Conductance Ratios and Cellular Identity

Recent experimental evidence suggests that coordinated expression of ion channels plays a role in constraining neuronal electrical activity. In particular, each neuronal cell type of the crustacean stomatogastric ganglion exhibits a unique set of positive linear correlations between ionic membrane conductances. These data suggest a causal relationship between expressed conductance correlations and features of cellular identity, namely electrical activity type. To test this idea, we used an existing database of conductance-based model neurons. We partitioned this database based on various measures of intrinsic activity, to approximate distinctions between biological cell types. We then tested individual conductance pairs for linear dependence to identify correlations. Contrary to experimental evidence, in which all conductance correlations are positive, 32% of correlations seen in this database were negative relationships. In addition, 80% of correlations seen here involved at least one calcium conductance, which have been difficult to measure experimentally. Similar to experimental results, each activity type investigated had a unique combination of correlated conductances. Finally, we found that populations of models that conform to a specific conductance correlation have a higher likelihood of exhibiting a particular feature of electrical activity. We conclude that regulating conductance ratios can support proper electrical activity of a wide range of cell types, particularly when the identity of the cell is well-defined by one or two features of its activity. Furthermore, we predict that previously unseen negative correlations and correlations involving calcium conductances are biologically plausible.     

Startling Sweet Temptations: Hedonic Chocolate Deprivation Modulates Experience,Eating Behavior,and Eyeblink Startle

Many individuals restrict their food intake to prevent weight gain. This restriction has both homeostatic and hedonic effects but their relative contribution is currently unclear. To isolate hedonic effects of food restriction, we exposed regular chocolate eaters to one week of chocolate deprivation but otherwise regular eating. Before and after this hedonic deprivation, participants viewed images of chocolate and images of high-calorie but non-chocolate containing foods, while experiential, behavioral and eyeblink startle responses were measured. Compared to satiety, hedonic deprivation triggered increased chocolate wanting, liking, and chocolate consumption but also feelings of frustration and startle potentiation during the intertrial intervals. Deprivation was further characterized by startle inhibition during both chocolate and food images relative to the intertrial intervals. Individuals who responded with frustration to the manipulation and those who scored high on a questionnaire of impulsivity showed more relative startle inhibition. The results reveal the profound effects of hedonic deprivation on experiential, behavioral and attentional/appetitive response systems and underscore the role of individual differences and state variables for startle modulation. Implications for dieting research and practice as well as for eating and weight disorders are discussed.     

Glycoconjugate pattern of membranes in the acinar cell of the rat pancreas

Summary Lectin-binding studies were performed at the ultrastructural level to characterize glycoconjugate patterns on membrane systems in pancreatic acinar cells of the rat. Five lectins reacting with different sugar moieties were applied to ultrathin frozen sections: concanavalin A (ConA): glucose, mannose; wheat-germ agglutinin (WGA): N-acetylglucosamine, sialic acid; Ricinus communis agglutinin I (RCA I): galactose; Ulex europaeus agglutinin I (UEA I): l-fucose; soybean agglutinin (SBA): N-acetylgalactosamine). Binding sites of lectins were visualized either by direct conjugation to colloidal gold or by the use of a three-step procedure involving additional immune reactions. The rough endoplasmic reticulum and the nuclear envelope of acinar cells was selectively labelled for ConA. The membranes of the Golgi apparatus bound all lectins applied with an increasing intensity proceeding from the cis-to the trans-Golgi area for SBA, UEA I and WGA. In contrast RCA I selectively labelled the trans-Golgi cisternae. The membranes of condensing vacuoles and zymogen granules were labelled for all lectins used although the density of the label differed between the lectins. In contrast the content of zymogen granules failed to bind SBA and WGA. Lysosomal bodies (membranes and content) revealed binding sites for all lectins used. The plasma membranes were heavily labelled by all lectins except for SBA which showed only a weak binding to the lateral and the apical plasma membrane. These results are in accordance to current biochemical knowledge of the successive steps in the glycosylation of membrane proteins. It could be demonstrated, that the cryo-section technique is suitable for the fine structural localisation of surface glycoconjugates of plasma membranes and internal membranes in pancreatic acinar cells using plant lectins.     

Correlation between low CSA plasma concentration and severity of acute GvHD in bone marrow transplantation

Between 1982 and 1986 51 patients were treated with ciclosporin a (CSA) to prevent graft versus host disease (GvHD) after bone marrow transplantation (BMT). Major side effects of the drug were tremor, hypertension, hepatotoxicity and nephrotoxicity. Acute GvHD 0 degree to II degree occurred in 80% of our patients, and GvHD III degree and IV degree in 20% despite the use of CSA. Two to four days before the onset of GvHD, CSA serum levels were significantly lower on the average in patients who developed GvHD III degree and IV degree compared to the others. Our data indicate that plasma CSA concentrations higher than 250 ng/ml should be achieved to reduce the severity of GvHD after BMT.     

