An assessment of time-dependent effects of lead exposure in algerian mice (Mus spretus) using different methodological approaches

Time-dependent effects of lead (Pb) toxicity were studied in Algerian mice (Mus spretus) treated with Pb acetate via drinking water (1 g Pb acetate/L) for different periods of exposure (15, 45, and 90 d). End points included the determination of hepatic Pb concentration and the assessment of some morphophysiological, biochemical and cytogenetical parameters. A control group receiving distilled water was also monitored for comparative purposes. Hepatic Pb accumulation increased with the time of exposure and was significantly higher in treated mice when compared to controls. In association with significant body mass loss in Pb-exposed mice, for 15 and 45 d, a significant increase in the relative spleen mass was observed after 45 d of intoxication. Pb-exposed mice also showed significant decreases in red blood cells, hematocrit, and mean corpuscular hemoglobin. On the contrary, changes in plasma transferases (aspartate aminotransferase and alanine aminotransferase) and hepatic superoxide dismutase activities did not reach statistical significance. A significant increase in the frequency of micronucleated polychromatic bone marrow erythrocytes was also found in the 90-d-exposed mice, compared to nontreated mice and the other exposed groups. Exposure to Pb acetate resulted also in a slight time-dependent decrease of the polychromatic-normochromatic ratio. These results support the concept that a long-term chronic exposure to Pb induced alterations upon some morphophysiological and genetic parameters in Algerian mice.     

An assessment of time-dependent effects of lead exposure in algerian mice (Mus spretus) using different methodological approaches

Time-dependent effects of lead (Pb) toxicity were studied in Algerian mice (Mus spretus) treated with Pb acetate via drinking water (1 g Pb acetate/L) for different periods of exposure (15, 45, and 90 d). End points included the determination of hepatic Pb concentration and the assessment of some morphophysiological, biochemical and cytogenetical parameters. A control group receiving distilled water was also monitored for comparative purposes. Hepatic Pb accumulation increased with the time of exposure and was significantly higher in treated mice when compared to controls. In association with significant body mass loss in Pb-exposed mice, for 15 and 45 d, a significant increase in the relative spleen mass was observed after 45 d of intoxication. Pb-exposed mice also showed significant decreases in red blood cells, hematocrit, and mean corpuscular hemoglobin. On the contrary, changes in plasma transferases (aspartate aminotransferase and alanine aminotransferase) and hepatic superoxide dismutase activities did not reach statistical significance. A significant increase in the frequency of micronucleated polychromatic bone marrow erythrocytes was also found in the 90-d-exposed mice, compared to nontreated mice and the other exposed groups. Exposure to Pb acetate resulted also in a slight time-dependent decrease of the polychromatic-normochromatic ratio. These results support the concept that a long-term chronic exposure to Pb induced alterations upon some morphophysiological and genetic paramaters in Algerian mice.     

Agmatine is transported into liver mitochondria by a specific electrophoretic mechanism

Agmatine, a divalent diamine with two positive charges at physiological pH, is transported into the matrix of liver mitochondria by an energy-dependent mechanism the driving force of which is DeltaPsi (electrical membrane potential). Although this process showed strict electrophoretic behaviour, qualitatively similar to that of polyamines, agmatine is most probably transported by a specific uniporter. Shared transport with polyamines by means of their transporter is excluded, as divalent putrescine and cadaverine are ineffective in inhibiting agmatine uptake. Indeed, the use of the electroneutral transporter of basic amino acids can also be discarded as ornithine, arginine and lysine are completely ineffective at inducing the inhibition of agmatine uptake. The involvement of the monoamine transporter or the existence of a leak pathway are also unlikely. Flux-voltage analysis and the determination of activation enthalpy, which is dependent upon the valence of agmatine, are consistent with the hypothesis that the mitochondrial agmatine transporter is a channel or a single-binding centre-gated pore. The transport of agmatine was non-competitively inhibited by propargylamines, in particular clorgilyne, that are known to be inhibitors of MAO (monoamine oxidase). However, agmatine is normally transported in mitoplasts, thus excluding the involvement of MAO in this process. The I2 imidazoline receptor, which binds agmatine to the mitochondrial membrane, can also be excluded as a possible transporter since its inhibitor, idazoxan, was ineffective at inducing the inhibition of agmatine uptake. Scatchard analysis of membrane binding revealed two types of binding site, S1 and S2, both with mono-co-ordination, and exhibiting high-capacity and low-affinity binding for agmatine compared with polyamines. Agmatine transport in liver mitochondria may be of physiological importance as an indirect regulatory system of cytochrome c oxidase activity and as an inducer mechanism of mitochondrial-mediated apoptosis.     

