bluuebunny/crossref_metadata_2025 huggingface dataset:
An ab initio molecular orbital study on the stacking interaction between nucleic acid bases: Dependence on the sequence and relation to the conformation
Authors: Aida Misako , Nagata Chikayoshi
Published: December 2004

The stacking interaction energies between nucleic acid bases in A DNA and B DNA are calculated by means of the ab initio molecular orbital method. The calculated values agree well with the experimental values of stacking enthalpy changes. The stacking interaction energy is shown to be highly sequence dependent, particularly when the sequence includes guanine or cytosine. The possibility is shown that the conformation of a DNA double helix fragment is determined by the constituent stacking interaction. Electrostatic energy is the cause of the sequence dependency of the stacking energy, while charge transfer and dispersion energies contribute to the overall stability.
Scattering of high‐energy electrons and x‐rays from molecules: The 10‐electon series Ne, HF, H2O, NH3, and Ch4
Authors: Kumar Mukesh , Tripathi A. N. , Smith Vedene H.
Published: December 2004

The elastic, inelastic, and total intensities for x‐ray and high‐energy electron scattering from the 10‐electron systems Ne, HF, H2O, NH3, and CH4 have been calculated by using SCF‐MO wave functions obtained with double‐zeta quality bases of Gaussian contractd wave functions. The effect of molecular binding and various other trends and systematics in the intensities have been examined with the help of difference functions computed between the present scattering intensities and those for the indpendent atom model (IAM).
Theoretical study of several Fe(H2o)n2+ clusters at different temperatures
Authors: Gonzáalez‐Lafont A. , Lluch J. M. , Oliva A. , Bertrágn J.
Published: December 2004

Several Fe(H2O)n2+ clusters, with n up to 20, have been studied, both by energy minimization in the pairwise approximation and by Monte Carlo simulation. In the last case the calculations have been carried out at three different temperatures in order to investigate the effect of thermal agitation. The most interesting result which can be deduced from this work is the existence of eight water molecules in the first hydration shell of the iron (II) ion. A microscopic analysis has shown that the minimum energy structure of the Fe(H2O)82+ cluster presents a D4d symmetry. This structure is slightly distorted as far as the temperature is increased. The validity of these theoretical predictions is discussed.
Dynamical and structural aspects of water in potassium ferrocyanide trihydrate
Authors: Savatinova I. , Anachkova E.
Published: December 2004

The present work reviews a systematic spectroscopic investigation of water in the single crystal K4Fe(CN)6 · 3H2O (KFCT) and its isotopic solid solutions. On the basis of precise polarization measurements of Raman spectra and infrared studies, the positions of the OH(OD) oscillators in the ordered crystal state (T < 150 K) are determined. Overtones and combinations of water vibrations in the near infrared region are studied that allow for the evalution of the coupling and anharmonicity constants of the modes. The isotopic dilution technique is used in order to investigate the influence of intra‐ and intermolecular interactions on the OH(OD) vibrations. Information about the distortion of the water molecules, as well as many correlations between spectral parameters of OH(OD) stretchings and structural characteristics of H bonds in KFCT, are derived. As a result, a complete picture of the vibrational dynamics and the structure of the crystallization water in KFCT is obtained.
Dynamic perturbation theory of energy transfer in nonrigid molecular systems: Vibrational predissociation of I2he van der waals molecule
Authors: Tachibana Akitomo , Nagaoka Masataka , Yamabe Tokio
Published: December 2004

The appearance of the maximum linewidth by the vibrational predissociation of I2He van der Waals (vdW) molecule as a function of the initial vibrational quantum number of I2 is predicted by the dynamic perturbation theory. The kinetic energy perturbation is introduced in addition to perturbation potential. The linewidth agrees quite well with experiment.
Theory of half‐collision cross sections
Authors: Girardeau M. D.
Published: December 2004

Standard Lippmann–Schwinger theory does not apply to decay of metastable or unstable states due to failure of the adiabatic hypothesis. In the Fock–Tani representation, discrete unstable states can be described by state vectors orthogonal to the asymptotic states representing their decay fragments, and a decay/formation interaction is exhibited explicitly as a portion of the total interaction Hamiltonian. This allows a straightforward derivation of a generalized Lippmann–Schwinger “half‐collision” differential decay cross section without the need of projection operators. It reduces in first order to the product of a resonance line shape by a Golden Rule matrix element squared. In the general case the line shape is non‐Lorentzian and the matrix element factor contains final‐state interaction contributions. The exact expression is expected to be applicable to a variety of processes such as predissociation, autoionization, and Auger effect. The derivation employs the van Hove resolvent formalism to exhibit the dependence of the cross section on the complex self energy of the decaying state.
The electronic structure of 4H‐pyran‐4‐one and its sulfur analogues
Authors: Friedman Paul , Allen Leland C.
Published: December 2004

The electronic structure of 4‐H‐pyran‐4‐one and its sulfur analogues were studied using ab initio wave‐functions. Bond lengths and overlap populations suggest low aromaticity for this group of compounds. Examination of Jorgensen plots of the lowest π orbitals of I‐‐IV leads to the aromaticity order 4H‐thiopyran‐4‐thione (IV) > 4H‐thiopyran‐4‐one (II) > 4H‐pyran‐4‐thione (III) > 4H‐pyran‐4‐one (I). The effects of including d orbitals were studied using the 3‐21G, 3‐21G* (6d), and 3‐21G* (5d) basis sets. Optimized bond lengths, vibrational frequencies, ionization energies, and dipole moments were also obtained, and results for different basis sets were compared.
The theoretical approach to surface chemistry and heterogeneous catalysis
Authors: Simonetta Massimo
Published: December 2004

