The contribution of picophytoplankton to community structure in a Mediterranean brackish environment

The seasonal composition of phytoplankton communities was investigatedin a Mediterranean brackish area (Varano lagoon). Twelve stationswere sampled monthly from March 1997 to February 1998. Numbersof prokaryotic and eukaryotic picophytoplankton cells were estimatedby epifluorescence microscopy, while larger phytoplankton (nanoand micro fractions) were enumerated by the Utermöhl settlingtechnique. Picophytoplankton densities ranged from 0.7 to 448.6cells x 10⁶ l^–1. Nano- and microphytoplankton abundancesvaried between 0.2 and 7.9 cells x 10⁶ l^–1. The picoplanktonfraction was represented mainly by cyanobacteria and the Utermöhlfraction by nano-sized phytoflagellates (56.2%) and diatoms(20.1%). The phytoflagellates had a greater abundance over timewhile diatoms reached the highest densities in summer and fall.In Varano lagoon, phytoplankton development is related to ‘nitrogen-poor'waters and to phosphorus availability. Suspension-feeding bivalves(Mytilus galloprovincialis) are sufficiently abundant to filtera volume equivalent to the volume of Varano lagoon at leastonce daily. These observations suggest that grazing exerts animportant influence on phytoplankton dynamics, mainly on themicro fraction, and that diatoms seem to play an important rolein the food web dynamics of this coastal fishery.     

A comparison of the receptor constants of morphine and ethylketocyclazocine for analgesia and inhibition of gastrointestinal transit in the rat

The efficacies and dissociation constants of proposed mu and kappa receptor agonists (morphine and ethylketocyclazocine, respectively) were compared using the method of partial irreversible blockade (with buprenorphine) and Stephenson's theory of drug action. While there was good agreement between the dissociation constant (KA) of morphine in analgesia (3.3 x 10(-5) M) and in inhibition of gastrointestinal transit (1.1 x 10(-5) M), the KA of ethylketocyclazocine differed by an order of magnitude in these endpoints (3.2 x 10(-6) M and 6.7 x 10(-5) M, respectively). The efficacies of morphine were found to be similar for the two effects studied (4.23 and 5.26), while those for ethylketocyclazocine differed markedly (2.06 and 10.39). The fraction of receptors remaining unblocked after buprenorphine was consistent for the test but not for the agonist, indicating a different distribution of receptors for the two endpoints. Our results strongly suggest that morphine induces analgesia, and slows transit in the small intestine, through the same type of receptor. The same conclusion cannot be drawn for ethylketocyclazocine.     

Cyclo(His-Pro) up-regulates heme oxygenase 1 via activation of Nrf2-ARE signalling

Paraquat (1,1'-dimethyl-4,4'-bipyridinium), a widely used non-selective herbicide, is a redox cycling agent with adverse effects on dopamine systems. Epidemiological data have shown that exposure to paraquat is one of the several risk factors for Parkinson's disease. We have already shown that cyclo(His-Pro), an endogenous cyclic dipeptide produced by the cleavage of the thyrotropin releasing hormone, has a cytoprotective effect through a mechanism involving Nrf2 activation that decreases production of reactive oxygen species and increases glutathione synthesis. Using primary neuronal cultures and PC12 cells as targets of paraquat neurotoxicity, we addressed whether and how cyclo(His-Pro) causes cellular protective response against paraquat-mediated cell death. We found that cyclo(His-Pro) attenuated reactive oxygen species production, and prevented glutathione depletion by up-regulating Nrf2 gene expression, triggering its nuclear accumulation and activating the expression of heme oxygenase1. These protective effects were abolished by RNA interference-mediated Nrf2 knock down whereas were unaffected by RNA interference-mediated Keap1 knock down. Inhibition of heme oxygenase activity decreased cyclo(His-Pro)-induced neuroprotection. These results suggest that cyclo(His-Pro), acting as a selective activator of the brain modulable Nrf2 pathway, may be a promising candidate as neuroprotective agent that act through induction of phase II genes.     

Maintenance of innate feeding preferences by a polyphagous insect despite ingestion of applied deleterious chemicals

The question of whether the appearance of a novel deleterious chemical in a preferred host plant could alter the relative degree of preference by a polyphagous insect during its lifetime was considered. The behavioral preference of fall armyworm, Spodoptera frugiperda (J. E. Smith), for corn (Zea mays L.) over red kidney bean Phaseolus spp. was quantified in a two-way choice test, and followed by a no-choice test in which the same larvae were fed either treated or untreated corn. Each treatment consisted of one of 15 compounds, including 13 naturally occurring allelochemicals and two synthetic insecticides. None of the test chemicals had any inherently deterrent effect at the rates tested. Deleterious effects on the larvae during exposure included reduced growth, reduced size, irritancy, and in some cases death. After this exposure the two way choice test was repeated. All test compounds failed to elicit a change in relative preference during the final two-way choice test. However, larvae exposed to gossypol and chrysanthemum monocarboxylic acid ester fed less than expected during the latter stages of no-choice conditions. The degree of aversion learning by each larva was related to the degree of prior sickness it had experienced.

