Variable nutrient stoichiometry (carbon:nitrogen:phosphorus) across trophic levels determines community and ecosystem properties in an oligotrophic mangrove system.

Our study investigated the carbon:nitrogen:phosphorus (C:N:P) stoichiometry of mangrove island of the Mesoamerican Barrier Reef (Twin Cays, Belize). The C:N:P of abiotic and biotic components of this oligotrophic ecosystem was measured and served to build networks of nutrient flows for three distinct mangrove forest zones (tall seaward fringing forest, inland dwarf forests and a transitional zone). Between forest zones, the stoichiometry of primary producers, heterotrophs and abiotic components did not change significantly, but there was a significant difference in C:N:P, and C, N, and P biomass, between the functional groups mangrove trees, other primary producers, heterotrophs, and abiotic components. C:N:P decreased with increasing trophic level. Nutrient recycling in the food webs was highest for P, and high transfer efficiencies between trophic levels of P and N also indicated an overall shortage of these nutrients when compared to C. Heterotrophs were sometimes, but not always, limited by the same nutrient as the primary producers. Mangrove trees and the primary tree consumers were P limited, whereas the invertebrates consuming leaf litter and detritus were N limited. Most compartments were limited by P or N (not by C), and the relative depletion rate of food sources was fastest for P. P transfers thus constituted a bottleneck of nutrient transfer on Twin Cays. This is the first comprehensive ecosystem study of nutrient transfers in a mangrove ecosystem, illustrating some mechanisms (e.g. recycling rates, transfer efficiencies) which oligotrophic systems use in order to build up biomass and food webs spanning various trophic levels.

[Epidural hematoma in a child with hemophilia: diagnostic difficulties]. / Hématome épidural chez l'enfant hémophile: difficultés diagnostiques.

UNLABELLED: Spinal epidural hematoma is an uncommon complication in hemophilia. CASE REPORTS: The cases of an extensive epidural hematoma in two boys with severe hemophilia are reported. CONCLUSION: Acute onset of severe neck pain or backache leads to the diagnosis of epidural hematoma in children with hemophilia, even in the absence of neurologic symptoms. Early diagnosis is important and relies on magnetic resonance imaging. Replacement therapy is mandatory and must be prescribed before neuroradiologic imaging. Generally, children have a good neurologic outcome.

Efficacy of essential oil of Ocimum basilicum L. and O. gratissimum L. applied as an insecticidal fumigant and powder to control Callosobruchus maculatus (Fab.)

Essential oils from sweet basil, Ocimum basilicum, and African basil, O. gratissimum, (Labiatae) grown in Guinea were obtained by steam distillation. Following exposure of newly emerged adult beetles (Callosobruchus maculatus) to 12h of fumigation using pure essential oils at a dose of 25&mgr;l/vial, 80% mortality was recorded for O. basilicum, 70% for O. gratissimum and 0% in the control. A significant difference was observed between the responses of males and females with males exhibiting greater sensitivity. When 1g of aromatized powder was applied to adults, a 50% lethal concentration at 48h was found to be 65&mgr;l/g for O. basilicum and 116&mgr;l/g of O. gratissimum oils. The essential oils from the two plant species exhibited a significant effect both on the egg hatch rate and on the emergence of adults. The egg hatch rate was reduced to 3% with O. basilicum and 15% with O. gratissimum using an essential oil concentration of 30&mgr;l, whereas the egg hatch rate for the control was 95%. When compared with the control (97%), adult emergence dropped to 0% with O. basilicum and to 4% with O. gratissimum. Storage bioassays were run to assess the long-term effect of powders aromatized with essential oils of Ocimum. Complete protection was observed over 3 months starting at a dose of 400&mgr;l in the case of both oils. From a germination test, it was concluded that aromatized powders have no significant effect on the seed germination rate. After 5d, a rate of 88% germination was seen in seeds treated with aromatized powder and protected from insects, compared with 97% for untreated seeds that were not exposed to insects.

Multielemental analysis of human fetal tissues using inductively coupled plasma-mass spectrometry.

Inductively coupled plasma-mass spectrometry (ICP-MS) was used to study the distribution of 26 major and trace elements in six tissues from 21 human fetuses aged 16-22 wk. Brain, lung, spleen, kidney, heart, and liver were analyzed following a microwave oven digestion step carried out according to clean techniques designed for ultratrace metal analyses. Precision and accuracy controls were conducted using standard reference material #1577b Bovine Liver. Significant differences among tissues were found for most of the elements. Essential trace elements seem to be increasingly retained as fetal tissues mature and become physiologically functional. The ranges of concentrations measured in fetal tissues at this stage of development are generally lower and much narrower than in adult tissues. The age of the fetus, which is not given in most studies, as well as the different techniques and levels of quality assurance could be responsible for the discrepancies in the trace metal concentrations reported here and in the literature. Intratissue homogeneity was also assessed in five human fetal brains. Frontal, occipital, parietal and temporal lobes, striatum, hippocampus, and thalamus were isolated and analyzed separately. No significant differences were found in the distribution of any of the elements at this stage of development. Because of the relatively narrow ranges of concentrations found for most elements, we believe that the results presented in this study represent the inorganic fingerprint of the main tissues of normal fetuses at midpregnancy for the Greater Montreal area.