Germination of Geonoma brevispatha (Arecaceae) in laboratory and its relation to the palm spatial distribution in a swamp forest

Geonoma brevispatha is a clonal palm species commonly found as tussocks in swamp and riparian forests in SE Brazil, occurring in the very transition between flooded pits/channels and dry mounds. Aiming to verify whether the germination responses could explain the spatial pattern of the palm tussocks in swamp forests, we investigated the germination in relation to the main environmental factors to which the seeds are subjected in their natural habitat. The seeds are recalcitrant since germination percentage is reduced with loss of moisture content. Germination did not differ on moist filter paper, semi-immersion (water up to half of the seed diameter) or complete immersion (water up to double of the seed diameter). Seeds did not germinate when stored in a closed bottle with water (that is, under low oxygen concentration), but remained viable for up to 8 weeks under this condition. The capacity to germinate in water with minimum oxygen availability may be considered ecologically advantageous in a swamp habitat. On the other hand, the capacity to germinate in moist filter paper indicates that, in natural conditions, the seed can germinate, provided there is a critical minimum of water availability. We concluded that the germination responses per se are not enough to explain the palm tussocks spatial pattern, but they are very well tuned with the conditions of the transitional zone between channels/pits (ever flooded micro-sites) and mounds (well-drained micro-sites), in which the species occurs in the swamp forest.     

Zooplankton and ichthyoplankton communities in a temperate estuary: spatial and temporal patterns

Zooplankton and ichthyoplankton assemblages were studied fromJanuary 2003 to June 2004 in a temperate shallow estuary (Mondegoestuary, Portugal). Monthly sampling was performed at five stationsat high and low tides, with subsurface tows with 335 and 500µm mesh Bongo nets. Analysis of variance (ANOVA) showeda significant effect (P < 0.05) of the mesh size of the neton the abundance of main zooplankton groups. On average, theabundance of the 500 µm taxocenosis was 67 and 102 timeslower than the 335 µm taxocenosis at high and low tidesrespectively, especially in the south arm. More than 80 specieswere identified in the zooplankton samples. The upper reachesof northern arm are dominated by freshwater crustacean mesozooplanktonlike Acanthocyclops robustus and Diaptomus spp. and the cladoceransDaphnia, Ceriodaphnia and Bosmina, often being codominant. Inthe southern arm, the resident estuarine copepod Acartia tonsawas dominant, eventually being the most abundant taxon. Marinereaches of estuary are usually dominated by the marine calanoidcopepods Acartia clausi and Temora longicornis and the siphonophoresMuggiaea atlantica. Concerning the ichthyoplankton, this wasdominated by the larvae of estuarine resident species, mainlyPomatoschistus sp., and eggs of Engraulis encrasicolus. Theabundance of Pomatoschistus sp. larvae was positively correlatedwith water temperature. Statistical analysis (canonical correspondenceanalysis) used to determine the spatiotemporal structure ofthe zooplankton assemblages and its correlation with environmentalvariables showed that salinity and temperature were the mainfactors influencing the distribution of zooplankton. The resultsobtained also showed that abundance was strongly influencedby the hydrological circulation pattern and direct or indirecthuman impacts that occur in each arm of the estuary. This article was presented at Plankton Symposium III, held atFiguera da Foz, portugal, between 17 and 20 March 2005, underthe auspices of the University of Coimbra and the Universityof Aveiro, and coordinated by Mário Jorge Pereira andUlisses M. Azeiteiro.     

Migratory connectivity and temporal segregation of dunlin (Calidris alpina) in Portugal: evidence from morphology, ringing recoveries and mtDNA

Migratory connectivity plays an important role in conservation of long-distance migrant birds. Here, we study migratory links of dunlin (Calidris alpina), focusing on a stopover and wintering region (Portugal) where it is known that migration routes of dunlin from a broad geographic range (three subspecies) converge, and populations occur simultaneously or separated in time. We combine three methods (ringing recoveries, morphometrics and molecular genetics) to assess breeding origins and extent of temporal segregation of dunlin assemblages. Ringing recoveries show temporal separation of dunlin from different migration routes. Birds found in Portugal during August and September, migrating via Britain, reveal links to breeding areas in Iceland and Greenland. In October, a clear shift to more eastern migration routes occurs, with most Portuguese winter records from stopover sites along migration routes of populations from northern Scandinavia and Russia. Mitochondrial DNA (mtDNA) of Portuguese dunlin was compared with breeding populations. Spring and autumn migrants in Portugal corresponded to C. a. schinzii and C. a. arctica populations, while the Portuguese winter population clearly differs by including mtDNA haplotypes of C. a. alpina. For genetically sexed individuals, we found significant differences in morphology (bill and tarsus length) supporting the temporal separation of populations/subspecies revealed by recoveries and mtDNA. Our results give evidence for migratory connectivity of dunlin populations between geographic areas previously not considered connected. They confirm the existence of clear differences in breeding origin between birds in Portugal at different times of year. These results are important in the consideration of future long-term conservation plans.     

