bluuebunny/crossref_metadata_2025_split huggingface dataset:
Selective fasciculation as a mechanism for the formation of specific chemical connections between Aplysia neurons in vitro
Authors: Hawver David B. , Schacher Samuel 
Published: May 2005

AbstractSelective fasciculation of growth cones along preestablished axon pathways expressing matching or complementary adhesion molecules is thought to be an important strategy in axon guidance. Growth cone inhibiting factors also appear to influence pathfinding decisions. We have used identified Aplysia neurons in vitro to explore the hypothesis that similar mechanisms could be involved in target selection. Co‐cultures of L10 neurons with RB neuron targets or R2 neurons with RUQ neuron targets reliably formed chemical connections. In contrast, co‐cultures of L10 with RUQ targets usually failed to form detectable chemical connections unless cell–cell contact was forced during plating by intertwining the major axons. These data suggested that differences in the ability to form cell–cell contacts might underlie the observed synaptic specificity. This notion was supported when fluorescent dye fills of L10 and R2 revealed a positive correlation between the amount of target contact and the frequency of synapse formation: L10–RUQ cultures showed much less target contact than L10–RB or R2–RUQ cultures. To examine the cellular mechanisms of these differences in target contact, presynaptic growth cones were observed as they interacted with target processes. L10–RUQ cultures showed much less fasciculation and more avoidance behavior compared to L10–RB and R2–RUQ cultures. This initial specificity suggested that the differences in amount of target contact arose through selective fasciculation and avoidance rather than through selective elimination after indiscriminate fasciculation. Selective fasciculation and avoidance might, therefore, aid in target selection by regulating the amount of contact between presynaptic processes and potential target cells. © 1993 John Wiley & Sons, Inc.
Formation of functional synapses by regenerating adult rat retinal ganglion cell axons in midbrain target regions in vitro
Authors: Bähr Mathias , Eschweiler Gerhard W. 
Published: May 2005

AbstractThe ability of adult rat retinal ganglion cell (RGC) axons to reinnervate normal target regions was examined in vitro. In co‐culture experiments, adult rat retinal explants were placed adjacent to fetal rat midbrain sections that contained the superior colliculus (SC) which is the main target for RGC axons. Adult rat RGCs regrew axons over more than 500 μm on a polylysine‐laminin substrate to reach the co‐cultured explants. By using neurofilament immunohistochemistry and the fluorescent dye Dil for anterograde and retrograde tracing, it was shown that (1) adult rat RGCs with a stereotyped morphology survived in explant cultures for more than 4 weeks in the presence of fetal midbrain explants, (2) regenerating RGC axons preferentially terminated within midbrain target regions, and (3) RGCs formed functional synapses. In addition, the maturation of the SC region in midbrain explants was examined histologically and ultrastructurally to demonstrate appropiate target development. © 1993 John Wiley & Sons, Inc.
Amitriptyline inhibits neurite outgrowth in chick cerebral neurons: A possible mechanism
Authors: Wong Ka L. , Chuang Tzu Y. , Bruch Richard C. , Farbman Albert I. 
Published: May 2005

AbstractPrevious studies showed that amitriptyline (AMI), a tricyclic antidepressant, inhibited neurite outgrowth from chick embryonic cerebral explants and inhibited adenylyl cyclase activity in cerebral membrane preparations. In the present study, we have investigated the possibility that AMI may have additional effects on cellular metabolism and signal transduction that underlie AMI‐mediated inhibition of neurite outgrowth. In vitro AMI inhibited phospholipase C in a dose‐ and GTP‐dependent manner in membranes from 8‐day‐old chick forebrain. Brain homogenates from 8‐day‐old chick embryos, treated in vivo for 6 days with AMI (20 μg/g/day), showed significant reductions in (1) phosphorylation of two polypeptides (49 and 105 kD), and (2) levels of three polypeptides (43, 53, and 92 kD). Western blots showed that the 43‐ and 53‐kD polypeptides corresponded to actin and tubulin, respectively. Diolein and dilinolein, potent activators of protein kinase C, stimulated neurite outgrowth and reversed the inhibitory effects of AMI. Sphingosine, a protein kinase C inhibitor, significantly inhibited neurite outgrowth and eliminated the stimulatory effects of diolein and dilinolein on neurite outgrowth. These data suggest that AMI‐mediated inhibition of neurite outgrowth involves multiple effects on cellular metabolism and signal transduction. A hypothesis consistent with our data is that AMI interferes in some manner with the action of G proteins in the signal transduction cascade. © 1993 John Wiley & Sons, Inc.
NGF and the local control of nerve terminal growth
Authors: Campenot Robert B. 
Published: May 2005