Transition metals are the most interesting items among heavy atoms due to their extensive use in catalysis. Present understanding of heterogeneous catalytic reactions is still very poor, and new experimental and theoretical techniques have been developed in recent years with the aim of elucidating the mechanism of adsorption and reaction of simple molecules over metal surfaces or clusters. Empirical, semiempirical, and ab initio methods of calculations are briefly reviewed: results and perspectives are presented.
Calculated electronic spectra of model ferric cytochrome P450 complexes
Authors: Waleh Ahmad , Collins Jack R. , Loew Gilda H. , Zerner M. C.
Published: December 2004

Restricted open‐shell ground state properties and electronic spectra of two closely related low‐spin, ferric, 6‐coordinate, model cytochrome P450 complexes, one with a methyl mercaptide and the other a mercaptan as the second axial ligands, have been calculated with a newly modified, semiempirical INDO‐SCF‐CI method. The sensitivity of the calculated spectra to protonation of the sixth axial ligand, and the ability of the method to predict characteristic spectral features for the complexes investigated, are determined. Assignment of transitions, including xy‐ and z‐polarized transitions, are made and compared with experimental observations where available. In particular, the origin of the anomalous split Soret spectrum observed in low‐spin ferric complexes with mercaptide but not a mercaptan is investigated. Finally, a two part hypothesis is presented which provides a general explanation for the origin of both the observed split Soret and the red‐shifted normal Soret in various ferrous and ferric P450 complexes in terms of the ground state orbital characters and simple symmetry considerations.
The proton affinity and the structure of protonated species of methylsilane
Authors: Kohda‐Sudoh S. , Katagiri S.
Published: December 2004

An ab initio LCAO‐MO‐SCF calculation was made on the proton affinity (PA) of methylsilane (CH3SiH3) by using STO‐3G, MIDI‐1, and MIDI‐1* basis sets. Three types of protonated methylsilane are taken into account, and their geometrical parameters are optimized. The calculated PA of CH3SiH3 is 160.5 kcal/mol, which exceeds that of SiH4 by 11.5 kcal/mol. The protonated species (I) which refers to Si—C bond protonation is shown to be most favorable, and to be a weak σ‐complex between CH4 and SiH. Other two species are also σ‐complexes between H2 molecule and SiH3CH or CH3SiH, and similar to CH, SiH, GeH, and C2H.
Molecular theory and cooperative mechanism of shock waves‐induced detonations in energetic molecular crystals
Authors: Odiot S. , Peyrard M. , Schnur J. , Oran E.
Published: December 2004

At a microscopic level, two molecular models, respectively one‐ and two‐dimensional, for describing the shock‐induced detonationmechanism of an energetic crystal have been previously successively presented (after initiation).

We put together, here, their characteristic features, and we discuss their respective contributions inorder to define the molecular and crystalline conditions that a crystal fulfills to sustain a shock induced wave detonation. The two‐dimensional model which allows longitunal but also transversal atomic motions, has enabled us to elicit the crystalline structure in relation with the existence of a wave detonation propagation in the crystal or not. By comparison to detonation experiments the coherence of the models is performed. It may thus be possible to form an idea as to why a molecular compound can detonate through a shock wave.
A DFT study of the ground state of the N3 radical
Authors: Słupski Romauld B. , Wasilewski Jan
Published: December 2004

The X2 Πg ground state of the N3 radical has been studied by means of the DFT approach with inclusion of nonlocal (gradient) terms. Many different Gaussian basis sets of increasing quality, from small split‐shell type up to the TZPP class, have been used. For each of the basis sets, the experimentally known linear symmetric conformation has been optimized using the analytical gradient technique and the vibrational fundamentals have been calculated in the harmonic approximation using the numerical Hessian. For comparison, the standard UHF‐type calculations have also been performed. Despite the fact that the Kohn‐Sham equations have been resolved in the spin‐ and symmetryunrestricted manner, the nonlocal version of DFT is able to describe correctly the geometric properties and vibrational spectrum of this open‐shell degenerate state, provided that a good quality polarized basis set is used. © 1995 John Wiley & Sons, Inc.
Self consistent reaction field theory of solvent effects in the framework of Gaussian density functional method
Authors: Mineva Tzonka , Russo Nino , Toscano Marirosa
Published: December 2004

Electrostatic and dispersion contributions of solute‐solvent interactions have been considered in the self‐consistent reaction field scheme and implemented in the LCGTO‐DF (linear combination of Gaussian‐type orbitals‐density functional) method. Results for the tautomeric equilibrium of formamide‐formamidic acid, for the cis‐trans energy difference in dichlorodiammineplatinum(II), and for H2OHF hydrogen‐bond systems are in agreement with the available experimental and previous high‐level ab initio data. The role of the dispersion energy is discussed for the different studied systems. © 1995 John Wiley & Sons, Inc.
Time‐dependent quantum fluid dynamics of the photoionization of the He atom under an intense laser field
Authors: Dey Bijoy Kr. , Deb B. M.
Published: December 2004

