Electrophysiological markers of mind wandering: A systematic review.

The ability to mentally wander away from the external environment is a remarkable feature of the human mind. Although recent years have witnessed a surge of interest in examining mind wandering using EEG, there is no comprehensive review that summarizes and accounts for the variable findings. Accordingly, we conducted a systematic review that synthesizes evidence from EEG studies that examined the electrophysiological measures of mind wandering. Our search yielded 42 studies that met eligibility criteria. The reviewed literature converges on a reduction in the amplitude of canonical ERP components (i.e., P1, N1 and P3) as the most reliable markers of mind wandering. Spectral findings were less robust, but point towards greater activity in lower frequency bands, (i.e., delta, theta, and alpha), as well as a decrease in beta band activity, during mind wandering compared to on-task states. The variability in these findings appears to be modulated by the task context. To integrate these findings, we propose an electrophysiological account of mind wandering that explains how the brain supports this inner experience. Conclusions drawn from this work will inform future endeavours in basic science to map out electrophysiological patterns underlying mind wandering and in translational science using EEG to predict the occurrence of this phenomenon.

Hypoxia downregulates PPARγ via an ERK1/2-NF-κB-Nox4-dependent mechanism in human pulmonary artery smooth muscle cells.

The ligand-activated transcription factor peroxisome proliferator-activated receptor γ (PPARγ) regulates metabolism, cell proliferation, and inflammation. Pulmonary hypertension (PH) is associated with reduced PPARγ expression, and hypoxia exposure regimens that cause PH reduce PPARγ expression. This study examines mechanisms of hypoxia-induced PPARγ downregulation in vitro and in vivo. Hypoxia reduced PPARγ mRNA and protein levels, PPARγ activity, and the expression of PPARγ-regulated genes in human pulmonary artery smooth muscle cells (HPASMCs) exposed to 1% oxygen for 72 h. Similarly, exposure of mice to hypoxia (10% O2) for 3 weeks reduced PPARγ mRNA and protein in mouse lung. Inhibiting ERK1/2 with PD98059 or treatment with siRNA directed against either NF-κB p65 or Nox4 attenuated hypoxic reductions in PPARγ expression and activity. Furthermore, degradation of H2O2 using PEG-catalase prevented hypoxia-induced ERK1/2 phosphorylation and Nox4 expression, suggesting sustained ERK1/2-mediated signaling and Nox4 expression in this response. Mammalian two-hybrid assays demonstrated that PPARγ and p65 bind directly to each other in a mutually repressive fashion. We conclude from these results that hypoxic regimens that promote PH pathogenesis and HPASMC proliferation reduce PPARγ expression and activity through ERK1/2-, p65-, and Nox4-dependent pathways. These findings provide novel insights into mechanisms by which pathophysiological stimuli such as hypoxia cause loss of PPARγ activity and pulmonary vascular cell proliferation, pulmonary vascular remodeling, and PH. These results also indicate that restoration of PPARγ activity with pharmacological ligands may provide a novel therapeutic approach in selected forms of PH.

Spinal manifestations of spontaneous intracranial hypotension.

OBJECT: The goal of the study was to elucidate the spinal manifestations of spontaneous intracranial hypotension. METHODS: The authors reviewed the medical records and imaging studies of 338 consecutive patients with spontaneous intracranial hypotension who were evaluated at their institution between 2001 and 2010. RESULTS: Twenty patients (6%; mean age 35.8 [range 16 to 60 years]; 5 males and 15 females) had convincing signs or symptoms referable to the spinal cord or spinal nerve roots. The spinal manifestations consisted of radiculopathy in 11 patients (unilateral in 8 and bilateral in 3), myelopathy in 8 patients, and bibrachial amyotrophy in 1 patient. The cervical spine was involved in 12 patients, the thoracic spine in 5, and the lumbosacral spine in 3. The spinal symptoms were positional in only 3 patients. The spinal manifestations occurred around the time of the headache onset in 16 patients, and months to years after the positional headache had resolved in 4 patients. A large extrathecal CSF collection causing compression of the spinal cord or nerve root was responsible for the spinal manifestations in the majority of patients. Treatment of the spinal CSF leak resulted in resolution of the spinal manifestations along with the headache, except for those in the patient with bibrachial amyotrophy. CONCLUSIONS: Spinal manifestations are uncommon in cases of spontaneous intracranial hypotension, occurring in about 6% of patients, but myelopathy and radiculopathy involving all spinal segments do occur. Unlike the headache, the spinal manifestations usually are not positional and are caused by mass effect from an extradural CSF collection.

