Determination of Dopamine and Its Acidic Metabolites in Brain Tissue by HPLC with Electrochemical Detection in a Single Run After Minimal Sample Pretreatment

A method, based on reverse-phase liquid-liquid chromatography, has been developed for the determination, in a single run, of dopamine (DA) and its acidic metabolites 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA), combined with electrochemical detection (ECD). If applied to brain tissue, sample pretreatment can be reduced to centrifugation, filtration and adjustment of pH and perchlorate concentration prior to introduction into the liquid chromatograph. The relation between the perchlorate (counterion) concentration of the mobile phase and the retention (k') of the amines is linear, as is the relation between the H+ concentration of the mobile phase and the retention of the acidic metabolites. This flexible phase system, combined with a simple and therefore reproducible sample pretreatment, warrants a high throughput of samples. The procedure offers good possibilities for routine analysis of catecholamines and their acidic metabolites in the picogram range. Some typical examples of the behaviour of this phase system and the electrochemical detector are presented and discussed.     

Bio-energetic data show weak spatial but strong seasonal differences in wetland quality for waders in a Mediterranean migration bottleneck

1. Assessing the quality of wetlands as refuelling areas for migrating waterbirds based on resource distribution patterns is challenging. Resources in wetlands can vary both horizontally and vertically and may be differentially available to different bird species at different times of the year. Therefore, the extent to which wetland quality can be generalised across seasons and for a diversity of birds remains unresolved.
2. Spatiotemporal variation in abundance and quality of macrobenthos as food for migrating waders was studied in a set of wetland areas near a Mediterranean migration bottleneck in the Balkan peninsula, during both spring and autumn migration. Samples were subdivided into different depth layers to differentiate between parts of the sediment that are accessible to different groups of wader species. To quantify food availability and the resulting refuelling capacity in different wetland habitat types, abundance, wet weight, and lipid and protein content of invertebrate taxa were determined for each sample.
3. Invertebrate food availability and quality were markedly higher in spring than in autumn. Given the higher abundance and protein and lipid content of prey in spring, the total energy that could be harvested in spring (3.81 ± 0.79 kJ/m²) was about 7 times higher than in autumn (0.56 ± 0.12 kJ/m²). Most prey were found in the top layer of the sediment (0–22 mm depth), but about a third of the total energy was present in the deepest soil layer that only longer-billed species could reach (55–200 mm depth). Higher quality prey items such as larger-bodied and heavier polychaetes and bivalves were found in the deeper sediment layers.
4. For other taxa, there was no evident vertical pattern of increasing individual body size. Prey abundance differed between certain habitat types but, overall, food availability could not be linked to distinct habitats. In spring, redox potential tended to be higher, while pH, vegetation cover, conductivity, and temperature were lower than in autumn.
5. Different wetland habitat classes used in a conservation framework may provide similar food resources for waders. As a result, linking food availability to habitat classifications is not straightforward. Furthermore, seasonal variation in wetland quality requires a re-evaluation of the importance of wetland areas during spring and autumn migration. Finally, nutritional analyses are essential for determining the capacity of wetlands to support refuelling by migratory waterbirds.

     

Should attractive males have more sons?

It is often argued that females with attractive partners shouldproduce more sons because these sons will inherit their father'sattractiveness. Numerous field and laboratory studies have addressedthis hypothesis, with inconsistent results, but there is surprisinglylittle theoretical work on the topic. Here, we present an extensiveinvestigation of the link between male attractiveness and offspringsex ratios, using evolutionary, individual-based computer simulations.In situations where sexual selection leads to the stable exaggerationof a costly male trait and a costly female preference, we findthat females with attractive partners produce more sons thanfemales with unattractive partners. This same qualitative patternis seen for a wide range of different models, with discreteor continuous variation in the male trait, under Fisherian orgood-genes sexual selection and for abrupt or gradual sex ratioadjustment. However, in all simulations, it takes a huge numberof generations to evolve, suggesting that selection acting onsex ratio adjustment is weak. Our models ignore many potentialcosts and constraints associated with manipulation, which impliesthat selection may be weaker still in natural populations. Theseresults may explain why published evidence for sex ratio biasin relation to male attractiveness is mixed.     

