Disappearance of back-to-back high-pT hadron correlations in central Au+Au collisions at sqrt[s NN ] =200 GeV

Azimuthal correlations for large transverse momentum charged hadrons have been measured over a wide pseudorapidity range and full azimuth in Au+Au and p+p collisions at sqrt[s(NN)]=200 GeV. The small-angle correlations observed in p+p collisions and at all centralities of Au+Au collisions are characteristic of hard-scattering processes previously observed in high-energy collisions. A strong back-to-back correlation exists for p+p and peripheral Au+Au. In contrast, the back-to-back correlations are reduced considerably in the most central Au+Au collisions, indicating substantial interaction as the hard-scattered partons or their fragmentation products traverse the medium.

Azimuthal anisotropy and correlations in the hard scattering regime at RHIC

Azimuthal anisotropy (v(2)) and two-particle angular correlations of high p(T) charged hadrons have been measured in Au+Au collisions at sqrt[s(NN)]=130 GeV for transverse momenta up to 6 GeV/c, where hard processes are expected to contribute significantly. The two-particle angular correlations exhibit elliptic flow and a structure suggestive of fragmentation of high p(T) partons. The monotonic rise of v(2)(p(T)) for p(T)<2 GeV/c is consistent with collective hydrodynamical flow calculations. At p(T)>3 GeV/c, a saturation of v(2) is observed which persists up to p(T)=6 GeV/c.

Coherent rho(0) production in ultraperipheral heavy-ion collisions

The STAR Collaboration reports the first observation of exclusive rho(0) photoproduction, AuAu-->AuAurho(0), and rho(0) production accompanied by mutual nuclear Coulomb excitation, AuAu-->Au*Au*rho(0), in ultraperipheral heavy-ion collisions. The rho(0) have low transverse momenta, consistent with coherent coupling to both nuclei. The cross sections at sqrt[s(NN)]=130 GeV agree with theoretical predictions treating rho(0) production and Coulomb excitation as independent processes.

Centrality dependence of high-p(T) hadron suppression in Au+Au collisions at sqrt[s(NN)]=130 GeV

Inclusive transverse momentum distributions of charged hadrons within 0.2<p(T)<6.0 GeV/c have been measured over a broad range of centrality for Au+Au collisions at sqrt[s(NN)]=130 GeV. Hadron yields are suppressed at high p(T) in central collisions relative to peripheral collisions and to a nucleon-nucleon reference scaled for collision geometry. Peripheral collisions are not suppressed relative to the nucleon-nucleon reference. The suppression varies continuously at intermediate centralities. The results indicate significant nuclear medium effects on high-p(T) hadron production in heavy-ion collisions at high energy.

Azimuthal anisotropy of K(0)(S) and Lambda+Lambda production at midrapidity from Au+Au collisions at sqrt[s(NN)]=130 GeV

We report STAR results on the azimuthal anisotropy parameter v(2) for strange particles K(0)(S), Lambda, and Lambda at midrapidity in Au+Au collisions at sqrt[s(NN)]=130 GeV at the Relativistic Heavy Ion Collider. The value of v(2) as a function of transverse momentum, p(t), of the produced particle and collision centrality is presented for both particles up to p(t) approximately 3.0 GeV/c. A strong p(t) dependence in v(2) is observed up to 2.0 GeV/c. The v(2) measurement is compared with hydrodynamic model calculations. The physics implications of the p(t) integrated v(2) magnitude as a function of particle mass are also discussed.

Midrapidity Lambda and Lambda(macro) production in Au+Au collisions at the square root of [s(NN)]=130 GeV

We report the first measurement of strange (Lambda) and antistrange (Lambda macro) baryon production from square root of [s(NN)]=130 GeV Au+Au collisions at the Relativistic Heavy Ion Collider (RHIC). Rapidity density and transverse mass distributions at midrapidity are presented as a function of centrality. The yield of Lambda and Lambda; hyperons is found to be approximately proportional to the number of negative hadrons. The production of Lambda; hyperons relative to negative hadrons increases very rapidly with transverse momentum. The magnitude of the increase cannot be described by existing hadronic string fragmentation models alone.