A time‐dependent (TD), nonperturbative quantum fluid density functional equation of motion, developed in our laboratory, is numerically solved for studying the photoionization dynamics of the He atom under an intense, ultrasharp, ultrashort laser pulse. The generalized nonlinear Schrödinger equation is obtained through a hydrodynamical continuity equation and an Euler‐type equation of motion. It yields the electron density, effective potential surface, and other density‐based quantities from start to finish. Starting from the ground‐state Hartree–Fock density for He at t = 0, various singlet and triplet states of singly and doubly excited (autoionizing) He as well as several states of He+ have been identified in the time‐evolved electron density, by a Fourier transformation of the time variable of the complex autocorrelation function. Computer visualizations of the TD difference density and difference potential show distinctly nonlinear and extremely interesting geometrical features of the oscillating atom. Detailed mechanistic routes for multiphoton, sequential, and above‐threshold ionization have been obtained, each route involving many states. The present, comprehensive method reveals the important physical features of the atom–laser interaction and the calculated results are consistent with current experimental and theoretical results. This emphasizes the validity of the hydrodynamical approach for studying TD quantum mechanical phenomena. © 1995 John Wiley & Sons, Inc.
A density functional study of chemical reactions
Authors: Andzelm Jan , Baker Jon , Scheiner Andrew , Wrinn Michael
Published: December 2004

Density functional theory (DFT) was used to study reactions involving small molecules. Relative energies of isomers and transition structures of diazene, formaldehyde, and methylenimine were determined using various DFT functionals and results were compared with MP2 and MP4 calculations. DFT reaction barriers were found to be consistently lower. For some reactions, such as OH + H2→ H2O + H, gradient‐corrected functionals predict very low or nonexistent barriers. The hybrid Hartree–Fock–DFT adiabatic connection method (ACM) often provides much better results in such cases. The performance of several density functionals, including ACM, was tested in calculations on over 100 atomization, hydrogenation, bond dissociation, and isodesmic reactions. The ACM functional provides consistently better geometries and reaction energetics than does any other functional studied. In cases where both HF and gradient‐corrected DFT methods underestimate bond distances, the ACM geometries may be inferior to those predicted by gradient‐corrected DFT methods. © 1995 John Wiley & Sons, Inc.
Maximum‐entropy analysis of atomic compton profiles
Authors: Angulo J. C. , Yáñez R. J. , Antolín J. , Zarzo A.
Published: December 2004

The maximum‐entropy formalism is used to obtain approximations to the atomic Compton profile, 𝚥(q), in terms of the first few radial expectation values 〈Pn〉 of the momentum density γ(p). This method leads to the least‐biased results by the information not used. In particular, analytical and numerical approximations to the kinetic energy T and to the height of the peak 𝚥(O) and the half‐width q0.5 of the Compton profile are obtained. Our results generalize and improve some approximations to 𝚥(q) previously obtained by other authors. For illustration, the accuracy of these approximations are studied by means of near‐Hartree–Fock wave functions. © 1995 John Wiley & Sons, Inc.
Antiferromagnetic ordering in a two‐dimensional electron liquid
Authors: Schweng Herwig K. , Böhm Helga M.
Published: December 2004

The possibility of an antiferromagnetic phase in a two‐dimensional electron gas is investigated within the density functional formalism of phase transitions. © 1995 John Wiley & Sons, Inc.
Direct calculations of charge densities of solids: Applications to the alkali‐earth sulfides
Authors: Cortona P. , Monteleone A. Villafiorita , Becker P.
Published: December 2004

We performed ab initio self‐consistent calculations for the five alkali–earth sulfides—BeS, MgS, CaS, SrS, and BaS—by a method which allows the direct calculation of the ground‐state electron density without a preliminar determination of the wave functions and of the energy eigenvalues of the system. We report the results for the standard cohesive properties (equilibrium lattice parameters, dissociation energies, bulk moduli), a study of the relative stability of the 131 (NaCl), B2 (CsCl), and B3 (ZnS) phases, and of the behavior under pressure of these compounds (equation of state; pressure and change of volume associated to the structural phase transition B1 → B2 or B3 → B1). © 1995 John Wiley & Sons, Inc.
Density functional theory of the collective electronic excitations in NanKn clusters
Authors: Bol A. , Alonso J. A. , López J. M.
Published: December 2004

The collective electronic response of NanKn clusters has been studied for some model structures. In their low‐temperature lowest‐energy structure, those clusters have all the K atoms on the surface. The collective oscillation frequencies for clusters with the K atoms segregated to the surface are red‐shifted with respect to the corresponding frequencies for isomers with a very similar underlying skeleton but with the Na atoms segregated to the surface. The collective frequency varies smoothly with respect to the degree of relative segregation. These results may be useful in the analysis of the collective response of large alloy clusters and microcrystals. © 1995 John Wiley & Sons, Inc.
Beam brightness modulation (BBM) method as applied to Auger electron spectroscopy
Authors: Mogami A.
Published: December 2004

The principle of the beam brightness modulation (BBM) method, as well as such advanced characteristics as high speed response, wide dynamic range of primary beam currents, selective signal detection, and signal‐to‐noise superiority in N(E) spectra, are reported by comparing with both the conventional analyzer energy modulation and the pulse counting methods. Some device‐related technologies for the BBM method are also described as well as advantages of Auger electron spectroscopy (AES) using N(E) spectra obtained by the BBM method.
AES and HRTEM study of an a‐SiNx: H/W/WSix/a‐SiNx: H multilayer structure realized by PEVCD
Authors: Monteil C. , Durand J. , Berjoan R. , Cros B. , Martinez J. P.
Published: December 2004

