Linear Discrete Population Models with Two Time Scales in Fast Changing Environments I: Autonomous Case

In this work we consider a structured population with groups and subgroups of individuals. The intra-group dynamics is assumed to be fast in comparison with the inter-group dynamics. We study linear discrete models where the slow dynamics is represented by a single matrix and the fast dynamics is described by means of the first k terms of a converging sequence of different matrices. The number k can be interpreted as the ratio between the two time scales.The aim of this work is to extend aggregation techniques to the case of fast changing environments. The main idea of aggregation is to build up a new system, with lower dimension, that summarizes the information concerning the fast process. This "aggregated" system provides essential information on the original one. It is shown that the asymptotic behavior of the original system can be approximated by the asymptotic behavior of the aggregated system when the ratio between the two time scales is large enough.We present an example of an age structured population in a patchy environment. The migration process is assumed to be fast in comparison with the demographic process. Numerical simulations illustrate that the asymptotic growth rate and the stable age distribution of the population in the original and the aggregated systems are getting closer as the ratio k increases.     

Cellular mechanisms by which oxytocin mediates ovine endometrial prostaglandin F2alpha synthesis: role of G(i) proteins and mitogen-activated protein kinases

Oxytocin stimulates a rapid increase in ovine endometrial prostaglandin (PG) F2alpha synthesis. The overall objective of these experiments was to investigate the cellular mechanisms by which oxytocin induces endometrial PGF2alpha synthesis. The objective of experiment 1 was to determine whether G(i) proteins mediate oxytocin-induced PGF2alpha synthesis. Uteri were collected from four ovary-intact ewes on Day 14 postestrus. Caruncular endometrial explants were dissected and subjected to in vitro incubation. Pertussis toxin, an inhibitor of G(i) proteins, had no effect on the ability of oxytocin to induce PGF2alpha synthesis (P > 0.10). The objective of experiment 2 was to determine whether any of the three mitogen-activated protein kinases (MAPKs), extracellular signal regulated protein kinase (ERK1/2), c-Jun N-terminal/stress-activated protein kinase (JNK/SAPK), or p38 MAPK, mediate oxytocin-induced PGF(2alpha) synthesis. Eleven ovary-intact ewes were given an injection of oxytocin (10 IU; i.v.; n = 5) or physiological saline (i.v.; n = 6) on Day 15 postestrus. Uteri were collected 15 min after injection and caruncular endometrium was dissected. Endometrial homogenates were prepared and subjected to Western blotting. Membranes were probed for both total and phosphorylated forms of all three classes of MAPK. All classes of MAPK were detected in ovine endometrium, but oxytocin treatment had no effect on the expression of these proteins (P > 0.10). ERK1/2 was the only phosphorylated MAPK detected and its concentrations were higher in oxytocin-treated ewes (P < 0.01). The objective of experiment 3 was to further investigate the role of ERK1/2 during oxytocin-induced PGF2alpha synthesis. Uteri were collected from four ovary-intact ewes on Day 14 postestrus. Caruncular endometrial explants were dissected and subjected to in vitro incubation. PD98059, a specific inhibitor of ERK1/2 activity, blocked the ability of oxytocin to stimulate PGF(2alpha synthesis in a dose-dependent manner (P < 0.05). These results indicate that the ovine oxytocin receptor is not coupled to G(i) proteins. These results indicate that oxytocin induces phosphorylation of ERK1/2 and that this MAPK appears to mediate oxytocin-induced PGF2alpha synthesis in ovine endometrium.     

Method for the characterization of size-exclusion chromatography media for preparative purification of DNA restriction fragments

A protocol has been developed to characterize the potential of size exclusion chromatography media for the separation of DNA fragments at a preparative scale. A standard DNA mixture composed of -DNA cut with the restriction enzymes, AluI and HaeIII, was chromatographed on a column packed with the gel of interest. Fractions were collected and examined by PAGE. A digitized image of the gel was analyzed with the aid of a computer software program to determine the DNA fractionation range and selectivity curve for each chromatography gel. Four gels were characterized using this protocol. The effect of the elution buffer ionic strength on the fractionation of DNA was also investigated.The US Government right to retain a non-exclusive royalty-freelicense in and to any copyright is acknowledged.     

