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We demonstrate laser frequency stabilization with at least 6 GHz of offset tunability using an in-phase/quadrature (IQ) modulator to generate electronic sidebands (ESB) on a titanium sapphire laser at 714 nm and we apply this technique to perform isotope shift spectroscopy of 226Ra and 225Ra. By locking the laser to a single resonance of a high finesse optical cavity and adjusting the lock offset, we determine the frequency difference between the magneto-optical trap (MOT) transitions in the two isotopes to be 2630.0 ± 0.3 MHz, a factor of 29 more precise than the previously available data. Using the known value of the hyperfine splitting of the 3P1 level, we calculate the isotope shift for the 1S0 to 3P1 transition to be 2267.0 ± 2.2 MHz, a factor of 8 more precise than the best available value. Our technique could be applied to countless other atomic systems to provide unprecedented precision in isotope shift spectroscopy and other relative frequency comparisons.
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We report the first precise measurement of a ß-recoil correlation from a radioactive noble gas (^{6}He) confined via a magneto-optical trap. The measurement is motivated by the search for exotic tensor-type contributions to the charged weak current. Interpreted as tensor currents with right-handed neutrinos, the measurements yield |C_{T}/C_{A}|^{2}≤0.022 (90% confidence limit, C.L.). On the other hand, for left-handed neutrinos the limits are 0.007
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The radioactive radium-225 ((225)Ra) atom is a favorable case to search for a permanent electric dipole moment. Because of its strong nuclear octupole deformation and large atomic mass, (225)Ra is particularly sensitive to interactions in the nuclear medium that violate both time-reversal symmetry and parity. We have developed a cold-atom technique to study the spin precession of (225)Ra atoms held in an optical dipole trap, and demonstrated the principle of this method by completing the first measurement of its atomic electric dipole moment, reaching an upper limit of |d((225)Ra)|<5.0×10(-22) e cm (95% confidence).
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We have demonstrated that the ion current resulting from collisions between metastable krypton atoms in a magneto-optical trap can be used to precisely measure the trap loading rate. We measured both the ion current of the abundant isotope 83Kr (isotopic abundance=11%) and the single-atom counting rate of the rare isotope 85Kr (isotopic abundanceâ¼1×10(-11)), and found the two quantities to be proportional at a precision level of 0.9%. This work results in a significant improvement in using the magneto-optical trap as an analytical tool for noble-gas isotope ratio measurements, and will benefit both atomic physics studies and applications in the earth sciences.
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We report the first experimental determination of the hyperfine quenching rate of the 6s(2) (1)S(0)(F = 1/2) - 6s6p (3)P(0)(F = 1/2) transition in (171)Yb with nuclear spin I = 1/2. This rate determines the natural linewidth and the Rabi frequency of the clock transition of a Yb optical frequency standard. Our technique involves spectrally resolved fluorescence decay measurements of the lowest lying (3)P(0,1) levels of neutral Yb atoms embedded in a solid Ne matrix. The solid Ne provides a simple way to trap a large number of atoms as well as an efficient mechanism for populating (3)P(0). The decay rates in solid Ne are modified by medium effects including the index-of-refraction dependence. We find the (3)P(0) hyperfine quenching rate to be (4.42 ± 0.35) × 10(-2) s(-1) for free (171)Yb, which agrees with recent ab initio calculations.
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Neutral ytterbium atoms embedded in solid neon qualitatively retain the structure of free atoms. Despite the atom-solid interaction, the 6s6p ³P(0) level is found to remain metastable with its lifetimes determined to be in the range of ten to hundreds of seconds. The atomic population can be almost completely transferred between the ground level and the metastable level via optical excitation and spontaneous decay. The dynamics of this process is examined and is used to explicitly demonstrate that the transition broadening mechanism is homogeneous.
