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At least 289 records · Page 16Linked to original sources

PubMed2007

The evolution of bird migration--a synthesis.

We approach the problem of the evolution of bird migration by asking whether migration evolves towards new breeding areas or towards survival areas in the non-breeding season. Thus, we avoid the ambiguity of the usually discussed "southern-home-theory" or "northern-home-theory". We argue that migration evolved in birds that spread to seasonal habitats through gradual dispersal to enhance survival during the non-breeding season; this in contrast to the alternative idea suggesting that migration evolved towards new breeding areas to increase reproductive success. Our synthesis is based on the threshold model explaining how migratory traits can change rapidly through microevolutionary processes. Our model brings former theories together and explains how bird migration, with the appropriate direction and time program, evolves through selection after genetically non-directed events such as dispersal and colonization. The model does not need the former untested assumptions such as competition as a reason for migration and for the disappearance of sedentary populations or higher reproductive success in temperate breeding areas. Our theory offers answers to questions such as how birds with a southern origin may gradually reach northern latitudes, why migration routes may follow historical expansion routes and why birds leave an area for the non-breeding season and move back instead of breeding on their wintering grounds. The theory proposes gradual change through selection and not sudden changes such as long distance dispersal or mutations and can be applied to migration at all latitudes and in all directions. The scenario provides a reasonable concept to understand most of the existing migratory phenomena on the basis of the ecology and genetics of migratory behaviour.

Animal Migration↗

PubMed2004

Theoretical consideration of olfactory axon projection with an activity-dependent neural network model.

Olfactory sensory neurons (OSNs) that express a given odorant receptor (OR) target their axons onto a few specific glomeruli in the olfactory bulb. Although the odorant receptor plays an indispensable role in olfactory axon targeting, the mechanisms underlying this guidance are largely unknown. In particular, there is much controversy regarding the involvement of activity-dependent mechanism in the targeting process. In this study, we developed an activity-dependent self-organization model of the glomerular layer in the olfactory bulb and simulated the targeting of olfactory axons onto the layer. Our model successfully constructed discrete glomeruli that received olfactory axons expressing a common odorant receptor through odorant-evoked neural activities. Furthermore, our model explained the perplexing experimental results that have been reported in olfactory axon targeting. For example, dispersion of olfactory axons in knockout mice for the odorant receptor gene was reasonably reproduced in the simulation. The segregated projection of the axons that express the same odorant receptor transcribed from the different alleles was also successfully simulated if the genetically modified allele was assumed to express a smaller amount of the receptor protein. The activity-dependent model even explained the inconsistent effects of disruption of the activity-evoking ion channel on axons expressing different odorant receptors, although some of these results were regarded as evidence for activity-independency of the olfactory targeting. Taken together, the activity-dependent targeting of olfactory axons seems to be a simple probable mechanism that can provide a unified explanation of glomerular formation.

Action Potentials↗

PubMed2004

Determinants of endogenous calcium entry into the gut.

BACKGROUND: In addition to food sources, calcium enters the gut by way of digestive secretions and shed mucosa. In health, such entry is as large as or larger than urinary calcium excretion. Because calcium absorption is inefficient, most of this endogenous intestinal calcium is excreted. OBJECTIVE: Our aim was to determine the dietary, anthropometric, and physiologic determinants of calcium entering the digestive stream from endogenous sources. DESIGN: Multiple regression modeling of intake and excretion data was used with 553 metabolic balance and kinetics studies performed in 190 midlife, white women. RESULTS: Endogenous intestinal calcium averaged 3.29 +/- 0.83 mmol/d. Multiple regression models explaining variation in this endogenous intestinal calcium were developed with use of dietary intake, anthropometric, and serum mineral variables. All 3 groups of predictor variables individually explained up to 22% of the variation in measured values for endogenous intestinal calcium. A composite model, incorporating all 3 groups explained 29% of the variation, with phosphorus and meat protein intakes, height, weight, and serum calcium and phosphorus concentrations all independently entering the model. Phosphorus intake dominated over all the other predictors, explaining 20% of the variance all by itself, with endogenous intestinal calcium rising by 0.037 mmol for every 1 mmol of phosphorus ingested. Meat protein (but not nonmeat protein) was the only other significant dietary contributor, exhibiting a negative coefficient. CONCLUSION: As a first approximation, the amount of endogenous calcium entering the digestive stream rises with body size and with the amount of phosphorus-rich food consumed.

