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1.
Proc Natl Acad Sci U S A ; 119(32): e2204630119, 2022 Aug 09.
Artigo em Inglês | MEDLINE | ID: mdl-35914123

RESUMO

The effect of Lifshitz transition on thermodynamics and superconductivity in hole-doped cuprates has been heavily debated but remains an open question. In particular, an observed peak of electronic specific heat is proposed to originate from fluctuations of a putative quantum critical point p* (e.g., the termination of pseudogap at zero temperature), which is close to but distinguishable from the Lifshitz transition in overdoped La-based cuprates where the Fermi surface transforms from hole-like to electron-like. Here we report an in situ angle-resolved photoemission spectroscopy study of three-dimensional Fermi surfaces in La2-xSrxCuO4 thin films (x = 0.06 to 0.35). With accurate kz dispersion quantification, the said Lifshitz transition is determined to happen within a finite range around x = 0.21. Normal state electronic specific heat, calculated from spectroscopy-derived band parameters, reveals a doping-dependent profile with a maximum at x = 0.21 that agrees with previous thermodynamic microcalorimetry measurements. The account of the specific heat maximum by underlying band structures excludes the need for additionally dominant contribution from the quantum fluctuations at p*. A d-wave superconducting gap smoothly across the Lifshitz transition demonstrates the insensitivity of superconductivity to the dramatic density of states enhancement.

2.
Proc Natl Acad Sci U S A ; 116(27): 13249-13254, 2019 Jul 02.
Artigo em Inglês | MEDLINE | ID: mdl-31160468

RESUMO

The CuO2 antiferromagnetic insulator is transformed by hole-doping into an exotic quantum fluid usually referred to as the pseudogap (PG) phase. Its defining characteristic is a strong suppression of the electronic density-of-states D(E) for energies |E| < [Formula: see text], where [Formula: see text] is the PG energy. Unanticipated broken-symmetry phases have been detected by a wide variety of techniques in the PG regime, most significantly a finite-Q density-wave (DW) state and a Q = 0 nematic (NE) state. Sublattice-phase-resolved imaging of electronic structure allows the doping and energy dependence of these distinct broken-symmetry states to be visualized simultaneously. Using this approach, we show that even though their reported ordering temperatures T DW and T NE are unrelated to each other, both the DW and NE states always exhibit their maximum spectral intensity at the same energy, and using independent measurements that this is the PG energy [Formula: see text] Moreover, no new energy-gap opening coincides with the appearance of the DW state (which should theoretically open an energy gap on the Fermi surface), while the observed PG opening coincides with the appearance of the NE state (which should theoretically be incapable of opening a Fermi-surface gap). We demonstrate how this perplexing phenomenology of thermal transitions and energy-gap opening at the breaking of two highly distinct symmetries may be understood as the natural consequence of a vestigial nematic state within the pseudogap phase of Bi2Sr2CaCu2O8.

3.
Sci Adv ; 3(8): e1700466, 2017 08.
Artigo em Inglês | MEDLINE | ID: mdl-28875162

RESUMO

A major problem in the field of high-transition temperature (Tc) superconductivity is the identification of the electronic instabilities near superconductivity. It is known that the iron-based superconductors exhibit antiferromagnetic order, which competes with the superconductivity. However, in the nonmagnetic state, there are many aspects of the electronic instabilities that remain unclarified, as represented by the orbital instability and several in-plane anisotropic physical properties. We report a new aspect of the electronic state of the optimally doped iron-based superconductors by using high-energy resolution angle-resolved photoemission spectroscopy. We find spectral evidence for the folded electronic structure suggestive of an antiferroic electronic instability, coexisting with the superconductivity in the nonmagnetic state of Ba1-x K x Fe2As2. We further establish a phase diagram showing that the antiferroic electronic structure persists in a large portion of the nonmagnetic phase covering the superconducting dome. These results motivate consideration of a key unknown electronic instability, which is necessary for the achievement of high-Tc superconductivity in the iron-based superconductors.