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Résumé Nous avons examiné si l'introduction d'une substance chimique nocive dans la plante-hôte préférée pouvait modifier la hiérarchie des choix durant le reste de la vie d'un insecte phytophage. Le comportement de préférence de Spodoptera frugiperda pour le maïs (Zea mays) vis à vis des Phaseolus, a été quantifié dans un dispositif à choix binaire, ont suivi des expériences au cours desquelles les chenilles devaient s'alimenter, soit sur maïs sain, soit sur maïs traité. Chaque essai concernait un composé chimique (15 au total), 13 étant des substances allélochimiques naturelles, 2 des insecticides de synthèse. Aux concentrations étudiées, aucun des produits n'a eu d'effet dissuasif. Les effets nocifs pendant l'exposition sur les chenilles comprenaient une croissance et une taille réduites, une irritation et, dans quelques cas, la mort. Aucune des expériences de choix binaire, avec des chenilles ayant subi cette exposition, n'a modifié les préférences. Cependant les chenilles, qui avaient été exposées au gossypol ou à l'acide monocarboxylique éthyl ester de chrysanthemum, ont consommé moins pendant les stades ultérieurs que ce que l'on pouvait attendre en absence de choix. Le degré d'aversion acquis par chaque chenille dépendait de l'importance des maux qu'elle avait subis précédemment.

     

Chiral escape of bark beetles from predators responding to a bark beetle pheromone

Summary Two species of predatory beetles that locate their prey, Ips pini, by responding to its aggregation pheromone have different chiral preferences to ispdienol than does the herbivore. This suggests that chiral disparity may provide some escape for bark beetles from predation, and that geographic variation in herbivore communication systems may be partially due to predator — imposed selection pressures. These results also suggest ways in which the semiochemical and biological control of North America's most damaging group of forest insects can be improved.     

Antibacterial activity of rufloxacin in theStaphylococcus aureus rat granuloma pouch model

The protective effects of rufloxacin againstStaphylococcus aureus-induced infections were compared with those of ciprofloxacin in the granuloma pouch model in the rat. Two strains with different in vitro sensitivity to the drugs were studied. Rufloxacin concentrations persisted longer than ciprofloxacin in the exudate in the pouch cavity and were about eight times higher. Equal doses of rufloxacin and ciprofloxacin had similar antibacterial activities. However, rufloxacin inhibitedStaphylococcus aureus bacterial growth significantly longer than did ciprofloxacin.     

Functional heterogeneity of GEF-free initiation factor 2 purified from suckling and adult rat brain

The functional behavior of initiation factor 2 was studied in purified preparations from the brains of suckling (4-12-day-old) and adult (60-day-old) rats. Adult eIF2 has lower GDP and GTP affinity than suckling eIF2, even in the presence of a large excess of GTP, whereas suckling eIF2 has a lower capacity to bind GTP. Since these two factors are free of guanine nucleotide exchange factor (GEF), and ribosomal fractions show an age-dependent difference in GEF activity, the observed functional heterogeneity may be due to a different ratio in eIF2 species (eIF2-GDP, eIF2(P)).

Developing brain Protein synthesis Initiation factor 2 Guanine nucleotide exchange factor     

The concept of a changing receptor concentration: implications for the theory of drug action

Drugs are considered to produce their effects on biological tissues either by altering some physical property of cells or by interacting with specific cellular components, called receptors. Most drugs and endogenous neurotransmitters act on highly selective receptors located on the outer surface membrane of cells. These receptors were believed, until recently, to be stationary on the cell surface and to be present in unvarying numbers. Consequently, most early theorists modeled the drug-receptor interaction on the basis of stationary and static receptor molecules. The substantial advances in our understanding of drug action based on these models have partly justified this view. However, recent electron microscopic studies have revealed the presence of structures, including "coated" pits and vesicles, that appear to provide a mechanism by which cell surface receptors might be internalized in a process of endocytosis. The precise intracellular fate of these internalized receptors is unknown, but based on present understanding, it seems reasonable to believe that some are destroyed intracellularly whereas others are recycled to the cell surface. The importance of such processes to pharmacologic theory is a new awareness of a cellular pathway that is capable of internalizing drugs, receptors, or both. The implications of such a process to the theory of drug action extends to some unexplained drug phenomena such as down regulation, drug tolerance, tachyphyllaxis, and partial agonism. We present herein the theoretical framework for a model of drug action that incorporates the possibility of receptor internalization and subsequent degradation, recycling, or replacement.     

6β-Hydroxyipolamiide,an iridoid glucoside from Stachytarpheta mutabilis

A new iridoid glucoside has been isolated from Stachytarpheta mutabilis and assigned the structure and configuration of 6β-hydroxyipolamiide on the basis of ¹H NMR and ¹³C NMR evidence. The conversion of this compound into penta- acetyllamiol proved the above assignment.