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Biomedical subjects

W G Clark

Publications and source records attributed to W G Clark.

At least 19 recordsLinked to original sources
PubMed2004

Self-similar evolution of parabolic pulses in a laser.

Self-similar propagation of ultrashort, parabolic pulses in a laser resonator is observed theoretically and experimentally. This constitutes a new type of pulse shaping in mode-locked lasers: in contrast to the well-known static (solitonlike) and breathing (dispersion-managed soliton) pulse evolutions, asymptotic solutions to the nonlinear wave equation that governs pulse propagation in most of the laser cavity are observed. Stable self-similar pulses exist with energies much greater than can be tolerated in solitonlike pulse shaping, and this has implications for practical lasers.

Lasers↗
PubMed2004

Inhomogeneous electronic structure probed by spin-echo experiments in the electron doped high-Tc superconductor Pr1.85Ce0.15CuO4-y.

63Cu nuclear magnetic resonance spin-echo decay rate (T-12) measurements are reported for the normal and superconducting states of a single crystal of Pr(1.85)Ce(0.15)CuO(4-y) in a magnetic field B(0)=9 T over the temperature range 2<T<200 K. The spin-echo decay rate is temperature dependent for T<55 K and has a substantial dependence on the radio frequency (rf) pulse parameters below T approximately 25 K. This dependence indicates that T-12 is strongly effected by a local magnetic field distribution that can be modified by the rf pulses, including ones that are not at the nuclear Larmor frequency. The low-temperature results are consistent with the formation of a static inhomogeneous electronic structure that couples to the rf fields of the pulses.

Journal Article↗
PubMed2003

Generation of 50-fs, 5-nJ pulses at 1.03 micrometre from a wave-breaking-free fiber laser.

We report the generation of 6-nJ chirped pulses from a mode-locked Yb fiber laser at 1.03 micrometre. A linear anomalous-dispersion segment suppresses wave-breaking effects of solitonlike pulse shaping at high energies. The dechirped pulse duration is 50 fs, and the energy is 5 nJ. This laser produces twice the pulse energy and average power, and approximately five times the peak power, of the previous best mode-locked fiber laser. It is to our knowledge the first fiber laser that directly offers performance similar to that of solid-state lasers such as Ti:sapphire.

Lasers↗
PubMed2002

Origin of the enhanced copper spin echo decay rate in the pseudogap regime of the multilayer high-T(c) cuprates.

We report measurements of the anisotropy of the spin echo decay for the inner layer Cu site of the triple layer cuprate Hg(0.8)Re(0.2)Ba(2)Ca(2)Cu(3)O(8) (T(c)=126 K). The angular dependence of the second moment (T(-2)(2M) identical with ) deduced from the decay curves indicates that T(-2)(2M) for H0 parallel c is enhanced in the pseudogap regime below T(pg) approximately 170 K, as seen in bilayer systems. Comparison of T(-2)(2M) between H0 parallel c and H0 perpendicular c indicates that this enhancement is caused by electron spin correlations between the inner and the outer CuO2 layers. The results provide the answer to the long-standing controversy regarding the opposite T dependences of (T1T)(-1) and T(-2)(2G) (T(2G): Gaussian component) in the pseudogap regime of multilayer systems.

Journal Article↗
PubMed2001

Triplet superconductivity in an organic superconductor probed by NMR Knight shift.

The nature of the superconducting state in quasi-one-dimensional organic conductors has remained controversial since its discovery. Here we present results of (77)Se NMR Knight shift (K(s)) experiments in (TMTSF)(2)PF(6) under 7 kbar of pressure with a magnetic field aligned along the most conducting a axis. We find no noticeable shift in K(s) upon cooling through the superconducting transition. Since K(s) directly probes the spin susceptibility chi(s), the fact that chi(s) remains unchanged through the superconducting transition strongly suggests spin-triplet superconductivity.

Journal Article↗
PubMed1999

The IRT1 protein from Arabidopsis thaliana is a metal transporter with a broad substrate range.

