bluuebunny/crossref_metadata_2025_split huggingface dataset:
Prostacyclin and Thromboxane Synthase: New Aspects of Hemethiolate Catalysis
Authors: Ullrich Volker , Brugger Roland 
Published: December 2003

AbstractThe arachidonic acid metabolites thromboxane A2 and prostacyclin are highly potent regulators of cell physiology. They are both formed by enzymatic rearrangement of the 9,11‐epidioxy prostaglandin H2 catalyzed, however, by thromboxane and prostacyclin synthase, respectively. The two enzymes have been isolated, sequenced, and characterized as hemethiolate (“P450”) enzymes. The different isomerization products can be explained on the same catalytic principle by a different ligation of the heme centers with the two epidioxy oxygens atoms. This requires different conformations for substrate binding at the active site, which is substantiated by the different inhibitors and amino acid sequences of the enzymes. In a hypothesis which has mechanistic principles in common with the P450‐monooxygenases and the allene oxide synthases, oxy radicals are formed first and rearrange to carbon radicals. These could then rapidly be converted into carbocations by the ferrylthiolate or iron(III)thiyl structures formed as intermediates.
Thermal and Optical Switching of Iron(II) Complexes
Authors: Gütlich Philipp , Hauser Andreas , Spiering Hartmut 
Published: December 2003

AbstractTransition metal chemistry contains a class of complex compounds for which the spin state of the central atom changes from high spin to low spin when the temperature is lowered. This is accompanied by changes of the magnetic and optical properties that make the thermally induced spin transition (also called spin crossover) easy to follow. The phenomenon is found in the solid state as well as in solution. Amongst this class, iron(II) spin crossover compounds are distinguished for their great variety of spin transition behavior; it can be anything from gradual to abrupt, stepwise, or with hysteresis effects. Many examples have been thoroughly studied by Mössbauer and optical spectroscopy, measurements of the magnetic susceptibilities and the heat capacities, as well as crystal structure analysis. Cooperative interactions between the complex molecules can be satisfactorily explained from changes in the elastic properties during the spin transition, that is, from changes in molecular structure and volume. Our investigations of iron(II) spin crossover compounds have shown that green light will switch the low spin state to the high spin state, which then can have a virtually unlimited lifetime at low temperatures (this phenomenom is termed light‐induced excited spin state trapping—acronym: LIESST). Red light will switch the metastable high spin state back to the low spin state. We have elucidated the mechanism of the LIESST effect and studied the deactivation kinetics in detail. It is now well understood within the theoretical context of radiationless transitions. Applications of the LIESST effect in optical information technology can be envisaged.
Novel High‐Performance Ceramics—Amorphous Inorganic Networks from Molecular Precursors
Authors: Baldus Hans‐Peter , Jansen Martin 
Published: December 2003

AbstractMaterials research is an interdisciplinary field in which engineers and physical scientists work together. Since the major binary oxides, nitrides, and carbides, which are currently used as high‐performance ceramics, were discovered in the last century, the role of chemistry in the development of materials has become barely noticeable. This has changed only in the recent past as, for example, purity and defined morphology of starting powders were recognized as crucial parameters for enhancing the reliability of ceramic workpieces. While the application of chemical methods led to gradual–though significant–improvements, the true potential of chemistry lies rather in the exploitation of new chemical systems and the development of new preparative routes to already known materials. Such an approach is the preparation of ceramics from molecular or polymeric precursors. Herein we survey the most important contributions to those preparative routes starting from the pioneering work in the 1960s and the 1970s; a certain emphasis is placed on the concepts that we have applied to the preparation of multinary, nonoxide materials and amorphous inorganic networks. The name “amorphous high‐performance ceramics” is in fact a contradiction in terms. Such materials are thermodynamically unstable with respect to the transformation or decomposition to crystalline phases, thus excluding their application in sensitive areas at high temperatures. However, the selection of element combinations for which the binding energies are derived from strong, local covalent bonds and which are therefore less dependent on a long‐range crystalline order, can yield amorphous materials of remarkable thermal and mechanical durability. This is exemplified by novel quaternary ceramics in the Si/B/N/C system, for which an efficient synthesis, starting from raw materials suitable for industrial production, has been developed. For instance, a material of the composition SiBN3C remains amorphous up to 1900°C, which is unique, and, with respect to oxidation, is the most stable nonoxide ceramic known to date. Another advantage of this in several respects unsurpassed material is the simple way, in which the viscosity of the polymeric precursors can be adjusted to various methods of shaping. So far infiltrations and coatings have been realized. Most developed is the preparation of fibers, which in terms of their performance characteristics are significantly better than those currently available.
Adsorption of Gases on Complex Solid Surfaces
Authors: Freund Hans‐Joachim 
Published: December 2003

