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Results for “environmental variability”

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PubMed1990

Evidence for functional differences between the two sites of rabbit transferrin: effects of serum and carbon dioxide.

A recently developed technique combining urea gel electrophoresis with Western immunoblotting has been modified for assessing the relative ability of each iron binding site of rabbit transferrin in delivering iron to rabbit reticulocytes. The two sites can be made to release iron at the same or differing rates, depending on the experimental conditions. In Hanks' balanced salts solution in an atmosphere of room air or 5% CO2, the acid-labile site in the N-terminal lobe of the protein was found to be 1.4- and 2.9-times more effective than its acid-stable counterpart in providing iron to reticulocytes after 90 min incubation. Both sequential and simultaneous release of iron from the two sites was observed, but sequential release was initiated only from the N-terminal site. The same site also proved to be a better iron donor by a factor of 2 when incubations were conducted in Hanks' medium enriched with 20% serum in 5% CO2. Only in 20% serum in air were the two sites found to be equivalent iron suppliers to reticulocytes. In the cases studied, an atmosphere of 5% CO2 increased 2-fold the effectiveness of iron donation by the acid-labile site to reticulocytes, while the presence of 20% serum enhanced the iron-donating ability of the acid-stable C-terminal site. Thus, the transferrin-reticulocyte interaction is sensitive to environmental variables, and such sensitivity may help account for apparent discrepancies in previous studies of the relative iron-donating abilities of the two sites of transferrin.

Animals↗

PubMed1989

School-based clinic use and other factors affecting adolescent contraceptive behavior.

Adolescent risk taking, preventive behavior, and contraceptive use were investigated using a self-administered questionnaire in a sample of 260 inner-city high school students targeted by a school-based health clinic. Multivariate models consisting of individual and environmental variables significantly predicted sexual activity and contraceptive use. Older age at first intercourse, higher number of welfare benefits received by the household (including Medicaid, food stamps, and free or reduced price lunch), and use of the school-based clinic were significant positive predictors of more frequent contraceptive use by adolescents. Results of our study suggest that programs may be having some success in encouraging and enabling sexually active adolescents to use contraception and to use it more consistently. Rigorous program evaluations should help program planners and policy makers design and refine adolescent pregnancy-prevention efforts.

Adolescent↗

PubMed1991

Homeless and runaway youth mental health issues: no access to the system.

Data from a center for homeless and runaway youth are presented in order to summarize the major mental health problems faced by these youth. This article also identifies indicators related to behavioral and environmental variables that may help in the development of intervention and prevention strategies for this population.

Adolescent↗

PubMed1987

The impact of acidification on macroinvertebrate assemblages in welsh streams: towards an empirical model.

The acidification of surface waters has profound ecological consequences. There is a need to predict the effects of possible future patterns of acid deposition on the biological components of fresh waters. This paper describes a model of the relationships between water chemistry and macroinvertebrate assemblages in eighteen streams in the upper Tywi whose catchments are subject to different land uses. Using established statistical techniques on data sets derived from riffle and margin samples taken in spring and summer, the macroinvertebrate assemblages were classified into three groups, which corresponded with streams draining conifer afforested catchments, acidic moorland streams and circumneutral moorland streams. Following principal components analysis to select key environmental variables, the application of multiple discriminant analysis generated two discriminant functions which were related most strongly to mean filterable aluminium concentration and mean total hardness, respectively. The discriminant functions were used to assign site-group membership with 100% success in the case of the spring data set with combined habitats. In addition, multiple regression of the primary ordination axis of each data set on mean aluminium concentration and mean hardness or pH, produced equations which explained 62.0%-87.2% of the variance. We conclude that the methods used here provide an effective analytical and potentially predictive tool for use in the understanding and management of the impact of acidification on freshwater ecosystems.

Journal Article↗

PubMed1989

A multivariate, time series model to relate alfalfa responses to chronic, ambient sulfur dioxide exposures.

A multivariate dual time series model is described here to relate chronic sulfur dioxide exposures to alfalfa responses under ambient conditions. The model considers the time series of SO(2) exposures and the growth dynamics of the crop in accounting for the final harvested biomass. The model also allows the inclusion of environmental variables such as temperature and precipitation. Coupled with the model, the 'best' regression method used facilitates the segregation or identification of the contribution of individual independent variables to the final coefficient of determination for the harvested biomass.

Journal Article↗

PubMed1994

Assessment of the impact of rising carbon dioxide and other potential climate changes on vegetation.

