bluuebunny/crossref_metadata_2025 huggingface dataset:
Chemical interpretation of the relaxed permittivity during epoxy resin cure
Authors: Sheppard Norman F. , Senturia Stephen D.
Published: December 2004

The isothermal cure of a diglycidyl ether of Bisphenol‐A (DGEBA) epoxy resin with diaminodiphenylsulfone has been characterized by microdielectrometry and differential scanning calorimetry. The cure temperatures ranged from 410 to 460K. The behavior of the relaxed (or static) dielectric permittivity vs. cure time and temperature was determined from the microdielectrometry data. The DSC data was fit to an autocatalyzed reaction kinetics model, which was then used to predict reactive group concentrations as a function of cure time and temperature. The temperature dependence of the relaxed permittivity at constant chemical conversion was examined in the context of the Onsager theory for the relaxed permittivity of a system of independent dipoles. This analysis indicated that the dipoles in the resin are not independent, as assumed by the Onsager theory, and that the behavior is similar to that observed in polyethers. An empirical modification to the Onsager theory was used in conjunction with the kinetic model to estimate dipole moments for the epoxide, primary amine, and reacted (secondary and tertiary) amine groups. The relative and absolute values of the dipole moments were in good agreement with estimates based on the structures, leading to the conclusion that the observed decrease of the relaxed permittivity during cure of this epoxy/amine system is due to the changing concentrations of polar reactive groups.
Measurement of interfacial tensions of molten polymer systems by means of the spinning drop method
Authors: Elmendorp J. J. , De Vos G.
Published: December 2004

The spinning drop method is used to measure the interfacial tension of molten polymer systems. It proves to be a simple and rather fast measuring method, while satisfactory agreement with literature values, obtained with the pendant drop method, is achieved.
Material modeling and solid phase forming of polycarbonate sheet
Authors: Lee D. , Luken P. C.
Published: December 2004

The Maxwell‐Voigt type mechanical model proposed by Haward and Thackray was further modified to describe the strain rate dependent stress‐strain behavior of polycarbonate under the uniaxial loading condition. Major modifications included effects associated with different hardening components of inelastic resistance and the related temperature dependent material behavior. The modified analytical model was shown to describe some of the important features of the stress‐strain behavior of polycarbonate specimens tested over the range of strain rates and temperatures. Using the stress‐strain relationship as input data; several finite element analyses were made to predict the behavior of polycarbonate sheets under a simple solid phase cup forming process. The computed strain distributions agreed reasonably with the measured values obtained from the gridded polycarbonate sheet that was formed at an elevated temperature. Some of the key assumptions that were used in the analysis are discussed.
Kinetics of alcohol assisted craze growth in polycarbonate
Authors: Kirloskar Mohan A. , Donovan James A.
Published: December 2004

The kinetics of alcohol assisted, relaxation controlled craze growth in polycarbonate (PC) were studied between 280 to 340K in methanol, ethanol, propanol, butanol, and pentanol. Viscous deformation of plasticized craze material controlled the growth rate of a single craze during stress relaxation in single edge notched (SEN) specimens. The activation energy increased with craze driving force in all alcohols, except methanol, because of diffusion limited plasticization. The craze stress increased with the alcohol's ability to plasticize; this is not understood, but may be due to solvent Induced crystallization.
Fourier transform mechanical analysis for determining the nonlinear viscoelastic properties of polymers
Authors: Ganeriwala Surendra N. , Rotz Christopher A.
Published: December 2004

Fourier Transform Mechanical Analysis (FTMA) has been used to study the strain amplitude dependent nonlinear dynamic mechanical properties of two elastomer compounds, nitrile rubber (NBR) and Neoprene, at various frequencies up to 750 Hz. Basic theory and experimental results are presented for one‐dimensional isothermal single frequency simple shear deformation. The Green‐Rivlin constitutive equation was used to model the observed behavior. The energy dissipation mechanism and a physical meaning for the material functions in the Green‐Rivlin representation have also been examined. The stress Fourier spectrum contained terms at the input frequency and its higher harmonics. It can qualitatively indicate the type of mathematical mode that best describes the observed behavior. The first harmonic storage and loss moduli showed strong dependence on the strain amplitude and frequency. The FTMA methodology presented can be used to systematically conduct nonlinear dynamic mechanical studies on any polymer. It can provide enough insight which, along with a knowledge of the molecular structure, may indicate a path for developing a better representative continuum constitutive model of these complex materials.
Draw resonance in polypropylene melt spinning
Authors: Yoo H. J.
Published: December 2004

An attempt is made to gain better physical insight on the draw resonance phenomenon occurring during melt spinning of polypropylene (PP). An experimental study is first carried ouit to determine effects of spinning variables and material parameters on draw resonance, using two PRO‐FAX PP resins and one PRO‐FAX/LDPE blend. Based on the experimental observations, our view on the cause of draw resonance is presented. With this new concept, we are able to explain various aspects of the draw resonance phenomenon observed experimentally during melt spinning of PRO‐FAX PP resins. It is concluded that the extensional viscosity versus strain relationship, as determined by an extensional rheometer, is one of the most valuable rheological measurements in analyzing flow instability occurring during polymer processing operations that utilize extensional flows.
Linear low density polyethylenes and their blends: Part 1. Molecular characterization
Authors: Schlund B. , Utracki L. A.
Published: December 2004