4.
Proc Natl Acad Sci U S A ; 113(45): 12661-12666, 2016 Nov 08.
Artigo em Inglês | MEDLINE | ID: mdl-27791157

RESUMO

Theories based upon strong real space (r-space) electron-electron interactions have long predicted that unidirectional charge density modulations (CDMs) with four-unit-cell (4a0) periodicity should occur in the hole-doped cuprate Mott insulator (MI). Experimentally, however, increasing the hole density p is reported to cause the conventionally defined wavevector QA of the CDM to evolve continuously as if driven primarily by momentum-space (k-space) effects. Here we introduce phase-resolved electronic structure visualization for determination of the cuprate CDM wavevector. Remarkably, this technique reveals a virtually doping-independent locking of the local CDM wavevector at [Formula: see text] throughout the underdoped phase diagram of the canonical cuprate Bi2Sr2CaCu2O8 These observations have significant fundamental consequences because they are orthogonal to a k-space (Fermi-surface)-based picture of the cuprate CDMs but are consistent with strong-coupling r-space-based theories. Our findings imply that it is the latter that provides the intrinsic organizational principle for the cuprate CDM state.

5.
Eur J Pharmacol ; 766: 25-30, 2015 Nov 05.
Artigo em Inglês | MEDLINE | ID: mdl-26415982

RESUMO

The adenosine A2A receptor antagonist, istradefylline improves motor function in patients with advanced Parkinson's disease (PD) optimally treated with a combination of L-DOPA and a dopamine agonist without increasing the risk of troublesome dyskinesia. However, the effects of istradefylline on motor function when administered in combination with low dose of L-DOPA and dopamine agonists as occurs in early PD are unknown. We investigated whether istradefylline enhances the combined anti-parkinsonian effects of a suboptimal dose of L-DOPA and a threshold dose of either the non-ergot dopamine agonist, ropinirole or the ergot dopamine agonist, pergolide in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated common marmoset. Threshold doses of ropinirole (0.025-0.075 mg/kg p.o.) and pergolide (0.01 mg/kg p.o.) produced a weak anti-parkinsonian effect. Co-administration of a suboptimal dose of L-DOPA (2.5mg/kg p.o.) with threshold doses of the dopamine agonists enhanced their anti-parkinsonian effect that led to increased 'ON' time without dyskinesia appearing. Administering istradefylline (10mg/kg p.o.) with the threshold doses of dopamine agonists and the suboptimal dose of L-DOPA in a triple combination caused a further enhancement of the anti-parkinsonian response but dyskinesia was still absent. In early PD, dopamine agonists are often used as first-line monotherapy, but efficacy is usually lost within a few years, at which time L-DOPA is added but with the risk of dyskinesia appearance. These results show that istradefylline is effective in improving motor function in combination with low dose dopaminergic drug treatment without provoking dyskinesia.


Assuntos
Antagonistas do Receptor A2 de Adenosina/uso terapêutico , Antiparkinsonianos/uso terapêutico , Agonistas de Dopamina/uso terapêutico , Levodopa/uso terapêutico , Intoxicação por MPTP/tratamento farmacológico , Purinas/uso terapêutico , Animais , Comportamento Animal/efeitos dos fármacos , Callithrix , Quimioterapia Combinada , Feminino , Indóis/uso terapêutico , Intoxicação por MPTP/induzido quimicamente , Masculino , Atividade Motora/efeitos dos fármacos , Pergolida/uso terapêutico
6.
Eur J Pharmacol ; 747: 160-5, 2015 Jan 15.
Artigo em Inglês | MEDLINE | ID: mdl-25499739

RESUMO

The adenosine A2A receptor antagonist, istradefylline, enhances anti-parkinsonian activity in patients with advanced Parkinson׳s disease (PD) already treated with combinations of L-DOPA and dopamine agonist drugs but who are still exhibiting prolonged 'OFF' periods. In contrast, the effects of istradefylline on motor function when administered in combination with low dose dopamine agonist therapy in early PD are unknown. We now investigate whether istradefylline administered with a threshold dose of either the non-ergot dopamine agonist, ropinirole or the ergot dopamine agonist, pergolide enhances anti-parkinsonian activity in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated common marmoset. Both ropinirole (0.01-0.1mg/kg p.o.) and pergolide (0.003-0.1mg/kg p.o.) administered alone produced dose dependent increases in locomotor activity, a reduction in motor disability. Threshold doses of ropinirole (0.025-0.075mg/kg p.o.) and pergolide (0.01-0.075mg/kg p.o.) were then selected that in individual animals caused a small but non-significant anti-parkinsonian effect. Administration of istradefylline (10mg/kg p.o.) alone resulted in a decrease in motor disability and increase in 'ON' time but dyskinesia was not observed. Combined administration of pergolide or ropinirole with istradefylline resulted in an increase in the reversal of motor disability and increase in 'ON' time compared to that produced by either treatment alone but dyskinesia was still not observed. These results show that istradefylline is effective in improving motor function when combined with low dose dopamine agonist treatment. In early PD, this may avoid dose escalation or allow a reduction in dopamine agonist dosage without a loss of efficacy and prevent dopaminergic side-effects from becoming treatment limiting.


