bluuebunny/crossref_metadata_2025 huggingface dataset:
Excitation Temperatures and Electron Number Densities Experienced by Analyte Species in Inductively Coupled Plasmas with and without the Presence of an Easily Ionized Element
Authors: Kalnicky D. J. , Fassel V. A. , Kniseley R. N.
Published: October 2005

Spatially resolved radial excitation temperatures and radial electron density distributions experienced by analyte species in the observation zone of 15 to 25 mm above the load coil of a toroidally shaped, inductively coupled argon plasma are presented and related to the analytical performance of these plasmas. A comparison of radial temperatures measured with support gas (Ar I) lines and with a typical analyte thermometric species (Pe I) at 15 mm above the load coil is given. Radial (Fe I) excitation temperatures obtained at three observation heights are compared for aerosol carrier flows of 1.0 and 1.3 liters/min. The addition of a large amount of an easily ionized element (6900 µg of Na per ml) did not significantly change Fe I excitation temperature distributions at the respective aerosol carrier flows and observation heights. A comparison of radial electron density distributions measured with Saha-Eggert ionization and with Stark broadening methods is given for an observation height of 15 mm above the load coil. The differences between electron density values obtained by these methods is discussed. The effect of addition of 6900 µg of Na per ml on Saha-Eggert electron density distributions at three observation heights is also discussed.
Organic Dyes as Spectroscopic Tools: Effects of Solution Equilibria for Phthalocyanines and Carbocyanines
Authors: Britt A. D. , Moniz W. B.
Published: October 2005

The use of phthalocyanines and carbocyanines in laser applications is reviewed from the perspective of the known solution chemistry of these two families of dyes. The optical behavior of such dyes is found to show certain effects which correlate with the chemistry of the dye family concerned. These chemical effects are identified for phthalocyanines and carbocyanines in their principal laser usages, so as to reduce their being confused with purely physical phenomena.
Effect of Solvent on the Complex Formation of Proton Donor Acceptor System
Authors: Kerim F. M. Abdel , Bassyouni A. H. , Shabaka A. A.
Published: October 2005

The effects of 16 solvents on the frequency and intensity of the OH stretching vibration of the complex formed between n-propyl alcohol as a proton donor and α-picoline as a proton acceptor were extensively studied. The equilibrium constants of the complex were determined in each solvent. The discussion of the results concludes that polar and aromatic solvents weaken the strength of the complex.
Measurement of Small Volume Flame Temperatures by the Two-Line Atomic Fluorescence Method
Authors: Haraguchi H. , Smith B. , Weeks S. , Johnson D. J. , Winefordner J. D.
Published: October 2005

Measurement of small volume temperatures of analytical flames by the two-line atomic fluorescence technique involving the use of direct-line Stokes and anti-Stokes fluorescence of indium and thallium has been examined. Spatial flame temperatures have been measured with a volume resolution of 0.3 mm by 2 mm by 5 mm in the flame. Theoretical and practical considerations of the method are given, particularly in terms of the limitation of using indium or thallium. The use of the two thallium lines (377.57 and 535.05 nm) was subject to fewer random errors than the use of the two indium lines (410.18 and 451.13 nm) for the range of temperatures studied. However, thallium lines are restricted to the measurement of temperatures above about 2000°K (for the air-acetylene and nitrous oxide-acetylene flames); for temperatures below about 2000°K, the fluorescence irradiance ratio could not be measured with sufficient signal/noise ratio due to the low intensity of the anti-Stokes fluorescence line. In the present experiment, indium lines were used for the measurement of a wide range of “low” flame temperatures (approximately 700 to 2600°K) owing to the better signal/noise ratios for both lines; indium lines were also preferable for the air-acetylene flame, even though the error produced by the random uncertainty in the fluorescence ratio was larger than for thallium. The present method has been successfully applied to the measurement of the spatial temperature profiles of analytical flames, such as argon-hydrogen(-entrained air), argon-oxygen-hydrogen, air-acetylene, and nitrous oxide-acetylene.
Recognizing Patterns in Trace Elements
Authors: McGill J. R. , Kowalski B. R.
Published: October 2005

There is a growing awareness in the scientific community that as methods of analysis become more efficient, a massive data explosion is ensuing. Reducing data to meaningful trends has become a major aspect of research because of the bulk of information involved and because scientific interest is focusing on more and more subtle phenomena. One aid to data reduction and trend detection is pattern recognition, which is a collection of computer-based data manipulation techniques that have proved useful in a number of problems. This paper is intended as an illustrative introduction to these techniques, with the aim of giving the reader an intuitive feel for the process of a real application of the methods. A problem in archaeology, solved by neutron activation analysis, is discussed.
Investigation of the Chemical Structure of Coal by Nuclear Magnetic Resonance and Infrared Spectrometry
Authors: Retcofsky H. L.
Published: October 2005

The distributions of hydrogen and carbon among various organic structures in solvent extracts of selected coals have been determined by high-resolution proton and carbon-13 magnetic resonance spectrometry. Structural parameters including the aromaticity, the degree of aromatic ring substitution, and the average size of the condensed aromatic ring system have been deduced for each extract using the nuclear magnetic resonance data in conjunction with the elemental analysis of the material. Complementary infrared spectral studies of the extracts and their parent coals have been used to estimate the aromaticities of whole coals. The potential of two other magnetic resonance techniques, proton-enhanced nuclear induction spectroscopy and proton-decoupled high-resolution carbon-13 magnetic resonance, in coal research is discussed. The results of the present investigation are in accord with commonly held views of coal metamorphism; they do not, however, support recent reports challenging the classical view that coals arc highly aromatic materials.
A Comparative Analysis of the Analytical Capabilities of Coherent Anti-Stokes Raman Spectroscopy (CARS) Relative to Raman Scattering and Absorption Spectroscopy
Authors: Tolles W. M. , Turner R. D.
Published: October 2005