Anthropometry↗

PubMed1993

Explaining variations in prescribing costs across England.

OBJECTIVE: To derive a predictive model for national prescribing behaviour in terms of basic morbidity and demographic factors. DESIGN: 24 demographic, morbidity, and practice factors were entered into a multiple regression analysis to determine the net ingredient cost per patient. SETTING: The 90 family health service authorities in England for 1989. RESULTS: For net ingredient cost per patient only two demographic factors (numbers of pensioners and the mobility of the registered population measured by list inflation) and two morbidity related factors (standardised mortality ratios and numbers of prepayment certificates issued) significantly contributed to a multiple regression model. This model explained 81% of the variation in net ingredient cost per registered patient between family health services authorities. The model also enabled a weighting factor of 4.6 (95% confidence interval 3.2 to 6.7) to be derived for the net ingredient cost for elderly patients (compared with the existing prescribing unit factor of 3). CONCLUSIONS: The model shows that variations in prescribing costs essentially reflect demand. It also suggests that the current prescribing unit value of 3 for patients aged 65 or more underestimates the extra costs of prescribing for elderly patients.

Drug Costs↗

PubMedDate not supplied

The orchestration of body iron intake: how and where do enterocytes receive their cues?

Our understanding of how iron transverses the intestinal epithelium has improved greatly in recent years, although the mechanism by which body iron demands regulate this process remains poorly understood. By critically examining the earlier literature in this field and considering it in combination with recent advances we have formulated a model explaining how iron absorption could be regulated by body iron requirements. In particular, this analysis suggests that signals to alter absorption exert a direct effect on mature enterocytes rather than influencing the intestinal crypt cells. We propose that the liver plays a central role in the maintenance of iron homeostasis by regulating the expression of hepcidin in response to changes in the ratio of diferric transferrin in the circulation to the level of transferrin receptor 1. Such changes are detected by transferrin receptor 2 and the HFE/transferrin receptor 1 complex. Circulating hepcidin then directly influences the expression of Ireg1 in the mature villus enterocytes of the duodenum, thereby regulating iron absorption in response to body iron requirements. In this manner, the body can rapidly and appropriately respond to changes in iron demands by adjusting the release of iron from the duodenal enterocytes and, possibly, the macrophages of the reticuloendothelial system. This model can explain the regulation of iron absorption under normal conditions and also the inappropriate absorption seen in pathological states such as hemochromatosis and thalassemia.

Antimicrobial Cationic Peptides↗

PubMed2001

Metabolisable energy value and digestibility of fat and fatty acids in linseed determined with growing broiler chickens.

1. In the first experiment, the AMEN of linseed was evaluated at rates of 40, 80, 160 and 240 g/kg in a basal diet with broiler chickens aged 28 d using the total collection method. 2. Increasing the concentration of linseed decreased the AMEN of diet, from 11.78 to 8.75 MJ/kg DM, and AMEN of linseed, from 16.64 to -2.96 MJ/kg DM. The negative values clearly indicated that linseed interacted with the other dietary ingredients and impaired their energy utilisation. 3. In the second experiment, a semipurified diet with graded addition of linseed (80, 120, 160 and 240 g/kg DM) was evaluated for crude fat and fatty acid apparent digestibilities. The coefficients decreased from 0.602 to 0.359 for crude fat and from 0.661 to 0.352 for individual fatty acids as the level of linseed increased. 4. In both experiments, a quadratic regression model explained the relationship between data better than the linear model. 5. The presence of mucilage and other antinutritional factors in linseed might explain the results obtained in this study.

Animal Nutritional Physiological Phenomena↗

PubMed1992

Far-field potentials in circular volumes: evidence to support the leading/trailing dipole model.

