Terahertz electric-field-driven dynamical multiferroicity in SrTiO3

The emergence of collective order in matter is among the most fundamental and intriguing phenomena in physics. In recent years, the dynamical control and creation of novel ordered states of matter not accessible in thermodynamic equilibrium is receiving much attention1-6. The theoretical concept of dynamical multiferroicity has been introduced to describe the emergence of magnetization due to time-dependent electric polarization in non-ferromagnetic materials7,8. In simple terms, the coherent rotating motion of the ions in a crystal induces a magnetic moment along the axis of rotation. Here we provide experimental evidence of room-temperature magnetization in the archetypal paraelectric perovskite SrTiO3 due to this mechanism. We resonantly drive the infrared-active soft phonon mode with an intense circularly polarized terahertz electric field and detect the time-resolved magneto-optical Kerr effect. A simple model, which includes two coupled nonlinear oscillators whose forces and couplings are derived with ab initio calculations using self-consistent phonon theory at a finite temperature9, reproduces qualitatively our experimental observations. A quantitatively correct magnitude was obtained for the effect by also considering the phonon analogue of the reciprocal of the Einstein-de Haas effect, which is also called the Barnett effect, in which the total angular momentum from the phonon order is transferred to the electronic one. Our findings show a new path for the control of magnetism, for example, for ultrafast magnetic switches, by coherently controlling the lattice vibrations with light.

Inverse-Perovskite Ba3 BO (B = Si and Ge) as a High Performance Environmentally Benign Thermoelectric Material with Low Lattice Thermal Conductivity

High energy-conversion efficiency (ZT) of thermoelectric materials has been achieved in heavy metal chalcogenides, but the use of toxic Pb or Te is an obstacle for wide applications of thermoelectricity. Here, high ZT is demonstrated in toxic-element free Ba3 BO (B = Si and Ge) with inverse-perovskite structure. The negatively charged B ion contributes to hole transport with long carrier life time, and their highly dispersive bands with multiple valley degeneracy realize both high p-type electronic conductivity and high Seebeck coefficient, resulting in high power factor (PF). In addition, extremely low lattice thermal conductivities (κlat ) 1.0-0.4 W m-1  K-1 at T = 300-600 K are observed in Ba3 BO. Highly distorted O-Ba6 octahedral framework with weak ionic bonds between Ba with large mass and O provides low phonon velocities and strong phonon scattering in Ba3 BO. As a consequence of high PF and low κlat , Ba3 SiO (Ba3 GeO) exhibits rather high ZT = 0.16-0.84 (0.35-0.65) at T = 300-623 K (300-523 K). Finally, based on first-principles carrier and phonon transport calculations, maximum ZT is predicted to be 2.14 for Ba3 SiO and 1.21 for Ba3 GeO at T = 600 K by optimizing hole concentration. Present results propose that inverse-perovskites would be a new platform of environmentally-benign high-ZT thermoelectric materials.

Epitaxy and transport properties of alkali-earth palladate thin films

Topological insulators and semimetals are an interesting class of materials for new electronic and optical applications owing to their characteristic electromagnetic responses originating from the spin-orbit coupled band structures. However, topological electronic structures are rare in oxide materials despite their chemical stability being preferable for applications. In this study, given the theoretical prediction of Dirac bands in CaPd3O4, we investigate the fabrication and transport properties of SrPd3O4 and CaPd3O4 thin films as candidates of oxide Dirac semimetals. We have found that these materials are epitaxially grown on MgO (100) substrate under limited growth conditions by pulsed laser deposition. The transport properties show a weak temperature dependence, suggestive of narrow-gap properties, although unintentionally doped holes hinder us from revealing the presence of the Dirac band. Our study establishes the basic thermodynamics of thin-film fabrication of these materials and will lead to interesting properties characteristic of topological band structure by modulating the electronic structure by, for example, chemical substitutions or pressure.

Implementation strategies in phonopy and phono3py

Scientific simulation codes are public property sustained by the community. Modern technology allows anyone to join scientific software projects, from anywhere, remotely via the internet.

The phonopy and phono3py codes are widely used open source phonon calculation codes. This review describes a collection of computational methods and techniques as implemented in these codes and shows their implementation strategies as a whole, aiming to be useful for the community. Some of the techniques presented here are not limited to phonon calculations and may therefore be useful in other areas of condensed matter physics.

First-Principles Phonon Quasiparticle Theory Applied to a Strongly Anharmonic Halide Perovskite

Understanding and predicting lattice dynamics in strongly anharmonic crystals is one of the long-standing challenges in condensed matter physics. Here, we propose a first-principles method that gives accurate quasiparticle (QP) peaks of the phonon spectrum with strong anharmonic broadening. On top of the conventional first-order self-consistent phonon (SC1) dynamical matrix, the proposed method incorporates frequency renormalization effects by the bubble self-energy within the QP approximation. We apply the developed methodology to the strongly anharmonic α-CsPbBr_{3} that displays phonon instability within the harmonic approximation in the whole Brillouin zone. While the SC1 theory significantly underestimates the cubic-to-tetragonal phase transition temperature (T_{c}) by more than 50%, we show that our approach yields T_{c}=404-423  K, in excellent agreement with the experimental value of 403 K. We also demonstrate that an accurate determination of QP peaks is paramount for quantitative prediction and elucidation of the phonon linewidth.

Exciton-Phonon and Trion-Phonon Couplings Revealed by Photoluminescence Spectroscopy of Single CsPbBr3 Perovskite Nanocrystals

Lead halide perovskite nanocrystals (NCs) have outstanding photoluminescence (PL) properties and excellent potential for light-emitting diodes and single-photon sources. Here, we report the multiple-peak structures originating from excitons, trions, and biexcitons in low-temperature PL spectra of single CsPbBr₃ NCs. We found fine-structure splitting in the PL peaks of bright excitons and biexcitons and also in the longitudinal-optical (LO)-phonon replicas of excitons. LO-phonon replicas of trions are clearly observed under strong photoexcitation, which do not show fine-structure splitting. From size-dependent analyses of these replicas, we clarified that both exciton-phonon and trion-phonon couplings become larger for smaller NCs and the coupling strengths of trions are larger than those of excitons in large NCs. These behaviors can be explained by the spatial distributions of the electron and hole wave functions in the NCs. Our findings provide essential information on electron-phonon couplings in perovskites and for the design of high-purity single-photon sources.

LO-mode phonon of KCl and NaCl at 300 K by inelastic x-ray scattering measurements and first principles calculations

Longitudinal-optical (LO) mode phonon branches of KCl and NaCl were measured using inelastic x-ray scattering (IXS) at 300 K and calculated by the first-principles phonon calculation with the stochastic self-consistent harmonic approximation. Spectral shapes of the IXS measurements and calculated spectral functions agreed well. We analyzed the calculated spectral functions that provide higher resolutions of the spectra than the IXS measurements. Due to strong anharmonicity, the spectral functions of these phonon branches have several peaks and the LO modes along Γ-L paths are disconnected.