Peroxynitrite causes endothelial cell monolayer barrier dysfunction.

Nitric oxide (.NO) attenuates hydrogen peroxide (H(2)O(2))-mediated barrier dysfunction in cultured porcine pulmonary artery endothelial cells (PAEC) (Gupta MP, Ober MD, Patterson C, Al-Hassani M, Natarajan V, and Hart, CM. Am J Physiol Lung Cell Mol Physiol 280: L116-L126, 2001). However,.NO rapidly combines with superoxide (O) to form the powerful oxidant peroxynitrite (ONOO(-)), which we hypothesized would cause PAEC monolayer barrier dysfunction. To test this hypothesis, we treated PAEC with ONOO(-) (500 microM) or 3-morpholinosydnonimine hydrochloride (SIN-1; 1-500 microM). SIN-1-mediated ONOO(-) formation was confirmed by monitoring the oxidation of dihydrorhodamine 123 to rhodamine. Both ONOO(-) and SIN-1 increased albumin clearance (P < 0.05) in the absence of cytotoxicity and altered the architecture of the cytoskeletal proteins actin and beta-catenin as detected by immunofluorescent confocal imaging. ONOO(-)-induced barrier dysfunction was partially reversible and was attenuated by cysteine. Both ONOO(-) and SIN-1 nitrated tyrosine residues, including those on beta-catenin and actin, and oxidized proteins in PAEC. The introduction of actin treated with ONOO(-) into PAEC monolayers via liposomes also resulted in barrier dysfunction. These results indicate that ONOO(-) directly alters endothelial cytoskeletal proteins, leading to barrier dysfunction.

Nitric oxide attenuates H(2)O(2)-induced endothelial barrier dysfunction: mechanisms of protection.

Nitric oxide (.NO) attenuates hydrogen peroxide (H(2)O(2))-mediated injury in porcine pulmonary artery endothelial cells (PAECs) and modulates intracellular levels of cGMP and cAMP. We hypothesized that.NO attenuates H(2)O(2)-induced PAEC monolayer barrier dysfunction through cyclic nucleotide-dependent signaling mechanisms. To examine this hypothesis, cultured PAEC monolayers were treated with H(2)O(2), and barrier function was measured as transmonolayer albumin clearance. H(2)O(2) caused significant PAEC barrier dysfunction that was attenuated by intracellular as well as extracellular.NO generation.NO increased PAEC cGMP and cAMP levels, but treatment with inhibitors of soluble guanylate cyclase or protein kinase G did not abrogate.NO-mediated barrier protection. In contrast, H(2)O(2) decreased protein kinase A activity, and inhibiting protein kinase A abrogated the protective effect of.NO. H(2)O(2)-induced barrier dysfunction was not associated with decreased levels of cGMP or cAMP. 3-Isobutyl-1-methylxanthine and the cGMP analog 8-bromo-cGMP had little effect on H(2)O(2)-mediated endothelial barrier dysfunction, whereas 8-bromo-cAMP plus 3-isobutyl-1-methylxanthine was protective. These results indicate that.NO modulates vascular endothelial barrier function through cAMP-dependent signaling mechanisms.

A Drosophila ESC-E(Z) protein complex is distinct from other polycomb group complexes and contains covalently modified ESC.