The projected doubling of current levels of atmospheric carbon dioxide concentration ([CO(2)]) during the next century along with increases in other radiatively active gases have led to predictions of increases in global air temperature and shifts in precipitation patterns. Additionally, stratospheric ozone depletion may result in increased ultraviolet-B (UV-B) radiation incident at the Earth's surface in some areas. Since these changes in the Earth's atmosphere may have profound effects on vegetation, the objectives of this paper are to summarize some of the recent research on plant responses to [CO(2)], temperature and UV-B radiation. Elevated [CO(2)] increases photosynthesis and usually results in increased biomass, and seed yield. The magnitude of these increases and the specific photosynthetic response depends on the plant species, and are strongly influenced by other environmental factors including temperature, light level, and the availability of water and nutrients. While elevated [CO(2)] reduces transpiration and increases photosynthetic water-use efficiency, increasing air temperature can result in greater water use, accelerated plant developmental rate, and shortened growth duration. Experiments on UV-B radiation exposure have demonstrated a wide range of photobiological responses among plants with decreases in photosynthesis and plant growth among more sensitive species. Although a few studies have addressed the interactive effects of [CO(2)] and temperature on plants, information on the effects of UV-B radiation at elevated [CO(2)] is scarce. Since [CO(2)], temperature and UV-B radiation may increase concurrently, more research is needed to determine plant responses to the interactive effects of these environmental variables.

Journal Article↗

PubMed1992

Periodicity and diversity in ant mating flights.

1. Flight hours and seasons are alike within species, but differ among species and among genera. 2. Laboratory studies indicate internal circadian control of the phase relation to the light-dark cycle, with field evidence for modification by temperature (or other environmental variables). 3. In at least two species there is abrupt loss of obvious rhythm after mating, suggesting some special function before loss, e.g. to facilitate cross-breeding within species or reproductive isolation between species.

Animals↗

PubMed1986

Milk consumption and multiple sclerosis--an etiological hypothesis.

Epidemiological studies of Multiple Sclerosis (MS) in the United States have shown an association with urban living and higher socio-economic groups and a higher incidence and earlier age at onset of symptoms in women. This study is based on the proposition that these trends may be a consequence of differences in exposure to an etiological factor around 15 years of age. As a result of variations in related United States and New Zealand data and other pertinent observations the possibility of a link between high childhood milk intake followed by a large or sudden reduction during the adolescent growth spurt, and the subsequent incidence of MS in young adults is proposed. The possible involvement of calcium and lead metabolism is also discussed. It may be that the elusive environmental variable associated with the incidence of MS is partly a behavioural one related to western social attitudes.

Adolescent↗

PubMed1993

Relapse management in neurobiological disorders: the Moller-Murphy Symptom Management Assessment Tool.

The Moller-Murphy Symptom Management Assessment Tool (MM-SMAT) was developed to assist in the identification of psychiatric symptoms, health, and environmental variables, problems related to medication management and provide a common language for everyone involved in the ongoing management of neurobiological disorders to use in identifying the frequency, intensity, and duration of symptoms. The Murphy Wellness Model is a framework that provides insight into health, environment, and attitudes/behavior variables that became triggers of relapse. The combined use of this model and the MM-SMAT provides data to be used for anticipatory guidance of relapse management and the development of symptom-specific interventions.

Humans↗

PubMedDate not supplied

Prenatal alcohol, marijuana, and tobacco use: infant mental and motor development.

These data are from a longitudinal study of prenatal alcohol and marijuana use in a low income sample. Half of the women were black and half were white. Women who used alcohol and/or marijuana during their pregnancies were light to moderate users; most decreased or discontinued their use after the first trimester. At the first follow-up phase, which occurred at a median age of 9 months, the children were functioning above average on the Bayley Scales of Infant Development (BSID). Prenatal alcohol and tobacco use did not predict BSID mental or motor scores at this phase. Third trimester marijuana use was associated with decreased BSID mental scores. Age at assessment was the most important predictor at this phase. The second follow-up occurred at a median age of 19 months when the group means for the BSID were lower. Prenatal alcohol and marijuana use did not predict outcome at this phase. Prenatal and current cigarette use were associated with decreased BSID mental scores. Demographic and environmental variables were important predictors at this phase.

Adolescent↗

PubMed1994

The effect of cell-culture conditions on the oligosaccharide structures of secreted glycoproteins.

Glycoprotein oligosaccharide structure influences numerous important protein properties. In recent years, a number of studies have demonstrated that cell-culture methodology can significantly affect the oligosaccharide structures of recombinant proteins and antibodies, and, in the past year in particular, several of the specific environmental variables responsible for these effects have been identified.

Animals↗

PubMed2004

Interactive effects of temperature and copper on immunocompetence and disease susceptibility in mussels (Mytilus edulis).

