Novel role of gp91(phox)-containing NAD(P)H oxidase in vascular endothelial growth factor-induced signaling and angiogenesis

Vascular endothelial growth factor (VEGF) induces angiogenesis by stimulating endothelial cell proliferation and migration, primarily through the receptor tyrosine kinase VEGF receptor2 (Flk1/KDR). Reactive oxygen species (ROS) derived from NAD(P)H oxidase are critically important in many aspects of vascular cell regulation, and both the small GTPase Rac1 and gp91(phox) are critical components of the endothelial NAD(P)H oxidase complex. A role of NAD(P)H oxidase in VEGF-induced angiogenesis, however, has not been defined. In the present study, electron spin resonance spectroscopy is utilized to demonstrate that VEGF stimulates O2*- production, which is inhibited by the NAD(P)H oxidase inhibitor, diphenylene iodonium, as well as by overexpression of dominant-negative Rac1 (N17Rac1) and transfection of gp91(phox) antisense oligonucleotides in human umbilical vein endothelial cells (ECs). Antioxidants, including N-acetylcysteine (NAC), various NAD(P)H oxidase inhibitors, and N17Rac1 significantly attenuate not only VEGF-induced KDR tyrosine phosphorylation but also proliferation and migration of ECs. Importantly, these effects of VEGF are dramatically inhibited in cells transfected with gp91(phox) antisense oligonucleotides. By contrast, ROS are not involved in mediating these effects of sphingosine 1-phosphate (S1P) on ECs. Sponge implant assays demonstrate that VEGF-, but not S1P-, induced angiogenesis is significantly reduced in wild-type mice treated with NAC and in gp91(phox-/-) mice, suggesting that ROS derived from gp91(phox)-containing NAD(P)H oxidase play an important role in angiogenesis in vivo. These studies indicate that VEGF-induced endothelial cell signaling and angiogenesis is tightly controlled by the reduction/oxidation environment at the level of VEGF receptor and provide novel insights into the NAD(P)H oxidase as a potential therapeutic target for angiogenesis-dependent diseases.

Peroxidase properties of extracellular superoxide dismutase: role of uric acid in modulating in vivo activity

OBJECTIVE

The cytosolic form of Cu/Zn-containing superoxide dismutase (SOD1) has peroxidase activity, with H2O2 used as a substrate to oxidize other molecules. We examined peroxidase properties of the extracellular form of SOD (SOD3), a major isoform of SOD in the vessel wall, by using recombinant SOD3 and an in vivo model of atherosclerosis.

METHODS AND RESULTS

In the presence of HCO3-, SOD3 reacted with H2O2 to produce a hydroxyl radical adduct of the spin trap 5-diethoxyphosphoryl-5methyl-1-pyrroline N-oxide (DEMPO). SOD1 and SOD3 were inactivated by H2O2 in a dose- and time-dependent fashion, and this was prevented by physiological levels of uric acid. To examine the in vivo role of uric acid on SOD1 and SOD3, control and apolipoprotein E-deficient (ApoE(-/-)) mice were treated with oxonic acid, which inhibits urate metabolism. This treatment increased plasma levels of uric acid in control and ApoE(-/-) mice by approximately 3-fold. Although increasing uric acid levels did not alter aortic SOD1 and SOD3 protein expression, aortic SOD1 and SOD3 activities were increased by 2- to 3-fold in aortas from ApoE(-/-) mice but not in aortas from control mice.

CONCLUSIONS

These studies show that SOD1 and SOD3 are partially inactivated in atherosclerotic vessels of ApoE(-/-) mice and that levels of uric acid commonly encountered in vivo may regulate vascular redox state by preserving the activity of these enzymes.

Extracellular superoxide dismutase and cardiovascular disease

Excessive production and/or inadequate removal of reactive oxygen species, especially superoxide anion (O(2)(*-)), have been implicated in the pathogenesis of many cardiovascular diseases, including atherosclerosis, hypertension, diabetes, and in endothelial dysfunction by decreasing nitric oxide (NO) bioactivity. Since the vascular levels of O(2)(*-) are regulated by the superoxide dismutase (SOD) enzymes, a role of SOD in the cardiovascular disease is of substantial interest. Particularly, a major form of SOD in the vessel wall is the extracellular SOD (ecSOD). This review will discuss the characteristics of ecSOD and the role of ecSOD in cardiovascular diseases.