Measurement of inclusive antiprotons from Au+Au collisions at square root of s(NN) = 130 GeV

We report the first measurement of inclusive antiproton production at midrapidity in Au+Au collisions at square root of s(NN) = 130 GeV by the STAR experiment at RHIC. The antiproton transverse mass distributions in the measured transverse momentum range of 0.25<p( perpendicular)<0.95 GeV/c are found to fall less steeply for more central collisions. The extrapolated antiproton rapidity density is found to scale approximately with the negative hadron multiplicity density.

d Macro and (3)He macro production in square root of s(NN) = 130 GeV Au+Au collisions

The first measurements of light antinucleus production in Au+Au collisions at the Relativistic Heavy-Ion Collider are reported. The observed production rates for d macro and (3)He macro are much larger than in lower energy nucleus-nucleus collisions. A coalescence model analysis of the yields indicates that there is little or no increase in the antinucleon freeze-out volume compared to collisions at CERN SPS energy. These analyses also indicate that the (3)He macro freeze-out volume is smaller than the d macro freeze-out volume.

Multiplicity distribution and spectra of negatively charged hadrons in Au+Au collisions at square root of (sNN) = 130 GeV

The minimum-bias multiplicity distribution and the transverse momentum and pseudorapidity distributions for central collisions have been measured for negative hadrons ( h(-)) in Au+Au interactions at square root of ([s(NN)]) = 130 GeV. The multiplicity density at midrapidity for the 5% most central interactions is dN(h(-))/d(eta)/(eta = 0) = 280+/-1(stat)+/-20(syst), an increase per participant of 38% relative to pp collisions at the same energy. The mean transverse momentum is 0.508+/-0.012 GeV/c and is larger than in central Pb+Pb collisions at lower energies. The scaling of the h(-) yield per participant is a strong function of p( perpendicular). The pseudorapidity distribution is almost constant within /eta/<1.

Pion Interferometry of square root of (s(NN)) =130 GeV Au + Au collisions at RHIC

Two-pion correlation functions in Au+Au collisions at square root of [s(NN)] = 130 GeV have been measured by the STAR (solenoidal tracker at RHIC) detector. The source size extracted by fitting the correlations grows with event multiplicity and decreases with transverse momentum. Anomalously large sizes or emission durations, which have been suggested as signals of quark-gluon plasma formation and rehadronization, are not observed. The Hanbury Brown-Twiss parameters display a weak energy dependence over a broad range in square root of [s(NN)].

Midrapidity antiproton-to-proton ratio from Au+Au collisions at sqrt [s(NN)]=130 GeV

We report results on the ratio of midrapidity antiproton-to-proton yields in Au+Au collisions at sqrt[s(NN)] = 130 GeV per nucleon pair as measured by the STAR experiment at RHIC. Within the rapidity and transverse momentum range of /y/<0.5 and 0.4<p(t)<1.0 GeV/c, the ratio is essentially independent of either transverse momentum or rapidity, with an average of 0.65+/-0.01((stat))+/-0.07((syst)) for minimum bias collisions. Within errors, no strong centrality dependence is observed. The results indicate that at this RHIC energy, although the p-p pair production becomes important at midrapidity, a significant excess of baryons over antibaryons is still present.

Transcriptional regulation of cytoskeletal functions and segmentation by a novel maternal pair-rule gene, lilliputian

Transcriptional control during early Drosophila development is governed by maternal and zygotic factors. We have identified a novel maternal transcriptional regulator gene, lilliputian (lilli), which contains an HMG1 (AT-hook) motif and a domain with similarity to the human fragile X mental retardation FMR2 protein and the AF4 proto-oncoprotein. Embryos lacking maternal lilli expression show specific defects in the establishment of a functional cytoskeleton during cellularization, and exhibit a pair-rule segmentation phenotype. These mutant phenotypes correlate with markedly reduced expression of the early zygotic genes serendipity alpha, fushi tarazu and huckebein, which are essential for cellularization and embryonic patterning. In addition, loss of lilli in adult photoreceptor and bristle cells results in a significant decrease in cell size. Our results indicate that lilli represents a novel pair-rule gene that acts in cytoskeleton regulation, segmentation and morphogenesis.