Assuntos
1-Metil-4-Fenil-1,2,3,6-Tetra-Hidropiridina/efeitos adversos , Antagonistas do Receptor A2 de Adenosina/farmacologia , Antiparkinsonianos/farmacologia , Agonistas de Dopamina/farmacologia , Purinas/farmacologia , Receptor A2A de Adenosina/metabolismo , Animais , Callithrix , Relação Dose-Resposta a Droga , Sinergismo Farmacológico , Feminino , Indóis/farmacologia , Levodopa/farmacologia , Masculino , Atividade Motora/efeitos dos fármacos , Pergolida/farmacologia
7.
Int Rev Neurobiol ; 119: 127-50, 2014.
Artigo em Inglês | MEDLINE | ID: mdl-25175964

RESUMO

Dopamine replacement therapy using the dopamine precursor, l-3,4-dihydroxyphenylalanine (l-DOPA), with a peripheral dopa decarboxylase inhibitor is the most effective treatment currently available for the symptoms of Parkinson's disease (PD). However, the long-term use of dopaminergic therapies for PD is often limited by the development of motor response complications, such as dyskinesia. Adenosine A2A receptors are a promising nondopaminergic target for the treatment of PD. The treatment of motor response complications involves combinations of regular and controlled release L-DOPA, perhaps with the addition of a COMT inhibitor or the use of a longer-acting dopamine agonist. However, when dyskinesia is already established, the increase in dopaminergic load produced by the addition of a dopamine agonist can result in an increase in the severity and duration of dyskinesia. Currently, there are no well-tolerated antidyskinesia agents available. Amantadine, which may exert its effects through the inhibition of N-methyl-D-aspartate (NMDA) receptors, shows some effects on established dyskinesia. Dyskinesia has a negative impact on the quality of life of patients, sometimes being more disabling than PD itself. Although some patients prefer experiencing dyskinesia than being in the OFF state and unable to move, alternative, more effective therapies are still required for severe disabling dyskinesia to afford patients an improved quality of life while in the ON state. The mechanisms causing and maintaining the dyskinesia have not been clarified. The application of a nondopaminergic approach to modify the basal ganglial activity would be helpful to better understand and treat dyskinesia. The use of an adenosine A2A receptor may provide one such approach. In this literature review, we will summarize the current knowledge from both clinical and nonclinical studies on the effects of adenosine A2A receptor blockade on dyskinesia.


Assuntos
Antagonistas do Receptor A2 de Adenosina/uso terapêutico , Discinesias/tratamento farmacológico , Doença de Parkinson/tratamento farmacológico , Antagonistas do Receptor A2 de Adenosina/farmacologia , Animais , Antiparkinsonianos/efeitos adversos , Modelos Animais de Doenças , Discinesias/etiologia , Humanos
8.
Int Rev Neurobiol ; 119: 169-89, 2014.
Artigo em Inglês | MEDLINE | ID: mdl-25175966

RESUMO

Parkinson's disease (PD) is primarily characterized by motor abnormalities, but cognitive changes also occur in the early and late stages of the disease process. In PD patients, cognitive dysfunction is associated with reduced quality of life, as well as increased morbidity and mortality, resulting in increases in caregiver burden, and health-related costs. Therefore, safe and effective approaches are needed to treat cognitive dysfunction in PD patients. The underlying pathophysiology of cognitive dysfunction is complex and not fully understood, however. α-Synuclein, amyloid-related proteins, and cholinergic deficits have been reported to partially contribute to cognitive dysfunction. Changes in cortical dopamine (DA) content may also be responsible for early cognitive changes in patients with PD. Certainly, dopaminergic afferents to the frontal cortex degenerate in PD, and there is a reduction of DA content in the prefrontal cortex (PFC). It has also been reported that PFC dopaminergic input plays an important role in working memory performance. Moreover, PFC DA levels and working memory performance are significantly reduced by a 6-hydroxydopamine lesion in the PFC of a rat. Recent findings in the areas of pharmacological manipulation and genetic ablation suggest that the adenosine A2A receptor is also related to cognitive functions, especially working memory. In addition, the blockade of adenosine A2A receptors reverses cognitive dysfunction in PFC-lesioned rats, and this blocking effect may be due to an increase in PFC DA content. Therefore, adenosine A2A receptor antagonists not only improve motor performance, but they may also lead to improved cognitive function in those with PD.


