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Long-term Exposure (long-term + exposure)
Selected AbstractsINCREASED AVOIDANCE OF SWIMMERS BY WILD BOTTLENOSE DOLPHINS (TURSIOPS TRUNCATUS) DUE TO LONG-TERM EXPOSURE TO SWIM-WITH-DOLPHIN TOURISMMARINE MAMMAL SCIENCE, Issue 4 2001Rochelle Constantine Abstract The responses of wild, non-provisioned bottlenose dolphins (Tursiops truncatus) to swim attempts from commercial swim-with-dolphin tour boats were systematically observed during two research periods: 1994,1995 and 1997,1998. A total of 255 groups of dolphins was encountered during boat-based surveys and 36% (n= 93) were exposed to at least one swim attempt. The operators' success with swim attempts, defined as at least one dolphin milling within 5 m of at least one swimmer, decreased from 48% in 1994,1995 to 34% in 1997,1998, and avoidance responses to swimmers increased from 22% to 31%. Dolphin response was found to vary according to swimmer placement. The greatest increase in avoidance occurred when swimmers were placed in the dolphins' path of travel. Based on sighting records of 266 individually identified dolphins, it was estimated that an average dolphin was exposed to 31 swim attempts per year. This level of exposure suggests that individual dolphins have, with cumulative experience, become sensitized to swim attempts. When a swim attempt was successful, on average it involved 19% of the group. Age-class differences in interaction rates showed that juveniles were significantly more likely to interact with swimmers than adults. This study highlights the importance of longitudinal studies in evaluating human impact and suggests the urgent need for similar studies of potential human impact on other toothed cetaceans. [source] LONG-TERM EXPOSURE TO EXTREMELY LOW-FREQUENCY MAGNETIC FIELDS IMPAIRS SPATIAL RECOGNITION MEMORY IN MICECLINICAL AND EXPERIMENTAL PHARMACOLOGY AND PHYSIOLOGY, Issue 7 2008Yu Fu SUMMARY 1In the present study, we investigated the short- and long-term effects of extremely low-frequency (ELF) magnetic fields on spatial recognition memory in mice by using a two-trial recognition Y-maze that is based on the innate tendency of rodents to explore novel environments. 2Mice were exposed to 25 or 50 Hz electromagnetic fields for either 7 (short term) or 25 days (long term) and then tested in the Y-maze. 3The results indicated that neither short- nor long-term exposure to magnetic fields affected the locomotor activity of mice in the Y-maze. However, long-term exposure to 50 Hz fields reduced recognition of the novel arm. 4Our findings suggest that ELF magnetic fields impair spatial recognition memory in the Y-maze depending on the field strength and/or duration of exposure. [source] Oral toxicity of the cyanobacterial toxin cylindrospermopsin in mice: Long-term exposure to low dosesENVIRONMENTAL TOXICOLOGY, Issue 6 2006A. Sukenik Abstract The hepatotoxin cylindrospermopsin, a sulfated-guanidinium alkaloid with substituted dioxypyrimidine (uracil) moiety, was isolated from several cyanobacteria species. The acute toxicity of cylindrospermopsin was well established based on intraperitoneal and oral exposure; however, only a few long-term subacute exposure studies were performed to permit a reliable guideline value for cylindrospermopsin in drinking water. In the study reported herein, female and male mice were exposed to cylindrospermopsin in their drinking water. Cylindrospermopsin-containing, Aphanizomenon ovalisporum (cyanobacterium)-free medium was provided as the only source of drinking water, whereas a control group was given a fresh medium for cyanobacteria as drinking water. Over a period of 42 weeks, experiment groups were exposed to cylindrospermopsin concentration, gradually increased from 100 to 550 ,g L,1 (daily exposure ranged between 10 and 55 ,g kg,1 day,1). Body and organ weights were recorded, and serum and hematology analyses were performed 20 and 42 weeks after the beginning of the experiment. The most pronounced effect of cylindrospermopsin was elevated hematocrit levels in both male and female mice after 16 weeks of exposure to cylindrospermopsin. The observed changes in the hematocrit level were accompanied by deformation of red blood cells, which were changed into acanthocyte. Based on these results, a daily cylindrospermopsin dose of 20 ,g kg,1 day,1 (equivalent to 200 ,g L,1) is proposed as the lowest-observed-adverse-effect level for both male and female mice. © 2006 Wiley Periodicals, Inc. Environ Toxicol 21: 575,582, 2006. [source] Reduced early growing season freezing resistance in alpine treeline plants under elevated atmospheric CO2GLOBAL CHANGE BIOLOGY, Issue 3 2010MELISSA MARTIN Abstract The frequency of freezing events during the early growing season and the vulnerability to freezing of plants in European high-altitude environments could increase under future atmospheric and climate change. We tested early growing season freezing sensitivity in 10 species, from four plant functional types (PFTs) spanning three plant growth forms (PGFs), from a long-term in situ CO2 enrichment (566 vs. 370 ppm) and 2-year soil warming (+4 K) experiment at treeline in the Swiss Alps (Stillberg, Davos). By additionally tracking plant phenology, we distinguished indirect phenology-driven CO2 and warming effects from direct physiology-related effects on freezing sensitivity. The freezing damage threshold (lethal temperature 50) under ambient conditions of the 10 treeline species spanned from ,6.7±0.3 °C (Larix decidua) to ,9.9±0.6 °C (Vaccinium gaultherioides). PFT, but not PGF, explained a significant amount of this interspecific variation. Long-term exposure to elevated CO2 led to greater freezing sensitivity in multiple species but did not influence phenology, implying that physiological changes caused by CO2 enrichment were responsible for the effect. The elevated CO2 effect on freezing resistance was significant in leaves of Larix, Vaccinium myrtillus, and Gentiana punctata and marginally significant in leaves of Homogyne alpina and Avenella flexuosa. No significant CO2 effect was found in new shoots of Empetrum hermaphroditum or in leaves of Pinus uncinata, Leontodon helveticus, Melampyrum pratense, and V. gaultherioides. Soil warming led to advanced leaf expansion and reduced freezing resistance in V. myrtillus only, whereas Avenella showed greater freezing resistance when exposed to warming. No effect of soil