The molecular basis for the transport of manganese across membranes in plant cells is poorly understood. We have found that IRT1, an Arabidopsis thaliana metal ion transporter, can complement a mutant Saccharomyces cerevisiae strain defective in high-affinity manganese uptake (smf1 delta). The IRT1 protein has previously been identified as an iron transporter. The current studies demonstrated that IRT1, when expressed in yeast, can transport manganese as well. This manganese uptake activity was inhibited by cadmium, iron(II) and zinc, suggesting that IRT1 can transport these metals. The IRT1 cDNA also complements a zinc uptake-deficient yeast mutant strain (zrt1zrt2), and IRT1-dependent zinc transport in yeast cells is inhibited by cadmium, copper, cobalt and iron(III). However, IRT1 did not complement a copper uptake-deficient yeast mutant (ctr1), implying that this transporter is not involved in the uptake of copper in plant cells. The expression of IRT1 is enhanced in A. thaliana plants grown under iron deficiency. Under these conditions, there were increased levels of root-associated manganese, zinc and cobalt, suggesting that, in addition to iron, IRT1 mediates uptake of these metals into plant cells. Taken together, these data indicate that the IRT1 protein is a broad-range metal ion transporter in plants.

Arabidopsis↗
PubMed1999

The multimedia power portfolio: creative strategy for core curriculum.

To address today's rapidly changing health care environment, educational programs for students in the health professions must also change by exploring new and innovative ways to better prepare students for their future as members of the health care team. This demand for change in allied health and nursing educational programs comes at a time when institutions of higher education are faced with shrinking funds. Therefore, creative efficient utilization of resources must be a prime consideration when implementing new educational models.

Allied Health Personnel↗
PubMed1996

Elicitation of dihydrobenzophenanthridine oxidase in Sanguinaria canadensis cell cultures.

Dihydrobenzophenanthridine (DHBP) oxidase catalyses the last step in the biogenesis of the benzo[c]phenanthridine alkaloid sanguinarine. Addition of autoclaved fungal preparations or putative plant defence signalling intermediates (jasmonic acid (JA), methyl jasmonate (MeJ), acetylsalicylic acid (ASA)) to Sanguinaria canadensis cell suspension cultures elicited an increase in the activity of DHBP oxidase. MeJ and ASA were better inducers of oxidase activity than were the fungal elicitor and JA. Enzyme-specific activity could be induced in a dose- and time-dependent manner up to 4- to 14-fold, respectively, when cells were treated with MeJ or with ASA. A change in total enzyme activity in cultured cells was observed only at the highest concentration of MeJ and not at any level of ASA tested. The results suggest that MeJ and ASA may play a role in the S. canadensis defence against pathogens by eliciting the enzymes involved in the synthesis of the phytoalexin benzophenanthridine alkaloids.

Cells, Cultured↗
PubMed1995

Studies of coat protein-mediated resistance to TMV. I. The PM2 assembly defective mutant confers resistance to TMV.

Tobacco mosaic virus mutant PM2 contains two amino acid changes in coat protein sequence relative to the sequence of the coat protein of TMV U1. This results in unstable infectivity, inability to cause normal systemic infection, and accumulation of elongated open helixes of coat protein. Using site-directed mutagenesis we demonstrated that the characteristics of PM2 are due to the change of Thr28-->Ile, while the second change, Glu95-->Asp, had no apparent effect on virion structure or infectivity. Transgenic Nicotiana tabacum cv Xanthi NN and Xanthi nn plants that accumulate coat protein that contains one or both of the amino acid changes are as resistant to TMV infection as transgenic plants that contain wild-type TMV coat protein. The implication of these results on a model for coat protein-mediated resistance that involves the interaction of transgenic coat protein with the challenge virus is discussed.

Amino Acids↗
PubMed1995

Studies of coat protein-mediated resistance to tobacco mosaic virus (TMV). II. Challenge by a mutant with altered virion surface does not overcome resistance conferred by TMV coat protein.

Transgenic tobacco plants expressing the coat protein (CP) gene of the U1 strain of tobacco mosaic virus (TMV) exhibit CP-mediated resistance (CP-MR) against some, but not all, tobamoviruses. To investigate the role of the amino acid sequences on the surface of the challenge virus in CP-MR, mutant strains of U1 TMV were constructed to contain the amino or carboxy termini of the CP of Sunn hemp mosaic tobamovirus (SHMV). The modified virus was unable to overcome CP-MR in transgenic plants that contained the TMV CP. In contrast, TMV in which the CP was replaced by the SHMV CP overcame CP-MR to the same extent as did SHMV. We conclude that CP-MR conferred by TMV CP involves interactions between amino acid sequences of the challenge viruses and the transgene protein other than those on the surface of the challenge virus.

Amino Acid Sequence↗
PubMed1995

Modulation of opioid binding associated with nuclear matrix and nuclear membranes of NG108-15 cells.