Ten commercial linear low‐density polyethylenes (LLDPE) were characterized by solution viscosity, size exclusion chromatography, SEC, and 13C nuclear magnetic resonance. The resins were copolymers of ethylene with butene, hexene, or octene. They were prepared in gas phase (with narrow or very broad molecular weight distribution), or in solution. The macromolecules were found to be linear. For all but the very broad molecular weight distribution resins the average comonomer sequence length was found to be 1; in the other case diad formation was observed. The weight average molecular weights calculated from SEC, and intrinsic viscosities agreed quite well. Mechanical degradation of LLDPE was observed during the solution viscosity measurements.
Correlations of elastic modulus, cohesive energy density and heat capacity jump of glassy polymers
Authors: Lee Chung J.
Published: December 2004

The elastic modulus of glassy polymers can be calculated from a measurable thermal property of polymers. The correlation of heat capacity jump data with molar modulus of 13 polymers indicated that the calculation of molar modulus from heat capacity jump energy for other glassy polymers is possible.
A boundary element simulation of compression mold filling
Authors: Osswald Tim A. , Tucker Charles L.
Published: December 2004

This paper presents the development of the boundary element equations for the compression molding process of isothermal Newtonian fluids. It shows the numerical implementation of the boundary element equations and presents a simple method of carrying out the domain integral present in the governing equations. The results and accuracy of a boundary element simulation are discussed, and the numerical results compared to experimental values.
A model process for the solvent recycling of polystyrene
Authors: Kampouris E. M. , Papaspyrides C. D. , Lekakou C. N.
Published: December 2004

A model solvent technique is presented according to which polystyrene (PS) foam scrap is recovered in the form of small grains. The process mainly comprises dissolution of the waste into benzene or toluene, filtering, dispersion of the solution into water, and subsequent distillation. The alternative solvent/non‐solvent systems have been studied on the basis of solution rheology, operating conditions during the recycling procedure, and extents of recovery of PS and solvent. Eventually, the toluene/water system has been chosen for a larger scale experiment (LSE), the product of which was used for characterization work. No influence on critical properties was detected due to the solvent technique followed.
Torsion Impregnated Cloth Analysis for resin rheological studies
Authors: Lee Charles Y‐C
Published: December 2004

This paper describes the utility of Torsion Impregnated Cloth Analysis, a very versatile technique to characterize resin behavior during cure or after repeated thermal and environmental treatment. Multi‐frequency scan data have been shown to help tremendously in interpreting the behavior during experimentation. The technique is also very useful in defining the cure conditions for new resin chemistry/systems.
Chemical structures and properties of low thermal expansion coefficient polyimides
Authors: Numata Shunichi , Kinjo Noriyuki , Makino Daisuke
Published: December 2004

The relationships, between chemical structures of various aromatic polyimides and their thermal expansion coefficients, were investigated and the properties of low thermal expansion polyimides were elucidated. Such low values were observed for polyimides obtained from pyromellitic dianhydride or 3,3′,4,4′‐biphenyltetracarboxyIic dianhydride and aromatic diamines, which included only benzene or pyridine rings fused at para‐positions without a flexible linkage. It was proposed that these low thermal expansion coefficients were related to the linearity of their polymer molecular skeletons. In particular, PIQ‐L100 (Hitachi Chemical Co. Ltd) is one such low thermal expansion polyimide and, it has excellent mechanical properties, thermal stability, and low absorbed moisture content.
Kinetic studies of the polymerization of nylon‐6 block copolymers
Authors: Limtasiri T. , Grossman S. J. , Huang J. C.
Published: December 2004

The kinetics of the activated anionic polymerization of caprolactam to nylon‐6 and its copolymers has been studied. Nylon‐6 block copolymer and nylon‐6 were prepared at various initial reaction temperatures (140°C to 165°C) by anionic polymerization in an adiabatic dewar flask. Different concentrations of poly(ethylene oxide) (PEO) in 4,4′‐diphenyl methane diisocyanate (MDI)‐capped PEO and 1 mole percent MDI, in a caprolactam solution, were used as the activators with the catalyst, the sodium salt of caprolactam. The kinetics of the reaction were analyzed from an adiabatic temperature rise. A new method was applied to determine the rate parameters. The activation energy, Ea, of nylon‐6 and nylon‐6 block copolymers were found to be 22 kcal/mole. The collision frequency factor, Ao, steadily decreased and the autocatalytic constant, Bo, decreased to a constant value of 16 with the introduction of PEO. However, it was found that the order of reaction, n, was almost a constant value at the second order for all experiments.
Polyolefin properties for rigid food packaging
Authors: Jabarin S. A. , Kollen W. J.
Published: December 2004

Polyolefins are used in many rigid plastic packages that are developed for food applications. Generally, the polyolefins used are selected for a balance of cost, ease of molding, and performance properties in a finished package. In this paper some of the physical and sorption properties of polyolefins that are critical to rigid plastic packages are discussed. Initially, a brief review of the performance requirements of plastic food packages will be presented. This is followed by discussions of specific properties of polyolefins such as impact resistance, adhesion and thermal resistance, and how they may be enhanced by coextrusion. Additionally, the sorption of food components such as flavors into polyolefin walls of packages is discussed. Here, the applicable theoretical considerations for sorption and their value for analyzing experimental data are presented. Finally, specific sorption properties of d‐limonene in ethylene‐propylene copolymers and their effects on package performance and design are reported and discussed.
Rheological properties of the liquid crystalline poly(γ‐benzyl α, L‐glutamate) gels in benzyl alcohol
Authors: Shukla Premal , Muthukumar M.
Published: December 2004