A multilayer insulator–metal–insulator capacitive structure was realized by plasma‐enhanced chemical vapour deposition for a discharge frequency of 35 kHz. The chosen materials were amorphous hydrogenated silicon nitride as the insulator and tungsten as the metal. An interlayer of tungsten silicide used as an adhesion layer is deposited between W and a‐SiNx:H. An AES depth profiling study coupled with high‐resolution transmission electron microscopy observation showed the presence of interphases: the interfacial zone between a‐SiNx:H and W is constituted by a WNx interphase ∼10 nm deep. Small crystallites are observed in tungsten‐based materials. The presence of a mixed phase containing tungsten, silicon, nitrogen and a small amount of oxygen is obvious and noticed on the AES spectra at the WSix/a‐SiNx:H interface: its thickness appears to be ∼7 nm.
Numerical methods for quantification of Auger sputter depth profiles from oxide films on stainless steels
Authors: Olsson Claes‐Olof A.
Published: December 2004

Accurate quantification of Auger sputter depth profiles from oxide films on stainless steels is complicated by two spectral overlaps: O/Cr and Cl/Mo. The chlorine/molybdenum overlap is readily resolved using target factor analysis or any other related method, assuming that there is no molybdenum on the surface. The O/Cr overlap is more difficult to resolve, because the oxide films on stainless steels usually contain large amounts of chromium. It is shown that by using a Cr base spectrum acquired from a sputter‐cleaned surface and an oxide spectrum acquired from Mo oxide, it is possible to resolve the O/Cr overlap for passive films as well as annealing oxides. This gives less noise and higher accuracy, because the operator‐dependent definition of a background at the higher binding energy side of the Cr 529 eV peak is avoided.
New technique for the simultaneous correction of topographical and backscattering artefacts in electron‐excited Auger spectroscopy and microscopy
Authors: Crone M. , Barkshire I. R. , Prutton M.
Published: December 2004

In order to relate an Auger signal to the atomic concentration in the surface of a solid, it is well known that corrections have to be made for matrix effects. Also, corrections may be needed to compensate for the effects of artefacts caused by properties of the sample other than the concentration of different elements. Large artefacts can be caused by the surface topography and subsurface composition variations often present in ‘real’ samples. This paper reports a new correction scheme that enables the quantitative analysis of samples with a structure for which no prior knowledge exists. The scheme uses the ratio of the Auger peak height to a background count rate above the energy of all significant Auger features, combined with a linear correction invoving the atomic number of the substrate and the Auger backscattering factor. Inhomogeneous samples with angle of incidence variations from 0° to 45° and an arbitrary atomic number can be analysed with an accuracy of ∼5 at.% using this method. Limitations exist for thin unsupported films.
Formation of barium carbide during AES depth profiling of thin BaF2 films
Authors: Kashin G. N. , Makhnjuk V. I.
Published: December 2004

Investigations of barium fluoride thin films by AES were performed. During AES depth profiling we observed the transformation of surface carbon from graphite to carbide form. The role of ion and electron bombardment in such a transformation has been investigated. We suggest that under Ar+ bombardment the surface barium carbide is formed due to recoil implantation of surface carbon atoms into the barium fluoride film and subsequent chemical reaction with barium.
Electrophysiological responses of serotoninergic dorsal raphe neurons to 5‐HT1A and 5‐HT1B agonists
Authors: Sprouse Jeffrey S. , Aghajanian George K.
Published: December 2004

A direct comparison was made of the effects of serotonin 5‐HT1A and 5‐HT1B selective compounds on the spontaneous firing rate of dorsal raphe serotoninergic neurons in chloral‐hydrate‐anesthetized rats. Following intravenous administration, the 5‐HT1A selective compounds ipsapirone (TVX Q 7821) and LY 165163 potently inhibited single‐unit activity in a dose‐dependent manner whereas the 5‐HT1B selective compounds, m‐chlorophenylpiperazine (mCPP) and trifluoromethylphenylpiperazine (TFMPP), displayed only weak or irregular actions. Low microiontophoretic currents of ipsapirone and LY 165163 were also effective in suppressing spontaneous firing; dose‐response relationships for the 5‐HT1A compounds were indistinguishable from that of 5‐HT itself. In contrast, dorsal raphe neurons were only weakly responsive to microiontophoretic application of mCPP and TFMPP; dose‐response relationships for the 5‐HT1B compounds were significantly displaced from that of 5‐HT. In intracellular studies, ipsapirone and LY 165163, when added to the media bathing brain slices, mimicked the actions of 5‐HT in hyperpolarizing dorsal raphe cell membranes and decreasing input resistance; however, the maximal effects of the 5‐HT1A compounds on these membrane properties exceeded those of 5‐HT. In summary, dorsal raphe 5‐HT neurons appear highly responsive to 5‐HT1A, but not to 5‐HT1B compounds; these findings are discussed with regard to the 5‐HT receptor subtypes as candidates for the somatodendritic autoreceptor of dorsal raphe neurons.
Development of presynaptic specializations induced by basic polypeptide‐coated latex beads in spinal cord cultures
Authors: Peng H. Benjamin , Markey Donald R. , Muhlach William L. , Pollack Emanuel D.
Published: December 2004