warming was found in any of the other species. Effects of elevated CO2 and soil warming on freezing sensitivity were not consistent within PFTs or PGFs, suggesting that any future shifts in plant community composition due to increased damage from freezing events will likely occur at the individual species level. [source] Effects of long-term exposure to ramelteon, a melatonin receptor agonist, on endocrine function in adults with chronic insomniaHUMAN PSYCHOPHARMACOLOGY: CLINICAL AND EXPERIMENTAL, Issue 2 2009Gary Richardson Abstract Objective To evaluate the effects of ramelteon, an MT1/MT2 melatonin receptor agonist used to treat insomnia, on endocrine function in adults with chronic insomnia. Methods This was a double-blind, placebo-controlled, trial of adults (18,45 years) with chronic insomnia. Subjects received either ramelteon 16,mg or placebo nightly for 6 months. Hormonal measures of the thyroid, reproductive, and adrenal axes were analyzed monthly and compared with baseline and placebo values. Results While isolated changes were detected at some time points, there were no consistent statistically significant differences between treatments on measures of thyroid function (total T4, free T4, TSH, and total T3), adrenal function (AM cortisol, and ACTH), or on most reproductive endocrine measures [LH, FSH, estradiol (women), total, and free testosterone (men)]. Prolactin concentrations were increased overall in women in the ramelteon group compared with placebo (p,=,0.003). No clinical effects of elevated prolactin were reported; average menstrual cycle length, duration of menses, and ovulation probability did not differ between groups. Conclusions Long-term exposure to ramelteon 16,mg, a potent melatonin receptor agonist, resulted in mild, transient increase in prolactin, in women only, that were not associated with measurable reproductive effects. There were no consistent changes in other endocrine measures. Copyright © 2008 John Wiley & Sons, Ltd. [source] Long-term exposure to elevated CO2 in a Florida scrub-oak forest increases herbivore densities but has no effect on other arthropod guildsINSECT CONSERVATION AND DIVERSITY, Issue 2 2010PETER STILING Abstract., 1.,This study uses pitfall traps and sticky traps to examine the effects of elevated CO2 on the densities of insect herbivores, insectivores, and detritivores. 2.,Pitfall trapping for the last 3 years of 11 years of continuously elevated CO2 revealed increases of insect herbivore species such as Thysanoptera (thrips), Hemiptera, and Lepidoptera, but no effects on insectivores such as spiders, parasitic wasps, and ants; or on detritivores such as Diptera (flies), Psocoptera (book lice), Blattodea (cockroaches), Collembola (spring tails), Orthoptera (crickets), and Coleoptera (beetles). 3.,As the bottom-up effects of elevated CO2 are transmitted through plants to herbivores, they do not appear to reach insect natural enemies or decomposers. [source] Effect of bile on the lipid composition and surface properties of bifidobacteriaJOURNAL OF APPLIED MICROBIOLOGY, Issue 5 2002A. Gómez Zavaglia Aim: The changes produced on the bacterial surface of Bifidobacteria cells when they are grown in bile were compared with those provoked by bile added to bacteria grown in the absence of bile. Methods and Results: The adhesive properties, the zeta potential and the lipid composition of Bifidobacterial strains, isolated from human faeces and grown in MRS medium, were determined. Bacteria grown in MRS with bile showed a loss of adherence and autoaggregation in correlation with a decrease in the surface hydrophobicity in comparison to those grown in MRS without bile, concomitant with the absence of two glycolipids, the increase of sugar content and minor changes in fatty acid composition. The surface changes caused by bile shock on bacteria grown in bile-free medium were much less pronounced and, in addition, no effect on the lipid composition was apparent. Conclusions: The comparison of the results indicates that bile action on surface properties is related to metabolic changes. Significance and Impact of the Study: Long-term exposure of bacteria to bile may cause metabolic changes affecting their adhesive properties irreversibly. This may be taken as a criterion to define the probiotic properties of different strains. [source] Inflammatory cytokines induce the transformation of human dermal microvascular endothelial cells into myofibroblasts: a potential role in skin fibrogenesisJOURNAL OF CUTANEOUS PATHOLOGY, Issue 2 2007V. Chaudhuri Background:, The myofibroblast plays a central role in wound contraction and in the pathology of fibrosis. The origin(s) of this important cell type in skin has not been firmly established. Methods:, Human epithelioid dermal microvascular endothelial cells (HDMEC) were isolated from foreskin tissue and maintained in cell culture. The transformation of epithelioid HDMEC into myofibroblasts (EMT) was induced by the inflammatory cytokines interleukin-1, (IL-1,) or tumour necrosis factor-, (TNF-,), and the transformed cells were characterized by electron microscopy, immunohistochemistry and quantitative RT-PCR. Results:, After short-term exposure to IL-1, or TNF-, (<3 days), EMT was reversible; after long-term exposure (>10 days), EMT was permanent. The transformed cells were identified as myofibroblasts by cytoplasmic microfilaments with dense bodies and attachment plaques, by the expression of ,-smooth muscle actin, type I collagen and calponin, and by quantitative RT-PCR gene expression of type I collagen and ,-smooth muscle actin. Conclusions:, Long-term exposure to TNF-, or IL-1, induced the permanent transformation of HDMEC into myofibroblasts in cell culture. A similar transformation following chronic inflammatory stimulation in vivo may explain one source of myofibroblasts in skin fibrogenesis. [source] Extracellular glucose concentration alters functional activity of the intestinal oligopeptide transporter (PepT-1) in Caco-2 cellsJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 3 2003Vanessa M. D'Souza Abstract The objective of this study was to determine the effect of different cell culture media glucose concentrations on the functional activity of PepT-1 in Caco-2 cells. Uptake kinetics of Gly-Sar into Caco-2 cells that were maintained in iso-osmotic media containing 25 or 5.5 mM glucose were determined in the presence and absence of amino acid-selective chemical