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Biomedical subjects

S Thayer

Publications and source records attributed to S Thayer.

15 recordsLinked to original sources
PubMed2001

Assessing photosynthetic downregulation in sunflower stands with an optically-based model.

Using a simple light-use efficiency model based on optical measurements, we explored spatial patterns of photosynthetic activity in fertilized and unfertilized sunflower stands. The model had two components: (1) absorbed photosynthetically active radiation (APAR), and (2) radiation-use efficiency. APAR was the product of photosynthetic photon flux density (PPFD) and leaf absorptance, which was derived from leaf reflectance. Radiation-use efficiency was either assumed to be constant or allowed to vary linearly with the photochemical reflectance index (PRI), a measure of xanthophyll cycle pigment activity. When efficiency was assumed to be constant, the model overestimated photosynthetic rates in upper canopy layers exposed to direct PPFD, particularly in the unfertilized canopy due to the greater photosynthetic downregulation associated with higher levels of photoprotective (de-epoxidized) xanthophyll cycle pigments in these conditions. When efficiency was allowed to vary according to the PRI, modeled photosynthetic rates closely matched measured rates for all canopy layers in both treatments. These results illustrate the importance of considering reduced radiation-use efficiency due to photosynthetic downregulation when modeling photosynthesis from reflectance, and illustrate the potential for detecting radiation-use efficiency through leaf optical properties. At least under the conditions of this study, these results also suggest that xanthophyll cycle pigment activity and net carbon uptake are coordinately regulated, allowing assays of Photosystem II activity to reveal changing rates of net assimilation. Because the optical methods in this study are adaptable to multiple spatial scales (leaf to landscape), this approach may provide a scalable model for estimating photosynthetic rates independently from flux measurements.

Journal Article↗
PubMed2000

Morphine inhibits human microglial cell production of, and migration towards, RANTES.

The beta-chemokine RANTES has recently been implicated in the neuropathogenesis of the human immunodeficiency virus. Based upon previous studies of the effects of morphine on microglial cell production of cytokines and chemotaxis towards the activated complement component C5a, we tested the hypothesis that this opiate would alter the production of and migration towards RANTES by human microglia. Treatment of highly purified microglial cell cultures with morphine (10(-8)-10(-6) M) potently inhibited RANTES production by lipopolysaccharide- and interleukin-1beta-stimulated cells. Using a chemotaxis chamber to assess directed migration towards RANTES, treatment of microglial cells with morphine (10(-10)-10(-6) M) was found to suppress chemotaxis. The inhibitory effects of morphine on RANTES production and on chemotaxis were blocked by naloxone and beta-funaltrexamine, indicating that morphine mediated its suppressive effects via activation of microglial p-opioid receptors. Morphine's inhibitory effect on chemotaxis did not appear to be associated with an alteration in RANTES-induced [Ca2+]i mobilization. While the clinical significance of these in-vitro findings is unknown, they suggest that mu-opioid receptor agonists could alter certain neurodegenerative and inflammatory processes within the brain.

Brain↗
PubMed1992

The validity of study group assignments based on occupational histories obtained from questionnaires.

This study examined the validity of self-reported work histories for use in epidemiological studies of toxic exposures. Two uses that were examined were the assignment of subjects to exposure groups and the estimation of exposure duration. Questionnaire responses and data extracted from employment files were compared for 161 retired automobile workers. The questionnaire method assigned subjects to two extreme groups with 99% accuracy but rejected 30% of the subjects because of ambiguous data. Self-reports of exposure duration correlated moderately with the file estimates (r = .63, P = .01). The discrepancy between subjects' estimates and actual exposure duration correlated with subjects' job mobility. The findings indicate that the validity of self-report data declines with the precision required of the data, but that self-reports may have sufficient validity for studies that use extreme-group designs.

Algorithms↗
PubMed1991

Parenteral lorazepam versus parenteral haloperidol for the control of psychotic disruptive behavior.

In a double-blind, prospective study, 2 mg of intramuscular lorazepam and 5 mg of intramuscular haloperidol were equally effective in controlling aggression, agitation, and assaultive behavior. Although lorazepam and haloperidol produced an equivalent mean decrease in aggression, significantly more subjects who received lorazepam had a greater decrease in aggression ratings than haloperidol recipients; this effect was independent of sedation. Lorazepam produced significantly fewer extrapyramidal symptoms. These data support the current clinical practice of using lorazepam (alone, or in combination with a neuroleptic) for control of acute aggressive and assaultive behavior.

Acute Disease↗
PubMed1984

Subcellular Localizations of Two Dolichos biflorus Lectins.

