Variable demography in relation to germination time in the annual plant Tagetes micrantha Cav. (Asteraceae)

This study tests whether variability in a life history trait such as emergence time has ecological and evolutionary significance in seasonal environments due to their relationship with fitness components. The population dynamics of nine different cohorts of seedlings emergence were analyzed in a natural population of the annual herb Tagetes micrantha Cav. (Asteraceae). Temporal variation in seedling emergence was related to the pattern of precipitation, while spatial variation could be related to topographical heterogeneity. Plants that emerged at the beginning of the season (early germination) had lower probabilities of survivorship than those that emerged at the end of the season (late germination). In contrast, plants that emerged early had, on average, higher fecundity than those that emerged late. The net result of these contrasting patterns of survival and fecundity constitute a life history trade-off in T. micrantha.     

Calpains and Delayed Calcium Deregulation in Excitotoxicity

Overactivation of glutamate receptors results in neurodegeneration in a variety of brain pathologies, including ischemia, epilepsy, traumatic brain injury and slow-progressing neurodegenerative disorders. In all these pathologies, it is well accepted that the calcium-dependent cysteine proteases calpains are key players in the mechanisms of neuronal cell death. Many research groups have been actively pursuing to establish a link between the deregulation of intracellular Ca²⁺ homeostasis associated with excitotoxicity and calpain activity. It is well established that these two events are connected and interact synergistically to promote neurodegeneration, but whether calpain activity depends on or contributes to Ca²⁺ deregulation is still under debate.     

Centrifugation of 2-cell mouse ova: cytoplasm stratification and recovery

Summary Two-cell mouse ova, which were centrifuged for l h at 70 000–90 000xg, showed a precise stratification of the cytoplasm and an elongation of the nucleus. The ova were fixed at different times and observed by light and electron microscopy using cytochemical methods and detergent extractions. Within 40 min after centrifugation the normal-looking morphology was recovered except for the persisting lipid caps at the centripetal poles of the blastomeres. Cleavage, compaction and blastulation were not prevented by centrifugation. Treatments with colcemid or cytochalasin D delayed but did not impair recovery. These results suggest that a resilient cytoskeletal structure may be involved in this kind of embryonic regulation.     

Effect of suramin on the human pathogen Candida albicans: implications on the fungal development and virulence

Candida albicans is an opportunistic pathogen that is of growing medical importance because it causes superficial, mucosal and systemic infections in susceptible individuals. Here, the effect of suramin, a polysulfonated naphthylurea derivative, on C. albicans development and virulence was evaluated. Firstly, it was demonstrated that suramin (500 microM) arrested its growth, showing a fungicidal action dependent on cell number. Suramin treatment caused profound changes in the yeast ultrastructure as shown by transmission electron microscopy. The more important changes were the enlargement of the fungi cytoplasmic vacuoles, the appearance of yeasts with an empty cytoplasm resembling ghost cells and a reduction in cell wall thickness. Suramin also blocked the transformation of yeast cells to the germ-tube and the interaction between C. albicans and epithelial cells. In order to ascertain that the action of suramin on C. albicans growth is a general feature instead of being strain-specific, the effects of suramin on 14 oral clinical strains isolated from healthy children and HIV-positive infants were analyzed. Interestingly, the strains of C. albicans isolated from HIV-positive patients were more resistant to suramin than strains isolated from healthy patients. Altogether, the results produced here show that suramin interfered with essential fungal processes, such as growth, differentiation and interaction with host cells.     

Geographical variation in cloacal microflora and bacterial antibiotic resistance in a threatened avian scavenger in relation to diet and livestock farming practices