The leading/trailing dipole model explains the production of far-field potentials as an asymmetry in the leading and trailing dipole moments of a propagating action potential detected by a referential montage. This investigation documents the production of far-field potentials produced by a pure dipole generator in a circular volume conductor. Multiple equipotential waveforms are recorded in an adjoining circular volume conductor attached to the one in which the dipole generator is located. This finding substantiates the "wick electrode" effect that explains the equipotential and instantaneous distribution of far-field potentials over relatively large distances in volume conductors. The present findings support a number of the leading/trailing dipole model proposals which explain far-field potential generation.

Action Potentials↗

PubMed1987

Depressive symptoms and persistence in treatment for alcohol dependence.

The relationship between alcoholics' depressive symptoms during their preadmission evaluations and persistence in treatment for alcohol dependence is evaluated. Hierarchical multiple regression was used to determine the contribution of Beck Depression Inventory (BDI) scores to the prediction of the criterion: number of continuous days in treatment (up to 120). After several sources of variance were removed (age, race, age X race interaction, number of previous treatments and referral source), BDI score explained 10.8% of the criterion's variance. The full model explained 28.2%. Early withdrawal occurred in association with freedom from measurable affective distress during preadmission evaluation. A model for the prediction of number of continuous days in treatment is presented.

Adult↗

PubMed1975

Integral control in accommodation.

Models of the accommodation system available inthe literature may be classified as proportional controller, optimal bang-bang controller and pure integral controller types. Each of these models explains only some aspects of the experimental behavior of the system and conflicts with other experimental observations. Based on two different experiments in which the built-in phyiological feedback loop has been opened, a leaky-integrator element is proposed for the accommodation controller. This element appears to resolve the conflict between the proportional and integral controller models and also explains the experimental observations better than any of the existing models.

Accommodation, Ocular↗

PubMed1999

Urine is a saturated equilibrium and not a metastable supersaturated solution: evidence from crystalluria and the general composition of calcium salt and uric acid calculi.

A computer algorithm is described which allows urine to be modelled as a saturated equilibrium solution with respect to any combination of the solids calcium oxalate, calcium hydrogen phosphate (brushite), amorphous calcium phosphate, uric acid, sodium hydrogen urate and ammonium hydrogen urate. It is demonstrated that this model of urine, unlike the widely accepted metastable supersaturated solution model, explains the long-known calcium salt crystalluria versus pH curves of both non-stone-forming and stone-forming urine. Further, the saturation model accounts for why most "infection" stones do not contain calcium oxalate and why most "urate" stones are composed solely of uric acid and not admixed with alkali metal hydrogen urate salts. The supersaturation model of urine cannot explain satisfactorily these well-known phenomena. For example, the supersaturation model predicts that virtually all "infection" stones should contain calcium oxalate along with calcium phosphate and, perhaps, struvite.

Calcium↗

PubMed1997

Exposure levels and determinants of inhalable dust exposure in bakeries.

The study's objectives were to measure full-shift exposure to inhalable dust in bakeries and define the determinants of full-shift exposure. Inhalable dust was measured gravimetrically. Ninety-six bakery workers, employed in seven different bakeries, participated in the study. Two side-by-side full-shift inhalable dust samples were obtained from each study participant on a single occasion. Samples were collected on 18 days selected at random. During the entire sampling period, bakers were observed and information on 14 different tasks was recorded at 15 min intervals. Other production characteristics were also recorded for each sampling day. These task and production variables were used in statistical modelling to identify significant predictors of exposure. The mean full-shift inhalable dust exposure was 8.2 mg/m3 (range: 0.1-110 mg/m3). A regression model explained 79% of the variability in exposure. The model indicated that tasks such as weighing, pouring and operating dough-brakers and reversible sheeters increased the exposure, while packing, catching and decorating decreased the exposure. Bread and bun production lines were associated with increased full-shift inhalable dust exposure, while cake production and substitution of dusting with the use of divider oil were associated with decreased exposure. Production tasks and characteristics are strong predictors of personal full-shift exposures to flour dust among bakers; these can be altered to reduce exposure levels.

Analysis of Variance↗

PubMed1998

Quantitative analysis of the effects of intrathylakoid pH and xanthophyll cycle pigments on chlorophyll a fluorescence lifetime distributions and intensity in thylakoids.

