Toxicty of a Serotonin-derived Neuromelanin

Neuroscience - Vision and Functional Brain Imaging Poster SessionIntroduction: POCD (Postoperative Cognitive Dysfunction) is associated with increased mortality and disability and may develop as a consequence of lipid peroxidative byproducts (i.e. acrolein), which accumulate with aging. We previously showed that sevoflurane sequesters acrolein, which promotes the formation of a novel species of neuromelanin (NM) that may play a role in POCD. In this current study, we examined the properties of NM and hypothesized that this novel serotonin-derived melanoid (SDM) product may be neurotoxic. Methods: SDM was produced at the interface of an upper aqueous phase containing serotonin and a lower sevoflurane phase containing acrolein. Uni-lamellar vesicles (ULVs) of dioleoyl-phosphatidylcholine were made using an extrusion technique. The interaction of SDM with ULVs was examined using two lipid membrane probes: diphenyl-hexatriene (DPH) and merocyanine (MC). Vesicle disruption was investigated by monitoring the leakage of dye from calcein-loaded ULVs. Absorbance spectra of SDM were also examined. Statistical analysis involved linear regression and unpaired Student t-tests (p<0.05). Results: We observed that SDM decreased DPH fluorescence anisotropy and increased the temperature-dependent change in anisotropy of DPH. SDM increased the ratio of absorbance (570nm/530nm) of MC-bound ULVs. Using calcein-loaded ULVs, SDM increased detergent-mediated calcein leakage. The intense absorbance band below 250nm of SDM was dramatically altered in the presence of ULVs, yielding three well-resolved peaks from a single broad band. Conclusion: From these data we conclude that SDM has the potential of being neurotoxic. Discussion: This study further characterizes SDM as an important species of NM. SDM disorganized the acyl chains and the phospholipid head groups of ULVs. The electronic structure of SDM was dramatically altered upon interaction with ULVs. We also observed that SDM enhanced detergent-mediated leakage of loaded ULVs, suggesting that SDM may be neurotoxic. We propose that inhalational agents that sequester acrolein [3], may promote the production of certain species of NM that deplete local serotonin and enhance neuronal vulnerability

Effects of Isoflurane on Plasma-Membrane Calcium ATPase

Neuroscience - Vision and Functional Brain Imaging Poster SessionIntroduction: Plasma membrane Ca2+-ATPase (PMCA) is a transmembrane enzymatic protein present in human neurons, myocytes, and RBCs which plays a role in controlling cellular Ca2+ levels by regulating intracellular ATP. Inhaled anesthetic agents, such as isoflurane, affect transmembrane Ca2+ levels by inhibiting PMCA activity. However, the effect of isoflurane on the interaction between ATP and PMCA has not been studied. We hypothesized that the inhibitory effects of isoflurane on PMCA involve modulation of the interaction between ATP and PMCA. Methods: RBC membranes (containing PMCA) were isolated from human subjects with a previously validated methodology using a calmodulin affinity chromatographic technique. The membranes were treated with isoflurane using human serum albumin as an intermediary with transfer occurring via a dialysis membrane. The treated membranes were then assayed for PMCA activity using the Malachite Green Colorimetric Assay. Activity of PMCA was determined by measuring the release of inorganic phosphate. Varying concentrations of ATP were used to determine the inhibitory effect on PMCA by isoflurane. Results: Isoflurane inhibited basal and CaM-stimulated PMCA activity (nmol of inorganic phosphate per mg PMCA per minute) by 28.6% (P < 0.04) and 66.9% (saturating concentration of 300nM) (P < 0.02), respectively. Significant inhibition of PMCA activity (77.7%) also occurred at CaM concentration as low as 2nM. Isoflurane also inhibited PMCA activity at ATP concentrations between 10[mu]M and 1000[mu]M. Conclusion: Isoflurane inhibited basal and calmodulin-stimulated PMCA activity. Significant inhibition of PMCA activity occurred at all concentrations of CaM and as low as 2nM. Isoflurane suppressed the Michaelis-Menton kinetics of PMCA activity as a function of ATP at concentrations from 10[mu]M to 1000[mu]M. Discussion: We showed for the first time that isoflurane decreases PMCA activity as a function of ATP concentration. We also illustrated that isoflurane decreases the ability of CaM to stimulate PMCA activity. In addition, we introduced a novel physiologic delivery system for isoflurane using albumin as a surrogate transfer molecule. The concentration of isoflurane used for these experiments was not determined. Due to difficulties in studying neuronal PMCA, the RBC isoform was used as a substitute. Further investigations could include exploring the direct effects of isoflurane on CaM and ATP using neuronal isoforms of PMCA, and ensuring clinically relevent concentrations of isoflurane. These data would suggest that a primary biochemical target for isoflurane neural inhibition is intracellular ATP via a direct effect on PMCA activity

Deconvolving Instrumental and Intrinsic Broadening in Excited State X-ray Spectroscopies