modifiers and dithiothreitol. Inhibition of Gly-Sar uptake into Caco-2 cells was measured in the presence of dipeptides and xenobiotics exhibiting various binding affinities for the PepT-1. The effect of extracellular glucose on PepT-1 gene expression was assessed using comparative RT-PCR. Long-term exposure of Caco-2 cells to 25 mM glucose reduced maximum transport capacity for Gly-Sar uptake without altering PepT-1 gene expression. In contrast, binding affinity of Gly-Sar and other dipeptides or xenobiotics was not significantly changed. Chemical modification of Lys and Tyr residues decreased Vmax, while Cys modification increased the maximum transport capacity of the carrier. Preincubation of Caco-2 cells with dithiothreitol restored PepT-1 activity in cells maintained at 25 mM glucose. In conclusion, cell culture media containing 25 mM glucose decreases maximum transport capacity of PepT-1 in Caco-2 cells without affecting substrate recognition, at least in part, mediated via an oxidative pathway. © 2003 Wiley-Liss Inc. and the American Pharmaeceutical Association J Pharm Sci 92:594,603, 2003 [source] The effect of aging on the dark conductivity and 1/f noise in hydrogenated microcrystalline silicon thin filmsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 3-4 2010M. Güne Abstract Aging hydrogenated microcrystalline silicon in air is found to affect both the dark conductivity and the 1/f noise. For a sample with a crystalline volume fraction of 0.39, the conductivity decreased by three orders of magnitude at 20 °C after short-term (10,20 hrs) exposure to air. The conductivity recovered after annealing to 160 °C. Long-term exposure (2 years) resulted in a permanent decrease by a factor of 16 at 20 °C even after annealing. Long-term aging also increased the conductivity activation energy from 0.193 eV to 0.342 eV. After short-term aging and below the annealing temperature, the conductivity prefactor ,0 and the activation energy E, follow a Meyer-Neldel type of relation. Conductance fluctuations measured for annealed and aged states show all the expected characteristics of 1/f noise. The spectra fit a power law with slope -1; the slope is not affected by temperature or aging. The magnitude of the noise decreases with temperature after aging, but by much less after annealing. A simple analysis of the product of conductivity and noise magnitude can be used to estimate the free carrier mobility (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Isoprenoid emission in trees of Quercus pubescens and Quercus ilex with lifetime exposure to naturally high CO2 environment,PLANT CELL & ENVIRONMENT, Issue 4 2004F. RAPPARINI ABSTRACT The long-term effect of elevated atmospheric CO2 on isoprenoid emissions from adult trees of two Mediterranean oak species (the monoterpene-emitting Quercus ilex L. and the isoprene-emitting Quercus pubescens Willd.) native to a high-CO2 environment was investigated. During two consecutive years, isoprenoid emission was monitored both at branch level, measuring the actual emissions under natural conditions, and at leaf level, measuring the basal emissions under the standard conditions of 30 °C and at light intensity of 1000 µmol m,2 s,1. Long-term exposure to high atmospheric levels of CO2 did not significantly affect the actual isoprenoid emissions. However, when leaves of plants grown in the control site were exposed for a short period to an elevated CO2 level by rapidly switching the CO2 concentration in the gas-exchange cuvette, both isoprene and monoterpene basal emissions were clearly inhibited. These results generally confirm the inhibitory effect of elevated CO2 on isoprenoid emission. The absence of a CO2 effect on actual emissions might indicate higher leaf temperature at elevated CO2, or an interaction with multiple stresses some of which (e.g. recurrent droughts) may compensate for the CO2 effect in Mediterranean ecosystems. Under elevated CO2, isoprene emission by Q. pubescens was also uncoupled from the previous day's air temperature. In addition, pronounced daily and seasonal variations of basal emission were observed under elevated CO2 underlining that correction factors may be necessary to improve the realistic estimation of isoprene emissions with empirical algorithms in the future. A positive linear correlation of isoprenoid emission with the photosynthetic electron transport and in particular with its calculated fraction used for isoprenoid synthesis was found. The slope of this relationship was different for isoprene and monoterpenes, but did not change when plants were grown in either ambient or elevated CO2. This suggests that physiological algorithms may usefully predict isoprenoid emission also under rising CO2 levels. [source] Long-term exposure of several marine benthic animals to static magnetic fieldsBIOELECTROMAGNETICS, Issue 7 2004R. Bochert Abstract Electrical currents in underwater sea cables could induce magnetic fields. The sea cables lie on or within the sea bottom and this is the living area for many invertebrate and vertebrate species. North Sea prawn Crangon crangon (Crustacea, Decapoda), round crab Rhithropanopeus harrisii (Crustacea, Brachyura), glacial relict isopod Saduria entomon (Crustacea, Isopoda), blue mussel Mytilus edulis (Bivalvia), and young flounder Plathichthys flesus (Pisces) were exposed to a static magnetic field (MF) of 3.7 mT for several weeks. The results showed no differences in survival between experimental and control animals. Mussels M. edulis were kept under static magnetic field conditions for 3 months during their reproductive period in spring. The determination of gonad index and condition index revealed no significant differences to the control group. Bioelectromagnetics 25:498,502, 2004. © 2004 Wiley-Liss, Inc. [source] Noninfectious dermatological diseases associated with chronic exposure to mine tailings in a Peruvian districtBRITISH JOURNAL OF DERMATOLOGY, Issue 1 2008W. Ramos Summary Background, Mine tailings are metallic wastes which are deposited in the environment due to mining activity. Long-term exposure to these metals is harmful to human health. Objective, To determine if chronic exposure to mine tailings constitutes a risk factor for the development of dermatological diseases in the district of San Mateo de Huanchor (Lima, Peru). Methods, An observational case,control study was carried out in the communities of Mayoc, Daza and Tamboraque (exposed to mine tailings, case group) located in the district of San Mateo de Huanchor, and also in the communities of Choccna and Caruya (not exposed to mine tailings, control group) located in the same district. Out of 230 adults, 121 were exposed and 109 were not exposed to mine tailings and out of 135 children, 71 were exposed and 64 were not exposed to mine tailings. Results, In the adult group, 71% of the exposed cases had some noninfectious dermatological disease while in the nonexposed group the frequency was 34% [P < 0·001; odds ratio (OR) 5·40; 95% confidence interval (CI) 3·02,9·68]. A statistically significant difference between groups was found for arsenical dermatitis, nonpruritic papulovesicular eruption, atopic dermatitis, contact dermatitis, seborrhoeic dermatitis and xerosis. In the paediatric population, 71 exposed and 64 nonexposed children were evaluated. Sixty-nine per cent of the exposed group had some noninfectious dermatological disease vs. 30% in the nonexposed group (P < 0·001; OR 6·00; 95% CI 2·71,13·31). A statistically significant difference between groups was found for xerosis and atopic dermatitis. Conclusion, Chronic exposure to mine tailings represents a risk factor for development of noninfectious dermatological diseases in both adults and children. [source] Interleukin-4 increases murine airway response to kinins, via up-regulation of bradykinin B1 -receptors and altered signalling along mitogen-activated protein kinase pathwaysCLINICAL & EXPERIMENTAL ALLERGY, Issue 8 2004M. Bryborn Summary Background IL-4 is believed to play a role in asthma and chronic obstructive pulmonary disease through promotion of eosinophilic inflammation and mucus hypersecretion. Whether IL-4 can induce a direct effect on airway smooth muscle remains unknown. Objective To investigate the effect of IL-4 on airway smooth muscle, focusing on the contractile response to des-Arg9 -bradykinin and bradykinin. Methods Tracheal segments from murine airways were cultured for 1,8 days in the absence and presence of IL-4. The smooth muscle response induced by des-Arg9 -bradykinin and bradykinin was investigated in myographs. Expression levels for the IL-4-, bradykinin B1 - and B2 -receptors were characterized using RT-PCR. Specific inhibitors were used to study signal changes along the IL-4 receptor- (IL-4R-) coupled mitogen-activated protein (MAP) kinase (MAPK) pathways. Results IL-4 treatment increased the contractile response to des-Arg9 -bradykinin and bradykinin in a concentration- and time-dependent manner. Dexamethasone and the transcriptional inhibitor actinomycin D blocked this effect. c-Jun N-terminal kinase inhibitor SP600125 also blocked the effect of both des-Arg9 -bradykinin and bradykinin, whereas p38 inhibitor SB203580 blocked only the former and the MAPKK inhibitor PD098059, only the latter agonist responses. IL-4 treatment increased the mRNA levels representing bradykinin B1 - but not B2 -receptors. Levels of IL-4R were not altered during culture. Conclusion Long-term exposure to IL-4 increases the contractile response induced by des-Arg9 -bradykinin and bradykinin in cultured murine airways. This effect appears to be mediated via an up-regulation of B1 -receptors and altered signalling along the MAPK pathways. [source] Acute exposure of human lung cells to 1,3-butadiene diepoxide results in G1 and G2 cell cycle arrestENVIRONMENTAL AND MOLECULAR MUTAGENESIS, Issue 4 2005Michael Schmiederer Abstract 1,3-butadiene (BD) causes genetic damage, including adduct formation, sister chomatid exchange, and point mutations. Previous studies have focused on the types of genetic damage and tumors found after long-term exposure of rodents to butadiene. This study examined the effect of the most active BD metabolite, butadiene diepoxide (BDO2), on cell cycle entry and progression in human lung fibroblasts (LU cells) with a normal diploid karyotype. Serum-arrested (G0) LU cells were exposed to BDO2 for 1 hr and stimulated to divide with medium containing 10% fetal bovine serum. The BDO2 -treated LU cells were evaluated for cell cycle progression, nuclear localization of arrest mediators, mitotic index, and cellular proliferation. The BDO2 -treated cells demonstrated a substantial inhibition of cell proliferation when treated with 100 ,M BDO2 for 1 hr. No appreciable levels of apoptosis or mitotic figures were observed in the BDO2 -treated cells through 96 hr posttreatment. Flow cytometric analysis revealed that the lack of proliferation in BDO2 -treated LU cells was related to G1 arrest in about half of the cells and a delayed progression through S and G2 arrest in nearly all of the remaining cells. Both G1 and G2 arrest were prolonged and only a very small percentage of BDO2 -treated cells were eventually able to replicate. Increased nuclear localization of both p53 and p21cip1 was observed in BDO2 -treated cells, suggesting that the cell cycle arrest was p21cip1 -mediated. These results demonstrate that BDO2 induces cell cycle perturbation and arrest even with short-term exposure that does not produce other pathologic cellular effects. Environ. Mol. Mutagen., 2005. © 2005 Wiley-Liss, Inc. [source] Arsenite induces delayed mutagenesis and transformation in human osteosarcoma cells at extremely low concentrationsENVIRONMENTAL AND MOLECULAR MUTAGENESIS, Issue 5 2003Kanae Mure Abstract Arsenite is a human multisite carcinogen, but its mechanism of action is not known. We recently found that extremely low concentrations (,0.1 ,M) of arsenite transform human osteosarcoma TE85 (HOS) cells to anchorage-independence. In contrast to other carcinogens which transform these cells within days of exposure, almost 8 weeks of arsenite exposure are required for transformation. We decided to reexamine the question of arsenite mutagenicity using chronic exposure in a spontaneous mutagenesis assay we previously developed. Arsenite was able to cause a delayed increase in mutagenesis at extremely low concentrations (,0.1 ,M) in a dose-dependent manner. The increase in mutant frequency occurred after almost 20 generations of growth in arsenite. Transformation required more than 30 generations of continuous exposure. We also found that arsenite induced gene amplification of the dihydrofolate reductase (DHFR) gene in a dose-dependent manner. Since HOS cells are able to methylate arsenite at a very low rate, it was possible that active metabolites such as monomethylarsonous acid (MMAIII) contributed to the delayed mutagenesis and transformation in these cells. However, when the assay was repeated with MMAIII, we found no significant increase in mutagenesis or transformation, suggesting that arsenite-induced delayed mutagenesis and transformation are not caused by arsenite's metabolites, but by arsenite itself. Our results suggest that long-term exposure to low concentrations of arsenite may affect signaling pathways that result in a progressive genomic instability. Environ. Mol. Mutagen. 