bluuebunny/crossref_metadata_2025 huggingface dataset:
Biuret and its sulfur analogs: Structures and energies
Authors: LeszczyńSki Jerzy , Sullivan Richard H.
Published: January 2005

The calculations for biuret (B) and its two sulfur analogs, thiobiuret (TB) and dithiobiuret (DTB), were carried out using the ab initio LCAO–MO method at the Hartree–Fock level. The molecular structure of B was fully optimized using standard 3‐21G and 6‐31G* basis sets, while geometry optimizations of the TB's and DTB's were performed at the 3‐21G* and 6‐31G* levels. Only trans‐isomers were found to be minimum structures on the HF/3‐21G* potential‐energy surfaces, whereas cis‐forms are the first‐order transition structures. The relative energies of the cis‐conformers at MP 2/6‐31G**//HF/6‐31G* + 0.9 zero point energy (ZPE) level are equal to 47.4, 51.7, and 59.7 kJ mol−1 for TB, B, and DTB, respectively. Because of relatively large dipole moments, cis‐conformers are predicted to be stabilized in polar solvents.
Comparison of MNDO to tight‐binding, total‐energy methods for surface atomic structure determination: Aluminum phosphide (110)
Authors: Godin T. J. , LaFemina John P.
Published: January 2005

Tight‐binding, total‐energy (TBTE) models have been successfully used to calculate the equilibrium surface atomic structures of a variety of materials, but are difficult to apply to substances with complicated interatomic repulsions. In these cases, the modified neglect of diatomic overlap (MNDO) method, which specifically includes longer‐range interactions, may provide an effective alternative. We present new calculations of the surface atomic structure of the AlP (110) surface using both techniques. This surface, whose structure has been determined quantitatively using a low‐energy, electron‐diffraction intensity analysis, displays a well‐known relaxation characteristic of (110) surfaces of zincblende‐structure semiconductors. The TBTE model, parameterized to bulk AlP properties, provides a more accurate prediction of the relaxed surface atomic positions, although MNDO, parameterized to small molecules, produces acceptable results. Despite the greater demands placed by MNDO on computer resources, it may prove useful in the study of materials that are difficult to model within a TBTE framework. © 1992 John Wiley & Sons, Inc.
Chirality and spin density: Ab initio and density functional approaches
Authors: Fluekiger P. , Weber J. , Chiarelli R. , Rassat A. , Ellinger Y.
Published: January 2005

The spin distribution in a stable nitroxide biradical that shows ferromagnetic interactions in the solid phase has been studied at three levels of theory: First, at the UHF level; then, including correlation effects in UMP2 calculations; and finally, the results are compared with the spin density obtained using the local density functional (LDF) approximation. It is shown that LDF spin densities are closer to UMP2 than to UHF predictions; the difference between the UHF and the (UMP2, LDF) results points to a redistribution of the spin repartition between N and O due to electronic correlation. For planar conformations of the NO group, there is symmetric distribution (D2d) of the spin density on the adamantane skeleton. For nonplanar nitroxides, the molecule is chiral (C2), which results in a breakdown of the spin transmission on part of the adamantane cage. © 1993 John Wiley & Sons, Inc.
Semi‐empirical molecular orbital studies of porphine and phthalocyanine derivatives, to simulate their intermolecular interactions
Authors: Gantchev Tsvetan G. , Beaudry Francis , Van Lier Johan E. , Michel André G.
Published: January 2005

Gound‐state electronic properties of porphine, phthalocyanine, and their derivatives, photosensitizers with potential use in the photodynamic therapy of tumors, were studied by semiempirical (MNDO) molecular orbital calculations. Geometry, bond orders, electron populations, and net atomic charges were analyzed. The obtained models were applied to study the intermolecular interactions of these molecules utilizing a classical mechanics approach. The dimerization characteristics of different derivatives were obtained by a separate evaluation of the contribution of electrostatic and steric factors. © 1993 John Wiley & Sons, Inc.
Effect of positive background on the ground‐state energy of a Wigner lattice
Authors: Sebasdiyar I. , Iyakutti K. , Mahendran M.
Published: January 2005

An attempt has been made to study the effect of a nonuniform positive background on the ground‐state energy of a nonmagnetic Wigner lattice. The background is modified with a variable “ripple” parameter in the background charge, represented by a Yukawa‐type charge distribution. Our calculation shows that a Yukawa‐type background leads to a lower ground‐state energy value compared to a Gaussian‐type and constant positive background. © 1993 John Wiley & Sons, Inc.
Nonlocal exchange and kinetic energy density functionals with correct asymptotic behavior for electronic systems
Authors: Glossman M. D. , Balbás L. C. , Rubio A. , Alonso J. A.
Published: January 2005

The search for a density functional theory (DFT) free of one‐electron orbitals needs the development of good kinetic energy functionals beyond the venerable Thomas–Fermi and gradient expansion functionals. With this goal in mind, we previously solved for several atoms and positive ions the Euler equation associated with the exchange and kinetic energy functionals of the nonlocal weighted density approximation (WDA). In this work, we improve the theory by enforcing the correct asymptotic behavior of the exchange potential following a prescription of Przybilsky and Borstel (PB). We have calculated electronic densities, density moments 〈rn〉 (n= −1,1,2) and the density at the nucleus ρ(0), as well as total and exchange energies and chemical potentials for neutral and charged atoms. All those quantities show a better agreement with Hartree–Fock results than those obtained using gradient‐corrected Thomas–Fermi functionals. The radial densities, 4πr2(r), show two local maxima at positions close to those of the first two maxima of Hartree–Fock radial densities. This effect, which is absent in the self‐consistent densities from the usual gradient‐corrected Thomas–Fermi functions, can be interpreted, in our view as an incipient emergence of the shell effect. © 1994 John Wiley & Sons, Inc.
Classification of substituents by σ and π electron energy separation
Authors: Jug Karl , Matuschewski Marta
Published: January 2005