The xanthophyll cycle-dependent dissipation of excitation energy in higher plants is one of the most important regulatory and photoprotective mechanisms in photosynthesis. Using parallel time-resolved and pulse-amplitude modulation fluorometry, we studied the influence of the intrathylakoid pH and the xanthophyll cycle carotenoids on the PSII chlorophyll (Chl) a fluorescence yield in thylakoids of Arabidopsis, spinach, and barley. Increases in concentrations of dithiothreitol in thylakoids, which have a trans-thylakoid membrane pH gradient and are known to have decreased conversion of violaxanthin (V) to zeaxanthin (Z), lead to (1) decreases in the fractional intensity of the approximately 0.5 ns Chl a fluorescence lifetime (tau) distribution component and simultaneous increases in a 1.6-1.8 ns fluorescence component and (2) increases in the maximal fluorescence intensity. These effects disappear when the pH gradient is eliminated by the addition of nigericin. To quantitatively explain these results, we present a new mathematical model that describes the simultaneous effects of the chloroplast trans-thylakoid membrane pH gradient and xanthophyll cycle pigments on the PSII Chl a fluorescence tau distributions and intensity. The model assumes that (1) there exists a specific binding site for Z (or antheraxanthin, A) among or in an inner antenna complex (primarily CP29), (2) this binding site is activated by a low intrathylakoid pH (pK approximately 4.5) that increases the affinity for Z (or A), (3) about one Z or A molecule binds to the activated site, and (4) this binding effectively "switches" the fluorescence tau distribution of the PSII unit to a state with a decreased fluorescence tau and emission intensity (a "dimmer switch" concept). This binding is suggested to cause the formation of an exciton trap with a rapid intrinsic rate constant of heat dissipation. Statistical analysis of the data yields an equilibrium association constant, Ka, that ranges from 0.7 to 3.4 per PSII for the protonated/activated binding site for Z (or A). The model explains (1) the relative fraction of the approximately 0.5 ns fluorescence component as a function of both Z and A concentration and intrathylakoid pH, (2) the dependence of the ratio of F'm/Fm on the fraction of the 0.5 ns fluorescence tau component (where F'm and Fm are maximal fluorescence intensities in the presence and the absence of a pH gradient), and (3) the dependence of the ratio of F'm/Fm on the concentration of Z and A and the intrathylakoid pH.

Carotenoids↗

PubMed2002

Sit-to-stand performance depends on sensation, speed, balance, and psychological status in addition to strength in older people.

BACKGROUND: Sit-to-stand (STS) performance is often used as a measure of lower-limb strength in older people and those with significant weakness. However, the findings of recent studies suggest that performance in this test is also influenced by factors associated with balance and mobility. We conducted a study to determine whether sensorimotor, balance, and psychological factors in addition to lower-limb strength predict sit-to-stand performance in older people. METHODS: Six hundred and sixty nine community-dwelling men and women aged 75-93 years (mean age 78.9, SD = 4.1) underwent quantitative tests of strength, vision, peripheral sensation, reaction time, balance, health status, and sit-to-stand performance. RESULTS: Many physiological and psychological factors were significantly associated with sit-to-stand times in univariate analyses. Multiple regression analysis revealed that visual contrast sensitivity, lower limb proprioception, peripheral tactile sensitivity, reaction time involving a foot-press response, sway with eyes open on a foam rubber mat, body weight, and scores on the Short-Form 12 Health Status Questionnaire pain, anxiety, and vitality scales in addition to knee extension, knee flexion, and ankle dorsiflexion strength were significant and independent predictors of STS performance. Of these measures, quadriceps strength had the highest beta weight, indicating it was the most important variable in explaining the variance in STS times. However, the remaining measures accounted for more than half the explained variance in STS times. The final regression model explained 34.9% of the variance in STS times (multiple R =.59). CONCLUSIONS: The findings indicate that, in community-dwelling older people, STS performance is influenced by multiple physiological and psychological processes and represents a particular transfer skill, rather than a proxy measure of lower limb strength.