Population based study of social and productive activities as predictors of survival among elderly Americans

ObjectivesTo examine any association between social, productive, and physical activity and 13 year survival in older people. DesignProspective cohort study with annual mortality follow up. Activity and other measures were assessed by structured interviews at baseline in the participants’ homes. Proportional hazards models were used to model survival from time of initial interview.SettingCity of New Haven, Connecticut, United States.Participants2761 men and women from a random population sample of 2812 people aged 65 and older.ResultsAll three types of activity were independently associated with survival after age, sex, race/ethnicity, marital status, income, body mass index, smoking, functional disability, and history of cancer, diabetes, stroke, and myocardial infarction were controlled for.ConclusionsSocial and productive activities that involve little or no enhancement of fitness lower the risk of all cause mortality as much as fitness activities do. This suggests that in addition to increased cardiopulmonary fitness, activity may confer survival benefits through psychosocial pathways. Social and productive activities that require less physical exertion may complement exercise programmes and may constitute alternative interventions for frail elderly people.

Key messages

• Little is known about predictors of survival among elderly people
• Physical activity is clearly good for health, but the potential benefits of social activities have not been studied
• Social and productive activities are as effective as fitness activities in lowering the risk of death
• Enhanced social activities may help to increase the quality and length of life

     

DDT concentrations in surficial sediments of three estuarine systems in Portugal

Levels of p,p-DDT and its metabolites in surficial sediments of Tagus and Sado Estuary and lagoon Ria Formosa varied one or two orders of magnitude. In general, p,-DDE and p,-DDD were the dominant metabolites and p,-DDT was a minor component. While concentrations of p,-DDT, p,-DDD and p,-DDE were hardly related to loss on ignition, concentrations of total DDT (tDDT) in surficial sediments of each studied system were positively correlated to that parameter. Higher contaminated samples were excluded from these relationships: a few sediment samples from the Tagus outlet channel, most of the sediments from the upper Sado Estuary, and some particulate matter samples collected in sediment traps in the adjoining area to the Ria Formosa. Concentration of tDDT appears, thus, to be related to sedimentary organic matter of these estuarine systems except near the actual sources of pollution. On the basis of the relationship slopes, one may conclude that lower Tagus Estuary is more contaminated than Ria Formosa and lower Sado Estuary.     

Drink composition, voluntary drinking, and fluid balance in exercising, trained, heat-acclimatized boys

This study examinedthe effects of beverage composition on the voluntary drinking pattern,body fluid balance, and thermoregulation of heat-acclimatized trainedboys exercising intermittently in outdoor conditions (wet bulb globetemperature 30.4 ± 1.0°C). Twelve boys (age 13.4 ± 0.4 yr) performed two 3-h sessions, each consisting of four20-min cycling bouts at 60% maximal aerobic power alternating with25-min rest. One of two beverages was assigned: unflavored water (W) orflavored water plus 6% carbohydrate and 18 mmol/l Na (CNa). Drinkingwas ad libitum. Total intake was higher(P < 0.05) during CNa (1,943 ± 190 g) compared with W (1,470 ± 143 g). Euhydration wasmaintained with CNa (+0.18% body wt), but a mild dehydration resultedwith W (0.94% body wt; P < 0.05). Sweat loss, much higher than previously published for children of similar age, was similar between conditions (CNa = 1,644.7 ± 117.5; W = 1,750.2 ± 152.7 g). The increase in rectaltemperature (CNa = 0.86 ± 0.3; W = 0.76 ± 0.1°C), heartrate, and all perceptual variables did not differ between conditions.In conclusion, a flavored carbohydrate-electrolyte drink preventsvoluntary dehydration in trained heat-acclimatized boys exercising in atropical climate despite their large sweat losses. Because hydrationchanges were minor, the thermoregulatory strain observed was similarbetween conditions.

     

Genetic transformation via particle bombardment of Catharanthus roseus plants through adventitious organogenesis of buds

In vitro propagation of Catharanthus roseus was achieved using nodal explants. Bud induction was best on medium containing 1.0 mg benzyl aminopurine l^–1. Hardening of rooted shoots to soil was very successful with 98% survival. Genetically transformed C. roseus plantlets were obtained after bombardment of nodal explants, which were then micropropagated, with DNA coated particles with green fluorescent protein (GFP) or -glucuronidase (GUS) reporter genes. Histological studies showed that the gene insertion method proved effective with many cells and different tissues displaying the reporter gene signals, showing that gene expressions were rather stable.