The performance capabilities of coherent anti-stokes Raman spectroscopy (CARS) relative to incoherent Raman scattering and absorption spectroscopy are considered for gases. Four gases are considered for model calculations: hydrogen, nitrogen, oxygen, and carbon monoxide. The signal/noise ratio is estimated for these molecules under a number of assumed experimental conditions. The signal/noise ratios for CARS and Raman scattering scale quite differently with partial pressure and temperature. CARS offers distinct advantages when detecting a major component of a gas mixture at total pressures of considerably less than 1 atm pressure. Raman scattering offers 1 to 2 orders of magnitude greater sensitivity for a signal/noise ratio of unity when detecting a minor component of a gaseous mixture at 1 atm total pressure. These model calculations should be of use when a specific experimental method is to be chosen for spectroscopic examination.
A Dual Wavelength Atomic Absorption Spectrophotometer Using a Pulsed Hollow Cathode Lamp
Authors: Araki Tsutomu , Uchida Teruo , Minami Shigeo
Published: October 2005

A novel use of pulsed hollow cathode lamps for the purpose of background correction with a dual wavelength atomic absorption spectrophotometer is described. The pulsed hollow cathode lamp in conjunction with a transient signal gating system behaves as if the analyte source and the background correction source are firing alternately in time. Determinations of Fe, Mg, and Cd are carried out in order to evaluate the performance in practical analyses. Procedures and results on the time-resolved measurement of emission spectra and resonance line profiles from several kinds of pulsed hollow cathode lamps are also demonstrated in detail.
Spatial Profiles of Emission from an Inductively Coupled Plasma Source Using a Self-Scanning Photodiode Array
Authors: Edmonds T. E. , Horlick Gary
Published: October 2005

Detailed spatial profiles of analyte emission in an inductively coupled plasma source have been measured using a self-scanning linear silicon photodiode array mounted vertically in the exit focal plane of a monochromator. These profiles were measured for both neutral atom and ion lines of several elements as a function of plasma power, central axial (nebulizer) flow rate, and coolant flow rate. The plasma has complex but characteristic emission spatial patterns; patterns that are highly dependent, at the submillimeter level, on both flow and power parameters of the plasma. These data also indicate that the spatial position of peak neutral atom line emission may depend on analyte excitation and/or ionization characteristics while the spatial position of peak ion line emission appears to be species independent for those elements studied.
Recent Applications of Fourier Transform Infrared Spectrometry in Chemical and Environmental Analysis
Authors: Griffiths Peter R.
Published: October 2005

Several different applications of Fourier transform infrared (FT-ir) spectrometry being developed at Ohio University are described. A dual-beam FT-ir system which enables identifiable GC-ir spectra to be measured from less than 100 ng of material is described. A method for removing the solvent from the effluent from a high performance liquid chromatograph is proposed, together with a device for on-line LC-ir at the submicrogram level. Calculations showing the effect of the instrument line shape function of an FT-ir spectrometer used with or without apodization on Lorentzian absorption bands are described, and the implications of the results of these calculations on spectral subtraction and remote sensing experiments are discussed.
Improved Sensitivity for in Situ Infrared Identification of Species Separated by Thin-Layer Chromatography Using Programmed Multiple Development
Authors: Gomez-Taylor Maria M. , Griffiths Peter R.
Published: October 2005

A method is described for measuring the infrared spectra of submicrogram quantities of materials separated by thin-layer chromatography (TLC) without removing the sample from the plate. The use of programmed multiple development for the chromatography concentrates each spot of sample on the TLC plate by approximately a factor of 4 compared to conventional TLC. A Fourier transform infrared spectrometer equipped with a mercury cadmium telluride detector enables recognizable spectra to be measured in less than 10 s.
Identifying the Source of Weathered Petroleum: Matching Infrared Spectra with Correlation Coefficients
Authors: Baer Carl D. , Brown Chris W.
Published: October 2005

A novel method is presented for identifying the source of weathered petroleum by measuring the similarity between the spectrum of a weathered oil and spectra of artificially weathered samples. The Pearson correlation coefficient is used as the similarity measure, and three separate K-nearest neighbor approaches are tested on the data set.
Least-Squares Curve-Fitting of Fourier Transform Infrared Spectra with Applications to Polymer Systems
Authors: Antoon M. K. , Koenig J. H. , Koenig J. L.
Published: October 2005

A method is presented for least-squares curve-fitting of Fourier transform infrared spectra. A demonstration of the determination of xylene solution compositions illustrates the accuracy of the method. Least-squares coefficients are shown to be valuable for the analysis of several polymer systems by digital subtraction of spectra.
Radical-mediated dehydration reactions in anaerobic bacteria
Authors: Buckel Wolfgang , Martins Berta M. , Messerschmidt Albrecht , Golding Bernard T.
Published: October 2005

