Effect of Improving the Lattice Gauge Action on QCD Topology

We use lattice topology as a laboratory to compare the Wilson action (WA) with the Symanzik-Weisz (SW) action constructed from a combination of (1x1) and (1x2) Wilson loops, and the estimate of the renormalization trajectory (RT) from a renormalization group transformation (RGT) which also includes higher representations of the (1x1) loop. Topological charges are computed using the geometric (L\"uscher's) and plaquette methods on the uncooled lattice, and also by using cooling to remove ultraviolet artifacts. We show that as the action improves by approaching the RT, the topological charges for individual configurations computed using these three methods become more highly correlated, suggesting that artificial lattice renormalizations to the topological susceptibility can be suppressed by improving the action.Comment: 4 pages, 4 figures, poster presented at LATTICE96(improvement

Topological Density and Instantons on a Lattice

We present an update on the study of topological structure of QCD. Issues addressed include a comparison between the plaquette and the geometric methods of calculating the topological density. We show that the improved gauge action based on sqrt(3) blocking transformation suppresses the formation of topologically charged dislocations with low action. Using a cooling method we identify the instantons' location, estimate their size and density, and calculate the renormalization constant Z_Q for the plaquette method.Comment: 3 Pages, submitted to Proceedings of XII International Symposium on Lattice Field Theory (Lattice 94, Bielefeld). uuencoded tar file includes figures as TeXDraw (.tex) file

The Eta-prime and Cooling with Staggered Fermions

We present a calculation of the mass of the eta-prime meson using quenched and dynamical staggered fermions. We also discuss the effects of "cooling" and suggest its use as a quantitative tool.Comment: 4 pages, LaTeX with 7 EPS figs, contribution to Lattice 9

Dopamine D(2 )receptors mediate two-odor discrimination and reversal learning in C57BL/6 mice

BACKGROUND: Dopamine modulation of neuronal signaling in the frontal cortex, midbrain, and striatum is essential for processing and integrating diverse external sensory stimuli and attaching salience to environmental cues that signal causal relationships, thereby guiding goal-directed, adaptable behaviors. At the cellular level, dopamine signaling is mediated through D(1)-like or D(2)-like receptors. Although a role for D(1)-like receptors in a variety of goal-directed behaviors has been identified, an explicit involvement of D(2 )receptors has not been clearly established. To determine whether dopamine D(2 )receptor-mediated signaling contributes to associative and reversal learning, we compared C57Bl/6J mice that completely lack functional dopamine D(2 )receptors to wild-type mice with respect to their ability to attach appropriate salience to external stimuli (stimulus discrimination) and disengage from inappropriate behavioral strategies when reinforcement contingencies change (e.g. reversal learning). RESULTS: Mildly food-deprived female wild-type and dopamine D(2 )receptor deficient mice rapidly learned to retrieve and consume visible food reinforcers from a small plastic dish. Furthermore, both genotypes readily learned to dig through the same dish filled with sterile sand in order to locate a buried food pellet. However, the dopamine D(2 )receptor deficient mice required significantly more trials than wild-type mice to discriminate between two dishes, each filled with a different scented sand, and to associate one of the two odors with the presence of a reinforcer (food). In addition, the dopamine D(2 )receptor deficient mice repeatedly fail to alter their response patterns during reversal trials where the reinforcement rules were inverted. CONCLUSIONS: Inbred C57Bl/6J mice that develop in the complete absence of functional dopamine D(2 )receptors are capable of olfaction but display an impaired ability to acquire odor-driven reinforcement contingencies. Furthermore, the ability of dopamine D(2 )receptor deficient mice to adjust their responding to a previously reinforced stimulus when unexpected outcomes are encountered is significantly impaired. These findings suggest that signaling mediated by the dopamine D(2 )receptor is important for regulating associative and reversal learning and may have implications for the treatment of human attention disorders

