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H Q Lin

Publications and source records attributed to H Q Lin.

10 recordsLinked to original sources
PubMed2004

Intermediate coupling theory of electronic ferroelectricity.

We calculate the quantum phase diagram of an extended Falicov-Kimball model for one- and two-dimensional systems in the intermediate coupling regime. Even though some features of the phase diagram are obtained analytically, the main results are calculated with a constrained path Monte Carlo technique. We find that this regime is dominated by a Bose-Einstein condensation of excitons with a built-in electric polarization. The inclusion of a finite hybridization between the bands removes the condensate but reinforces the ferroelectricity.

Journal Article↗
PubMed2001

Single hole motion in LaMnO3.

We study single hole motion in LaMnO3 using the classical approximation for Jahn-Teller lattice distortions, a modified Lang-Firsov approximation for dynamical breathing-mode phonons, and the self-consistent Born approximation (verified by exact diagonalization) for hole-orbital-excitation scattering. We show that in the realistic parameter space for LaMnO3, quantum effects of electron-phonon interaction are small. The quasiparticle bandwidth is about 2.2J in the purely orbital t-J model. It is strikingly broadened to be of order t by strong static Jahn-Teller lattice distortions even when the polaronic band narrowing is taken into account.

Journal Article↗
PubMed2000

Chiral derivatives of 2-cyclohexylideneperhydro-4,7-methanoindenes, a novel class of nonsteroidal androgen receptor ligand: synthesis, X-ray analysis, and biological activity.

A series of 2-cyclohexylideneperhydro-4,7-methanoindene derivatives was synthesized as novel androgen receptor ligands. Asymmetric hydroboration of key intermediate 2 afforded single enantiomer alcohol derivatives (3aR)-3 and (3aS)-3 which could be further transformed to give 12 variously substituted keto alcohol target compounds. X-ray crystallography of the 4-bromobenzenesulfonyl ester (3aS)-13 was used to establish their absolute configuration. The binding of these compounds to the rat ventral prostate androgen receptor showed moderate affinity with IC(50) values of 1.2 microM and above but with substantial enantiomeric dependencies which varied in accordance to Pfieffer's rule. Surprisingly, the (3aS)-5alpha-alcohols displayed similar affinity to the (3aR)-5beta-alcohols, and molecular modeling suggested an alternative mode of binding for the (3aS) series. The three compounds with the best androgen receptor affinity were assayed in vivo for antiandrogenic and androgenic effects on sex accessory organ growth in castrated immature rats and were found to be ineffective.

Androgen Antagonists↗
PubMed1999

The anxiogenic-like and anxiolytic-like effects of MDMA on mice in the elevated plus-maze: a comparison with amphetamine.

Many abused substances have been found to possess anxiogenic-like or/and anxiolytic-like properties. Discrepancies about the effects of MDMA, one of the most popular recreational drugs in recent years, on anxiety have been seen in the literature, and almost all of the data in this respect were derived from retrospective studies. The present study was thus designed to examine the drug's actions by using an animal model of anxiety, the elevated plus-maze test in male mice. Intraperitoneal MDMA at 1 mg/kg was ineffective, at 4 mg/kg decreased the percent of open arm entries (p < 0.01), and increased enclosed entries (p < 0.05), at 12 mg/kg had no significant effect, and at 20 mg/kg induced an increase of percent of open time (p < 0.01). As control drugs, amphetamine (0.5-4 mg/kg, i.p.) produced a dose-dependent, anxiogenic-like effect and diazepam (1 mg/kg, i.p.) induced an anxiolytic-like effect in the test. The results indicate that MDMA has anxiogenic-like properties at lower doses and anxiolytic-like at higher doses. The effects of MDMA and amphetamine on the mouse's responses to the plus-maze are compared. These findings provide a possible explanation for the controversies over MDMA's effects on anxiety in the literature.

Amphetamine↗
PubMed1998

Propylene glycol elicits anxiolytic-like responses to the elevated plus-maze in male mice.

Propylene glycol is a common solvent often contained in injectable solutions of anxiolytics of low water-solubility, such as diazepam (Valium) and pentobarbital (Nembutal). Several studies have shown that propylene glycol can have an inhibitory effect on the central nervous system. This study, using ethanol for comparison, further examined whether propylene glycol has anti-anxiety properties. Use of the elevated plus-maze test with male mice revealed that propylene glycol at doses (27 or 41 mmol kg-1, i.p.) which did not affect general activity, increased the number of entries into open arms and of head dips over open arm edges, indicative of an anxiolytic effect. In parallel, ethanol (14 and 27 mmol kg-1, i.p.) caused an increase in the amount of time spent on open arms and number of entries into open arms, accompanied by reduction of returns into closed arms. These doses of ethanol had no significant effect on motor ability. The results suggest that propylene glycol can act as an anxiolytic agent and that its anxiolytic potency is weaker than that of ethanol. In addition to previous warnings about the pharmacological effects of propylene glycol, the findings of this study alert investigators to the anxiolytic properties of the compound when it is employed as a solvent in anxiety or anxiety-related studies.