The previously introduced σ and π energy separation is extended to subsystems. σ and π electron donor and acceptor properties of the substituents are tested with a Löwdin population analysis. The influence of the substituents on the σ and π electron energies is calculated for substituted benzene, cyclobutadiene, butadiene, and borazine. A linear relationship is found which shows that an increase of σ electron energy is accompanied by a decrease in π electron energy and vice versa. This allows a classification of substituent groups in terms of reactivity. © 1994 John Wiley & Sons, Inc.
Density functionals for exchange and correlation energies: Exact conditions and comparison of approximations
Authors: Levy Mel , Perdew John P.
Published: January 2005

A set of exact conditions is compiled for the purpose of developing and testing approximations for the exchange‐correlation energy as a functional of the electron density. Special emphasis is placed upon recently developed density‐scaling relationships. Commonly used generalized gradient approximations are compared against several of these conditions. A direct tabular comparison of these functionals (not of calculated properties) with one another is also made. © 1994 John Wiley & Sons, Inc.
Localized Hartree product orbitals in correlated studies of molecules
Authors: Perera S. Ajith , Bernholdt David E. , Bartlett Rodney J.
Published: January 2005

Use of orthogonalized Hartree product (OHP) orbitals as the reference orbitals in coupled‐cluster (cc) calculations is presented. Since such orbitals are determined without exchange, they provide as “classical” a description as possible. The OHP orbitals were generated by implementing Harris's formulation of the original Hartree method. Some computational considerations of the formulation are discussed. A critical evaluation of the OHP method as an orbital localization scheme is presented. The OHP orbitals were used as the reference in CCD and CCSD calculations and compared with corresponding Hartree‐Fock (HF) reference CC results. The average variation of localized Hartree product (LHP) reference CCSD energy from that of the HF reference is 0.83 kcal/mol, whereas for CCD, the average variation is 234 kcal/mol, indicating the importance of single‐excitation effects in CC calculations with non‐HF references. © 1994 John Wiley & Sons, Inc.
Does antiaromaticity imply net destabilization?
Authors: Murray Jane S. , Seminario Jorge M. , Politzer Peter
Published: January 2005

An analysis is presented of the results of earlier ab initio computational studies of cyclobutadiene, cyclooctatetraene, and 1,4‐dihydropyrazine. The first and third of these are normally categorized as antiaromatic. All three molecules are polyenes, even when the last two are forced into planar conformations. There is no driving force for extensive π delocalization, even when it would appear to have been facilitated. Calculated isodesmic energies show a net destabilization only in the case of cyclobutadiene, which we attribute to strain and repulsion between the π electrons of the CC double bonds. The other two molecules have negative isodesmic energies, indicative of net stabilizing effects. We conclude that the concept of antiaromaticity is useful for identifying molecules that resist the apparent opportunity for extensive © delocalization, but that it does not intrinsically imply net destabilization. © 1994 John Wiley & Sons, Inc.
The orthogonal and the natural representation for symmetric groups
Authors: Wu Wei , Zhang Qianer
Published: January 2005

In the present article, improved algorithms for evaluating the irreducible representations of the symmetric group associated with an arbitrary partition, such as the orthogonal, the natural, and the seminormal representation, are introduced and the relations among them are discussed. With the new algorithms, a representation matrix for the orthogonal or the seminormal representation is expressed as the product of three matrices, where two of them are the triangular intrinsic matrices depending on the irreducible representation of the symmetric group; the other relating to the permutation can be given explicitly. Furthermore, we give a concise description for the irreducible representations of the symmetric group and reach an interesting conclusion that the conjugation transformation matrix between the orthogonal and the natural representation is the intrinsic matrix of the symmetric group. © 1994 John Wiley & Sons, Inc.
Eclipsed and staggered conformations of (SIH3)2F+: An ab initio study
Authors: Palafox M. Alcolea
Published: January 2005

Ab initio calculations at 6–31G**, 6–31++G**, and MP2/6–31G** levels were performed on disilyl–fluoronium, (SiH3)2F+, with the SiH3 group eclipsed or staggered. Optimized geometries, total energies, dipole moments, atomic charges, electronic density, and vibrational frequencies were computed. The results were compared with calculated structural parameters and vibrational frequencies of H3SiF, H2SiF+, H2SiF−, and H4SiF+ ions. The basis‐set effects were studied. Several thermochemistry parameters—ZPE, thermal energy, rotational constants, and entropies—were also calculated. © 1994 John Wiley & Sons, Inc.
Ab initio study of the inversion barrier in NF3+
Authors: Wetzel T. L. , Shorrosh R. , Borkman R. F.
Published: January 2005