The interactive effects of temperature and copper on immune function and consequently disease susceptibility of the marine mussel, Mytilus edulis were investigated. Two studies were carried out, the first involved sequential exposure to copper at 0.02 and 0.05 ppm followed by the bacterium Vibrio tubiashii. In the second study, mussels were simultaneously exposed to copper and V. tubiashii. Both studies were carried out at 10 and 15 degrees C, to ascertain whether temperature had an additional effect on immunocompetence. A multi-assay approach was used to obtain an overall view of immune function in the mussels. Assays carried out included total and differential haemocyte counts, production of intracellular superoxide and phagocytosis by haemocytes. Data are presented showing significant effects on immune parameters of sequential and simultaneous exposure to copper and V. tubiashii at 10 and 15 degrees C. Each of the factors considered were shown to have a significant effect on at least one of the immune parameters measured. There were also significant effects due to the interaction of these factors. The response of total and differential blood cell counts to copper were shown to alter, if mussels were exposed in a sequential manner as opposed to simultaneous exposure. The results confirmed that the immune system of M. edulis is susceptible to copper at relatively low concentrations. Furthermore, the effects of copper alter with environmental variables, including temperature and the presence of a potential pathogen. The complexity of the interactions demonstrate that extrapolation of data obtained from single stressor studies into field situations could give a misleading picture.

Animals↗

PubMed2004

Arsenic availability, toxicity and direct role of GSH and phytochelatins in As detoxification in the green alga Stichococcus bacillaris.

Accumulation and toxicity of inorganic arsenic forms As(III) and As(V) to the green microalga Stichococcus bacillaris depended on environmental variables. pH of exposure and to a lesser extent elevated concentrations of humic acid, chloride and orthophosphate ions affected arsenic accumulation and its toxicity. As(V) was more toxic than As(III), especially at the near neutral pH 6.8. Intracellular As(V) uptake by algal cells was greater at pH 6.8 than at 8.2. In response to As(III) and As(V) the alga produced phytochelatins (PC(2-3)), but at As(V) exposure, their levels in cells were higher than with As(III), suggesting higher As(V) than As(III) availability and uptake. Arsenic in algal cells occurred in various complexes with non-protein SH groups. Some of these complexes dissociated under acidic conditions, but others were able to dissociate only at an alkaline pH. The former consisted of SH groups of phytochelatins. Those dissociating at an alkaline pH involved SH groups from both glutathione (GSH) and phytochelatins (PC) or their derivatives. In the predominant acid-stable mixed As-SH complex, the ratio of SH (PC(2)) to SH (GSH) was 2:1, which suggests that one molecule of PC(2) (containing two SH groups) together with one molecule of GSH were involved in intracellular complexation of each As atom. This is the first demonstration of GSH involvement in arsenic complexation, in vivo. The intracellular concentration of As was greater than that of non-protein SH groups which suggests that not all the arsenic in algal cells was complexed and detoxified by thiol groups.

Arsenic↗

PubMed2004

Temperature influences on the accumulation and elimination of mercury in a freshwater cladoceran, Daphnia magna.

Temperature is an important environmental variable affecting the physiology and metabolism of aquatic invertebrates and can potentially affect the rate and pathway of the uptake and elimination of contaminants. In this study, we studied the effects of the ambient temperature on the uptake (from water and food) and elimination of inorganic mercury [Hg(II)] and methymercury (MeHg) in a freshwater cladoceran, Daphnia magna, in the laboratory. At different temperatures (i.e., 14, 19 and 24 degrees C), the assimilation efficiencies of both Hg species from ingested alga were not significantly different while the dissolved uptake rates were 32 and 73% lower at 14 degrees C than at 24 degrees C for Hg(II) and MeHg, respectively. The reduced uptake rates of Hg(II) at 14 degrees C could be adequately explained by the reduced filtration rate (40% reduction), but for MeHg, the reduced filtration rate could not completely explain reduction in MeHg uptake rate. Despite the elimination rates of both Hg compounds not being affected by the temperature, the relative importance of different routes of Hg loss (i.e., excretion, egestion, molting and reproduction) was significantly different at various temperatures. The relative importance of excretion to MeHg loss increased from 24 to 14 degrees C (i.e., 52 to 85% of Hg loss) while that of reproduction to MeHg loss decreased from 43 to 11% simultaneously. Using a kinetic model, we showed that the fraction of MeHg accumulated in the daphnids coming from the dietary phase was higher at lower temperature, while there was increased accumulation of both Hg(II) and MeHg in the daphnids at higher temperatures. Nevertheless, the trophic transfer potentials for both Hg species in this algae-daphnids food chain were not influenced by the temperature.

Analysis of Variance↗

PubMed2005

Adaptive value of host discrimination in parasitoids: when host defences are very costly.