Elliptic flow in Au+Au collisions at square root(S)NN = 130 GeV

Elliptic flow from nuclear collisions is a hadronic observable sensitive to the early stages of system evolution. We report first results on elliptic flow of charged particles at midrapidity in Au+Au collisions at square root(S)NN = 130 GeV using the STAR Time Projection Chamber at the Relativistic Heavy Ion Collider. The elliptic flow signal, v2, averaged over transverse momentum, reaches values of about 6% for relatively peripheral collisions and decreases for the more central collisions. This can be interpreted as the observation of a higher degree of thermalization than at lower collision energies. Pseudorapidity and transverse momentum dependence of elliptic flow are also presented.

Crystal structure of the HIV-1 integrase catalytic core and C-terminal domains: a model for viral DNA binding

Insolubility of full-length HIV-1 integrase (IN) limited previous structure analyses to individual domains. By introducing five point mutations, we engineered a more soluble IN that allowed us to generate multidomain HIV-1 IN crystals. The first multidomain HIV-1 IN structure is reported. It incorporates the catalytic core and C-terminal domains (residues 52-288). The structure resolved to 2.8 A is a Y-shaped dimer. Within the dimer, the catalytic core domains form the only dimer interface, and the C-terminal domains are located 55 A apart. A 26-aa alpha-helix, alpha6, links the C-terminal domain to the catalytic core. A kink in one of the two alpha6 helices occurs near a known proteolytic site, suggesting that it may act as a flexible elbow to reorient the domains during the integration process. Two proteins that bind DNA in a sequence-independent manner are structurally homologous to the HIV-1 IN C-terminal domain, suggesting a similar protein-DNA interaction in which the IN C-terminal domain may serve to bind, bend, and orient viral DNA during integration. A strip of positively charged amino acids contributed by both monomers emerges from each active site of the dimer, suggesting a minimally dimeric platform for binding each viral DNA end. The crystal structure of the isolated catalytic core domain (residues 52-210), independently determined at 1.6-A resolution, is identical to the core domain within the two-domain 52-288 structure.

Carbonyl J Derivatives: A New Class of HIV-1 Integrase Inhibitors

Integration of a DNA copy of the HIV-1 genome is required for viral replication and pathogenicity, and this highly specific molecular process is mediated by the virus-encoded integrase protein. The requirement for integration, combined with the lack of a known analogous process in mammalian cells, makes integrase an attractive target for therapeutic inhibitors of HIV-1 replication. While many reports of HIV-1 IN inhibitors exist, no such compounds have yet emerged to treat HIV-1 infection. As such, new classes of integrase inhibitors are needed. We have combined molecular modeling and combinatorial chemistry to identify and develop a new class of HIV-1 integrase inhibitors, the Carbonyl J [N,N'-bis(2-(5-hydroxy-7-naphthalenesulfonic acid)urea] derivatives. This new class includes a number of compounds with sub-micromolar IC(50) values for inhibiting purified HIV-1 integrase in vitro. Herein we describe the chemical characteristics that are important for integrase inhibition and cell toxicity within the Carbonyl J derivatives. Copyright 2000 Academic Press.