We have determined the degree of stiffness of a poly(γ‐benzyl α, L‐glutamate) (PBLG) chain in benzyl alcohol by measuring the intrinsic viscosities of dilute Solutions with differing molecular weights. Viscoelastic properties in oscillatory shear flow have been studied and the dependence of the loss and storage moduli on temperature, composition, and frequency are reported. We have also studied the transient shear stress relaxation behavior of the PBLG gel at different temperatures and concentrations. A comparison has been made between these gels and a classical poly(dimethyl siloxane) (PDMS) network, as well as, typical glassy polymers. Shear creep and recovery measurements have been made for this system. Some extensional step strain experiments using lubricated squeezing have been investigated. Tensile experiments have been made to determine stress‐strain relationship during elongation. Preliminary experiments using the impulse approach to viscoelasticity further indicate the high elastic contribution in the gel.
Interpretation of dynamic mechanical measurements on butyl‐acrylate vinyl‐acetate based systems
Authors: Jourdan C. , Cavaille J. Y. , Perez J.
Published: December 2004

Dynamic mechanical measurements have been performed in order to get information on the morphology of butyl‐acrylate (BuA)‐vinyl‐acetate (V Ac) based systems. The samples were obtained after emulsion polymerization by three different pathways: (a) Physical blending from homopolymer latexes (b) a conventional batch process leading to a BuA rich core‐V Ac rich shell latex particle (c) a two‐step polymerization leading to an abrupt concentration gradient Inside the particle. Films were obtained by evaporation of water at room temperature. The spectra of the films were interpreted with the help of Kerner's model, and new information has been obtained on the morphology: (i) in the simple blend (case a), the p(V Ac) latexes tend to coalesce to form the matrix; and (ii) it is possible to determine whether random copolymer formed during a polymerization process is located at the interface of p(BuA) and P(V Ac) (case b) or inside the p(BuA) inclusion (case c).
Preamble
Authors: Utracki L. A. , Favis B. D.
Published: December 2004

No Absract.
The pressure drop/flow rate equation for non‐Newtonian flow in channels of irregular cross‐section
Authors: Liu Ta‐Jo , Hong Chin‐Nan
Published: December 2004

The pressure drop/flow rate equation for non‐Newtonian fluid flow in channels of irregular cross‐section is determined theoretically by two numerical methods. Two representative non‐Newtonian fluid models, the Ellis and the Herschel‐Bulkley models, have been studied for several commonly encountered non‐circular channels. The empirical methods proposed by Kozicki, et al, and Miller have been analyzed. The validity of their methods is discussed.
Mechanical properties of miscible phenolphthalein poly(ether ether ketone)/polysulfone blends
Authors: Qipeng Guo , Jinyu Huang , Tianlu Chen , Hongfang Zhang , Yuhua Yang , Chunrong Hou , Zhiliu Feng
Published: December 2004

The properties of miscible phenolphthalein poly(ether ether ketone) (PEK‐C)/polysulfone blends have been measured by dynamic mechanical analysis and tensile testing. The blends are found to have single glass transitions that vary continuously with the composition. The tensile moduli exhibit positive deviations from simple additivity as expected for miscible blends. Remarkably, positive deviations were also observed for tensile strength. Embrittlement, or transition from the brittle to ductile mode of failure, occurs at 50‐30 wt % PEK‐C. These observations suggest that mixing on the segmental level has occurred and that there is enough interaction between the components to retard internal mobility significantly.
Isothermal crystallization of isotactic polypropylene in dotriacontane. II: Effect of nucleating agent addition on growth rate
Authors: Lim Gordon B. A. , Lloyd Douglas R.
Published: December 2004

Isothermal crystallization growth rates of nucleated and non‐nucleated isotactic polypropylene (iPP) in dotriacontane were determined experimentally by thermal optical microscopy. Adipic acid was used as the nucleating agent. The Lauritzen and Hoffman analysis was used to determine the fold surface energy of the nucleated and non‐nucleated mixtures.
Synthesis and characterization of aromatic polyamides containing an s‐triazine ring with thiophenoxy linkages
Authors: Pal Ravindra R , Patil Prashant S , Salunkhe Manikrao M , Maldar Noormahamad N , Wadgaonkar Prakash P
Published: January 2005

A series of aromatic polyamides containing an s‐triazine ring with thiophenoxy linkages was synthesized from two new diacids, namely 2,4‐bis‐(4‐carboxyphenoxy)‐6‐thiophenoxy‐s‐triazine and 2,4‐bis‐(3‐carboxyphenoxy)‐6‐thiophenoxy‐s‐triazine, and commercially available aromatic diamines by using Yamazaki's phosphorylation reaction. The polyamides were obtained in good yields and were characterized by solubility tests, viscosity measurements, FTIR, 1H and 13C NMR spectroscopy, X‐ray diffraction studies and thermogravimetric analysis. The polyamides were found to have inherent viscosities in the range of 0.35 to 0.56 dl g−1 in N,N‐dimethylacetamide (DMAc) at 30 ± 0.1 °C. All the polyamides were readily soluble in solvents such as DMAc, N‐methyl‐2‐pyrrolidone (NMP), N,N‐dimethylformamide (DMF) and m‐cresol. Thermogravimetric analysis of the polyamides indicated no weight loss below 345 °C under a nitrogen atmosphere. Copyright © 2004 Society of Chemical Industry
The Problems of Quantifying Mineral Liberation: A review
Authors: Austin Leonard G. , Luckie Peter T.
Published: December 2004