AbstractDuring the last thirty years the research field of surface science with its various disciplines has progressively played a more and more important role in the field of catalysis. The main focus of attention for a long time was research on metal surfaces, on which, in time, the whole spectrum of developed surface analytical methods was applied. This led to a better understanding of the mechanisms of catalytic reaction, such as the synthesis of ammonia and the oxidation of CO, especially through the work of Gerhard Ertl.[1, 2] In contrast to clean metal surfaces, surfaces of real catalysts are complex entities, the structures of which can have a strong influence on the processes occurring on the surface. Thus, it seems logical to employ the typical structural characteristics and the morphology of the catalytic surface as guidelines in the investigation of complex model systems. In this review the preparation, and structural and electronic characterization of such model systems will be dicussed. Clean surfaces of catalytically active oxides, as well as model systems for dispered transition metal/support catalysts will be characterized in terms of their morphology and electronic structure as well as their adsorption and reaction capabilities.
Unprecedented Layered Structure of a Fulleride: Synthesis, Structure, and Magnetic Properties of a Potassium‐Containing Salt with a C Counterion
Authors: Fässler Thomas F. , Spiekermann Annette , Spahr Michael E. , Nesper Reinhard 
Published: December 2003

AbstractFor corrigendum see DOI:10.1002/anie.199709511For corrigendum see DOI:10.1002/anie.199713711
Organometallic Homogeneous Catalysis—Quo vadis?
Authors: Herrmann Wolfgang A. , Cornils Boy 
Published: December 2003

AbstractHomogeneous catalysis is the success story of organometallic chemistry. Otto Roelen's initial discovery of hydroformylation in 1938 not only entailed large‐capacity production plants but was later followed by systematic research into the catalytic chemistry of the ever‐growing class of organometallic compounds. Further developments in industrial chemistry towards clean, low‐temperature, low‐pressure, and economic processes—in feedstock or in the fine chemicals and polymer area—clearly depend on improved catalysts. Molecularly defined, tailor‐made structures are the safest prerequisites for chemical selectivity; hence, organometallic compounds with their overwhelming variety of compositions and structures offer the most promising approach. Wilkinson's catalysts [HRh(CO){P(C6H5)3] and [ClRh{P(C6H5)}3}3] are outstanding examples. On the other hand, process technology has to be considered also (for example catalyst‐product separation and hear‐exchange problems). The following review attempts to critically assess the future trends and present demands in the applied area of orgnometallic catalysis–a “gentle art” that is far from being a mature field.
Play deprivation without social isolation: Housing controls
Authors: Holloway Kevin S. , Suter Robert B. 
Published: December 2003

AbstractThree experiments were conducted to control for the effects of housing conditions during play deprivation on subsequent play rebound in periadolescent rats. To address play deprivation without the confound of social isolation, in Experiment 1 pairs of subjects were housed either in cages divided by wire mesh that allowed for olfactory, visual, auditory, and tactile interactions with a same‐sex agemate but prevented rough and tumble play or in standard cages. Running wheels were provided to similarly housed subjects in Experiment 2 to control for the ability to engage in physical activity. In Experiment 3, standard and brooder cages were used to control for the effects of housing area. Play‐deprived subjects in all conditions showed a greatly increased number of play responses immediately following deprivation. The results from these experiments more clearly indicate that the absence of play is the crucial feature that brings about play rebound following deprivation. © 2003 Wiley Periodicals, Inc. Dev Psychobiol 44: 58–67, 2004.
Working memory and inhibitory control in early childhood: Contributions from physiology, temperament, and language
Authors: Wolfe Christy D. , Bell Martha Ann 
Published: December 2003