Noise-tolerant stimulus discrimination by synchronization with depressing synapses

Some synapses between cortical pyramidal neurons exhibit a rapid depression of excitatory postsynaptic potentials for successive presynaptic spikes. Since depressing synapses do not transmit information on sustained presynaptic firing rates, it has been speculated that they are favorable for temporal coding. In this paper. we study the dynamical effects of depressing synapses on stimulus-induced transient synchronization in a simple network of inhibitory interneurons and excitatory neurons, assuming that the recurrent excitation is mediated by depressing synapses. This synchronization occurs in a temporal pattern which depends on a given stimulus. Since the presence of noise is always a potential hazard in temporal coding, we investigate the extent to which noise in stimuli influences the synchronization phenomena. It is demonstrated that depressing synapses greatly contribute to suppressing the influences of noise on the stimulus-specific temporal patterns of synchronous firing. The timing-based Hebbian learning revealed by physiological experiments is shown to stabilize the temporal patterns in cooperation with synaptic depression. Thus, the times at which synchronous firing occurs provides a reliable information representation in the presence of synaptic depression.

Fokker-Planck approach to the pulse packet propagation in synfire chain

We applied the Fokker-Planck method to the so-called 'synfire chain' network model and showed how a synchronous population spike (pulse packet) evolves to a narrow pulse packet (width < 1 ms) or fades away, depending on its initial size and width. The results of numerical integration of the Fokker-Planck equation are in good agreement with those of simulations on a network of leaky integrate-and-fire neurons. For a narrow input pulse packet, the integration of the Fokker-Planck equation requires careful numerical treatment. However, we can construct a precise analytical waveform of an output packet, which proves valid for narrow input pulse packets, from the stationary solution to the Fokker-Planck equation and a previously proposed approximate input-output relationship. Our methods enable us also to understand an essential role of the synaptic noise in the evolution, the peculiar temporal evolution of a broader pulse packets, and the irrelevance of the refractory period in determining the waveform of a pulse packet. Furthermore, we elucidate possible functional roles of multiple interactive pulse packets in spatiotemporal information processing, i.e. the association of information and the temporal competition.

Cytotoxic and DNA damage-inducing activities of low molecular weight phenols from rhubarb

Six new phenol (anthraquinone or stilbene) glycosides with an acyl group at 6-position of the glucopyranose moiety were isolated from rhubarb (the roots of Rheum palmatum) cultivated in Japan, together with 22 known compounds. Most of these compounds were evaluated for cytotoxic activity against tumor and normal cells and for induction of DNA damage by spore rec-assay. Among them, emodin and aloe-emodin showed higher cytotoxic activities against human oral squamous cell carcinoma (HSC-2) and salivary gland tumor (HSG) cell lines than against normal human gingival fibroblasts (HGF). Chrysophanol 8-O-beta-(6'-acetyl)glucopyranoside, 4-(4'-hydroxyphenyl)-2-butanone 4'-O-beta-D-(2"-O-galloyl-6"-O-cinnamoyl) glucopyranoside, and 6"-O-(4'''-hydroxybenzoyl) resveratroloside exhibited relatively higher cytotoxic activities against all these cells. The other glycosides of anthraquinone or stilbene showed weaker cytotoxic activity against these tumor cell lines, but may be considered as cancer chemopreventive agents. Spore rec-assay with a recombination deficient mutant of Bacillus subtilis M45 demonstrated the DNA damage-inducing activity of emodin and aloe-emodin 15-O-beta-D-glucopyranoside among, rhubarb phenols.