41:322,331, 2003. © 2003 Wiley-Liss, Inc. [source] Chronic toxicity and responses of several important enzymes in Daphnia magna on exposure to sublethal microcystin-LRENVIRONMENTAL TOXICOLOGY, Issue 3 2005Wei Chen Abstract In the current study, the toxicological mechanisms of microcystin-LR and its disadvantageous effects on Daphnia magna were examined. Survival rate, number of newborn, activity of several important enzymes [glutathione S-transferase (GST), lactate dehydrogenase (LDH), phosphatases, and glutathione], accumulated microcystins, and ultrastructural changes in different organs of Daphnia were monitored over the course of 21-day chronic tests. The results indicated that low concentrations of dissolved microcystin had no harmful effect on Daphnia. On the contrary, stimulatory effects were detected. In the presence of toxin at high dosage and for long-term exposure, GST and glutathione levels decreased significantly. The decreased enzyme activity in the antioxidant system probably was caused by detoxification reactions with toxins. And these processes of detoxification at the beginning of chronic tests may enable phosphatases in Daphnia magna to withstand inhibition by the toxins. At the same time, we also found that the LDH activity in test animals increased with exposure to microcystin-LR, indicating that adverse effects occurred in Daphnia. With microcystin given at a higher dosage or for a longer exposure, the effect on Daphnia magna was fatal. In the meantime, microcystin began to accumulate in Daphnia magna, and phosphatase activity started to be inhibited. From the ultrastructure results of cells in D. magna, we obtained new information: the alimentary canal may be the target organ affected by exposure of microcystins to D. magna. The results of the current study also suggested that the oxidative damage and PPI (protein phosphatase inhibition) mechanisms of vertebrates also are adapted to Daphnia. © 2005 Wiley Periodicals, Inc. Environ Toxicol 20: 323,330, 2005. [source] Comparative study of microcystin-LR-induced behavioral changes of two fish species, Danio rerio and Leucaspius delineatusENVIRONMENTAL TOXICOLOGY, Issue 6 2004Daniela Baganz Abstract The spontaneous locomotor behavior separated into day/night activity phases of two fish species Danio rerio and Leucaspius delineatus was recorded and quantified continuously under sublethal long-term exposure to microcystin-LR in tanks. Microcystin-LR was applied in concentrations of 0.5, 5, 15, and 50 ,g L,1. By using an automated video-monitoring and object-tracing system, the average motility (swimming velocity) and the average number of turns were assessed. Clear dose-dependent effects of microcystin-LR on the behavior of both test fish were measured. During the daytime, the motility of Danio rerio as well as Leucaspius delineatus increased significantly by exposure to the lowest concentrations, whereas higher concentrations led to significantly decreased motility. Influenced by microcystin-LR, the swimming time of Leucaspius delineatus reversed, going from a prominently diurnal activity to a nocturnal one; Danio rerio remained active during the daytime. Most of the relative changes in the behavioral patterns of Danio rerio and Leucaspius delineatus suggest these fish have comparable susceptibility to microcystin-LR and may indicate some adverse consequences for fish populations, for example, in connection with reproduction and predator,prey interactions. © 2004 Wiley Periodicals, Inc. Environ Toxicol 19: 564,570, 2004. [source] Immunocompetence of bivalve hemocytes as evaluated by a miniaturized phagocytosis assayENVIRONMENTAL TOXICOLOGY, Issue 3 2002C. Blaise Abstract Immune function in bivalves can be adversely affected by long-term exposure to environmental contaminants. Investigating alterations in immunity can therefore yield relevant information about the relationship between exposure to environmental contaminants and susceptibility to infectious diseases. We have developed a rapid, cost-effective, and miniaturized immunocompetence assay to evaluate the phagocytic activity, viability, and concentration of hemocytes in freshwater and marine bivalves. Preliminary experiments were performed to optimize various aspects of the assay including 1) the time required for adherence of hemocytes to polystyrene microplate wells, 2) the time required for internalization of fluorescent bacteria, 3) the ratio of hemocytes to fluorescent bacteria in relation to phagocytosis, 4) hemolymph plasma requirements, and 5) the elimination of fluorescence from (noninternalized) bacteria adhering to the external surface of hemocytes. The results of these experiments showed the optimal adherence time for hemocytes in microplate wells to be 1 h, that phagocytosis required at least 2 h of contact with fluorescently labeled E. coli cells, that the number of fluorescent E. coli cells had a positive effect on phagocytic activity, that at least 2.5 million cells/mL were required to measure a significant intake, and that a linear increase in uptake of bacteria (R = 0.91; p < 0.01) could be obtained with concentrations of up to 1.3 × 106 hemocytes/mL. Afterward, the assay was used in two field studies to identify sites having the potential to affect the immunocompetence of bivalves. The first study was conducted on Mya arenaria clams collected at selected contaminated sites in the Saguenay River (Quebec, Canada), and the second examined Elliptio complanata freshwater bivalves that had been exposed to a municipal effluent plume in the St. Lawrence River (Quebec, Canada). In the Saguenay River field study a significant increase in phagocytosis was observed at sites closest to polluted areas. Phagocytotic activity varied over time and was highest during the warmest months (June, July, and August), closely paralleling the spawning period of Mya arenaria clams. In contrast, a drop in phagocytic activity