AbstractIt is generally believed that the mechanism of action of neurotrophic factors involves uptake of neurotrophic factor by nerve terminals and retrograde transport through the axon and back to the cell body where the factor exerts its neurotrophic effect. This view originated with the observation almost 20 years ago that nerve growth factor (NGF) is retrogradely transported by sympathetic axons, arriving intact at the neuronal cell bodies in sympathetic ganglia. However, experiments using compartmented cultures of rat sympathetic neurons have shown that neurite growth is a local response of neurites to NGF locally applied to them which does not directly involve mechanisms in the cell body. Recently, several NGF‐related neurotrophins have been identified, and several unrelated molecules have been shown to act as neurotrophic or differentiation factors for a variety of types of neurons in the peripheral and central nervous systems. It has become clear that knowledge of the mechanisms of action of these factors will be crucial to understanding neurodegenerative diseases and the development of treatments as well as the means to repair or minimize neuronal damage after spinal injury. The concepts derived from work with NGF suggest that the site of exposure of a neuron to a neurotrophic factor is important in determining its response. 1994 John Wiley & Sons, Inc.
Target‐derived molecules that influence the development of neurons in the avian ciliary ganglion
Authors: Nishi Rae 
Published: May 2005

AbstractThe developing avian ciliary ganglion has been a particularly amenable system for the identification, isolation, and characterization of putative target‐derived molecules that mediate retrograde interaction. To date a number of biochemically distinct activities that regulate neuronal survival, transmitter phenotype, and chemosensitivity of ciliary ganglion neruons have been identified. Of these, only two survival‐promoting molecules have been purified to homogeneity: ciliary neurotrophic factor and a related molecule, growth‐promoting activity. A somatostatin‐inducing activity found in cultured choroid cells is very likely to be chick activin A. Other molecules that regulate acetylcholine and acetylcholine receptor expression comigrate on a gel filtration column at a molecular weight of 50–60 kD, but they have yet to be isolated. Once molecules that mimic retrorgrade influences are identified, a number of criteria must be met before their physiological significance can be established. These criteria are (1) availability of the molecule from the target at the appropriate time in development: (2) ability of the neurons to respond to the molecule at the appropriate time in development: (3) demonstration that blocking the activity or availability of the molecule is able to block the target‐derived developmental change expressed in the neurons. Of the molecules that are thought to retrogradely influence ciliary neuron development, only growth‐promoting activity is known to meet criteria 1 and 2, and experiments of growth‐promoting activity in vivo will exacerbate normal cell death. 1994 John Wiley & Sons, Inc.
Voltage‐activated lonic currents in differentiating rat cerebellar granule neurons cultured from the external germinal layer
Authors: Stewart Randall R. , Bossu Jean‐Louis , Muzet Muriel , Dupont Jean‐Luc , Feltz Anne 
Published: May 2005