Age Factors↗

PubMed2006

Estimating parametric line-source models with electroencephalography.

We develop three parametric models for electroencephalography (EEG) to estimate current sources that are spatially distributed on a line. We assume a realistic head model and solve the EEG forward problem using the boundary element method (BEM). We present the models with increasing degrees of freedom, provide the forward solutions, and derive the maximum-likelihood estimates as well as Cramér-Rao bounds of the unknown source parameters. A series of experiments are conducted to evaluate the applicability of the proposed models. We use numerical examples to demonstrate the usefulness of our line-source models in estimating extended sources. We also apply our models to the real EEG data of N20 response that is known to have an extended source. We observe that the line-source models explain the N20 measurements better than the dipole model.

Action Potentials↗

PubMed2005

Molecular markers for seed colour in Brassica juncea.

A detailed RFLP map was used to map QTLs associated with seed colour in Brassica juncea using a doubled-haploid population derived from a cross between a black/brown-seeded cultivar and a yellow-seeded breeding line. Segregation analysis suggested that seed colour was under control of 2 unlinked loci with duplicate gene action. However, QTL analysis revealed 3 QTLs, SC-B4, SC-A10 and SC-A6, affecting seed colour. The QTLs were consistent across environments, and individually explained 43%, 31%, and 16%, respectively, and collectively 62% of the phenotypic variation in the population. Digenic interaction analysis showed that closest flanking locus of QTL SC-B4, wg7b6cNM, had strong epistasis with the locus wg5a1a, which is tightly linked to QTL SC-A6. The interaction of these 2 loci explained 27% of the phenotypic variation in the population, while the whole model explained 84%. In a multiple regression model, the effects of QTL SC-A10, as well as its interaction with other loci, were non-significant, whereas the effects of loci wg7b6cNM and wg5a1a and their interaction were significant. Ninety-eight percent of the DH lines carried the expected alleles of loci wg7b6cNM and wg5a1a for seed colour, confirming that only these 2 loci were linked to seed colour in B. juncea. Four additional digenic interactions significantly affected seed colour, and all 5 digenic interactions were consistent across environments.

Analysis of Variance↗

PubMed2006

Estrogen and progesterone levels in nipple aspirate fluid of healthy premenopausal women: relationship to steroid precursors and response proteins.

BACKGROUND: Concentrations of estrogen and progesterone within the breast could provide a better reflection of breast cancer risk than levels in the circulation. We developed highly sensitive immunoassays for multiple steroid hormones and proteins in the nipple aspirate fluid (NAF), which can be obtained noninvasively with a simple suction device. Previous studies showed that NAF hormone levels are strongly correlated between breasts and within a single breast over time and are predictably related to hormone replacement therapy or use of oral contraceptives. This study evaluates the relationship of NAF estrogen and progesterone levels to those in serum and saliva, the relationship of NAF estradiol to androgenic and estrogenic precursors in NAF, and the relationship of NAF hormone levels to those of response proteins such as cathepsin D and epidermal growth factor (EGF). METHODS: Normal premenopausal women collected saliva daily and donated blood and NAF in the midluteal phases of menstrual cycles at intervals of 0, 4, 12, and 15 months. Analytes were measured by immunoassays after solvent fractionation. Log-transformed values were fit to repeated measures analysis of covariance models to ascertain associations between analytes. RESULTS: Small nonsignificant associations were found between NAF and serum or salivary estradiol. However, progesterone in NAF was significantly associated with progesterone in serum and saliva (R=0.18 and 0.32, respectively). Within NAF, the estradiol precursors estrone sulfate, androstenedione, and dehydroepiandrosterone were significantly associated with estradiol concentration (P<0.06), and a multiprecursor model explained the majority of variance in NAF estradiol (model R(2)=0.83). Cathepsin D and EGF in NAF could not be predicted from serum or salivary steroid measurements; however, both could be predicted from estradiol and its precursors in NAF (model R(2)=0.70 and 0.93, respectively). CONCLUSIONS: By showing consistent associations between estradiol and its precursors and response proteins, these data provide support for the biological validity of NAF hormone measurements and for the importance of steroid interconversion by aromatase and sulfatase within the breast. The low correlation between estrogen levels in NAF and those in serum or saliva suggests that the degree of association between estrogen or its androgen precursor levels and risk of breast cancer observed in epidemiologic studies using serum estimates might be highly attenuated.

