1,720,961 research outputs found
Developmental exposure to xenoestrogen enhances spatial learning in male rats
No full textSteroid hormones have profound effects on the development and function of the nervous system. Environmental estrogens or xenoestrogens are manmade or are natural compounds, which mimics the action of estrogen hormones. The experimental evidence for impairment of cognitive functions in humans and mammals following exposure to xenoestrogens has been fiercely debated. The strongest arguments against such studies have been that the route, time course, and intensity of exposure did not simulate environmental exposure, and that the chemicals tested have additional, non-estrogenic toxic effects, hindering a generalization of actual "xenoestrogenic" effects. Here we show that an environmental-like exposure to the pure estrogen, 17 alpha-ethynylestradiol (EE2) during development enhances spatial learning abilities in adult male Sprague-Dawley rats. To simulate an environmental exposure, we used a very low dose (4 ng/kg/day) of EE2 equivalent to concentrations measured in European and US streams which was given orally with a non-invasive method, and we extended the treatment for the entire course of development, from conception to puberty. The animals were tested in a Morris water maze protocol at 6 months of age. Male rats treated with EE2 during development showed a faster learning during the training phase, and remembered better the position of the bidden platform in the short term. Our study demonstrates that actual levels of exposure to xenoestrogens can permanently alter cognitive abilities of a mammalian species. (c) 2007 Elsevier Inc. All rights reserved
Environmental-Like Exposure to Low Levels of Estrogen Affects Sexual Behavior and Physiology of Female Rats
No full textXenoestrogens are endocrine-disrupting chemicals that mimic the action of endogenous estrogen hormones. Effects of xenoestrogen on aquatic wildlife are well documented, whereas the experimental evidence for impairment of reproductive behavior and physiology in mammals after exposure to xenoestrogens has been debated. The strongest arguments against such studies have been that the route, time course, and intensity of exposure did not simulate environmental exposure and that the chemicals tested have additional nonestrogenic toxic effects, hindering generalization of actual xenoestrogenic effects. Here we show that environmentallike exposure to the pure estrogen 17 alpha-ethinylestradiol during development alters reproductive behavior and physiology in adult female Sprague-Dawley rats. We simulated environmental exposure by giving low doses (0.4 and 0.004 mu g/kg.d) of 17 alpha-ethinylestradiol orally to pregnant females from conception to weaning of the pups, which continued to receive the treatment until puberty. We studied the sexual behavior, estrous cycle, and estradiol plasma levels of intact female rats when they reached 3 months of age. Exposure to the higher dose strongly affected female sexual behavior and physiology, with suppression of lordosis and the estrous cycle and enhanced aggression toward males. The lower dose disrupted appetitive components of sexual behavior that influence the rate of copulation. Estradiol plasma levels were not affected by the treatment. Our study revealed that exposure to low oral doses of a pure estrogen during development alters female sexual behavior and physiology. These results suggest potential risks of reproductive failure from xenoestrogen exposure in realistic ecological conditions. (Endocrinology 149: 5592-5598, 2008
Female competition in wild house mice depends upon timing of female/male settlement and kinship between females
No full textWe assessed the effects of different situational or social determinants on the regulation of female-female competition. We carried out a laboratory study to examine aggression and reproductive success of pairs of wild female mice, Mus musculus domesticus spp., as a function of the timing of settlement of females relative to that of males and the genetic relatedness and familiarity between females (sibling versus nonsibling females). After a few days of cohabitation with a male, females were highly aggressive towards, and intolerant of, any intruder female, regardless of relatedness and familiarity. In this condition, monogamy was the resulting mating pattern in approximately 80% of cases. Conversely, pairs of females who made contact With each other at the same time, or prior to cohabitation with a male, showed comparatively little aggression and a high degree of reciprocal tolerance. Only in these latter conditions did genetic relatedness and familiarity between females inf! luence their behavioural interactions and reproductive success. Although nonsibling pairs showed higher frequencies of aggressive interactions than siblings, polygyny resulted in 97% of cases. However, in most sibling groups both the females weaned young and had greater reproductive success than nonsiblings. Nonsibling females appeared to compete for reproduction through the inhibition of reproduction or infanticide. These findings suggest that the timing of male/female settlement in a deme determines the level of female competition, which, in turn, affects the resulting mating pattern. Only when females showed social tolerance did genetic relatedness and familiarity influence reproductive success
Altered reproductive success in rat pairs after environmental-like exposure to xenoestrogen
No full textEndocrine-disrupting compounds (EDCs) have the capacity of altering the normal function of the endocrine system. EDCs have shown dramatic effects on the reproductive biology of aquatic wildlife and may affect human reproduction as well. Studies on EDCs in mammalian species have often investigated the effects of short-term, high doses on male and female reproductive physiology. However, it is difficult to predict from such studies the effects of EDC on populations that are exposed to very low doses throughout their life via contaminated food and water. We studied the effects of EDC on mammalian reproduction with an environmental-like protocol where the endpoint is the reproductive success of exposed pairs. We focused on a subclass of EDC, the xenoestrogens, which mimic the action of natural oestrogen hormones. Male and female rats were exposed to low doses of the pure oestrogen, ethynyloestradiol, during development, by oral administration to their mothers during pregnancy and lactation, and to them until puberty. We evaluated the effects of the exposure on development and reproductive physiology of individuals, and on fertility and fecundity of pairs in which both members had been exposed to the same treatment. We found that low doses caused major reproductive deficits in the experimental animals. Very low, environmentally relevant doses did not have evident effects on exposed animals; however, the fecundity of exposed pairs was substantially altered. Environmentally relevant doses of xenoestrogens which have no evident physiological effects can alter the reproductive success of exposed pairs in natural populations
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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