Non-random distribution of individual genetic diversity along an environmental gradient

Improving our knowledge of the links between ecology and evolution is especially critical in the actual context of global rapid environmental changes. A critical step in that direction is to quantify how variation in ecological factors linked to habitat modifications might shape observed levels of genetic variability in wild populations. Still, little is known on the factors affecting levels and distribution of genetic diversity at the individual level, despite its vital underlying role in evolutionary processes. In this study, we assessed the effects of habitat quality on population structure and individual genetic diversity of tree swallows (Tachycineta bicolor) breeding along a gradient of agricultural intensification in southern Québec, Canada. Using a landscape genetics approach, we found that individual genetic diversity was greater in poorer quality habitats. This counter-intuitive result was partly explained by the settlement patterns of tree swallows across the landscape. Individuals of higher genetic diversity arrived earlier on their breeding grounds and settled in the first available habitats, which correspond to intensive cultures. Our results highlight the importance of investigating the effects of environmental variability on individual genetic diversity, and of integrating information on landscape structure when conducting such studies.     

Effects of phorbol dibutyrate on M currents and M current inhibition in bullfrog sympathetic neurons

1. Effects of bath-applied phorbol dibutyrate (PDBu) on M currents (IM) and on the inhibition of IM by muscarine and luteinizing hormone-releasing hormone (LHRH) were recorded in voltage-clamped bullfrog lumbar sympathetic ganglion cells. 2. PDBu (0.1-30 microM) produced a slowly developing, irreversible and partial (less than or equal to 60%) inhibition of IM. This effect was not replicated by 4-alpha-phorbol or by vehicle. 3. After treatment with PDBu, residual IM showed a reduced sensitivity to inhibition by muscarine or LHRH but not by Ba2+. The reduced response to muscarine appeared to result from a 10-fold shift in the concentration dependence for inhibition. 4. PDBu did not clearly reproduce the ability of muscarine to inhibit the slow, Ca-activated K current IAHP or to increase the leak conductance at hyperpolarized potentials. The latter effect of muscarine was enhanced, rather than inhibited, by PDBu. 5. IM and IAHP were not inhibited by 1 mM dibutyryl cyclic AMP or by 20 microM forskolin. 6. It is concluded that activation of protein kinase C, but not protein kinase A, partly replicates the effect of muscarine on frog sympathetic neurons.     

Comparative incidence of reticuloendothelial tumors in C57BL mice after exposure to tritiated water

A total of 2,377 C 57 Bl/6M mice were assigned to control groups and experimental groups exposed to tritiated water administered as a pulse injection or in drinking water, at a dose of 1.0 microCi per injection or per ml of drinking water. Weanlings were observed for the duration of life span. Data analysis was based on two coefficient estimates (1) individual carcinogenic induction coefficient and (2) specific tumorigenic induction coefficient. The carcinogenic potency of tritium was found to be dual in nature in enhancing the absolute induction of lymphocytic lymphomas in both sexes as well as their relative induction in competition with reticulo-endothelial tumors of other types.     

Purification of human plasma fibronectin by double affinity chromatography on gelatin and heparin-Trisacryl

In this work the human plasma fibronectin was purified by affinity chromatography using a tandem column system. The first affinity column was filled with gelatin-Trisacryl whereas the second one contained heparin-Trisacryl. This double affinity chromatography demonstrated its high efficiency in term of purity and yield. Several analytical methods (electrophoresis, immunoelectrophoresis, F.P.L.C. and adhesion assay on cultured eucaryotic cells) evidenced in fact the high purity of the preparation as well as its biological behaviour in term of cell adhesion and spreading. The performances of the sorbents used facilitate the scaling up when large quantities of FNP are needed.     

Thrombopoietic activity induced by blood withdrawal and administration of antithrombocyte serum in nephrectomized rats. Role of kidneys in the production of thrombopoietin

The thrombopoietic serum activity was examined in rats during thrombocytopenia produced by bleeding or after treatment with antithrombocyte serum (ATS). 6 hours after both treatments the thrombopoietic activity of the serum, i.e. its content of thrombopoietin, is increased. After the ATS treatment of nephrectomized animals a similar increase of thrombopoietic activity as in normal animals could be achieved. In contrast to that, no similar increase of thrombopoietic activity was observed in nephrectomized animals after blood loss. According to the results of the authors the increase of thrombopoietic activity produced by different stimuli can be attributed to different mechanisms.