Role of CCL3/MIP-1α and CCL5/RANTES during acute Trypanosoma cruzi infection in rats

Chagas’ disease is caused by Trypanosoma cruzi infection and is characterized by chronic fibrogenic inflammation and heart dysfunction. Chemokines are produced during infection and drive tissue inflammation. In rats, acute infection is characterized by intense myocarditis and regression of inflammation after control of parasitism. We investigated the role of CCL3 and CCL5 during infection by using DNA vaccination encoding for each chemokine separately or simultaneously. MetRANTES treatment was used to evaluate the role of CCR1 and CCR5, the receptors for CCL3 and CCL5. Vaccination with CCL3 or CCL5 increased heart parasitism and decreased local IFN-γ production, but did not influence intensity of inflammation. Simultaneous treatment with both plasmids or treatment with MetRANTES enhanced cardiac inflammation, fibrosis and parasitism. In conclusion, chemokines CCL3 and CCL5 are relevant, but not essential, for control of T. cruzi infection in rats. On the other hand, combined blockade of these chemokines or their receptors enhanced tissue inflammation and fibrosis, clearly contrasting with available data in murine models of T. cruzi infection. These data reinforce the important role of chemokines during T. cruzi infection but suggest that caution must be taken when expanding the therapeutic modulation of the chemokine system in mice to the human infection.     

History-dependent excitability as a single-cell substrate of transient memory for information discrimination

Neurons react differently to incoming stimuli depending upon their previous history of stimulation. This property can be considered as a single-cell substrate for transient memory, or context-dependent information processing: depending upon the current context that the neuron "sees" through the subset of the network impinging on it in the immediate past, the same synaptic event can evoke a postsynaptic spike or just a subthreshold depolarization. We propose a formal definition of History-Dependent Excitability (HDE) as a measure of the propensity to firing in any moment in time, linking the subthreshold history-dependent dynamics with spike generation. This definition allows the quantitative assessment of the intrinsic memory for different single-neuron dynamics and input statistics. We illustrate the concept of HDE by considering two general dynamical mechanisms: the passive behavior of an Integrate and Fire (IF) neuron, and the inductive behavior of a Generalized Integrate and Fire (GIF) neuron with subthreshold damped oscillations. This framework allows us to characterize the sensitivity of different model neurons to the detailed temporal structure of incoming stimuli. While a neuron with intrinsic oscillations discriminates equally well between input trains with the same or different frequency, a passive neuron discriminates better between inputs with different frequencies. This suggests that passive neurons are better suited to rate-based computation, while neurons with subthreshold oscillations are advantageous in a temporal coding scheme. We also address the influence of intrinsic properties in single-cell processing as a function of input statistics, and show that intrinsic oscillations enhance discrimination sensitivity at high input rates. Finally, we discuss how the recognition of these cell-specific discrimination properties might further our understanding of neuronal network computations and their relationships to the distribution and functional connectivity of different neuronal types.     

Gene expression in mycorrhizal orchid protocorms suggests a friendly plant–fungus relationship

Main conclusion

Orchid mycorrhiza has been often interpreted as an antagonistic relationship. Our data on mycorrhizal protocorms do not support this view as plant defence genes were not induced, whereas some nodulin-like genes were significantly up-regulated. Orchids fully depend on symbiotic interactions with specific soil fungi for seed germination and early development. Germinated seeds give rise to a protocorm, a heterotrophic organ that acquires nutrients, including organic carbon, from the mycorrhizal partner. It has long been debated if this interaction is mutualistic or antagonistic. To investigate the molecular bases of the orchid response to mycorrhizal invasion, we developed a symbiotic in vitro system between Serapias vomeracea, a Mediterranean green meadow orchid, and the rhizoctonia-like fungus Tulasnella calospora. 454 pyrosequencing was used to generate an inventory of plant and fungal genes expressed in mycorrhizal protocorms, and plant genes could be reliably identified with a customized bioinformatic pipeline. A small panel of plant genes was selected and expression was assessed by real-time quantitative PCR in mycorrhizal and non-mycorrhizal protocorm tissues. Among these genes were some markers of mutualistic (e.g. nodulins) as well as antagonistic (e.g. pathogenesis-related and wound/stress-induced) genes. None of the pathogenesis or wound/stress-related genes were significantly up-regulated in mycorrhizal tissues, suggesting that fungal colonization does not trigger strong plant defence responses. In addition, the highest expression fold change in mycorrhizal tissues was found for a nodulin-like gene similar to the plastocyanin domain-containing ENOD55. Another nodulin-like gene significantly more expressed in the symbiotic tissues of mycorrhizal protocorms was similar to a sugar transporter of the SWEET family. Two genes coding for mannose-binding lectins were significantly up-regulated in the presence of the mycorrhizal fungus, but their role in the symbiosis is unclear.     

Genome sequence of the human pathogen Vibrio cholerae Amazonia

Vibrio cholerae O1 Amazonia is a pathogen that was isolated from cholera-like diarrhea cases in at least two countries, Brazil and Ghana. Based on multilocus sequence analysis, this lineage belongs to a distinct profile compared to strains from El Tor and classical biotypes. The genomic analysis revealed that it contains Vibrio pathogenicity island 2 and a set of genes related to pathogenesis and fitness, such as the type VI secretion system, present in choleragenic V. cholerae strains.     