Most dehydratases catalyse the elimination of water from β-hydroxy ketones, β-hydroxy carboxylic acids or β-hydroxyacyl-CoA. The electron-withdrawing carbonyl functionalities acidify the α-hydrogens to enable their removal by basic amino acid side chains. Anaerobic bacteria, however, ferment amino acids via α- or γ-hydroxyacyl-CoA, dehydrations of which involve the abstraction of a β-hydrogen, which is ostensibly non-acidic (pKca. 40). Evidence is accumulating that β-hydrogens are acidified via transient conversion of the CoA derivatives to enoxy radicals by one-electron transfers, which decrease the pKto 14. The dehydrations of (R)-2-hydroxyacyl-CoA to (E)-2-enoyl-CoA are catalysed by heterodimeric [4Fe-4S]-containing dehydratases, which require reductive activation by an ATP-dependent one-electron transfer mediated by a homodimeric protein with a [4Fe-4S] cluster between the two subunits. The electron is further transferred to the substrate, yielding a ketyl radical anion, which expels the hydroxyl group and forms an enoxy radical. The dehydration of 4-hydroxybutyryl-CoA to crotonyl-CoA involves a similar mechanism, in which the ketyl radical anion is generated by one-electron oxidation. The structure of the FAD- and [4Fe-4S]-containing homotetrameric dehydratase is related to that of acyl-CoA dehydrogenases, suggesting a radical-based mechanism for both flavoproteins.
Unusual reactions involved in anaerobic metabolism of phenolic compounds
Authors: Boll Matthias , Fuchs Georg
Published: October 2005

Aerobic bacteria use molecular oxygen as a common co-substrate for key enzymes of aromatic metabolism. In contrast, in anaerobes all oxygen-dependent reactions are replaced by a set of alternative enzymatic processes. The anaerobic degradation of phenol to a non-aromatic product involves enzymatic processes that are uniquely found in the aromatic metabolism of anaerobic bacteria: (i) ATP-dependent phenol carboxylation to 4-hydroxybenzoate via a phenylphosphate intermediate (biological Kolbe-Schmitt carboxylation); (ii) reductive dehydroxylation of 4-hydroxybenzoyl-CoA to benzoyl-CoA; and (iii) ATP-dependent reductive dearomatization of the key intermediate benzoyl-CoA in a ‘Birch-like’ reduction mechanism. This review summarizes the results of recent mechanistic studies of the enzymes involved in these three key reactions.
Dopamine Depletion Does Not Protect against Acute 1-Methyl-4-Phenyl-1,2,3,6-Tetrahydropyridine ToxicityIn Vivo
Authors: Hasbani Daphne M. , Perez Francisco A. , Palmiter Richard D. , O'Malley Karen L.
Published: October 2005

Dopamine (DA) has been postulated to play a role in the loss of dopaminergic substantia nigra (SN) neurons in Parkinson's disease because of its propensity to oxidize and form quinones and other reactive oxygen species that can alter cellular function. Moreover, DA depletion can attenuate dopaminergic cell lossin vitro. To test the contribution of DA to SN impairmentin vivo, we used DA-deficient mice, which lack the enzyme tyrosine hydroxylase in dopaminergic cells, and mice pharmacologically depleted of DA by α-methyl-p-tyrosine pretreatment. Mice were treated with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), a toxin that produces parkinsonian pathology in humans, nonhuman primates, and rodents. In contrast toin vitroresults, genetic or pharmacologic DA depletion did not attenuate loss of dopaminergic neurons in the SN or dopaminergic neuron terminals in the striatum. These results suggest that DA does not contribute to acute MPTP toxicityin vivo.
Topography of Arc/Arg3.1 mRNA Expression in the Dorsal and Ventral Hippocampus Induced by Recent and Remote Spatial Memory Recall: Dissociation of CA3 and CA1 Activation
Authors: Gusev Pavel A. , Cui Changhai , Alkon Daniel L. , Gubin Alexander N.
Published: October 2005

The understanding of the mechanisms of memory retrieval and its deficits, and the detection of memory underlying neuronal plasticity, is greatly impeded by a lack of precise knowledge of the brain circuitry that underlies the functions of memory. The specific roles of anatomically distinct hippocampal subdivisions in recent and long-term memory retention and recall are essentially unknown. To address these questions, we mapped the expression of Arc/Arg 3.1 mRNA, a neuronal activity marker, in memory retention at multiple rostrocaudal levels of the dentate gyrus, CA3, CA1, subiculum, and lateral and medial entorhinal cortices after a platform search in a water-maze spatial task at 24 h and 1 month compared with swim and naive controls. We found that the entorhinohippocampal neuronal activity underlying the recall of recent and remote spatial memory has an anatomically distributed and time-dependent organization throughout both the dorsal and ventral hippocampus that is subdivision specific. We found a dissociation in the activity of the entorhinal cortex, CA3, and CA1 over a period of memory consolidation. Although CA3, the dorsal hippocampus, and the entorhinal cortex demonstrated the most persistent learning-specific signal during both recent and long-term memory recall, CA1 and the ventral hippocampus displayed the most dramatic signal decline. We determined the coordinates of activity clusters in the hippocampal subdivisions during the platform search and their dynamics over time. Our mapping data suggest that although the level of corticohippocampal interaction is similar during the retrieval of recent and remote spatial memories, the mnemonic function of the hippocampus may have changed, and the activity underlying remote spatial memory could be anatomically segregated within hippocampal subdivisions in small segments.
A Role for the β1-β2Loop in the Gating of 5-HT3Receptors
Authors: Reeves David C. , Jansen Michaela , Bali Moez , Lemster Thomas , Akabas Myles H.
Published: October 2005