Opioid binding sites were found in nuclear matrix preparations from NG108-15 neurohybrid cells. Binding parameters of delta-specific radioligands indicated that high-affinity binding sites discovered in purified nuclei were present in nuclear membranes and nuclear matrix fractions. Agonists bind with low affinity, if at all, to nuclear matrix preparations. Neither sensitivity of agonist binding to the GTP analog 5-guanylylimidodiphosphate nor adenylyl cyclase activity were detected in this fraction, suggesting the presence of guanine nucleotide binding regulatory protein/effector uncoupled sites. Opioid inhibition of basal and forskolin-stimulated adenylyl cyclase activity was found in nuclear membrane preparations. Cycloheximide treatment of cells inhibited opioid binding to nuclear membrane fractions to a greater extent than that associated with membranes sedimenting at 20,000 x g (P20) or nuclear matrix. Colchicine, a microtubule disrupter and inhibitor of receptor internalization, caused up-regulation of nuclear membrane and P20 opioid receptors and a loss in nuclear matrix associated sites. Taxol, a microtubule stabilizing agent, prevented the effect of colchicine. Etorphine-elicited down-regulation increased nuclear matrix associated binding while diminishing that in nuclear membranes and P20 fractions. Agonist-induced desensitization completely abolished nuclear matrix binding. In vitro preincubation of nuclear matrix preparations with protein kinase A catalytic subunit mimicked the desensitization effect. Forskolin treatment of cells potentiated nuclear matrix and P20 binding. These data suggest that nuclear membrane opioid receptors represent newly synthesized molecules en route to the cell surface, whereas nuclear matrix contains internalized delta sites.

Analgesics↗
PubMed1994

Elevation of plasma ACTH concentration in rabbits made febrile by systemic injection of bacterial endotoxin.

This study was carried out to investigate the adrenocorticotropic hormone (ACTH) response in rabbits made febrile by systemic injection of lipopolysaccharide (LPS, Salmonella typhosa endotoxin). Intravenous (i.v.) injection of LPS (0.1 microgram/kg and 1.0 microgram/kg) increased rectal temperature (biphasic fever) and the plasma concentration of ACTH (ACTH response) in a dose-related manner. These responses were suppressed by pretreatment with indomethacin (20 mg/kg, subcutaneously). Intracerebroventricular (i.c.v.) administration of indomethacin (400 micrograms) had no effect on the ACTH response to LPS, although it significantly suppressed febrile response. Small increases in plasma concentration of ACTH and significant fevers followed i.c.v. administration of prostaglandin E2 (2 micrograms) or F2 alpha (2 micrograms). I.v. administration of corticotropin releasing factor (CRF) antagonist [alpha-helical CRF (9-41) (200 micrograms/kg)] partly suppressed the ACTH increase induced in plasma by i.v. LPS. These results suggest that prostaglandins synthesized outside the blood-brain barrier play an important role in the ACTH response and that the mechanism for induction of the ACTH response is not exactly the same as that for the febrile response, although prostaglandins are involved in both responses.

Adrenocorticotropic Hormone↗
PubMed1994

Group therapy with chronically depressed geriatric patients.

The case study and the discussion of a framework for treating severely depressed elderly inpatients with group therapy illustrate many of the modifications in group process necessary for successfully treating chronically depressed geriatric patients. Group therapy is a highly effective treatment modality when integrated into an overall treatment plan that includes medications, activities, and patient/family education.

Aged↗
PubMed1993

Novel opioid binding sites associated with nuclei of NG108-15 neurohybrid cells.

Nuclear opioid binding sites have been discovered in NG108-15 neurohybrid cells. Marker enzyme analyses as well as electron and fluorescence microscopy studies attested to the high degree of purity of the nuclear preparations. Immunohistochemical studies on cryostat sections of NG108-15 cells with an antibody to the opioid receptor corroborated a nuclear localization. 3H-[D-Pen2,D-Pen5]enkephalin (3H-DPDPE), 3H-[D-Ala2,D-Leu5]enkephalin (3H-DADLE), and 3H-diprenorphine binding parameters, Kd and Bmax values, and heterologous competition binding and stereospecificity data satisfied criteria for the presence of delta-opioid sites in purified nuclear preparations. Neither mu-([D-Ala2,mephe4,gly-ol5] enkephalin), dihydromorphine, nor kappa-(U69593) specific binding was detectable in purified nuclear preparations. Rates of association and dissociation of 3H-[D-Ser2,L-Leu5]enkephalyl-Thr were comparable to values obtained previously for opioid receptors. Opioid binding was also shown in subnuclear preparations from NG108-15 cell cultures. Agonists, 3H-DADLE and 3H-DPDPE, bind with high affinity to nuclear membranes and with lower affinity to chromatin. In contrast, partial agonist 3H-diprenorphine high-affinity binding sites were predominant in chromatin, while low-affinity binding was found in the nuclear membrane. Accordingly, 5'-guanylylimidodiphosphate sensitivity of 3H-DADLE binding was detected in nuclear membranes but not in chromatin. Both agonist and partial agonist opioid binding to nuclear membrane and chromatin were abolished upon cycloheximide treatment of NG108-15 cells. Taken together, the results suggest that NG108-15 cells contain newly synthesized GTP binding regulatory protein (G-protein)-coupled delta-opioid receptors in nuclear membranes and uncoupled opioid binding sites in chromatin.

