On the organogenesis of Seuratum cadarachense Desportes, 1947 (Nematoda Seuratoidea) and the cellular reactions of the intermediate insect host Locusta migratoria (author's transl)]

The adaptation of primitive heteroxenous nematodes, parasites of vertebrates, to the intermediate host, is detailed by studying the organogenesis of the first larval stages of the Seuratoid nematode Seuratum cadarachense and an histological approach of the cellular reactions caused by the penetration and the development of the parasite in the insect Locusta migratoria. The larval organization of Seuratum at hatching is similar to that of Subuluridae and characterized by a large number of initial cells: among them, eight cells alined in a row forming the intestinal primordia, and two mesenchymal cells. In Seuratum, as in Subulurid in general, the first larval stage has a slow development. The larval migration occurs in the wall of the mesenteron. Hemocytic capsules are observed in the hemocoel in contact with the muscle fibers of the mesenteron. Some of them show necrotic features which bear witness to an imperfect adaptation of the nematode to the intermediate host.     

Temperature and nutrient effects on the relative importance of brown and green pathways for stream ecosystem functioning: A mesocosm approach

1. In addition to global warming, aquatic ecosystems are currently facing multiple global changes among which include changes in nitrogen (N) loads. While several studies have investigated both temperature and N impacts on aquatic ecosystems independently, knowledge on their interactive effects remains scarce.
2. In forested headwater streams, decomposition of leaf litter represents the main process ensuring the transfer of nutrients and energy to higher trophic levels, followed by autochthonous primary production, mainly ensured by phototrophic biofilms. The main aim of this study was to disentangle the independent and combined effects of temperature increase and nutrient availability on the relative importance of brown and green processes involved in stream functioning. We hypothesised that water temperature and nutrients would lead to a general increase in leaf-litter decomposition and primary production, but that the intensity of these effects would be largely modulated by competitive interactions arising between microorganisms as well as by the top-down control of microorganisms by macro-invertebrates. Macro-invertebrates would, in turn, be bottom-up controlled by microbial resources quality.
3. To test these hypotheses, we conducted a 56-day experiment in artificial streams containing leaf litter, microbial decomposers and biofilm inoculum, and an assemblage of macro-invertebrates. Two water inorganic N:phosphorus (P) ratios (33 and 100, molar ratios) and two temperatures (ambient, +2°C) were manipulated, each treatment being replicated three times. Fungal and biofilm growth as well as leaf-litter decomposition and primary production were quantified. Top-down impacts of invertebrate primary consumers on brown and green compartments were evaluated using exclosures while bottom-up control was evaluated through the measurement of resource stoichiometry and fatty acid profiles, as well as quantification of macro-invertebrate growth and survival.
4. Contrary to expectations, microbial decomposition was not significantly stimulated by nutrient or temperature manipulations, while primary production was only improved under ambient temperature. In the + 2°C treatment with high N:P, greater biofilm biomass was associated with lower fungal development, which indicates competition for nutrients in these conditions. Temperature increased macro-invertebrate growth and leaf-litter consumption, but this effect was independent of any improvement of basal resource quality, suggesting that temperature mediated changes in consumer metabolism and activity was the main mechanism involved.
5. Most of our hypotheses that were based on simplified laboratory observations have been rejected in our semi-controlled mesocosms. Our study suggests that the complexity of biological communities might greatly affect the response of ecosystems to multiple stressors, and that interactions between organisms must be explicitly taken into account when investigating the impacts of global change on ecosystem functioning.

     

Human and simian immunodeficiency viruses: virus-receptor interactions

The major cellular receptor for the primate immunodeficiency viruses is the CD4 molecule. As well as mediating virion attachment to the cell surface, CD4 is thought to activate the viral fusion pathway. CD4 is not, however, sufficient for viral entry; other molecules are probably involved, and in certain circumstances these may substitute for CD4. Viral tropism and cytopathogenicity are also influenced by receptor interactions.     

Bean tumbling as a control measure for the common bean weevil, Acanthoscelides obtectus

Recognizing that it takes Acanthoscelides obtectus (Say)(Coleoptera: Bruchidae) larvae over 24 h to bore into a dry red kidney bean (Phaseolus vulgaris L.) and that boring can occur only at particular sites where a bean abuts some other surface, we postulated that this pest might be controlled by periodic tumbling of beans so as to place initiated holes out of register with requisite touching surfaces. Larvae repeatedly forced to initiate holes might die of exhaustion, if not smashed by tumbling beans. Indeed, brief daily tumbling of beans held in half-filled jars, buckets, and gunny sacks reduced A. obtectus populations by 97% relative to stationary controls. We recommend that small lots of beans can be protected indefinitely from the bean weevil when stored in <75% filled cylinders rolled ca 1 circumference every morning and evening. This control method should be immediately useful, particularly among subsistence families, since the only external input is knowledge. Also, this control principle might be broadly applicable to other bean and grain pests having strict spatial and temporal requirements for seed penetration.     

Identification of the Cationic Amino Acid Transporter (System y+) of the Rat Blood-Brain Barrier

Abstract: Cationic amino acids are transported from blood into brain by a saturable carrier at the blood-brain barrier (BBB). The transport properties of this carrier were examined in the rat using an in situ brain perfusion technique. Influx into brain via this system was found to be sodium independent and followed Michaelis-Men-ten kinetics with half-saturation constants (K_m) of 50–100 μM and maximal transport rates of 22–26 nmol/min/g for L-lysine, L-arginine, and L-ornithine. The kinetic properties matched that of System y⁺, the sodium-independent cationic amino acid transporter, the cDNA for which has been cloned from the mouse. To determine if the cloned receptor is expressed at the BBB, we assayed RNA from rat cerebral microvessels and choroid plexus for the presence of the cloned transporter mRNA by RNase protection. The mRNA was present in both cerebral microvessels and choroid plexus and was enriched in microvessels 38-fold as compared with whole brain. The results indicate that System y⁺ is present at the BBB and that its mRNA is more densely expressed at cerebral microvessels than in whole brain.