The impact on wildlife health of the increase in the use of antimicrobial agents with the intensification of livestock production remains unknown. The composition, richness and prevalence of cloacal microflora as well as bacterial resistance to antibiotics in nestlings and full-grown Egyptian vultures Neophron percnopterus were assessed in four areas of Spain in which the degree of farming intensification differs. Differences in diet composition, especially the role of stabled livestock carrion, appear to govern the similarities of bacterial flora composition among continental populations, while the insular vulture population (Fuerteventura, Canary Islands) showed differences attributed to isolation. Evidence of a positive relationship between the consumption of stabled livestock carrion and bacterial resistance to multiple antibiotics was found. Bacterial resistance was high for semisynthetic penicillins and enrofloxacin, especially in the area with the most intensive stabled livestock production. The pattern of antibiotic resistance was similar for the different bacterial species within each area. Bacterial resistance to antibiotics may be determined by resistance of bacteria present in the livestock meat remains that constituted the food of this species, as indicated by the fact that resistance to each antibiotic was correlated in Escherichia coli isolated from swine carrion and Egyptian vulture nestlings. In addition, resistance in normal faecal bacteria (present in the microflora of both livestock and vultures) was higher than in Staphylococcus epidermidis, a species indicator of the transient flora acquired presumably through the consumption of wild rabbits. Potential negative effects of the use of antimicrobials in livestock farming included the direct ingestion of these drug residues and the effects of bacterial antibiotic resistance on the health of scavengers.     

Human and rat monoamine oxidase-A are differentially inhibited by (S)-4-alkylthioamphetamine derivatives: insights from molecular modeling studies

Four enantiomerically pure (S)-4-alkylthioamphetamine derivatives were evaluated as monoamine oxidase (MAO) inhibitors using the human and rat isoforms of the enzyme. Molecular dockings were performed in order to gain insights regarding the binding mode of these inhibitors. All compounds were potent and selective MAO-A inhibitors although different rank orders of potencies were observed against the enzymes from different species. This behavior can be rationalized on the basis of different binding modes to each enzyme, as determined in silico. These findings further support the concept that MAO inhibitory activity of novel compounds, determined with enzymes from diverse mammalian species, should be considered with caution if human MAO is the final target to be addressed.     

The ingestion of a Nectandra membranacea extract changes the bioavailability of technetium-99m radiobiocomplex in rat organs

The radiobiocomplexes labeled with technetium-99m (Tc-99m) have been widely used in nuclear medicine in single photon emission computed tomography and in basic research. The aim of this study was to assess the influence of a Nectandra membranacea extract on the bioavailability of the sodium pertechnetate (Na(99m)TcO(4)) radiobiocomplex in rat organs. The animals were treated with a N. membranacea extract (30 mg/ ml), for 6 days. Na(99m)TcO(4) was injected, the organs were isolated and weighed, and the radioactivity was determined in each organ (%ATI/organ). The %ATI/organ was divided by the mass of each organ to calculate the %ATI/g. A significant increase of the %ATI/organ of Na(99m)TcO(4) was observed in muscle and thyroid as well as in the %ATI/g in the heart, kidney and thyroid. These findings could result from the interaction between components of the plant extract and the radiobiocomplex which may influence the uptake Na(99m)TcO(4) in rat organs. Therefore, precaution is suggested in the interpretation of nuclear medicine results in patients using this herb.     

Oxygenase domain of Drosophila melanogaster nitric oxide synthase: unique kinetic parameters enable a more efficient NO release

Although nitric oxide (NO) is important for cell signaling and nonspecific immunity in the fruit fly Drosophila melanogaster, little is known about its single NO synthase (dNOS). We expressed the oxygenase domain of dNOS (dNOSoxy), characterized its spectroscopic, kinetic, and catalytic properties, and interpreted them in light of a global kinetic model for NO synthesis. Single turnover reactions with ferrous dNOSoxy showed it could convert Arg to N'omega-hydroxy-l-arginine (NOHA), or NOHA to citrulline and NO, when it was given 6R-tetrahydrobiopterin and O2. The dNOSoxy catalyzed Arg hydroxylation and NOHA oxidation at rates that matched or exceeded the rates catalyzed by the three mammalian NOSoxy enzymes. Consecutive heme-dioxy, ferric heme-NO, and ferric heme species were observed in the NOHA reaction of dNOSoxy, indicating that its catalytic mechanism is the same as in the mammalian NOS. However, NO dissociation from dNOSoxy was 4 to 9 times faster than that from the mammalian NOS enzymes. In contrast, the dNOSoxy ferrous heme-NO complex was relatively unreactive toward O2 and in this way was equivalent to the mammalian neuronal NOS. Our data show that dNOSoxy has unique settings for the kinetic parameters that determine its NO synthesis. Computer simulations reveal that these unique settings should enable dNOS to be a more efficient and active NO synthase than the mammalian NOS enzymes, which may allow it to function more broadly in cell signaling and immune functions in the fruit fly.