Binding Sites↗
PubMed1992

Purification and characterization of dihydrobenzophenanthridine oxidase from elicited Sanguinaria canadensis cell cultures.

Upon treatment of Papaveracea cells with fungal elicitors, the biosynthesis of benzo[c]phenanthridine alkaloids is induced. Dihydrobenzophenanthridine oxidase, which catalyzes a later step in the biogenesis of these alkaloids, is one of the enzymes whose activity is elevated in the process. Here we report the 211-fold purification of the oxidase from elicited Sanguinaria canadensis by a combination of ammonium sulfate fractionation, DEAE-Sephadex, CM-Sephadex, Sephadex G-200, and either phenyl Superose or gel filtration chromatography. The purified enzyme utilized molecular oxygen to oxidize dihydrosanguinarine to sanguinarine with concomitant formation of hydrogen peroxide. A pH optimum of 7.0, Vmax of 27 nkat/mg protein, and apparent Km of 6.0 microM for dihydrosanguinarine were determined. Dihydrochelerythrine was also found to be a substrate for the purified enzyme, displaying an apparent Km of 10 microM. However, neither dihydronorsanguinarine nor the indole alkaloid ajmalicine was oxidized, indicating that the enzyme has some substrate specificity. Apparent molecular weight estimates by sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed that the most purified enzyme preparation obtained contained a major component of 77 kDa and two minor components between 59 and 67 kDa that can be associated with oxidase activity. Purified enzyme preparations possessed activity that was inhibited by sodium diethyldithiocarbamate, sodium azide, potassium cyanide, 1,4-DL-dithiothreitol, and mercaptoethanol.

Cells, Cultured↗
PubMed1990

Tissue-specific expression of the TMV coat protein in transgenic tobacco plants affects the level of coat protein-mediated virus protection.

Transgenic tobacco plants were produced that express a chimeric gene encoding the coat protein (CP) of tobacco mosaic virus (TMV) under the control of the promoter from a ribulose bisphosphate carboxylase small subunit (rbcS) gene. Plant lines expressing comparable levels of CP from the rbcS and cauliflower mosaic virus 35S promoters were compared for resistance to TMV. In whole plant assays the 35S:CP constructs gave higher resistance than the rbcS:CP constructs. On the other hand, leaf mesophyll protoplasts isolated from both plant lines were equally resistant to infection by TMV. This indicated that the difference in resistance between the lines in the whole plant assay reflects differences at the level of short- and/or long-distance spread of TMV. Therefore, we propose that the difference in tissue-specific expression between the 35S and rbcS promoters accounts for greater resistance in the plant lines that express the 35S:CP chimeric genes.

Blotting, Western↗
PubMed1987

Changes in body temperature after administration of antipyretics, LSD, delta 9-THC and related agents: II.

Antipyretics, in particular acetaminophen, aspirin and ibuprofen, constitute the single most important class of drugs used therapeutically for an effect on body temperature. Hallucinogens exert prominent actions on the central nervous system, and it is not surprising that, like so many other centrally-acting agents, they too often affect temperature. This compilation primarily covers the considerable amount of data published from 1981 through 1985 on the interactions of these drugs and thermoregulation, but data from many earlier papers not included in a previous compilation are also tabulated. The effects of agents not classically considered as antipyretics on temperatures of febrile subjects are also covered. The information listed includes the species used, the route of administration and dose of drug, the environmental temperature at which experiments were performed, the number of tests, the direction and magnitude of change in body temperature and remarks on special conditions, such as age or brain lesions. Also indicated is the influence of other drugs, such as antagonists, on the response to the primary agent.

Anti-Inflammatory Agents, Non-Steroidal↗