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Atom trap trace analysis, a laser-based atom counting method, has been applied to analyze atmospheric 39Ar (half-life=269 yr), a cosmogenic isotope with an isotopic abundance of 8×10(-16). In addition to the superior selectivity demonstrated in this work, the counting rate and efficiency of atom trap trace analysis have been improved by 2 orders of magnitude over prior results. The significant applications of this new analytical capability lie in radioisotope dating of ice and water samples and in the development of dark matter detectors.
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Directed outgrowth of neural processes must involve transmission of signals from the tips of filopodia to the central region of the growth cone. Here, we report on the distribution and dynamics of one possible element in this process, actin, in live growth cones which are reorienting in response to in situ guidance cues. In grasshopper embryonic limbs, pioneer growth cones respond to at least three types of guidance cues: a limb axis cue, intermediate target cells, and a circumferential band of epithelial cells. With time-lapse imaging of intracellularly injected rhodamine-phalloidin and rhodamine-actin, we monitored the distribution of actin during growth cone responses to these cues. In distal limb regions, accumulation of actin in filopodia and growth cone branches accompanies continued growth, while reduction of actin accompanies withdrawal. Where growth cones are reorienting to intermediate target cells, or along the circumferential epithelial band, actin selectively accumulates in the proximal regions of those filopodia that have contacted target cells or are extending along the band. Actin accumulations can be retrogradely transported along filopodia, and can extend into the central region of the growth cone. These results suggest that regulation and translocation of actin may be a significant element in growth cone steering.
Assuntos
Actinas/metabolismo , Axônios/metabolismo , Transdução de Sinais , Animais , Epitélio/crescimento & desenvolvimento , Fêmur/inervação , Gafanhotos , Larva , Microscopia de Fluorescência , Neurônios/fisiologia , Faloidina , Coelhos , RodaminasRESUMO
The growth of an axon toward its target results from the reorganization of the cytoskeleton in response to environmental guidance cues. Recently developed imaging technology makes it possible to address the effect of such cues on the neural cytoskeleton directly. Although high resolution studies can be carried out on neurons in vitro, these circumstances do not recreate the complexity of the natural environment. We report here on the arrangement and dynamics of microtubules in live neurons pathfinding in response to natural guidance cues in situ using the embryonic grasshopper limb fillet preparation. A rich microtubule network was present within the body of the growth cone and normally extended into the distal growth cone margin. Complex microtubule loops often formed transiently within the growth cone. Branches both with and without microtubules were regularly observed. Microtubules did not extend into filopodia. During growth cone steering events in response to identified guidance cues, microtubule behaviour could be monitored. In turns towards guidepost cells, microtubules selectively invaded branches derived from filopodia that had contacted the guidepost cell. At limb segment boundaries, microtubules displayed a variety of behaviors, including selective branch invasion, and also invasion of multiple branches followed by selective retention in branches oriented in the correct direction. Microtubule invasion of multiple branches also was seen in growth cones migrating on intrasegmental epithelium. Both selective invasion and selective retention generate asymmetrical microtubule arrangements within the growth cone, and may play a key role in growth cone steering events.
Assuntos
Axônios/metabolismo , Microtúbulos/metabolismo , Neurônios/ultraestrutura , Animais , Axônios/ultraestrutura , Gafanhotos/embriologia , Microscopia Eletrônica , Microscopia de Fluorescência , Microtúbulos/ultraestrutura , Neurônios/citologia , Rodaminas/metabolismo , Tubulina (Proteína)/metabolismoRESUMO
In neurons, tubulin is synthesized only in the cell body or dendrites, yet the growing axon requires a steady supply of this protein at the growth cone. Hence, some mechanism must exist to move tubulin from the cell body to the growth cone. Transport could conceivably occur by simple diffusion, translocation of polymer, or some form of monomer or oligomer transport. Evidence for all these has been presented in a variety of experimental systems. We have directly studied the movement of microtubules in 12 growing axons in live grasshopper Ti1 neurons in their natural environment by labeling the polymer with a caged fluorophore, biscaged fluorescein. No evidence of polymer transport was found. Hence, tubulin movement in these neurons must occur by movement of monomeric tubulin, either by transport or diffusion. To resolve these conflicting views, we discuss the conditions under which diffusion is feasible as a transport mechanism.
