Disordering two-dimensional magnet-particle configurations using bidispersity.

In various types of many-particle systems, bidispersity is frequently used to avoid spontaneous ordering in particle configurations. In this study, the relation between bidispersity and disorder degree of particle configurations is investigated. By using magnetic dipole-dipole interaction, magnet particles are dispersed in a two-dimensional cell without any physical contact between them. In this magnetic system, bidispersity is introduced by mixing large and small magnets. Then, the particle system is compressed to produce a uniform particle configuration. The compressed particle configuration is analyzed by using Voronoi tessellation for evaluating the disorder degree, which strongly depends on bidispersity. Specifically, the standard deviation and skewness of the Voronoi cell area distribution are measured. As a result, we find that the peak of standard deviation is observed when the numbers of large and small particles are almost identical. Although the skewness shows a non-monotonic behavior, a zero skewness state (symmetric distribution) can be achieved when the numbers of large and small particles are identical. In this ideally random (disordered) state, the ratio between pentagonal, hexagonal, and heptagonal Voronoi cells becomes roughly identical, while hexagons are dominant under monodisperse (ordered) conditions. The relation between Voronoi cell analysis and the global bond orientational order parameter is also discussed.

Energy dissipation of a sphere rolling up a granular slope: Slip and deformation of the granular surface.

We experimentally investigate the dynamics of a sphere rolling up a granular slope. During the rolling-up motion, the sphere experiences slipping and penetration (groove formation) on the surface of the granular layer. The former relates to the stuck motion of the rolling sphere, and the latter causes energy dissipation due to the deformation of the granular surface. To characterize these phenomena, we measured the motion of a sphere rolling up a granular slope of angle α. The initial velocity v_{0}, initial angular velocity ω_{0}, angle of slope α, and density of the sphere ρ_{s} were varied. As a result, the penetration depth can be scaled solely by the density ratio between the sphere and granular layer. By considering the rotational equation of motion, we estimate the friction due to the slips. Besides, by considering energy conservation, we define and estimate the friction due to groove formation. Moreover, the translational friction is proportional to the penetration depth. Using these results, we can quantitatively predict the sphere's motion including stuck behavior.

Nitric oxide and peroxynitrite as factors to stimulate neurotransmitter release in the CNS.

This review summarizes the stimulatory potentials of NO and peroxynitrite (OONO-) on neurotransmitter release in the central nervous system. Exogenous and endogenous NO stimulates to release neurotransmitter. NO synthesized intracellularly diffuses out through neuronal membrane and acts on the outer side of membrane to depolarize neuronal membrane, which triggers neurotransmitter release. NO-induced release of neurotransmitters is mediated by Ca2+-dependent and -independent processes. The latter process is operated by reverse process of the Na+-dependent carrier-mediated neurotransmitter uptake system or by unknown mechanisms. Ca2+-dependent release of neurotransmitter occurs in part subsequent to increase in Ca2+ influx via VDCCs, although N-type VDCCs may not involve in this action of NO because of suppression of Ca2+ influx through N-type VDCCs by NO. Participation of cGMP formation by NO on neurotransmitter release is controversial. A superoxide scavenger, Ca2+, Zn(2+)-superoxide dismutase, abolishes NO-induced neurotransmitter release and synthesized OONO- induces neurotransmitter release, indicating that OONO- participates in NO-evoked neurotransmitter release.

Oxidative modification of low-density lipoprotein by human polymorphonuclear leucocytes to a form recognised by the lipoprotein scavenger pathway.

The oxidative modification of low-density lipoprotein (LDL) results in the formation of cytotoxic and chemotactic lipids which are thought to be of importance in the development of atherosclerotic lesions. In the present study we show that polymorphonuclear leucocytes (PMNs) can modify LDL to a form which is rapidly incorporated by macrophages via a scavenger receptor pathway. Incubation of 125I-labelled LDL with PMNs in Ham's F-10 medium resulted in oxidation as shown by the appearance of thiobarbituric acid-reactive substances, increased electrophoretic mobility of the LDL and increased degradation of the LDL by mouse peritoneal macrophages. The presence of the anti-oxidant butylated hydroxytoluene or the metal ion chelator, EDTA inhibited the PMN-mediated modification. The degradation of 125I-labelled PMN modified LDL by macrophages was competitively inhibited by unlabelled copper-oxidised LDL but not by native LDL, indicating that the degradation was mediated by the scavenger receptor. The oxidative modification of LDL by PMNs could be of pathophysiological importance in inflammation and in the accelerated atherosclerosis seen following cardiac reperfusion injury.