Host acceptance decision in parasitic wasps strongly depends on the parasitism status of the encountered host. In solitary species, a host only allows the development of a single parasitic larva and then, any oviposition in an already parasitised host leads to larval competition and loss of offspring. Females of many parasitoid species are able to discriminate between parasitised hosts and healthy ones. However, the host discrimination process may require more time than oviposition, exposing the wasp to high risks when the host has efficient defences. Consequently, depending on the degree of success of the host defence, the cost of host inspection for discrimination can outweigh the benefit of superparasitism avoidance. In the present paper, a theoretical approach was developed for determining how host defences may affect optimal host acceptance behaviour in parasitoids. The present model compares the lifetime reproductive success over the strategy used, discrimination and no-discrimination: a discriminating wasp sets a relatively greater value in its current oviposition, while a non-discriminating female sets a greater value in its own survival and future reproduction. The model predicts that depending on physiological state variables and environmental state variables, the optimal policy is not discriminating. Our results suggest that the low discriminating ability observed in some parasitic wasps could probably be an evolutionary response to host defences pressure.

Adaptation, Physiological↗

PubMed2005

The role of biomarkers in the assessment of lupus.

Although considered a prototypic autoimmune disease, the hallmark of systemic lupus erythematosus (SLE) is its heterogeneity. Accordingly, manifestations can vary widely from person to person, with the potential involvement of virtually any bodily organ. Furthermore, the genetic abnormalities underlying this condition are complicated, with diverse genetic polymorphisms described in different ethnic groups, strongly suggesting that the actual pathology underlying the immunologic disarray might not be the same for each patient. Evolving concepts of genetics and immunity have clarified that patients can carry unique arrays of exacerbating and protective factors. These factors, in conjunction with variable environmental triggers for SLE, probably determine the sequelae that an individual experiences. Therefore, it is not surprising that the clinical manifestations are diverse, the temporal sequence of organ involvement often unpredictable, and that the flares of inflammatory activity that characterize SLE can either remit without consequence or leave permanent damage in their wake. It is widely accepted that the current standard of care for SLE patients is inadequate. Programs to develop and test new drug and/or device therapies have been ongoing since the mid-1990s but have encountered formidable obstacles. With the current burst of drug discovery and the advent of several large international trials of promising new agents, the challenge to overcome these obstacles has never been greater. A burgeoning literature in the past decades nevertheless suggests that despite the complexities of the many immunologic pathways that impact on SLE, characteristic biologic markers are emerging as potential signposts that can characterize patient subgroups, predict prognosis, mark the exacerbations and remissions of SLE flares, and serve as endpoints in the determination of the dosing and timing of immune-modulating treatments. Several of the promising biomarkers are addressed in this chapter.

Biomarkers↗

PubMed2006

Alterations in medial prefrontal cortical activity and plasticity in rats with disruption of cortical development.

BACKGROUND: Psychiatric disorders such as schizophrenia are believed to emerge from an interaction of several factors. Thus, a genetic predisposition can lead to developmental compromises that may leave the system more susceptible to deficits induced by subsequent environmental variables such as stress. METHODS: The impact of neurodevelopmental interruption induced by exposure of rats prenatally to a compound methylazoxymethanol acetate (MAM) that disrupts neuronal proliferation was investigated using in vivo electrophysiologic recordings from the prefrontal cortex of adult rats. RESULTS: Prenatal exposure to MAM resulted in alterations in the medial prefrontal cortex indicative of a compromise in information processing. Specifically, we observed a disruption in activity patterns consistent with deficits in neuronal synchronization and abnormal augmentation of synaptic plasticity that was more severely disrupted by stress exposure than in normal animals. Furthermore, these deficits could be reversed by manipulating the mesocortical dopamine system. CONCLUSIONS: These results suggest that disruption of early cortical development causes impairments in medial prefrontal cortical function at adulthood that are more vulnerable to disruptive influences, despite the presence of only subtle structural alterations in the brain.

Action Potentials↗

PubMed2006

Microassays for a set of enzymes in individual small marine copepods.

Fluorogenic assays for a set of five hydrolytic enzymes involved in digestion and food utilization (alanine and arginine aminopeptidase, lipase/esterase, chitobiase, and beta-glucosidase) were optimized to measure activities of these enzymes in the same extracts of individual small North Sea copepods. The enzyme activities of Acartia clausi, Centropages typicus, Corycaeus anglicus, Paracalanus parvus, and Temora longicornis showed distinct species specific activity patterns, but also high intra-specific variability. Protein, lipids, carbon and nitrogen (C, N) were determined with micro-scale assays in individual copepods or in batches of 10 to 50 animals. Water soluble protein contents ranged from 16% to 38%, and lipid contents from 2.4% to 5.5% of dry mass. The molar C/N ratios were between 4.1 and 4.5. The presented microassays provide suitable tools for studying physiological reactions of copepods and other small pelagic crustaceans in response to variable environmental conditions.

Animals↗