Comparisons between the inorganic content of healthy and hypertensive rat tissues by inductively coupled plasma-mass spectrometry.

The inorganic contents of bone, brain, erythrocyte, heart, kidney cortex, kidney medulla, liver, lung, muscle and plasma from spontaneously hypertensive rats were compared with those of the same tissues from healthy Sprague-Dawley rats. A general inductively coupled plasma-mass spectrometry method developed for multi-element determinations of most of the elements present in biological tissues was used. Variations were found not only for major elements, as expected, but also for many trace elements in several tissues.

Complete analysis of the trace elements of the kidney.

The distribution of trace elements in kidney cortex and medulla and in their subcellular fractions was studied by inductively coupled plasma mass spectrometry (ICP-MS). This technology allows the analysis of almost all the elements of the periodic table, along with their isotopes, in the same experiment. Acid digestion of the tissue (samples) was required before ICP-MS elemental analysis. Mineralization in 8 N nitric acid for 2 min in a Parr microwave acid digestion bomb, inside a regular microwave oven working at medium power, gave good sensitivity and reproducible results. Trace element determinations could be precisely performed, despite the presence of a considerable amount of organic matter. Cortex/plasma and medulla/plasma inorganic ratios were taken as indicators of the inorganic bioaccumulation. The highest enrichment factors of elements found in the cortex were Mn greater than Co greater than Tl greater than Zn greater than Rb greater than Mo greater than Cu and the highest element enrichments of the medulla were Tl greater than Mn greater than Co greater than Rb greater than Zn greater than Bi greater than Mo greater than Ni greater than Cu. Subcellular fragmentation of the kidney cortex and medulla indicated that the majority of the trace elements was located in the cytosolic fraction. The membrane fraction of the medulla contained significant amounts of Hg and Al: 120.7 and 32.0 mg/g protein, respectively. Cu and Zn were the most abundant trace elements found in the brush border membrane from the cortex: 120.7 and 68.2 mg/g protein, respectively. These quantities are largely in excess of what is bound, for example, to alkaline phosphatase.(ABSTRACT TRUNCATED AT 250 WORDS)

The cytotoxic effects of cadmium chloride and mercuric chloride mixtures in rat primary hepatocyte cultures.

The toxic effects of Cd and Hg mixtures were studied using primary monolayer cultures of rat hepatocytes. Cytotoxicity was assessed by measuring the release of lactic dehydrogenase from the cells. Cytotoxic and non-cytotoxic metal levels were used. At the higher exposure concentrations (0.2 micrograms Cd.ml-1 and 2.0 micrograms Hg.ml-1), Cd was very toxic to hepatocytes whereas Hg was only marginally toxic. The combination of Cd and Hg was more toxic than predicted by summation of the individual metal toxicities. The incorporation of [35S]cysteine into protein of the cytosol and insoluble cell fraction was increased in response to Cd or Hg exposure and was directly related to cell 35S accumulation. Combinations of Cd and Hg significantly increased the proportion of total 35S which was incorporated in cell protein, an effect that was attributed to the accumulation of protein in the insoluble cell fraction. Cd uptake by hepatocytes was related to exposure concentration but was lower when Hg was also present in the incubation medium. Gel chromatography of the cytosol from Cd-exposed cells showed 3 Cd containing fractions which corresponded to the elution positions of high Mr proteins, metallothionein (MT) and low Mr molecules. When hepatocytes were exposed to Hg in combination with Cd, the MT-like fraction was no longer evident and Cd in the low Mr fraction was greatly reduced. Regardless of the presence or absence of Cd in the exposure medium, 98% of cytosol Hg in Hg-exposed cells was found to elute after the low Mr fraction, at a position equivalent to inorganic salts. This indicates that the enhanced cytotoxicity of Cd and Hg may be related to a decrease in the MT-like protein in the cytosol and not due to a direct competitive binding interaction in relation to the protein.

Structure and conformation of glucocorticoids.

The approaches currently available for determining the structure and conformation of glucocorticoids are reviewed. We discuss the optimization of steroid geometry based on the relative molecular energy calculated by a Westheimer equation. This method permits an extensive description of steroid molecules in a state free of external constraints and which can be assumed to correspond to the minimum internal energy. The structures, conformations, surface areas, and volumes of fifteen steroid molecules that interact with the glucocorticoid receptor have been studied. The basic structure of the A ring is a 1 alpha,2 beta-half-chair, whatever the substitutions. Rings B and C are semi-rigid chairs virtually uninfluenced by substituent groups. In contrast, the shape of the D ring depends on the nature and environment of the substituents. As to the fundamental conformation of the side chain, the steroids fall into two categories, depending on the pressure of a 17-hydroxyl group. For a given molecule, the energy changes associated with conformations of the side chain other than that corresponding to the minimum energy have also been explored. The hypothesis is formulated that receptor binding requires a particular conformation of the side chain. Finally, the overall shape of the molecule can be influenced by the summation of minor but numerous changes brought about by various substitutions, such as 11 beta-hydroxyl, which increases the convexity of the molecule. These investigations should help in elucidating structure-activity relationships for glucocorticoids. They may improve our knowledge of the interaction between these hormones and their receptor and of the molecular mechanism of glucocorticoid action.