Collective Cell Behavior in Mechanosensing of Substrate Thickness

Extracellular matrix stiffness has a profound effect on the behavior of many cell types. Adherent cells apply contractile forces to the material on which they adhere and sense the resistance of the material to deformation—its stiffness. This is dependent on both the elastic modulus and the thickness of the material, with the corollary that single cells are able to sense underlying stiff materials through soft hydrogel materials at low (<10 μm) thicknesses. Here, we hypothesized that cohesive colonies of cells exert more force and create more hydrogel deformation than single cells, therefore enabling them to mechanosense more deeply into underlying materials than single cells. To test this, we modulated the thickness of soft (1 kPa) elastic extracellular-matrix-functionalized polyacrylamide hydrogels adhered to glass substrates and allowed colonies of MG63 cells to form on their surfaces. Cell morphology and deformations of fluorescent fiducial-marker-labeled hydrogels were quantified by time-lapse fluorescence microscopy imaging. Single-cell spreading increased with respect to decreasing hydrogel thickness, with data fitting to an exponential model with half-maximal response at a thickness of 3.2 μm. By quantifying cell area within colonies of defined area, we similarly found that colony-cell spreading increased with decreasing hydrogel thickness but with a greater half-maximal response at 54 μm. Depth-sensing was dependent on Rho-associated protein kinase-mediated cellular contractility. Surface hydrogel deformations were significantly greater on thick hydrogels compared to thin hydrogels. In addition, deformations extended greater distances from the periphery of colonies on thick hydrogels compared to thin hydrogels. Our data suggest that by acting collectively, cells mechanosense rigid materials beneath elastic hydrogels at greater depths than individual cells. This raises the possibility that the collective action of cells in colonies or sheets may allow cells to sense structures of differing material properties at comparatively large distances.     

A double coil chromatin sub-unit model

A model is proposed for the structure of DNA in chromatin sub-units. Each sub-unit is proposed to contain two turns of an inner coil, with a pitch of about 40and an external diameter of 70 . Around the inner coil is wound, in opposite handedness, a slightly larger amount of DNA at a diameter of about 150 . The total contour length consistent with the electron micrographs and X-ray scattering is 600–700 , or about 200 base pairs. It is suggested that the inner coil is protein rich and contains all of the histones except H1, which is associated with the outer coil. The double-coil model is consistent with previous biochemical and biophysical studies of chromatin. The existence of 200 and 100 base pair digestion fragments and a 6 to 1 DNA compaction are readily explained.This model is based upon the electron microscopic observation of replicas of frozen chromatin and X-ray and neutron scattering. Structural details of 25are preserved and visualized by the freeze fracture electron microscopy techniques employed.     

Biofeedback and applied psychophysiology at the crossroads

Biofeedback and applied psychophysiology, as tools, as objects of scientific inquiry, and as clinical interventions, have progressed from speculative experiment to data-based research, from trial clinical intervention to efficacy studies and accountability. These are multidisciplinary approaches, crossing the boundary between traditional professions such as medicine, psychology, physical therapy, occupational therapy, and other health care related fields. Along the way we as an Association, our members both scientists and practitioners, have encountered the many hurdles and stumbling blocks that stand in the way of developing new technologies. How we deal with these obstacles shapes us as a group and shapes the perceptions of others who view us. An attempt will be made to place the current development of the field within the context of the rapidly changing health care environment, and to address the challenges, and sometimes conflicting demands, of experimental science and clinical practice.     

Antimicrobial resistance in humans,livestock and the wider environment

Antimicrobial resistance (AMR) in humans is inter-linked with AMR in other populations, especially farm animals, and in the wider environment. The relatively few bacterial species that cause disease in humans, and are the targets of antibiotic treatment, constitute a tiny subset of the overall diversity of bacteria that includes the gut microbiota and vast numbers in the soil. However, resistance can pass between these different populations; and homologous resistance genes have been found in pathogens, normal flora and soil bacteria. Farm animals are an important component of this complex system: they are exposed to enormous quantities of antibiotics (despite attempts at reduction) and act as another reservoir of resistance genes. Whole genome sequencing is revealing and beginning to quantify the two-way traffic of AMR bacteria between the farm and the clinic. Surveillance of bacterial disease, drug usage and resistance in livestock is still relatively poor, though improving, but achieving better antimicrobial stewardship on the farm is challenging: antibiotics are an integral part of industrial agriculture and there are very few alternatives. Human production and use of antibiotics either on the farm or in the clinic is but a recent addition to the natural and ancient process of antibiotic production and resistance evolution that occurs on a global scale in the soil. Viewed in this way, AMR is somewhat analogous to climate change, and that suggests that an intergovernmental panel, akin to the Intergovernmental Panel on Climate Change, could be an appropriate vehicle to actively address the problem.