Optical probe of carrier doping by X-ray irradiation in organic dimer Mott insulator κ\kappa-(BEDT-TTF)2_{2}Cu[N(CN)2]_{2}]Cl

We investigated the infrared optical spectra of an organic dimer Mott insulator $\kappa$-(BEDT-TTF)$_{2}$Cu[N(CN)$_{2}$]Cl, which was irradiated with X-rays. We observed that the irradiation caused a large spectral weight transfer from the mid-infrared region, where interband transitions in the dimer and Mott-Hubbard bands take place, to a Drude part in a low-energy region; this caused the Mott gap to collapse. The increase of the Drude part indicates a carrier doping into the Mott insulator due to irradiation defects. The strong redistribution of the spectral weight demonstrates that the organic Mott insulator is very close to the phase border of the bandwidth-controlled Mott transition.Comment: 4 pages, 4 figure

Role of dopamine D1 and D2 receptors in the nucleus accumbens in mediating reward

The objectives of this study were to examine the involvement of D1 and D2 receptors within the nucleus accumbens (ACB) in mediating reinforcement. The intracranial self-administration (ICSA) of D1 and D2 agonists was used to determine whether activating D1 and/or D2 receptors within the ACB of Wistar rats is reinforcing. At concentrations of 0.25, 0.50, and 1.0 mM (25, 50, and 100 pmol/100 nl of infusion), neither the D1 agonist R(+)-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine-7,8-diol [SKF 38393 (SKF)] hydrochloride nor the D2 agonist (-)-quinpirole (Quin) hydrochloride was self-administered into the shell region of the ACB. On the other hand, equimolar mixtures of SKF and Quin (SKF+Quin), at concentrations of 0.25, 0.50, and 1.0 mM each, were significantly self-infused into the ACB shell. The core region of the ACB did not support the ICSA of SKF+Quin at any of these concentrations. Rats increased lever pressing when the response requirement was increased from a fixed ratio 1 (FR1) to FR3, and they responded significantly more on the infusion lever than they did on the control lever. Coadministration of either 0.50 mM R(+)-7-chloro-8-hydroxy-3-methyl-1-phenyl-2,3,4, 5-tetrahydro-1H-3-benzazepine (SCH 23390) hydrochloride, a D1 antagonist, or 0.50 mM S(-)-sulpiride, a D2 antagonist, completely abolished the ICSA of the mixture of SKF+Quin (each at 0.50 mM) into the ACB shell. The present results suggest that concurrent activation of D1- and D2-type receptors in the shell of the ACB had a cooperative effect on DA-mediated reward processes

Amphetamine Administration into the Ventral Striatum Facilitates Behavioral Interaction with Unconditioned Visual Signals in Rats

Administration of psychomotor stimulants like amphetamine facilitates behavior in the presence of incentive distal stimuli, which have acquired the motivational properties of primary rewards through associative learning. This facilitation appears to be mediated by the mesolimbic dopamine system, which may also be involved in facilitating behavior in the presence of distal stimuli that have not been previously paired with primary rewards. However, it is unclear whether psychomotor stimulants facilitate behavioral interaction with unconditioned distal stimuli.We found that noncontingent administration of amphetamine into subregions of the rat ventral striatum, particularly in the vicinity of the medial olfactory tubercle, facilitates lever pressing followed by visual signals that had not been paired with primary rewards. Noncontingent administration of amphetamine failed to facilitate lever pressing when it was followed by either tones or delayed presentation or absence of visual signals, suggesting that visual signals are key for enhanced behavioral interaction. Systemic administration of amphetamine markedly increased locomotor activity, but did not necessarily increase lever pressing rewarded by visual signals, suggesting that lever pressing is not a byproduct of heightened locomotor activity. Lever pressing facilitated by amphetamine was reduced by co-administration of the dopamine receptor antagonists SCH 23390 (D1 selective) or sulpiride (D2 selective).Our results suggest that amphetamine administration into the ventral striatum, particularly in the vicinity of the medial olfactory tubercle, activates dopaminergic mechanisms that strongly enhance behavioral interaction with unconditioned visual stimuli