The extra sex combs (ESC) and Enhancer of zeste [E(Z)] proteins, members of the Polycomb group (PcG) of transcriptional repressors, interact directly and are coassociated in fly embryos. We report that these two proteins are components of a 600-kDa complex in embryos. Using gel filtration and affinity chromatography, we show that this complex is biochemically distinct from previously described complexes containing the PcG proteins Polyhomeotic, Polycomb, and Sex comb on midleg. In addition, we present evidence that ESC is phosphorylated in vivo and that this modified ESC is preferentially associated in the complex with E(Z). Modified ESC accumulates between 2 and 6 h of embryogenesis, which is the developmental time when esc function is first required. We find that mutations in E(z) reduce the ratio of modified to unmodified ESC in vivo. We have also generated germ line transformants that express ESC proteins bearing site-directed mutations that disrupt ESC-E(Z) binding in vitro. These mutant ESC proteins fail to provide esc function, show reduced levels of modification in vivo, and are still assembled into complexes. Taken together, these results suggest that ESC phosphorylation normally occurs after assembly into ESC-E(Z) complexes and that it contributes to the function or regulation of these complexes. We discuss how biochemically separable ESC-E(Z) and PC-PH complexes might work together to provide PcG repression.

Evidence for an antagonistic relationship between the boundary element-associated factor BEAF and the transcription factor DREF.

Boundary elements interfere with communication between enhancers and promoters, but only when interposed. Understanding this activity will require identifying the proteins involved. The boundary element-associated factor BEAF is one protein that is implicated in boundary element function. Three genomic fragments (scs', BE76 and BE28) containing BEAF binding sites function as boundary elements in transgenic Drosophila, suggesting that this is an intrinsic property of the numerous genomic regions to which BEAF binds. To characterize additional proteins that interact with boundary elements, we have isolated a protein that binds to two of these boundary elements (BE76 and BE28) and have identified it as the transcription factor DREF. We present evidence that BEAF and DREF compete for binding to overlapping binding sites, and that this competition occurs in vivo. DREF is believed to regulate genes whose products are involved in DNA replication and cell proliferation, suggesting that the activation of transcription predicted to result from the displacement of BEAF by DREF might be limited to certain rapidly proliferating tissues. This is the first suggestion that the activity of a subset of boundary elements might be regulated.

Nitric oxide in adult lung disease.

Advances in the understanding of nitric oxide as a biological mediator and a therapeutic tool continue to accumulate at a rapid rate. This review provides an update on recent developments pertinent to the role of nitric oxide in adult lung disease. After a brief review of basic nitric oxide biochemistry and physiology, the evidence supporting the role of nitric oxide in the regulation of vascular and airway tone in the normal lung is considered. Clinical studies addressing the pathophysiological role of nitric oxide in pulmonary hypertension, airway disease, and lung injury are reviewed, and the application of inhaled nitric oxide therapy is discussed.

Identification of a class of chromatin boundary elements.

Boundary elements are thought to define the ends of functionally independent domains of genetic activity. An assay for boundary activity based on this concept measures the ability to insulate a bracketed, chromosomally integrated reporter gene from position effects. Despite their presumed importance, the few examples identified to date apparently do not share sequence motifs or DNA binding proteins. The Drosophila protein BEAF binds the scs' boundary element of the 87A7 hsp70 locus and roughly half of polytene chromosome interband loci. To see if these sites represent a class of boundary elements that have BEAF in common, we have isolated and studied several genomic BEAF binding sites as candidate boundary elements (cBEs). BEAF binds with high affinity to clustered, variably arranged CGATA motifs present in these cBEs. No other sequence homologies were found. Two cBEs were tested and found to confer position-independent expression on a mini-white reporter gene in transgenic flies. Furthermore, point mutations in CGATA motifs that eliminate binding by BEAF also eliminate the ability to confer position-independent expression. Taken together, these findings suggest that clustered CGATA motifs are a hallmark of a BEAF-utilizing class of boundary elements found at many loci. This is the first example of a class of boundary elements that share a sequence motif and a binding protein.

Facilitation of chromatin dynamics by SARs.

Metaphase chromosome condensation is a dynamic process that must utilize cis elements to form and maintain the final structure. Likewise, cis elements must regulate the accessibility of chromatin domains to protein machines involved in processes such as transcription. Scaffold associated regions appear to play important roles in both of these dynamic processes.

Attenuation of oxidant-mediated endothelial cell injury with docosahexaenoic acid: the role of intracellular iron.

