African rainforest vegetation and rumen microbes: Phenolic compounds and nutrients as correlates of digestibility

Summary In order to refine hypotheses concerning food selection by generalist herbivores with ruminant-like digestive systems the chemical correlates of digestibility in such a system have been studied. Samples of seeds and leaves from tree species growing in two African rainforests (Douala-Edea Forest Reserve, Cameroon, and Kibale Forest, Uganda) were assayed for phenolic content and nutrient content, and in-vitro dry matter digestibility was analysed utilizing rumen inoculum from a fistulated steer. Both forests studied carry populations of colobine monkeys with ruminant like digestive tracts. Content of condensed tannins and, to a lesser extent of total phenolics, was found to be negatively correlated with digestibility; a result that may be attributable to the inctivation of microbial enzymes by tannins. The negative association of tannin content and digestibility was stronger in material from the Cameroon site, the vegetation of which contains considerably higher concentrations of tannins and is generally less digestible than that from the Ugandan site. Gross energy content of leaves was also found to be persistently negatively correlated with digestibility. The interpretation of this result is uncertain; however, gross energy yield may well reflect variation in content of cell wall polymers, especially lignin. For the complete set of data, tannins presented the strongest observed correlation with digestibility, but when only mature leaves were considered the relationship with gross energy appeared stronger. No strong association was noted between high nutrient content and high digestibility. This was attributed to the fact that the assay measured the extent of digestion under standardised and very favourable conditions of nutrient supply. The results obtained are discussed in relation to observations of leaf and seed selection preferences of Colobus spp. in these two forests.Publication 19-013 of the Wisconsin Regional Primate Research Center     

S1P-receptors in PC12 and transfected HEK293 cells: molecular targets of hypotensive imidazoline I(1) receptor ligands

The present study aimed at elucidating the molecular identity of the proposed “I₁-imidazoline receptors”, i.e. non-adrenoceptor recognition sites via which the centrally acting imidazolines clonidine and moxonidine mediate a major part of their effects. In radioligand binding experiments with [³H]clonidine and [³H]lysophosphatidic acid on intact, ₂-adrenoceptor-deficient PC12 cells, moxonidine, clonidine, lysophosphatidic acid and sphingosine-1-phosphate (S1P) competed for the specific binding sites of both radioligands with similar affinities. RNA interference with the rat S1P₁-, S1P₂- or S1P₃-receptor abolished specific [³H]lysophosphatidic acid binding. [³H]Clonidine binding was markedly decreased by siRNA targeting S1P₁- and S1P₃-receptors but not by siRNA against S1P₂-receptors. Finally, in HEK293 cells transiently expressing human S1P₃-receptors, sphingosine-1-phosphate, clonidine and moxonidine induced increases in intracellular calcium concentration, moxonidine being more potent than clonidine; this is in agreement with the known properties of the “I₁-imidazoline receptors”.

The present results indicate that the “I₁-imidazoline receptors” mediating effects of clonidine and moxonidine in PC12 and the transfected HEK293 cells belong to the S1P-receptor family; in particular, the data obtained in PC12 cells suggest that the I₁ imidazoline receptors represent a mixture of S1P₁- and S1P₃-receptors and/or hetero-dimers of both.     

Friendly food for fitter flies? – Influence of dietary microbial species on food choice and parasitoid resistance in Drosophila

Nutrition fuels any activity performed by an organism and has been shown to affect its ability to withstand pathogens and parasites. Furthermore, animals over a wide range of taxa have been shown to exhibit a choice of foods and nutrients that are beneficial to their fitness. Saprophagous animals most often feed on microorganisms growing on dead organic matter rather than the organic matter itself. Various yeast species play an important role in both larval and adult nutrition of saprophagous Drosophila melanogaster. We hypothesised the dietary microbial species to affect life‐history traits of D. melanogaster, including the ability to fend offparasitoids, and larvae to prefer to devour those yeast species beneficial to their development and immunocompetence. Particular yeast species known to be associated with D. melanogaster could be shown to have a substantial influence on various larval and adult fitness traits including the ability to encapsulate eggs of the parasitoid wasp Asobara tabida. It also turned out that larvae chose to devour those yeast species which supported their ability to encapsulate parasitoid eggs. Which yeast species was preferred and had a beneficial impact on encapsulation ability, was subject to inter‐individual variability within the investigated population, hinting at the existence of an adaptive heritable variability regarding individual choice and salubriousness of food. The results suggest that the dietary microbial species of saprophagous insects may influence the resistance against parasitoid attacks and thus the outcome of the interaction between a saprophagous host and its parasitoids.     

Model diagnosis for parametric regression in high-dimensional spaces

We study tools for checking the validity of a parametric regressionmodel. When the dimension of the regressors is large, many ofthe existing tests face the curse of dimensionality or requiresome ordering of the data. Our tests are based on the residualempirical process marked by proper functions of the regressors.They are able to detect local alternatives converging to thenull at parametric rates. Parametric and nonparametric alternativesare considered. In the latter case, through a proper principalcomponent decomposition, we are able to derive smooth directionaltests which are asymptotically distribution-free under the nullmodel. The new tests take into account precisely the ‘geometryof the model’. A simulation study is carried through andan application to a real dataset is illustrated.     

Synthesis, characterization, DFT studies and DNA binding of mixed platinum (II) complexes containing quinoxaline and 1,2-dithiolate ligands

The complexes Pt(pq)Cl2(1) and Pt(pq)(bdt) (2) (where pq = 2-(2'pyridyl)quinoxaline and bdt=benzene-1,2-dithiolate) have been synthesized and fully characterized by UV-visible (UV-Vis), Fourier Transformer Infrared Spectra (FTIR), 1 and 2D NMR and cyclic voltammetry (CV). Interactions of the tested systems (the aforementioned complexes 1 and 2) and the free ligands pq and bdt with double stranded calf thymus DNA (CT-DNA) were studied by UV-spectrophotometric (melting curves) and circular dichroism (CD) measurements. The results suggest that both complexes 1 and 2, are able to form adducts with DNA and to distort the double helix by changing the base stacking. Complex 2 forms stronger adducts to CT-DNA than complex 1 and this is probably due to the substitution of the chlorine atoms of 1 by the 1,2-dithiolate ligand (bdt) in 2. The latter induces an extensive distortion in the planarity of 2 as density functional theory (DFT) calculations reveal. Besides, the light absorbing complex 2 possess intense mixed metal ligand to ligand charge transfer (MM'LLCT) transition in the visible region of the spectrum and could act as photoluminescent metal-based probe for the study of DNA binding. Thus, the photocleavage of DNA by 2 has been studied by UV-Vis and CD spectra and monitored by agarose gel electrophoresis. Under our experimental conditions, it is unclear that complex 2 can photocleave DNA. Furthermore, the ability of 2 to inhibit proliferation of human tumor cell lines was tested and the results indicate some cytoxytic effect on the SF-286 cells.