Using a runway paradigm to assess the relative strength of rats' motivations for enrichment objects

Laboratory animals should be provided with enrichment objects in their cages; however, it is first necessary to test whether the proposed enrichment objects provide benefits that increase the animals’ welfare. The two main paradigms currently used to assess proposed enrichment objects are the choice test, which is limited to determining relative frequency of choice, and consumer demand studies, which can indicate the strength of a preference but are complex to design. Here, we propose a third methodology: a runway paradigm, which can be used to assess the strength of an animal’s motivation for enrichment objects, is simpler to use than consumer demand studies, and is faster to complete than typical choice tests. Time spent with objects in a standard choice test was used to rank several enrichment objects in order to compare with the ranking found in our runway paradigm. The rats ran significantly more times, ran faster, and interacted longer with objects with which they had previously spent the most time. It was concluded that this simple methodology is suitable for measuring rats’ motivation to reach enrichment objects. This can be used to assess the preference for different types of enrichment objects or to measure reward system processes

DNA binding of dinuclear iron(II) metallosupramolecular cylinders. DNA unwinding and sequence preference

[Fe2L3]4+ (L = C25H20N4) is a synthetic tetracationic supramolecular cylinder (with a triple helical architecture) that targets the major groove of DNA and can bind to DNA Y-shaped junctions. To explore the DNA-binding mode of [Fe2L3]4+, we examine herein the interactions of pure enantiomers of this cylinder with DNA by biochemical and molecular biology methods. The results have revealed that, in addition to the previously reported bending of DNA, the enantiomers extensively unwind DNA, with the M enantiomer being the more efficient at unwinding, and exhibit preferential binding to regular alternating purine–pyrimidine sequences, with the M enantiomer showing a greater preference. Also, interestingly, the DNA binding of bulky cylinders [Fe2(L-CF3)3]4+ and [Fe2(L-Ph)3]4+ results in no DNA unwinding and also no sequence preference of their DNA binding was observed. The observation of sequence-preference in the binding of these supramolecular cylinders suggests that a concept based on the use of metallosupramolecular cylinders might result in molecular designs that recognize the genetic code in a sequence-dependent manner with a potential ability to affect the processing of the genetic code

Imaging phase separation near the Mott boundary in the correlated organic superconductors κ\kappa-(BEDT-TTF)2_{2}X

Electronic phase separation consisting of the metallic and insulating domains with 50 -- 100 $\mu$m in diameter is found in the organic Mott system $\kappa$-[($h$8-BEDT-TTF)$_{1-x}$($d$8-BEDT-TTF)$_{x}$]$_{2}$Cu[N(CN)$_{2}$]Br by means of scanning micro-region infrared spectroscopy using the synchrotron radiation. The phase separation appears below the critical end temperature 35 -- 40 K of the first order Mott transition. The observation of the macroscopic size of the domains indicates a different class of the intrinsic electronic inhomogeneity from the nano-scale one reported in the inorganic Mott systems such as High-$T_{c}$ copper and manganese oxides.Comment: 4 pages, 3 figure

Electronic properties of alkali-metal loaded zeolites -- a "supercrystal" Mott insulator

First-principles band calculations are performed for the first time for an open-structured zeolite (LTA) with guest atoms (potassium) introduced in their cages. A surprisingly simple band structure emerges, which indicates that this system may be regarded as a "supercrystal", where each cluster of guest atoms with diameter $\sim$10\AA acts as a "superatom" with well-defined $s$- and $p$-like orbitals, which in turn form the bands around the Fermi energy. The calculated Coulomb and exchange energies for these states turn out to be in the strongly-correlated regime. With the dynamical mean-field theory we show the system should be on the Mott-insulator side, and, on a magnetic phase diagram for degenerate-orbital systems, around the ferromagnetic regime, in accord with experimental results. We envisage this class of systems can provide a new avenue for materials design.Comment: 4 pages, 4 figure