Structural insights into the interaction between prion protein and nucleic acid

The infectious agent of transmissible spongiform encephalopathies (TSE) is believed to comprise, at least in part, the prion protein (PrP). Other molecules can modulate the conversion of the normal PrP(C) into the pathological conformer (PrP(Sc)), but the identity and mechanisms of action of the key physiological factors remain unclear. PrP can bind to nucleic acids with relatively high affinity. Here, we report small-angle X-ray scattering (SAXS) and nuclear magnetic resonance spectroscopy measurements of the tight complex of PrP with an 18 bp DNA sequence. This double-stranded DNA sequence (E2DBS) binds with nanomolar affinity to the full-length recombinant mouse PrP. The SAXS data show that formation of the rPrP-DNA complex leads to larger values of the maximum dimension and radius of gyration. In addition, the SAXS studies reveal that the globular domain of PrP participates importantly in the formation of the complex. The changes in NMR HSQC spectra were clustered in two major regions: one in the disordered portion of the PrP and the other in the globular domain. Although interaction is mediated mainly through the PrP globular domain, the unstructured region is also recruited to the complex. This visualization of the complex provides insight into how oligonucleotides bind to PrP and opens new avenues to the design of compounds against prion diseases.     

Immunostimulatory nature of beta-glucans and baker's yeast in gnotobiotic Artemia challenge tests

The use of new preventive approaches such as immunostimulants to reduce stress and mortalities, to maintain good health of cultured organisms and to stimulate the non-specific defence mechanism, is becoming increasingly important in aquaculture. Yet detailed analysis reveals that in most experiments the validity of some conclusions with respect to the benefit of immunostimulation is still doubtful, especially in invertebrates. The use of standardized trials under controlled rearing conditions, complemented with fundamental research on defence mechanisms can provide unequivocal evidence for the beneficial effects of immunostimulants in reducing invertebrate susceptibility to diseases or infections. This study investigated the use of small amounts of baker's yeast Saccharomyces cerevisiae and glucan particles (obtained from baker's yeast) in gnotobiotic Artemia to overcome the pathogenicity of two organisms: Vibrio campbellii and V proteolyticus. Artemia supplemented with small quantities of a yeast strain presenting higher concentrations of beta-glucans or with glucan particles seemed to completely resist the detrimental effects of both pathogens. The higher amount and/or availability of beta-glucans in that yeast might play an essential role in such protection, as most probably glucans stimulate the immune response of the nauplii.     

Effects of Metarhizium anisopliae (Metsch.) Sorok. and Beauveria bassiana (Bals.) Vuill. on the predatory stinkbug Podisus nigrispinus (Dallas) (Hemiptera: Pentatomidae)

Entomopathogenic fungi and the predatory stinkbug Podisus nigrispinus (Dallas) can target simultaneously the same or different pests in agroecosystems. Topical contact during fungal dispersion or spraying, walking on plant surfaces and ingestion of contaminated prey are some of possible ways of interactions between fungi and the predatory stinkbug. The impact of three isolates of Metarhizium anisopliae (Metsch.) Sorok. (866, 1022 and 1189) and Beauveria bassiana (Bals.) Vuill. (604, 634 and 561) against nymphs and adults of P. nigrispinus was investigated under laboratory conditions. M. anisopliae caused higher mortality compared to B. bassiana either by topical application or by dry residue on cotton leaves. Topic contact with both fungi caused higher mortality to the predator. No mortality confirmation was reported for the adults. Nymphs fed with cotton leafworm larvae Alabama argillacea (Hübner) (Lepidoptera: Noctuidae) contaminated by the fungi had their reproduction affected, but this was not observed when adult predators fed on contaminated larvae. These findings suggest that isolates of M. anisopliae can cause mortality of P. nigrispinus nymphs by topical contact, while isolates of B. bassiana were less harmful by all ways of infection as compared to M. anisopliae.