AbstractThe electrical properties of the precursor cells of the external germinal layer of rat cerebellum were assessed during their differentiation in control medium (Dulbecco's modified Eagle's medium) supplemented or not with either basic fibroblast growth factor (bFGF) or 25 mM potassium chloride (KCI). Resting potential was shown to be –10 mV in all three conditions 3 hours after plating [days in vitro (DIV)0]. By DIV 5, it reached ‐63 mV for cells cultured in 25 mM KCI but only –28 mV in control and bFGF media. The main voltage‐sensitive ionic current measured at DIV 0 under all conditions was a composite Ik consisting in a sustained K+ current blocked by tetraethylammonium (Ik(TEA)), plus a rapidly activating and inactivating TEA‐insensitive Ik(A). Both currents increased with time in all conditions, but after 5 days IK(A) became dominant in terms of density. IK(TEA) is likely an IK(Ca), since it was blocked by 67% in 1 mM TEA. On DIV O, INa and ICa were absent or small in amplitude. By DIV 3, 80% of the cells had currents able to generate a spike. Interestingly, ICa mean amplitude and current density measured at –10 mV in control condition on DIV 1 was singnificantly larger than those recorded in bFGF and 25 mM KCI. The order of appearance of the ionic currents, IK, ICa, and INa, leads directly to fast spike activity allowing for poor calcium entry. Firing rate likely depends on IK(A), which increased during the first 6 days of development but could be differentially regulated by bFGF. © 1995 John Wiley & Sons, Inc.
Gap junctions are required for the propagation of spreading depression
Authors: Nedergaard Maiken , Cooper Arthur J. L. , Goldman Steven A. 
Published: May 2005

AbstractSpreading depression (SD) is a slowly propagating depression of cerebral neuronal activity and transmembrance ionic gradients, that arises in response to a variety of noxious stimuli. SD bears a strong resemblance to gap junction‐mediated calcium waves among cultured astrocytes. Here, we show that gap junction‐mediated intercellular diffusion is necessary for the generation of SD. Waves of SD in the isolated chicken retina were blocked by five different inhibitors of gap junctional coupling, which was assessed by the intercellular transit of Lucifer Yellow (LY). Each of these gap junction blockers inhibited both the migration of SD and the diffusion of LY in a dose‐dependent manner. In contrast, glutamate‐evoked calcium influx into retinal cells was not affected by these compounds. The results indicate that intercellular coupling through gap junctions is required for SD. Gap junction‐mediated communication might therefore constitute an important mechanism in both normative and pathological brain function. © 1995 John Wiley & Sons, Inc.
Modulation of transmitter release from the terminals of the locust wing stretch receptor neuron by muscarinic antagonists
Authors: Leitch Beulah , Pitman Robert M. 
Published: May 2005

AbstractThe forewing stretch receptor (SR) neuron makes monosynaptic connections with wing depressor motoneruons; in this article the pharmacology of its output onto the first baslar motoneuron (BA1) has been investigated. The SR, like other insect afferents that have been studied so far, appears to be cholinergic; transmission was suppressed reversibly by the nicotinic antagonist gallamine (10−4M) and irreversibly by α‐bungarotoxin (10−6 M). The choline reuptake blocker hemicholinium‐3 (10−4 M) also caused a reversible reduction in the amplitude of SR excitatory postsynaptic potentials (EPSPs) recorded in BA1. The receptor subtype nonselective muscarinic antagonists atropine (10−4 M), scopolamine (10−4 M), and quinuclidinyl benzilate (10−5 M), unlike nicotinic antagonists, caused an augmentation in EPSP amplitude. This effect does not appear to be caused by an increase in sensitivity of the motoneuron to acetylcholine (ACh), since atropine produced a marked reduction rather than an increase in the amplitude of responses to ACh pressure applied to the soma of BA1. Scopolamine only caused a modest reduction in the amplitude of ACh somatic responses. The simplest explanation for these observations is that muscarinic antagonists bring about an increase in EPSP amplitude by blockade of presynaptic autoreceptors that normally down‐regulate the release of ACh from SR terminals. The effects of muscarinic receptor subtype‐selective antagonists indicate that presynaptic receptors in this preparation may have a pharmacological profile more similar to that of vertebrate M2 receptors than to that of M1 or M2 subtypes. The functional significance of autoreceptors in this preparation are discussed. © 1995 John Wiley & Sons, Inc.
Synthesis and dynamic NMR studies of the 3,7‐diazabicyclo[4.1.0]heptane system
Authors: Majchrzak Michal W. , Kotełko Antoni , Lambert Joseph B. 
Published: May 2005