A possible functional organization of the corticostriatal input within the weakly-correlated striatal activity: a modeling study

Recently, it was reported in an in vivo study that pairs of the striatal projection neurons (medium-sized spiny neurons) of the basal ganglia show asynchronous spiking within weakly-correlated subthreshold depolarized states. In this computational study, we investigate a possible functional organization of corticostriatal inputs that accounts for the experimental observations within known anatomical and physiological constraints. In a pair of medium-sized spiny neurons, a small fraction of corticostriatal fibers is common to both neurons. To explain the weak correlations in sub- and supra-threshold activities of the neuron pair, we postulate that the two input channels, common or specific to the individual neurons, have distinct functional roles. The common input channel delivers random spike trains and is primarily responsible for the initiation and maintenance of the depolarized states. In contrast, the input through the neuron-specific channels elicit postsynaptic spikes by delivering intermittently-synchronized spikes. The results of this model were compared with those derived from a newly-performed analysis of the previous double-intracellular recording data. We show that the behavior of this model agrees qualitatively and quantitatively with that of the medium-sized spiny neurons observed in the experiments in a certain range of the coincident time window.

Neural mechanism for a cognitive timer

To examine a possible biological mechanism for a cognitive timer, the stochastic dynamics of a network of neurons possessing two stable states ("on" and "off" states) is studied. The fraction of on neurons existing at t = 0 remains large for an extended interval, and then abruptly falls. The distribution of the lengths of the interval is scale invariant in the following sense: The ratio (k root of (mu(k))/m, with m and mu(k) being the mean and the kth central moment, respectively, is invariant under scale transformations of m and mu(k). In the special case k = 2, this gives Weber's law, a hallmark of cognitive timing.

Endothelial regulation of vasomotion in apoE-deficient mice: implications for interactions between peroxynitrite and tetrahydrobiopterin

BACKGROUND

Altered endothelial cell nitric oxide (NO(*)) production in atherosclerosis may be due to a reduction of intracellular tetrahydrobiopterin, which is a critical cofactor for NO synthase (NOS). In addition, previous literature suggests that inactivation of NO(*) by increased vascular production superoxide (O(2)(*-)) also reduces NO(*) bioactivity in several disease states. We sought to determine whether these 2 seemingly disparate mechanisms were related.

METHODS AND RESULTS

Endothelium-dependent vasodilation was abnormal in aortas of apoE-deficient (apoE(-/-)) mice, whereas vascular superoxide production (assessed by 5 micromol/L lucigenin) was markedly increased. Treatment with either liposome-entrapped superoxide dismutase or sepiapterin, a precursor to tetrahydrobiopterin, improved endothelium-dependent vasodilation in aortas from apoE(-/-) mice. Hydrogen peroxide had no effect on the decay of tetrahydrobiopterin, as monitored spectrophotometrically. In contrast, superoxide modestly and peroxynitrite strikingly increased the decay of tetrahydrobiopterin over 500 seconds. Luminol chemiluminescence, inhibitable by the peroxynitrite scavengers ebselen and uric acid, was markedly increased in apoE(-/-) aortic rings. In vessels from apoE(-/-) mice, uric acid improved endothelium-dependent relaxation while having no effect in vessels from control mice. Treatment of normal aortas with exogenous peroxynitrite dramatically increased vascular O(2)(*-) production, seemingly from eNOS, because this effect was absent in vessels lacking endothelium, was blocked by NOS inhibition, and did not occur in vessels from mice lacking eNOS.

CONCLUSIONS

Reactive oxygen species may alter endothelium-dependent vascular relaxation not only by the interaction of O(2)(*-) with NO(*) but also through interactions between peroxynitrite and tetrahydrobiopterin. Peroxynitrite oxidation of tetrahydrobiopterin may represent a pathogenic cause of "uncoupling" of NO synthase.