Ab initio Hartree–Fock, Møller–Plesset perturbation theory (MP2), and quadratic configuration interaction, using single and double substitutions (QCISD), calculations were carried out for the NF3+ ion. Optimized structures were examined at the various levels of theory. Calculation of the inversion barrier height shows the importance of optimizing the geometry at the post‐Hartree–Fock level and the inclusion of polarization functions. The best calculated inversion barrier was 13.3 kcal/mol, compared to an experimental value of 17.3 kcal/mol. The dissociation transition state was computed to determine the well depth of the NF3+ ion and its stability toward dissociation. The computed well depth was 28 and 48 kcal/mol at the SCF and MP2 levels, respectively. © 1994 John Wiley & Sons, Inc.
Quantum chemical study of catalysts based on oxides of transition metals
Authors: Shcheka Oleg L. , Dobrodey Nickolay V. , Emelina Tatyna B.
Published: January 2005

Catalysts based on oxides of transition metals were studied by Xα–DV calculations. The chemical composition and electronic structure of surface layers for platinum(IV) oxide catalysts modified under percompound electrosynthesis were determined by X‐ray photoelectron spectroscopic, quantum chemical, and electrochemical data. The main regularities in electronic structure change under the transition from solid pure oxide PtO2 to its, in part, N‐substituted PtO2–xNx were analyzed. Then, we looked for perspective catalysts, calculating the electronic structure for analogous compounds of Ir(III), Ir(IV), Rh(III), and Pd(II). We found that the changes in electronic structure of rhodium oxide under O—N‐substitution allowed us to predict the excellent properties of its compound as a catalyst for percompound electrosynthesis reactions. © 1994 John Wiley & Sons, Inc.
Orbital binding effect in molecular orbital theory
Authors: Wang Xiang‐Yang
Published: January 2005

Based on the virial theorem and the virial function, a description of the orbital binding effect and the definition of orbital bond order are developed within the framework of molecular orbital theory for both diatomic and polyatomic molecules. Orbital binding effect calculations for N2, CH4, C2H4, C2H2, and C4H4 molecules show that the definition is reasonable. © 1994 John Wiley & Sons, Inc.
A comparison of semiempirical and ab initio transition states for HF elimination in unimolecular decompositions
Authors: Mulholland Adrian J. , Richards W. Graham
Published: January 2005

The transition states for unimolecular HF elimination from a series of methylene halides and vinyl halides have been located and properly characterized at the AM1, MNDO, PM3, RHF/6‐311G (d, p), and MP2/6‐311G (d, p) levels. Whereas the semiempirical MO methods deal well with the structures of the stable molecules, the structural differences between the ab initio and semiempirical transition states are considerably larger. The AM1 and PM3 activation energies appear to be relatively more accurate. © 1994 John Wiley & Sons, Inc.
A density‐functional method for calculating atomic polarizabilities: Application to negative ions
Authors: Harbola Manoj K.
Published: January 2005

We recently proposed a variational method for determining static polarizabilities that uses the ground‐state density, rather than the orbitals, of the system for calculations. Thus, the method is different from, and numerically easier than, the perturbation theory approach in which changes in each of the single‐particle orbitals have to be obtained self‐consistently. For neutral atoms and cations, it leads to results that are comparable to the results obtained by the perturbation theory. In this article, we apply this method, employing Hartree–Fock densities, to obtain polarizabilities for negative ions and show that for negative ions also the results are quite accurate. Thus, the method may prove useful in making quick and accurate estimates of the polarizabilities of more complex systems where orbital based self‐consistent calculations become quite complicated. © 1994 John Wiley & Sons, Inc.
Theoretical study of structure and basicity of some alkali metal oxides, hydroxides, and amides
Authors: Burk Peeter , Koppel Ilmar
Published: January 2005

Ab initio (TZV*, SBK*, and 3–21G* or 6–31G* basis sets) calculations were performed to predict the geometries and gas‐phase proton affinities of Li2O, LiOH, LiNH2, Na2O, NaOH, NaNH2, K2O, KOH, and KNH2. © 1994 John Wiley & Sons, Inc.
Continuum wave functions by least‐squares scheme in a B‐spline basis: Multicenter and multielectron formulations
Authors: Decleva P. , Brosolo M. , Lisini A. , Venuti M.
Published: January 2005

Application of a purely algebraic least‐squares approach in a spline basis to the determination of continuum orbitals in the single‐electron molecular case illustrates the excellent numerical properties of the method. Initial work based on a single‐center expansion is extended to an LCAO formulation within a single‐particle Hamiltonian and to the full multielectron problem in the one‐center scheme. Preliminary results on H and He photoionization are reported. © 1994 John Wiley & Sons, Inc.
Computation of expectation values with Dirichlet one‐dimensional wave functions
Authors: Núñez Marco A.
Published: January 2005

Recently, it was proven that the wave functions ψ of one‐dimensional Schrödinger operators can be approximated by those ψn corresponding to the Dirichlet eigenproblem in a finite box sufficiently large. In this article, sufficient conditions to compute expectation values are used to prove that the expectation value 〈ψ, Sψ〉 can be approximated by 〈ψn, Sψn〉 as n → ∞, for a wide class of unbounded symmetric operators S. © 1995 John Wiley & Sons, Inc.
Electronic structures of large, extended, nonperiodic systems by using the elongation method: Model calculations for the cluster series of a polymer and the molecular stacking on a surface
Authors: Mitani Masaki , Aoki Yuriko , Imamura Akira
Published: January 2005