Two novel missense mutations of the OCTN2 gene (W283R and V446F) in a patient with primary systemic carnitine deficiency.

Primary systemic carnitine deficiency (SCD) is an autosomal recessive disorder of fatty acid oxidation caused by defective cellular carnitine transport. The disease is characterized by metabolic derangement simulating Reye's syndrome, hypoglcaemia, progressive cardiomyopathy and skeletal myopathy. Recently, it was shown that SCD is caused by mutations in the organic cation/carnitine transporter OCTN2 (SLC22A5). We report two novel mutations, W283R and V446F, which are both missense mutations in an affected infant. In vitro expression studies demonstrated that both are actually function-loss mutations with virtually no uptake activity. This is the first report of compound heterozygosity for two missense mutations in a patient with SCD. Hum Mutat 15:118, 2000.

Human recombinant interleukin-1 alpha increases biosynthesis of collagenase and hyaluronic acid in cultured human chorionic cells.

The influence of human recombinant interleukin-1 alpha (hrIL-1) on biosynthesis of collagenase and glycosaminoglycans was investigated with fibroblast-like cells of human chorionic membrane. hrIL-1 stimulated cells to produce procollagenase in a dose-dependent manner. Furthermore, it similarly accelerated both biosynthesis and secretion of hyaluronic acid in chorionic cells, but did not modulate the biosynthesis of sulfated glycosaminoglycans. Therefore, the relative concentration of hyaluronic acid vs total glycosaminoglycans increased significantly. These results are connected with the decrease in tensile strength observed in ruptured fetal membranes. Thus, it is proposed that IL-1 from effused leukocytes in fetal membranes plays an important role in connective tissue metabolism, especially in premature rupture of membranes with chorioamnionitis.

Ethanol stimulates diazepam binding inhibitor (DBI) mRNA expression in primary cultured neurons.

Changes in expression of diazepam binding inhibitor (DBI) mRNA in cerebral cortical neurons following long-term ethanol (EtOH) exposure were examined. A significant increase in DBI mRNA expression was observed by the exposure of neurons to 50 mM EtOH for up to 5 days and to EtOH (1-100 mM) for 3 days. These EtOH-induced increases in DBI mRNA expression were further elevated after the additional cultivation of neurons under EtOH-free condition. beta-Actin mRNA expression was not altered by similar EtOH treatments. These results indicate that EtOH possesses the activity to increase the expression of DBI mRNA in cerebral cortical neurons.

Involvement of peroxynitrite in N-methyl-D-aspartate- and sodium nitroprusside-induced release of acetylcholine from mouse cerebral cortical neurons.

Functional roles of peroxynitrite in N-methyl-D-aspartate (NMDA)- and sodium nitroprusside (SNP)-evoked releases of acetylcholine (ACh) from cerebral cortical neurons in primary culture have been investigated. NMDA increased the release of ACh in a dose-dependent manner, which was significantly suppressed by (+)-5-methyl-10,11-dihydro-5H-dibenzo-[a,d]cycloheptan-5,10-imine (MK-801), a non-competitive antagonist specific for the NMDA receptor complex, and NO synthase inhibitors. SNP also showed a concentration-dependent increase in ACh release. Hemoglobin significantly abolished the stimulatory effects of both NMDA and SNP on ACh release. In addition, superoxide anion scavengers such as superoxide dismutase and ceruloplasmin significantly reduced the increased ACh release evoked by NMDA and SNP. Synthesized peroxynitrite dose-dependently elevated the release of ACh. These results indicate that the increased release of ACh by NMDA and SNP is mediated through peroxynitrite formed in the reaction of superoxide anion with nitric oxide produced by NMDA receptor activation and liberated from SNP rather than nitric oxide itself.

Nitric oxide-evoked [3H] gamma-aminobutyric acid release is mediated by two distinct release mechanisms.