AbstractThis study examined the cognitive skills of working memory and inhibitory control (WMIC) in relation to physiological functioning, temperament, and language in early childhood. WMIC skills were assessed in twenty‐five 4½‐year‐old children using the day–night Stroop‐like task and the yes–no task; each task required the child to remember two rules and to inhibit a dominant response. Electroencephalogram (EEG) and heart period (HP) were recorded during baseline and WMIC tasks. An increase in 6‐ to 9‐Hz EEG power from baseline to task was found for the medial frontal region. In addition, a decrease in HP (i.e., an increase in heart rate) was found from baseline to task. Associations were found between performance on the WMIC tasks and scales of the Children's Behavioral Questionnaire (CBQ) related to the effortful control of behavior. The Peabody Picture Vocabulary Test‐III (PPVT‐III) distinguished between high and low WMIC performance. Results of a discriminant function analysis indicated that physiology, temperament, and language were able to correctly predict 90% of WMIC performance. © 2003 Wiley Periodicals, Inc. Dev Psychobiol 44: 68–83, 2004.
Expression and functional properties of group I metabotropic glutamate receptors in bovine chromaffin cells
Authors: Arce C. , del Campo A.B. , Figueroa S. , López E. , Aránguez I. , Oset‐Gasque M.J. , González M.P. 
Published: December 2003

AbstractWe demonstrate the presence and functional properties of Group I metabotropic glutamate receptors (mGluRs) expressed in chromaffin cells. Immunocytochemical techniques revealed that two mGluR subtypes (mGluR1α and mGluR5) are expressed in chromaffin cells, located in both the cytoplasmic membrane and the cytosol surrounding the nucleus. These mGluRs are functionally active on catecholamine (CA) secretion in chromaffin cells because both (1S, 3R)‐1‐aminocyclopentane‐1,3‐dicarboxylic acid (t‐ACPD) and the specific agonist of Group I mGluRs, (S)‐3,5‐dihydroxyphenylglycine (DHPG), were able to stimulate the release of CAs (adrenaline and noradrenaline) in a dose‐response manner. These effects were specifically reversed by L‐(+)‐2‐amino‐3‐phosphonopropionic acid (L‐AP3), a selective antagonist of the Group I metabotropic glutamate receptors. t‐ACPD induced an increase in CA secretion in both the presence and absence of extracellular calcium, the former effect being accompanied by cell membrane depolarization. Noradrenaline (NA) release was higher in the presence of extracellular calcium than in its absence, whereas adrenaline release was of the same order under both conditions. These results indicate that different subtypes of Group I mGluRs are present in noradrenergic and adrenergic cells. Fluorescence imaging techniques in single cells showed different t‐ACPD‐induced increases in intracellular calcium in different chromaffin cells: in chromaffin cells, 67% expressed functional metabotropic glutamate receptors and with nicotinic receptors, whereas the remaining 33% expressed only nicotinic receptors. In the absence of external calcium, only about 25% of cells responded to t‐ACPD‐increased intracellular calcium by increasing inositol 1,4,5‐trisphosphate (IP3) concentration and subsequent calcium mobilization from intracellular stores, whereas the remaining 75% increased intracellular calcium by promoting Ca2+ influx from the extracellular medium through L‐ and N‐ but not P/Q voltage‐dependent calcium channels. © 2003 Wiley‐Liss, Inc.
Retinoic acid‐induced neuritogenesis of human neuroblastoma SH‐SY5Y cells is ERK independent and PKC dependent
Authors: Miloso Mariarosaria , Villa Daniela , Crimi Marco , Galbiati Stefania , Donzelli Elisabetta , Nicolini Gabriella , Tredici Giovanni 
Published: December 2003