The elongation method based on the molecular orbital (MO) theory, which enables us to extend a polymer with any molecular fragments theoretically, has recently been developed by our group. As the next step, we introduced an approach based on the crystal orbital (CO) theory into above treatment. In the present work, the elongation method was developed at the Hartree–Fock level with CNDO/2 parameters and applied to model systems composed of the cluster series of a polymer and the molecular stacking on a surface. In the cluster‐series calculations, the hydrogen molecule [(H2)n], hydrogen fluoride [(HF)n], polyethylene, and polyacetylene were created successively to approximate their one‐dimensional periodic polymers by using the MO‐based elongation method. In the molecular‐stacking models, we described the hypothetical surface of crystal as periodically arranged hydrogen molecules by the COs, and several hydrogen molecules were stacked up on the surface one after another with the elongation procedure. Furthermore, the lattice defect on surface in which a part of stacked layer is lacking was dealt with by our approach. We also treated carbon monoxide chemisorption on a periodic magnesium chain as a more realistic model. Results for these systems support the applicability of our method for nonperiodic interactions in one‐ and two‐dimensional large systems. © 1995 John Wiley & Sons, Inc.
Spectroscopic constants of SiH2, GeH2, SnH2, and their cations and anions from density functional computations
Authors: Mineva Tzonka , Russo Nino , Sicilia Emilia , Toscano Marirosa
Published: December 2004

Local (LSD) and nonlocal (NLSD) spin density calculations using different exchangecorrelation functionals have been performed to determine equilibrium geometries, harmonic vibrational frequencies (ωe), ionization potentials (IP), electron affinities (EA), dipole moments (μ), and singlet‐triplet energy gaps (Δ EST) of SiH2, GeH2, and SnH2. Geometrical structures as well as vibrational frequencies are in agreement with the available experimental data and compare favorably with the most sophisticated postHartree‐Fock computations performed until now. Both computed IPS (9.15 and 9.25 eV for SiH2 and GeH2, respectively) and EA of SiH2 (1.17 eV) compare favorably with experimental data (9.17, 9.21, and 1.2 eV). Accurate values are obtained also for singlet‐triplet energy gaps. We report for the first time the electron affinities of all neutral systems and the spectroscopic constants of the cations and anions. © 1995 John Wiley & Sons, Inc.
Ground‐state energies of atomic chains in superstrong magnetic fields
Authors: Relovsky B. M. , Ruder H.
Published: December 2004

The ground‐state energies of hydrogenic and helium chains in superstrong magnetic fields (B ≈︁ 107−109 Tesla) have been calculated within the single‐particle scheme of a heuristic density functional method. Applying the local density approximation (LDA), the simple Dirac exchange functional was used neglecting correlation effects. The equations were solved iteratively using a basis set of Landau functions in the transverse directions and directly integrating along the longitudinal direction. We obtained binding lengths and, by comparing the binding energies of the chains with the ground‐state energies of single atoms, we found condensation energies. © 1995 John Wiley & Sons, Inc.
SiO compound formation by oxygen ion implantation into silicon
Authors: Hensel E. , Wollschläger K. , Schulze D. , Kreissig U. , Skorupa W. , Finster J.
Published: December 2004

High dose oxygen ion implantation into silicon at 30 keV was performed to produce understoichiometric and stoichiometric surface oxide layers of ∼160 nm thickness. The oxygen depth profile and oxide stoichiometry was determined by RBS and XPS. SiO compound formation was found by IR spectroscopy and XPS in the unannealed samples as well as after target heating, furnace or flash lamp annealing. As implanted understoichiometric layers consist of random bonding like SiOx (O < x < 2), demixing into Si and SiO2 after annealing. Unannealed stoichiometric layers are bond strained SiO2. The activation energies of demixing and of the annealing of bond strains are determined to 0.19 and 0.13 eV, respectively. The removing of bond strains occurs at temperatures ≥800 °C in a time shorter than 1 s. The SiO2/Si transition region of unannealed stoichiometric layers consists of SiOx with an extent of about 10 nm. After annealing this extent diminishes to 0.8–1 nm in consequence of oxidation by excess oxygen from the overstoichiometric oxide region. This thickness is comparable with that of thermal oxide.
Quantitative analysis of impurities in HgCdTe using secondary ion mass spectrometry
Authors: Lapides L. E.
Published: December 2004

SIMS has been used to analyze impurities in epitaxial layers of HgCdTe because of its sensitivity to trace impurities and because it makes it possible to obtain impurity concentration profiles through the thickness of the epitaxial layer. The impurity profiles are quantified using relative sensitivity factors calculated from ion implantation profiles obtained on standard reference samples. Unintentional impurities, such as Cu, and low‐level deliberately added impurities, such as As, In, and Ag, have been analyzed. Specialized techniques such as molecular ion spectrometry (As analysis with TeAs−) and secondary ion acceleration voltage offset (Ag analysis) have been applied to improve sensitivity and decrease background signals. The use of these techniques has allowed the establishment of detection limits of less than 0.1 parts per billion atomic (3 × 1015 cm−3). The error in the analyses is, in general, estimated to be less than ±50%. Results from relative sensitivity factor measurements and impurity profiles are presented, and detection limits and accuracy of impurity analysis in HgCdTe using SIMS are discussed.
Dependence of SERS signal on surface roughness
Authors: Kruszewski Stefan
Published: December 2004

