The presence of immunoreactive vertebrate bioactive peptide substances in hemocytes of the freshwater snailViviparus ater (gastropoda,prosobranchia)

1. Using an immunocytochemical procedure a wide range of immunoreactive vertebrate bioactive peptides (BAPs) has been found in hemocytes of Viviparus ater: bombesin, calcitonin, CCK-8, CCK-39, GH, glucagon, insulin, oxytocin, neurotensin, secretin, serotonin, somatostatin, substance P, vasopressin, and VIP. 2. No immunostaining was observed for antigastrin and antithyroglobulin antibodies. 3. The presence of BAP-like molecules in hemocytes suggests a correlation between hemocyte and APUD cells and is evidence of a relationship between the neuroendocrine and the immune systems.     

Phospholipid base exchange enzyme activity in sarcolemmal membranes from the heart of cardiomyopathic hamsters

The activity of phospholipid base exchange enzymes has been evaluated in cardiac sarcolemmal membranes from Syrian Golden hamsters and from a hamster strain (UM-X7.1) characterized by a genetic form of hypertrophic cardiomyopathy. No choline base exchange activity and only a little serine base exchange activity were detected, whereas the ethanolamine base exchange enzyme was found highly active in membranes from both strains. For this reason, the present study is focussed on the ethanolamine base exchange enzyme. The apparent Km for ethanolamine of ethanolamine base exchange enzyme from Syrian Golden membranes and from UM-X7.1 strain membranes are 18 and 32 μM, respectively. The specific activity of the sarcolemmal ethanolamine base exchange enzyme is lower in the UM-X7.1 strain than in Syrian Golden hamsters. The calcium-dependence of the enzyme appears different when the membranes from the two strains are compared. Indeed, after removal of the membrane-bound divalent cations, comparable activities are found in both membrane preparations, whereas, upon addition of Ca²⁺ to the incubation mixtures, the activity of the enzyme is enhanced in the membranes from Syrian Golden strain more than in those from UM-X7.1 strain. The cholesterol content of sarcolemmal membranes is higher in the cardiomyopathic strain than in the Syrian Golden hamsters. A possible relation between changes of the membrane lipid composition and of the ethanolamine base exchange activity is discussed.     

A unified neural network model of spatiotemporal processing in X and Y retinal ganglion cells

This article makes use of a push-pull shunting network, which was introduced in the companion article, to model certain properties of X and Y retinal ganglion cells. Input to the push-pull network is preprocessed by a nonlinear mechanism for temporal adaptation, which is ascribed here to photoreceptor dynamics. The complete circuit is used to show that a simple change in receptive field morphology within a single model equation can change the network's response characteristics to closely resemble those of either X or Y cells. Specifically, an increase in width of the receptive field center mechanism is sufficient to account for generation of on-off (Y-like) instead of null (X-like) responses to modulated gratings. In agreement with experimental data, the Y cell on-off response is independent of spatial phase. Also, the model accurately predicts that on-off responses can be observed in X cells for particular stimulus configurations. Taken together, the results show how the retina combines individually inadequate modules to efficiently handle the tasks required for accurate spatial and temporal visual information processing. The model is also able to clarify a number of controversial experimental findings on the nature of spatiotemporal visual processing in the retina.     

Phenylarsine oxide induces the cyclosporin A-sensitive membrane permeability transition in rat liver mitochondria

This paper reports an investigation on the effects of the hydrophobic, bifunctional SH group reagent phenylarsine oxide (PhAsO) on mitochondrial membrane permeability. We show that PhAsO is a potent inducer of the mitochondrial permeability transition in a process which is sensitive to both the oxygen radical scavanger BHT and to cyclosporin A. The PhAsO-induced permeability transition is stimulated by Ca²⁺ but takes place also in the presence of EGTA in a process that maintains its sensitivity to BHT and cyclosporin A. Our findings suggest that, at variance from other known inducers of the permeability transition, PhAsO reacts directly with functional SH groups that are inaccessible to hydrophilic reagents in the absence of Ca²⁺.     