Cytotoxic flavonoids with isoprenoid groups from Morus mongolica

A new pyranoflavanone, sanggenol L (1), a Diels-Alder type adduct regarded as a cycloaddition product of a dehydrogeranylflavanone and a prenylchalcone, sanggenol M (2), along with four new 2-arylbenzofurans with isoprenoid units, mulberrofurans W-Z (3-6), were isolated together with 10 known flavonoids from Chinese Morus mongolica. The structures of these novel compounds were elucidated by spectroscopic methods. All flavanones investigated here showed higher cytotoxicity against human oral tumor cell lines (HSC-2 and HSG) than against normal human gingival fibroblasts (HGF). Among them, the cytotoxicity of compound 2 and the Diels-Alder type flavanone sanggenon C (7) isolated from Morus cathayana were the most potent. On the other hand, seven 2-arylbenzofurans exhibited lower cytotoxicity and tumor specificity as compared with flavanones.

Benzophenones and xanthones with isoprenoid groups from Cudrania cochinchinensis

Four new benzophenones with two isoprenoid groups, cudraphenones A-D (1-4), and three new xanthones also with two isoprenoid units, cudraxanthones P-R (5-7), were isolated from the roots of Cudraniacochinchinensis, together with 19 known phenolic compounds. The structures of the new compounds were elucidated by spectroscopic methods. Some compounds exhibited weak cytotoxicity against human oral squamous carcinoma cells (HSC-2) and normal human gingival fibroblasts (HGF). Among them, benzophenones 1-4 showed more potent cytotoxic activities against HSC-2 cells than against HGF cells. On the other hand, xanthones bearing isoprenoid groups showed much lower tumor specificity as compared with the benzophenones, except for geronthxanthone H and isoalvaxanthone. The presence of two sets of hydrophobic and hydrophilic groups in separate domains in each molecule might play a role in the mediation of tumor-specific action.

Collision-induced dissociation of ring-opened cyclic depsipeptides with a guanidino group by electrospray ionization/ion trap mass spectrometry

The characteristics shown in the electrospray ionization/ion trap mass spectra of ring-opened LI-F antibiotics (cyclic depsihexapeptides with a 15-guanidino-3-hydroxypentadecanoic group as a side-chain) were examined. Collision-induced dissociation (CID) MS of protonated molecules of the depsipeptides produced many fragment ions. Most of these fragment ions contained information for determining the amino acid sequences of antifungal antibiotics. The fragment ions were classified into six groups (b(n'), B(n'), B'(n'), beta(n'), y(n) and Y(n)). According to MS(3) spectra, the B(n'), B'(n) and beta(n) ions can be considered to be derived with a cleavage at each CO--NH in the peptide bonds of [MH--NH(3)](+),[MH--NH(3)--OH](+) and [MH--NH(3)--2H(2)O](+), respectively, in ion trap MS. Losses of NH(3) and H(2)O from the amino acid residues of the depsipeptides in ion trap MS are likely to be smaller than those from the side-chain. The measurements with electrospray ionization (ESI)/ion trap MS of depsipeptides with a side chain containing polar groups may provide useful information for structural determination.

Neuronal communication within synchronous gamma oscillations

The gamma-band oscillatory activity notably appears in the primary sensory and motor cortical areas. Because both sensory and motor responses are characterized by many static and dynamic variables, questions are raised regarding how cortical neurons manage to transmit analog information within the gammaoscillatory activity. Here, a possible way of communication among pyramidal neurons in the gamma frequency range is proposed based on the sampling theorem in communication theory.

Early effects of arterial hemodynamic conditions on human saphenous veins perfused ex vivo

Exposure to the arterial hemodynamic environment is thought to be a potential trigger for the pathological remodeling of saphenous vein grafts. Using matched pairs of freshly isolated human saphenous vein, we analyzed the early effects of ex vivo hemodynamic conditions mimicking the venous (native) compared with arterial (graft) environment on the key components of vascular remodeling, ie, matrix metalloproteinase (MMP)-9 and MMP-2 and cell proliferation. Interestingly, we found that arterial conditions halved latent MMP-9 (50+/-11%, P=0.01) and MMP-2 (44+/-6%, P=0.005) levels relative to matched vein pairs maintained ex vivo under venous perfusion for up to 3 days. Immunostaining supported decreased MMP levels in the innermost area of arterially perfused veins. Either decreased synthesis or increased posttranslational processing may decrease MMP zymogen levels. Biosynthetic radiolabeling showed that arterial perfusion actually increased MMP-9 and MMP-2 production. When we then examined potential pathways for MMP zymogen processing, we found that arterial conditions did not affect the expression of MT-MMP-1, a cell-associated MMP activator, but that they significantly increased the levels of superoxide, another MMP activator, suggesting redox-dependent MMP processing. Additional experiments indicated that increased superoxide under arterial conditions was due to diminished scavenging by decreased extracellular superoxide dismutase. Arterial perfusion also stimulated cell proliferation (by 220% to 750%) in the majority of vein segments investigated. Our observations support the hypothesis that arterial hemodynamic conditions stimulate early vein graft remodeling. Furthermore, physiological arterial flow may work to prevent pathological remodeling, particularly the formation of intimal hyperplasia, through rapid inactivation of secreted MMPs and, possibly, through preferential stimulation of cell proliferation in the outer layers of the vein wall.