A review is given of recent publications concerning the theory of liberation of component B from AB material as particle size is reduced, with a view to combining models of liberation with models of size reduction. Although a number of approaches are promising, it is concluded that there is no adequate model of liberation of binary systems suitable for incorporation into a mill model.
Properties of Sprays
Authors: Lefebvre Arthur H.
Published: December 2004

The spray properties of most practical importance, namely mean drop size, drop size distribution, radial and circumferential liquid distribution, cone angle and penetration, are discussed in the context of plain orifice, pressure‐swirl, plain‐jet airblast and prefilming airblast atomization. Equations are presented for estimating mean drop size and spray cone angle in terms of the relevant liquid properties, gas properties, atomizer dimensions, and atomizer operating conditions. The relative merits of these equations are discussed and compared. Some aspects of atomization in need of further research are indicated.
Applied Fractal Geometry and the Fineparticle Specialist. Part I: Rugged boundaries and rough surfaces
Authors: Kaye Brian H.
Published: December 2004

Fractal Geometry developed in 1977 by B. Mandelbrot describes the structure of rugged systems by extending the concepts of classical dimensional analysis to include a fractional addendum to the topological dimension of a system in order to describe the space filling properties of the rugged system. In the 15 years since the publication of Mandelbrot's book describing his seminal ideas fractal geometry has found many applications in fineparticle science and technology. This body of applied knowledge is now known as Applied Fractal Geometry. The purpose of this review is to focus on the various branches of applied fractal geometry of interest to the fineparticle specialist in a systematic manner. The first part is concerned with ruggedness of fineparticle boundaries, the structure of simple porous bodies, fragmentation and powder production, the assessment of the properties of such materials as paper, and the characterization of rough surfaces. The second part will explore the use of fractal dimensions to describe mixing operations, composite bodies, such as synthetic bones, and paint films.
Johnson's SB Distribution Function as Applied in the Mathematical Representation of Particle Size Distributions. Part 2: Application of numerical results
Authors: Yu Ai‐Bing
Published: December 2004

The validity of the numerical results obtained in Part 1 is examined via some typical examples. The results indicate that the numerical results can be applied to the particle size distribution transformation within the practically tolerated error. On this basis an equation was derived to calculate analytically the mean diameters of a powder. The verification and application of this equation are demonstrated by a typical example. It is shown that the Hatch‐Choate relationship used in the transformation of particle size distributions expressed by the log‐normal distribution is only a special (extreme) case of the present numerical results. Although the numerical simulation cannot always provide a consistent transformation, this approach can greatly facilitate the application of the SB distribution function in powder technology by simplifying the transformation between particle size distributions and the calculation of mean diameters.
The identification of choline and its esters by secondary ion mass spectrometry
Authors: Unger S. E. , Ryan T. M. , Cooks R. G.
Published: December 2004

Secondary ion mass spectrometry is shown to provide mass spectra of choline and its esters from which molecular weights and structures are evident. Structure‐spectral correlations are developed using analogies from other forms of mass spectrometry. Spectra can be recorded on metal or paper substrates and individual components can be identified even in complex samples.
Factor analysis and superposition of Auger electron spectra applied to room temperature oxidation of Ni and NiCr21Fe12
Authors: Hofmann S. , Steffen J.
Published: December 2004

Low energy valence band Auger transitions are advantageous for the study of the initial stages of metal and alloy oxidation owing to their high surface sensitivity and to their chemical bonding features. However, the latter property leads to difficulties in quantification of the spectra, particularly by using peak‐to‐peak heights in the derivative mode. Therefore, two other methods are applied for a quantitative evaluation of the different elemental bonding states: (a) superposition of standard spectra according to the least mean squares fitting method and (b) factor analysis. The reliability of both methods is compared for the quantitative determination of the kinetics of oxygen reaction with pure Ni and with a NiCr21Fe12 alloy at oxygen pressures between 10−6 Pa and 10−4 Pa. Although both methods give comparable results, only method (b) allows the determination of the chemisorbed oxygen bonding state on Ni using the low energy Ni M23 VV transition. For the NiCrFe alloy, only method (a) gives a clear distinction between nickel and iron oxides.
XPS analysis of ion‐beam‐induced oxidation of silicon substrates
Authors: Alay J. L. , Vandervorst W.
Published: December 2004

XPS analysis was used to characterize Si (100) targets bombarded with an O2+ beam with energies ranging between 5.00 and 0.50 keV and incident angles between 0° and 75°. In this energy range and at normal incidence a homogeneous SiO2 layer is built up in a sequential suboxide replacement mechanism, while for bombardments at 5.00 keV and incident angles between 28° and 55° only a heterogeneous layer is formed. The latter contain elemental silicon, evenly spread in the altered layer, and all possible oxidized chemical states. For bombardments at high glancing angles (55°–75°) only a few suboxides are observed. Finally, a linear enhancement for the Si+ secondary ion yield w.r.t. the Si4+ relative concentration is found, except for very high Si4+ level concentrations where a strong non‐linear increase takes place.
Use of Si 2p x‐ray photoelectron diffraction as a test of epitaxial thin film growth by Si evaporation on Si(001)
Authors: Kubler L. , Lutz F. , Bischoff J. L. , Bolmont D.
Published: December 2004