Rheology of hydroxyethyl guar gum derivatives

The rheological properties of aqueous solutions of hydroxyethyl guar gum, a synthetic derivative of guar gum, have been studied under continuous and oscillatory shear flow conditions. Data obtained from both experimental techniques were satisfactorily fitted according to Cross-type models. The effect of polymer concentration, molecular weight and temperature on the rheological behavior of hydroxyethyl guar gum systems have been investigated and discussed in terms of rheological parameters like the zero-shear viscosity η₀ and the characteristic times λ and λ′.     

Hidden smectic properties of a chiral side-chain co-oligomer

We recently showed that a side-chain industrial co-oligosiloxane presents a quenchable enlarged blue phase behaviour at the cholesteric-isotropic phase transition. In this paper, we present the results of a structural study based on X-ray diffraction, differential scanning calorimetry and optical measurements. In particular, the smectic A organisation is demonstrated in the lower temperature domain, which was hitherto understood as a cholesteric phase. A structural model for this phase is proposed on the basis of the analysis of the anisotropic scattering of stretched fibers. Our results also suggest that the observed glass transition is indeed a rather complex phenomenon, which seems to involve not only the freezing of the main chains, but also smectic correlations at the side-chain level. Moreover, the calorimetric study indicates that, notwithstanding the conservation of the processed film's optical properties, low kinetic reorganisations occur at room temperature.     

Genetic determinants of glutamine synthetase inDrosophila melanogaster: A gene for glutamine synthetase I resides in the 21B3-6 region

Recombinational and deletion mapping of electrophoretic variants of the glutamine synthetase I isozyme (GSI) in Drosophila melanogaster locates the gene in the 21B region on the second chromosome. We have conducted a genetic analysis of the region extending cytologically from 21A to 21B4-6. Recessive lethal mutations were generated by ethyl methanesulfonate (EMS) and ethyl nitrosourea (ENU) mutagenesis and by hybrid dysgenesis (HD). These lethals fall into seven functional groups, which were partially ordered by complementation with cytologically defined deficiencies of this region generated by hybrid dysgenesis. Two of the EMS- and two of the ENU-induced lethals fulfill biochemical criteria expected for null alleles of the GSI gene.     

Computer-assisted mathematical analysis of sigmoid biological events

A program in BASIC is described which allows accurate quantificationof some numerical parameters that can be objectively correlatedto biological indexes in sigmoid biological events. Attentionwas focused on the polymerization process of actin (a muscleprotein with a mol. wt of 42 000 daltons) studied as the variationin the OD₃₆₀ index with time. The experimental points, if plotted,can be well approximated by a rational function of the typeOD₃₆₀ = f(t), which passes through the origin and can be representedgraphically by a sigmoid curve. The program was very helpfulin comparing the experimental curves and in analysing significantparameters, such as maximum velocity and asymptote, that characterizethese curves and whose interpretation would otherwise be purelysubjective. Received on July 11, 1985; accepted on January 13, 1986     

Estimation of the size of freshwater ciliate populations by a sub-sampling technique

A technique is described for the estimation of the size of ciliate populations based on replicated counts. Sample drops were taken by automatic pipettes of different volume from activated sludge and from a small oligotrophic stream. Specific aims were: 1) the estimation of the number of species; 2) the estimation of the number of individual in each species; 3) the selection of a suitable sub-sample size and number of replicates. For each volume the cumulative increase in species taken in successive sub-samples was determined. For each species the minimum permissible sub-sample volume and the number of replicates required for an allowable error of 10% and 25% were determined. Lastly, the relationship between the mean number of individuals counted for each species and the relative coefficient of variation was visualized.     

Dion tomasellii (Zamiaceae), a new species with two varieties from western Mexico

Dion tomasellii sp. nov. occurs with an interrupted distribution from Guerrero to central Sonora. It is characterized by falcate to subfalcate leaflets. The populations from Sonora and northern Sinaloa are segregated asD. tomasellii var.sonorense on the basis of their narrower and glaucous leaflets.