Assuntos
Antagonistas do Receptor A2 de Adenosina/uso terapêutico , Transtornos Cognitivos/tratamento farmacológico , Transtornos Cognitivos/etiologia , Doença de Parkinson/complicações , Peptídeos beta-Amiloides/metabolismo , Animais , Córtex Cerebral/efeitos dos fármacos , Córtex Cerebral/metabolismo , Humanos , Ratos , alfa-Sinucleína/metabolismo
9.
Proc Natl Acad Sci U S A ; 111(30): E3026-32, 2014 Jul 29.
Artigo em Inglês | MEDLINE | ID: mdl-24989503

RESUMO

The identity of the fundamental broken symmetry (if any) in the underdoped cuprates is unresolved. However, evidence has been accumulating that this state may be an unconventional density wave. Here we carry out site-specific measurements within each CuO2 unit cell, segregating the results into three separate electronic structure images containing only the Cu sites [Cu(r)] and only the x/y axis O sites [Ox(r) and O(y)(r)]. Phase-resolved Fourier analysis reveals directly that the modulations in the O(x)(r) and O(y)(r) sublattice images consistently exhibit a relative phase of π. We confirm this discovery on two highly distinct cuprate compounds, ruling out tunnel matrix-element and materials-specific systematics. These observations demonstrate by direct sublattice phase-resolved visualization that the density wave found in underdoped cuprates consists of modulations of the intraunit-cell states that exhibit a predominantly d-symmetry form factor.

10.
J Pharmacol Sci ; 124(4): 480-5, 2014.
Artigo em Inglês | MEDLINE | ID: mdl-24681641

RESUMO

The adenosine A2A-receptor antagonist istradefylline decreases OFF time in patients with Parkinson's disease who are already treated with optimal doses of dopaminergic medication but can cause an increase in non-troublesome dyskinesia. Preclinical experiments have shown that A2A antagonists are most effective in potentiating motor function when combined with sub-maximal doses of L-DOPA. However, the effects of combining istradefylline with sub-optimal L-DOPA treatment on established dyskinesia have not been studied. We now examine the effects of acute and repeated administration of istradefylline on dyskinesia in MPTP-treated common marmosets previously primed to exhibit involuntary movements by prior exposure to L-DOPA. In these animals, single dose acute oral administration of istradefylline (10 mg/kg) enhanced and prolonged the anti-parkinsonian effects of a sub-optimal dose of L-DOPA (2.5 mg/kg). The chronic co-administration of istradefylline (10 mg/kg) with L-DOPA (2.5 mg/kg) for 21 days did not worsen the severity of existing dyskinesia. Rather, the severity of dyskinesia tended to be reduced over the 21-day treatment period. These results suggest that istradefylline can be used to potentiate the effects of sub-optimal doses of L-DOPA in the treatment of Parkinson's disease without causing or worsening dyskinesia.


Assuntos
Antagonistas do Receptor A2 de Adenosina/farmacologia , Antiparkinsonianos/farmacologia , Discinesias/fisiopatologia , Levodopa/farmacologia , Atividade Motora/efeitos dos fármacos , Transtornos Parkinsonianos/fisiopatologia , Purinas/farmacologia , Administração Oral , Animais , Antiparkinsonianos/administração & dosagem , Callithrix , Sinergismo Farmacológico , Feminino , Levodopa/administração & dosagem , Masculino , Purinas/administração & dosagem
11.
J Am Chem Soc ; 135(8): 3158-63, 2013 Feb 27.
Artigo em Inglês | MEDLINE | ID: mdl-23343190

RESUMO

To unravel the role of doping in iron-based superconductors, we investigated the in-plane resistivity of BaFe(2)As(2) doped at one of the three different lattice sites, Ba(Fe(1-x)Co(x))(2)As(2), BaFe(2)(As(1-x)P(x))(2), and Ba(1-x)K(x)Fe(2)As(2), focusing on the doping effect in the low-temperature antiferromagnetic/orthorhombic (AFO) phase. A major role of doping in the high-temperature paramagnetic/tetragonal (PT) phase is known to change the Fermi surface by supplying charge carriers or exerting chemical pressure. In the AFO phase, we found a clear correlation between the magnitude of the residual resistivity and the resistivity anisotropy. This indicates that the resistivity anisotropy originates from anisotropic impurity scattering due to dopant atoms. The magnitude of the residual resistivity was also found to be a parameter controlling the suppression rate of the AFO ordering temperature. Therefore, the dominant role of doping in the AFO phase is to introduce disorder to the system, distinct from that in the PT phase.