The development of the neuromuscular synapse in initiated by an interaction between the motoneuron processes and the skeletal muscle. Previously we showed that basic polypeptide‐coated latex beads can mimic the nerve in effecting a postsynaptic differentiation (Peng, H.B. and Cheng, P. ‐ C.: J. Neurosci., 2:1760–1774, 1982). In this study, we examined whether these beads can also induce a presynaptic differentiation along the nerve processes. Explant cultures were prepared from the spinal cords of Xenopus larvae and polyornithine‐coated latex beads (0.45–4.5 μm in diameter) were applied. After 1–2 days, the cultures were processed for light and electron microscopy. For light microscopy, the cells were permeabilized and labeled with a monoclonal antibody against a 65‐KD antigen on synaptic vesicles. Indirect immunofluorescence revealed that this antigen was concentrated at 60% of the bead‐neurite contacts, therefore suggesting the clustering of synaptic versicles at these sites. This phenomenon was not observed at the contacts between neurites and negatively charged (polycarboxylate) beads. However, a concentration of this antigen was also observed at the varicosities along the neurites cultured on polylysine substrate. Thin‐section electron microscopy showed the following features: (1) The neurites formed terminal‐like varicosities on the bead. (2) Within these varicosities, clusters of 50–60‐nm clear vesicles were prominent at the bead‐neurite contact. (3) Large (80–100 nm) dense‐cored vesicles were also present in the varicosity, but they did not form clusters. (4) Basement membrane did not form at the bead‐neurite interface, in contrast to its appearance at the bead‐muscle contact from our previous study. (5) Coated pits were occasionally observed at the contact area. Thus, our results show that the beads can induce a differentiation characteristic of the presynaptic nerve terminal along the spinal cord neurites.
Calmodulin stimulates the degradation of brain spectrin by calpain
Authors: Seubert P. , Baudry M. , Dudek S. , Lynch G.
Published: December 2004

Brain spectrin has been shown to be a preferential substrate of calciumdependent proteases (Baudry, Bundman, Smith, and Lynch: Science 212:937–938, 1981) and a major calmodulin‐binding protein (Kakiuchi, Sobue, and Fujita: FEBS Lett. 132:144–148, 1981). Since calmodulin, spectrin, and a proteolytically derived spectrin fragment are all components of isolated postsynaptic density preparations (Grab, Berzins, Cohen, and Siekevitz: J. Biol. Chem. 254:8690–8696, 1979; Carlin, Bartelt, and Siekevitz: J. Cell Biol. 96:443–448, 1983), we investigated the functional role of calmodulin binding to brain spectrin with respect to its susceptibility to digestion by proteases. We report that calmodulin's interaction with brain spectrin results in a marked acceleration of the rate of spectrin degradation by calcium‐dependent proteases (calpains I and II), but not by chymotrypsin. The cleavage of erythrocyte spectrin (which lacks a high‐affinity calmodulin binding site) by calpain I is unaffected by the presence of calmodulin. The stimulatory effect of calmodulin is blocked by trifluoperazine, a calmodulin antagonist, which by itself does not modify brain spectrin proteolysis by calcium‐dependent proteases. These results suggest a novel role for calmodulin in neuronal function—namely, a synergistic interaction with calcium‐dependent proteases in the regulation of cytoskeletal integrity.
Localization of neuropeptide Y messenger ribonucleic acid in rat and mouse brian by in situ hybridization
Authors: Gehlert D. R. , Chronwall B. M. , Schafer M. P. , O'Donohue T. L.
Published: December 2004

The distribution of neuropeptide Y (NPY) messenger ribonucleic acid (mRNA) in the rat and mouse brain has been examined. A 28‐mer oligonucleotide probe complementary to a distinctive region of NPY mRNA was 3′‐end labeled with [35S]‐deoxycytosine triphosphate ([35S]‐dCTP) by using terminal transferase and was hybridized to fixed sections of rat and mouse brain. The hybridization of the labeled probe to the mRNA in the tissue section was then detected autoradiographically. A strong hybridization signal was seen corresponding to the arcuate nucleus of the hypothalamus. Scattered NPY‐mRNA‐containing cell bodies were seen throughout the cerebral cortex. Experiments which compared the distribution of NPY mRNA with immunohistochemically detected NPY indicated a similar distribution in the arcuate nucleus of the hypothalamus and cerebral cortex. These results indicate that active transcription of the NPY gene occurs within the brain and this transcription takes place in NPY‐containing cell bodies.
An endogenous ligand for the sigma opioid binding site
Authors: Contreras Patricia C. , Dimaggio Debora A. , O'Donohue Thomas L.
Published: December 2004

It had been suggested that phencyclidine (PCP) and sigma opioids exert their similar psychotomimetic effects through a common receptor. Recently, however, there have been several reports demonstratin significant differences between the binding of PCP and SKF 10,047, a sigma opioid agonist, which suggests that there may be distinct PCP and sigma opioid receptors. If these differences in binding represent different receptors, then there may be different endogenous ligands for each receptor. Using porcine brains, which have already been used to isolate and purify an endogenous ligand for the PCP receptor, another factor has been isolated that inhibited the binding of [3H]‐(+)SKF 10,047 and not the binding of [3H]‐PCP. This factor appears to be a peptide or protein because incubation of the active fraction with pronase, a nonspecific peptidase, eliminated the ability of the procine fractions to inhibit the binding of [3H]‐(+)SKF 10,047. These findings suggest the existence of an endogenous ligand for sigma opioid receptors, which is different from the previously identified endogenous ligand for PCP receptors.
A critical level of protein synthesis is required for long‐term potentiation
Authors: Deadwyler Sam A. , Dunwiddie Tom , Lynch Gary
Published: December 2004

