for the different sources of variability. A reduced data set was developed for easier model parameterization using one season, and validated for the four other seasons. KEY RESULTS AND CONCLUSIONS: The analysis of parameter stability among plants sharing the same environment and among populations grown in different environments indicated that the model explains some of the inter-seasonal variability of phenotype (parameters varied less than the phenotype itself), but not inter-plant variability (parameter and phenotype variability were similar). Parameter variability among developmental stages was small, indicating that parameter values were largely development-stage independent. The authors suggest that the high level of parameter stability observed in GREENLAB can be used to conduct comparisons among genotypes and, ultimately, genetic analyses.

Agriculture↗

PubMedDate not supplied

[Revealing key interactions in the metabolic network: a model of primary phosphate transport in bacteria].

One of the main problems of metabolic engineering is to determine the genetically controlled limiting links of a metabolic network. We have built a model of the primary transport of inorganic phosphates (Pi), analyzed the Pi metabolic network in Gram-negative bacteria, and determined the factors controlling the phosphate exchange. The model explains why the Pi primary transport is not observed at the release stage. The nonlinearity of primary transport and the differences in its parameters in the membrane and within the cell give rise to transport asymmetry, i.e., the Pi release rate is low as compared with the uptake rate, and is small at the background of secondary transport. Discussed is a general scheme of coordination between primary and secondary transport, which are interconnected through the substrate-product reration.

Bacteria↗

PubMed1998

Muscarinic agonists with antipsychotic-like activity: structure-activity relationships of 1,2,5-thiadiazole analogues with functional dopamine antagonist activity.

Muscarinic agonists were tested in two models indicative of clinical antipsychotic activity: conditioned avoidance responding (CAR) in rats and inhibition of apomorphine-induced climbing in mice. The standard muscarinic agonists oxotremorine and pilocarpine were both active in these tests but showed little separation between efficacy and cholinergic side effects. Structure-activity relationships of the alkylthio-1,2,5-thiadiazole azacyclic type muscarinic partial agonists are shown, revealing the exo-6-(3-propyl/butylthio-1,2, 5-thiadiazol-4-yl)-1-azabicyclo[3.2.1]octane analogues (4a,b and 9a, b) to be the most potent antipsychotic agents with large separation between efficacy and cholinergic side effects. The lack of enantiomeric selectivity suggests the pharmacophoric elements are in the mirror plane of the compounds. A model explaining the potency differences of closely related compounds is offered. The data suggest that muscarinic agonists act as functional dopamine antagonists and that they could become a novel treatment of psychotic patients.

Animals↗