Mechanisms underlying the release of [3H] gamma-aminobutyric acid (GABA) evoked by nitric oxide (NO) were investigated by use of primary cultured neurons prepared from the mouse cerebral cortex. NO generators such as sodium nitroprusside (SNP) and S-nitroso-N-a etylpenicillamine (SNAP) increased both [3H]GABA release from the neurons and [45Ca2+] influx into the neurons in a dose-dependent manner, which was significantly diminished by hemoglobin. The removal of Ca2+ significantly reduced the NO-induced [3H]GABA release by about 50%. Nipecotic acid and 1-(2-(((diphenylmethylene)amino)oxy)ethyl)-1, 2, 5, 6-tetrahydro-3- pyridinecarboxylic acid (NO-711), GABA uptake inhibitors dose-dependently inhibited the NO-evoked [3H]GABA release in either the presence or absence of Ca2+. The concentration of these GABA uptake inhibitors to suppress the NO-induced release of [3H]GABA was sufficiently lower than that to exhibit the inhibition of [3H]GABA transport into the neurons. In addition, the NO-evoked [3H]GABA release was reduced by approximately 50% when total Na+ in incubation buffer was replaced with equimolar choline, and was also completely abolished by the removal of both Ca2+ and Na+. These results indicate that the release of [3H]GABA evoked by NO is mediated by two release mechanisms, a Ca2+ -dependent release system and the reverse process of the Ca2+ -independent and Na+ -dependent carrier-mediated GABA uptake system.

Withdrawal from nicotine facilitates diazepam binding inhibitor mRNA expression in mouse cerebral cortex.

Changes in diazepam binding inhibitor (DBI) mRNA expression after withdrawal from nicotine were examined. Withdrawal from nicotine Increased DBI mRNA expression in cerebral cortices derived from nicotine-dependent mice and in the neurons continuously exposed to nicotine (0.1 microM). These results indicate that withdrawal from nicotine after its long-term exposure induces steep increase of DBI mRNA expression as reported previously in ethanol- and morphine-dependent animals.

Mechanism for increase in expression of cerebral diazepam binding inhibitor mRNA by nicotine: involvement of L-type voltage-dependent calcium channels.

We investigated the mechanisms underlying the increase in diazepam binding inhibitor (DBI) and its mRNA expression induced by nicotine (0.1 microM) exposure for 24 h using mouse cerebral cortical neurons in primary culture. Nicotine-induced (0.1 microM) increases in DBI mRNA expression were abolished by hexamethonium, a nicotinic acetylcholine (nACh) receptor antagonist. Agents that stabilize the neuronal membrane, including tetrodotoxin (TTX), procainamide (a Na(+) channel inhibitor), and local anesthetics (dibucaine and lidocaine), dose-dependently inhibited the increased expression of DBI mRNA by nicotine. The nicotine-induced increase in DBI mRNA expression was inhibited by L-type voltage-dependent Ca(2+) channel (VDCC) inhibitors such as verapamil, calmodulin antagonist (W-7), and Ca(2+)/calmodulin-dependent protein kinase II (CAM II kinase) inhibitor (KN-62), whereas P/Q- and N-type VDCC inhibitors showed no effects. In addition, nicotine exposure for 24 h induced [3H]nicotine binding to the particulate fractions of the neurons with an increased B(max) value and no changes in K(d). Under these conditions, the 30 mM KCl- and nicotine-induced 45Ca(2+) influx into the nicotine-treated neurons was significantly higher than those into non-treated neurons. These results suggest that the nicotine-stimulated increase in DBI mRNA expression is mediated by CAM II kinase activation resulting from the increase in intracellular Ca(2+) through L-type VDCCs subsequent to the neuronal membrane depolarization associated with nACh receptor activation.

Hydroxyl radical scavengers enhance nitric oxide-evoked acetylcholine release from mouse cerebral cortical neurons.

The effect of hydroxyl radical scavengers on acetylcholine (ACh) release evoked by nitric oxide (NO) generators and N-methyl-D-aspartate (NMDA) was investigated. Dimethylthiourea enhanced dose-dependently NO generators-evoked ACh release. Similarly, uric acid and mannitol significantly facilitated ACh release evoked by NO generators. The NMDA-induced ACh release was also significantly facilitated by hydroxyl radical scavengers. These scavengers themselves showed no effects on ACh release. These results suggest that hydroxyl radicals may modify the mechanism for NO-evoked ACh release.

GABAA receptor stimulation enhances NMDA-induced Ca2+ influx in mouse cerebral cortical neurons in primary culture.