Previous studies have demonstrated that altering the fatty acid composition of porcine pulmonary artery endothelial cells (PAEC) significantly modulates their susceptibility to oxidative stimuli, e.g. H2O2. Based on observations that fatty acids also function to transport iron, an important catalyst for H2O2-mediated hydroxyl radical generation, we hypothesized that fatty acid-induced alterations in PAEC iron metabolism contribute to modulation of PAEC oxidant susceptibility. To test this hypothesis, PAEC were treated with culture medium supplemented with 0.1 mM oleic (18:1), linolenic (18:3) or docosahexaenoic (22:6) acids or with an equivalent volume of ethanol vehicle for 3 h. After thorough washing and incubation in unsupplemented culture medium for 24 h, PAEC monolayers were subjected to additional studies. Supplementation with 22:6 attenuated lactate dehydrogenase (LDH) release from PAEC 2 h following treatment with 100 microM H2O2 for 30 min (% LDH release: ETOH-control = 7.9 +/- 1.6, 22:6-control = 5.9 +/- 0.9, ETOH-H2O2 = 26.4 +/- 4.2, 22:6-H2O2* = 16.2 +/- 2.9; *P < 0.05 vs ETOH-H2O2). In a non-cellular system, 18:1 and 18:3 were more effective than their methyl ester derivatives or 22:6 at translocating iron from aqueous to hydrophobic environments. In contrast, only supplementation with 22:6 significantly increased PAEC uptake of 57Fe and human umbilical vein endothelial cell (HUVEC) ferritin content, whereas none of the supplementation conditions altered PAEC catalytic iron measured with bleomycin. These novel observations indicate that specific fatty acids are capable of altering PAEC iron uptake and ferritin content thereby contributing to the understanding of the mechanisms by which fatty acids modulate the oxidant susceptibility of vascular endothelial cells.

Rapid recurrence of pulmonary hypertension following cessation of nifedipine.

In a young woman with primary pulmonary hypertension, treatment with low-dose nifedipine resulted in resolution of symptoms and of tricuspid regurgitation. On withdrawal of nifedipine, symptomatic pulmonary hypertension recurred within 48 hours and was controlled by reintroduction of low-dose nifedipine.

H2O2 causes endothelial barrier dysfunction without disrupting the arginine-nitric oxide pathway.

We have previously demonstrated that nitric oxide (.NO) donors attenuate and that inhibition of endogenous nitric oxide synthase (NOS) enhances hydrogen peroxide (H2O2)-mediated porcine pulmonary artery endothelial cell (PAEC) injury. The current study investigates the hypothesis that oxidant-mediated inhibition of NOS contributes to PAEC injury. PAEC barrier function, measured as the transmonolayer clearance of albumin, was significantly impaired by H2O2 (10-100 microM) in the absence of cytotoxicity. Treatment with H2O2 did not alter NOS activity, measured as the conversion of [3H]arginine to [3H]citrulline in PAEC lysates, either immediately after treatment with 0-250 microM H2O2 for 30 min or for up to 120 min after treatment with 100 microM H2O2. H2O2 had little effect on NOS activity in intact PAECs, measured as 1) the formation of [3H]citrulline in [3H]arginine-loaded PAECs, 2) PAEC guanosine 3',5'-cyclic monophosphate content, and 3) PAEC.NO release to the culture media. These results indicate that the arginine-.NO pathway remains intact after exposure to oxidant conditions sufficient to promote functional derangements of vascular endothelial cells.

Role of 8-epi PGF2alpha, 8-isoprostane, in H2O2-induced derangements of pulmonary artery endothelial cell barrier function.