Based on theTorpedoacetylcholine receptor structure, Unwin and colleagues (Miyazawa et al., 2003; Unwin, 2005) hypothesized that the transduction of agonist binding to channel gate opening involves a “pin-into-socket” interaction between αV46 at the tip of the extracellular β1-β2loop and the transmembrane M2 segment and M2-M3 loop. We mutated to cysteine the aligned positions in the 5-HT3Aand 5-HT3Bsubunit β1-β2loops K81 and Q70, respectively. The maximal 5-HT-activated currents in receptors containing 5-HT3A/K81C or 5-HT3B/Q70C were markedly reduced compared with wild type. Desensitization of wild-type currents involved fast and slow components. Mutant currents desensitized with only the fast time constant. Reaction with several methanethiosulfonate reagents potentiated currents to wild-type levels, but reaction with other more rigid thiol-reactive reagents caused inhibition. Single-channel conductances of wild type, K81C, and K81C after modification were similar. We tested the proximity of K81C to the M2-M3 loop by mutating M2-M3 loop residues to cysteine in the K81C background. Disulfide bonds formed in 5-HT3A/K81C/A304C and 5-HT3A/K81C/I305C when coexpressed with 5-HT3B. We conclude that in the resting state, K81 is not in a hydrophobic pocket as suggested by the pin-into-socket hypothesis. K81 interacts with the extracellular end of M2 and plays a critical role in channel opening and in the return from fast desensitization. We suggest that during channel activation, β1-β2loop movement moves M2 and the M2-M3 loop so that the M2 segments rotate/translate away from the channel axis, thereby opening the lumen. Recovery from fast desensitization requires the interaction between K81 and the extracellular end of M2.
Interaction of SPIN90 with Dynamin I and Its Participation in Synaptic Vesicle Endocytosis
Authors: Kim Yujin , Kim Sunyun , Lee Suho , Kim Sung Hyun , Kim Yoonju , Park Zee Yong , Song Woo Keun , Chang Sunghoe
Published: October 2005

SH3 protein interacting with Nck, 90 kDa (SPIN90) is an Nck-binding protein that contains one Src homology 3 (SH3) domain, three proline-rich domains (PRDs), a serine/threonine-rich region, and a hydrophobic C-terminal region. Previously, we have shown that SPIN90 plays roles in the sarcomere assembly in cardiac muscles and in the formation of focal contacts in HeLa cells. Besides in heart, SPIN90 is also highly expressed in the brain, but its role in the neuronal system is completely unknown. Here, we found that SPIN90 is expressed in the presynaptic compartment in which it binds dynamin I, a key component of the endocytic machinery, and that it participates in synaptic vesicle endocytosis. Pull-down analysis and coimmunoprecipitation proved the associations of SPIN90 with dynamin I through SH3-PRD interaction. Overexpression of SPIN90 or knocking down SPIN90 by small interfering RNA impaired synaptic vesicle endocytosis. We further confirmed by the rescue experiments that the endocytic defects by SPIN90 expression come from its interaction with dynamin I. Exocytosis kinetics was not affected by SPIN90 expression. Together, our findings suggest that SPIN90 could modulate the interactions of dynamin I with other endocytic proteins that cooperate in the coated vesicle formation, thus regulating synaptic vesicle endocytosis.
Disruption and Recovery of Patterned Retinal Activity in the Absence of Acetylcholine
Authors: Stacy Rebecca C. , Demas Jay , Burgess Robert W. , Sanes Joshua R. , Wong Rachel O. L.
Published: October 2005

Many developing neural circuits generate synchronized bursting activity among neighboring neurons, a pattern thought to be important for sculpting precise neural connectivity. Network output remains relatively constant as the cellular and synaptic components of these immature circuits change during development, suggesting the presence of homeostatic mechanisms. In the retina, spontaneous waves of activity are present even before chemical synapse formation, needing gap junctions to propagate. However, as synaptogenesis proceeds, retinal waves become dependent on cholinergic neurotransmission, no longer requiring gap junctions. Later still in development, waves are driven by glutamatergic rather than cholinergic synapses. Here, we asked how retinal activity evolves in the absence of cholinergic transmission by using a conditional mutant in which the gene encoding choline acetyltransferase (ChAT), the sole synthetic enzyme for acetylcholine (ACh), was deleted from large retinal regions. ChAT-negative regions lacked retinal waves for the first few days after birth, but by postnatal day 5 (P5), ACh-independent waves propagated across these regions. Pharmacological analysis of the waves inChATknock-out regions revealed a requirement for gap junctions but not glutamate, suggesting that patterned activity may have emerged via restoration of previous gap-junctional networks. Similarly, in P5 wild-type retinas, spontaneous activity recovered after a few hours in nicotinic receptor antagonists, often as local patches of coactive cells but not waves. The rapid recovery of rhythmic spontaneous activity in the presence of cholinergic antagonists and the eventual emergence of waves inChATknock-out regions suggest that homeostatic mechanisms regulate retinal output during development.
Intracellular Trafficking of Histone Deacetylase 4 Regulates Neuronal Cell Death
Authors: Bolger Timothy A. , Yao Tso-Pang
Published: October 2005

