White matter injury following systemic endotoxemia or asphyxia in the fetal sheep

White matter injury is the most frequently observed brain lesion in preterm infants. The etiology remains unclear, however, both cerebral hypoperfusion and intrauterine infections have been suggested as risk factors. We compared the neuropathological outcome, including the effect on oligodendrocytes, astrocytes, and microglia, following either systemic asphyxia or endotoxemia in fetal sheep at midgestation. Fetal sheep were subjected to either 25 minutes of umbilical cord occlusion or systemic endotoxemia by administration of Escherichia coli lipopolysaccharide (LPS O111:B4, 100 ng/kg, IV). Periventricular white matter lesions were observed in 2 of 6 asphyxiated fetuses, whereas the remaining animals showed diffuse injury throughout the subcortical white matter and neuronal necrosis in subcortical regions, including the striatum and hippocampus. LPS-treatment resulted in focal inflammatory infiltrates and cystic lesions in periventricular white matter in 2 of 5 animals, but with no neuron specific injury. Both experimental paradigms resulted in microglia activation in the white matter, damaged astrocytes, and loss of oligodendrocytes. These results show that the white matter at midgestation is sensitive to injury following both systemic asphyxia and endotoxemia. Asphyxia induced lesions in both white and subcortical grey matter in association with microglia activation, and endotoxemia resulted in selective white matter damage and inflammation.     

Modelling mating success of saproxylic beetles in relation to search behaviour, population density and substrate abundance

We compared the efficiency of two mate-finding strategies exploited by representatives of the beetle families Cisidae and Anobiidae (genus Dorcatoma) that live inside fruiting bodies of wood-decaying fungi. In the Cisidae both sexes are attracted to host odour, but no pheromones seem to be present (nonpheromone strategy). In the Dorcatoma species only the females are attracted to host odour, but having found a host they attract males with a sexual pheromone (pheromone strategy). With a simulation model, we compared the efficiency of the two strategies at four densities of trees hosting fungal fruiting bodies and at three relative densities of insects. We found only small differences in efficiency between the two strategies at high relative densities of conspecific individuals, regardless of host tree density. The pheromone strategy was relatively more efficient when the relative density of insects or the density of host trees decreased. Thus, species adopting the nonpheromone strategy are probably more sensitive to habitat fragmentation and more likely to decline and go extinct at low population densities (because of Allee effects) than species using the pheromone strategy. Copyright 2003 Published by Elsevier Science Ltd on behalf of The Association for the Study of Animal Behaviour.      

Pine Forest Floor Carbon Accumulation in Response to N and PK Additions: Bomb <Superscript>14</Superscript>C Modelling and Respiration Studies

The addition of nitrogen via deposition alters the carbon balance of temperate forest ecosystems by affecting both production and decomposition rates. The effects of 20 years of nitrogen (N) and phosphorus and potassium (PK) additions were studied in a 40-year-old pine stand in northern Sweden. Carbon fluxes of the forest floor were reconstructed using a combination of data on soil ¹⁴C, tree growth, and litter decomposition. N-only additions caused an increase in needle litterfall, whereas both N and PK additions reduced long-term decomposition rates. Soil respiration measurements showed a 40% reduction in soil respiration for treated compared to control plots. The average age of forest floor carbon was 17 years. Predictions of future soil carbon storage indicate an increase of around 100% in the next 100 years for the N plots and 200% for the NPK plots. As much as 70% of the increase in soil carbon was attributed to the decreased decomposition rate, whereas only 20% was attributable to increased litter production. A reduction in decomposition was observed at a rate of N addition of 30 kg C ha^–1 y^–1, which is not an uncommon rate of N deposition in central Europe. A model based on the continuous-quality decomposition theory was applied to interpret decomposer and substrate parameters. The most likely explanations for the decreased decomposition rate were a fertilizer-induced increase in decomposer efficiency (production-to-assimilation ratio), a more rapid rate of decrease in litter quality, and a decrease in decomposer basic growth rate.     

Microplate screening for apoptosis with antibody to single-stranded DNA distinguishes anticancer drugs from toxic chemicals

The effect of anticancer drugs and toxic compounds on cultures of human leukemic cells was evaluated by an enzyme-linked immunosorbent assay (Apoptosis ELISA) that uses a monoclonal antibody against single-stranded DNA to quantitate the apoptotic cells. The concentrations of 13 anticancer drugs, which increased Apoptosis ELISA absorbance, were close to the cytotoxic concentrations determined by the long-term cell survival assay. Short-term tetrazolium-based microculture tetrazolium (MTT) assay was significantly less sensitive than the Apoptosis ELISA and the cell survival assay for all anticancer drugs. For 6 drugs, cytotoxic concentrations measured by the MTT assay were at least 1 log higher than the concentrations inducing apoptosis. Importantly, in contrast to the anticancer drugs, 14 toxic chemicals did not increase the Apoptosis ELISA absorbance at cytotoxic concentrations. The difference in apoptosis induction by the anticancer drugs and the toxic chemicals was especially large in cultures treated with drug concentrations 2-fold higher than the IC(50) dose. Although all of the anticancer drugs tested induced intense ELISA reaction (mean absorbance 2.0), all toxic chemicals tested did not induce apoptosis. The Apoptosis ELISA assay could have useful applications in drug development as it can distinguish between clinically useful anticancer drugs and toxic compounds, has sensitivity similar to that of the long-term cell survival assay, and provides insight into the mechanism of drug cytotoxicity by differentiating between compounds killing cells by apoptosis and necrosis.     