AbstractRetinoic acid (RA), an active metabolite of vitamin A, is a natural morphogen involved in development and differentiation of the nervous system. To elucidate signaling mechanisms involved in RA‐induced neuritogenesis, we used human neuroblastoma SH‐SY5Y cells, an established in vitro model for studying RA action, to examine the role of extracellular signal‐regulated kinase (ERK) 1 and 2 in RA‐induced neuritogenesis and cell survival. From immunoblotting experiments, we observed that RA induced delayed but persistent ERK1 and ERK2 phosphorylation (until 96 hr) that was reduced significantly by the specific mitogen‐activated protein kinase (MAPK)/ERK kinase (MEK) inhibitor U0126. For the subsequent studies we chose 24 hr as the reference time. Inhibition of ERK activation did not affect RA‐induced neuritogenesis (percentage of neurite‐bearing cells and neurite length) but significantly reduced cell survival. In addition, we analyzed the signaling pathway that mediates ERK activation. Our results suggest that RA‐induced ERK phosphorylation does not follow the classic Raf kinase‐dependent pathway. Protein kinase C (PKC) and phosphatidylinositol 3‐kinase (PI 3‐K) are possible alternative kinases involved in the ERK signaling pathway. In fact, in the presence of the specific PKC inhibitor GF 109203X, or the specific PI 3‐K inhibitor wortmannin, we observed a significant dose‐dependent reduction in ERK phosphorylation. RA‐induced neuritogenesis and cell survival were reduced by GF 109203X in a concentration‐dependent manner. These results suggest that rather than ERK1 and ERK2, it is PKC that plays an important role during early phases of RA‐induced neuritogenesis. © 2003 Wiley‐Liss, Inc.
Repetitive transcranial magnetic stimulation improves open field locomotor recovery after low but not high thoracic spinal cord compression‐injury in adult rats
Authors: Poirrier Anne‐Lise , Nyssen Yves , Scholtes Felix , Multon Sylvie , Rinkin Charline , Weber Géraldine , Bouhy Delphine , Brook Gary , Franzen Rachelle , Schoenen Jean 
Published: December 2003

AbstractElectromagnetic fields are able to promote axonal regeneration in vitro and in vivo. Repetitive transcranial magnetic stimulation (rTMS) is used routinely in neuropsychiatric conditions and as an atraumatic method to activate descending motor pathways. After spinal cord injury, these pathways are disconnected from the spinal locomotor generator, resulting in most of the functional deficit. We have applied daily 10 Hz rTMS for 8 weeks immediately after an incomplete high (T4–5;n= 5) or low (T10–11;n= 6) thoracic closed spinal cord compression‐injury in adult rats, using 6 high‐ and 6 low‐lesioned non‐stimulated animals as controls. Functional recovery of hindlimbs was assessed using the BBB locomotor rating scale. In the control group, the BBB score was significantly better from the 7th week post‐injury in animals lesioned at T4–5 compared to those lesioned at T10–11. rTMS significantly improved locomotor recovery in T10–11‐injured rats, but not in rats with a high thoracic injury. In rTMS‐treated rats, there was significant positive correlation between final BBB score and grey matter density of serotonergic fibres in the spinal segment just caudal to the lesion. We propose that low thoracic lesions produce a greater functional deficit because they interfere with the locomotor centre and that rTMS is beneficial in such lesions because it activates this central pattern generator, presumably via descending serotonin pathways. The benefits of rTMS shown here suggest strongly that this non‐invasive intervention strategy merits consideration for clinical trials in human paraplegics with low spinal cord lesions. © 2003 Wiley‐Liss, Inc.
Subpopulations of rat dorsal root ganglion neurons express active vesicular acetylcholine transporter
Authors: Tata Ada Maria , De Stefano M. Egle , Srubek Tomassy Giulio , Vilaró M. Teresa , Levey Allan I. , Biagioni Stefano 
Published: December 2003