was observed in Elliptio complanata mussels exposed to surface water 4 km downstream of a major municipal effluent plume, with a concomitant increase in the number of hemocytes in the hemolymph. It appears that both immunosuppressive and immunostimulative effects are likely to occur in the field and that responses will be influenced by the type and intensity of contaminants at play. © 2002 Wiley Periodicals, Inc. Environ Toxicol 17: 160,169, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/tox.10047 [source] Assessing the fate and effects of nano aluminum oxide in the terrestrial earthworm, Eisenia fetidaENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 7 2010Jessica G. Coleman Abstract Nano-sized aluminum is currently being used by the military and commercial industries in many applications including coatings, thermites, and propellants. Due to the potential for wide dispersal in soil systems, we chose to investigate the fate and effects of nano-sized aluminum oxide (Al2O3), the oxidized form of nano aluminum, in a terrestrial organism. The toxicity and bioaccumulation potential of micron-sized (50,200,µm, nominal) and nano-sized (11,nm, nominal) Al2O3 was comparatively assessed through acute and subchronic bioassays using the terrestrial earthworm, Eisenia fetida. Subchronic (28-d) studies were performed exposing E. fetida to nano- and micron-sized Al2O3 -spiked soils to assess the effects of long-term exposure. No mortality occurred in subchronic exposures, although reproduction decreased at ,3,000,mg/kg nano-sized Al2O3 treatments, with higher aluminum body burdens observed at 100 and 300,mg/kg; no reproductive effects were observed in the micron-sized Al2O3 treatments. In addition to toxicity and bioaccumulation bioassays, an acute (48-h) behavioral bioassay was conducted utilizing a soil avoidance wheel in which E. fetida were given a choice of habitat between control, nano-, or micron-sized Al2O3 amended soils. In the soil avoidance bioassays, E. fetida exhibited avoidance behavior toward the highest concentrations of micron- and nano-sized Al2O3 (>5,000,mg/kg) relative to control soils. Results of the present study indicate that nano-sized Al2O3 may impact reproduction and behavior of E. fetida, although at high levels unlikely to be found in the environment. Environ. Toxicol. Chem. 2010;29:1575,1580. © 2010 SETAC [source] Exposure assessment of 17,-ethinylestradiol in surface waters of the United States and Europe,ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 12 2009Robert Hannah Abstract An evaluation of measured and predicted concentrations of 17,-ethinylestradiol in surface waters of the United States and Europe was conducted to develop expected long-term exposure concentrations for this compound. Measured environmental concentrations (MECs) in surface waters were identified from the literature. Predicted environmental concentrations (PECs) were generated for European and U.S. watersheds using the GREAT-ER and PhATEÔ models, respectively. The majority of MECs are nondetect and generally consistent with model PECs and conservative mass balance calculations. However, the highest MECs are not consistent with concentrations derived from conservative (worst-case) mass balance estimates or model PECs. A review of analytical methods suggests that tandem or high-resolution mass spectrometry methods with extract cleanup result in lower detection limits and lower reported concentrations consistent with model predictions and bounding estimates. Based on model results using PhATE and GREAT-ER, the 90th-percentile low-flow PECs in surface water are approximately 0.2 and 0.3 ng/L for the United States and Europe, respectively. These levels represent conservative estimates of long-term exposure that can be used for risk assessment purposes. Our analysis also indicates that average concentrations are one to two orders of magnitude lower than these 90th-percentile estimates. Higher reported concentrations (e.g., greater than the 99th-percentile PEC of ,1 ng/L) could result from methodological problems or unusual environmental circumstances; however, such concentrations are not representative of levels generally found in the environment, warrant special scrutiny, and are not appropriate for use in risk assessments of long-term exposures. [source] Stimulation of reproductive growth in rainbow trout (Oncorhynchus mykiss) following exposure to treated sewage effluentENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 10 2006Birgit Hoger Abstract Rainbow trout (Oncorhynchus mykiss) were exposed to 1.5 and 15% v/v secondary treated sewage effluent for 32 weeks in flow-through mesocosms. The exposure encompassed the full period of reproductive development for rainbow trout. Trout did not show any evidence of a dose-dependent change in growth. Fish exposed to 15% effluent were the only group to show mortality (5%) over the duration of the experiment. Trout at the highest effluent concentration had significantly higher liver size than reference water fish. Both male and female trout in the 15% exposure group also exhibited significantly higher gonad weight than the reference group. In female trout, this gonad size increase could be explained by higher egg numbers. Female and male trout both displayed a significant increase in plasma 17,-estradiol levels after exposure to 15% effluent, while neither sex had dose-dependent differences in plasma testosterone. Male trout displayed elevated vitellogenin levels and reduced plasma 11-ketotestosterone concentration after exposure to 15% effluent. Chemical examination of steroidal compounds, including both estrogens and androgens, in the wastewater revealed that only estrone was detectable at a mean concentration of 4.5 ng/L. It is assumed that the effects observed in trout exposed to 15% effluent were consistent with stimulation of reproductive development due to very low levels of estrogens. Overall, long-term exposure to treated sewage effluent containing low levels of estrogen did not have significant negative implications for reproductive development in rainbow trout. [source] Effects of nonylphenol, bisphenol a, and their mixture on the viviparous swordtail fish (Xiphophorus helleri)ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 4 2001Hyeong-Il Kwak Abstract A number of fish species have been used for studies on endocrine disrupting chemicals (EDCs). However, despite the widespread use