Degenerated Hole Doping and Ultra-Low Lattice Thermal Conductivity in Polycrystalline SnSe by Nonequilibrium Isovalent Te Substitution

Tin mono-selenide (SnSe) exhibits the world record of thermoelectric conversion efficiency ZT in the single crystal form, but the performance of polycrystalline SnSe is restricted by low electronic conductivity (σ) and high thermal conductivity (κ), compared to those of the single crystal. Here an effective strategy to achieve high σ and low κ simultaneously is reported on p-type polycrystalline SnSe with isovalent Te ion substitution. The nonequilibrium Sn(Se1- x Tex ) solid solution bulks with x up to 0.4 are synthesized by the two-step process composed of high-temperature solid-state reaction and rapid thermal quenching. The Te ion substitution in SnSe realizes high σ due to the 103 -times increase in hole carrier concentration and effectively reduced lattice κ less than one-third at room temperature. The large-size Te ion in Sn(Se1- x Tex ) forms weak SnTe bonds, leading to the high-density formation of hole-donating Sn vacancies and the reduced phonon frequency and enhanced phonon scattering. This result-doping of large-size ions beyond the equilibrium limit-proposes a new idea for carrier doping and controlling thermal properties to enhance the ZT of polycrystalline SnSe.

Descriptors of intrinsic hydrodynamic thermal transport: screening a phonon database in a machine learning approach

Machine learning techniques are used to explore the intrinsic origins of the hydrodynamic thermal transport and to find new materials interesting for science and engineering. The hydrodynamic thermal transport is governed intrinsically by the hydrodynamic scale and the thermal conductivity. The correlations between these intrinsic properties and harmonic and anharmonic properties, and a large number of compositional (290) and structural (1224) descriptors of 131 crystal compound materials are obtained, revealing some of the key descriptors that determines the magnitude of the intrinsic hydrodynamic effects, most of them related with the phonon relaxation times. Then, a trained black-box model is applied to screen more than 5000 materials. The results identify materials with potential technological applications. Understanding the properties correlated to hydrodynamic thermal transport can help to find new thermoelectric materials and on the design of new materials to ease the heat dissipation in electronic devices.

Breaking of Thermopower-Conductivity Trade-Off in LaTiO3 Film around Mott Insulator to Metal Transition

Introducing artificial strain in epitaxial thin films is an effective strategy to alter electronic structures of transition metal oxides (TMOs) and to induce novel phenomena and functionalities not realized in bulk crystals. This study reports a breaking of the conventional trade-off relation in thermopower (S)-conductivity (σ) and demonstrates a 2 orders of magnitude enhancement of power factor (PF) in compressively strained LaTiO3 (LTO) films. By varying substrates and reducing film thickness down to 4 nm, the out-of-plane to the in-plane lattice parameter ratio is controlled from 0.992 (tensile strain) to 1.034 (compressive strain). This tuning induces the electronic structure change from a Mott insulator to a metal and leads to a 103 -fold increase in σ up to 2920 S cm-1 . Concomitantly, the sign of S inverts from positive to negative, and both σ and S increase and break the trade-off relation between them in the n-type region. As a result, the PF (=S2 σ) is significantly enhanced to 300 µW m- 1 K-2 , which is 102 times larger than that of bulk LTO. Present results propose epitaxial strain as a means to finely tune strongly correlated TMOs close to their Mott transition, and thus to harness the hidden large thermoelectric PF.

Large phonon drag thermopower boosted by massive electrons and phonon leaking in LaAlO3/LaNiO3/LaAlO3 heterostructure

An unusually large thermopower (S) enhancement is induced by heterostructuring thin films of the strongly correlated electron oxide LaNiO₃. The phonon-drag effect, which is not observed in bulk LaNiO₃, enhances S for thin films compressively strained by LaAlO₃ substrates. By a reduction in the layer thickness down to three unit cells and subsequent LaAlO₃ surface termination, a 10 times S enhancement over the bulk value is observed due to large phonon drag S (S_g), and the S_g contribution to the total S occurs over a much wider temperature range up to 220 K. The S_g enhancement originates from the coupling of lattice vibration to the d electrons with large effective mass in the compressively strained ultrathin LaNiO₃, and the electron-phonon interaction is largely enhanced by the phonon leakage from the LaAlO₃ substrate and the capping layer. The transition-metal oxide heterostructures emerge as a new playground to manipulate electronic and phononic properties in the quest for high-performance thermoelectrics.

Luminescence Fine Structures in Single Lead Halide Perovskite Nanocrystals: Size Dependence of the Exciton-Phonon Coupling

Lead halide perovskite nanocrystals (NCs) have superior photoluminescence (PL) properties, such as high PL quantum yields and wide PL wavelength tunability, for optoelectronic applications. Here, we report the PL spectra of single formamidinium lead halide perovskite FAPbX₃ (X = Br, I) NCs examined by single-dot spectroscopy at low temperature. We found four PL peaks in the low-energy region below the strong exciton PL peak that originate from two longitudinal-optical (LO) phonon replicas of the exciton PL, biexcitons, and charged excitons (trions). The binding energies of the biexcitons and trions become larger as the NCs decrease in size. The LO phonon energies show no size dependence, but the Huang-Rhys factors, which reflect the strength of the exciton-phonon coupling, become larger for smaller NCs. Our findings provide important insights into the exciton properties of perovskite NCs.

Reversible 3D-2D structural phase transition and giant electronic modulation in nonequilibrium alloy semiconductor, lead-tin-selenide

Material properties depend largely on the dimensionality of the crystal structures and the associated electronic structures. If the crystal-structure dimensionality can be switched reversibly in the same material, then a drastic property change may be controllable. Here, we propose a design route for a direct three-dimensional (3D) to 2D structural phase transition, demonstrating an example in (Pb_1-x Sn _x )Se alloy system, where Pb²⁺ and Sn²⁺ have similar ns² pseudo-closed shell configurations, but the former stabilizes the 3D rock-salt-type structure while the latter a 2D layered structure. However, this system has no direct phase boundary between these crystal structures under thermal equilibrium. We succeeded in inducing the direct 3D-2D structural phase transition in (Pb_1-x Sn _x )Se alloy epitaxial films by using a nonequilibrium growth technique. Reversible giant electronic property change was attained at x ~ 0.5 originating in the abrupt band structure switch from gapless Dirac-like state to semiconducting state.

Anharmonic lattice dynamics and thermal transport of monolayer InSe under equibiaxial tensile strains

Two-dimensional (2D) InSe, which exhibits high electron mobility and a wide band gap has emerged as a promising material for photoelectric and thermoelectric applications. The inadequate understanding of the lattice thermal conductivity (κ), however, hampers the advancement of 2D InSe. Herein, by taking into account anharmonicity up to the fourth order and introducing the equibiaxial tensile strain (ϵ), we have performed an in-depth study on the lattice dynamics of 2D InSe. Interestingly, the κ exhibits a non-monotonic behaviour as a function of equibiaxial tensile strain, which can be attributed to the changes in acoustic phonon lifetimes. At the Γ point, a blue-shift of the lowest optical mode and a red-shift of the uppermost optical mode are reported for the first time. More strikingly, the blue-shift can be largely suppressed by equibiaxial tensile strain. Further study indicates that the unique transition of the potential energy surface is responsible for the disappearance of the blue-shift. Our work may enlighten the future research on phonon engineering and management of the lattice thermal conductivity of 2D InSe.