Piperazine imidazo[1,5-a]quinoxaline ureas as high-affinity GABAA ligands of dual functionality

A series of imidazo[1,5-a]quinoxaline piperazine ureas appended with a tert-butyl ester side chain at the 3-position was developed. Analogues within this series have high affinity for the gamma-aminobutyric acid A (GABAA)/benzodiazepine receptor complex with efficacies ranging from inverse agonists to full agonists. Many analogues were found to be partial agonists as indicated by [35S]TBPS and Cl- current ratios. Uniquely, a number of these analogues were found to have a bell-shaped dose-response profile in the alpha1 beta2 gamma2 subtype as determined by whole cell patch-clamp technique, where in vitro efficacy was found to decrease with increasing drug concentration. Many of the compounds from this series were effective in antagonizing metrazole-induced seizures, consistent with anticonvulsant and possibly anxiolytic activity. Additionally, several analogues were also effective in lowering cGMP levels (to control values) after applied stress, also consistent with anxiolytic-like properties. The most effective compounds in these screens were also active in animal models of anxiety such as the Vogel and Geller assays. The use of the piperazine substituent allowed for excellent drug levels and a long duration of action in the central nervous system for many of the quinoxalines, as determined by ex vivo assay. Pharmacokinetic analysis of several compounds indicated excellent oral bioavailability and a reasonable half-life in rats. From this series emerged two partial agonists (55, 91) which had good activity in anxiolytic models, acceptable pharmacokinetics, and minimal benzodiazepine-type side effects.

A genetic screen to identify components of the sina signaling pathway in Drosophila eye development

Specification of the R7 photoreceptor cell in the developing Drosophila eye requires the seven in absentia (sina) gene. We demonstrate that ectopic expression of sina in all cells behind the morphogenetic furrow disrupts normal eye development during pupation, resulting in a severely disorganized adult eye. Earlier events of cell fate specification appear unaffected. A genetic screen for dominant enhancers and suppressors of this phenotype identified mutations in a number of genes required for normal eye development, including UbcD1, which encodes a ubiquitin conjugating enzyme; SR3-4a, a gene previously implicated in signaling downstream of Ras1; and a Drosophila homolog of the Sin3A transcriptional repressor.

PHYL acts to down-regulate TTK88, a transcriptional repressor of neuronal cell fates, by a SINA-dependent mechanism

We show that Tramtrack (TTK88) expression represses neuronal fate determination in the developing Drosophila eye. Phyllopod (PHYL) acts to antagonize this repression by a mechanism that requires Seven In Absentia (SINA) and is associated with decreased TTK88 protein levels, but not reduced ttk88 gene transcription or mRNA stability. We present evidence that SINA, PHYL, and TTK88 physically interact and that SINA interacts genetically and physically with UBCD1, a component of the ubiquitin-dependent protein degradation pathway. Our results suggest a model in which activation of the Sevenless receptor tyrosine kinase induces PHYL expression, which then acts with SINA to target the transcriptional repressor TTK88 for degradation, thereby promoting R7 cell fate specification.

Anxiolytic-like effects of PNU-101017, a partial agonist at the benzodiazepine receptor

PNU-101017 is a chemically novel ligand at the benzodiazepine recognition site of cloned GABAA receptors. It was reported to potentiate GABA-mediated chloride current in cultured cells with a moderate intrinsic activity and a biphasic dose-response relationship. In this study, we confirmed that PNU-101017 has a partial agonist-like effect in the antagonism of metrazole-induced seizures in mice. It produced no sedation or ataxia, but did antagonize diazepam-induced motor deficit of mice in the rotarod test. PNU-101017 was weakly active in anti-conflict anxiolytic tests, but attenuated the plasma corticosteroid response to mild stress in rats. It also antagonized stress-induced elevation of cerebellar cGMP levels in mice. Like chlordiazepoxide, it increased drinking of saline solution in thirsty rats. PNU-101017 did not potentiate the CNS-depressant effects of ethanol, and produced no evidence of physical dependence when administered repeatedly. Agonists with low intrinsic activity at the benzodiazepine receptor, such as PNU-101017, should be further explored for therapeutic uses.