Geometric Measurement of Topological Susceptibility on Large Lattices

The topological susceptibility of the quenched QCD vacuum is measured on large lattices for three $\beta$ values from $6.0$ to $6.4$. Charges possibly induced by $O(a)$ dislocations are identified and shown to have little effect on the measured susceptibility. As $\beta$ increases, fewer such questionable charges are found. Scaling is checked by examining the ratios of the susceptibility to previously existing values of the rho mass, string tension, F-pi, and lambda-lattice.Comment: LaTeX article, 3 pages, uuencoded compressed tar file, 2 figures included as tex files using axismacros, DVIPS driver required to show figures. Talk presented by Jeffrey Grandy at Lattice 93, Dallas, Texas. Los Alamos Preprint number pendin

Failure of Intravenous Morphine to Serve as an Effective Instrumental Reinforcer in Dopamine D2 Receptor Knock-Out Mice

The rewarding effects of opiates are thought to be mediated through dopaminergic mechanisms in the ventral tegmental area, dopamine-independent mechanisms in the nucleus accumbens, or both. The purpose of the present study was to explore the contribution of dopamine to opiate-reinforced behavior using D2 receptor knock-out mice. Wild-type, heterozygous, and D2 knock-out mice were first trained to lever press for water reinforcement and then implanted with intravenous catheters. The ability of intravenously delivered morphine to maintain lever pressing in these mice was studied under two schedules of reinforcement: a fixed ratio 4 (FR4) schedule (saline, 0.1, 0.3, or 1.0 mg/kg, per injection) and a progressive ratio (PR) schedule (1.0 mg/kg, per injection). In the wild-type and heterozygous mice, FR4 behavior maintained by morphine injections was significantly greater than behavior maintained by vehicle injections. Response rate was inversely related to injection dose and increased significantly in the wild-type and heterozygous mice when the animals were placed on the PR schedule. In contrast, the knock-out mice did not respond more for morphine than for saline and did not respond more when increased ratios were required by the PR schedule. Thus, morphine served as a positive reinforcer in the wild-type and heterozygous mice but failed to do so in the knock-out mice. Under this range of doses and response requirements, the rewarding effects of morphine appear to depend critically on an intact D2 receptor systemFil: Elmer, Greg I.. University of Maryland; Estados UnidosFil: Pieper, Jeanne O.. National Institutes of Health; Estados UnidosFil: Rubinstein, Marcelo. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Investigaciones en Ingeniería Genética y Biología Molecular "Dr. Héctor N. Torres"; ArgentinaFil: Low, Malcolm J.. Oregon Health and Sciences University; Estados UnidosFil: Grandy, David K.. Oregon Health and Sciences University; Estados UnidosFil: Wise, Roy A.. National Institutes of Health; Estados Unido

Mixing materials within zone boundaries using shape overlays

Shape overlays provide a means of statically imposing a physical region containing specified material properties onto a zoned mesh. In the most general case, material interface boundaries are unrelated to mesh zone boundaries, causing zones to contain a mixture of materials, and the mesh itself is not uniform in physical space. We develop and apply an algorithm for shape overlays on nonorthogonal, nonuniform meshes in two dimensions. Examples of shape generation in a multiblock uid dynamics code are shown

Dysfunctional Light-Evoked Regulation of cAMP in Photoreceptors and Abnormal Retinal Adaptation in Mice Lacking Dopamine D4 Receptors