The roughness of the silver electrode was changed by variation of parameters of the oxidation–reduction procedure. The roughness size has been estimated qualitatively from the angle distribution of elastically scattered light. Quantitatively measurement of roughness by scanning electron microscopy and transmission electron microscopy also have been performed. Investigations of surface‐enhanced Raman scattering (SERS) intensity as a function of parameters of oxidation‐reduction cycle procedure and electrode roughness have been performed. The experimentally observed relationship between the roughness size and SERS signal is compared with the predictions of the classical electromagnetic enhancement model.
Void formation at silicon nitride/silicon interfaces studied by variable‐energy positrons
Authors: Halec Andrzej , Schultz Peter J. , Boudreau Marcel , Boumerzoug Mohamed , Mascher Peter , McCaffrey John P. , Jackman T. E.
Published: December 2004

Variable‐energy positrons (VEP) were used to study the deppth distribution of defects in SiNx/Si structures fabricated using ditertiary butyl silane (CONSI 4000) as the silicon precursor in an electron cyclotron resonance plasma chemical vapour deposition system. Films were grown to thicknesses ranging from 500 to 3500 Å at substrate temperatures between room temperature and 400°C and under various plasma conditions. The VEP results give evidence for differing concentrations of very large open‐volume defects at several of the SiNx/Si interfaces, confirmed by transmission and scanning electron microscopy. Their presence was correlated with non‐reactive organosilicon adsorption on the substrates prior to the thin film deposition.
Dual signaling mechanisms of estrogen: Phosphorylation of P53 at Ser15 in aging HMEC in the absence of estrogen receptor
Authors: Hass Ralf , von Wasielewski Reinhard , Fazekas Ursula , Bartels Helmut , Jans Erik , Lück Hans‐Joachim
Published: December 2004

Primary cultures of human mammary epithelial cells (HMEC) ex vivo underwent significant morphological and functional changes during the process of aging. Cells in S phase significantly declined after 19 d and accumulated in G0/G1 and G2/M phase after 50 d. Simultaneously, the initial estrogen receptor expression of 32,3% dropped to less than 1% in 19 d and 50 d aged HMEC, respectively. Estrogen treatment of HMEC demonstrated unaltered levels of P53 and phosphorylated P53 after 60 min. After 24 h of estrogen treatment, however, Western blot analysis revealed a significantly enhanced phosphorylation of P53 at Ser15 in 5 d and 19 d HMEC populations, respectively. A phospho‐P53 ELISA confirmed a significant Ser15‐phosphorylation of P53 in both HMEC populations following 24 h of estrogen stimulation, but no significant changes after 60 min, respectively. According to the estrogen receptor depletion in 19 d aged HMEC, these data indicated a receptor‐independent estrogen signaling.
Effects of fimbria‐fornix transection and ganglioside treatments on histochemical staining for glucose‐6‐phosphate dehydrogenase in the lateral septum
Authors: Fass Barry , Stein Donald G.
Published: December 2004

The present study examined whether ganglioside treatments would affect an enzyme marker (glucose‐6‐phosphate dehydrogenase; G6PDH) of neural metabolism in an established model system (the hippocamposeptal projection) of deafferentation and sprouting. Rats were subjected to unilateral transections of the fimbria‐fornix (FF) in order to (1) interrupt the hippocamposeptal projection, (2) deafferent the lateral septal nucleus (LSN) ipsilaterally, and (3) induce sprouting by the contralateral FF.

In untreated rats which were killed at 2–4 days postlesion, histochemical staining for G6PDH was reduced by 35–40% in the deafferented LSN relative to the contralateral side. However, at 6–8 days (i.e., when sprouting begins), staining intensity returned toward contralateral values (i.e., recovered). This pattern of changes in G6PDH staining was not observed in the caudate nucleus adjacent to the LSN.

In ganglioside‐treated rats which were killed at 4 days, there was a significantly smaller reduction of G6PDH staining in the deafferented LSN (23%; P=.05). This effect was not observed in the LSN of treated rats killed at 2 days, nor in the caudate nucleus at either time point.

The present data indicate that (1) FF transection results in a reduction and subsequent recovery of G6PDH staining in the deafferented LSN; and (2) ganglioside treatments may accelerate the onset of the recovery of G6PDH activity. We suggest that gangliosides' effect on G6PDH reflects an acute enhancement of biosynthetic events in deafferented neurons.
The serotoninergic innervation of cerebral cortex: Different classes of axon terminals arise from dorsal and median raphe nuclei
Authors: Kosofsky Barry E. , Molliver Mark E.
Published: December 2004