How reliable is the double‐ended pressure sleeve technique for assessing xylem vulnerability to cavitation in woody angiosperms?

The reliability of a double-ended pressure sleeve technique was evaluated on three woody angiosperm species with contrasting maximum vessel lengths. Vulnerability curves (VCs) were constructed by varying sample length and the size of the pressure sleeves. VCs were compared against curves obtained with reference techniques. For the two diffuse-porous species, Betula pendula and Prunus persica, VCs built with shoot segments shorter than maximum vessel length strongly overestimated species vulnerability. Furthermore, increasing the size of the pressure sleeve also tended to lead to overestimated VCs. For the ring-porous species Quercus robur, the technique strongly overestimated vulnerability to embolism, whatever the sample length or chamber tested. In conclusion, the double-ended pressure sleeve technique only gives reliable VCs on diffuse-porous angiosperms with short pressure sleeves, only when segments are longer than maximum vessel length.     

Physiologic and metagenomic attributes of the rhodoliths forming the largest CaCO3 bed in the South Atlantic Ocean

Rhodoliths are free-living coralline algae (Rhodophyta, Corallinales) that are ecologically important for the functioning of marine environments. They form extensive beds distributed worldwide, providing a habitat and nursery for benthic organisms and space for fisheries, and are an important source of calcium carbonate. The Abrolhos Bank, off eastern Brazil, harbors the world''s largest continuous rhodolith bed (of ∼21 000 km²) and has one of the largest marine CaCO₃ deposits (producing 25 megatons of CaCO₃ per year). Nevertheless, there is a lack of information about the microbial diversity, photosynthetic potential and ecological interactions within the rhodolith holobiont. Herein, we performed an ecophysiologic and metagenomic analysis of the Abrolhos rhodoliths to understand their microbial composition and functional components. Rhodoliths contained a specific microbiome that displayed a significant enrichment in aerobic ammonia-oxidizing betaproteobacteria and dissimilative sulfate-reducing deltaproteobacteria. We also observed a significant contribution of bacterial guilds (that is, photolithoautotrophs, anaerobic heterotrophs, sulfide oxidizers, anoxygenic phototrophs and methanogens) in the rhodolith metagenome, suggested to have important roles in biomineralization. The increased hits in aromatic compounds, fatty acid and secondary metabolism subsystems hint at an important chemically mediated interaction in which a functional job partition among eukaryal, archaeal and bacterial groups allows the rhodolith holobiont to thrive in the global ocean. High rates of photosynthesis were measured for Abrolhos rhodoliths (52.16 μmol carbon m⁻²s⁻¹), allowing the entire Abrolhos rhodolith bed to produce 5.65 × 10⁵ tons C per day. This estimate illustrates the great importance of the Abrolhos rhodolith beds for dissolved carbon production in the South Atlantic Ocean.     

Neuroprotective role of quercetin in locomotor activities and cholinergic neurotransmission in rats experimentally demyelinated with ethidium bromide

Aim

The purpose of this study was to investigate whether the flavonoid quercetin can prevent alterations in the behavioral tests and of cholinergic neurotransmission in rats submitted to the ethidium bromide (EB) experimental demyelination model during events of demyelination and remyelination.

Main methods

Wistar rats were randomly distributed into four groups (20 animals per group): Control (pontine saline injection and treatment with ethanol), Querc (pontine saline injection and treatment with quercetin), EB (pontine 0.1% EB injection and treatment with ethanol), and EB + Querc (pontine 0.1% EB injection and treatment with quercetin). The groups Querc and Querc + EB were treated once daily with quercetin (50 mg/kg) diluted in 25% ethanol solution (1 ml/kg) and the animals of the control and EB groups were treated once daily with 25% ethanol solution (1 ml/kg). Two stages were observed: phase of demyelination (peak on day 7) and phase of remyelination (peak on day 21 post-injection). Behavioral tests (beam walking, foot fault and inclined plane test), acetylcholinesterase (AChE) activity and lipid peroxidation in pons, cerebellum, hippocampus, hypothalamus, striatum and cerebral cortex were measured.

Key findings

The quercetin promoted earlier locomotor recovery, suggesting that there was demyelination prevention or further remyelination velocity as well as it was able to prevent the inhibition of AChE activity and the increase of lipidic peroxidation, suggesting that this compound can protect cholinergic neurotransmission.

Significance

These results may contribute to a better understanding of the neuroprotective role of quercetin and the importance of an antioxidant diet in humans to provide benefits in neurodegenerative diseases such as MS.     

Organic matter composition in coastal sediments at Terra Nova Bay (Ross Sea) during summer 1995

We illustrate the spatial and vertical distribution of sediment phytopigments and organic matter biochemical composition at Terra Nova Bay (Ross Sea) during summer 1995. Coastal sediments displayed high phytopigments concentrations associated with huge amounts of labile organic matter largely dominated by proteins. This result was opposite to previous observations in the same area. Such comparison suggested that whilst organic matter quantity in the sediments depended upon the vertical input from the water column, temporal changes in its biochemical composition were related to benthic processes. As considerably high concentrations of biopolymeric organic carbon were found even at 6-cm depth and according to the “loss type” functioning of the coastal waters of the Ross Sea, we stress the summer time occurrence in coastal sediments of an important organic matter burial. Accepted: 24 October 1999