The effect of GABAA receptor stimulation on N-methyl-D-aspartate(NMDA)-induced [45Ca2+]influx has been examined using primary cultured cerebral cortical neurons. NMDA induced a dose-dependent increase in [45Ca2+]influx, which was blocked by MK-801 in a dose-dependent manner. GABAA receptor agonists significantly enhanced the NMDA-induced [45Ca2+]influx, and this enhancement was dose-dependently inhibited by bicuculline, although picrotoxin and tert-butyl-bicyclo[2.2.2]phosphoro-thionate (TBPS) exhibited no alterations in this stimulatory action of GABAA receptor agonists. Blockers of L-type voltage-dependent calcium channels significantly reduced the NMDA-induced [45Ca2+]influx. The increased [45Ca2+]influx by both NMDA and GABAA receptor agonists was also reduced by verapamil and nifedipine. These results suggest that the enhancement of NMDA-induced [45Ca2+]influx by GABAA receptor stimulation in immature cerebral cortical neurons may be due to the increased opening of voltage-dependent calcium channel by synergestic actions between NMDA and GABAA receptors.

Presence of N-methyl-D-aspartate (NMDA) receptors in neuroblastoma x glioma hybrid NG108-15 cells-analysis using [45Ca2+]influx and [3H]MK-801 binding as functional measures.

In the present study, we have attempted to clarify whether neuroblastoma glioma hybrid NG 108-15 cells (NG cells) possess the NMDA receptor complex using [45Ca2+]influx and [3H]MK-801 binding as functional measures. Glutamate and NMDA dose-dependently increased [45Ca2+]influx and these increases were further enhanced by glycine. Scatchard analysis revealed the presence of a high-affinity binding site for [3H]MK-801 with a KD of 18.8 nM and a Bmax of 0.328 pmol/mg protein. This [3H]MK-801 binding was also increased by NMDA in a dose-dependent manner and this increase was further enhanced by glycine. Both ketamine and MK-801 inhibited glutamate- and NMDA-induced [45Ca2+]influx as well as the increase of [3H]MK-801 binding in a dose-dependent manner. Similarly, Mg2+ and Zn2+ dose-dependently reduced both glutamate-induced [45Ca2+]influx and [3H]MK-801 binding. Spermine, one of the polyamines, showed a biphasic stimulatory effects on glutamate-induced [45Ca2+]influx and [3H]MK-801 binding. These results indicate that NG cells possess a pharmacologically distinct NMDA receptor complex and suggest that these cells may be useful for the analyses on pharmacological and biochemical characteristics of the NMDA receptor complex.

Removal of hydroxyl radical facilitates Ca2+-dependent [3H]GABA release by peroxynitrite.

We investigated mechanisms for enhancement of peroxynitrite (OONO-; 5 microM)-evoked [3H] gamma-aminobutyric acid (GABA) release. Hydroxyl radical scavengers such as N,N'-dimethylthiourea (DMTU), mannitol, and uric acid, significantly increased OONO--evoked [3H]GABA release, whereas urea showed no effects on the release. Removal of Ca2+ from incubation buffer abolished the enhancement of the release by DMTU, although DMTU showed no effects on the basal release with and without Ca2+ in extracellular space. These results indicate that hydroxyl radical scavengers facilitate OONO--evoked [3H]GABA release dependent on Ca2+.

Continuous treatment with nicotine increases diazepam binding inhibitor (DBI) and its mRNA in the mouse brain.

Effect of chronic treatment with nicotine on DBI and its mRNA in mouse cerebral cortex were examined. Continuous treatment of mice with nicotine significantly increased DBI content and its mRNA expression, which was completely abolished by simultaneous administration of mecamylamine (1 mg/kg, i.p.). These results indicate that chronic functional interaction between nicotine and nicotinic acetylcholine receptors has a critical role in increases in DBI content and its mRNA expression.

Functional involvement of benzodiazepine receptors in ethanol-induced increases of diazepam binding inhibitor (DBI) and its mRNA in the mouse brain.

We have attempted to clarify the mechanisms for alcohol (EtOH)-induced elevation of diazepam binding inhibitor (DBI) mRNA and to investigate whether the increase in DBI mRNA is paralleled with that in DBI using EtOH-treated mice and primary cultured neurons. Both the DBI content and the expression of DBI mRNA were elevated in the cerebral cortex of EtOH-inhaled and -withdrawn mice. Simultaneous administration of flunitrazepam (FLN) and Ro15-1788 with EtOH vapor completely abolished the EtOH-induced elevation of DBI mRNA. In addition, the exposure of the neurons for 3 days significantly elevated the expression of DBI mRNA, which was completely inhibited by concomitant exposure of FLN, Ro15-4513 and Ro-15-1788 with EtOH, while muscimol and bicuculline showed no effects on the EtOH-induced increase of DBI mRNA expression. These results indicate that functional interaction between EtOH and benzodiazepine (BDZ) receptors is a critical role in the increased expression of DBI mRNA.