Assuntos
Transporte Axonal , Gafanhotos , Neurônios/metabolismo , Tubulina (Proteína)/metabolismo , Animais , Axônios/ultraestrutura , Dextranos/metabolismo , Difusão , Fluoresceínas/metabolismo , Gafanhotos/embriologia , Cinética , Luz , Microtúbulos/metabolismo , Neurônios/ultraestrutura , RodaminasRESUMO
We have used a new technique, micro-CALI (chromophore-assisted laser inactivation), to investigate the function of the neural cell adhesion molecules fasciclin I and II in the development of the grasshopper Ti1 neurons. Micro-CALI of fasciclin I results in defasciculation of the Ti1 axons similar to that achieved using large scale CALI (Jay and Keshishian, 1990). The initial point of axon separation corresponds to the site of laser irradiation, and defasciculation always continues distal to this point. Micro-CALI of fasciclin II prevents the initiation of Ti1 axon outgrowth but has no effect on fasciculation. This effect is restricted to a 3 hr interval between cytokinesis and growth cone emergence.
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Moléculas de Adesão Celular Neuronais/fisiologia , Neurônios/fisiologia , Animais , Axônios/fisiologia , Axônios/efeitos da radiação , Axônios/ultraestrutura , Senescência Celular/fisiologia , Gafanhotos/embriologia , Lasers , Neurônios/ultraestruturaRESUMO
Monoclonal antibody 6F8 was used to characterize and clone fasciclin IV, a new axonal glycoprotein in the grasshopper, and to study its function during growth cone guidance. Fasciclin IV is dynamically expressed on a subset of axon pathways in the developing CNS and on circumferential bands of epithelial cells in developing limb buds. One of these bands corresponds to the location where the growth cones of the Ti1 pioneer neurons make a characteristic turn while extending toward the CNS. Embryos cultured in the 6F8 antibody or Fab exhibit aberrant formation of this axon pathway. cDNA sequence analysis suggests that fasciclin IV has a signal sequence; long extracellular, transmembrane, and short cytoplasmic domains; and shows no homology with any protein in the available data bases. Thus, fasciclin IV appears to be a novel integral membrane protein that functions in growth cone guidance.
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Axônios/fisiologia , Moléculas de Adesão Celular Neuronais/genética , Moléculas de Adesão Celular Neuronais/fisiologia , Expressão Gênica , Gafanhotos/embriologia , Semaforinas , Sequência de Aminoácidos , Animais , Anticorpos Monoclonais , Moléculas de Adesão Celular Neuronais/química , DNA/química , DNA/genética , Epitélio/metabolismo , Extremidades/embriologia , Gafanhotos/genética , Proteínas de Membrana/química , Proteínas de Membrana/genética , Proteínas de Membrana/fisiologia , Dados de Sequência Molecular , Sistema Nervoso/embriologia , Sistema Nervoso/metabolismo , Fases de Leitura AbertaRESUMO
Transmembrane and secreted glycoproteins of the semaphorin family are typically classified as inhibitory neuronal guidance molecules. However, although chemorepulsive activity has been demonstrated for several semaphorin family members, little is known about the function of the numerous transmembrane semaphorins identified to date. Here we demonstrated that the extracellular semaphorin domain of a transmembrane semaphorin, semaphorin-1a, could actively perturb axon pathfinding in vivo when presented homogenously as a recombinant freely soluble factor. When ectopic overexpression was limited to defined epithelial regions, semaphorin-1a could directly steer axons by acting as an attractive guidance molecule.