Histone deacetylase 4 (HDAC4) undergoes signal-dependent shuttling between the cytoplasm and nucleus, which is regulated in part by calcium/calmodulin-dependent kinase (CaMK)-mediated phosphorylation. Here, we report that HDAC4 intracellular trafficking is important in regulating neuronal cell death. HDAC4 is normally localized to the cytoplasm in brain tissue and cultured cerebellar granule neurons (CGNs). However, in response to low-potassium or excitotoxic glutamate conditions that induce neuronal cell death, HDAC4 rapidly translocates into the nucleus of cultured CGNs. Treatment with the neuronal survival factor BDNF suppresses HDAC4 nuclear translocation, whereas a proapoptotic CaMK inhibitor stimulates HDAC4 nuclear accumulation. Moreover, ectopic expression of nuclear-localized HDAC4 promotes neuronal apoptosis and represses the transcriptional activities of myocyte enhancer factor 2 and cAMP response element-binding protein, survival factors in neurons. In contrast, inactivation of HDAC4 by small interfering RNA or HDAC inhibitors suppresses neuronal cell death. Finally, an increase of nuclear HDAC4 in granule neurons is also observed inweavermice, which harbor a mutation that promotes CGN apoptosis. Our data identify HDAC4 and its intracellular trafficking as key effectors of multiple pathways that regulate neuronal cell death.
Endocannabinoid Signaling Dynamics Probed with Optical Tools
Authors: Heinbockel Thomas , Brager Darrin H. , Reich Christian G. , Zhao Jun , Muralidharan Sukumaran , Alger Bradley E. , Kao Joseph P. Y.
Published: October 2005

Intercellular signaling dynamics critically influence the functional roles that the signals can play. Small lipids are synthesized and released from neurons, acting as intercellular signals in regulating neurotransmitter release, modulating ion channels on target cells, and modifying synaptic plasticity. The repertoire of biological effects of lipids such as endocannabinoids (eCBs) is rapidly expanding, yet lipid signaling dynamics have not been studied. The eCB system constitutes a powerful tool for bioassaying the dynamics of lipid signaling. The eCBs are synthesized in, and released from, postsynaptic somatodendritic domains that are readily accessible to whole-cell patch electrodes. The dramatic effects of these lipid signals are detected electrophysiologically as CB1-dependent alterations in conventional synaptic transmission, which therefore serve as a sensitive reporter of eCB actions. We used electrophysiological recording, photolytic release of caged glutamate and a newly developed caged AEA (anandamide), together with rapid [Ca2+]imeasurements, to investigate the dynamics of retrograde eCB signaling between CA1 pyramidal cells and GABAergic synapses in rat hippocampusin vitro. We show that, at 22°C, eCB synthesis and release must occur within 75-190 ms after the initiating stimulus, almost an order of magnitude faster than previously thought. At 37°C, the time could be <50 ms. Activation of CB1 and downstream processes constitute a significant fraction of the total delay and are identified as major rate-limiting steps in retrograde signaling. Our findings imply that lipid messenger dynamics are comparable with those of metabotropic neurotransmitters and can modulate neuronal interactions on a similarly fast time scale.
Neuregulin-1 Reverses Long-Term Potentiation at CA1 Hippocampal Synapses
Authors: Kwon Oh-Bin , Longart Marines , Vullhorst Detlef , Hoffman Dax A. , Buonanno Andres
Published: October 2005

Neuregulin-1 (NRG-1) has been identified genetically as a schizophrenia susceptibility gene, but its function in the adult brain is unknown. Here, we show that NRG-1β does not affect basal synaptic transmission but reverses long-term potentiation (LTP) at hippocampal Schaffer collateral→CA1 synapses in an activity- and time-dependent manner. Depotentiation by NRG-1β is blocked by two structurally distinct and selective ErbB receptor tyrosine kinase inhibitors. Moreover, ErbB receptor inhibition increases LTP at potentiated synapses and blocks LTP reversal by theta-pulse stimuli. NRG-1β selectively reduces AMPA, not NMDA, receptor EPSCs and has no effect on paired-pulse facilitation ratios. Live imaging of hippocampal neurons transfected with receptors fused to superecliptic green fluorescent protein, as well as quantitative analysis of native receptors, show that NRG-1β stimulates the internalization of surface glutamate receptor 1-containing AMPA receptors. This novel regulation of LTP by NRG-1 has important implications for the modulation of synaptic homeostasis and schizophrenia.
Neuronal Depolarization Controls Brain-Derived Neurotrophic Factor-Induced Upregulation of NR2C NMDA Receptor via Calcineurin Signaling
Authors: Suzuki Kazunori , Sato Masaaki , Morishima Yosuke , Nakanishi Shigetada
Published: October 2005

