Home About us Contact
|
Home About us Contact | ||
|
|
||
Continuous Presence (continuous + presence)
Selected AbstractsHolocene pollen records from the central Arctic Foothills, northern Alaska: testing the role of substrate in the response of tundra to climate changeJOURNAL OF ECOLOGY, Issue 6 2003W. Wyatt Oswald Summary 1To explore the role of edaphic controls in the response of arctic tundra to climate change, we analysed Holocene pollen records from lakes in northern Alaska located on glaciated surfaces with contrasting soil texture, topography and tundra communities. Using indicator taxa, pollen accumulation rates (PARs) and multivariate comparison of fossil and modern pollen assemblages, we reconstructed the vegetational changes at Upper Capsule Lake (Sagavanirktok surface) and Red Green Lake (Itkillik II surface) in response to increased effective moisture between the early and middle Holocene. 2In the Red Green record, low PARs and the continuous presence of taxa indicative of prostrate-shrub tundra (PST; Equisetum, Polypodiaceae, Thalictrum and Rosaceae) indicate that the vegetation resembled PST throughout the Holocene. During the warm, dry early Holocene (11 300,10 000 cal years BP), PST also occurred on Sagavanirktok surfaces, as evidenced by PST indicators (Bryidae, Polypodiaceae, Equisetum and Rosaceae) in this interval of the Upper Capsule record. However, PARs increased, suggesting increased vegetation cover, PST taxa declined and taxa indicative of dwarf-shrub tundra (DST; Rubus chamaemorus and Lycopodium annotinum) increased between 10 000 and 7500 cal years BP. 3We hypothesize that between the early and middle Holocene the fine-textured soils and smooth topography of Sagavanirktok surfaces led to increased soil moisture, greater vegetation cover, permafrost aggradation, anoxic and acidic soil conditions, slower decomposition and the development of a thick organic layer. In contrast, soil moisture remained low on the better-drained Itkillik II surface, and vegetational changes were minor. 4Landscape-scale substrate variations have an effect on how tundra responds to climate change, suggesting that the response of arctic ecosystems to future variability may be spatially heterogeneous. [source] Dipyridamole protects cultured rat embryonic cortical neurons from neurotoxic insultJOURNAL OF NEUROCHEMISTRY, Issue 2002A. D. Blake The effects of a clinically useful cardiovascular agent, dipyridamole, were examined in a rodent tissue culture model of neural protection. Dipyridamole effectively protected rat embryonic day 18 (E18) cortical neurons from either trophic deprivation or endogenous glutathione depletion by l -buthionine (R,S) sulfoximine (BSO). Trophic deprivation was associated with an increase in intracellular oxidative stress, as determined by the increased fluorescence of dichloro, dihydrofluorescein (H2DCFDA). Dipyridamole's neural protection was time and concentration-dependent (EC50 = 342 nm), and its continuous presence in the culture medium was required. Dipyridamole or exogenously added glutathione markedly decreased trophic deprivation induced H2DCFDA fluorescence, indicating a reduction in neuronal oxidative stress. These results demonstrate that dipyridamole protects primary neuronal cultures against either trophic or chemically mediated insults, and suggest that dipyridamole has a potent antioxidant ability that compensates for glutathione depletion in primary neuronal cells. [source] Geochemistry of Persististrombus latus Gmelin from the Pleistocene Iberian Mediterranean realmLETHAIA, Issue 2 2010TRINIDAD De TORRES De Torres, T., Ortiz, J.E., Arribas, I., Delgado, A., Julià, R. & Martín-Rubí, J.A. 2009: Geochemistry of Persististrombus latus Gmelin from the Pleistocene Iberian Mediterranean realm. Lethaia, Vol. 43, pp. 149,163. In this paper the organic and inorganic geochemistry of fossil and extant Persististrombus latus are compared, together with other strombid species (Lentigo lentiginosus, Lobatus gigas, Strombus alatus, Lobatus raninus, Laevistrombus canarium and Tricornis latissimus). Using a large sample of well-preserved fossil P. latus shells from the Mediterranean realm, we examined the warming period of sea water in the Middle Pleistocene. A mineralogical study of the shells demonstrates the continuous presence of calcite and a complex organic matter distribution, which was well preserved in many cases, thereby making the U/Th dating of strombid shells unreliable. U/Th analysis of coral samples and amino acid racemization dating of pelecypod shells confirmed that P. latus entered the Mediterranean realm in MIS 7 and 5. The oscillations of the ,18O values reflect annual growth periods and provide a mixing of the first signal record (primary growth) and successive overgrowths. ,Amino acid racemization, Mediterranean Sea, Persististrombus latus, shell mineralogy, U/Th, ,18O. [source] Elevated Histone H1 (MPF) and Mitogen-activated Protein Kinase Activities in Pig Oocytes Following In Vitro Maturation do not Indicate Cytoplasmic