Assuntos
Axônios/fisiologia , Moléculas de Adesão Celular Neuronais/farmacologia , Moléculas de Adesão Celular Neuronais/fisiologia , Neurônios/fisiologia , Semaforinas , Sequência de Aminoácidos , Animais , Axônios/efeitos dos fármacos , Células COS , Moléculas de Adesão Celular Neuronais/química , Linhagem Celular , Sinais (Psicologia) , Drosophila melanogaster , Embrião não Mamífero/fisiologia , Gafanhotos , Dados de Sequência Molecular , Neurônios/efeitos dos fármacos , Fragmentos de Peptídeos/farmacologia , Proteínas Recombinantes/química , Proteínas Recombinantes/farmacologia , TransfecçãoRESUMO
A room-temperature beam of krypton atoms in the metastable 5s[3/2]2 level is demonstrated via an optical excitation method. A Kr-discharge lamp is used to produce vacuum ultraviolet photons at 124 nm for the first-step excitation from the ground level 4p6 1S0 to the 5s[3/2]1 level. An 819 nm Ti:sapphire laser is used for the second-step excitation from 5s[3/2]1 to 5s[3/2]2 followed by a spontaneous decay to the 5s[3/2]2 metastable level. A metastable atomic beam with an angular flux density of 3 x 10(14) s(-1) sr(-1) is achieved at the total gas flow rate of 0.01 cm3/s at STP (or 3 x 10(17) at./s). The dependences of the flux on the gas flow rate, laser power, and lamp parameters are investigated.
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A method for alignment of a vector magnetometer to a rigidly attached prism is presented. This enables optical comparison of the magnetometer axes to physical surfaces in the apparatus, and thus an absolute determination of the magnetic field direction in space. This is in contrast with more common techniques, which focus on precise determination of the relative angles between magnetometer axes, and so are more suited to measuring differences in the direction of magnetic fields. Here we demonstrate precision better than 500 µrad on a fluxgate magnetometer, which also gives the coil orthogonality errors to a similar precision. The relative sensitivity of the three axes is also determined, with a precision of about 5 × 10-4.
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Oriented neural outgrowth is dependent upon the capability of growth cones to reorient the direction of their migration in response to contact with guidance information. Recent observations have directed attention toward the role of actin distribution and concentration in transmitting localized peripheral signals to central elements of the growth cone, particularly microtubules.
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Citoesqueleto/fisiologia , Neurônios/fisiologia , Actinas/metabolismo , Actinas/fisiologia , Animais , Microtúbulos/fisiologiaRESUMO
Neuronal outgrowth is a fundamental process for normal development of the nervous system. Despite recent advances, the molecular mechanisms governing neuronal motility are still poorly understood. To provide insight into the intracellular signaling mechanisms required for neuronal outgrowth, we have characterized the effects of a compound previously identified for its anti-motility effects on transformed cells. We show that this compound, motuporamine C, acts as a robust inhibitor of chick neurite outgrowth in a dose-dependent fashion. Furthermore, in the presence of motuporamine C, growth cone collapse is observed, followed by neurite retraction. After removal, growth cones re-extend lamellipodial and filopodial processes and re-establish motility. Neurons exposed to motuporamine C exhibit a significant upregulation of active Rho-GTP. Additionally, effector-blocking experiments using Rho and Rho-associated kinase inhibitors indicate that the Rho pathway plays a critical role in motuporamine C-mediated growth cone collapse. Thus, we have characterized a novel anti-motility compound that has a robust inhibitory effect on neuronal outgrowth and involves signaling through the Rho-Rho kinase collapse pathway. Due to these robust effects, motuporamine C may serve as a valuable tool in further examining the intracellular mechanisms associated with growth cone motility.