Cytotoxic activity of low molecular weight polyphenols against human oral tumor cell lines

A total of 150 chemically-defined natural and synthetic polyphenols (flavonoids, dibenzoylmethanes, dihydrostilbenes, dihydrophenanthrenes and 3-phenylchromen-4-ones), with molecular weights ranging from 224 to 824, were investigated for cytotoxic activity against normal, tumor and human immunodeficiency virus (HIV)-infected cells. They showed higher cytotoxic activity against human oral squamous cell carcinoma HSC-2 and salivary gland tumor HSG cell lines than against normal human gingival fibroblasts HGF. Many of the active compounds had a hydrophilic group (hydroxyl group) in the vicinity of a hydrophobic group (prenyl, phenyl, methylcyclohexene or methylbenzene moiety), similar to isoprenoid-substituted flavones. Substitution of hydrophobic group (prenyl or geranyl group) did not significantly change the cytotoxic activity of flavanones, isoflavans, chalcones or 5-hydroxy-3-phenoxychromen-4-ones. However, the prenylation(s) of an isoflavone and a 2-arylbenzofuran significantly enhanced the cytotoxic activity. Agarose gel electrophoresis showed that active components induced internucleosomal DNA fragmentation in human promyelocytic leukemic HL-60 cells, but not in HSC-2 cells. Most of the polyphenols failed to reduce the cytophathic effect of HIV infection in MT-4 cells.

Regulation of the vascular extracellular superoxide dismutase by nitric oxide and exercise training

The bioactivity of endothelium-derived nitric oxide (NO) reflects its rates of production and of inactivation by superoxide (O(2)(*-)), a reactive species dismutated by extracellular superoxide dismutase (ecSOD). We have now examined the complementary hypothesis, namely that NO modulates ecSOD expression. The NO donor DETA-NO increased ecSOD expression in a time- and dose-dependent manner in human aortic smooth muscle cells. This effect was prevented by the guanylate cyclase inhibitor ODQ and by the protein kinase G (PKG) inhibitor Rp-8-CPT-cGMP. Expression of ecSOD was also increased by 8-bromo-cGMP, but not by 8-bromo-cAMP. Interestingly, the effect of NO on ecSOD expression was prevented by inhibition of the MAP kinase p38 but not of the MAP kinase kinase p42/44, suggesting that NO modulates ecSOD expression via cGMP/PKG and p38MAP kinase-dependent pathways, but not through p42/44MAP kinase. In aortas from mice lacking the endothelial nitric oxide synthase (eNOS), ecSOD was reduced more than twofold compared to controls. Treadmill exercise training increased eNOS and ecSOD expression in wild-type mice but had no effect on ecSOD expression in mice lacking eNOS, suggesting that this effect of exercise is meditated by endothelium-derived NO. Upregulation of ecSOD expression by NO may represent an important feed-forward mechanism whereby endothelial NO stimulates ecSOD expression in adjacent smooth muscle cells, thus preventing O(2)(*-)-mediated degradation of NO as it traverses between the two cell types.

