Interaction of the organic anion 1-aniline 8-naphthalene sulfonate (ANS) with isolated rat hepatocytes

The interaction of ANS with rat hepatocytes in time was studied by fluorescence spectroscopy. The intercept of the first linear portion of the time curve of interaction showed a positive value over all the ANS concentration range employed. This value was maintained after cellular disruption by homogenization. It was affected by ionic strength, pH, and divalent cation in the incubation medium, all conditions affecting the cellular surface. These data suggest that this phenomenon might be a binding of the compound to the hepatocytes surface. Due to the time constant and its disappearance after cellular disruption the other slower component of the curve seems to correspond to a process of translocation across the membrane.     

A Temporally Explicit Production Efficiency Model for Fuel Load Allocation in Southern Africa

Abstract We present a regional fuel load model (1 km² spatial resolution) applied in the southern African savanna region. The model is based on a patch-scale production efficiency model (PEM) scaled up to the regional level using empirical relationships between patch-scale behavior and multi-source remote sensing data (spatio-temporal variability of vegetation and climatic variables). The model requires the spatial distribution of woody vegetation cover, which is used to determine separate respiration rates for tree and grass. Net primary production, grass and tree leaf death, and herbivory are also taken into account in this mechanistic modeling approach. The fuel load model has been calibrated and validated from independent measurements taken from savanna vegetation in Africa southward from the equator. A sensitivity analysis on the effect of climate variables (incoming radiation, air temperature, and precipitation) has been conducted to demonstrate the strong role that water availability has in determining productivity and subsequent fuel load over the southern African region. The model performance has been tested in four different areas representative of a regional increasing rainfall gradient—Etosha National Park, Namibia, Mongu and Kasama, Zambia, as well as in Kruger National Park, South Africa. Within each area, we analyze model output from three different magnitudes of canopy coverage (<5, 30, and 50%). We find that fuel load ranges predicted by the model are globally in agreement with field measurements for the same year. High rainfall sustains green herbaceous production late in the dry season and delays tree leaf litter production. Effect of water on production varies across the rainfall gradient with delayed start of green material production in more arid regions.     

Short- and Long-Term Alterations of Gene Expression in Limbic Structures by Repeated Electroconvulsive-Induced Seizures

Rats were submitted to a series of 10 daily electroconvulsive shocks (ECS). A first group of animals was killed 1 day after the last seizure and a second group 30 days later. Tyrosine hydroxylase (TH) activity was measured using an in vitro assay in the nucleus caudatus, anterior cortex, amygdala, substantia nigra, ventral tegmental area, and locus ceruleus. The mRNA corresponding to this enzyme (TH-mRNA) was evaluated using a cDNA probe at the cellular level in the ventral tegmental area, substantia nigra, and locus ceruleus. Met-enkephalin (MET)-immunoreactivity and the mRNA coding for the preproenkephalin (PPE-mRNA) were assayed in striatum and the central nucleus of the amygdala. The day after the last ECS an increase of TH activity was observed in the ventral tegmental area, locus ceruleus, and substantia nigra in parallel with a similar increase in the amygdala and striatum; in the anterior cortex TH activity remained unchanged. TH-mRNA was increased in the locus ceruleus, evidencing the presence in this structure of a genomic activation. The amounts of MET and PPE-mRNA were unaffected in the striatum but increased in the amygdala. Thirty days after the last ECS we observed a decrease of TH activity in the amygdala and of TH-mRNA amount in the ventral tegmental area. In the locus ceruleus TH-mRNA remained higher in treated animals than in controls whereas TH activity returned to control levels. These results demonstrate that a series of ECS induces an initial increase of the activity of mesoamygdaloid catecholaminergic neurons followed by a sustained decrease through alterations of TH gene expression which could mediate the clinical effect of the treatment.     

Stimulation of the Cyclic GMP Pathway by NO Induces Expression of the Immediate Early Genes c-fos and junB in PC12 Cells

Abstract: Stimulation of several second messenger pathways induces the expression of immediate early genes such as c- fos , c- jun , junB , and junD , but little is known about their induction via the stimulation of the cyclic GMP pathway. Here we looked at the expression of early genes in pheochromocytoma PC12 cells after activation of cytosolic guanylate cyclase by sodium nitroprusside. This compound spontaneously releases NO, a molecule known to be involved in cell communication. We found that expression of c- fos and junB but not of c- jun or junD is increased upon activation of cyclic GMP pathway. c- fos mRNA expression was the most activated (fourfold at 30 min), whereas junB response was more modest (2.2-fold activation at 60 min). Nuclear extracts of stimulated cells show increased binding capacity to the AP1 binding site consistent with the dose-response curve. The activating effect of nitroprusside could be reproduced by dipyridamole, a selective cyclic GMP phosphodiesterase inhibitor and by 8- p -chlorophenylthio-cyclic GMP, a permeant selective cyclic GMP-dependent protein kinase activator, and abolished by KT5823, an inhibitor of that kinase. The results show that NO promotes early gene activation and AP1 binding enhancement through the stimulation of the cyclic GMP pathway.     