MaturationREPRODUCTION IN DOMESTIC ANIMALS, Issue 2 2009MA Setiadi Contents Effects of different media (TCM 199 + BSA, TCM 199 + FCS, TCM 199 + NBCS, Whitten's medium + BSA) supplemented with estradiol-17, and two isolated and everted follicle shells on MPF and MAP kinase activities and the sensitivity to parthenogenetic activation of pig oocytes were examined at the end of culture (48 h). Elevated (P < 0.05) activities of MAP kinase were recorded in metaphase II oocytes following culture in Whitten's medium, whereas MPF levels were lowest (P < 0.05) in MII oocytes matured in TCM 199 supplemented with BSA. Oocytes matured in TCM 199 based media showed higher (P < 0.05) activation rates when compared to oocytes incubated in Whitten's medium. Whitten's medium supplemented with different protein sources (amino acids, FCS, BSA) was used to study the effects of different exposure periods to eCG/hCG stimulation on MPF and MAP kinase activities and in vivo fertilisability following culture for 48 h. MPF and MAP kinase activities were significantly increased by eCG/hCG stimulation of COCs during maturation. Further, the continuous presence of eCG/hCG during culture (48 h) significantly increased the levels of both kinases in comparison to stimulation by gonadotrophins alone during the first 24 h of incubation. In vivo fertilisation of oocytes matured in Whitten's medium supplemented with eCG/hCG for 24 or 48 h led to a significant retardation of early embryonic development compared to ovulated oocytes. In conclusion, media composition and gonadotrophin stimulation affect MPF/MAP kinase activities and the susceptibility to parthenogenetic activation of IVM oocytes. However, elevated kinase levels in pig oocytes following culture do not indicate complete cytoplasmic maturation. [source] Sexual size dimorphism in Asian colobines revisitedAMERICAN JOURNAL OF PRIMATOLOGY, Issue 7 2009Cyril C. Grueter Abstract Asian colobines exhibit a wide range of sexual dimorphism in body mass. Some species are monomorphic, whereas others are strongly dimorphic. Strong sexual dimorphism is generally viewed as the consequence of intense male contest competition over access to mates, but this idea appears not to explain variation in sexual dimorphism in Asian colobines. Our results show that modular colobines, i.e. species in which social units aggregate into higher-level bands or often associate, have significantly higher levels of sexual dimorphism in body mass than the nonmodular ones. This finding was corroborated by means of phylogenetically controlled methods and multiple regression analyses. The results suggest that living in a modular society intensifies the contest competition among males, which is further exacerbated by the continuous presence of all-male units. Am. J. Primatol. 71:609,616, 2009. © 2009 Wiley-Liss, Inc. [source] Population Dynamics of a Resident Colony of Leptonycteris curasoae (Chiroptera: Phyllostomidae) in Central MéxicoBIOTROPICA, Issue 3 2004Cristobal Galindo G. ABSTRACT We studied the population dynamics of the lesser long,nosed bat Leptonycteris curasoae in a cave in central Mexico for a two-year time. The population had substantial seasonal changes in size and composition during this time. Colony size was largest from February to July (22,000,27,000 adults) and contained equal numbers of males and females. In June and July, males had enlarged testes and presumably mated with females. In August, the population size began to decline and was mostly composed of pregnant females. Between September and December, the colony was composed exclusively of pregnant and lactating females and their young, and population size decreased to about one,third of the observed maximum size. In January, adult males returned to the roost and the population size increased. We also observed an increase in body mass and fat accumulation in both sexes, apparently related to reproductive activity. This is the first report of the continuous presence of a substantial female population of L. curasoae throughout the year in a single roost in Mexican tropics, indicating that some populations of L curasoae in central Mexico complete their life cycle without having to migrate. RESUMEN Se estudió la dinámica poblacional del murciélago nectarivoro Leptonycteris curasoae en una cueva localizada en el centro de México durante dos años. La población presentó cambios sustanciales en su tamaño y composición durante este periodo. El tamaño más grande de la población se registró entre febrero y julio (22,000,27,000 individuos) con una proporción similar de hembras y machos. En junio y Julio los testfculos de los machos crecieron y aparentemente se aparearon con las hembras. En agosto, la población empezó a disminuir y se encontraron casi exclusivamente hembras preñadaz. Entre septiembre y diciembre, la colonia estuvo compuesta exclusãvamente de hembras preñadaz o lactantes y de sus cri'as. La población disminuyó en este periodo hasta equivaler a una tercera pane del tamaño máximo registrado en el año. En