Anharmonicity Explains Temperature Renormalization Effects of the Band Gap in SrTiO3

Soft phonon modes in strongly anharmonic crystals are often neglected in calculations of phonon-related properties. Herein, we experimentally measure the temperature effects on the band gap of cubic SrTiO₃, and compare with first-principles calculations by accounting for electron-phonon coupling using harmonic and anharmonic phonon modes. The harmonic phonon modes show an increase in the band gap with temperature using either Allen-Heine-Cardona theory or finite-displacement approach, and with semilocal or hybrid exchange-correlation functionals. This finding is in contrast with experimental results that show a decrease in the band gap with temperature. We show that the disagreement can be rectified by using anharmonic phonon modes that modify the contributions not only from the significantly corrected soft modes, but also from the modes that show little correction in frequencies. Our results confirm the importance of soft-phonon modes that are often neglected in the computation of phonon-related properties and particularly in electron-phonon coupling.

Quartic Anharmonicity of Rattlers and Its Effect on Lattice Thermal Conductivity of Clathrates from First Principles

We investigate the role of the quartic anharmonicity in the lattice dynamics and thermal transport of the type-I clathrate Ba_{8}Ga_{16}Ge_{30} based on ab initio self-consistent phonon calculations. We show that the strong quartic anharmonicity of rattling guest atoms causes the hardening of vibrational frequencies of low-lying optical modes and thereby affects calculated lattice thermal conductivities κ_{L} significantly, resulting in an improved agreement with experimental results including the deviation from κ_{L}∝T^{-1} at high temperature. Moreover, our static simulations with various different cell volumes shows a transition from crystal-like to glasslike κ_{L} around 20 K. Our analyses suggest that the resonance dip of κ_{L} observed in clathrates with large guest free spaces is attributed mainly to the strong three-phonon scattering of acoustic modes along with the presence of higher-frequency dispersive optical modes.

Impact of rattlers on thermal conductivity of a thermoelectric clathrate: a first-principles study

We investigate the role of rattling guest atoms on the lattice thermal conductivity of a type-I clathrate Ba_{8}Ga_{16}Ge_{30} by first-principles lattice dynamics. Comparing phonon properties of filled and empty clathrates, we show that rattlers cause tenfold reductions in the relaxation time of phonons by increasing the phonon-phonon scattering probability. Contrary to the resonant scattering scenario, the reduction in the relaxation time occurs in a wide frequency range, which is crucial for explaining the unusually low thermal conductivities of clathrates. We also find that the impact of rattlers on the group velocity of phonons is secondary because the flattening of phonon dispersion occurs only in a limited phase space in the Brillouin zone.

Anharmonic force constants extracted from first-principles molecular dynamics: applications to heat transfer simulations

A systematic method to calculate anharmonic force constants of crystals is presented. The method employs the direct-method approach, where anharmonic force constants are extracted from the trajectory of first-principles molecular dynamics simulations at high temperature. The method is applied to Si where accurate cubic and quartic force constants are obtained. We observe that higher-order correction is crucial to obtain accurate force constants from the trajectory with large atomic displacements. The calculated harmonic and anharmonic force constants are, then, combined with the Boltzmann transport equation (BTE) and non-equilibrium molecular dynamics (NEMD) methods in calculating the thermal conductivity. The BTE approach successfully predicts the lattice thermal conductivity of bulk Si, whereas NEMD shows considerable underestimates. To evaluate the linear extrapolation method employed in NEMD to estimate bulk values, we analyze the size dependence in NEMD based on BTE calculations. We observe strong nonlinearity in the size dependence of NEMD in Si, which can be ascribed to acoustic phonons having long mean-free-paths and carrying considerable heat. Subsequently, we also apply the whole method to a thermoelectric material Mg2Si and demonstrate the reliability of the NEMD method for systems with low thermal conductivities.

Angiotensin (1-7) prevents angiotensin II-induced nociceptive behaviour via inhibition of p38 MAPK phosphorylation mediated through spinal Mas receptors in mice

BACKGROUND

We have recently demonstrated that intrathecal (i.t.) administration of angiotensin II (Ang II) induces nociceptive behaviour in mice accompanied by a phosphorylation of p38 mitogen-activated protein kinase (MAPK) mediated through Ang II type 1 (AT1 ) receptors. The N-terminal fragment of Ang II, Ang (1-7), plays a pivotal role in counterbalancing many of the well-established actions induced by Ang II. However, the role of Ang (1-7) in spinal nociceptive transmission remains unclear. Therefore, we examined whether i.t. administration of Ang (1-7) can inhibit the Ang II-induced nociceptive behaviour in mice.

METHODS

In the behavioural experiments, the accumulated response time of nociceptive behaviour consisting of scratching, biting and licking in conscious mice was determined during a 25-min period starting after i.t. injection. The distribution and localization of AT1 or Mas receptors were analysed using a MapAnalyzer and confocal microscope, respectively. Phosphorylation of p38 MAPK in the dorsal spinal cord was measured by Western blotting.

RESULTS

The nociceptive behaviour induced by Ang II was dose-dependently inhibited by the co-administration of Ang (1-7). The inhibitory effect of Ang (1-7) was reversed by the co-administration of A779, a Mas receptor antagonist. Western blot analysis showed that the increase in spinal p38 MAPK phosphorylation following the i.t. administration of Ang II was also inhibited by Ang (1-7), and the Ang (1-7) induced-inhibition was prevented by A779.

CONCLUSIONS

Our data show that the i.t. administration of Ang (1-7) attenuates an Ang II-induced nociceptive behaviour and is accompanied by the inhibition of p38 MAPK phosphorylation mediated through Mas receptors.

On the brain monoaminergic systems relating to ejaculation. I. Brain dopamine and ejaculation

The effects of psychotropic drugs on ejaculation in dogs and on brain monoamines in dogs and rats were investigated. The results obtained in this study indicate that ejaculation is activated by the dopaminergic system in the brain, and that dopamine in the anterior hypothalamus is closely related to the occurrence of ejaculation.