The objective of the present study was to characterize the morphology of serotoninergic axons in cerebral cortex of the rat and to determine whether dissimilar axon terminals arise from the dorsal vs. the median raphe nuclei. The anterograde tracer PHA‐L was administered by iontophoresis into the dorsal (DR) and median (MR) raphe nuclei, and the morphologic features of the respective axonal projections from raphe to forebrain were analyzed. We have observed consistent structural differences between the axons from these two nuclei. Anterogradely labeled axons which arise from cells in the MR are characterized by large, spherical varicosities (type M axons) and by variations in axonal diameter. In contrast, DR fibers are very fine and typically have small, pleomorphic varicosities that are granular or fusiform in shape (type D axons). Similar features of serotonin (5‐HT) axon morphology are also evident in 5‐HT immunocytochemical preparations. In addition to structural differences, there is differential topographic distribution of MR vs. DR fibers, with MR axons concentrated in particular areas of limbic cortex such as dentate gyrus, posterior cingulate, and entorhinal areas as well as in parietal cortex. Immunofluorescence with dual labels shows that over two‐thirds of the raphe‐cortical axons are serotoninergic. The dissimilarities in axon morphology indicate that individual raphe nuclei may form different patterns of synaptic organization. Based on the evidence that the dorsal and median raphe nuclei give rise to morphologically different axon terminals, we conclude that 5‐HT axons in cortex may be subdivided into two distinct projections. This proposal is in accord with other, recent data showing that the two axon types have different pharmacologic properties and are likely to be functionally different.
On the distribution of cholecystokinin receptor binding sites in the human brain: An autoradiographic study
Authors: Dietl Monika M. , Probst Alphonse , Palacios José M.
Published: December 2004

Cholecystokinin (CCK) binding sites were localized by in vitro autoradiography in human postmortem brain materials from 12 patients without reported neurological diseases using [125I]Bolton‐Hunter CCK octapeptide (BHCCK‐8) as a ligand. The pharmacological characteristics of BHCCK‐8 binding to mounted tissue section were comparable to those previously reported in the rat. CCK‐8 being the most potent displacer, followed by caerulein, CCK‐4, and gastrin I. The distribution of BHCCK‐8 binding sites was heterogeneous. These sites were highly concentrated in a limited number of gray matter areas and nuclei. The highest binding densities were seen in the glomerular and external plexiform layers of the olfactory bulb. BHCCK‐8 binding sites were also enriched in the neocortex, where they presented a laminar distribution with low levels in lamina I, moderate concentration in laminae II to IV, high density in lamina V, and low levels in lamina VI. A different laminar distribuition was seen in the visual cortex, where a low receptor density was observed in lamina IV but higher density in laminae II and VI. In the basal ganglia the nucleus accumbens, caudatus, and the putamen presented moderate to high densities of binding sites, while the globus pallidus lacked sites of BHCCK‐8 binding. In the limbic system the only area presenting moderate to high density was the amygdaloid complex, particularly in the granular nucleus, while most of the thalamic nuclei were extremely poor or lacked BHCCK‐8 binding. The hippocample formation showed low (CA1‐3) to moderate (subiculum) densities. Midbrain areas generally disclosed very low levels of BHCCK‐8 binding sites. The pontine gray and the nucleus reticularis tegmenti pontis showed a relatively high density of CCK‐8 receptor specific binding. Moderate to very high densities were found in few nuclei of the lower brainstem and spinal cord as the inferior olives and their accessory nuclei, the arcuate nuclei, the striae medullares, the efferent (motor) nucleus of the vagus, and the substantia gelatinosa of the cervical and thoracis spinal cord.

These results are discussed in relation to the distribution of endogenous peptide and to the known physiological and pharmacological effects of substances acting of on these receptors.
In vitro studies of the role of γ‐aminobutyric acid in inhibition in the lateral septum of the rat
Authors: Stevens David R. , Gallagher Joel P. , Shinnick‐Gallagher Patricia
Published: December 2004

Focal stimulation, stimulation of the fimbria, and stimulation of the medial septal area result in an inhibitory postsynaptic potential (IPSP) in lateral septal neurons. Increased stimulus intensity results in the appearance of a late hyperpolarizing potential (LHP). Treatment of the slice with bicuculline methiodide or picrotoxin results in blockade of the IPSP. When present, LHPs are enhanced in the presence of bicuculline or picrotoxin. Spontaneous and evoked IPSPs reverse near –70 mV, and LHPs reverse near –90 mV.

Iontophoretic application of γ‐amino‐butyric acid (GABA) results in hyperpolarizing, depolarizing, or biphasic potentials. Treatment with bicuculline or picrotoxin results in depression of biphasic GABA responses that appears selective for the depolarizing portion of the potential. At high concentrations of bicuculline, a portion of the hyperpolarizing GABA potential persists.

The reversal potential of the depolarizing GABA potential in near –30 mV, and the reversal potential of monophasic hyperpolarizing GABA potential is near –70 mV. The bicuculline‐resistant hyperpolarizing GABA response has a reversal potential near –90 mV.

GABA activates three separate conductances on septal neurons, which are similar to those reported on hippocampal neurons. The resistance of the hyperpolarizing GABA potential to bicuculline appears to be due to the presence of a GABA‐activated potassium conductance, which is similar to that activated by baclofen.
Primordial synaptic structures and synaptogenesis in rat olfactory cortex
Authors: Kunkel D. D. , Westrum L. E. , Bakay R. A. E.
Published: December 2004

Mature synaptic contacts and various primordidal synaptic elements were studied, counted, and analyzed in rat olfactory cortex from birth to 30 days of age. Primordial structures possess one or a few, but not all, of the features of a true mature synapse and have been grouped into two major classes based upon type of apposition: (1) single or (2) partial and multiple, with vacant postsynaptic sites included in the latter. There is a classical fivefold increase in number of mature synapses between birth and 30 days, but different patterns in the primordial appositions are observed. It is suggested that single apposition contribute to early synapse formation, while partial and multiple appositions participate later on during a time of rapid growth of new afferents to the area. The results suggest a clear role for primordial synaptic structures in synaptogenesis; that the sequence may be more divers than originally hypothesized, occurring at different stages; and that competition, synapse elimination, and replacement may be more prevalent in normal synaptogenesis than has been previously suspected.
Cholinergic transmission at newly formed synapses made by retinal neurons in culture
Authors: Stockbridge Norman , Puro Donald G.
Published: December 2004