Long‐term potentiation (LTP) of the hippocampal population spike in area CA1 was studied in the hippocampal slice before, during, and after inhibition of protein synthesis. LTP was tested 15 and 30 min following addition of the protein synthesis inhibitor cycloheximide (CXM) to the bathing medium. Stimulation‐induced LTP of the population spike was reduced in slices incubated in CXM for 15 min and completely blocked if incubated for 30 min. Measures of protein synthesis inhibition under the same conditions showed 79% at 15 min and 85% after 30 min. Tests of the effects of repeated LTP treatments at these same time points in the absence of CXM and evaluation of the time course of recovery of LTP from CXM blockade were also conducted. The results confirm previous observations and indicate that a critical amount of protein synthesis inhibition is required to completely block LTP in the hippocampal slice.
Differential effects of selective lesions of cholinergic and dopamingergic neurons on serotonin‐type 1 receptors in rat brain
Authors: Quirion Réami , Richard Jean
Published: December 2004

Serotonin (5‐HT)‐type1 (abbreviated as a subscript 1) receptor binding sites are discretely distributed in rat brain. High densities of [3H]5‐HT1 binding sites are especially located in areas enriched with cholinergic and dopaminergic innervation, such as the substantia innominata/ventral pallidum, striatum, septal nuclei, hippocampus and substantia nigra. The possible association of [3H]5‐HT1 binding sites with cholinergic or dopminergic cell bodies and/or nerve fiber terminals was investigated by selective lesions of the substantia innominata/ventral pallidum‐cortical and septohippocampal cholinergic pathways and the nigrostriatal dopaminergic projection. [3H]5‐HT1 receptor binding sites are possibly located on cholinergic cell bodies in the ventral pallidum‐cortical pathway since [3H]5‐HT1 binding in the substantia innominata/ventral pallidal area was markedly decreased following kainic acid lesions. Fimbriaectomies markedly decreased [3H]5‐HT1 binding in the hippocampus, suggesting the presence of 5‐HT1 binding sites on cholinergic nerve fiber terminals in the septohippocampal pathway. Lesions of the nigrostriatal dopaminergic projection did not modify [3H]5‐HT1 binding in the substantia nigra and the striatum, suggesting that 5‐HT1 receptors are not closely associated with dopaminergic cell bodies and nerve terminals in this pathway. These results demonstrate differential association between 5‐HT1 receptors and cholinergic and dopaminergic innervation in rat brain.
Epinephrine and norepinephrine modulate neuronal responses to excitatory amino acids and agonists in frog spinal cord
Authors: Wohlberg C. J. , Hackman J. C. , Davidoff R. A.
Published: December 2004

The interaction of catecholamines epinephrine (E) and norepinephrine (NE) (1.0–100 μM) and excitatory amino acids on motoneurons of the isolated superfused frog spinal cord was investigated by sucrose gap recordings from ventral roots. Exposure of the cord to E or NE 30 sec prior to application of L‐aspartate or L‐glutamate reduced the motoneuron depolarizations produced by the amino acids. The reduction of responses to the mixed receptor agonists L‐glutamate and L‐aspartate may be the result of opposite actions of the catecholamines on the activation of specific excitatory receptors by the amino acids. Thus, E and NE facilitated depolarizations caused by application of N‐methyl‐D‐aspartate (NMDA) and depressed those produced by quisqualate. The effect on NMDA responses appeared to ne β‐adrenoceptor mediated because it was mimicked by the β‐agonist isoprotereno and blocked by propranolol. The effect on quisqualate depolarizations appeared to require activation of α2‐adrenoceptors; it was mimicked by the α2‐agonists clonidine and α‐methylnorepinephrine and antagonized by yohimbine and piperoxan. These results are important in understanding the actions of catecholamines on reflex transmission in spinal pathways which use excitatory amino acids as transmitters.
Short‐term lithium treatment enhances responsiveness of postsynaptic 5‐HT1A receptors without altering 5‐HT autoreceptor sensitivity: An electrophysiological study in the rat brain
Authors: Blier Pierre , De Montigny Claude , Tardif Danielle
Published: December 2004

Short‐term lithium administration to rats has previously been shown to enhance 5‐HT neurotransmission through a modification of 5‐HT neuron properties. In the first part of the present study, the effect of lithium on the function of terminal 5‐HT autoreceptors was assessed by comparing in controls and lithium‐treated rats the differential effect of two frequencies of stimulation (0.8 and 5 Hz) and that of methiothepin, a terminal 5‐HT autoreceptor antagonist, on the effectiveness of the electrical activation of the ascending 5‐HT pathway in suppressing dorsal hippocampus pyramidal neuron firing activity. Both procedures produced similar effects in controls and lithium‐treated rats. In the second part of the study, the function of somatodendritic 5‐HT autoreceptors was studied. The effect of intravenous LSD, an agonist of the somatodendritic 5‐HT autoreceptor, on the firing activity of 5‐HT neurons was not modified by the lithium treatment, whereas that of intravenous 8‐OH‐DPAT, a 5‐HT1A receptor agonist, was increased two‐fold. However, lithium did not alter the responsiveness of 5‐HT neurons to direct microiontophoretic applications of 8‐OH‐DPAT as well as of LSD and 5‐HT. It is concluded that short‐term lithium treatment does not alter the function of terminal and somatodendritic 5‐HT autoreceptors and that it enhances the sensitivity of subset of postsynaptic 5‐HT1A receptors involved in controlling 5‐HT neuron firing activity, presumably through a feedback loop.
Noradrenergic denervation prevents sensitization of rat forebrain neurons to serotonin by tricyclic antidepressant treatment
Authors: Gravel Pauline , De Montigny Claude
Published: December 2004