Enhanced head-twitch response to 5-HT-related agonists in thiamine-deficient mice

While many studies suggest an involvement of brain serotonergic systems in neuro-psychiatric disorders such as schizophrenia and depression, their role in Wernicke-Korsakoff syndrome (WKS) remains unclear. Since dietary thiamine deficiency (TD) in mice is considered as a putative model of WKS, it was used in the present study to investigate the function of serotonergic neurons in this disorder. After 20 days of TD feeding, the intensity of tryptophan hydroxylase immunofluorescence was found to be significantly decreased in the dorsal and medial raphe nuclei. In addition, the head-twitch response (HTR) elicited by the intracerebroventricular administration of the 5-HT(2A) agonist 2,5-dimethoxy-4-iodoamphetamine hydrochloride (DOI) was significantly increased in TD versus control mice, whereas the injection of ketanserin, a 5-HT(2A) receptor antagonist, prevented this enhancement. A single injection of thiamine HCl on the 19th day of TD feeding did not reduce the enhanced DOI-induced HTR. On the other hand, the administration of d-fenfluramine, a 5-HT releaser, did not enhance the HTR in TD mice. Together, our results indicate that TD causes a super-sensitivity of 5-HT(2A) receptors by reducing presynaptic 5-HT synthesis derived from degenerating neurons projecting from the raphe nucleus.

Effects of NMDA receptor-related agonists on learning and memory impairment in olfactory bulbectomized mice

A significant impairment of learning and memory-related behavior was induced in mice on the 7th and 14th days after olfactory bulbectomy (OBX), as measured by a passive avoidance task. The involvement of the N-methyl-D-aspartate (NMDA) receptor ion-channel complex for learning and memory-related behavior impairment was examined by the intracerebroventricular administration of several NMDA receptor-related agonists and in combination with antagonists. The NMDA receptor agonist NMDA (1 ng/mouse) and the polyamine site agonist spermidine (1 micro g/mouse) improved learning and memory-related behavior impairment. In contrast, the glycine agonist D-cycloserine (0.2, 1 and 5 micro g/mouse) had no effect on learning and memory-related behavior impairment. The improved effects by NMDA and spermidine were reversed by the coadministration of D-APV, a competitive NMDA receptor antagonist, MK-801, an NMDA ion-channel blocker and ifenprodil, a polyamine site antagonist, respectively. These results suggest that the degeneration of NMDA receptors and polyamine sites in the NMDA receptor ion-channel complex may be involved in the OBX-induced impairment of learning and memory-related behavior.

Effect of kami-untan-to on the impairment of learning and memory induced by thiamine-deficient feeding in mice

We have recently reported that thiamine deficient (TD) mice show an impairment of learning and memory on the 20th day after start of TD feeding. Interestingly, it has been reported that the kampo medicine, "kami-untan-to" (KUT) may be useful as a potential therapeutic agent in diseases associated with cholinergic deficit such as Alzheimer's disease. In the present study, we investigated the effects of KUT on the impairment of memory-related behavior concomitant with psychoneuronal symptoms after TD feeding in mice. Oral administration of KUT had no effect on the food intake, body weight or locomotor activity in TD mice, but the mortality rate in the KUT-treated TD group was significantly lower compared with that in the non-treated TD group. Daily administration of KUT from the 1st day of TD feeding protected against the impairment of memory-related behavior induced by TD. The intensity of the choline acetyltransferase fluorescence decreased in the field of CA1 and dentate gyrus in the hippocampus in TD mice compared with pair-fed mice as the control group, and KUT treatment inhibited this decrease. These results suggest that the effect of KUT on the impairment of memory-related behavior induced by TD feeding may be closely related to the activation of cholinergic neurons in the hippocampus.

Enhancement of 5-hydroxytryptamine-induced head-twitch response after olfactory bulbectomy

5-Hydroxytryptamine(2A) receptor agonists evoke the head-twitch response in mice. The head-twitch response in olfactory bulbectomized mice elicited by the administration of 5-hydroxytryptamine (40 microgram/mouse, i.c.v.) was increased about threefold as compared with controls on the 14th day after the operation. The injection of ketanserin (1 mg/kg, i.p.), a 5-hydroxytryptamine(2A) receptor antagonist, inhibited this enhancement of 5-hydroxytryptamine-induced head-twitch response after olfactory bulbectomized. On the 14th day, the number of head-twitch response induced by 5-hydroxytryptophan (40, 80 and 160 mg/kg, i.p.), a precursor of 5-hydroxytryptamine, did not differ between olfactory bulbectomized and control mice. Monoamine oxidase-B activity in the forebrain of olfactory bulbectomized mice was higher than that in controls while monoamine oxidase-A activities were unchanged. The 5-hydroxytryptamine uptake into synaptosomes in the forebrain homogenates of olfactory bulbectomized mice was lower than that in controls. These findings indicate that olfactory bulbectomized causes the enhancement of head-twitch response by a supersensitivity of 5-hydroxytryptamine(2A) receptors in cerebral cortex derived from degeneration of neurons projecting from the olfactory bulb.

Pharmacological studies of geissoschizine methyl ether, isolated from Uncaria sinensis Oliv., in the central nervous system

The pharmacological properties of geissoschizine methyl ether, isolated from Uncaria sinensis Oliv., were analyzed in vitro and in vivo using mice central serotonin neurons. In the in vitro experiment, geissoschizine methyl ether inhibited [3H]8-hydroxy-2-(di-n-propylamino)tetralin) ([3H]8-OH-DPAT) (K(i)=0.8 microM), [3H]mesulergine (K(i)=0.9 microM) and [3H]ketanserin (K(i)=1.4 microM), but had less affinity toward [3H]prazosin (K(i) > 10 microM) and [3H]spiperone (K(i) >15 microM) binding to mouse brain membranes. The in vivo studies showed that geissoschizine methyl ether dose-dependently reduced 5-hydroxy-L-tryptophan (I-5-HTP) plus clorgyline-induced head twitch response without inhibiting the I-5-HTP plus clorgyline and 8-OH-DPAT-induced head weaving. On the other hand, geissoschizine methyl ether also decreased the rectal temperature of mice (hypothermic response) in a dose-dependent manner. These results suggest that geissoschizine methyl ether possesses mixed 5-HT(1A) receptor agonist/5-HT(2A/2C) receptor antagonist activities and inhibits the head twitch response by blocking the 5-HT(2A) receptors, and possibly, at least in part, by stimulating the 5-HT(1A) receptors in the central nervous system.

Central serotonergic mechanisms on head twitch response induced by benzodiazepine receptor agonists

Intraperitoneal injection of benzodiazepine receptor agonists (estazolam, zopiclone, triazolam: 0.03-0.24 mmol/kg) induces the head twitch response (HTR). The present study was undertaken to examine the possible participation of the serotonergic system in the mechanism of head twitches induced by benzodiazepine receptor agonists (BZ-RAs). The HTR induced by BZ-RAs was suppressed by pretreatment with ketanserine (1 mg/kg, i.p.), a selective 5-HT(2) receptor antagonist. Pretreatment with fluoxetine (10 mg/kg, i.p.), a 5-HT reuptake inhibitor, and 8-hydroxy-2-(di-n-propylamino)tetralin, a 5-HT(1A) receptor agonist, also suppressed the HTR induced by BZ-RAs. These results suggest that the HTR induced by BZ-RAs may be the result of an activation of postsynaptic 5-HT(2) receptors, probably due to direct action.