The non-enzymatic peroxidation product of arachidonic acid, 8-epi-PGF2alpha or 8-isoprostane (8-IP) was measured in H2O2-exposed cultured pulmonary artery endothelial cell (PAEC) monolayers using a commercially-available enzyme immunoassay kit. H2O2 (50 microM for 1-30 min) significantly increased 8-IP production in a time-dependent fashion. Treatment with higher H2O2 concentrations (100 or 250 microM) failed to further increase 8-IP generation. Determinations of thiobarbituric acid reactive substances (TBARS) and lipid hydroperoxides (LOOH) were not sufficiently sensitive to detect lipid peroxidation in PAEC exposed to 50 microM H2O2 for 15 min. 8-IP (100 pM-500 nM for 2 h) caused PAEC monolayer barrier dysfunction measured as the transmonolayer clearance of albumin without causing significant PAEC cytotoxicity (measured as intracellular lactate dehydrogenase release). This is the first report to provide evidence that 8-IP generated in H2O2-exposed PAEC contributes to oxidant-mediated alterations in monolayer barrier function at non-cytotoxic concentrations.

Oleic acid reduces oxidant stress in cultured pulmonary artery endothelial cells.

Altering the fatty acid composition of cultured porcine pulmonary artery endothelial cells (PAEC) modulates their susceptibility to oxidant stress. This study demonstrates that supplementing PAEC with oleic acid (18:1 omega 9), but not gamma-linolenic acid (18:3 omega 6), provided dose-dependent protection from hydrogen peroxide (H2O2)-induced cytotoxicity. It was hypothesized that 18:1 reduced PAEC susceptibility to oxidant stress by altering H2O2 metabolism. To test this hypothesis, confluent PAEC monolayers were treated with 100-200 microM H2O2 or control conditions 24 h after supplementation with 0.1 mM 18:1, 18:3, or vehicle for 3 h. Intracellular [H2O2] in control cells (14.4-29.0 pM), estimated from the rate of aminotriazole-mediated inactivation of endogenous catalase activity, increased following treatment with 200 microM H2O2 (19.0-37.3 pM). Supplementation with 18:1 attenuated increases in intracellular [H2O2] only in oxidant-exposed cells, whereas supplementation with 18:3 attenuated intracellular [H2O2] only in control cells. Supplementation with 18:1 or 18:3 tended to reduce or enhance PAEC lipid hydroperoxide content following H2O2 exposure, respectively, but did not alter PAEC reduced glutathione content, the activities of glutathione peroxidase or catalase, or H2O2 uptake and release. Alteration of H2O2 metabolism in cultured PAEC may contribute to the ability of fatty acids to modulate cellular oxidant susceptibility.

Mechanisms of ionomycin-induced endothelial cell barrier dysfunction.

Myosin light chain (MLC) phosphorylation catalyzed by the Ca(2+)- calmodulin-dependent MLC kinase (MLCK) is critical to thrombin-mediated endothelial cell gap formation and barrier dysfunction. We have tested the hypothesis that the Ca2+ ionophore ionomycin stimulates MLCK-dependent endothelial cell contraction and permeability. Ionomycin significantly increased albumin clearance and decreased electrical resistance across confluent bovine pulmonary microvascular and macrovascular endothelial cell monolayers in a concentration-dependent manner that was temporally similar to that produced by thrombin. In contrast, however, ionomycin produced a significant Ca(2+)-dependent reduction in the levels of phosphorylated MLC with evidence of serine/threonine phosphatase activation. Potential MLCK-independent mechanisms of endothelial cell permeability were examined with little evidence to support a role for stimulated nitric oxide synthase or phospholipase A2 activities. Importantly, ionomycin produced 1) reductions in the activities of the barrier protective adenylate cyclase and the adenosine 3',5'-cyclic monophosphate-dependent protein kinase A, 2) dramatic dose- and time-dependent inhibition of endothelial cell tyrosine kinase activities, and 3) marked decreases in the phosphotyrosine content of the p125 focal adhesion kinase. These data indicate that ionomycin produces endothelial cell barrier dysfunction by mechanisms that are independent of MLCK activation and may involve reductions in endothelial cell tethering forces via inhibition of protein kinase A and tyrosine kinase activities, especially the p125 focal adhesion kinase.

Nitric oxide attenuates hydrogen peroxide-mediated injury to porcine pulmonary artery endothelial cells.

