Selénio e a importância para o organismo humano

O selénio (Se) é um micronutriente essencial para o crescimento, desenvolvimento e normal metabolismo dos animais, incluindo o ser humano. É parte integrante de um conjunto de proteínas, as selenoproteínas, com ação antioxidante (protegendo as membranas celulares contra danos dos radicais livres), envolvidas no metabolismo das hormonas da tiróide, na regulação do crescimento e viabilidade celular, nas funções do sistema imune e na reprodução. É introduzido na dieta alimentar (principalmente nas formas de selenometionina e selenocisteína) através das plantas, e de produtos que delas derivam, que assimilam os compostos de selénio presentes no solo. Uma vez que a quantidade de selénio existente nos solos é muito variável, o teor nos alimentos vai depender da sua origem geográfica e, por consequência, a ingestão de selénio varia entre regiões e países. Baixos níveis de selénio estão associados a um declínio na função imune e problemas cognitivos. A deficiência de Se pode também ocasionar problemas musculares e cardiomiopatia. Concentrações reduzidas foram observadas em indíviduos com crises epiléticas e também em casos de pré-eclampsia. A deficiência de selénio pode também desenvolver-se durante a nutrição parenteral. Atualmente, a Dose Diária Recomendada (DDR) é de 55 μg/dia para homens e mulheres adultos e saudáveis. No entanto, existem evidências clínicas de que a ingestão em doses superiores (200-300 μg/dia) pode ter um papel benéfico na prevenção de alguns tipos de cancro e doenças cardiovasculares, na melhoria da resposta imunológica, como neuroprotetor e na fertilidade. O Se desempenha um papel importante na fertilidade masculina, sendo necessário na biossíntese da testosterona e na formação e normal desenvolvimento dos espermatozóides. Em mulheres grávidas o Se, ajuda a prevenir complicações antes e durante o parto e promove o normal desenvolvimento do feto. Como antioxidante o selénio vai combater os danos provocados pelos radicais livres, impedindo que estes exerçam o seu papel prejudicial no organismo. Sendo o sistema imunológico muito suscetível aos danos provocados pelo stress oxidativo, o Se vai exercer efeitos benéficos combatendo os danos por ele causados. Relativamente à capacidade viral, não é possível saber com exatidão qual a quantidade de Se necessária ou concentração ideal no plasma para evitar a ocorrência e desenvolvimento de infeções virais. No entanto, sabe-se que tem um efeito benéfico em pacientes HIV positivos e em indivíduos infetados com o vírus da hepatite (B ou C) contra a progressão para o neoplasia de fígado. Em teoria, a nível cardiovascular, este elemento pode exercer um efeito protetor, embora alguns estudos epidemiológicos não tenham mostrado uma associação clara entre o risco cardiovascular e os níveis selénio. A nível cerebral o Se vai atuar como neuroprotetor, prevenindo o aparecimento de patologias como demência e doença de Alzheimer. Apesar destes indicadores, a maioria dos países europeus, incluindo Portugal, regista uma deficiente ingestão de selénio por parte da população. A suplementação poderá constituir uma opção para garantir os níveis nutricionais recomendados e/ou ser utilizada com o objetivo de prevenir algumas doenças e o envelhecimento. No entanto o selénio pode também ser tóxico se ingerido em excesso, estando a dose máxima admissível fixada em 400 μg/dia. A intoxicação por selénio é chamada selenose e os sintomas comuns incluem: hálito a alho, distúrbios gastrointestinais, perda de cabelo, descamação das unhas, danos neurológicos e fadiga. Assim, atualmente acredita-se que enquanto indivíduos com baixo nível de Se podem obter benefícios da suplementação, esta pode ser prejudicial aqueles com valores normais ou elevados.

Ubuntu, Jesus, and Earth: Integrating African Religion and Christianity in Ecological Ethics

Africa faces problems of ecological devastation caused by economic exploitation, rapid population growth, and poverty. Capitalism, residual colonialism, and corruption undermine Africa's efforts to forge a better future. The dissertation describes how in Africa the mounting ecological crisis has religious, political, and economic roots that enable and promote social and environmental harm. It presents the thesis that religious traditions, including their ethical expressions, can effectively address the crisis, ameliorate its impacts, and advocate for social and environmental betterment, now and in the future. First, it examines African traditional religion and Christian teaching, which together provide the foundation for African Christianity. Critical examination of both religious worldviews uncovers their complementary emphases on human responsibility toward planet Earth and future generations. Second, an analysis of the Gwembe Tonga of Chief Simamba explores the interconnectedness of all elements of the universe in African cosmologies. In Africa, an interdependent, participatory relationship exists between the world of animals, the world of humans, and the Creator. In discussing the annual lwiindi (rain calling) ceremony of Simamba, the study explores ecological overtones of African religions. Such rituals illustrate the involvement of ancestors and high gods in maintaining ecological integrity. Third, the foundation of the African morality of abundant life is explored. Across Sub-Saharan Africa, ancestors' teachings are the foundation of morality; ancestors are guardians of the land. A complementary teaching that Christ is the ecological ancestor of all life can direct ethical responses to the ecological crisis. Fourth, the eco-social implications of ubuntu (what it means to be fully human) are examined. Some aspects of ubuntu are criticized in light of economic inequalities and corruption in Africa. However, ubuntu can be transformed to advocate for eco-social liberation. Fifth, the study recognizes that in some cases conflicts exist between ecological values and religious teachings. This conflict is examined in terms of the contrast between awareness of socioeconomic problems caused by population growth, on the one hand, and advocacy of a traditional African morality of abundant children, on the other hand. A change in the latter religious view is needed since overpopulation threatens sustainable living and the future of Earth. The dissertation concludes that the identification of Jesus with African ancestors and theological recognition of Jesus as the ecological ancestor, woven together with ubuntu, an ethic of interconnectedness, should characterize African consciousness and promote resolution of the socio-ecological crisis.