Characteristics of depressive behavior induced by feeding thiamine-deficient diet in mice

We produced thiamine-deficient (TD) mice by TD diet treatment. The growth curve of mice on TD feeding was sharply increased until on the 10th day and subsequently the body weight gradually decreased. The mortality rate in mice was about 67% on the 30th day after the start of TD feeding. We performed the forced swimming test on the 10th and 20th day after the start of TD feeding. The duration of immobility in the forced swimming test was increased on the 20th day of TD feeding. Locomotor activity and motor co-ordination between the pair-fed control group and TD group on the 20th day of TD feeding were not significantly changed. Only a single injection of thiamine HCI (50 mg/kg, s.c.) on the 10th day after the start of a TD diet shortened the increased duration of immobility in the forced swimming test on the 20th day after the start of TD feeding. Whereas these reversal effects of thiamine treatment on the 20th day were not found when the treatment was given on the 19th day after the start of a TD diet. On the 20th day after the start of TD feeding, the increased duration of immobility time induced by TD was shortened by chronic administration of the tricyclic antidepressant imipramine (10 mg/kg, i.p.). These results suggested that behavioral changes in the forced swimming test might be involved in the degeneration of serotonergic and noradrenergic neurons.

Antinociceptive effect following dietary-induced thiamine deficiency in mice: involvement of substance P and somatostatin

We produced thiamine deficiency by treating mice with a thiamine deficient (TD) diet, but not with pyrithiamine, a thiamine antagonist. Twenty days after TD feeding, a significant antinociceptive effect was observed in the formalin test. A single injection of thiamine HCl (50 mg/kg, s.c.) on the 19th day after TD feeding (on the late TD stage) failed to reverse the antinociceptive effect, the muricide effect, and impairment of avoidance learning induced by TD feeding, as compared to pair-fed controls. These results indicate the possibility that the TD-induced antinociceptive effect may result from irreversible changes in the spinal and/or brain neurons. To clarify the involvement of substance P (SP) and somatostatin (SST) systems in the spinal cord, we examined the effect of intrathecal (i.t.) injections of these agonists on TD feeding-inducd elevation of pain threshold. I.t. injection of SP and SST elicited a behavioral response consisting of reciprocal hindlimb scratching, biting and/or licking of hindpaws. There was no significant difference in the behavioral response to SP between TD mice and PF mice on the 5th day after feeding. However, on the 10th and 20th day after TD feeding the response to SP was significantly increased compared with PF mice. This phenomenon was also observed with SST on the 20th day after TD feeding. These results indicate the possibility that TD feeding may produce an increased behavioral response to SP and SST through an enhanced sensitivity of neurokinin-1 and SST receptors in the spinal cord. Taken together, the antinociceptive effect following TD feeding may result from a decrease in spinal SP and SST contents.

Distribution of various calcium channel alpha(1) subunits in murine DRG neurons and antinociceptive effect of omega-conotoxin SVIB in mice

Immunohistological study revealed the differential localization of subtypes of voltage-dependent calcium channels in the dorsal root ganglion neurons. Intrathecal injection of omega-conotoxin SVIB, an analogue of omega-conotoxin GVIA, which acts on N-type voltage-dependent calcium channels, significantly shortened the licking time in the late phase of a formalin test.

Antinociceptive action of amlodipine blocking N-type Ca2+ channels at the primary afferent neurons in mice

We investigated the antinociceptive action of amlodipine, a dihydropyridine derivative, which acts on both L- and N-type voltage-dependent Ca2+ channels (VDCCs), in mice. Intrathecal injection of amlodipine (300 nmol/kg) significantly shortened the licking time in the late phase of a formalin test, while no effect was found with another dihydropyridine derivative, nicardipine (300 nmol/kg). Cilnidipine and omega-conotoxin GVIA also showed marked analgesic effects under the same experimental conditions. Transcripts of alpha1A, alpha1B, alpha1E, alpha1F, alpha1H, beta3, and beta4 subunits were detected by polymerase-chain reaction (PCR) in the dorsal root ganglion, suggesting the existence of a variety of voltage-dependent Ca2+ channels. Electrophysiological experiments showed that amlodipine and cilnidipine inhibit N-type currents in the dorsal root ganglion cells. These results suggest that amlodipine, cilnidipine, and omega-conotoxin GVIA exert their antinociceptive actions by blocking N-type Ca2+ channels in the primary nociceptive afferent fibers. Blocking of the Ca2+ channels results in attenuation of synaptic transmission of nociceptive neurons. Furthermore, it is suggested that some N-type Ca2+ channel blockers might have therapeutic potential as analgesics when applied directly into the subarachnoidal space.

Antinociceptive effect produced by intracerebroventricularly administered dynorphin A is potentiated by p-hydroxymercuribenzoate or phosphoramidon in the mouse formalin test

The antinociceptive effects of intracerebroventricularly (i.c.v.) administered dynorphin A, an endogenous agonist for kappa-opioid receptors, in combination with various protease inhibitors were examined using the mouse formalin test in order to clarify the nature of the proteases involved in the degradation of dynorphin A in the mouse brain. When administered i.c.v. 15 min before the injection of 2% formalin solution into the dorsal surface of a hindpaw, 1-4 nmol dynorphin A produced a dose-dependent reduction of the nociceptive behavioral response consisting of licking and biting of the injected paw during both the first (0-5 min) and second (10-30 min) phases. When co-administered with p-hydroxymercuribenzoate (PHMB), a cysteine protease inhibitor, dynorphin A at the subthreshold dose of 0.5 nmol significantly produced an antinociceptive effect during the second phase. This effect was significantly antagonized by nor-binaltorphimine, a selective kappa-opioid receptor antagonist, but not by naltrindole, a selective delta-opioid receptor antagonist. At the same dose of 0.5 nmol, dynorphin A in combination with phosphoramidon, an endopeptidase 24.11 inhibitor, produced a significant antinociceptive effect during both phases. The antinociceptive effect was significantly antagonized by naltrindole, but not by nor-binaltorphimine. Phenylmethanesulfonyl fluoride (PMSF), a serine protease inhibitor, bestatin, a general aminopeptidase inhibitor, and captopril, an angiotensin-converting enzyme inhibitor, were all inactive. The degradation of dynorphin A by mouse brain extracts in vitro was significantly inhibited only by the cysteine protease inhibitors PHMB and N-ethylmaleimide, but not by PMSF, phosphoramidon, bestatin or captopril. The present results indicate that cysteine proteases as well as endopeptidase 24.11 are involved in two steps in the degradation of dynorphin A in the mouse brain, and that phosphoramidon inhibits the degradation of intermediary delta-opioid receptor active fragments enkephalins which are formed from dynorphin A.