12.
Phys Rev Lett ; 107(17): 176402, 2011 Oct 21.
Artigo em Inglês | MEDLINE | ID: mdl-22107545

RESUMO

We show that the Fermi surface (FS) in the antiferromagnetic phase of BaFe(2)As(2) is composed of one hole and two electron pockets, all of which are three dimensional and closed, in sharp contrast to the FS observed by angle-resolved photoemission spectroscopy. Considerations on the carrier compensation and Sommerfeld coefficient rule out existence of unobserved FS pockets of significant sizes. A standard band structure calculation reasonably accounts for the observed FS, despite the overestimated ordered moment. The mass enhancement, the ratio of the effective mass to the band mass, is 2-3.

13.
Bioorg Med Chem Lett ; 20(12): 3768-71, 2010 Jun 15.
Artigo em Inglês | MEDLINE | ID: mdl-20483600

RESUMO

Based on the previously reported lead compound, a series of benzofuran derivatives were prepared to study their antagonistic activities to A(2A) receptor. The replacement of the phenyl group at the 4-position with a heterocyclic ring improved the PK profile and aqueous solubility. From these studies, we discovered a potent new A(2A) antagonist, 12a, which has both a good oral bioavailability and in vivo efficacy on motor disability in MPTP-treated common marmosets.


Assuntos
Antagonistas do Receptor A2 de Adenosina , Benzofuranos/síntese química , Benzofuranos/farmacologia , Animais , Benzofuranos/química , Disponibilidade Biológica , Callithrix , Transtornos das Habilidades Motoras/tratamento farmacológico , Solubilidade , Relação Estrutura-Atividade
14.
Nature ; 446(7133): E5, 2007 Mar 15.
Artigo em Inglês | MEDLINE | ID: mdl-17361133

RESUMO

The possibility that a pairing boson might act as the 'glue' to bind electrons into a Cooper pair in superconductors with a high critical temperature (T(c)) is being actively pursued in condensed-matter physics. Gweon et al. claim that there is a large and unusual oxygen-isotope effect on the electronic structure, indicating that phonons have a special importance in high-temperature superconductors. However, we are unable to detect this unusual oxygen-isotope effect in new data collected under almost identical material and experimental conditions. Our findings point towards a more conventional influence of phonons in these materials.

15.
Bioorg Med Chem Lett ; 17(6): 1616-21, 2007 Mar 15.
Artigo em Inglês | MEDLINE | ID: mdl-17257841

RESUMO

The synthesis of a series of 4-(6,7-dimethoxy-1,2,3,4-tetrahydroisoquinolin-2-yl)methyl-2-arylbenzofuran and 4-(6,7-dimethoxy-1,2,3,4-tetrahydroisoquinolin-2-yl)methylbenzofuran-2-carboxamide derivatives as novel alpha(2C)-adrenergic receptor antagonists are described. Their affinity at three different human alpha(2)-adrenergic receptors is reported, and some of these compounds exhibited high affinity for the alpha(2C)-adrenergic receptor with high subtype selectivity. Among them, compound 10e has been found to show the anti-L-dopa-induced dyskinetic activity in marmosets. The structure-activity relationship of these compounds is also discussed.


Assuntos
Antagonistas de Receptores Adrenérgicos alfa 2 , Antagonistas Adrenérgicos alfa/síntese química , Antagonistas Adrenérgicos alfa/farmacologia , Benzofuranos/síntese química , Benzofuranos/farmacologia , Isoquinolinas/síntese química , Isoquinolinas/farmacologia , Animais , Callithrix , Dopaminérgicos/farmacologia , Discinesia Induzida por Medicamentos/fisiopatologia , Humanos , Indicadores e Reagentes , Levodopa/antagonistas & inibidores , Levodopa/farmacologia , Receptores Adrenérgicos alfa 2 , Relação Estrutura-Atividade
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