Seasonal plankton dynamics along a cross-shelf gradient

Much interest has recently been devoted to reconstructing the dynamic structure of ecological systems on the basis of time-series data. Using 10 years of monthly data on phyto- and zooplankton abundance from the Bay of Biscay (coastal to shelf-break sites), we demonstrate that the interaction between these two plankton components is approximately linear, whereas the effects of environmental factors (nutrients, temperature, upwelling and photoperiod) on these two plankton population growth rates are nonlinear. With the inclusion of the environmental factors, the main observed seasonal and inter-annual dynamic patterns within the studied plankton assemblage also indicate the prevalence of bottom-up regulatory control.     

Lipid Auxotrophy and the Effect on Lipid Composition of Entamoeba invadens*†

SYNOPSIS. A medium for the axenic cultivation of Entamoeba invadens has been developed. Serum, an essential constituent of conventional media, has been replaced by a mixture of albumin, unsaturated fatty acids, Tween, and cholesterol to control the lipid composition of the medium. Entamoeba invadens requires both cholesterol and unsaturated fatty acids for growth. The fatty acid composition of the phospholipids of the ameba reflects that of the medium to a great extent, especially with regard to the unsaturated fatty acids. The amount of membrane bounded cholesterol depends on the cholesterol concentration in the medium.     

Astrocytic Mechanisms Explaining Neural-Activity-Induced Shrinkage of Extraneuronal Space

Neuronal stimulation causes ~30% shrinkage of the extracellular space (ECS) between neurons and surrounding astrocytes in grey and white matter under experimental conditions. Despite its possible implications for a proper understanding of basic aspects of potassium clearance and astrocyte function, the phenomenon remains unexplained. Here we present a dynamic model that accounts for current experimental data related to the shrinkage phenomenon in wild-type as well as in gene knockout individuals. We find that neuronal release of potassium and uptake of sodium during stimulation, astrocyte uptake of potassium, sodium, and chloride in passive channels, action of the Na/K/ATPase pump, and osmotically driven transport of water through the astrocyte membrane together seem sufficient for generating ECS shrinkage as such. However, when taking into account ECS and astrocyte ion concentrations observed in connection with neuronal stimulation, the actions of the Na⁺/K⁺/Cl⁻ (NKCC1) and the Na⁺/HCO₃⁻ (NBC) cotransporters appear to be critical determinants for achieving observed quantitative levels of ECS shrinkage. Considering the current state of knowledge, the model framework appears sufficiently detailed and constrained to guide future key experiments and pave the way for more comprehensive astroglia–neuron interaction models for normal as well as pathophysiological situations.     

Orchestrating aquaporin-4 and connexin-43 expression in brain: Differential roles of α1- and β1-syntrophin

Aquaporin-4 (AQP4) water channels and gap junction proteins (connexins) are two classes of astrocytic membrane proteins critically involved in brain water and ion homeostasis. AQP4 channels are anchored by α1-syntrophin to the perivascular astrocytic endfoot membrane domains where they control water flux at the blood-brain interface while connexins cluster at the lateral aspects of the astrocytic endfeet forming gap junctions that allow water and ions to dissipate through the astrocyte syncytium. Recent studies have pointed to an interdependence between astrocytic AQP4 and astrocytic gap junctions but the underlying mechanism remains to be explored. Here we use a novel transgenic mouse line to unravel whether β1-syntrophin (coexpressed with α1-syntrophin in astrocytic plasma membranes) is implicated in the expression of AQP4 isoforms and formation of gap junctions in brain. Our results show that while the effect of β1-syntrophin deletion is rather limited, double knockout of α1- and β1-syntrophin causes a downregulation of the novel AQP4 isoform AQP4ex and an increase in the number of astrocytic gap junctions. The present study highlight the importance of syntrophins in orchestrating specialized functional domains of brain astrocytes.     

Liver cytochrome P-450 system in rats with a varying susceptibility to the development of experimental alcoholism

The cytochrome P-450-dependent monooxygenase system of the liver was studied in laboratory noninbred male rats selected according to the intensity of their initial alcohol motivation and the dynamics of these parameters was followed up during 10-day alcoholisation. It was shown that in the animals inclined to the development of alcoholism the activity of the monooxygenase system (cytochrome P-450, B5; enzymes: aminopyrine N-demethylase, aniline p-hydroxylase, NADPH-cytochrome c-reductase) is higher than in the animals noninclined to the development of this disease. 10-day alcohol consumption in the free-choice situation between water and 15% ethanol solution did not change the parameters investigated. The only exception was NADPH-cytochrome c-reductase: its activity grew in both the groups of the animals by 40-75%.     

Tolerated wobble mutations in siRNAs decrease specificity, but can enhance activity in vivo

RNA interference (RNAi) has become an invaluable tool for functional genomics. A critical use of this tool depends on an understanding of the factors that determine the specificity and activity of the active agent, small interfering RNA (siRNA). Several studies have concluded that tolerance of mutations can be considerable and hence lead to off-target effects. In this study, we have investigated in vivo the toleration of wobble (G:U) mutations in high activity siRNAs against Flap Endonuclease 1 (Fen1) and Aquaporin-4 (Aqp4). Mutations in the central part of the antisense strand caused a pronounced decrease in activity, while mutations in the 5′ and 3′ends were tolerated very well. Furthermore, based on analysis of nine different mutated siRNAs with widely differing intrinsic activities, we conclude that siRNA activity can be significantly enhanced by wobble mutations (relative to mRNA), in the 5′ terminal of the antisense strand. These findings should facilitate design of active siRNAs where the target mRNA offers limited choice of siRNA positions.     

Immunocytochemistry of glutamate at the synaptic level

High concentrations of glutaraldehyde (2-5%) were found optimal for fixation of glutamate. In the absence of glutaraldehyde, (para)formaldehyde does not permanently retain L-[3H]-glutamate or D-[3H]-aspartate previously taken up into brain slices. Rats were fixed by rapid transcardial perfusion with 2.5% glutaraldehyde/1% (para)formaldehyde, and brain samples osmicated, embedded in epoxy resin, sectioned, and exposed to specific antisera to glutamate (conjugated to carrier protein by glutaraldehyde), followed by colloidal gold-labeled second antibody. The gold particle density was higher over putative glutamatergic nerve terminals than over any other tissue elements (two to three times tissue average in cerebellum and hippocampus). Calibration by test conjugates containing known concentrations of fixed glutamate processed in the same fluid drops as the tissue sections indicated that the concentration of fixed glutamate in putative glutamatergic terminals in hippocampus CA1 was c. 20 mmol/liter. The grain density over the parent cell bodies was only slightly higher than the tissue average. (Grain densities over test conjugates of other amino acids, aldehyde-fixed to brain macromolecules, were similar to that over empty resin. Labeling was blocked by glutamate-glutaraldehyde but not by other glutaraldehyde-treated amino acids.) In other experiments, brain slices were incubated in oxygenated artificial cerebrospinal fluid (CSF) and then immersion-fixed and processed as above. Here, the ration of grain densities in putative glutamatergic terminals vs other tissue elements was greater than in perfusion-fixed material. Comparison of intra-terminal areas poor and rich in synaptic vesicles suggested that in this preparation vesicles contained at least three times the glutamate concentration of cytosol. In the glutamatergic synapses of the giant reticulospinal axons in lamprey the ratio was over 30. Prolonged K+ depolarization of hippocampal and cerebellar slices reduced the nerve terminal glutamate immunoreactivity in a Ca2(+)-dependent manner. The results suggest that glutamate is released by exocytosis at excitatory synapses and show that immunocytochemistry can be used to study the cellular processing of small molecules.