High state of order of isolated bacterial lipopolysaccharide and its possible contribution to the permeation barrier property of the outer membrane.

The conformational properties of the isolated S form of Salmonella sp. lipopolysaccharide (LPS), of Re mutant LPS, and of free lipid A were investigated by using X-ray diffraction and conformational energy calculations. The data obtained showed that LPS in a dried, in a hydrated, and probably also in an aqueous dispersion state is capable of forming bilayered lamellar arrangements similar to phospholipids. From the bilayer packing periodicities, a geometrical model of the extensions of the LPS regions lipid A, 2-keto-3-deoxyoctulosonic acid, and O-specific chain along the membrane normal could be calculated. Furthermore, the lipid A component was found to assume a remarkably high ordered conformation: its fatty acid chains were tightly packed in a dense hexagonal lattice with a center-to-center distance of 0.49 nm. The hydrophilic backbone of lipid A showed a strong tendency to form domains in the membrane, resulting in a more or less parallel arrangement of lipid A units. According to model calculations, the hydrophilic backbone of lipid A appears to be oriented approximately 45 degrees to the membrane surface, which would lead to a shed roof-like appearance of the surface structure in the indentations of which the 2-keto-3-deoxyoctulosonic acid moiety would fit. In contrast, the O-specific chains assume a low ordered, heavily coiled conformation. Comparison of these structural properties with those known for natural phospholipids in biological membranes indicates that the high state of order of the lipid A portion of LPS might be an important factor in the structural role and permeation barrier functions of LPS in the outer membrane of gram-negative bacteria.     

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Change in climatically suitable breeding distributions reduces hybridization potential between Vermivora warblers

Aim

Climate change is affecting the distribution of species and subsequent biotic interactions, including hybridization potential. The imperiled Golden-winged Warbler (GWWA) competes and hybridizes with the Blue-winged Warbler (BWWA), which may threaten the persistence of GWWA due to introgression. We examined how climate change is likely to alter the breeding distributions and potential for hybridization between GWWA and BWWA.

Location

North America.

Methods

We used GWWA and BWWA occurrence data to model climatically suitable conditions under historical and future climate scenarios. Models were parameterized with 13 bioclimatic variables and 3 topographic variables. Using ensemble modeling, we estimated historical and modern distributions, as well as a projected distribution under six future climate scenarios. We quantified breeding distribution area, the position of and amount of overlap between GWWA and BWWA distributions under each climate scenario. We summarized the top explanatory variables in our model to predict environmental parameters of the distributions under future climate scenarios relative to historical climate.

Results

GWWA and BWWA distributions are projected to substantially change under future climate scenarios. GWWA are projected to undergo the greatest change; the area of climatically suitable breeding season conditions is expected to shift north to northwest; and range contraction is predicted in five out of six future climate scenarios. Climatically suitable conditions for BWWA decreased in four of the six future climate scenarios, while the distribution is projected to shift east. A reduction in overlapping distributions for GWWA and BWWA is projected under all six future climate scenarios.

Main Conclusions

Climate change is expected to substantially alter the area of climatically suitable conditions for GWWA and BWWA, with the southern portion of the current breeding ranges likely to become climatically unsuitable. However, interactions between BWWA and GWWA are expected to decline with the decrease in overlapping habitat, which may reduce the risk of genetic introgression.     

Enrichment of adeno-associated virus serotype 5 full capsids by anion exchange chromatography with dual salt elution gradients

Adeno-associated virus-based gene therapies have demonstrated substantial therapeutic benefit for the treatment of genetic disorders. In manufacturing processes, viral capsids are produced with and without the encapsidated gene of interest. Capsids devoid of the gene of interest, or “empty” capsids, represent a product-related impurity. As a result, a robust and scalable method to enrich full capsids is crucial to provide patients with as much potentially active product as possible. Anion exchange chromatography has emerged as a highly utilized method for full capsid enrichment across many serotypes due to its ease of use, robustness, and scalability. However, achieving sufficient resolution between the full and empty capsids is not trivial. In this work, anion exchange chromatography was used to achieve empty and full capsid resolution for adeno-associated virus serotype 5. A salt gradient screen of multiple salts with varied valency and Hofmeister series properties was performed to determine optimal peak resolution and aggregate reduction. Dual salt effects were evaluated on the same product and process attributes to identify any synergies with the use of mixed ion gradients. The modified process provided as high as ≥75% AAV5 full capsids (≥3-fold enrichment based on the percent full in the feed stream) with near baseline separation of empty capsids and achieved an overall vector genome step yield of >65%.