AbstractA new bicyclic system, 3,7‐diazabicyclo[4.1.0]heptane, has been prepared from 3‐(ethoxycarbonyl)‐7,3‐oxazabicyclo[4.1.0]heptane by reaction with sodium azide and reduction of the resulting tosyloxy azide with lithium aluminum hydride. The molecule can exist in four stereoisomeric half‐chairs, depending on the configuration of the two nitrogen atoms. Half‐chair ring reversal and piperidine nitrogen inversion are fast on the NMR time scale at all observed temperatures. Inversion of the secondary aziridine nitrogen becomes slow as the temperature is lowered (Tc= −10°C). Complete analysis of the 1H spectrum was possible with the 1,5,5‐trideuteriated analog. At slow exchange, two aziridine invertomers are present with an exo/endo ratio of approximately 0.7 in toluene‐d8, 0.7 in CH2Cl2 and 1.7 in CHCl3/CH2Cl2. The free energy of activation for nitrogen inversion is 13.2 kcal mol−1 at −10°C in CHCl3/CH2Cl2.
Elucidation of the structure of alkane chains in solution by means of 1H NMR
Authors: Nikki Kunio , Nakagawa Naoya 
Published: May 2005

AbstractSolvent shifts of a series of alkanes have been studied in perfluorohexane, carbon tetrachloride and diiodomethane. The methylene proton resonances for longer alkyl chains are shifted downfield in perfluorohexane, but upfield in diiodomethane. It is suggested that n‐alkanes have a tendency to adopt folded structures in solution, the degree of folding for n‐alkane chains in perfluorohexane being larger than that in diiodomethane.
15N NMR studies of amino acids and their reaction products with formaldehyde
Authors: Naulet N. , Tomé D. , Martin G. J. 
Published: May 2005

AbstractNatural abundance 15N NMR spectroscopy has been used to investigate the effect of pH on the 15N chemical shifts of lysine and of ε‐hydroxymethyllysine. A computer calcualtion which fits the chemical shifts of both α‐and ε‐nitrogen atoms versus pH has been used to predict the pKa values. 15N chemical shifts and some 1J(15NH) values of some other amino acids and of their reaction products with formaldehyde are also reported.
Silicon‐29 NMR spectroscopy in carbohydrate chemistry: Galactose derivatives
Authors: Gale D. J. , Evans N. A. 
Published: May 2005

Abstract29Si NMR spectra of the O‐trimethylsilyl (OTMS) derivatives of various methyl α‐ and β‐D‐galactopyranosides have been recorded. The effect of changes in the anomeric configuration provides a means of assigning the resonance of the 2‐OTMS substituent. Whereas the signal of the OTMS group attached at the 6‐position can be assigned readily, those of the OTMS group at the 3‐ or 4‐position cannot be assigned unequivocally.
Carbon‐13 NMR study of substituted benzyl N,N‐dimethylcarbamates
Authors: Yamagami Chisako , Takao Narao , Takeuchi Yoshito 
Published: May 2005

AbstractThe 13C NMR chemical shifts of m‐ and p‐substituted benzyl N,N‐dimethylcarbamates were measured in CDCl3. The meta and para 13C substituent chemical shifts were analysed by means of dual substituent parameter (DSP) equations. Good correlations were obtained, especially for the para‐carbon substituent chemical shifts. The computed transmission coefficients, ρI and ρR, are consistent with the general features of the fitting parameters. It has been shown that no significant electron demand is imposed by the CH2OCON(CH3)2 substituent.
Gas‐phase NMR studies of chemical equilibria: 1—Methodology
Authors: Harris Robin K. , Rao Renée C. 
Published: May 2005