Accurate mass measurement of low molecular weight compounds by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

We report the application of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) for the accurate measurement of mass of low molecular weight compounds (smaller than 1500 Da), a linear peptide, two types of cyclic depsipeptides, a polyhydroxy-macrocyclic lactone, and two prenylated flavonoids, with delayed extraction in the reflector mode. The performance of the MALDI-TOF instrument was less than those of fast atom bombardment and Fourier-transform ion cyclotron resonance mass spectrometry instruments and insufficient to give acceptable accuracy for literature reporting. Nevertheless, when combined with NMR spectrometry and/or amino acid analysis to give information on the numbers of carbon atoms and index of hydrogen deficiency, MALDI was useful for determination of the elemental composition of the low molecular weight compounds available in small quantities.

A model for neural representation of temporal duration

To address how temporal duration is encoded in neural systems, we put forward a simple model for recurrent neural networks. Particular assumptions are only the following two: (1) neuronal bistability and; (2) environmental effects described by a heat bath. The results of Monte Carlo simulation show that population activity triggered at an initial time continues for a prolonged duration, followed by an abrupt self-termination. This time course seems highly suitable for neural representation of temporal duration. The time scale of this prolonged duration is much longer than the time scale of neuronal firing which is of the order of ms. The former time scale implies that of interval timing in cognition and behaviour. Thus, the model provides a possible explanation for a link between these two separated time scales. The Weber law, a hallmark of humans and animals' interval timing, can also be reproduced in our model.

Induction of apoptosis by flavones, flavonols (3-hydroxyflavones) and isoprenoid-substituted flavonoids in human oral tumor cell lines

Various flavones, flavonols (3-hydroxyflavones) and isoprenoid-substituted flavones (flavonols) were investigated for their cytotoxic activity. Most of these compounds were more cytotoxic against human oral squamous cell carcinoma and salivary gland tumor cell lines than human gingival fibroblasts. The cytotoxic activity of flavonoids was generally higher than that of tannin-related compounds. Flavonoids induced apoptotic cell death characterized by DNA fragmentation (as identified by TUNEL method) and activation of caspase(s) (as identified by degradation products of cytokeratin 18 with M30 monoclonal antibody). ESR spectroscopy revealed that higher concentrations of flavonoids produced radicals under alkaline conditions. However, not all of them enhanced the radical intensity of sodium ascorbate, suggesting that the redox potential of flavonoids differs considerably from samples to samples. Catalase failed to eliminate the cytotoxic activity of flavonoids, reducing the possibility of the involvement of hydrogen peroxide for the cytotoxicity induction by them.

The role of costimulatory molecules B7-1 and B7-2 in mice with experimental autoimmune uveoretinitis

BACKGROUND

Onset of experimental autoimmune uveoretinitis (EAU) is believed to involve a CD4-positive type 1 T helper cell (Th1) immune response, with inhibition involving a Th2 immune response. Development of Th1 and Th2 responses involves the participation of the costimulatory molecules B7-1 and B7-2, respectively. The purpose of this study was to investigate the role of B7-1 and B7-2 in the EAU model in mice.

METHODS

B10.A mice were immunized with interphotoreceptor retinoid-binding protein (IRBP) and given daily intraperitoneal injections of either phosphate-buffered saline (control), mouse monoclonal antibody (mAb) to B7-1, mAb to B7-2, or mAb to both B7-1 and B7-2. Eyes were evaluated by histopathological criteria and cytokines were assayed in culture medium of IRBP-stimulated lymphocytes. Cellular immune responses were measured by cell proliferation assay under IRBP stimulation.

RESULTS

Rates of EAU onset were 5/10 (50%) for control mice, 1/9 (11%) for mice treated with anti-B7-1 mAb, 5/6 (83%) for mice treated with anti-B7-2 mAb, and 2/6 (33%) for mice treated with both anti-B7-1 and anti-B7-2 mAb. Mean histopathological severity scores were 2. 4+/-0.8, 1.0+/-0, 2.6+/-1.0, and 1.0+/-0, respectively. Production of IL-5 was significantly increased in mice treated with anti-B7-1 mAb, while IFN-gamma was increased in mice treated with anti-B7-2 mAb. Spleen cell proliferation was significantly reduced in mice treated with anti-B7-1 mAb.