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Alcaloides/farmacologia , Cones de Crescimento/efeitos dos fármacos , Neurônios/citologia , Fármacos Neuroprotetores/farmacologia , Amidas/farmacologia , Animais , Western Blotting/métodos , Embrião de Galinha , Relação Dose-Resposta a Droga , Inibidores Enzimáticos/farmacologia , Gânglios Espinais/citologia , Imuno-Histoquímica/métodos , Imunoprecipitação/métodos , Microscopia de Vídeo/métodos , Neuritos/efeitos dos fármacos , Técnicas de Cultura de Órgãos , Piridinas/farmacologia , Fatores de Tempo , Proteínas rho de Ligação ao GTP/metabolismoRESUMO
The effects of intervention by diets with high or low levels of dietary fat on the development of preneoplastic pancreatic lesions were examined. Wistar rats were treated ip at 14 days of age with a 30-mg/kg dose of L-azaserine [CAS: 115-02-6; diazoacetate serine (ester)] and weaned onto the test diets. Animals fed 5% corn oil had fewer preneoplastic lesions compared to animals fed 20% corn oil throughout the 4-month posttreatment period. The strong response observed in rats fed 20% corn oil could be markedly reduced by intervention with a 5% corn oil diet halfway through the posttreatment period. Similarly, the low response in animals fed 5% corn oil could be markedly elevated by intervention with a high-fat diet. These results provide evidence for the hypothesis that tumor development may be modified by dietary means.
Assuntos
Azasserina/toxicidade , Gorduras na Dieta/administração & dosagem , Neoplasias Pancreáticas/induzido quimicamente , Lesões Pré-Cancerosas/induzido quimicamente , Animais , Óleo de Milho , Feminino , Masculino , Óleos/administração & dosagem , Neoplasias Pancreáticas/prevenção & controle , Lesões Pré-Cancerosas/prevenção & controle , Ratos , Ratos EndogâmicosRESUMO
The effect of dietary intake of fish (menhaden) oil and fish (cod) protein on the development of pancreatic preneoplastic lesions was examined in male Wistar rats. Fourteen-day-old animals were given a single ip injection of 30 mg L-azaserine/kg body weight [CAS: 115-02-6; diazoacetate serine (ester)]. At 21 days of age they were weaned and maintained on dietary treatment for 4 months. Fish protein did not appear to produce a significantly different preneoplastic response when compared to casein as a protein source. However, a 20% menhaden oil diet, rich in omega 3 fatty acids, produced a significant decrease in the development of both the size and number of preneoplastic lesions when compared to a 20% corn oil diet rich in omega 6 fatty acids. This study provides evidence that fish oils, rich in omega 3 fatty acids, may have potential as inhibitory agents in cancer development.
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Azasserina/toxicidade , Proteínas Alimentares/farmacologia , Óleos de Peixe/farmacologia , Produtos Pesqueiros , Neoplasias Pancreáticas/induzido quimicamente , Lesões Pré-Cancerosas/induzido quimicamente , Animais , Caseínas/farmacologia , Óleo de Milho , Feminino , Masculino , Óleos/farmacologia , Neoplasias Pancreáticas/prevenção & controle , Lesões Pré-Cancerosas/prevenção & controle , Ratos , Ratos EndogâmicosRESUMO
We examined the effect of varying the ratio of dietary omega-3 (omega 3) to omega-6 (omega 6) on the development of pancreatic preneoplastic lesions in male Wistar rats given azaserine at 14 days of age. As the ratio of dietary omega 3 to omega 6 fatty acids increased in a diet totaling 20% by weight of fat, the development of preneoplastic atypical acinar cell nodules (AACNs) at 4 months after dosing with azaserine decreased significantly. In addition, serum levels of prostaglandin thromboxane B2, prostaglandin E2, and 6-keto-prostaglandin F1 alpha decreased significantly. The fatty acid composition of the rbc membrane was also significantly influenced by the ratio of dietary omega 3 to omega 6 fatty acids. In a second experiment, we examined the effect of dietary intervention with a different type of fat (corn oil or menhaden oil) 2 months into the 4-month postdosing period on AACN development at the end of the post-dosing period. Intervention of the omega 6 fatty acid-rich diet with the omega 3 fatty acid-rich diet significantly decreased focal development. The opposite was true when intervention involved substituting the omega 3 fatty acid-rich diet with the omega 6 fatty acid-rich diet.