AbstractMethods for obtaining 1H NMR spectra of gases are discussed. Particular attention is paid to the nature of the tube and to the use of ‘second sample’ field/frequency locking. The question of the chemical shift reference is examined, and some results for tetramethylsilane gas are presented. Representative spectra are shown for three types of organic equilibria in the gas phase: keto‐enol tautomerism, addition of methanol to acetaldehyde and Z‐E isomerism of acetaldoxime.
The mass spectra of some alkyl and aryl imidazolines
Authors: Ohashi M. , Ohno N. , Kakisawa H. , Tatematsu A. , Yoshizumi H. 
Published: May 2005

AbstractThe mass spectra of mono‐ and di‐substituted alkyl and aryl imidazolines have been measured and the spectra analysed with the aid of deuterium labelling and high resolution techiques.In contrast to the fragmentation of thiazolines, all principal fragments of the imidazoline ring contain one nitrogen with or without hydrogen migration. In the case of 2,4‐disubstituted imidazolines, the presence of two tautomeric molecular ions are suggested.
Electron‐impact studies of organometallic molecules—VIII: Some transition metal derivatives of polyfluorobenzenes
Authors: Bruce M. I. , Thomas Mair A. 
Published: May 2005

AbstractThe mass spectra of (π‐C5H5)2Ti(C6F5)X (X  Cl and C6F5), C6F5Re(CO)5, RfFe(CO)2(π‐C5H5) (Rf  C6F5, 4‐HC6F4, and three isomeric H2C6F3), and C6F5Ru(CO)2(π‐C5H5) are compared to those of C6F5X (X  F, Cl, Br, I) and the three isomers of C6F4H2. Significant differences occur, apparently depending on the relative thermodynamic stabilities of the various fragments which may be formed. Comparison of the mass spectra of pentafluorophenyl‐ and pentafluorobicyclo[2.2.0]hexa‐2,5‐dien‐2‐yl‐Re(CO)5 show that similar ions are produced by both complexes, perhaps because of thermal isomerisation before ionisation.
The elimination of small neutral molecules and fragments in mass spectra—I. Substituted salicylic acids and their derivatives
Authors: Scott Ward M. , Wacks Morton E. , Eskelson C. D. , Towne J. C. , Cazee C. 
Published: May 2005

AbstractThe mass spectra of various ring‐substituted salicylic acids and derivatives thereof have been examined. Fragmentation pathways for derivatives of salicylic acid; 3‐NO2 salicylic acid; 5‐I salicylic acid; 3‐NO2, 5‐I salicylic acid; and 3‐NH2, 5‐I salicylic acid are suggested. The major dissociations of these compounds are by elimination of the elements of neutral molecules, e.g. water, methanol, ketene (from the acetylated compounds) carbon monoxide, nitric oxide and nitrogen dioxide, leading to (iodo) phenoxy and (iodo) quinone type ion structures. These ions further decompose to yield the corresponding substituted cyclopentadienyl and cyclopropylium ions.
Mass spectral studies on thiobenzoates and thioacetates
Authors: Ohno A. , Koizumi T. , Ohnishi Y. , Tsuchihashi G. 
Published: May 2005

AbstractThe mass spectra of O‐methyl and O‐ethyl thiobenzoates and their derivatives have been recorded together with those of the corresponding S‐alkyl thiobenzoates. The direct fragmentations of the O‐alkyl thiobenzoates are almost identical to those of alkyl benzoates and of S‐alkyl thio‐benzoates. Several important differences in rearrangements upon electron‐impact can be observed between them, however. These are the migration of the alkyl group from the alkoxy oxygen to the thiocarbonyl sulphur and the migration of a hydrogen from the alkoxy group to the thiocarbonyl group. O‐methyl and O‐ethyl thioacetates behave similarly. The mass spectra of the thioesters obtained with low electron‐accelerating voltages have also been studied.
Mass spectrometric studies of phenoxarsine derivatives
Authors: Tou James C. , Wang C. S. 
Published: May 2005