Inhibition of Tissue-Bound Semicarbazide-Sensitive Amine Oxidase by Two Haloamines, 2-Bromoethylamine and 3-Bromopropylamine

Various mammalian tissues contain membrane-bound amine oxidase termed semicarbazide-sensitive amine oxidase (SSAO). A variety of compounds has been identified as relatively selective SSAO inhibitors, but those inhibitors currently available also inhibit monoamine oxidase (MAO). In the present study, inhibitory properties of 2-bromoethylamine (2-BEA) and 3-bromopropylamine (3-BPA) toward rat lung-bound SSAO have been studied. Regardless of preincubation, 2-BEA could not appreciably inhibit MAO-A and MAO-B activity, but 3-BPA at relatively high concentrations inhibited only MAO-B activity. 3-BPA was a competitive and reversible SSAO inhibitor with a Ki value of 17 microM regardless of preincubation. In contrast, without preincubation, 2-BEA competitively inhibited SSAO activity with the Ki value of 2.5 microM and after preincubation, the mode of inhibition changed to be noncompetitive, indicating irreversible inhibition after the preincubation. Dialysis experiments with 2-BEA-pretreated homogenate resulted in no recovery of SSAO activity even after overnight dialysis. A decreased rate of SSAO inhibition under N2 atmosphere to that obtained under O2 was produced upon preincubation of enzyme with 2-BEA, suggesting that oxidized intermediate was necessary for its inhibitory activity. Thus, 2-BEA first interacts with SSAO to form a reversible complex with a subsequent reaction, leading this complex to the covalently bound enzyme-inhibitor adduct. The data analyzed by the plot of 1/k' vs 1/2-BEA concentrations intersected on the y-axis indicate that the inhibition by 2-BEA is not mediated by a bimolecular reaction; thus it is not an affinity-labeling agent, but a suicide SSAO inhibitor. 2-BEA may be employed as a useful compound in the studying SSAO.

Exploring the structural basis of neurotoxicity in C(17)-polyacetylenes isolated from water hemlock

Water hemlock, Cicuta virosa, belonging to the Umbelliferae, is well-known as a toxic plant responsible for lethal poisonings in humans as well as animals, causing tonic and clonic convulsions and respiratory paralysis. Cicutoxin (1), being a major violent toxin of the plant, is a chemical in the class of C(17)-polyacetylenes bearing a long pi-bond conjugation system, a terminal hydroxyl, and an allylic hydroxyl in its structure, and a variety of its analogues have been isolated from the plant. In the present study, various derivatives of these toxins were synthesized through acetylation, methylation, and oxidation of cicutoxin (1) and virol A (3) and B (4). 1-Dehydroxyvirol A (28) was prepared through the coupling of (7S)-dodeca-3,5-dien-1-yn-7-ol and 1-iodopentyne under Sonogashira's conditions. A monoacetylenic compound (29) was also prepared through the coupling of (5S)-1-chlorodeca-1,3-dien-5-ol and 1-iodopentyn-5-ol. The structure-activity relationships involved in the acute toxicity of cicutoxin derivatives in mice were investigated, and the length and geometry of pi-bond conjugation and the O-functional groups were found to be important for activity. The potency in inhibition of the specific binding of the noncompetitive GABA antagonist, [(3)H]EBOB, to GABA-gated Cl(-) channels of GABA receptors in rat brain cortex was found to be correlated with acute toxicity, indicating that the ability to bind to these channels plays an important role in the acute toxicity of these compounds.

Pain threshold, learning and formation of brain edema in mice lacking the angiotensin II type 2 receptor

The main biological role of angiotensin II type 2 receptor (AT2) has not been established. We made use of targeted disruption of the mouse AT2 gene to examine the functional role of the AT2 receptor in the central nervous system (CNS). We have previously shown that AT2-deficient mice displayed anxiety-like behavior in comparisons with wild-type mice. In the present study, we analyzed the pain threshold, learning behavior and brain edema formation using the tail-flick test, the tail-pinch test, the passive avoidance task and cold injury, respectively. In the passive avoidance task and cold injury, no differences were found between wild-type mice and AT2-deficient mice. In contrast, the pain threshold was significantly lower in AT2-deficient mice, compared with findings in wild-type mice. The immunohistochemical distribution of beta-endorphin in the brain was analyzed quantitatively in AT2-deficient mice and wild-type mice, using microphotometry. The fluorescence intensity of beta-endorphin in the arcuate nucleus of the medial basal hypothalamus (ARC) was significantly lower in AT2-deficient mice, compared with findings in wild-type mice. We found that the AT2 receptor does not influence learning behavior and brain edema formation. As AT2-deficient mice have increased sensitivity to pain and decreased levels of brain beta-endorphin, AT2 receptors may perhaps mediate regulation of the pain threshold.

Effect of Zena F-III, a liquid nutritive and tonic drug, on the neurochemical changes elicited by physical fatigue in mice

The effects of a liquid nutritive and tonic drug (NTD) on the neurochemical changes elicited by physical fatigue in mice were investigated in terms of the calcium-dependent dopamine synthesizing function of the brain. In this study, Zena F-III (Taisho Pharmaceutical Co., Ltd., Japan), one of the most popular NTDs in Japan, containing 15 crude drug extracts together with taurine, caffeine, and vitamins, and formulated based on the precepts of traditional Chinese medicine, was used. Male mice were forced to walk for 0-6 h at a speed of 3 m/min using a programmed motor-driven wheel cage. The serum and brain calcium levels in the mice were significantly increased following forced walking. The increase in brain calcium level began later and was more gradual than that in the serum calcium level, and reached its maximum value following forced walking for 3 h. The neostriatal dopamine level was also significantly increased, and locomotor activity significantly decreased following forced walking for 3 h. Prior oral administration of F-III (10 ml/kg) attenuated the increases in the serum and brain calcium levels, the increase in the brain dopamine levels, and the decrease in locomotor activity induced by forced walking. Taking into consideration these findings with our previous reports, it is suggested that physical fatigue leads to an increase in dopamine synthesis in the brain through a calcium/calmodulin-dependent system, thereby inducing behavioral changes, and that F-III inhibits this pathway and may alleviate overwork-induced physical fatigue.

The effects of traditional tonics on fatigue in mice differ from those of the antidepressant imipramine: a pharmacological and behavioral study

The present studies were undertaken to investigate the differences between the antidepressant drug, imipramine, and liquid nutritive and tonic drugs (NTDs) that consist of Ginseng radix, Epimedii herba, Holen and an additional eight to twelve crude drugs. After preloading forced swimming, the NTD (applied orally, 0.1 ml/10 g) significantly increased the duration time of swimming and decreased the duration time of immobility, while the administration of imipramine (5, 10 and 20 mg/kg, i.p.) under the same conditions and after the same treatment did not produce these positive effects. After pretreatment with 100 mg/kg tetrabenazine, the NTDs also elicited both the increased locomotor activity and the decreased duration time of immobility. The behavioral effect was similar to treatment with imipramine. The NTDs showed a long lasting effect on swimming behavior in the forced swimming test for 15 min, indicating a prolonged efficacy, not like the short effect of imipramine. The present results indicate that the effect of NTDs on fatigued subjects is different from that of imipramine, probably due to involvement of another factor in addition to the antidepressant effect.