Clean Si(001) surfaces are crystallographically characterized by x‐ray photoelectron diffraction (XPD). The anisotropic core level electron emission in the space, due to forward scattering mainly in the direction of the internuclear axes, is given by polar and azimuthal scans of the Si 2p core level intensities I(θ) and I(θ) in some particular high‐symmetry space directions. As an ilustration we apply this technique to a study of the homoepitaxial growth of thin (∼200 Å) evaporated silicon epilayers. Particular attention is paid to comparison of the epitaxy temperature dependence where the amorphous‐crystalline transition occurs by varying either the substrate temperature Ts at which the evaporation is done of the annealing temperature TA after a room temperature evaporation (solid phase epitaxy). We also suggest using the anisotropy factor deduced from the XPD patterns in oder to get information about the epitaxy quality.
Surface characterization and electrochemical behaviour of nitrogen‐ and carbon‐implanted titanium
Authors: Heide N. , Siemensmeyer B. , Schultze J. W.
Published: December 2004

Owing to their combination of metallic and covalent properties, TiN and TiC are used as coating materials. In this work thin layers (layer thickness about 10 nm) of TiN and TiC were prepared by low‐energy ion implantation (3 keV N2+, 4 keV C2H4+) into Ti. The change in surface composition as a function of ion dose was followed by XPS. The electrochemical behaviour was studied in an electrochemical cell attached to the surface equipment; therefore no surface oxidation due to air contact took place. TiN and TiC revealed a stability up to 1.5 and 1.0 V respectively. Above these potentials oxidation to TiO2 and N2 in the case of TiN and to TiO2, CO2 and CO in the case of TiC occurred. The gaseous oxidation products were dissolved in the oxide layer and influenced its properties.
Multifactorial control of pituitary hormone secretion: The “Wheels” of the brain
Authors: Jacobowitz David M.
Published: January 2005

An attempt is made to deal with the complexity of the nerve fibers in the median eminence. Visual aids are presented in the shape of “wheels” that depict a dynamic interplay of neurochemicals which result in the release of hormones from the anterior pituitary gland. The multiplicity of neurochemicals in the median eminence is perceived to be responsible for the integrated control of pituitary hormone releasing factors.
Heterogeneity of motilin immunoreactivity in mammalian tissue
Authors: Nilaver Gajanan , Beinfeld Margery C. , Bond Chris T. , Daikh David , Godfrey Bruce , Adelman John P.
Published: January 2005

Motilin is a 22 amino acid peptide first isolated and sequenced from porcine gut. The use of antisera directed to the synthetic porcine gut motilin sequence has produced conflicting results as to regional distribution and histological localization of motilin in mammalian brain and gut. Motilin immunoreactivity has been detected (by RIA) in brain regions where no immunostaining is discernible. Variations in the patterns of staining are also observed with different antisera. These discrepancies have been explained by postulating species‐, tissue‐, and region‐specific variations in peptide immunoreactivity, and variable cross reactivities of the independent antisera with these forms. The use of cloned porcine cDNA encoding gut prepromotilin in Northern blot analysis of brain regions expressing motilin‐like immunoreactivity has also failed to reveal a homologous message, questioning the true nature of the immunoreactive material in the brain. Physiological studies, however, have suggested central roles for motilin in a variety of CNS (feeding behavior, bladder control, cerebral and brain stem modulation, pituitary growth hormone release) and gastrointestinal (gastric emptying, intestinal motility) functions. The motilin immunoreactive material detected in brain may be encoded by a distinct non‐homologous gene, and still share amino acid homologies with the motilin sequence. Molecular biological characterization of the cell systems which contain motilin and motilin‐like immunoreactivity should allow a better definition of their roles in these tissues.
Norepinephrine uptake dependent upon apparent Mg++‐ATPase activity and proton transport in storage vesicles in axoplasm
Authors: Bogdanski D. F.
Published: January 2005

A Ca++‐dependent secretion of norepinephrine ([3H]NE) was evoked in adrenergic nerve endings in rat heart ventricle slices incubated in a modified KrebsHCO3 medium containing choline C1 as the replacement for NaC1 (Ch+‐Ca++). Exogenous ATP inhibited secretion and lithium ion, a known inhibitor of NE uptake dependent upon Mg++‐ATPase activity in vesicles (but not ouabain) prevented the response to ATP (Bogdanski, 1983, 1986). It was suggested that vesicles attached to the axolemma recaptured[3H]NE from the extracellular fluid. This report indicates that other known inhibitors of uptake in isolated vesicles also inhibited the response to ATP in the attached vesicles. Included were two inhibitors of Mg++‐ATPase activity, N‐ethylmaleimide (NEM) and dicyclohexylcarbodiimide (DCCD), and the proton transporters 2,4‐dinitrophenol (2,4‐ DNP 1.0 mM) and chlorpromazine (CPZ). Potassium ionophores (valinomycin with 2,4‐DNP 0.1 mM and, nigericin) and a pH neutralizing reagent for vesicles (NH3 from ammonium sulfate in solution) were also effective. The uptake inhibitors, except 2,4‐DNP, could also increase the rate of depletion of stored NE and its deamination in nonsecreting nerve endings incubated in Krebs‐HCO3 (KRB) medium. Valinomycin by itself stimulated uptake in the presence of ATP. It is sugested that mechanisms of uptake and retention of NE in isolated vesicles (symposium (1982) Fed. Proc. 41:2742–2780) apply to the axoplasmic vesicles as well. Thus, the activity of Mg++‐ATPase drives proton transport to establish the electrochemical gradients of H+, which drive the transport of NE. A lowering of the gradients can mobilize amines and evoke secretion. However, isolated vesicles in the presence of ATP and C1− eventually take up a sufficient number of ions to cause osmotic lysis. By contrast, exocytosis was not biochemically apparent in the model vesicular‐axolemmal secretory and transmitter recovery unit.
Substance P‐mediated membrane currents in voltage‐clamped guinea pig inferior mesenteric ganglion cells
Authors: Griffith William H. , Hills Judith M. , Brown David A.
Published: January 2005