The effect of prior lesioning of noradrenergic neurons with 6‐hydroxydopamine (6‐OHDA) on the ability of amitriptyline to enhance the responsiveness of hippocampal pyramidal neurons to serotonin (5‐HT) was examined in Sprague‐Dawley rats. In control rats, amitriptyline (5 mg/kg/day for 14 days), administered either by daily injection or by an osmotic minipump, enhanced the responsiveness of these neurons to microionto‐phoretically applied 5‐HT, leaving their responsiveness to norepinephrine (NE) and to acetylcholine unaltered. However, in 6‐OHDA‐pretreated rats, amitriptyline failed to enhance the responsiveness of hippocampal pyramidal neurons to 5‐HT. The effect of NE and, to a lesser extent, that of 5‐HT were prolonged in 6‐OHDA‐pretreated rats, presumably because NE and 5‐HT released by microiontophoresis are taken up by NE terminals in the intact rat. The present results provide additional evidence that the integrity of the NE system is required for antidepressant treatments to modify 5‐HT neurotransmission.
Characterization and autoradiographic distribution of hemicholinium‐3 high‐affinity choline uptake sites in mammalian brain
Authors: Quirion Rémi
Published: December 2004

[3H]hemicholinium‐3 (HC‐3) binding characteristics have been investigated using membrane binding assays and in vitro receptor autoradiography. In rat brain membrane preparations, [3H]HC‐3 binds with high affinity to an apparent single class of sites. [3H]HC‐3 selectivity labels the high affinity choline uptake (HACU) in brain membranes (HC‐3 > choline > carbamylcholine > acetylcholine). This hypothesis is also supported by quantitative autoradiographic data which demonstrate that the discrete distribution of [3H]HC‐3 binding sites correlates very well with the known distribution of other cholinergic markers such as choline acetyltransferase (ChAT), acetylcholinesterase (AChE), HACU, and [3H]AH‐5183 (blocker of the vesicular transport of acetylcholine). For example, high densities of labelling are observed for these different markers in the interpeduncular nucleus, anteroventral nucleus of the thalamus, striatum, basolateral nucleus of the amygdala, and an exquisite laminar distribution in the hippocampus. Similar autoradiographic distributions of [3H]HC‐3 binding sites are observed in other mammalian species such as guinea pig and monkey. Finally, 7‐day unilateral kainic acid lesions of the nucleus basalis magnocellularis (nbm) decrease cortical [3H]HC‐3 binding and ChAT activity, although not to a similar extent. In summary, these results demonstrate that [3H]HC‐3 is a selective ligand of the HACU in mammalian brain. Thus, it is now possible to characterize precisely various structural components of the cholinergic synapses using markers such as [3H]HC‐3, ChAT, HACU, [3H]AH‐5183, and selective muscarinic and nicotinic receptor radioligands.
Changes in synaptic morphology associated with presynaptic and postsynaptic activity: An in vitro study of the electrosensory organ of the thornback ray
Authors: Fields R. Douglas , Ellisman Mark H. , Waxman Stephen G.
Published: December 2004

The influence of synaptic activity on synaptic structure was studied by selectively stimulating the presynaptic or postsynaptic membranes of ribbon synapses in an in vitro preparation, and examining the ultrastructure of synapses with conventional electron microscopic methods. Functionally significant changes in synaptic morphology were observed after direct depolarization of the presynaptic membrane or incubation with the neurotransmitter glutamate to depolarize the postsynaptic membrane. After depolarizing the presynaptic membrane for 30 seconds, the depth of the postsynaptic trough was reduced, and other morphological changes correlated with decreased sensitivity and spontaneous activity were evident. Depolarizing the postsynaptic membrane by incubating synapses with the neurotransmitter glutamate, produced opposite effects. These results suggest that synapses can undergo functionally significant morphological changes in response to certain patterns of activity. The mechanism for these changes might include synaptic vesicle recycling processes, changes in ion concentration, or cytoskeletal alterations in the presynaptic, postsynaptic, or support cells. These mechanisms could operate in association with long‐term changes in synaptic efficacy or account for some physiological phenomena such as synaptic fatigue or accommodation.
Review: D1 dopamine receptor—the search for a function: A critical evaluation of the D1/D2 dopamine receptor classification and its functional implications
Authors: Clark David , White Francis J.
Published: December 2004

The present review focuses on the hypothesized D1/D2 dopamine (DA) receptor classification, originally based on the form of receptor coupling to adenylate cyclase activity. The pharmacological effects of compounds exhibiting putative selective agonist or antagonist profiles at those DA receptors positively coupled to adenylate cyclase activity (D1 DA receptors) are extensively reviewed. Comparisons are made with the effects of putative selective D2 DA receptor agonists and antagonists, and on the basis of this work, the DA receptor classification is critically evaluated. A variety of biochemical, behavioral, and electrophysiological evidence is presented which supports the view that D1 and D2 DA receptors can interact in both an opposing and synergistic fashion. Particular attention is focused on the possibility that D1 receptor stimulation is required to enable the expression of certain D2 receptor‐mediated effects, and the functional consequences of this form of interaction are considered. A hypothetical model is presented which considers how both the opposing and enabling forms of interaction between D1 and D2 DA receptos can control behavioral expression. Finally, the clinical relevance of this work is discussed and the potential use of selective D1 receptor agonists and antagonists in the treatment of psychotic states and Parkinson's disease is considered.
Actions of serotonin recorded intracellularly in rat dorsal lateral septal neurons
Authors: Joëls M. , Gallagher J. P.
Published: December 2004

The actions of serotonin (5HT) on passive and active membrane properties of neurons in the rat dorsal lateral septal nucleus (LSN) were studied by using intracellular recordings in transverse, septal slices. Superfusion with 10 μm 5HT induced a hyperpolarization of the membrane in almost all neurons tested in the dorsolateral part of the LSN. The hyperpolarization was accompanied by a decrease in membrane resistance. These effects of 5HT persisted in a low‐Ca2+/high‐Mg2+‐containing medium or medium with tetrodotoxin, indicating a post‐synaptic site of action for 5HT. The reversal potential for the hyperpolarizing effect was ca. ‐95 mV. If the extracellular K+‐concentration was raised, the reversal potential became less negative. These data suggest that 5HT hyperpolarizes LSN neurons by increasing a K+‐conductance.