To examine the role of nitric oxide (.NO) in vascular endothelial cell injury, cultured porcine pulmonary artery endothelial cells (PAEC) were treated with H2O2 (100-500 microM) for 30 min in the presence or absence of the .NO donors (+/-)S-nitroso-N-acetylpenicillamine (SNAP) or diethylamine nitric oxide (DEANO). H2O2 caused dose-dependent PAEC cytotoxicity detected 2 h after H2O2 treatment as the release of lactate dehydrogenase. SNAP (100 microM) and DEANO (100 microM) attenuated H2O2-induced cytotoxicity if present during H2O2 treatment. In contrast, restricting treatment with .NO donors to periods before (30 min) or after (2 h) incubation with H2O2 did not prevent PAEC injury. Furthermore, the .NO synthase inhibitor NG-nitro-L-arginine methyl ester (1 mM) sensitized PAEC to H2O2-induced injury. SNAP also attenuated H2O2-induced PAEC lipid peroxidation even if restricted to periods before or after exposure to H2O2. Thus, although .NO effectively attenuated H2O2-mediated PAEC lipid peroxidation and cytotoxicity, these effects were clearly dissociated, suggesting that the antiperoxidative effects of .NO are not sufficient to account for its cytoprotective properties.

Endothelial cell monolayer dysfunction caused by oxidized low density lipoprotein: attenuation by oleic acid.

Oleic acid (18:1) may exert beneficial effects on the pathogenesis of vascular disease by a variety of mechanisms. To determine if 18:1 exerts direct protective effects on vascular endothelial cells, porcine pulmonary artery endothelial cells (PAEC) were supplemented with 0.1 mM 18:1, gamma-linolenic acid (18:3), or ethanol vehicle (ETOH) prior to treatment with low density lipoprotein (LDL), or CU(2+)-oxidized LDL (OXLDL). Treatment with neither LDL nor OXLDL (100 micrograms protein/ml) for 24-48 h caused PAEC cytotoxicity, whereas OXLDL, but not LDL, caused derangements in PAEC actin microfilament architecture and monolayer barrier dysfunction. Supplementation with 18:1, but not 18:3, attenuated derangements caused by OXLDL and lysophosphatidylcholine, a component of OXLDL. These results demonstrate that monounsaturated fatty acids directly alter the response of vascular endothelial cells to OXLDL and may retard the atherosclerotic process by decreasing the efflux of macromolecules (e.g. LDL) into the vessel wall.

Exogenous fatty acids modulate the functional and cytotoxic responses of cultured pulmonary artery endothelial cells to oxidant stress.

We previously reported that supplementation with exogenous fatty acids modulated the susceptibility of cultured pulmonary artery endothelial cells (PAEC) to oxidant-mediated cytotoxicity. The current study investigates the effects of fatty acids with increasing degrees of unsaturation on oxidant-mediated dysfunction and cytotoxicity in cultured porcine pulmonary artery and aortic endothelial cells (AEC). Monolayers supplemented with 0.1 mmol/L oleic (18:1), linoleic (18:2), or gamma-linolenic (18:3) acids were exposed to oxidant stress (100 mumol/L hydrogen peroxide (H2O2)) or to control conditions for 30 minutes. Gas chromatographic analysis of the PAEC fatty acids confirmed incorporation of supplemental fatty acids into PAEC lipids. Cytotoxicity, measured as the release of intracellular lactate dehydrogenase (LDH), and PAEC monolayer barrier function, assessed by measuring the monolayer clearance of Evans blue dye bound to albumin, were determined for 1 to 3 hours after oxidant stress. The PAEC and AEC demonstrated comparable responses to H2O2. Hydrogen peroxide caused increases in monolayer permeability and detachment of cells from the monolayer that were most attenuated by supplementation with 18:2 or 18:3, and to a lesser degree with 18:1. In contrast, H2O2-mediated LDH release was attenuated by supplementation with 18:1, whereas 18:2 and 18:3 potentiated cytotoxicity after exposure to H2O2. These results indicate that the relationship between PAEC lipid composition and oxidant susceptibility is complex and that the extent of fatty acid unsaturation does not predict the functional or cytotoxic responses of PAEC to oxidant stress. Furthermore, these results suggest that functional derangements may not correlate with traditional assays of cytotoxicity induced by oxidant injury in cultured endothelium.