Animals↗
PubMed1997

Serotonergic modulation of 3,4-methylenedioxymethamphetamine (MDMA)-elicited reduction of response rate but not rewarding threshold in accumbal self-stimulation.

In a fixed interval 5-s rate-frequency function paradigm with rats, 3,4-methylenedioxymethamphetamine (MDMA; 0.5, 2 and 4 mg/kg) dose-dependently decreased response rate for nucleus accumbens self-stimulation while both D-amphetamine (0.3 and 1 mg/kg) and cocaine (5 and 15 mg /kg) increased response rates. The highest doses of MDMA caused a cessation of responding in many of the rats tested, but in those rats that continued to respond a significant reduction in frequency threshold for self-stimulation was seen. Cocaine and amphetamine dose-dependently reduced frequency threshold in all rats tested. The non-specific serotonin antagonist, methysergide (5 mg/kg), reversed the inhibitory effects of MDMA on response rates and caused all rats to respond following MDMA (4 mg/kg). Methysergide did not affect MDMA's threshold-lowering properties and when administered alone methysergide had not effect on self-stimulation. These results suggest serotonergic involvement in the performance but not reinforcement-modulating effect of MDMA in the self-stimulation paradigm.

Animals↗
PubMed1994

Contrasting effects of dopaminergic blockade on MDMA and d-amphetamine conditioned taste aversions.

A series of experiments examined the role of dopamine in the conditioned taste aversion (CTA) produced by 3,4-methylenedioxymethamphetamine (MDMA) and d-amphetamine in rats. The CTA induced by MDMA (1.0 mg/kg) was unaffected by the D1 dopamine receptor antagonist SCH23390 (0.3 or 0.6 mg/kg), the D2 receptor antagonist raclopride (0.3 or 0.6 mg/kg), SCH23390 and raclopride combined (both 0.3 or 0.6 mg/kg), or the D1/D2 receptor antagonist haloperidol (0.4 mg/kg). In contrast, the CTA produced by d-amphetamine (0.5 mg/kg) was attenuated by SCH23390 and raclopride combined (both 0.3 mg/kg) as well as haloperidol (0.4 mg/kg), but not by SCH23390 (0.3 or 0.6 mg/kg) or raclopride (0.3 or 0.6 mg/kg) alone. These results suggest that dopamine plays different roles in MDMA and amphetamine CTAs, and that the D1 and D2 receptors independently mediate the aversive effect of amphetamine in CTA.

3,4-Methylenedioxyamphetamine↗
PubMed1993

Comparison of conditioned taste aversions produced by MDMA and d-amphetamine.

Many drugs of abuse such as d-amphetamine support the development of taste aversion in a conditioned taste aversion paradigm. However, it has yet to be established whether methylenedioxymethamphetamine (MDMA), an amphetamine-like stimulant, has this property. A direct comparison was made between MDMA and d-amphetamine over a dose range of 0.125-2.0 mg/kg (SC). Two pairings of either drug with saccharin produced dose-related taste aversions to saccharin that were retained for at least three successive testing trials. The minimally effective dose was 1 mg/kg for MDMA and 0.5 mg/kg for d-amphetamine. The relative potency of MDMA to amphetamine was 4.5, similar to that previously reported for drug discrimination and self-stimulation.

3,4-Methylenedioxyamphetamine↗
PubMed1991

Prefrontal cortex alpha 2 adrenoceptors and energy balance.

The sulcal prefrontal cortex (SPC) influences thermogenesis, energy substrate utilization and feeding behaviour. The present study examined the role of SPC alpha noradrenergic receptors in these effects. Fifty nmol norepinephrine (NE) injected into the SPC produced a large and long-lasting increase in respiratory quotient (RQ), indicating enhanced carbohydrate utilization and fat synthesis. This dose also reduced energy expenditure without corresponding decreases in locomotor activity, suggesting an inhibition of thermogenesis. Neither a lower dose of NE (25 nmol) injected into the SPC, nor injections of NE (50 nmol) into a variety of sites adjacent to the SPC affected energy balance. The alpha 2 agonist clonidine (20 nmol) injected into the SPC produced similar effects to 50 nmol NE, with a large increase in RQ and a decrease in thermogenesis. Forty nmol clonidine, however, decreased RQ and reduced both energy expenditure and activity. The alpha 1 agonist L-phenylephrine (20 and 40 nmol) injected into the SPC had no clear effect on energy balance. Finally, it was shown that clonidine or NE injected into the SPC promotes food intake. These results implicate alpha 2 adrenoceptors in the sulcal prefrontal cortex in the control of food intake, thermogenesis and metabolic substrate utilization.

Animals↗