Spontaneous, synaptically evoked action potentials and action potentials induced in LSN neurons by a depolarizing current step typically display a fast Na+‐spike with a subsequent K+‐afterhyperpolarization, followed by a much slower Ca2+‐dependent afterdepolarization. The amplitude of the K+‐afterhyperpolarization was decreased by 5HT, while at the same time the afterdepolarization became more pronounced. The Ca2+‐spike of LSN neurons was not affected by 5HT.

Synaptic responses that were evoked in LSN neurons by stimulation of the dorsal part of the LSN consisted of a fast EPSP or spike, followed by a Cl−−‐dependent fast IPSP and a K+‐dependent late IPSP. Of these synaptic responses, 5HT suppressed particularly the late IPSP. The present data indicate that 5HT affects the conductance for active and passive K+‐channels in LSN neurons. While the increased conductance for passive K+‐channels directly hyperpolarizes and inhibits LSN neurons, the 5HT‐evoked changes in the shape of the action potential and IPSPs could facilitate transmission of excitatory signals in the LSN.
Serial reconstructions of granule cell spines in the mammalian olfactory bulb
Authors: Woolf Thomas B. , Shepherd Gordon M. , Greer Charles A.
Published: December 2004

The Morphology of olfactory bulb granule cell spines and their dendrodendritic synaptic relations with mitral and tufted cell dendrites were examined using serial electron micrographs and 3D computer reconstructions. Most granule cell spines were pedunculated with large elliptical heads necks (stems) longer than those described for exclusively postsynaptic spines elsewhere in the nerous system. The spines typically contained a mitochondrion, which most likely reflects the metabolic requirements of the presynaptic functions of these spines. In several cases multiple spine heads were observed connected to the parent dendritic trunk via a common neck. In addition, dendritic varicosities making synaptic connections were noted. In the data set sampled, all of the reconstructions supported the hypothesis of divergence of granule cell conectivity: in no instance was granule cell found to contact repeatedly the same mitral or tufted cell dendrite. Examination of the toplogical organization of reciprocal dendrodendritic synaptic connections with mitral/tufted cell dendrites revealed paralled rows of spine heads on mitral/tufted secondary dendrites separted by intervening zones of several microns in which no synaptic appositions were found. The results provide evidence regarding rules of connectivity underlying the function of local circuits in mediating lateral inhibition in the external plexiform layer of the olfactory bulb.
MK‐801 inhibition of nicotinic acetylcholine receptor channels
Authors: Amador Mariano , Dani John A.
Published: December 2004

MK‐801 is a potent inhibitor of the NMDA subtype of glutamate receptors. Single‐channel and macroscopic current indicate that MK‐801 also inhibits nicotinic acetylcholine receptors (nAChRs). MK‐801 does not significantly increase desensitization of the nAChR, the main action of MK‐801 is to enter and block the open channel. The voltage dependence for block is consistent with a single binding site within the channel that is 50% of the way through the membrane field. The IC50 for block is 3 μM at‐70 mV for currents induced by 0.5 μ;M ACh. The data from both single‐channel and macroscopic currents can be used to estimate a Kd (0) of 7 μM, which is about 40 times higher than the Kd(0) for MK‐801 binding to the NMDA receptor. The relative potency of tricyclic compounds like MK‐801 for various neurotransmitter systems points out that the pharmacologic action of these drugs could involve complicated interactions in vivo.
Synaptic plasticity at crayfish neuromuscular junctions: Presynaptic inhibition
Authors: Baxter Douglas A. , Bittner George D.
Published: December 2004

Intracellular recordings at sites electrotnically near terminals of the opener excitor axon in the claw of crayfish (Procambarus simulans) show that stimulation of the inhibitor neuron produces hyperpolarizing or depolarzing presynaptic inhibitory potentials (PIPs). GABA applied anywhere along the length of the opener excitor or inhibitor axons also produces hyperpolarizing or depolarizing potentials. The amplitude of action potentials (APs) at recording sites near some excitor terminals is reduced by an average of 6 mV during presynaptic inhibition, which also reduces excitatory postsynaptic Potentials (EPSPs) by 50–70%. The time course of AP reduction equals the time course of EPSP reduction and the amount of AP reduction is independent of the sign or amplitude of the PIPs. All these data are consistent with a hypothesis that a conductance increase produced by GABA in these presynaptic terminals of the excitor axon is responsible for presynaptic inhibition. However, the effect of presynaptic inhibition upon the accumulation of short‐term facilitation of excitatory transmitter release is not the same in all muscle fibers. In some terminals, the accumulation of Short‐term facilitation during shourt, high‐frequency trains of ction potentials which are presynaptically inhibited often equals the accumulation of facilitation without inhibition. In other terminals, short‐term facilitation accumulated during presynaptic inhibition often does not equal facilitation accumulated in the absence of presynaptic inhibition. These data suggest that some other factor which may contribute to presynaptic inhibition, such as a direct effect to decrease calcium currents, may also affect short‐term facilitation in some terminals.