PNU-96415E, a potential antipsychotic agent with clozapine-like pharmacological properties

The atypical antipsychotic drug clozapine interacts with multiple transmitter systems, among them the D4 subtype of dopamine receptors. PNU-96415E is chemically unrelated to clozapine and has its highest binding affinity for the D4 and 5-HT2A receptors. In comparison to clozapine, PNU-96415E is weaker in binding to D1, D2, alpha1 and muscarinic receptors. PNU-96415E inhibited exploratory locomotor activity in mice and rats, and antagonized d-amphetamine-induced locomotor stimulation in rats. It antagonized apomorphine-induced cage climbing, and blocked head and body twitch produced by 5-HTP in mice. Like clozapine, but unlike haloperidol, PNU-96415E did not antagonize stereotypic behaviors produced by a high dose of d-amphetamine or methylphenidate in rats and mice. PNU-96415E blocked conditioned avoidance in rats but produced no catalepsy, a pattern similar to clozapine but different from haloperidol. In rats trained to discriminate clozapine from saline injections, the stimulus effect generalized completely with PNU-96415E, but not haloperidol. This profile of pharmacological activities is consistent with that of an atypical antipsychotic and, as in the case with clozapine, the behavioral effects of PNU-96415E cannot be ascribed to a single receptor mechanism.

Pharmacology of U-91356A, an agonist for the dopamine D2 receptor subtype

U-91356A [(R)-5,6-dihydro-5-(propylamino)4H-imidazo[4,5,1-ij]quinolin -2-(1H)-one, monohydrochloride], bound with highest affinity to the dopamine D2 receptor subtype, although it also bound with somewhat lower affinities to the dopamine D3 and D4, as well as the 5-HT1A receptor subtypes. In addition to depressing dopamine synthesis and turnover, injection of U-91356A increased striatal acetylcholine concentrations. U-91356A also depressed firing rates of dopamine neurons. In mice, this compound stimulated cage climbing and locomotor activity in reserpinized animals; it also antagonized D-amphetamine-stimulated locomotor activity. It produced contralateral turning in rats with unilateral lesions of the substantia nigra. These data are consistent with roles for the dopamine D2 receptor subtype as a dopamine autoreceptor and as a stimulatory, postsynaptic dopamine receptor.

Pharmacological characterization of U-101387, a dopamine D4 receptor selective antagonist

Dopamine D2-like receptors play an important role in the pharmacotherapy of psychotic disorders. Molecular and cellular techniques have identified distinct gene products (D2-long, D2-short, D3 and D4) displaying the D2 receptor pharmacology. However, the contribution of each subtype in antipsychotic effects of or their physiological role remain unclear. Here we describe the pharmacological effects of a selective D4 antagonist, U-101387. U-101387 displayed moderately high affinity (Ki = 10 nM) and selectivity for the dopamine D4.2 receptor expressed in clonal cell lines. It lacked measurable affinity for not only other dopamine receptors but also noradrenalin, serotonin and histamine receptor families (Ki > 2000 nM). It fully and dose-dependently antagonized quinpirole-induced cAMP inhibition (without producing any effect by itself) in stably transfected cells. U-101387 also displayed excellent oral bioavailability, brain penetration and other pharmacokinetic characteristics. Unlike classical neuroleptics (e.g., haloperidol), U-101387 neither blocked acute behavioral effects of amphetamine or apomorphine nor did it alter spontaneous locomotion by itself. Additionally, U-101387 was without effect in behavioral and biochemical tests predictive of extrapyramidal and neuroendocrine side effects. Consistent with the lack of autoreceptor function of D4, acute administration of U-101387 failed to alter dopamine neuronal firing by itself or reverse the inhibition produced by dopamine agonists and to affect monoamine turnover in areas innervated by the mesencephalic or hypothalamic dopamine neurons. However, U-101387 potently induced c-fos mRNA expression in the infralimbic/ventral prelimbic cortex to a level similar to that produced by the atypical antipsychotic, clozapine. This is consistent with the predominantly cortical distribution of the D4 receptor. Taken together, these results demonstrate that the D4-selective antagonist, U-101387, produces effects that are distinct from those of the nonselective D2 antagonists as well as D3-preferring agents. U-101387 offers a unique tool to understand the role of dopamine D4 receptors in diseases involving central dopamine systems.

