Exploring the dynamics of collective synchronizations in large ensembles of brain signals.

Developing methods characterizing the dynamics of synchronization in large ensemble of electromagnetic brain signals has become an important issue. In this article, we review a recently introduced method for analyzing multivariate phase synchronization in brain signals. The approach is based on the equivalence between phase locking and frequency locking in narrow band signals, which allows tracking multivariate phase synchronization in the time-frequency domain as periods of common frequency among multiple channels. The method is illustrated with simulations of multivariate phase dynamics in coupled oscillators and real multichannel electro- and magnetoencephalographic data recorded prior and during epileptic seizures. The reviewed results support the relevance of this method in the context of brain synchronization, in particular to track transient collective dynamics fluctuating in time, frequency and space.     

The impact of the fourth disulfide bridge in scorpion toxins of the alpha-KTx6 subfamily

Animal toxins are highly reticulated and structured polypeptides that adopt a limited number of folds. In scorpion species, the most represented fold is the alpha/beta scaffold in which an helical structure is connected to an antiparallel beta-sheet by two disulfide bridges. The intimate relationship existing between peptide reticulation and folding remains poorly understood. Here, we investigated the role of disulfide bridging on the 3D structure of HsTx1, a scorpion toxin potently active on Kv1.1 and Kv1.3 channels. This toxin folds along the classical alpha/beta scaffold but belongs to a unique family of short-chain, four disulfide-bridged toxins. Removal of the fourth disulfide bridge of HsTx1 does not affect its helical structure, whereas its two-stranded beta-sheet is altered from a twisted to a nontwisted configuration. This structural change in HsTx1 is accompanied by a marked decrease in Kv1.1 and Kv1.3 current blockage, and by alterations in the toxin to channel molecular contacts. In contrast, a similar removal of the fourth disulfide bridge of Pi1, another scorpion toxin from the same structural family, has no impact on its 3D structure, pharmacology, or channel interaction. These data highlight the importance of disulfide bridging in reaching the correct bioactive conformation of some toxins.     

Spasmolytic flavonoids from Syzygium samarangense (Blume) Merr. & L.M. Perry

The hexane extract of Syzygium samarangense (Ss.Hex) dose-dependently (10-1000 microg/ ml) relaxed the spontaneously contracting isolated rabbit jejunum. Four rare C-methylated flavonoids with a chalcone and a flavanone skeleton were isolated from Ss.Hex and were subsequently tested for spasmolytic activity. All flavonoids, identified as 2'-hydroxy-4',6'-dimethoxy-3'-methylchalcone (1), 2',4'-dihydroxy-6'-methoxy-3',5'-dimethylchalcone (2), 2',4'-dihydroxy-6'-methoxy-3'-methylchalcone (3), and 7-hydroxy-5-methoxy-6,8-dimethyl-flavanone (4), showed dose-dependent spasmolytic activity in the rabbit jejunum with IC50 values of 148.3 +/- 69.4, 77.2 +/- 43.5, 142.4 +/- 58.6 and 178.5 +/- 37.5 microg/ml (mean +/- SEM), respectively. The dihydrochalcone derivative of compound 1, 2'-hydroxy-4',6'-dimethoxy-3'-methyldihydrochalcone (5), when tested for spasmolytic activity, did not significantly relax the smooth muscle relative to the other compounds. Verapamil, a standard spasmolytic, has an IC50 value of 0.16 +/- 0.04 microg/ml. This is the first report of the relaxant activity of chalcones, specifically of compounds 1-3.     

Cooperative prey-retrieving in the ant Cataglyphis floricola: an unusual short-distance recruitment

Cataglyphis ants are mostly scavengers adapted to forage individually in arid environments. Although they are widely thought to have lost the capacity of recruitment, we provide evidence that C. floricola foragers that find a large prey near their nest are able to solicit the help of nestmates to carry it cooperatively. After discovering a non-transportable prey, these ants readily return to their nest and stimulate the exit of several recruits. This rudimentary form of recruitment, which is absent in the sympatric species C. rosenhaueri, is only employed when the prey is sufficiently close to the nest entrance (<1 m) and does not allow the food location to be communicated. Instead, C. floricola recruits search for the prey in all directions until they discover it and transport it cooperatively to their nest.     

Sunlight-activated insecticides: historical background and mechanisms of phototoxic activity

Several photosensitizing agents, which are activated by illumination with sunlight or artificial light sources, have been shown to be accumulated in significant amounts by a variety of insects when they are administered in association with suitable baits. The subsequent exposure of such insects to UV/visible light leads to a significant drop in survival. Of the photosensitizers tested so far, xanthenes (e.g. phloxin B) and porphyrins (e.g. haematoporphyrin) appear to be endowed with the highest photoinsecticidal activity. In particular, porphyrins absorb essentially all the UV/visible light wavelengths in the emission spectrum of the sun; hence they are active at very low doses. Thus, 1 h irradiation of Ceratitis capitata, Bactrocera oleae (also known as Dacus oleae) or Stomoxys calcitrans which ingested a few nanomoles of porphyrin per fly with light intensities of the order of 1000 microE s(-1) m(-2) causes about 100% death in laboratory tests. Present evidence suggests that such photosensitizers act on the membranes of the midgut with consequent feeding inhibition, as well as on the neuromuscular sheath. No apparent onset of photoresistance has been observed. The rapid photobleaching of xanthenes and porphyrins when illuminated by visible light, as well as the lack of significant toxicity of such compounds in the dark, minimizes the risk of an important environmental impact of such photoinsecticidal agents.     