Activation in mesolimbic and visuospatial neural circuits elicited by smoking cues: evidence from functional magnetic resonance imaging.

OBJECTIVE: The authors sought to increase understanding of the brain mechanisms involved in cigarette addiction by identifying neural substrates modulated by visual smoking cues in nicotine-deprived smokers. METHOD: Event-related functional magnetic resonance imaging (fMRI) was used to detect brain activation after exposure to smoking-related images in a group of nicotine-deprived smokers and a nonsmoking comparison group. Subjects viewed a pseudo-random sequence of smoking images, neutral nonsmoking images, and rare targets (photographs of animals). Subjects pressed a button whenever a rare target appeared. RESULTS: In smokers, the fMRI signal was greater after exposure to smoking-related images than after exposure to neutral images in mesolimbic dopamine reward circuits known to be activated by addictive drugs (right posterior amygdala, posterior hippocampus, ventral tegmental area, and medial thalamus) as well as in areas related to visuospatial attention (bilateral prefrontal and parietal cortex and right fusiform gyrus). In nonsmokers, no significant differences in fMRI signal following exposure to smoking-related and neutral images were detected. In most regions studied, both subject groups showed greater activation following presentation of rare target images than after exposure to neutral images. CONCLUSIONS: In nicotine-deprived smokers, both reward and attention circuits were activated by exposure to smoking-related images. Smoking cues are processed like rare targets in that they activate attentional regions. These cues are also processed like addictive drugs in that they activate mesolimbic reward regions.

Freezing behaviour facilitates bioelectric crypsis in cuttlefish faced with predation risk.

Cephalopods, and in particular the cuttlefish Sepia officinalis, are common models for studies of camouflage and predator avoidance behaviour. Preventing detection by predators is especially important to this group of animals, most of which are soft-bodied, lack physical defences, and are subject to both visually and non-visually mediated detection. Here, we report a novel cryptic mechanism in S. officinalis in which bioelectric cues are reduced via a behavioural freeze response to a predator stimulus. The reduction of bioelectric fields created by the freeze-simulating stimulus resulted in a possible decrease in shark predation risk by reducing detectability. The freeze response may also facilitate other non-visual cryptic mechanisms to lower predation risk from a wide range of predator types.

Studies On Benzo[A]Pyrene Mono-Oxygenase In The Shore Crab Carcinus-Maenas

A cytochrome P-450-dependent benzo[a]pyrene mono-oxygenase enzyme system (BPM) has been identified and partially characterized in males of the shore crab Carcinus maenas (L.). Apparent Km values obtained at 30 °C using microsomal preparations from the antennary glands of animals collected during summer were in the range 1.61–2.11 µM. The cytochrome P-450 content was 0·022 nmol/mg microsomal protein when BPM activity in the same preparation was 0·085 nmol/mg protein/min.

Intraguild predation may explain an amphipod replacement: evidence from laboratory populations

In a laboratory experiment that permitted both observations of the behaviour of individuals and the monitoring of small populations, the role of 'intraguild predation' in the elimination of the freshwater amphipod Gammarus duebeni celticus by the introduced G. pulex was examined. Over 18 weeks, deaths in single and mixed species replicates were monitored. Rates of 'mortality' (deaths not due to cannibalism or predation) did not differ between the species. Gammarus cl. celticus, however, was more cannibalistic than G. pulex and, in both species, males were more often cannibalized than females. In mixed species replicates, the mean proportions of animals preyed upon did not differ among replicates with differing starting proportions of the two species, nor was there a difference between the sexes in numbers preyed upon. G. pulex, however, preyed more frequently on G. d celticus than vice versa, and this became more pronounced over time. In 87% of mixed species replicates, G. pulex eliminated G. d. celticus. The results support the proposition that intraguild predation may be the primary mechanism whereby G. pulex rapidly replaces G. d. celticus in freshwater. Integrating behavioural observations with population level monitoring may thus link pattern and process in behaviour and ecology.