Responses to substance P (SP) and to hypogastric nerve stimulation were recorded from voltage‐clamped guinea pig inferior mesenteric ganglion (IMG) neurons, and compared with those to muscarine. Muscarine produced a voltage‐dependent inward current accompanied by a reduced input conductance and inhibition of IM a time‐ and voltage‐dependent K+‐current (Brown and Adams: Nature 283:673–676, 1980). SP also produced an inward current, accompanied by a fall in input conductance (20 out of 31 cells) or a rise in input conductance (7 out of 31 cells). The fall in input conductance was not accompanied by an inhibition of M‐current (unlike frog ganglia: Adams et al.: British Journal of Pharmacology 79:330–333, 1983) or an inhibition of the inward rectifier current (unlike globus pallidus neurons: Stanfield et al.: Nature 315:498–501, 1985). Repetitive hypogastric nerve stimulation (10–20 Hz, 2–10 s) produced a slow inward postsynaptic current lasting 1–3 min, with decreases or increases of input conductance matching those produced by SP. The postsynaptic current did not show a consistent or reproducible change in amplitude on varying the holding potential between ‐90 and ‐25 mV. It is concluded that SP and hypogastric stimulation produce complex and variable changes in ionic conductance in IMG neurons.
A1 Noradrenergic action on medial preoptic‐medial septal neurons: A neuropharmacological study
Authors: Kim Yang I. , Dudley Carol A. , Moss Robert L.
Published: January 2005

In an attempt to determine whether the excitatory and inhibitory orthodromic responses of single medial preoptic‐medial septal (MPO‐S) neurons to discrete electrical stimulation of the A1 noradrenergic region were mediated specifically by norepinephrine (NE) and involved different types of adrenoreceptors, a series of electrophysiological and neuropharmacological experiments was conducted. Extracellular single unit recording and local drug application techniques were used in female rats under urethane anesthesia. Chemical lesion of the catecholaminergic nerve terminal plexus in the medial preoptic area with 6‐hydroxydopamine abolished both excitatory and inhibitory orthodromic effects of A1 region stimulation on MPO‐S neurons, suggesting the noradrenergic nature of the effects. This conclusion was corroborated by the observation that the orthodromic effects were mimicked by locally applied exogenous NE. The excitatory effects were reliably mimicked by a low concentration of NE (0.5 mM; in‐barrel concentration) and methoxamine (1.0 mM, an alpha‐1 agonist), but not by either low or high concentration (1 and 100 mM) of clonidine (an alpha‐2 agonist) and isoproterenol (a beta agonist). The inhibitory orthodromic effects of A1 region stimulation were reliably mimicked by a high concentration of NE (50 mM), clonidine (100 mM) and isoproterenol (100 mM), but not by a low concentration of NE (0.5 mM), methoxamine (1mM), clonidine (1 mM) or isoproterenol (1 mM). A high concentration (100 mM) of methoxamine mimicked the inhibitory effects less than 40% of the time. The low concentration (0.5 mM) NE‐induced excitation that matched the excitatory orthodromic effect of A1 region stimulation was blocked by phentolamine (100 mM), an alpha blocker, but not by timolol (100 mM), a beta blocker. On the other hand, the high concentration (50 mM) NE‐induced inhibition that matched the inhibitory orthodromic effect of A1 region stimulation was blocked by timolol, but not by phentolamine.

Taken together, the present results are consistent with the hypothese that the ascending noradrenergic projections from the A1 region affect the excitability of MPO‐S neurons directly through NE and that the excitatory and inhibitory orthodromic effects involve different types of adrenoreceptors, i.e., alpha‐1 and beta receptors, respectively.
Organization of dopamine D1 and D2 receptors in human striatum: Receptor autoradiographic studies in Huntington's disease and schizophrenia
Authors: Joyce Jeffrey N. , Lexow Nedra , Bird Edward , Winokur Andrew
Published: January 2005