First chromosome scale genomes of ithomiine butterflies (Nymphalidae: Ithomiini): Comparative models for mimicry genetic studies

The ithomiine butterflies (Nymphalidae: Danainae) represent the largest known radiation of Müllerian mimetic butterflies. They dominate by number the mimetic butterfly communities, which include species such as the iconic neotropical Heliconius genus. Recent studies on the ecology and genetics of speciation in Ithomiini have suggested that sexual pheromones, colour pattern and perhaps hostplant could drive reproductive isolation. However, no reference genome was available for Ithomiini, which has hindered further exploration on the genetic architecture of these candidate traits, and more generally on the genomic patterns of divergence. Here, we generated high-quality, chromosome-scale genome assemblies for two Melinaea species, M. marsaeus and M. menophilus, and a draft genome of the species Ithomia salapia. We obtained genomes with a size ranging from 396 to 503 Mb across the three species and scaffold N50 of 40.5 and 23.2 Mb for the two chromosome-scale assemblies. Using collinearity analyses we identified massive rearrangements between the two closely related Melinaea species. An annotation of transposable elements and gene content was performed, as well as a specialist annotation to target chemosensory genes, which is crucial for host plant detection and mate recognition in mimetic species. A comparative genomic approach revealed independent gene expansions in ithomiines and particularly in gustatory receptor genes. These first three genomes of ithomiine mimetic butterflies constitute a valuable addition and a welcome comparison to existing biological models such as Heliconius, and will enable further understanding of the mechanisms of adaptation in butterflies.     

In vivo release of adenosine from cat basal ganglia—studies with a push pull cannula

The release of newly synthesized [³H]adenosine has been studied in vivo in cat caudate nucleus and substantia nigra, using a push pull cannula. In the presence of [³H]adenosine as precursor, spontaneously released [³H]adenosine was easily detectable in superfusates of the push pull cannula. In the caudate nucleus, potassium and veratridine caused a marked and reversible increase in [³H]adenosine release. The effect of veratridine was completely blocked by tetrodotoxin (TTX) although TTX had no action by itself. Ouabain as well as glutamate, also markedly increased the release of [³H]adenosine.The specific 5′ nucleotidase inhibitor α,β-methylene ADP, did not alter the increase in the amount of [³H]adenosine obtained by veratridine, although it diminished the spontaneous release of [³H]adenosine by about 20%.Push pull cannulae were also implanted simultaneously into the caudate nucleus and substantia nigra. Potassium applied into the caudate nucleus increased the local release of adenosine but did not change that observed in the substantia nigra. When potassium was applied into the substantia nigra, it also increased the local release of adenosine but did not change that observed in the caudate nucleus.The results are discussed in term of the possible existence of “purinergic neurons” and of the relation between the adenosine release and central nervous activity.     

The rates of introgression and barriers to genetic exchange between hybridizing species: sex chromosomes vs autosomes

Interspecific crossing experiments have shown that sex chromosomes play a major role in reproductive isolation between many pairs of species. However, their ability to act as reproductive barriers, which hamper interspecific genetic exchange, has rarely been evaluated quantitatively compared to Autosomes. This genome-wide limitation of gene flow is essential for understanding the complete separation of species, and thus speciation. Here, we develop a mainland-island model of secondary contact between hybridizing species of an XY (or ZW) sexual system. We obtain theoretical predictions for the frequency of introgressed alleles, and the strength of the barrier to neutral gene flow for the two types of chromosomes carrying multiple interspecific barrier loci. Theoretical predictions are obtained for scenarios where introgressed alleles are rare. We show that the same analytical expressions apply for sex chromosomes and autosomes, but with different sex-averaged effective parameters. The specific features of sex chromosomes (hemizygosity and absence of recombination in the heterogametic sex) lead to reduced levels of introgression on the X (or Z) compared to autosomes. This effect can be enhanced by certain types of sex-biased forces, but it remains overall small (except when alleles causing incompatibilities are recessive). We discuss these predictions in the light of empirical data comprising model-based tests of introgression and cline surveys in various biological systems.     

PON1 Paraoxonase Activity is Reduced During HDL Oxidation and is an Indicator of HDL Antioxidant Capacity

The aim of this study was to investigate the effect of HDL oxidation on PON1 paraoxonase activity. Also, we were interested in investigating the mechanism by which PON1 could be inactivated and the correlation between its enzymatic activity and the antioxidant properties of HDL. Three different oxidation systems were used for the HDL oxidation: (1) oxidation induced by THP1 cells, (2) oxidation induced by copper ions at a concentration 10 &#119 M, and (3) oxidation induced by &#148 OH and O 2 &#148 &#109 oxygen free radicals produced by &#110 -radiolysis. HDL oxidation was followed by the measurement of lipid peroxide formation, and PON1 activity was determined by measuring the rate of paraoxon hydrolysis. Our results show that HDL oxidation is accompanied by a reduction in the PON1 paraoxonase activity. The extent of PON1 inactivation depends both on the extent of HDL oxidation and on the oxidation system used. The rates of HDL oxidation and PON1 inactivation were significantly correlated ( r =0.93, p <0.0054). Our results show that oxidized HDL loses its protective effect toward LDL oxidation. The antioxidant action of HDL towards LDL oxidation and the degradation of PON1 paraoxonase activity were significantly correlated ( r =0.95, p <0.04).