In the developing cerebellum, switching of subunit composition of NMDA receptors occurs in granule cells from NR2B subunit-containing receptors to NR2C subunit-containing receptors. This switching of subunit composition plays an important role in the establishment of functional mossy fiber- granule cell synaptic transmission in the mature cerebellar network. The mechanism underlying NR2C upregulation in developing granule cells, however, has to date remained to be determined. In granule cells cultured in low (5 mm) KCl, brain-derived neurotrophic factor (BDNF) upregulated NR2C mRNA via the TrkB-extracellular signal-regulated kinase (ERK) 1/2 cascade and promoted the formation of an NR2C-containing NMDA receptor complex. In granule cells cultured in high (25 mm) KCl, depolarization stimulated voltage-sensitive Ca2+channels. The resultant increase in intracellular Ca2+activated Ca2+/calmodulin-dependent calcineurin phosphatase and blocked NR2C mRNA upregulation. Interestingly, the depolarization-induced Ca2+increase simultaneously upregulated BDNF mRNA via Ca2+/calmodulin-dependent protein kinase (CaMK). Consequently, when calcineurin was inhibited by its inhibitor FK506 under the depolarizing condition, the CaMK-mediated increase in BDNF became a stimulatory signal, and the endogenous BDNF autocrine system was capable of upregulating NR2C mRNA via the common TrkB-ERK cascade. The importance of the BDNF-TrkB pathway was further supported by a significant reduction in NR2C in normally migrated granule cells ofTrkB-/-knock-out micein vivo. The convergent mechanism of the BDNF and Ca2+signaling cascades thus plays an important regulatory role in NR2C induction in granule cells during cerebellar development.
Mechanisms of Late-Onset Cognitive Decline after Early-Life Stress
Authors: Brunson Kristen L. , Kramár Enikö , Lin Bin , Chen Yuncai , Colgin Laura Lee , Yanagihara Theodore K. , Lynch Gary , Baram Tallie Z.
Published: October 2005

Progressive cognitive deficits that emerge with aging are a result of complex interactions of genetic and environmental factors. Whereas much has been learned about the genetic underpinnings of these disorders, the nature of “acquired” contributing factors, and the mechanisms by which they promote progressive learning and memory dysfunction, remain largely unknown. Here, we demonstrate that a period of early-life “psychological” stress causes late-onset, selective deterioration of both complex behavior and synaptic plasticity: two forms of memory involving the hippocampus, were severely but selectively impaired in middle-aged, but not young adult, rats exposed to fragmented maternal care during the early postnatal period. At the cellular level, disturbances to hippocampal long-term potentiation paralleled the behavioral changes and were accompanied by dendritic atrophy and mossy fiber expansion. These findings constitute the first evidence that a short period of stress early in life can lead to delayed, progressive impairments of synaptic and behavioral measures of hippocampal function, with potential implications to the basis of age-related cognitive disorders in humans.
The Nonkinase Phorbol Ester Receptor α1-Chimerin Binds the NMDA Receptor NR2A Subunit and Regulates Dendritic Spine Density
Authors: Van de Ven Thomas J. , VanDongen Hendrika M. A. , VanDongen Antonius M. J.
Published: October 2005

Abnormalities in dendritic spines have long been associated with cognitive dysfunction and neurodevelopmental delay, whereas rapid changes in spine shape underlie synaptic plasticity. The key regulators of cytoskeletal reorganization in dendrites and spines are the Rho GTPases, which modify actin polymerization in response to synaptic signaling. Rho GTPase activity is modulated by multiple regulatory proteins, some of which have been found to associate with proteins localized to spines. Here, we show that the nonkinase phorbol ester receptor α1-chimerin is present in dendrites and spines, where it binds to the NMDA receptor NR2A subunit in a phorbol ester-dependent manner. α1-Chimerin contains a GTPase activating (GAP) domain, with activity toward the Rho family member Rac1. Overexpression of α1-chimerin in cultured hippocampal neurons inhibits formation of new spines and removes existing spines. This reduction in spine density is mediated by Rac1 inhibition, because it depends critically on the presence of a functional GAP domain. Conversely, depletion of α1-chimerin leads to an increase in spine density, indicating that a basal inhibition of Rac1 maintains the number of spines at a submaximal level. The ability of α1-chimerin to modulate spine number requires an interaction with the NMDA receptor, because an α1-chimerin mutant that binds weakly to NR2A fails to decrease spine density. Together, these results suggest that α1-chimerin is able to modulate dendritic spine morphology by binding to synaptic NMDA receptors and locally inactivating Rac1.
Q/R Site Editing Controls Kainate Receptor Inhibition by Membrane Fatty Acids
Authors: Wilding Timothy J. , Zhou Yun , Huettner James E.
Published: October 2005

RNA editing within the pore loop controls the pharmacology and permeation properties of ion channels formed by neuronal AMPA and kainate receptor subunits. Genomic sequences for the glutamate receptor 2 (GluR2) subunit of AMPA receptors and the GluR5 and GluR6 subunits of kainate receptors all encode a neutral glutamine (Q) residue within the channel pore that can be converted by RNA editing to a positively charged arginine (R). Receptors comprised of unedited subunits are permeable to calcium and display inwardly rectifying current-voltage relationships, because of blocking of outward current by intracellular polyamines. In contrast, receptors that include edited subunits conduct less calcium, resist polyamine block, and have relatively linear current-voltage relationships. We showed previously thatcis-unsaturated fatty acids, including arachidonic acid and docosahexanoic acid, exert a potent block of native kainate receptors as well as homomeric recombinant receptors formed by transfection of heterologous cells with cDNA for the GluR6(R) subunit. Here, we show that fatty acid blockade of recombinant homomeric and heteromeric kainate receptors is strongly dependent on editing at the Q/R site. Recombinant channels that include unedited subunits exhibit significantly weaker block than channels made up of fully edited subunits. Inhibition of fully edited channels is equivalent at voltages from -70 to +40 mV and is noncompetitive, consistent with allosteric regulation of channel function.
Functional Correction of CNS Phenotypes in a Lysosomal Storage Disease Model Using Adeno-Associated Virus Type 4 Vectors
Authors: Liu Gumei , Martins Inês , Wemmie John A. , Chiorini John A. , Davidson Beverly L.
Published: October 2005