The technique of quantitative autoradiography was used to examine the effects of Huntington's disease (HD) and schizophrenia on the organization of striatal dopamine (DA) D1 and D2 receptors. Whereas the striatum of HD cases showed a reduction in the density of D1 ([3H]SCH 23390) and D2 ([3H]spiroperidol) receptors, the patterning of D2 receptor loss did not match that of the D1 receptor loss. The HD loss of D1 D1 receptors (65%) is far greater than the loss of D2 receptors (28%). Whereas there was a dorsal‐ventral gradient of effect on both receptor subtypes, the effects of HD on D2 receptors in the ventral putamen (PUT) and nucleus accumben septi (NAS) were minimal. Similarly, muscarinic M1 and M2 receptors demonstrate different patterns of alteration in HD. The M2 subtype, labeled with [3H]N‐methylscopolamine (in the presence of excess pirenzepine to occlude M1 sites), was depleted far more than the M1 receptor subtype, labeled with [3H]pirenzepine. Although the effects of HD on [3H]mazindol labeling of DA terminals were more heterogeneous, there appeared to be a relative preservation of this afferent input to the striatum of the HD cases. In the schizophrenic cases, our autoradiographic studies confirm previous reports of an elevation of D2 receptor density in the striata of many schizophrenics. This increase was evident even though two of the three cases were known to have not been treated with neuroleptics, and the third case may also have been drug naive. however, the increase was far greater in the NAS (164%) and ventral PUT (173%) than more dorsally in the striatum (68%). The density of D1 receptors and DA terminals labeled with [3H]mazindol in the striatum of schizophrenics was not significantly different from that of control cases. Thus in both HD and schizophrenia, the ratio of D2/D1 receptors is altered in favor of the D2 population, particularly in the NAS.
Norepinephrine stimulation of adenylate cyclase potentiates protein kinase C action: Electrophysiological studies in the dentate gyrus
Authors: Stratton Kathleen R. , Baraban Jay M. , Worley Paul F.
Published: January 2005

Protein kinase C and norepinephrine‐stimulated adenylate cyclase have been linked to formation of long‐term potentiation in the dentate gyrus. However, little is known about second messenger system interactions regulating synaptic transmission. In electrophysiological studies of the dentate gyrus, we observe synergistic interactions between norepinephrine and phorbol esters, activators of protein kinase C. Norepinephrine markedly potentiates the block of adenosine's inhibitory action by phorbol esters. Norepinephrine's action is mimicked by the β‐adrenoceptor agonist isoproterenol and blocked by the β‐adrenoceptor antagonists timolol and propranolol. Forskolin also mimicks norepinephrine's action. Accordingly, norepinephrine's potentiation of protein kinase C appears to be mediated by the cyclic AMP second messenger system. This mechanism may contribute to norepinephrine's facilitation of long‐term potentiation in the dentate gyrus.
Reciprocal zones of excitation and inhibition in the neostriatum
Authors: Rebec George V. , D. Curtis Stephen
Published: January 2005

Single‐unit activity was recorded in the rat neostriatum at different distances from the point of an infusion of either glutamate or serotonin. In each case, firing rate at the distant site (0.8–1.5 mm) was the mirror image of that at the near site (0.1–0.3 mm). These reciprocal changes were blocked by a subsequent injection of haloperidol, a dopamine antagonist. It appears that a lateral inhibitory network, intrinsic to the neostriatum and possibly modulated by dopamine, plays an important role in the operation of the neostriatum.
Cocaine: An in vivo microdialysis evaluation of its acute action on dopamine transmission in rat striatum
Authors: Hurd Yasmin L. , Ungerstedt Urban
Published: January 2005

The effects of cocaine on dopamine (DA) neurotransmission were evaluated by in vivo microdialysis in the striatum of halothane‐anesthetized rats. Intravenous cocaine produced a dose‐dependent, transient increase of the extracellular concentration of DA, with a peak response within 10 min and a return to control level by 30 min. The sharp DA response pattern was abolished in a calcium‐free environment, indicating that DA release enhanced by cocaine originates from a vesicular storage pool. Continuous administration of cocaine (via the perfusion medium) directly into the nigrostriatal terminal region also produced a dose‐dependent increase in DA release. Low concentrations (10−5 M and 10−6 M) of cocaine maintained DA at a constant stable level, consistent with the effects observed after potent DA uptake inhibitory agents (e.g., nomifensine and Lu19005). However, continuous exposure to high concentrations (< 10−4 M) induced a transient elevation of DA within 20 min, following which DA decreased to a stable but high level; this decrease might reflect tolerance to the effect of cocaine. Administration of cocaine (10−3 M) into the substantia nigra did not change striatal DA release. The local striatal action of cocaine was less potent than amphetamine in elevating DA overflow and in its effect on DA metabolism. These findings suggest that the fast transient enhancement of DA by intravenous cocaine is most likely a consequence of the transient presence of cocaine in the terminal region, correlating with the well‐known rapid pharmacokinetic and behavioral aspects of the drug.
Cocaine alters opiate receptor binding in critical brain reward regions
Authors: Hammer Ronald P.
Published: January 2005

Brain reward systems are thought to be involved in the reinforcing effect of both cocaine and opiates. In vitro receptor autoradiography was used to determine the effect of chronic, continuous cocaine exposure of 2 weeks duration on [3H]naloxone binding in various regions of rat brain. Although cocaine action in the central nervous system is usually associated with altered dopamine function, we observed that opiate receptor density as labeled by [3H]naloxone was altered by chronic cocaine exposure in critical brain reward regions, including the nucleus accumbens, ventral pallidum, and lateral hypothalamus. Endogenous opioid activity at opiate receptors in these critical regions may be associated with the reinforcement induced by both cocaine and opiates.
Rate‐limiting step for transmission at excitatory synapses in hippocampus
Authors: Muller Dominique , Lynch Gary
Published: January 2005

To examine mechanisms that might be responsible for limiting transmission at excitatory synapses in hippocampus, we analyzed the relationship between extracellular calcium concentrations (1‐6 mM) and postsynaptic responses in field CA1 of hippocampal slices using low stimulation intensities and a paired‐pulse paradigm. Three effects were observed

One, the relationship between calcium levels and the slope (or amplitude) of the postsynaptic response was described by a sigmoidal function with an asymptote at about 4 mM. Double reciprocal pilots relating calcium concentration to the initial slope of EPSPs provided evidence for the cooperativity expected between calcium ions and transmitter release.