The subcellular localizations of the Dolichos biflorus seed lectin and the structurally related lectin (cross-reactive material [CRM]) from the stems and leaves of this plant were determined by immunofluorescence, immunocytochemistry, and cell fractionation procedures. Subcellular fractionation of the cotyledons using a nonaqueous procedure to minimize disruption of the protein bodies showed that the majority of the seed lectin was associated with the protein body fraction and some lectin was also present in the starch granules. Immunofluorescence and immunocytochemistry at the light microscopic level showed that the seed lectin was mainly localized at the peripheries of these organelles. Lectin was also found in the cytoplasm of the cells, although the amount appeared to be dependent upon the degree of protein body disruption.Immunofluorescence and immunocytochemistry studies of the stem and leaf lectin (CRM) indicated that a significant portion of this lectin may be associated with the cell walls, although lectin was also seen in the cytoplasm of plasmolyzed cells. Extraction and cell fractionation studies showed that a large portion of the CRM is readily solubilized and most of the remainder is pelleted at 1000g. The CRM can be extracted from these pellets by treatment with cellulase and pectinase; other reagents such as NaCl, detergents, and EDTA could also release significant amounts of CRM. These studies suggest that the CRM is noncovalently bound to the cell walls. A comparison of the distribution of exogenously supplied [(125)I]CRM with the endogenous CRM during extraction and cell fractionation indicates that soluble CRM is not adsorbed to the 1000g pellet during fractionation.The different subcellular distributions of these two structurally related lectins suggest that different tissues of the same plant may utilize lectins for different functions.

Journal Article↗
PubMed1980

Does sex make a difference? Gender, age, and stimulus realism in perception and evaluation of aggression.

Judged aggressiveness and its justifiability were examined with caricature cartoons and films of people doing comparable things. Effects of viewer gender, interactant gender, and facial expression were examined. Facial expression strongly affected both types of judgment, viewer gender had no influence, and interactant gender contributed slightly. Real-cartoon differences were significant, but accounted for little variance. Major response patterns were similar for films of people and cartoons. In two developmental studies, only facial expression influenced judgments of friendliness-hostility in cartoons, but condemnation of aggression decreased as viewer age increased. Results with films of real children followed those for cartoons. Facial expression influenced judged aggressiveness, but only viewer age affected judged justifiability. Cross-experiment comparisons revealed that facial expression and the facial expression X real-cartoon interaction yielded major differences on both dependent variables. Subject and interactant gender were not significant for major dependent variables. Results of the developmental studies were similar to adults' suggesting that for judgments of simple aggressive acts, sex makes no difference, but facial expression does make a difference.

Adolescent↗
PubMed1975

The relationship between locus of control and temporal experience.

As locus of control involves generalized expectancies regarding the determination of events, it should relate to temporal attitudes and experiences. Correlational data from 89 subjects on the Rotter-Mirels Locus of Control and Ricks-Epley-Wessman Temporal Experience Questionnaire scales supported the hypothesis that the reported time experiences and orientations of external control subjects would be significantly more harassed and pressured, ciscontinuous and undirected, procrastinating and inefficient, and inconsistent and changeable than those of internal control subjects. Discussion forcuses on the self-defeating cycle of disorganization and victimization experienced by individuals with an external locus of control.

Adult↗
PubMedDate not supplied

DNA fingerprinting of plasmid-containing serotype A: 3,4 Pasteurella multocida isolated from cases of fowl cholera in chickens and turkeys.

The live, attenuated vaccine strains of Pasteurella multocida have been hypothesized to be responsible for homologous serotype outbreaks of fowl cholera on farms that use the commercial vaccines. We have further hypothesized that the naturally occurring Clemson University (CU) vaccine strain may be transformed to virulence by the acquisition of plasmid DNA. To test this hypothesis, we obtained seven homologous serotype (A:3,4) P. multocida isolates, all plasmid bearing, that were cultured from fowl cholera cases in vaccinated flocks and compared the isolates with the CU reference vaccine by molecular methods. Restriction fragment length polymorphisms (RFLPs) were detected by DNA/DNA hybridization with labeled probes specific for the cya, aroA, and rrn genes of P. multocida. The RFLPs obtained from BglII-digested genomic DNA probed with cya demonstrated no differences among the isolates. Although three isolates probed with aroA showed a RFLP identical to the vaccine strain, five isolates were distinctly different. Isolates probed with rrn grouped into three different restriction patterns that were dissimilar from that of the vaccine strain. Therefore, we have shown that these fowl cholera isolates are different from the CU vaccine strain and that these outbreaks were not vaccine related.

Animals↗