Dopamine is a retinal neuromodulator that has been implicated in many aspects of retinal physiology. Photoreceptor cells express dopamine D4 receptors that regulate cAMP metabolism. To assess the effects of dopamine on photoreceptor physiology, we examined the morphology, electrophysiology, and regulation of cAMP metabolism in mice with targeted disruption of the dopamine D4 receptor gene. Photoreceptor morphology and outer segment disc shedding after light onset were normal in D4 knock-out (D4KO) mice. Quinpirole, a dopamine D2/ D3/D4 receptor agonist, decreased cAMP synthesis in retinas of wild-type (WT) mice but not in retinas of D4KO mice. In WT retinas, the photoreceptors of which were functionally isolated by incubation in the presence of exogenous glutamate, light also suppressed cAMP synthesis. Despite the similar inhibition of cAMP synthesis, the effect of light is directly on the photoreceptors and independent of dopamine modulation, because it was unaffected by application of the D4 receptor antagonist L-745,870. Nevertheless, compared with WT retinas, basal cAMP formation was reduced in the photoreceptors of D4KO retinas, and light had no additional inhibitory effect. The results suggest that dopamine, via D4 receptors, normally modulates the cascade that couples light responses to adenylyl cyclase activity in photoreceptor cells, and the absence of this modulation results in dysfunction of the cascade. Dark-adapted electroretinogram (ERG) responses were normal in D4KO mice. However, ERG b-wave responses were greatly suppressed during both light adaptation and early stages of dark adaptation. Thus, the absence of D4 receptors affects adaptation, altering transmission of light responses from photoreceptors to inner retinal neurons. These findings indicate that dopamine D4 receptors normally play a major role in regulating photoreceptor cAMP metabolism and adaptive retinal responses to changing environmental illumination.Fil: Nir, Izhak. The University of Texas Health Science Center; Estados UnidosFil: Harrison, Joseph M.. The University of Texas Health Science Center; Estados UnidosFil: Haque, Rashidul. Emory University School of Medicine; Estados UnidosFil: Low, Malcolm J.. Oregon Health and Science University; Estados UnidosFil: Grandy, David K.. Oregon Health and Science University; Estados UnidosFil: Rubinstein, Marcelo. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Investigaciones en Ingeniería Genética y Biología Molecular "Dr. Héctor N. Torres"; ArgentinaFil: Iuvone, P. Michael. Emory University School of Medicine; Estados Unido

Conditioned place preference and locomotor activity in response to methylphenidate, amphetamine and cocaine in mice lacking dopamine D4 receptors

Methylphenidate (MP) and amphetamine (AMPH) are the most frequently prescribed medications for the treatment of attention-deficit/hyperactivity disorder (ADHD). Both drugs are believed to derive their therapeutic benefit by virtue of their dopamine (DA)-enhancing effects, yet an explanation for the observation that some patients with ADHD respond well to one medication but not to the other remains elusive. The dopaminergic effects of MP and AMPH are also thought to underlie their reinforcing properties and ultimately their abuse. Polymorphisms in the human gene that codes for the DA D4 receptor (D4R) have been repeatedly associated with ADHD and may correlate with the therapeutic as well as the reinforcing effects of responses to these psychostimulant medications. Conditioned place preference (CPP) for MP, AMPH and cocaine were evaluated in wild-type (WT) mice and their genetically engineered littermates, congenic on the C57Bl/6J background, that completely lack D4Rs (knockout or KO). In addition, the locomotor activity in these mice during the conditioning phase of CPP was tested in the CPP chambers. D4 receptor KO and WT mice showed CPP and increased locomotor activity in response to each of the three psychostimulants tested. D4R differentially modulates the CPP responses to MP, AMPH and cocaine. While the D4R genotype affected CPP responses to MP (high dose only) and AMPH (low dose only) it had no effects on cocaine. Inasmuch as CPP is considered an indicator of sensitivity to reinforcing responses to drugs these data suggest a significant but limited role of D4Rs in modulating conditioning responses to MP and AMPH. In the locomotor test, D4 receptor KO mice displayed attenuated increases in AMPH-induced locomotor activity whereas responses to cocaine and MP did not differ. These results suggest distinct mechanisms for D4 receptor modulation of the reinforcing (perhaps via attenuating dopaminergic signalling) and locomotor properties of these stimulant drugs. Thus, individuals with D4 receptor polymorphisms might show enhanced reinforcing responses to MP and AMPH and attenuated locomotor response to AMPH.Fil: Thanos, P. K.. NIAAA Intramural Program; Estados Unidos. Brookhaven National Laboratory; Estados Unidos. Universidad de Buenos Aires; ArgentinaFil: Bermeo, C.. Brookhaven National Laboratory; Estados UnidosFil: Rubinstein, Marcelo. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Buenos Aires; ArgentinaFil: Suchland, K. L.. Oregon Health & Science University; Estados UnidosFil: Wang, G. J.. Brookhaven National Laboratory; Estados UnidosFil: Grandy, David K.. Oregon Health & Science University; Estados UnidosFil: Volkow, N. D.. NIAAA Intramural Program; Estados Unido