Two, both the rise time and half‐decay time of the postsynaptic responses were reduced with increasing calcium concentrations. These effects of calcium were more pronounced on the first response elicited by paired‐pulse stimulation and were considerably attenuated by 2 μM bicuculline, indicating that feed‐forward inhibition was positively related to calcium concentration and differentially activated by repetitive stimulation. However, inhibition was not responsible for the asymptotic relationship observed between calcium and response size.

Three, while increasing the calcium concentration beyond 4 mM did not further affect the initial slope of excitatory postsynaptic potentials (EPSPs), paired‐pulse facilitation and 4‐aminopyridine were still effective in increasing response size. These results suggest (1)that neither the number of postsynaptic receptors nor the number of transmitter quanta available for release were limiting transmission as a function of the calcium concentration; and (2)that calcium entry into presynaptic terminals was likely to represent the limiting step under the conditions used.
Cholinergic modulation of frequency receptive fields in auditory cortex: II. Frequency‐specific effects of anticholinesterases provide evidence for a modulatory action of endogenous Ach
Authors: Ashe John H. , McKenna Thomas M. , Weinberger Norman M.
Published: January 2005

Exogenously applied muscarinic agonists—for example, acetylcholine (ACh) and acetyl‐beta‐methacholine (MCh)—modify frequency receptive fields in auditory cortex of unanesthetized animals in a frequency‐specific rather than global manner. The present study sought to relate these findings to endogenous actions of ACh by using the anticholinesterase agents eserine sulphate and soman (0‐1,2,2‐trimethylpropylmethylphosphonofluoridate) to facilitate the effects of endogenous ACh. Frequency receptive fields (FRF) were determined by presenting sequences of different isointensity tones before, during, and after application of ACh, MCh, eserine, or soman; also the cholinesterase blockers were applied between applications of ACh or MCh. The major effects produced by the inhibitors were similar to those of the agonists. Predominant effects were frequency‐specific changes in FRF. Further, eserine and soman, similar to ACh and MCh, produced shifts in the best frequency (BF) of FRF due mainly to coordinated depression of responses to the BF and increased responses to adjacent, non‐BF. The results indicate that exogenous and endogenous ACh, acting via muscarinic receptors, can significantly influence the physiological functioning of cortical neurons and consequently their processing of sensory information.
Ultrastructural description of taurine‐like immunoreactive cells and processes in the rat hippocampus
Authors: Clements Jane Reichert , Magnusson Kathy Ruth , Beitz Alvin James
Published: January 2005

A monoclonal antibody against taurine conjugated to KLH was used to identify and describe taurine‐like immunoreactive processes in the rat hippocampus. Tissue from perfused rats was processed for immunohistochemical visualization of taurine and embedded for electron microscopy. Representative tissue samples from three regions, the dentate gyrus, CA3, and CA1, were sectioned, examined, and photographed. In the dentate gyrus, both granule cells and pyramidal basket cells were taurine‐like immunoreactive. Some axon terminals in the dentate gyrus molecular layer as well as some mossy fiber boutons in the hilus were also taurine‐like immunoreactive. In the CA3 region both pyramidal neurons and glial cells were taurine‐like immunoreactive. A few small‐diameter axon terminals in stratum radiatum and some mossy fiber boutons in stratum lucidum were taurine‐like immunoreactive. In CA1, pyramidal neurons and some glia were intensely taurine‐like immunoreactive. A few immunoreactive axon terminals were seen in stratum radiatum and stratum oriens. In all regions, dendritic staining predominated. Our results support the hypothesis that while taurine may act as a neurotransmitter in a small portion of hippocampal terminals, its main function is probably as a neuromodulator or ionic regulator.
Differential effect of cocaine on extracellular dopamine levels in rat medial prefrontal cortex and nucleus accumbens: Comparison to amphetamine
Authors: Moghaddam Bita , Bunney Benhamin S.
Published: January 2005

The technique of in vivo microdialysis was used to measure the extracellular levels of dopamine in the nucleus accumbens septi and medial prefrontal cortex of chloral‐hydrate‐anaesthetized rats following systemic administration of cocaine and amphetamine. Intravenous injection of cocaine increased the extracellular levels of dopamine in the medial prefrontal cortex and the nucleus accumbens septi in a dose‐dependent manner. However, the magnitude of increase was significantly greater in nucleus accumbens than in medial prefrontal cortex. In comparison to cocaine, amphetamine increased the extracellular levels of dopamine in the nucleus accumbens and medial prefrontal cortex to the same degree. Based on the relatively small increase of extracellular dopamine levels in medial prefrontal cortex by cocaine, it is postulated that dopaminergic innervation of other structures besides medial prefrontal cortex may be involved in maintenance of cocaine self‐administration.