The purpose of this study was to investigate the properties of cholinergic transmission at nascent synapses formed by neurons from the embryonic chick retina. By using a cell culture system in which striated muscle cells served as postsynaptic targets for dissociated retinal neurons, it was possible to record synaptic activity soon after the establishment of a functional cholinergic synapse. Postsynaptic potentials ranged from a few hundred microvolts to greater than 10 mV. The high temperature dependence (Q10 of 10) of this cholinergic transmission indicated that the release of acetylcholine from the embryonic retinal neurons was not injury‐related. The wide range in event amplitudes did not appear to be due to electrotonic conduction from adjacent myotubes. Rather, a lack of correlation between event amplitude and rise time indicated that the release of acetylcholine occurred over a confined area of contact. Amplitude histograms of these events always showed a unimodal distribution, with small events being most common. No pattern to the timing of the events was evident. In addition, the inward current blockers, tetrodotoxin and cadmium did not affect this activity.

Taken together, our findings indicate that the embryonic retinal neurons studied in this culture system spontaneously release acetylcholine in a pulsatile manner by a mechanism that is stimulus‐independent and highly temperature sensitive. A hypothesis is that the large variation in size of postsynaptic events at these newly formed synapses is caused by the spontaneous release of packets containing differing amounts of acetylcholine.
Reversible shifts in the Ca2+‐dependent release of aspartate and glutamate from hippocampal slices with changing glucose concentrations
Authors: Szerb John C. , O'Regan Patrick A.
Published: December 2004

It is known that low glucose concentrations increase the aspartate and decrease the glutamate content of brain tissue both in vivo and in vitro. To see whether these changes occur in the transmitter compartment or not, the release of aspartate and glutamate evoked by electrical‐field stimulation or by high K+ was followed in slices of rat hippocampus superfused with 5 or 0.2 mM glucose. Superfusion with 0.2 mM glucose increased the evoked release of aspartate about ten times and that of glutamate about threefold. This shift in the ratio of aspartate to glutamate released was accompanied by a similar increae in the relative amount of aspartate contained in the slices. The high evoked release of aspartate and glutamate was well maintained, provided 0.5 mM glutamine was added to the medium. Changing the concentration of glucose after the first period of stimulation rapidly altered the relative amounts of aspartate and glutamate released but not the enhanced release of glutamate. The large evoked release of both aspartate and glutamate in 0.2 mM glucose was almost entirely Ca2+‐dependent. The relative amounts of aspartate and glutamate released by 50 mM K+ also changed when the glucose concentration was reduced. Results suggest two effects of low glucose concentrations: an increase in the overflow of synaptically released glutamate due to a decreased uptake and an increase in the proportion of aspartate to glutamate formed and released from the transmitter pool. These observations are consistent with the interpretation that these two transmitters can be released in different proportions from the same terminals.
Calcium‐Insensitive miniature endplate potentials at the neuromuscular junction
Authors: Lupa Mark T.
Published: December 2004

Several different types of acetylcholine secretion have been shown to coexist at the neuromuscular junction along with the Ca2+‐dependent quantal release producing miniature endplate potentials (mepps) and endplate potentials. One of these, the Ca2+‐insensitive, slow‐rising mepps (slow mepps), is present in normal untreated muscles but is most prominent in many conditions where the Ca2+‐dependent quantal release mechanism is not functioning properly. Slow mepps occur at a frequency of less than 0.1 Hz in normal muscles, with large variability between fibres and muscles, and can reach frequencies of 1–2 Hz in several pathological conditions. The potentials are also highly variable in size and shape, being generally of high amplitude (0.1–15 mV) and prolonged time course (1–15 ms rise time). Most importantly, slow mepps are not affected by procedures which increase the intraterminal Ca2+ > concentration, including nerve stimulation, thus being unable to contribute to the function of synaptic transmission.

The cellular source of the Ca2+‐insensitive mepps has been determined to be the nerve terminal and not the Schwann cells or nerve sprouts. The release process producing slow mepps is gererally insensitive to many drugs, ions, and procedures, stimulation being observed with vinblastine, cytochalasin B, and caffeine. Depression of this secretion is effected by uncouplers of oxidative phosphorylation and by a drug (AH5183) which inhibits the vesicular active acetylcholine transport system. It is concluded that the slow mepps are due to an exocytic fusion of unique synaptic vesicles with the plasma membrane near the active zones, in a process insensitive to many intracellular ions and regulators. Since slow mepps are prominent in many pathological conditions of nerve and muscle, it is speculated that they play some role in the recovery or development of synaptic function.
Vasopressin promotes neurite growth in cultured embryonic neurons
Authors: Brinton Roberta E. , Gruener Raphael
Published: December 2004