of oviparous fish, relatively little attention has been given to viviparous species. This study investigated the effects of EDCs in a viviparous fish and examined the possible usefulness of the fish as an alternative model for the studies on EDCs. Swordtails (Xiphophorus helleri) were exposed to nonylphenol (NP), bisphenol A (BPA), and their mixture. Both short-term (3-d) and relatively long-term (60-d) exposures were carried out using adult male and 30-d-old juvenile fish, respectively. Following the short-term exposure, both NP and BPA caused vitellogenin mRNA expression. Flow cytometric analysis and terminal deox-ynucleotidyl transferase assay on the testes of treated fish indicated reproductive damage. Histopathological analysis found degenerative and necrotic cells in seminiferous tubules following the exposure to 100 ppb NP. The testes with lesions were also associated with highly suppressed spermatogenesis. Following the long-term exposure, both NP and BPA exposures significantly affected the growth of swordtails. In all cases, the results showed that the mixture was always more potent than a single chemical and that swordtail fish can be a useful model for the study of endocrine disruptors. [source] Alcohol self-administration acutely stimulates the hypothalamic-pituitary-adrenal axis, but alcohol dependence leads to a dampened neuroendocrine stateEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 8 2008Heather N. Richardson Abstract Clinical studies link disruption of the neuroendocrine stress system with alcoholism, but remaining unknown is whether functional differences in the hypothalamic-pituitary-adrenal (HPA) axis precede alcohol abuse and dependence or result from chronic exposure to this drug. Using an operant self-administration animal model of alcohol dependence and serial blood sampling, we show that long-term exposure to alcohol causes significant impairment of HPA function in adult male Wistar rats. Acute alcohol (voluntary self-administration or experimenter-administered) stimulated the release of corticosterone and its upstream regulator, adrenocorticotropic hormone, but chronic exposure sufficient to produce dependence led to a dampened neuroendocrine state. HPA responses to alcohol were most robust in ,low-responding' non-dependent animals (averaging < 0.2 mg/kg/session), intermediate in non-dependent animals (averaging ,0.4 mg/kg/session), and most blunted in dependent animals (averaging ,1.0 mg/kg/session) following several weeks of daily 30-min self-administration sessions, suggesting that neuroendocrine tolerance can be initiated prior to dependence and relates to the amount of alcohol consumed. Decreased expression of corticotropin-releasing factor (CRF) mRNA expression in the paraventricular nucleus of the hypothalamus and reduced sensitivity of the pituitary to CRF may contribute to, but do not completely explain, neuroendocrine tolerance. The present results, combined with previous studies, suggest that multiple adaptations to stress regulatory systems may be brought about by excessive drinking, including a compromised hormonal response and a sensitized brain stress response that together contribute to dependence. [source] GABA and glycine are protective to mature but toxic to immature rat cortical neurons under hypoxiaEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 2 2005Peng Zhao Abstract Although recent studies suggest that ,-aminobutyric acid (GABA) and glycine may be ,inhibitory' to mature neurons, but ,excitatory' to immature neurons under normoxia, it is unknown whether inhibitory neurotransmitters are differentially involved in neuronal response to hypoxia in immature and mature neurons. In the present study, we exposed rat cortical neurons to hypoxia (1% O2) and examined the effects of three major inhibitory neurotransmitters (GABA, glycine and taurine) on the hypoxic neurons at different neuronal ages [days in vitro (DIV)4,20]. Our data showed that the cortical neurons expressed both GABAA and glycine receptors with differential developmental profiles. GABA (10,2000 µm) was neuroprotective to hypoxic neurons of DIV20, but enhanced hypoxic injury in neurons of <,DIV20. Glycine at low concentrations (10,100 µm) exhibited a similar pattern to GABA. However, higher concentrations of glycine (1000,2000 µm) for long-term exposure (48,72 h) displayed neuroprotection at all ages (DIV4,20). Taurine (10,2000 µm), unlike GABA and glycine, displayed protection only in DIV4 neurons, and was slightly toxic to neurons >,DIV4. In comparison with delta-opioid receptor (DOR)-induced protection in DIV20 neurons exposed to 72 h of hypoxia, glycine-induced protection was weaker than that of DOR but stronger than that of GABA and taurine. These data suggest that the effects of the inhibitory neurotransmitters on hypoxic cortical neurons are age-dependent, with GABA and glycine being neurotoxic to immature neurons and neuroprotective to mature neurons. [source] Carbon dioxide balance of a fen ecosystem in northern Finland under elevated UV-B radiationGLOBAL CHANGE BIOLOGY, Issue 4 2009JAANA K. HAAPALA Abstract The effect of elevated UV-B radiation on CO2 exchange of a natural flark fen was studied in open-field conditions during 2003,2005. The experimental site was located in Sodankylä in northern Finland (67°22,N, 26°38,E, 179 m a.s.l.). Altogether 30 study plots, each 120 cm × 120 cm in size, were randomly distributed between three treatments (n=10): ambient control, UV-A control and UV-B treatment. The UV-B-treated plots were exposed to elevated UV-B radiation level for three growing seasons. The instantaneous net ecosystem CO2 exchange (NEE) and dark respiration (RTOT) were measured during the growing season using a closed chamber method. The wintertime CO2 emissions were estimated using a gradient technique by analyzing the CO2 concentration in the snow pack. In addition to the instantaneous CO2 exchange, the seasonal CO2 balances during the growing seasons were modeled using environmental data measured at the site. In general, the instantaneous NEE at light saturation was slightly higher in the UV-B treatment compared with the ambient control, but the gross photosynthesis was unaffected by the exposure. The RTOT was significantly lower under elevated UV-B in the third study year. The modeled seasonal (June,September) CO2 balance varied between the years depending on the ground water level and temperature conditions. During