Adult↗

PubMed1991

Atrial natriuretic peptide in habitual snorers.

We studied nocturnal and early morning variations in the concentration of plasma atrial natriuretic peptide (ANP) in 17 men who habitually snored. The subjects had a mean age of 51.0 +/- 5.8 years, range 41-62 y with a mean body mass index (BMI) of 32.9 +/- 7.3 kg/m2. The concentration of plasma ANP was measured by radioimmunoassay of venous samples at 10 p.m., midnight, 6 p.m. and 8 p.m. All night sleep recordings were conducted with the static charge sensitive bed to monitor body and breathing movements and a BIOX III Pulse Oximeter for the blood oxygen saturation level. Nine patients were defined as having the obstructive sleep apnea syndrome (OSAS). No significant diurnal variation for ANP concentrations was detected. At 8 a.m. five OSAS patients and two others had ANP concentrations above normal (70 pg/ml). Neither mean oxygen saturation during the night nor arterial hypertension discriminated between the high and low ANP groups at 8 a.m. The best discriminators for a high concentration of ANP at 8 p.m. were marked obesity (BMI greater than or equal to 30 kg/m2), over 400 movements lasting less than five seconds, and over 30% of active sleep per night. In a multivariate regression analysis age, percentage of active sleep during the night, BMI and the median oxygen saturation level during the night explained 76.4% of the total variance of ANP at 8 a.m. In a similar analysis the median oxygen saturation level during the night and BMI both explained the variance of ANP significantly. The whole model explained 53.7% of the variance of the ANP concentrations at 6 a.m.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1996

Predictors of carbon monoxide and hydrogen cyanide exposure in smoke inhalation patients.

OBJECTIVE: A prospective study of civilian (nonfirefighter) smoke inhalation patients was carried out to test the hypotheses that: 1) absorption of carbon monoxide and hydrogen cyanide from smoke can be predicted by clinical examination and historical data; and, more specifically 2) a history of exposure to burning synthetic polymers is an important predictor of systemic cyanide levels. METHODS: The study was conducted over a three-year period at six urban hospitals. Patients with or without burns who were exposed to smoke within five hours of hospital arrival were sampled for carboxyhemoglobin, whole blood cyanide, urine cotinine and urine creatinine. Controls consisted of a smaller group of smoking status-matched, nonsmoke-exposed burn patients. ANALYSIS: Historical information was obtained on SMOKING status, FIRETYPE (structural vs other), MATERIAL burned (natural vs synthetic) and LAGTIME (from exposure to sampling). A smoke inhalation SCORE (0-10) was assigned to each case, based on physical examination findings and changes on chest X ray, and carboxyhemoglobin and cyanide levels were entered into various multivariate linear regression models. RESULTS: A total of 40 cases and 9 controls were recruited, ranging in age from 15 to 92 years. Thirty-four cases were discharged alive and six expired in-hospital. Observed carboxyhemoglobin levels ranged from 1.2% to 41.6% in cases (mean 8.6%), and from 0.5 to 7.3% in controls (mean 2.9%). Observed cyanide levels ranged from nondetectable (< 0.05 micrograms/mL) to 2.79 micrograms/mL in cases (mean 0.25 micrograms/mL), and from nondetectable to 0.11 micrograms/mL in controls (mean 0.03 micrograms/mL). Among cases, linear regression models explained up to 35% of the observed variance in carboxyhemoglobin levels (p < 0.001) and up to 48% of the variance in cyanide levels (p = 0.0001). CONCLUSIONS: SCORE was the strongest predictor of both carboxyhemoglobin and cyanide levels; LAGTIME also explained significant variance for [log-transformed] carboxyhemoglobin. Historical factors, such as FIRETYPE, MATERIAL, and SMOKING status, did not explain significant variance in most of the statistical models employed.

Adolescent↗