Antinociceptive effect of cilnidipine, a novel N-type calcium channel antagonist

We investigated the antinociceptic effects of cilnidipine, a dihydropyridine derivative which acts on both L- and N-type voltage-dependent calcium channels, in mice. Intrathecally injected cilnidipine showed significant analgesic effect in formalin test. Cilnidipine significantly suppressed N-type currents in dorsal root ganglion (DRG) cells. Our findings apparently support the idea that cilnidipine attenuates synaptic neurotransmission by inhibiting N-type calcium channels in DRG neurons.

Immunohistochemical estimation of brain choline acetyltransferase and somatostatin related to the impairment of avoidance learning induced by thiamine deficiency

We have found that thiamine-deficient (TD) rats show significant impairment of avoidance learning on the 25th day after the start of TD diet, as measured by passive-avoidance task. Administration of physostigmine (0.1 mg/kg, i.p.) from the 14th day after the start of TD diet improved the impairment of avoidance learning to the pair-fed (PF) control level by the 25th day. However, the recovery effect of physostigmine did not occur on the 25th day when the treatment was begun on the 21st day. To ascertain the correlation between the cholinergic neuronal function in rat brain and the avoidance learning impairment induced by TD, the immunohistochemical distribution of brain choline acetyltransferase (ChAT) was determined by fluorescence intensity using two-dimensional microphotometry. The intensity of the ChAT fluorescence started to decrease in the cortex and hippocampus on the 14th day and showed a marked decrease in the cortex, hippocampus and thalamus on the 25th day of TD feeding in comparison with PF controls. The intensity of the somatostatin (SST) fluorescence was unchanged on the 14th day of TD feeding, but on the 25th day, SST was significantly decreased in comparison with PF controls. Furthermore, physostigmine treatment from 14th day after the start of TD diet reversed SST fluorescence intensity to the control level by the 25th day. These results suggest that the impairment of avoidance learning induced by TD may involve not only cholinergic but also somatostatinergic systems.

2-Bromoethylamine, a suicide inhibitor of tissue-bound semicarbazide-sensitive amine oxidase

Various mammalian tissues contain plasma membrane-bound amine oxidase, termed semicarbazide-sensitive amine oxidase (SSAO). In the present study, 2-bromoethylamine has been studied with regard to inhibitory properties towards tissue-bound SSAO in rat lung. Without preincubation, 2-bromoethylamine was a competitive and reversible SSAO inhibitor with a Ki value of 2.5 microM. After preincubation, it time-dependently and non-competitively inhibited SSAO activity, probably by forming the covalently-bound enzyme-inhibitor adduct. The data presented suggest that 2-bromoethylamine may act as a suicide inhibitor of SSAO.

Intrathecally administered spermine produces the scratching, biting and licking behaviour in mice

Intrathecal (i.t.) administration of spermine (0.1-10000 fmol), an endogenous polyamine, produced the behavioural response mainly consisting of biting and/or licking of the hindpaw along with a slight hindlimb scratching directed toward the flank in mice, which peaked at 5-15 min and almost disappeared at 30 min after an injection. The behaviour induced by spermine (10 pmol) was dose-dependently inhibited by intraperitoneal injection of morphine (0.125-0.5 mg/kg). The characteristic behaviour was also inhibited dose-dependently by i.t. co-administration of ifenprodil (62.5-4000 pmol), a competitive antagonist of the polyamine recognition site on N-methyl-D-aspartate (NMDA) receptor ion-channel complex, and D(-)-2-amino-5-phosphonovaleric acid (D-APV) (0.5-2 nmol) and 3-((+/-)-2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid (CPP) (7. 8-500 pmol), the competitive NMDA receptor antagonists, and (5R, 10S)-(+)-5-methyl-10,11-dihydro-5H-dibenzo[a,b]cycloheptene-5, 10-imine hydrogen maleate (MK-801) (0.5-4 nmol), an NMDA ion-channel blocker, but not by 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), a non-NMDA receptor antagonist. Both (2S, 3S)-[cis-2-(diphenylmethyl)-N-[(2-methoxyphenyl)-methyl]-1-azabicy clo [2.2.2]octane-3-amine] (CP-96,345), a non-peptidic neurokinin-1 (NK-1) receptor antagonist, and CP-96,344, its inactive 2R,3R enantiomer, inhibited spermine-induced behavioural response in a dose-dependent manner. However, [Tyr(6), D-Phe(7), D-His(9)]-substance P(6-11) (sendide) and [D-Phe(7), D-His(9)]-substance P(6-11), the selective antagonists for NK-1 receptors, were without affecting spermine-induced behaviour. These results indicate that spermine-induced behaviour is mediated through the polyamine recognition site on NMDA receptor ion-channel complex without the involvement of substance P system in the mouse spinal cord.

Inhibitory effect of intracerebroventricularly-administered [D-Arg(2), beta-Ala(4)]-dermorphin (1-4) on gastrointestinal transit

The inhibitory effect of intracerebroventricularly-administered [D-Arg(2), beta-Ala(4)]-dermorphin (1-4) (TAPA), a highly selective mu(1)-opioid receptor agonist, on mouse gastrointestinal transit was compared with that of morphine and [D-Ala(2), N-methyl-Phe(4), Gly(5)-ol]-enkephalin (DAMGO). When administered intracerebroventricularly 5 min before the oral injection of charcoal meal, TAPA (10-100 pmol), morphine (0.25-4 nmol), and DAMGO (20-80 pmol) dose-dependently inhibited gastrointestinal transit of charcoal. The inhibitory effect of each mu-opioid receptor agonist was completely antagonized by naloxone, a nonselective opioid receptor antagonist. The inhibitory effects of morphine and DAMGO were significantly antagonized by both beta-funaltrexamine, a selective mu-opioid receptor antagonist, and naloxonazine, a selective mu(1)-opioid receptor antagonist. In contrast, the inhibitory effect of TAPA was not affected at all by beta-funaltrexamine, naloxonazine, nor-binaltorphimine (a selective kappa-opioid receptor antagonist), or naltrindole (a selective delta-opioid receptor antagonist). These results suggest that the inhibitory effect of TAPA on gastrointestinal transit may be mediated through an opioid receptor mechanism different from that of morphine and DAMGO.

Immunohistochemical estimation of rat brain somatostatin on avoidance learning impairment induced by thiamine deficiency

In rats, on the 25th day after the start of a thiamine-deficient (TD) diet, impairment of avoidance learning was significantly induced in proportion to the decrease somatostatin (SST) fluorescence intensity in the cortex, amygdala, thalamus, hypothalamus, and hippocampus, including the CA1, CA2, and dentate gyrus (DG). Only a single injection of thiamine HCl (0.5 mg/rat, subcutaneous) on the 14th day after the start of a TD diet improved the amnesia to the level of the pair-fed control and prevented the decrease in the SST level. Whereas these reversal effects of thiamine treatment were not found when the treatment was given on the 21st day after the start of a TD diet. These results indicate that, after a certain degree of thiamine deficiency, TD-induced behavioral effects might be reversible, but some neuronal fibers might be irreversibly damaged, probably due to the reduction of thiamine-dependent enzymes in brain mitochondria. The results also suggest the possibility that SST in the brain may be closely related to the avoidance learning impairment induced by TD.