The use of ethylene-suppressed lines to assess differential sensitivity to ethylene of the various ripening pathways in Cantaloupe melons

Physiological characterization of ethylene-suppressed Cantaloupe Charentais melons ( Cucumis melo var. cantalupensis Naud cv. Védrantais) revealed that some ripening-associated events, like degreening of the rind and cell separation in the peduncular abscission zone, are totally dependent on ethylene. By contrast, some other ripening events, like softening and membrane deterioration, depend only partially on ethylene and display some ethylene-independent components. Application of increasing levels of exogenous ethylene on these antisense 1-aminocyclopropane-1-carboxylic acid oxidase fruits enabled the determination of the gradual sensitivity of various ripening pathways to the hormone. The threshold level of ethylene capable of physiological activity varied from 1 ppm for degreening of the rind to 2.5 ppm for softening, membrane deterioration and cell separation in the peduncular abscission zone. Up to a saturating dose of 5 ppm, the extent of rind degreening was proportionally related to the level of applied ethylene. The saturating levels of ethylene for flesh softening (2.5 ppm) and for membrane deterioration and cell separation in the peduncular abscission zone (5 ppm) were much lower than the internal ethylene found at the climacteric peak of wild-type fruit (over 100 ppm). The cessation of ethylene treatment resulted in a complete arrest of the rind degreening and peduncular cell separation indicating that both ripening pathways are completely dependent on ethylene. On the contrary, softening and membrane deterioration, though significantly slowed upon removal of ethylene treatment, continued to proceed in the absence of the hormone, thereby unmasking the ethylene-independent component of softening and membrane deterioration. The presence of ethylene-independent components in the regulation of individual pathways indicates that the ripening of climacteric fruit involves a substantial portion of non-climacteric regulation.     

Role of ethylene in the biosynthetic pathway of aliphatic ester aroma volatiles in Charentais Cantaloupe melons.

Compared to other melon types, Cantaloupe Charentais melons are highly aromatic with a major contribution to the aroma being made by aliphatic and branched esters. Using a transgenic line in which the synthesis of the plant hormone ethylene has been considerably lowered by antisense ACC oxidase mRNA (AS), the aliphatic ester pathway steps at which ethylene exerts its regulatory role were found. The data show that the production of aliphatic esters such as hexyl and butyl acetate was blocked in AS fruit and could be reversed by ethylene. Using fruit discs incubated in the presence of various precursors, the steps at which ester formation was inhibited in AS fruit was shown to be the reduction of fatty acids and aldehydes, the last step of acetyl transfer to alcohols being unaffected. However, treating AS fruit with the ethylene antagonist 1-methylcyclopropene resulted in about 50% inhibition of acetyl transfer activity, indicating that this portion of activity was ethylene-dependent and this was supported by the low residual ethylene concentration of AS fruit discs (around 2 microl l(-1)). In conclusion, the reduction of fatty acids and aldehydes appears essentially to be ethylene-dependent, whilst the last step of alcohol acetylation has ethylene-dependent and ethylene-independent components, probably corresponding to differentially regulated alcohol acetyltransferases.     

Biofilter performance and characterization of a biocatalyst degrading alkylbenzene gases

A biofilter treating alkylbenzene vapors was characterized for its optimal running conditions and kinetic parame-ters. Kinetics of the continuous biofilter were compared to batch kinetic data obtained with biofilm samples as well as with defined microbial consortia and with pure culture isolates from the biofilter. Both bacteria and fungi were present in the bioreactor. Five strains were isolated. Two bacteria, Bacillus and Pseudomonas, were shown to be dominant, as well as a Trichosporon strain which could, however, hardly grow on alkylbenzenes in pure culture. The remaining two strains were most often overgrown by the other three organisms in liquid phase batch cultures μ _max, K_S, K_I values and biodegradation rates were calculated and compared for the difterent mixed and pure cultures. Since filter bed acidification was observed during biofiltration studies reaching a pH of about 4, experiments were also undertaken to study the influence of pH on performance of the different cultures. Biodegradation and growth were possible in all cases, over the pH range 3.5–7.0 at appreciable rates, both with mixed cultures and with pure bacterial cultures. Under certain conditions, microbial activity was even observed in the presence of alkylbenzenes down to pH 2.5 with mixed cultures, which is quite unusual and explains the ability of the present biocatalyst to remove alkylbenzenes with high efficiency in biofilters under acidic conditions.     

Morphological assessment of the Octopus vulgaris species complex evaluated in light of molecular‐based phylogenetic inferences

Cryptic species are common in the ocean, particularly among marine invertebrates such as octopuses. Delineating cryptic species is particularly problematic in octopus taxonomy where the plasticity recorded among taxonomic characters often results in low resolution at the species level. This study investigated the morphological relationships among seven phylogenetic clades (identified using cytochrome c oxidase subunit I) of the broadly distributed Octopus vulgaris species complex and close relatives. Morphological analyses in this study were successful in delimiting O. sinensis, Brazilian O. vulgaris and O. vulgaris sensu stricto, which was congruent with the molecular findings of this study. Analyses based on male morphology were successful in distinguishing 14 of 15 total pairwise comparisons and proved to be a more reliable indicator of species‐level relationships in comparison with female morphology. The majority of characters with the greatest discriminatory power were male sexual traits. Significant morphological differences were also recorded among sampling localities of conspecifics, with phenotype showing correlation with local environmental data. The findings of this study support the hypothesis that multiple O. vulgaris‐like species are currently being incorrectly treated under a single species name, O. vulgaris. Octopuses being exported globally under the name O. vulgaris are of extremely high fisheries market value and profile. Our findings have potentially significant implications for the naming and conservation of commercially harvested members of this species complex throughout their ranges.