enero, la población empezo a crecer de nuevo con la incorporación de machos adultos. Durante el ano, en ambos sexos se observaron también cambios en la masa corporal y en la acumulación de grasa aparentemente relacionados con la actividad reproductiva. Este es el primer estudio que reporta la presencia continua de hembras en una colonia de L. curasoae en la misma cueva durante todo el ano para el centro de México. Nuestros resultados indican que esta población no es migratoria a diferencia de otras poblaciones de esta especie. [source] A Randomized Controlled Trial of Continuous Labor Support for Middle-Class Couples: Effect on Cesarean Delivery RatesBIRTH, Issue 2 2008Susan K. McGrath PhD ABSTRACT: Background: Previous randomized controlled studies in several different settings demonstrated the positive effects of continuous labor support by an experienced woman (doula) for low-income women laboring without the support of family members. The objective of this randomized controlled trial was to examine the perinatal effects of doula support for nulliparous middle-income women accompanied by a male partner during labor and delivery. Methods: Nulliparous women in the third trimester of an uncomplicated pregnancy were enrolled at childbirth education classes in Cleveland, Ohio, from 1988 through 1992. Of the 686 prenatal women recruited, 420 met enrollment criteria and completed the intervention. For the 224 women randomly assigned to the experimental group, a doula arrived shortly after hospital admission and remained throughout labor and delivery. Doula support included close physical proximity, touch, and eye contact with the laboring woman, and teaching, reassurance, and encouragement of the woman and her male partner. Results: The doula group had a significantly lower cesarean delivery rate than the control group (13.4% vs 25.0%, p = 0.002), and fewer women in the doula group received epidural analgesia (64.7% vs 76.0%, p = 0.008). Among women with induced labor, those supported by a doula had a lower rate of cesarean delivery than those in the control group (12.5% vs 58.8%, p = 0.007). On questionnaires the day after delivery, 100 percent of couples with doula support rated their experience with the doula positively. Conclusions: For middle-class women laboring with the support of their male partner, the continuous presence of a doula during labor significantly decreased the likelihood of cesarean delivery and reduced the need for epidural analgesia. Women and their male partners were unequivocal in their positive opinions about laboring with the support of a doula. (BIRTH 35:2 June 2008) [source] The Na-K-ATPase is a target for an EDHF displaying characteristics similar to potassium ions in the porcine renal interlobar arteryBRITISH JOURNAL OF PHARMACOLOGY, Issue 5 2002Eckhart Büssemaker The present study was performed to determine the characteristics of the endothelium-derived hyperpolarizing factor (EDHF) that mediates the nitric oxide (NO)- and prostacyclin (PGI2)-independent hyperpolarization and relaxation of porcine renal interlobar arteries. Bradykinin-induced changes in isometric force or smooth muscle membrane potential were assessed in rings of porcine renal interlobar artery preconstricted with the thromboxane analogue U46619 in the continuous presence of N, -nitro- L -arginine and diclofenac to inhibit NO synthases and cyclo-oxygenases. Inhibition of NO- and PGI2 -production induced a rightward shift in the concentration-relaxation curve to bradykinin without affecting maximal relaxation. EDHF-mediated relaxation was abolished by a depolarizing concentration of KCl (40 mM) as well as by a combination of charybdotoxin and apamin (each 100 nM), two inhibitors of calcium-dependent K+ (K+Ca) channels. Charybdotoxin and apamin also reduced the bradykinin-induced, EDHF-mediated hyperpolarization of smooth muscle cells from 13.7±1.3 mV to 5.7±1.2 mV. In addition to the ubiquitous ,1 subunit of the Na-K-ATPase, the interlobar artery expressed the , subunit as well as the ouabain-sensitive ,2, ,3 subunits. A low concentration of ouabain (100 nM) abolished the EDHF-mediated relaxation and reduced the bradykinin-induced hyperpolarization of smooth muscle cells (13.6±2.8 mV versus 5.20±1.39 mV in the absence and presence of ouabain). Chelation of K+, using cryptate 2.2.2., inhibited EDHF-mediated relaxation, without affecting NO-mediated responses. Elevating extracellular KCl (from 4 to 14 mM) elicited a transient, ouabain-sensitive hyperpolarization and relaxation that was endothelium-independent and insensitive to charybdotoxin and apamin. These results indicate that in the renal interlobar artery, EDHF-mediated responses display the pharmacological characteristics of K+ ions released from endothelial K+Ca channels. Smooth muscle cell hyperpolarization and relaxation appear to be dependent on the activation of highly ouabain-sensitive subunits of the Na-K-ATPase. British Journal of Pharmacology (2002) 137, 647,654. doi:10.1038/sj.bjp.0704919 [source] | |||||||||||||