Lysosomal storage diseases (LSDs) represent a significant portion of inborn metabolic disorders. More than 60% of LSDs have CNS involvement. LSD therapies for systemic diseases have been developed, but efficacy does not extend to the CNS. In this study, we tested whether adeno-associated virus type 4 (AAV4) vectors could mediate global functional and pathological improvements in a murine model of mucopolysaccharidosis type VII (MPS VII) caused by β-glucuronidase deficiency. Recombinant AAV4 vectors encoding β-glucuronidase were injected unilaterally into the lateral ventricle of MPS VII mice with established disease. Transduced ependyma expressed high levels of recombinant enzyme, with secreted enzyme penetrating cerebral and cerebellar structures, as well as the brainstem. Immunohistochemical studies revealed close association of recombinant enzyme and brain microvasculature, indicating that β-glucuronidase reached brain parenchyma via the perivascular spaces lining blood vessels. Aversive associative learning was tested by context fear conditioning. Compared with age-matched heterozygous controls, affected mice showed impaired conditioned fear response and context discrimination. This behavioral deficit was reversed 6 weeks after gene transfer in AAV4 β-glucuronidase-treated MPS VII mice. Our data show that ependymal cells can serve as a source of enzyme secretion into the surrounding brain parenchyma and CSF. Secreted enzymes subsequently spread via various routes to reach structures throughout the brain and mediated pathological and functional disease correction. Together, our proof-of-principal experiments suggest a unique and efficient manner for treating the global CNS deficits in LSD patients.
The CRAL/TRIO and GOLD Domain Protein CGR-1 Promotes Induction of Vulval Cell Fates in Caenorhabditis elegans and Interacts Genetically With the Ras Signaling Pathway
Authors: Goldstein Jessica L , Glossip Danielle , Nayak Sudhir , Kornfeld Kerry
Published: October 2005

Ras-mediated signaling is necessary for the induction of vulval cell fates during Caenorhabditis elegans development. We identified cgr-1 by screening for suppressors of the ectopic vulval cell fates caused by a gain-of-function mutation of the let-60 ras gene. Analysis of two cgr-1 loss-of-function mutations indicates that cgr-1 positively regulates induction of vulval cell fates. cgr-1 is likely to function at a step in the Ras signaling pathway that is downstream of let-60, which encodes Ras, and upstream of lin-1, which encodes a transcription factor, if these genes function in a linear signaling pathway. These genetic studies are also consistent with the model that cgr-1 functions in a parallel pathway that promotes vulval cell fates. Localized expression studies suggest that cgr-1 functions cell autonomously to affect vulval cell fates. cgr-1 also functions early in development, since cgr-1 is necessary for larval viability. CGR-1 contains a CRAL/TRIO domain likely to bind a small hydrophobic ligand and a GOLD domain that may mediate interactions with proteins. A bioinformatic analysis revealed that there is a conserved family of CRAL/TRIO and GOLD domain-containing proteins that includes members from vertebrates and Drosophila. The analysis of cgr-1 identifies a novel in vivo function for a member of this family and a potential new regulator of Ras-mediated signaling.
Genetic Evidence That Nonhomologous Disjunction and Meiotic Drive Are Properties of Wild-Type Drosophila melanogaster Male Meiosis
Authors: Boschi Manuela , Belloni Massimo , Robbins Leonard G
Published: October 2005

We have followed sex and second chromosome disjunction, and the effects of these chromosomes on sperm function, in four genotypes: wild-type males, males deficient for the Y-linked crystal locus, males with an X chromosome heterochromatic deficiency that deletes all X–Y pairing sites, and males with both deficiencies. Both mutant situations provoke chromosome misbehavior, but the disjunctional defects are quite different. Deficiency of the X heterochromatin, consonant with the lack of pairing sites, mostly disrupts X–Y disjunction with a decidedly second-level effect on major autosome behavior. Deleting crystal, consonant with the cytological picture of postpairing chromatin-condensation problems, disrupts sex and autosome disjunction equally. Even when the mutant-induced nondisjunction has very different mechanics, however, and even more importantly, even in the wild type, there is strong, and similar, meiotic drive. The presence of meiotic drive when disjunction is disrupted by distinctly different mechanisms supports the notion that drive is a normal cellular response to meiotic problems rather than a direct effect of particular mutants. Most surprisingly, in both wild-type and crystal-deficient males the Y chromosome moves to the opposite pole from a pair of nondisjoined second chromosomes nearly 100% of the time. This nonhomologous interaction is, however, absent when the X heterochromatin is deleted. The nonhomologous disjunction of the sex and second chromosomes may be the genetic consequence of the chromosomal compartmentalization seen by deconvolution microscopy, and the absence of Y–2 disjunction when the X heterochromatin is deleted suggests that XY pairing itself, or a previously unrecognized heterochromatic function, is prerequisite to this macrostructural organization of the chromosomes.
Lysis Timing and Bacteriophage Fitness
Authors: Wang Ing-Nang
Published: October 2005