CONCLUSIONS

These results suggest that the costimulatory molecules B7-1 and B7-2, via their influence on generating Th1 and Th2 immune responses, play an important role in the clinical outcome of EAU in mice immunized with IRBP.

Sequence generation in arbitrary temporal patterns from theta-nested gamma oscillations: a model of the basal ganglia-thalamo-cortical loops

A computational model that is able to generate sequences at arbitrary rates in a given serial order is presented for the cortico-basal ganglia (BG)-thalamic neural circuitry. Upon generating a sequence, this model stores information on the serial order of components in a cortical buffer by means of theta-nested gamma frequency oscillations observed experimentally in cortico-striatal neurons. This model assumes the existence of at least two functionally different classes of striatal spiny neurons. One class of striatal projection neurons (S-cells) select the first component in the cortical buffer through a temporal winner-take-all mechanism implemented by lateral inhibition. The inhibition should last for at least a few hundred milliseconds. In reality, it may be mediated by GABA(B) receptors at the presynaptic terminals of the cortico-striatal projection. The other class of striatal projection neurons (M-cells) retain the currently executed component in a cortico-BG-thalamic loop, for which the strong nonlinearity in transitions between up and down states of striatal neurons is crucial. For sequence generation at the level of striatum, the cortical neurons encoding the component selected for execution are inactivated by the feedback from the activated cortico-BG-thalamic loop. This model predicts that the transition to next component is triggered by a single external signal, i.e. the subthalamic input to the globus pallidum. This input gives a neural substrate for adjusting the rate of sequence generation.

Modulation of extracellular superoxide dismutase expression by angiotensin II and hypertension

Angiotensin II and hypertension increase vascular oxidant stress. We examined how these might affect expression of the extracellular superoxide dismutase (ecSOD), a major form of vascular SOD. In mice, angiotensin II infusion (1.1 mg/kg for 7 days) increased systolic blood pressure from 107+/-3 to 152+/-9 mm Hg and caused a 3-fold increase in ecSOD, but there was no change in the cytosolic Cu/Zn SOD protein, as determined by Western blot analysis. This was associated with a similar increase in ecSOD mRNA as assessed by RNase protection assay and was prevented by losartan. Induction of ecSOD by angiotensin II was not due to hypertension alone, because hypertension caused by norepinephrine (5.6 mg. kg-1. d-1) had no effect on ecSOD. Similarly, exposure of mouse aortas to angiotensin II (100 nmol/L) in organoid culture increased ecSOD by approximately 2-fold. In the organoid culture, angiotensin II-induced upregulation of ecSOD was prevented by losartan (10 micromol/L) and PD985059 (30 micromol/L), a specific inhibitor of p42/44 MAP kinase kinase. Angiotensin II activates the NADH/NADPH oxidase; however, diphenyleneiodonium chloride (10 micromol/L), an inhibitor of this oxidase, did not prevent p42/44 MAP kinase phosphorylation or ecSOD induction by angiotensin II. Finally, in human aortic smooth muscle cells, angiotensin II moderately increased transcriptional rate (as assessed by nuclear run-on analysis) but markedly increased ecSOD mRNA stability. Thus, angiotensin II increases ecSOD expression independent of hypertension, and this increase involves both an increase in ecSOD transcription and stabilization of ecSOD mRNA. This effect of angiotensin II on ecSOD expression may modulate the oxidative state of the vessel wall in pathological processes in which the renin-angiotensin system is activated.

A subthreshold MOS circuit for the Lotka-Volterra neural network producing the winners-share-all solution

An analog MOS circuit is proposed for implementing a Lotka-Volterra (LV) competitive neural network which produces winners-share-all solutions. The solutions give multiple winners receiving large inputs and are particularly useful for selecting a set of inputs through "decision by majority". We show that the LV network can easily be implemented using subthreshold MOS transistors. Results of extensive circuit simulations prove that the proposed circuit does exhibit a reliable selection compared with winner-take-all circuits, in the possible presence of device mismatches. These results pave a way to future implementation on a real device.