Intrinsic and experimental mechanisms frequently lead to broadening of spectral features in excited-state spectroscopies. For example, intrinsic broadening occurs in x-ray absorption spectroscopy (XAS) measurements of heavy elements where the core-hole lifetime is very short. On the other hand, nonresonant x-ray Raman scattering (XRS) and other energy loss measurements are more limited by instrumental resolution. Here, we demonstrate that the Richardson-Lucy (RL) iterative algorithm provides a robust method for deconvolving instrumental and intrinsic resolutions from typical XAS and XRS data. For the K-edge XAS of Ag, we find nearly complete removal of ~9.3 eV FWHM broadening from the combined effects of the short core-hole lifetime and instrumental resolution. We are also able to remove nearly all instrumental broadening in an XRS measurement of diamond, with the resulting improved spectrum comparing favorably with prior soft x-ray XAS measurements. We present a practical methodology for implementing the RL algorithm to these problems, emphasizing the importance of testing for stability of the deconvolution process against noise amplification, perturbations in the initial spectra, and uncertainties in the core-hole lifetime.Comment: 35 pages, 13 figure

Resistive Transition and Upper Critical Field in Underdoped YBa_2Cu_3O_{6+x} Single Crystals

A superconducting transition in the temperature dependence of the ab-plane resistivity of underdoped YBa_2Cu_3O_{6+x} crystals in the range T_c<30 K has been investigated. Unlike the case of samples with the optimal level of doping, the transition width increased insignificantly with magnetic field, and in the range T_c<13 K it decreased with increasing magnetic field. The transition point T_c(B) was determined by analyzing the fluctuation conductivity. The curves of B_{c2}(T) measured in the region T/T_c>0.1 did not show a tendency to saturation and had a positive second derivative everywhere, including the immediate neighborhood of T_c. The only difference among the curves of B_{c2}(T) for different crystal states is the scales of T and B, so they can be described in terms of a universal function, which fairly closely follows Alexandrov's model of boson superconductivity.Comment: 10 Revtex pages, 6 figures, uses psfig.st

Jekyll and Hyde: men's constructions of feminism and feminists

Research and commentary on men's responses to feminism has demonstrated the range of ways in which men have mobilised both against and for feminist principles. This paper argues that further analyses of men's responses require a sophisticated theory of discourse acknowledging the fragmented and contradictory nature of representation. A corpus of men's talk on feminism and feminists was studied to identify the pervasive patterns in men's accounting and regularities in rhetorical organisation. Material from two samples of men was included: a sample of white middle-class 17-18 year old school students and a sample of 60 interviews with a more diverse sample of older men aged 20 to 64. Two interpretative repertoires of feminism and feminists were identified. These set up a 'Jekyll and Hyde' binary and positioned feminism along with feminists very differently as reasonable versus extreme and monstrous. Both repertoires tended to be deployed together and the paper explores the ideological and interactional consequences of typical deployments along with the identity work accomplished by the men as they positioned themselves in relation to these

Cooperativity in sandpiles: statistics of bridge geometries

Bridges form dynamically in granular media as a result of spatiotemporal inhomogeneities. We classify bridges as linear and complex, and analyse their geometrical characteristics. In particular, we find that the length distribution of linear bridges is exponential. We then turn to the analysis of the orientational distribution of linear bridges and find that, in three dimensions, they are {\it vertically diffusive but horizontally superdiffusive}; thus, when they exist, long linear bridges form `domes'. Our results are in good accord with Monte Carlo simulations of bridge structure; we make predictions for quantities that are experimentally accessible, and suggest that bridges are very closely related to force chains.Comment: 15 pages, 10 figures. Minor changes and update

Never the twain shall meet: a critical appraisal of the combination of discourse and psychoanalytic theory in studies of men and masculinity

In recent years there has been a number of attempts by different researchers to study men and masculinity using a combination of discourse theory and psychoanalysis. The main reason for this development is the sense that, on its own, discourse theory provides an incomplete account of masculine subjectivity. Psychoanalysis is thought to be able to fill those gaps. In this paper I want to begin by reviewing these arguments. I will provide an outline of the alleged deficiencies in discursive approaches to men and masculinity before going on to examine some of the work that has attempted the above synthesis. What I aim to show is that, for a number of reasons, such attempts are bound to fail. Instead, I will argue that better progress can be made in studies of masculinity by remaining within the theoretical boundaries of Discursive Psychology

Atomic structures of TDP-43 LCD segments and insights into reversible or pathogenic aggregation.

The normally soluble TAR DNA-binding protein 43 (TDP-43) is found aggregated both in reversible stress granules and in irreversible pathogenic amyloid. In TDP-43, the low-complexity domain (LCD) is believed to be involved in both types of aggregation. To uncover the structural origins of these two modes of β-sheet-rich aggregation, we have determined ten structures of segments of the LCD of human TDP-43. Six of these segments form steric zippers characteristic of the spines of pathogenic amyloid fibrils; four others form LARKS, the labile amyloid-like interactions characteristic of protein hydrogels and proteins found in membraneless organelles, including stress granules. Supporting a hypothetical pathway from reversible to irreversible amyloid aggregation, we found that familial ALS variants of TDP-43 convert LARKS to irreversible aggregates. Our structures suggest how TDP-43 adopts both reversible and irreversible β-sheet aggregates and the role of mutation in the possible transition of reversible to irreversible pathogenic aggregation

Duality Near Quantum Hall Transitions

A recent experiment by Shahar et al, on the phase transitions between quantum Hall states and the insulator, found that the current-voltage characteristics in the two phases are related by symmetry. It was suggested in this work that this is evidence for charge-flux duality near quantum Hall transitions. Here we provide details of this analysis. (Appearances notwithstanding, this is a theoretical paper.)Comment: 26 pages, Revtex 3.