the driest year, the seasonal CO2 balance was negative (net release of CO2) in the ambient control and the UV-B treatment was CO2 neutral. During the third year, the seasonal CO2 uptake was 43±36 g CO2 -C m,2 in the ambient control and 79±45 g CO2 -C m,2 in the UV-B treatment. The results suggest that the long-term exposure to high UV-B radiation levels may slightly increase the CO2 accumulation to fens resulting from a decrease in microbial activity in peat. However, it is unlikely that the predicted development of the level of UV-B radiation would significantly affect the CO2 balance of fen ecosystems in future. [source] Squamous cell carcinoma arising in the skin of a deltopectoral flap 27 years after pharyngeal reconstruction,HEAD & NECK: JOURNAL FOR THE SCIENCES & SPECIALTIES OF THE HEAD AND NECK, Issue 1 2002Tim A. Iseli MBBS Abstract Background Development of a second primary squamous cell carcinoma in the skin of a flap used for pharyngeal reconstruction is rare. Methods A case of squamous cell carcinoma is presented arising in a deltopectoral flap used to reconstruct the hypopharynx 27 years after total laryngectomy. Three previous reports found on review of the literature are summarized. Results A second primary squamous cell carcinoma may arise in the skin of a myocutaneous flap in the absence of any obvious risk factors. Conclusion We suspect that long-term exposure of the skin of the flap lining the pharynx to saliva may have been a significant factor in the development of this malignancy. Long-term follow up and awareness of this complication is required for patients with soft tissue reconstruction of the oral cavity and pharynx. © 2002 John Wiley & Sons, Inc. Head Neck 24: 87,90, 2002. [source] Effects of long-term exposure to ramelteon, a melatonin receptor agonist, on endocrine function in adults with chronic insomniaHUMAN PSYCHOPHARMACOLOGY: CLINICAL AND EXPERIMENTAL, Issue 2 2009Gary Richardson Abstract Objective To evaluate the effects of ramelteon, an MT1/MT2 melatonin receptor agonist used to treat insomnia, on endocrine function in adults with chronic insomnia. Methods This was a double-blind, placebo-controlled, trial of adults (18,45 years) with chronic insomnia. Subjects received either ramelteon 16,mg or placebo nightly for 6 months. Hormonal measures of the thyroid, reproductive, and adrenal axes were analyzed monthly and compared with baseline and placebo values. Results While isolated changes were detected at some time points, there were no consistent statistically significant differences between treatments on measures of thyroid function (total T4, free T4, TSH, and total T3), adrenal function (AM cortisol, and ACTH), or on most reproductive endocrine measures [LH, FSH, estradiol (women), total, and free testosterone (men)]. Prolactin concentrations were increased overall in women in the ramelteon group compared with placebo (p,=,0.003). No clinical effects of elevated prolactin were reported; average menstrual cycle length, duration of menses, and ovulation probability did not differ between groups. Conclusions Long-term exposure to ramelteon 16,mg, a potent melatonin receptor agonist, resulted in mild, transient increase in prolactin, in women only, that were not associated with measurable reproductive effects. There were no consistent changes in other endocrine measures. Copyright © 2008 John Wiley & Sons, Ltd. [source] An assessment of endocrine disruption in mollusks and the potential for developing internationally standardized mollusk life cycle test guidelines,INTEGRATED ENVIRONMENTAL ASSESSMENT AND MANAGEMENT, Issue 3 2008Peter Matthiessen Abstract This paper summarizes what is known about the endocrine systems of mollusks and how they can be disrupted by exogenous substances. It then examines the various possibilities for using mollusk-based toxicity tests to detect and assess the environmental risks of endocrine-disrupting chemicals (EDCs). It is concluded that there are no internationally standardized tests with mollusks available at present that are suitable for assessing the risks of long-term exposure to EDCs but that several published methods show potential. At the present state of knowledge, the most promising mollusk species for use in partial life cycle testing is probably the fresh- and brackish-water mesogastropod, Potamopyrgus antipodarum, which is known to be responsive to both direct and indirect androgens and to estrogens (and their mimics). Less experience of full life cycle testing exists with mollusks, but the freshwater pulmonate gastropod Lymnaea stagnalis at present offers the best possibility for a practical procedure. In both cases, there is a need for substantial test optimization and validation before these procedures could form the basis of international guidelines. [source] Nicotine induces the fragile histidine triad methylation in human esophageal squamous epithelial cellsINTERNATIONAL JOURNAL OF CANCER, Issue 5 2006Toshiya Soma Abstract The fragile histidine triad (FHIT) gene has been proposed to have an important role in very early carcinogenesis. Methylation of the FHIT gene is associated with transcriptional inactivation in esophageal squamous cell carcinoma, and FHIT inactivation has been linked to smoking-related carcinogenesis. In this study, we confirmed methylation of the FHIT gene in human esophageal squamous epithelial cells (HEECs) and examined whether nicotine induced alteration of FHIT. Methylation status in the promoter region of the FHIT gene and p16INK4A gene was determined by methylation-specific PCR in HEECs exposed to nicotine under various conditions. Methylation status of the FHIT gene was confirmed by DNA-sequencing analysis. Protein expression of Fhit and the DNA methyltransferases (DNMTs) DNMT1 and DNMT3a were assessed by immunoblot analysis. In the absence of nicotine, methylation of the FHIT gene and attenuation of Fhit protein were not detected in HEECs. Nicotine induced the methylation of FHIT gene and attenuated Fhit protein in association with increased expression of DNMT3a. Reexpression of Fhit protein in HEECs was found after cessation of moderate- to long-term exposure to nicotine. Our results show that nicotine induces methylation of the FHIT gene followed by loss of Fhit protein expression in HEECs. Continuous smoking may thus increase the risk of esophageal cancer. © 2006 Wiley-Liss, Inc. [source] | ||||||||||||||||||||||||||||||||||||||||