AbstractThe vesicular acetylcholine transporter (VAChT) is a transmembrane protein required, in cholinergic neurons, for selective storage of acetylcholine into synaptic vesicles. Although dorsal root ganglion (DRG) neurons utilize neuropeptides and amino acids for neurotransmission, we have previously demonstrated the presence of a cholinergic system. To investigate whether, in sensory neurons, the vesicular accumulation of acetylcholine relies on the same mechanisms active in classical cholinergic neurons, we investigated VAChT presence, subcellular distribution, and activity. RT‐PCR and Western blot analysis demonstrated the presence of VAChT mRNA and protein product in DRG neurons and in the striatum and cortex, used as positive controls. Moreover, in situ hybridization and immunocytochemistry showed VAChT staining located mainly in the medium/large‐sized subpopulation of the sensory neurons. A few small neurons were also faintly labeled by immunocytochemistry. In the electron microscope, immunolabeling was associated with vesicle‐like elements distributed in the neuronal cytoplasm and in both myelinated and unmyelinated intraganglionic nerve fibers. Finally, [3H]acetylcholine active transport, evaluated either in the presence or in the absence of ATP, also demonstrated that, as previously reported, the uptake of acetylcholine by VAChT is ATP dependent. This study suggests that DRG neurons not only are able to synthesize and degrade ACh and to convey cholinergic stimuli but also are capable of accumulating and, possibly, releasing acetylcholine by the same mechanism used by the better known cholinergic neurons. © 2003 Wiley‐Liss, Inc.
Water maze learning and forebrain mRNA expression of the neural cell adhesion molecule L1
Authors: Venero César , Tilling Thomas , Hermans‐Borgmeyer Irm , Herrero Ana I. , Schachner Melitta , Sandi Carmen 
Published: December 2003

AbstractL1 and NCAM, two cell adhesion molecules of the immunoglobulin superfamily, have been implicated in the formation of neural circuits, synaptic plasticity, and cognitive function. In this study, we sought to investigate whether differences in the steady‐state levels of L1 and NCAM expression in specific brain regions could account for individual differences in learning abilities. Using adult male Wistar rats, we evaluated mRNA levels of L1, NCAM, and the NCAM180 isoform in different brain regions (hippocampus, thalamus, striatum, prefrontal and frontal cortices) immediately after submitting rats to a massed training protocol in the water maze. The results showed that untrained and trained rats exhibited similar levels of mRNA for these molecules, which supports the view that training did not influence their immediate level of expression. However, in most of the brain regions we investigated (with the exception of prefrontal and frontal cortices), L1 mRNA levels were positively correlated with the latency to find the hidden platform in the water maze task and with posttraining plasma corticosterone levels. However, no correlations were observed for total NCAM or NCAM180 mRNA in the brain regions examined in this study. Given that animals with a slower spatial acquisition curve exhibited more anxiety‐like responses, including thigmotactic behavior in the water maze and increased corticosterone levels, and that recent genetic studies indicate a role for L1 in anxiety, the current findings suggest a relationship among L1, anxiety, and cognitive processes. © 2003 Wiley‐Liss, Inc.
Axonal transport and neuronal transcytosis of trophic factors, tracers, and pathogens
Authors: von Bartheld Christopher S. 
Published: December 2003

AbstractNeurons can specifically internalize macromolecules, such as trophic factors, lectins, toxins, and other pathogens. Upon internalization in terminals, proteins can move retrogradely along axons, or, upon internalization at somatodendritic domains, they can move into an anterograde axonal transport pathway. Release of internalized proteins from neurons after either retrograde or anterograde axonal transport results in transcytosis and trafficking of proteins across multiple synapses. Recent studies of binding properties of several such proteins suggest that pathogens and lectins may utilize existing transport machineries designed for trafficking of trophic factors. Specific pathways may protect trophic factors, pathogens, and toxins from degradation after internalization and may target the trophic or pathogenic cargo for transcytosis after either retrograde or anterograde transport along axons. Elucidating the molecular mechanisms of sorting steps and transport pathways will further our understanding of trophic signaling and could be relevant for an understanding and possible treatment of neurological diseases such as rabies, Alzheimer's disease, and prion encephalopathies. At present, our knowledge is remarkably sparse about the types of receptors used by pathogens for trafficking, the signals that sort trophins or pathogens into recycling or degradation pathways, and the mechanisms that regulate their release from somatodendritic domains or axon terminals. This review intends to draw attention to potential convergences and parallels in trafficking of trophic and pathogenic proteins. It discusses axonal transport/trafficking mechanisms that may help to understand and eventually treat neurological diseases by targeted drug delivery. © 2003 Wiley Periodicals, Inc. J Neurobiol 58: 295–314, 2004