Multiple actions of nitric oxide on voltage-dependent Ca2+ channels in mouse cerebral cortical neurons.

We investigated the effects of nitric oxide (NO) on voltage-dependent Ca2+ channels (VDCCs) by examining [45Ca2+]influx into mouse cerebral cortical neurons. S-nitroso-N-acetylpenicillamine (SNAP) induced a dose-dependent increase in [45Ca2+]influx, which was completely abolished by hemoglobin, tetrodotoxin and dibucaine. The NO-induced [45Ca2+influx was significantly inhibited by verapamil and omega-agatoxin VIA (omega-AGX), whereas omega-conotoxin GVIA (omega-CTX) had no effects on the NO-induced [45Ca2+]influx. KCl (30 mM) stimulated [45Ca2+]influx, and verapamil, omega-CTX and omega-AGX reduced the KCl-induced [45Ca2+]influx by about 40, 26 and 34%, respectively, indicating that the neurons used here possess L-, N- and P-typed VDCCs. SNAP itself reduced KCl-induced [45Ca2+]influx by about 28.5%. In the presence of both KCl and SNAP, omega-CTX showed no effects on the influx, while verapamil and omega-AGX significantly inhibited the influx and the concomitant presence of verapamil and omega-AGX completely abolished the influx. These results indicate that NO induces [45Ca2+] influx via the opening of L- and P-typed VDCCs subsequent to neuronal membrane depolarization and that NO itself inhibited the function of N-typed VDCC in the cerebral cortical neurons.

Suppression of Ca2+ influx through L-type voltage-dependent calcium channels by hydroxyl radical in mouse cerebral cortical neurons.

In the present study, we investigated the effect of hydroxyl radical (.OH) produced by the Fenton reaction with FeSO(4) to H(2)O(2) on Ca2+ influx by measuring [(45)Ca2+] influx into mouse cerebral cortical neurons in primary culture.OH formed from 3 microM FeSO(4) and 0.01 microM H(2)O(2) significantly reduced 30 mM KCl-induced [(45)Ca2+] influx and this reduction was abolished by .OH scavengers such as N,N'-dimethylthiourea and mannitol. Nifedipine (1 microM), an inhibitor for L-type voltage-dependent Ca2+ channels (VDCCs) showed no additive effect on the reduction of the 30 mM KCl-induced [(45)Ca2+] influx, while the inhibitors for P/Q- and N-type VDCCs showed further suppression of the KCl-induced [(45)Ca2+] influx even in the presence of .OH. Bay k 8644, an activator of L-type VDCCs, dose-dependently stimulated [(45)Ca2+] influx, and this stimulation disappeared in the presence of nifedipine. Similarly, .OH also suppressed significantly [(45)Ca2+] influx induced by Bay k 8644. These inhibitory actions of .OH on the KCl- and Bay k 8644-induced [(45)Ca2+] influx were completely abolished by .OH scavengers. These results indicate that .OH has the activity to suppress Ca2+ influx through L-type VDCCs.

NMDA receptor activation enhances diazepam binding inhibitor and its mRNA expressions in mouse cerebral cortical neurons.

Effects of N-methyl-D-aspartate (NMDA) on diazepam binding inhibitor (DBI) and its mRNA expression in mouse cerebral cortical neurons were examined. A significant increase in DBI mRNA expression was observed 1 day after the exposure to 0.1 microM NMDA and the maximal expression occurred 2 days after the exposure, whereas transient exposure to 0.1 microM NMDA for 15 min, 1 and 3 h produced no changes in the expression. Similarly, no changes in the expression were found by the concomitant exposure to NMDA and MK-801, a NMDA receptor antagonist, for 72 h subsequent to the incubation with NMDA alone for 3 h. Such NMDA-induced increases in DBI mRNA expression were dose-dependently inhibited by MK-801. Moreover, neuronal DBI content significantly increased by treatment with NMDA, which was completely abolished by MK-801. These results indicate that continuous activation of NMDA receptors is an essential factor for increasing DBI expression in the neurons.