Changes in beta-endorphin and stress-induced analgesia in mice after exposure to forced walking stress

In this study, we attempted to clarify the correlation between changes in the level of beta-endorphin (beta-EP) in the mouse brain and the stress-induced analgesia (SIA) after exposing animals to forced walking stress. The immunohistochemical distribution of beta-EP after stress was first analyzed quantitatively in mice and then more specifically using a microphotometry system with results showing that the fluorescence intensity of beta-EP in the peri-aqueductal gray matter (PAG) and arcuate nucleus of the medial basal hypothalamus (ARC) was increased 6 h after exposure to forced walking stress. Further, SIA was examined after exposing animals to the forced walking stress and the formalin test. At 6 h after forced walking stress, significant SIA was observed in the second phase (from 10 to 30 min after formalin injection) of the formalin-induced paw licking behavior, but not in the first phase (from 0 to 10 min after formalin injection). This SIA was antagonized by beta-EP-(1-27), an opioid epsilon receptor antagonist. In nonstressed mice, the injection of beta-EP produced a reduction in formalin-induced paw-licking in the second phase. A significant antinociceptive effect by beta-EP was well antagonized by beta-EP-(1-27). Thus, the present results suggest that the increase in beta-EP levels in PAG and/or ARC may be involved in SIA after exposure of mice to the forced walking stress.

Induction of nociceptive responses by intrathecal injection of interleukin-1 in mice

Intrathecal (i.t.) injection (between lumbar vertebrae 5 and 6) into mice of a markedly low dose of IL-1alpha (3x10(-4) fmol or 5.4 fg in 5 microl per mouse) induced behaviors involving scratching, biting, and licking of non-stimulated hindpaws. The IL-1-induced behaviors appeared within 10 min of the injection of IL-1alpha, peaked at 20-40 min, and had disappeared 60 min after the injection. The IL-1-induced behaviors were similar to the nociceptive responses induced in mice by i.t. injection of substance P (SP) or subcutaneous (s.c.) injection of formalin into the footpad. The IL-1-induced behaviors were suppressed by intraperitoneal morphine, indicating that they are nociceptive responses. The nociceptive responses induced by 3x10(-4) (5.4 fg) of IL-1alpha were almost completely suppressed by co-injection of 0.3 fmol (7.2 pg) of an IL-1 receptor antagonist (IL-1ra). An antiserum against substance P, but not an antiserum against somatostatin, suppressed the IL-1-induced nociceptive responses. The nociceptive responses induced by s.c. injection of 2% formalin into the footpad were also inhibited by i.t. injection of 30 pmol (720 ng) of IL-1ra. These results suggest that IL-1 may play a role in hyperalgesia in mice by acting as a factor augmenting pain transmission in the spinal cord at least in part by either directly or indirectly releasing substance P.

Effects of ginkgo biloba extract on impairment of learning induced by cerebral ischemia in mice

The effect of Ginkgo biloba extract (GbE) on cerebral ischemia induced by 10-min bilateral occlusion of the carotid arteries in mice was studied. Severe impairment of memory was apparent when the passive avoidance test was carried out 48 hr after bilaterally induced ischemia. When GbE at doses of 50 and 100 mg/kg was given p.o. 1 hr before the 10-min occlusion, there was a significant improvement in memory. The i.p. injection of ifenprodil (30 mg/kg) also showed improvement on learning tasks. The p.o. administration of flavonoid, a fraction isolated from GbE, showed high step-through latency on scopolamine-induced amnesia. All these findings indicate that GbE is beneficial for clinical use in amnesia accompanied with cerebral vascular disease.

Behavioural characterization and amounts of brain monoamines and their metabolites in mice lacking histamine H1 receptors

Behavioural assessments were made of mutant mice lacking histamine H1 receptors to reveal the function of H1 receptors in the behaviour of mice. Exploratory behaviour of mice in a new environment was examined to discover whether the absence of H1 receptors in mice affects actions relating to their emotions. The H1 receptor-deficient mice showed a significant decrease in ambulation in an open field and on an activity wheel. Cognitive functions and anxiety were examined using passive avoidance response test and the elevated plus-maze test, respectively. The passive avoidance test did not show any change in latency. The elevated plus-maze test revealed that the transfer latency of the mutant mice was significantly prolonged, indicating that H1 receptors are partly associated with the control of anxiety. Aggressive behaviour was examined by a resident-intruder aggression test. When confronted with an intruder, the mutant mice attacked the intruder significantly slower and less frequently than did wild-type mice after a six-month isolation period. A formalin test and a forced swimming test were used to evaluate the nociceptive response and depressive or despairing state, respectively, of both groups. The mutant mice showed a significant decrease of nociceptive response in the late phase without affecting the early phase. There was no significant difference in the forced swimming test between the two groups. The brain content of monoamines and their metabolites was measured in the H1 receptor null and wild-type mice. The turnover rate of 5-hydroxytryptamine defined by the ratio of 5-hydroxyindoleacetic acid and 5-hydroxytryptamine was significantly increased in the cerebral cortex and hippocampus of H1 receptor null mice. These results support the previous pharmacological findings that histamine modulates various neurophysiological functions such as locomotor activity, emotion, memory and learning, nociception and aggressive behaviour through H1 receptors.

Intrathecal administration of p-hydroxymercuribenzoate or phosphoramidon/bestatin-combined induces antinociceptive effects through different opioid mechanisms

The antinociceptive effect of intrathecally (i.t.) administered protease inhibitors was tested against capsaicin (800 ng) injected into the dorsal surface of a hindpaw. Both p-hydroxymercuribenzoate (2-8 nmol), a cysteine protease inhibitor, and phosphoramidon (1-4 nmol), an endopeptidase 24.11 inhibitor in the presence of bestatin (0.25 nmol) an aminopeptidase inhibitor, administered i.t. 60 min prior to the injection of capsaicin produced a dose-dependent reduction of the capsaicin-induced paw licking and biting response. p-Hydroxymercuribenzoate (4 nmol)-induced antinociception was significantly antagonized by nor-binaltorphimine, a selective kappa-opioid receptor antagonist, but not by naltrindole, a selective delta-opioid receptor antagonist. On the other hand, phosphoramidon (4 nmol) /bestatin-induced antinociception was significantly antagonized by naltrindole, but not by nor-binaltorphimine. The results indicate that the antinociceptive effect of p-hydroxymercuribenzoate may be due to the inhibition of a cysteine protease degrading endogenous dynorphins whereas phosphoramidon in the presence of bestatin blocks the degradation of enkephalins.