Cytogenetic studies of mice exposed to styrene by inhalation.

The data for the in vivo genotoxicity of styrene (STY) are equivocal. To evaluate the clastogenicity and sister-chromatid exchange (SCE)-inducing potential of STY in vivo under carefully controlled conditions, B6C3F1 female mice were exposed by inhalation for 6 h/day for 14 consecutive days to either 0, 125, 250 or 500 ppm STY. One day after the final exposure, peripheral blood, spleen, and lungs were removed and cells were cultured for the analysis of micronucleus (MN) induction using the cytochalasin B-block method, chromosome breakage, and SCE induction. Peripheral blood smears were also made for scoring MN in erythrocytes. There was a significant concentration-related elevation of SCE frequency in lymphocytes from the spleen and the peripheral blood as well as in cells from the lung. However, no statistically significant concentration-related increases were found in the frequency of chromosome aberrations in the cultured splenocytes or lung cells, and no significant increases in MN frequencies were observed in binucleated splenocytes or normochromatic erythrocytes in peripheral blood smears.     

Antenna organization in purple bacteria investigated by means of fluorescence induction curves

Fluorescence induction curves of purple bacteria (Rs. rubrum, Rps. viridis and Rb. capsulatus) were measured in the sub-millisecond time range employing a xenon flash technique. The induction curves of all three species displayed a sigmoidal shape. Analysis of the curves showed that none of the species examined had an antenna organization of a lake (i.e. unrestricted energy transfer between photosynthetic units). The apparent time constants of inter-unit exciton transfer were estimated to be approximately 24 ps in the case of LHC 1-containing species (Rs. rubrum and Rps. viridis) and 40 ps in the case of the LHC 2-containing species Rb. capsulatus. This result demonstrates that LHC 2 (B800–850) acts as a sort of insulator between photosynthetic units. Assuming a coordination number of 6 in the LHC 1-containing species the mean single step energy transfer time between adjacent LHC 1 can be estimated to be 4–5 ps. This is not perfectly compatible with the much faster Förster transfer rate of <1ps that follows from the minimal chromophore-chromophore distances estimated from digital image processing of micrographs from stained membranes. It thus may be concluded that the photosynthetic units (reaction center plus LHC 1) are loosely arranged in the photosynthetic membrane, like in the fluid-mosaic-membrane model, rather than in a hexagonally crystalline configuration.Abbreviations A antenna pigment - APD avalanche photodiode - LHC 1 light-harvesting complex 1 of purple bacteria - LHC 2 light-harvesting complex 2 of purple bacteria - P primary donor - PSU photosynthetic unit - Q_A first quinone acceptor - RC reaction center     

Head-down bed rest impairs vagal baroreflex responses and provokes orthostatic hypotension

We studied vagally mediated carotid baroreceptor-cardiac reflexes in 11 healthy men before, during, and after 30 days of 6 degrees head-down bed rest to test the hypothesis that baroreflex malfunction contributes to orthostatic hypotension in this model of simulated microgravity. Sigmoidal baroreflex response relationships were provoked with ramped neck pressure-suction sequences comprising pressure elevations to 40 mmHg followed by serial R-wave-triggered 15-mmHg reductions to -65 mmHg. Each R-R interval was plotted as a function of systolic pressure minus the neck chamber pressure applied during the interval. Compared with control measurements, base-line R-R intervals and the minimum, maximum, range, and maximum slope of the R-R interval-carotid pressure relationships were reduced (P less than 0.05) from bed rest day 12 through recovery day 5. Baroreflex slopes were reduced more in four subjects who fainted during standing after bed rest than in six subjects who did not faint (-1.8 +/- 0.7 vs. -0.3 +/- 0.3 ms/mmHg, P less than 0.05). There was a significant linear correlation (r = 0.70, P less than 0.05) between changes of baroreflex slopes from before bed rest to bed rest day 25 and changes of systolic blood pressure during standing after bed rest. Although plasma volume declined by approximately 15% (P less than 0.05), there was no significant correlation between reductions of plasma volume and changes of baroreflex responses. There were no significant changes of before and after plasma norepinephrine or epinephrine levels before and after bed rest during supine rest or sitting.(ABSTRACT TRUNCATED AT 250 WORDS)     

A day in the half-life of a protein

Researchers describe a method called bleach-chase to quantitatively measure the half-lives of fluorescently tagged proteins in human cancer cells.     

Effects of cycloSal-D4TMP Derivatives in H9 Cells with Induced AZT Resistance Phenotype

Abstract

Cytotoxic and antiretroviral activity of cycloSal-d4TMP derivatives were tested in a new AZT-resistant H9 cell subline (H9^rAZT²⁵⁰). The results showed, that cycloSal-d4TMP derivatives overcame resistance of HIV-1 to d4T in H9^rAZT²⁵⁰ cells, which exert decreased thymidine kinase (TK) gene expression.     

Learning related interactions among neuronal systems involved in memory processes

Functional neuroimaging techniques using positron emission tomography (PET) and functional magnetic resonance imaging (fMRI) have provided new insights in our understanding of brain function from the molecular to the systems level. While subtraction strategy based data analyses have revealed the involvement of distributed brain regions in memory processes, covariance analysis based data analysis strategies allow functional interactions between brain regions of a neuronal network to be assessed. The focus of this chapter is to (1) establish the functional topography of episodic and working memory processes in young and old normal volunteers, (2) to assess functional interactions between modules of networks of brain regions by means of covariance based analyses and systems level modelling and (3) to relate neuroimaging data to the underpinning neural networks. Male normal young and old volunteers without neurological or psychiatric illness participated in neuroimaging studies (PET, fMRI) on working and episodic memory. Distributed brain areas are involved in memory processes (episodic and working memory) in young volunteers and show much of an overlap with respect to the network components. Systems level modelling analyses support the hypothesis of bihemispheric, asymmetric networks subserving memory processes and revealed both similarities in general and differences in the interactions between brain regions during episodic encoding and retrieval as well as working memory. Changes in memory function with ageing are evident from studies in old volunteers activating more brain regions compared to young volunteers and revealing more and stronger influences of prefrontal regions. We finally discuss the way in which the systems level models based on PET and fMRI results have implications for the understanding of the underlying neural network functioning of the brain.     

A quantum chemical investigation of the electronic structure of thionine

We have examined the electronic and molecular structure of 3,7-diaminophenothiazin-5-ium dye (thionine) in the electronic ground state and in the lowest excited states. The electronic structure was calculated using a combination of density functional theory and multi-reference configuration interaction (DFT/MRCI). Equilibrium geometries were optimized employing (time-dependent) density functional theory (B3LYP functional) combined with the TZVP basis set. Solvent effects were estimated using the COSMO model and micro-hydration with up to five explicit water molecules. Our calculated electronic energies are in good agreement with experimental data. We find the lowest excited singlet and triplet states at the ground state geometry to be of π→π* (S(1), S(2), T(1), T(2)) and n→π* (S(3), T(3)) character. This order changes when the molecular structure in the electronically excited states is relaxed. Geometry relaxation has almost no effect on the energy of the S(1) and T(1) states (~0.02 eV). The relaxation effects on the energies of S(2) and T(2) are moderate (0.14-0.20 eV). The very small emission energy results in a very low fluorescence rate. While we were not able to locate the energetic minimum of the S(3) state, we found a non-planar minimum for the T(3) state with an energy which is very close to the energy of the S(1) minimum in the gas phase (0.04 eV above). When hydration effects are taken into account, the n→π* states S(3) and T(3) are strongly blueshifted (0.33 and 0.46 eV), while the π→π* states are only slightly affected (<0.06 eV).