AbstractNine phenoxarsine derivatives with arsenic in the trivalent state and the pentavalent state are synthesized and studied by mass spectrometry. Their characteristic fragmentation modes and the fragment ions with common structures are discussed. Phenoxarsinic acids are found to be unstable in the gaseous phase at the temperatures studied and tend to form their corresponding anhydrides.
Ion‐molecule reactions in alkyl cyanides: Identification of reactive hydrogen in precursor ions
Authors: Heerma W. , Dijkstra G. 
Published: May 2005

AbstractThe relative abundance of [M + H]+ ions in the spectra of different nitriles depends on the nature of the nitrile. A new method for the identification of ion‐molecule reactions has been applied, by determining the [M + D]+ ion intensity with respect to the [M + H]+ ion intensity in the spectra of partially deuteriated alkyl cyanides. This intensity ratio is correlated with the hydrogen‐deuterium content of the suspected primary ions. In addition not only the reacting primary ions, but also the reactive hydrogen atom in the primary ion could be indicated. There is clear evidence that the proton attached to the nitrogen atom in the H2CCN+˙H rearrangement ion is transferred to the nitrile molecule.
Mass spectrometry of aralkyl compounds with a functional group—VIII: Comparison of the breakdown of 3‐phenylnitropropane with that of 3‐phenylpropyl nitrite upon electron‐impact
Authors: Nibbering N. M. M. , De Boer Th. J. 
Published: May 2005

AbstractMass spectra of 3‐phenylnitropropane and of its analogues, specifically deuterated in the aliphatic chain and in the phenyl ring, show that the molecular ion loses a molecule of water in two different modes, viz. either with both α‐hydrogen atoms or with a γ‐ and an ortho‐hydrogen atom. Moreover, a molecule of nitric oxide is eliminated from the molecular ion and the resulting [M ‐ NO]+‐ion appears to decompose further in many complicated ways. This loss of nitric oxide does not arise from an isomerization of the nitro group to a nitrite group, because the [M ‐ NO]+‐ion of 3‐phenylpropyl nitrite breaks down in an altogether different manner than that of 3‐phenylnitropropane. This is demonstrated by the spectra of specifically deuterated analogues of 3‐phenylpropyl nitrite.
Mass spectrometry in the investigation of β‐lysine‐containing peptides
Authors: Rostovtseva L. I. , Kiryushkin A. A. 
Published: May 2005

AbstractMass spectrometry can be used for amino acid sequence determination in β‐lysine‐containing peptides and for the identification of α‐ and β‐lysine residues in peptides, as well as for amide bond type determination in β‐lysine peptides. The peptide bond in streptothricin D is shown to be formed through the participation of an ε‐amino group of the L‐β‐lysine residue.
A novel fragmentation of trimethylsilyl ethers of 3β‐hydroxy‐Δ5‐steroids
Authors: Björkhem Ingemar , Gustafsson Jan‐Årke , Sjövall Jan 
Published: May 2005

AbstractAn ion formed by loss of 56 mass units from the molecular ion is often seen in mass spectra of trimethylsilyl ethers of C19 and C21 steroids having a 3β‐hydroxy‐Δ5 structure and an oxo group at C‐17 or C‐20. The nature of this fragment was investigated by the use of perdeuteriotrimethylsilyl ether derivatives and of [4‐14C], [3‐18O], [4,4‐2H2] and [2,2,4,4‐2H] labelled derivatives of 3β‐hydroxy‐5‐androsten‐17‐one and 3β‐hydroxy‐5‐pregnen‐20‐one. Evidence is presented to show that the neutral fragment of mass 56 is composed of carbon atoms 1, 2 and 3, the oxygen at C‐3 and four hydrogen atoms. During the fragmentation process, the trimethylsilyl group and one of the hydrogens at C‐2 are transferred to the fragment that carries the charge.