Vasopressin (AVP) has been identified as a neural peptide which may influence memory function. Because of this action, we investigated the effect of AVP on neurons growing in culture. Vasopressin was found to markedly increase neurite outgrowth from cultured embryonic neurons and to also accelerate the rate of neuritic growth. Maximal stimulation of neurite production occurred after 24‐hour incubation in the presence of 1 μM AVP. In AVP‐treated cultures the profuse neuritic arborization was characterized by numerous microspikes along the neuritic shafts and at the perimeters of growth cones. These data provide strong evidence for a neurotrophic effect of AVP which, we suggest, may be relevant to neuronal development as well as to morphological changes which occur in the mature nervous system, possibly during memory formation.
Neurotrophic effects of GABA in cultures of embryonic chick brain and retina
Authors: Spoerri P. E.
Published: December 2004

The present study examined whether GABA treatments would affect the growth and development of embryonic chick cortical and retinal neurons in culture. Incubation of these cells in the presence of 10−−5 M GABA produced several responses. It promoted the proliferation and the differentiation of the neurons studied by affecting the length and branching of the neurites as well as synaptogenesis, as revealed by morphometric measures. At the ultrastructural level, GABA treatment also led to an increased density of neurotubules, rough endoplasmic reticulum (RER), Golgi apparatus, coated vesicles, and other vesicles. These data support the hypothesis that GABA functions as a trophic or regulatory factor of at least certain neuron types.
Morphometric study of synaptic patterns in the rat caudate nucleus and hippocampus under haloperidol treatment
Authors: Uranova Natalya A. , Orlovskaya Diana D. , Apel Katrin , Klintsova Anna J. , Haselhorst Uwe , Schenk Herwart
Published: December 2004

A morphometric study of the synapses on dendritic shafts and spines was performed in the rat caudate nucleus and the CAI area of the hippocampus under chronic haloperidol treatment. In the nucleus caudatus, the synaptic density of dendritic shafts increased by 83% and those on spines by 53%. Most of the parameters measured in axospinous synapses were significantly increased: the area of presynptic axon terminals (20%), the number of mitochondria per axon terminal (51%), the length of active zone (11%), the area of postsynaptic density (23%), and the perimeter of postsynaptic density (12.5%). The area of postsynaptic spines showed no changes. In the synapses on dendritic shafts, the area of presynaptic terminals decreased (31%), the area of mitochondria per terminal decreased (40%), the lingth of active zone increased (14%), and other parameters were unchanged. There were no significant differences in the same parameters measured in the hippocampus. The data are discussed as morphological correlates of behavioral supersensitivity and dopamine D2 receptor up‐regulation.
Receptor selectivity of cholecystokinin effects on mesoaccumbens dopamine neurons
Authors: Kelland Mark D. , Zhang Jing , Chiodo Louis A. , Freeman Arthur S.
Published: December 2004

Extracellular recording techniques were combined with antidromic stimulation to examine the effects of C‐terminal cholecystokinin (CCK) fragments and CCK antagonists on the activity of identified mesoaccumbens dopamine (MADA) neurons in chloral hydrate‐anesthetized rats. These experiments were designed to determine the receptor selectivity of sulfated CCK octapeptide (CCK‐8S) effects on MADA cells. Neither CCK tetrapeptide (CCK‐4) nor unsulfated CCK octapeptide (CCK‐8U) significantly altered MADA cell basal firing rate or responsiveness to the inhibitory effects of the D2 DA agonist quinpirole. As reported previously for ventral tegmental area DA cells, CCK‐8S produced increases or decreases in the firing rate of most MADA cells sampled. CCK‐8S also enhanced the sensitivity of MADA neurons to quinpirole‐induced inhibition. This increase in sensitivity to quinpirole was blocked by pretreatment with the nonselective CCK receptor antagonist proglumide and the preferential CCK‐A receptor antagonist CR 1409 but not by the preferential CCK‐B receptor antagonist L‐365, 260. The inactivity of CCK‐4 and CCK‐8U in these tests and the results with the antagonists suggest that the effects of CCK‐8S on MADA neuronal activity are mediated by CCK‐A receptors.
Some pharmacological differences between hippocampal excitatory and inhibitory synapses in transmitter release: An in vitro study
Authors: Kamiya Haruyuki
Published: December 2004

The effects of adenosine, carbachol, and baclofen on synaptic transmission between neurons in cultured rat hippocampal explants were studied using the tight‐seal whole cell clamp technique. In the culture, stimulations of neurites cause postsynaptic currents (PSCs) in nearby neurons under voltage‐clamp condition. In the presence of 20 μM bicuculline, most PSCs were considered as glutamatergic excitatory postsynaptic currents (EPSCs), because they were blocked by glutamate antagonist, kynurenate at 1 mM. In the presence of 1 mM kynurenate, PSCs seemed to be inhibitory postsynaptic currents mediated by γ‐aminobutyric acid (GABA), because they were blocked by GABA antagonist, bicuculline at 20 μM. Adenosine at 100 μM and carbachol at 10 μM suppressed these EPSCs to about 35% of control. However, adenosine and carbachol at the same concentration did not suppress the IPSCs. Baclofen at 10 μM suppressed both EPSCs and IPSCs significantly (EPSCs: to about 40% of control, IPSCs: to about 30% of control). In contrast, membrane currents elicited by ionophoretically applied glutamate and GABA were not suppressed by 100 μM adenosine, 10 μM carbachol, and 10 μM baclofen. From these results, it is suggested that the pharmacological sensitivities of transmitter release from presynaptic terminals are different between glutamatergic excitatory synapses and GABAergic inhibitory synapses in hippocampal cultures.