Dilemmatic human-animal boundaries in Britain and Romania: Post-materialist and materialist dehumanization

Theories of dehumanization generally assume a single clear-cut, value-free and non-dilemmatic boundary between the categories 'human' and 'animal'. The present study highlights the relevance of dilemmas involved in drawing that boundary. In six focus groups carried out in Romania and Britain, 42 participants were challenged to think about dilemmas pertaining to animal and human life. Four themes were identified: rational autonomy, sentience, speciesism and maintaining materialist and post-materialist values. Sentience made animals resemble humans, while humans' rational autonomy made them distinctive. Speciesism underlay the human participants' prioritization of their own interests over those of animals, and a conservative consensus that the existing social system could not change supported this speciesism when it was challenged. Romanian participants appealed to Romania's lack of modernity and British participants to Britain's modernity to justify such conservatism. The findings suggest that the human-animal boundary is not essentialized; rather it seems that such boundary is constructed in a dilemmatic and post hoc way. Implications for theories of dehumanization are discussed.

Dogs as a diagnostic tool for ill-health in humans

Researchers have long reported that dogs and cats improve the physical and psychological health of their human caregivers, and while it is still inconclusive, a substantial amount of research now lends support for the commonly held view that "pets are good for us." Recently, studies have directed attention toward exploring the use of animals, most notably dogs, in the detection of disease and other types of health problems in people. This article reviews the evidence for dogs' ability to detect ill health in humans, focusing specifically on the detection of cancer, epileptic seizures, and hypoglycemia. The author describes the research carried out in this area and evaluates it in an effort to determine whether dogs have a role to play in modern health care as an "alert" tool or screening system for ill health. Where necessary, the author has highlighted weaknesses in the work and proposed directions for future studies.

SHELL COLOUR IN CALLIOSTOMA ZIZYPHINUM (L.) FROM STRANGFORD LOUGH, N. IRELAND

Shells of Calliostoma zizyphinum taken from Strangford Lough, N. Ireland are divisible into three distinct colour forms: white (=var lyonsi) intermediate (a pale variegated form) and purple (a dark variegated form). The predominance of white and pale shelled individuals within and the absence of white Calliostoma outside the lough was confirmed. The proportions of animals with white and variegated shells at selected sites were almost identical with those previously documented, suggesting a temporal stability of colour form ratios. No differences in shell thickness and pedal adhesion were demonstrated between these forms. Snails with white shells reflect radiant heat better, have lighter coloured feet, move more rapidly, show a greater incidence of shell repair and are more frequently exposed on weed at low tide, than those with either intermediate or purple shells. Increased proportions of white individuals may be associated with high population densities. Under such circumstances, it is suggested that increased mobility may, by increasing dispersion, reduce intraspecific competition. In the event of exposure at low tide a white shell would help minimize thermal stress.

The bird GPS - long-range navigation in migrants

Nowadays few people consider finding their way in unfamiliar areas a problem as a GPS (Global Positioning System) combined with some simple map software can easily tell you how to get from A to B. Although this opportunity has only become available during the last decade, recent experiments show that long-distance migrating animals had already solved this problem. Even after displacement over thousands of kilometres to previously unknown areas, experienced but not first time migrant birds quickly adjust their course toward their destination, proving the existence of an experience-based GPS in these birds. Determining latitude is a relatively simple task, even for humans, whereas longitude poses much larger problems. Birds and other animals however have found a way to achieve this, although we do not yet know how. Possible ways of determining longitude includes using celestial cues in combination with an internal clock, geomagnetic cues such as magnetic intensity or perhaps even olfactory cues. Presently, there is not enough evidence to rule out any of these, and years of studying birds in a laboratory setting have yielded partly contradictory results. We suggest that a concerted effort, where the study of animals in a natural setting goes hand-in-hand with lab-based study, may be necessary to fully understand the mechanism underlying the long-distance navigation system of birds. As such, researchers must remain receptive to alternative interpretations and bear in mind that animal navigation may not necessarily be similar to the human system, and that we know from many years of investigation of long-distance navigation in birds that at least some birds do have a GPS-but we are uncertain how it works.

Coxiella burnetii (Q fever) seroprevalence in cattle

Human cases of Q fever appear to be common in Northern Ireland compared to the rest of the British Isles. The purpose of this study was to describe the seroepidemiology of Coxiella burnetii infection in cattle in Northern Ireland in terms of seroprevalence and determinants of infection. A total of 5182 animals (from a stratified systematic random sample of 273 herds) were tested with a commercial C. burnetii phase 2 IgG ELISA. A total of 6.2% of animals and 48.4% of herds tested positively. Results from a multilevel logistic regression model indicated that the odds of cattle being infected with Q fever increased with age, Friesian breed, being from large herds and from dairy herds. Large dairy herd animal prevalence was 12.5% compared to 2.1% for small beef herds. Preliminary seroprevalence in sheep (12.3%), goats (9.3%), pigs (0%) rats (9.7%) and mice (3.2%) using indirect immunofluorescence is reported.