High-affinity alpha-aminobutyric acid A/benzodiazepine ligands: synthesis and structure-activity relationship studies of a new series of tetracyclic imidazoquinoxalines

A series of tetracyclic imidazoquinoxaline analogs was developed which constrain the carbonyl group of the partial agonist 3-(5-cyclopropyl-1,2,4-oxadiazol-3-yl)-5-[(dimethylamino)carbonyl] - 4,5-dihydroimidazo[1,5-alpha]quinoxaline (2, U-91571) away from the benzene ring. These analogs orient the carbonyl group in the opposite direction of the previously reported full agonist 1-(5- cyclopropyl-1,2,4-oxadiazol-3-yl)-12,12a-dihydroimidazo[1,5- alpha]pyrrolo [2,1-c]quinoxalin-10(11H)-one (3, U-89267). A number of approaches were utilized to form the "bottom" ring of this tetracyclic ring system including intramolecular cyclizations promoted by Lewis acids or base, as well as metal-carbenoid conditions. The size and substitution pattern of the additional ring was widely varied. Analogs within this series had high affinity for the benzodiazepine receptor on the alpha-aminobutyric acid A chloride ion channel complex. From TBPS shift and Cl- current assays, the in vitro efficacy of compounds within this class ranged from antagonists to partial agonists with only 18a identified as a full agonist. Additionally, several analogs were quite potent at antagonizing metrazole-induced seizures indicating possible anticonvulsant or anxiolytic activity. Unlike 3, analogs in this series did not have high affinity for the diazepam insensitive alpha 6 beta 2 delta 2 subtype. These results suggest that either constraining the carbonyl group away from the benzene ring or the greater planarity that results from the additional cyclic structure provides analogs with partial agonist properties and prevents effective interaction with the alpha 6 beta 2 delta 2 subtype.

3-Phenyl-substituted imidazo[1,5-alpha]quinoxalin-4-ones and imidazo[1,5-alpha]quinoxaline ureas that have high affinity at the GABAA/benzodiazepine receptor complex

A series of imidazo[1,5-alpha]quinoxalin-4-ones and imidazo[1,5-alpha]quinoxaline ureas containing substituted phenyl groups at the 3-position was developed. Compounds within the imidazo[1,5-alpha]quinoxaline urea series had high affinity for the GABAA/benzodiazepine receptor complex with varying in vitro efficacy, although most analogs were partial agonists as indicated by [35S]TBPS and Cl- current ratios. Interestingly, a subseries of piperazine ureas was identified which had biphasic efficacy, becoming more antagonistic with increasing concentration. Analogs within the imidazo[1,5-alpha]quinoxalin-4-one series had substantially decreased binding affinity as compared to the quinoxaline urea series. These compounds ranged from antagonists to full agonists by in vitro analysis, with several derivatives having roughly 4-fold greater intrinsic activity than diazepam as indicated by Cl- current measurement. Numerous compounds from both series were effective in antagonizing metrazole-induced seizures, consistent with anti-convulsant properties and possible anxiolytic activity. Most of the quinoxaline ureas and quinoxalin-4-ones were active in an acute electroshock physical dependence side effect assay in mice precluding further development.

High-affinity partial agonist imidazo[1,5-a]quinoxaline amides, carbamates, and ureas at the gamma-aminobutyric acid A/benzodiazepine receptor complex

A series of imidazo[1,5-a]quinoxaline amides, carbamates, and ureas which have high affinity for the gamma-aminobutyric acid A/benzodiazepine receptor complex was developed. Compounds within this class have varying efficacies ranging from antagonists to full agonists. However, most analogs were found to be partial agonists as indicated by [35S]TBPS and Cl- current ratios. Many of these compounds were also effective in antagonizing metrazole-induced seizures in accordance with anticonvulsant and possible anxiolytic activity. Selected quinoxalines displayed limited benzodiazepine-type side effects such as ethanol potentiation and physical dependence in animal models. Dimethylamino urea 41 emerged as the most interesting analog, having a partial agonist profile in vitro while possessing useful activity in animal models of anxiety such as the Vogel and Geller assays. In accordance with its partial agonist profile, 41 was devoid of typical benzodiazepine side effects.