Variations au cours de la journée de l'incorporation in vivo de la leucine tritiée dans les protéines du cervelet et du cerveau du jeune rat normal et hypothyroïdien

Summary In the normal and hypothyroid 6-day-old rat, the specific radioactivity (RSA) and the relative RSA (ratio of the RSA to the [³H] leucine concentration of the acido soluble phase) of the cerebral and cerebellar proteins, change during the day synchronally. They show a maximum at 15.00 h and a minimum at 03.00 h. At all stages studied, these values are significantly lower in the hypothyroid animals than in normal ones.     

Biological properties of synthetic Ser4-Arg8-oxytocin (Ile3-Ser4-Arginine vasopressin): Role of the residue No. 4 in the hormone-pressor receptor interaction

Résumé Les propriétés pharmacologiques de la Ser⁴-Arg⁸-ocytocine (Ser⁴-vasotocine) synthétique ont été étudiées. La substitution en position 4 de la glutamine par la sérine diminue considérablement l'activité pressique de la vasotocine, ce qui montre l'importance de cette position dans les interactions entre les hormones neurohypophysaires et le récepteur vasopressique.

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The authors are indebted to Dr.Albert Jöhl (Ciba-Geigy Laboratories) for a sample of synthetic Ser⁴-Arg⁸-oxytocin. They thank Mrs.Christine Gaullier for ther skilled technical assistance.     

Repopulation of thymus,spleen and bone-marrow of irradiated AKR mice injected with normal or irradiated bone-marrow cells

Résumé L'utilisation d'une race de souris (AKR/T1Ald) ne possédant que 38 chromosomes a permis de montrer que les cellules de moelle que l'on injecte à un individu irradié repeuplent directement la moelle, le thymus et la rate du receveur. Si le donneur est irradié, la pénétration des cellules n'est importante que dans la rate du receveur.

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Acknowledgements. This work was supported by grants from the Fonds de la Recherche scientifique fondamentale collective. The helpful assistance of Mr.G. Linden andG. Mattelin is gratefully acknowledged.     

Adaptive divergence in pigment composition promotes phytoplankton biodiversity

The dazzling diversity of the phytoplankton has puzzled biologists for decades. The puzzle has been enlarged rather than solved by the progressive discovery of new phototrophic microorganisms in the oceans, including picocyanobacteria, pico-eukaryotes, and bacteriochlorophyll-based and rhodopsin-based phototrophic bacteria. Physiological and genomic studies suggest that natural selection promotes niche differentiation among these phototrophic microorganisms, particularly with respect to their photosynthetic characteristics. We have analysed competition for light between two closely related picocyanobacteria of the Synechococcus group that we isolated from the Baltic Sea. One of these two has a red colour because it contains the pigment phycoerythrin, whereas the other is blue-green because it contains high contents of the pigment phycocyanin. Here we report theory and competition experiments that reveal stable coexistence of the two picocyanobacteria, owing to partitioning of the light spectrum. Further competition experiments with a third marine cyanobacterium, capable of adapting its pigment composition, show that this species persists by investing in the pigment that absorbs the colour not used by its competitors. These results demonstrate the adaptive significance of divergence in pigment composition of phototrophic microorganisms, which allows an efficient utilization of light energy and favours species coexistence.     

Physical performance and Darwinian fitness in lizards

Strong evidence for a genetic basis of variation in physical performance has accumulated. Considering one of the basic tenets of evolutionary physiology--that physical performance and darwinian fitness are tightly linked--one may expect phenotypes with exceptional physiological capacities to be promoted by natural selection. Why then does physical performance remain considerably variable in human and other animal populations? Our analysis of locomotor performance in the common lizard (Lacerta vivipara) demonstrates that initial endurance (running time to exhaustion measured at birth) is indeed highly heritable, but natural selection in favour of this trait can be unexpectedly weak. A manipulation of dietary conditions unravels a proximate mechanism explaining this pattern. Fully fed individuals experience a marked reversal of performance within only one month after birth: juveniles with low endurance catch up, whereas individuals with high endurance lose their advantage. In contrast, dietary restriction allows highly endurant neonates to retain their locomotor superiority as they age. Thus, the expression of a genetic predisposition to high physical performance strongly depends on the environment experienced early in life.     

Involvement of penaeidins in defense reactions of the shrimp Litopenaeus stylirostris to a pathogenic vibrio

The present study reports for the first time the involvement of an antimicrobial peptide in the defense reactions of a shrimp infected by a pathogenic Vibrio, Vibrio penaeicida. New members of the penaeidin family were characterized in the shrimp Litopenaeus stylirostris by RT-PCR and RACE-PCR from hemocyte total RNAs, and by mass spectrometry detection and immunolocalization of mature peptides in shrimp hemocytes. In infected shrimps, bacteria and penaeidin distribution colocalized in the gills and the lymphoid organ that represented the main infected sites. Moreover, the shrimp immune response to infection involved massive hemocyte recruitment to infection sites where released penaeidin may participate in the isolation and elimination of the bacteria, We show that the ability of the shrimps to circumvent shrimp infections is closely related to a recovery phase based on the hematopoietic process.Received 25 November 2003; received after revision 8 January 2004; accepted 21 January 2004     

Cortisone sensitive T-cells in Peyer's patches

Summary Pretreatment of donor lymphoid cells with cortisone has been shown to depress the T-cell subpopulation responsible for cellular proliferation in the GVH reaction. A quantitative assay as well as the histological criteria of the GVH reaction have been used in this study to demonstrate the presence of cortisone-sensitive T-cells within the Peyer's patches as well as in the spleen and mesenteric lymph nodes in the rat.This work was supported by a grant of the Délégation Générale à la Recherche Scientifique et Technique (No. 74-7-0619).     

The effect of oxine-5-sulphonic acid on the hepatic drug metabolism in the rat

Summary Oxine-5-sulphonic acid inhibits the metabolism of aminopyrine in the rat liver in vitro. The characteristics of this inhibition vary according to whether the oxidativeN-demethylation of the substrate is determined by the formation of the metabolite 4-aminoantipyrine or by the production of formaldehyde.