Mutual influences of Pseudomonas aeruginosa and Desulfovibrio desulfuricans on their adhesion to stainless steel

The mutual influences of Pseudomonas aeruginosa PAO1 and Desulfovibrio desulfuricans subsp. desulfuricans (ATCC 29577) on their adhesion to stainless steel were investigated in batch and column experiments. It was found that P. aeruginosa promoted the adhesion of D. desulfuricans under conditions of turbulence, but not under quiescent conditions. The enhancement involved the alignment of most D. desulfuricans along P. aeruginosa cells and was attributed to the additional interaction surface area provided by adhered P. aeruginosa to aligning D. desulfuricans cells. A slightly positive effect of preadhered D. desulfuricans on the adhesion of P. aeruginosa was found. Under condition of laminar flow, substantially better adhesion of D. desulfuricans to confluent P. aeruginosa biofilms than to steel was observed. The mutual influences are discussed in terms of more favorable adhesion energies and the influence of changed hydraulic conditions due to the roughness of P. aeruginosa biofilms.     

Sorting out bacterial viability with optical tweezers

We have developed a method, using laser, optical tweezers and direct microscopic analysis of reproductive potential and membrane integrity, to assess single-cell viability in a stationary-phase Escherichia coli population. It is demonstrated here that a reduction in cell integrity, determined by using the fluorescent nucleic acid stain propidium iodide, correlated well with a reduction in cell proliferating potential during the stationary-phase period studied. Moreover, the same cells that exhibited reduced integrity were found to be the ones that failed to divide upon nutrient addition. A small but significant number of the intact cells (496 of 7,466 [6.6%]) failed to replicate. In other words, we did not find evidence for the existence of a large population of intact but nonculturable cells during the stationary-phase period studied but it is clear that reproductive ability can be lost prior to the loss of membrane integrity. In addition, about 1% of the stationary-phase cells were able to divide only once upon nutrient addition, and in a few cases, only one of the two cells produced by division was able to divide a second time, indicating that localized cell deterioration, inherited by only one of the daughters, may occur. The usefulness of the optical trapping methodology in elucidating the mechanisms involved in stationary-phase-induced bacterial death and population heterogeneity is discussed.     

Correlation between caspase-3 activation and three different markers of DNA damage in neonatal cerebral hypoxia-ischemia

Caspase-3 has been identified as a key protease that, by targeting a limited number of proteins, can disrupt essential homeostatic processes and initiate an orderly disassembly of cells, including degradation of genomic DNA. We demonstrate the usefulness of an antibody specific for activated caspase-3 in a model of neonatal rat hypoxia-ischemia (Hl) and correlate the spatial and temporal activation of caspase-3 with three different markers of DNA damage and with the loss of a neuronal marker [microtubule-associated protein 2 (MAP 2)]. An oligonucleotide hairpin probe (HPP) with one base overhang in the 3' end displayed a close colocalization with caspase-3 activation at 3 h post-Hl, whereas terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL) appeared later (24 h post-Hl). A monoclonal antibody against single-stranded DNA appeared to stain an entirely different population of cells, not positive for active caspase-3, HPP, or TUNEL at this time point. After 24 h of reperfusion, however, when cellular injury is extensive, all markers stained a large number of cells with a high degree of colocalization, and all markers delineated regions with loss of MAP 2. We conclude that the HPP shows the best correlation with pathological caspase-3 activation in this model.     

Uncertain biotic and abiotic interactions in benthic communities

We analyze marine benthic communities at different sites in Skagerrak with the purpose of understanding the role of exogenous and endogenous factors in explaining the species' temporal dynamics. The previous finding that the dynamics of these species communities are mainly driven and synchronized by environmental (temperature) forcing was only weakly supported when analyzing single-species dynamics at five sites where four of the species were present every year. There was no consistent pattern in how the temperature affected the realized per capita growth rate, either across species at a given site, or among sites for a given species. Furthermore, there was no net-interaction from the community on a given species strong enough to give rise to second-order dynamics. However, when implementing a Multi Dimensional Scaling (MDS) analysis and incorporating all sampling sites and species -we found that the different communities clustered in relation to depth, hence, communities at the same depth were more "similar" than communities at different depth. Revealing the underlying interactions shaping these marine benthic communities is a challenge that calls for an array of various and complementary approaches.