The effect of lysis timing on bacteriophage (phage) fitness has received little theoretical or experimental attention. Previously, the impact of lysis timing on phage fitness was studied using a theoretical model based on the marginal value theorem from the optimal foraging theory. An implicit conclusion of the model is that, for any combination of host quantity and quality, an optimal time to lyse the host would exist so that the phage fitness would be the highest. To test the prediction, an array of isogenic λ-phages that differ only in their lysis times was constructed. For each phage strain, the lysis time, burst size, and fitness (growth rate) were determined. The result showed that there is a positive linear relationship between lysis time and burst size. Moreover, the strain with an intermediate lysis time has the highest fitness, indicating the existence of an optimal lysis time. A mathematical model is also constructed to describe the population dynamics of phage infection. Computer simulations using parameter values derived from phage λ-infection also showed an optimal lysis time. However, both the optimum and the fitness are different from the experimental result. The evolution of phage lysis timing is discussed from the perspectives of multiple infection and life-history trait evolution.
Nuclear–Mitochondrial Epistasis and Drosophila Aging: Introgression of Drosophila simulans mtDNA Modifies Longevity in D. melanogaster Nuclear Backgrounds
Authors: Rand David M , Fry Adam , Sheldahl Lea
Published: October 2005

Under the mitochondrial theory of aging, physiological decline with age results from the accumulated cellular damage produced by reactive oxygen species generated during electron transport in the mitochondrion. A large body of literature has documented age-specific declines in mitochondrial function that are consistent with this theory, but relatively few studies have been able to distinguish cause from consequence in the association between mitochondrial function and aging. Since mitochondrial function is jointly encoded by mitochondrial (mtDNA) and nuclear genes, the mitochondrial genetics of aging should be controlled by variation in (1) mtDNA, (2) nuclear genes, or (3) nuclear–mtDNA interactions. The goal of this study was to assess the relative contributions of these factors in causing variation in Drosophila longevity. We compared strains of flies carrying mtDNAs with varying levels of divergence: two strains from Zimbabwe (<20 bp substitutions between mtDNAs), strains from Crete and the United States (∼20–40 bp substitutions between mtDNAs), and introgression strains of Drosophila melanogaster carrying mtDNA from Drosophila simulans in a D. melanogaster Oregon-R chromosomal background (>500 silent and 80 amino acid substitutions between these mtDNAs). Longevity was studied in reciprocal cross genotypes between pairs of these strains to test for cytoplasmic (mtDNA) factors affecting aging. The intrapopulation crosses between Zimbabwe strains show no difference in longevity between mtDNAs; the interpopulation crosses between Crete and the United States show subtle but significant differences in longevity; and the interspecific introgression lines showed very significant differences between mtDNAs. However, the genotypes carrying the D. simulans mtDNA were not consistently short-lived, as might be predicted from the disruption of nuclear–mitochondrial coadaptation. Rather, the interspecific mtDNA strains showed a wide range of variation that flanked the longevities seen between intraspecific mtDNAs, resulting in very significant nuclear × mtDNA epistatic interaction effects. These results suggest that even “defective” mtDNA haplotypes could extend longevity in different nuclear allelic backgrounds, which could account for the variable effects attributable to mtDNA haplogroups in human aging.
Convergence to the Island-Model Coalescent Process in Populations With Restricted Migration
Authors: Matsen Frederick A , Wakeley John
Published: October 2005

In this article we apply some graph-theoretic results to the study of coalescence in a structured population with migration. The graph is the pattern of migration among subpopulations, or demes, and we use the theory of random walks on graphs to characterize the ease with which ancestral lineages can traverse the habitat in a series of migration events. We identify conditions under which the coalescent process in populations with restricted migration, such that individuals cannot traverse the habitat freely in a single migration event, nonetheless becomes identical to the coalescent process in the island migration model in the limit as the number of demes tends to infinity. Specifically, we first note that a sequence of symmetric graphs with Diaconis–Stroock constant bounded above has an unstructured Kingman-type coalescent in the limit for a sample of size two from two different demes. We then show that circular and toroidal models with long-range but restricted migration have an upper bound on this constant and so have an unstructured-migration coalescent in the limit. We investigate the rate of convergence to this limit using simulations.
Detection of Genes for Ordinal Traits in Nuclear Families and a Unified Approach for Association Studies
Authors: Zhang Heping , Wang Xueqin , Ye Yuanqing
Published: October 2005

There is growing interest in genomewide association analysis using single-nucleotide polymorphisms (SNPs), because traditional linkage studies are not as powerful in identifying genes for common, complex diseases. Tests for linkage disequilibrium have been developed for binary and quantitative traits. However, since many human conditions and diseases are measured in an ordinal scale, methods need to be developed to investigate the association of genes and ordinal traits. Thus, in the current report we propose and derive a score test statistic that identifies genes that are associated with ordinal traits when gametic disequilibrium between a marker and trait loci exists. Through simulation, the performance of this new test is examined for both ordinal traits and quantitative traits. The proposed statistic not only accommodates and is more powerful for ordinal traits, but also has similar power to that of existing tests when the trait is quantitative. Therefore, our proposed statistic has the potential to serve as a unified approach to identifying genes that are associated with any trait, regardless of how the trait is measured. We further demonstrated the advantage of our test by revealing a significant association (P = 0.00067) between alcohol dependence and a SNP in the growth-associated protein 43.