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Biomedical subjects

E A Johnson

Publications and source records attributed to E A Johnson.

At least 55 records · Page 3Linked to original sources
PubMed1998

Corticotropin-releasing factor and defensive withdrawal: inhibition of monoamine oxidase prevents habituation to chronic stress.

There is growing evidence for a role of extrahypothalamic corticotropin-releasing factor (CRF) in the pathogenesis of anxiety. A modified form of the defensive withdrawal test was used to test the anxiogenic effects of acute administration of intracerebroventricular (1 microg, i.c.v.) CRF in adult male rats. Habituation to the mild stress of daily handling and subcutaneous (s.c.) saline injection over 2-6 weeks abolished the anxiogenic effects of exogenous CRF. At 6 weeks this habituation also resulted in attenuation of baseline withdrawal behavior. CRF receptor binding was significantly decreased in the amygdala of chronically handled animals and may have been responsible for this habituation phenomenon. Comparison of rats treated with the monoamine oxidase (MAO) inhibitor, phenelzine [3 mg/kg, s.c., daily for 2-6 weeks] to the saline-treated groups revealed a failure to habituate to the chronic handling, as the baseline withdrawal (after injection of artificial CSF) by the phenelzine-treated animals was not different from the baseline withdrawal by unhandled rats. In comparison to rats treated chronically with saline, phenelzine treatment enhanced the anxiogenic effect of CRF. In summary, habituation to a mild chronic stress decreased baseline defensive withdrawal. Intraventricular administration of CRF produced an anxiogenic response as measured in the defensive withdrawal test, which was lost through exposure to mild chronic stress. Two or 6 weeks of daily handling and SC saline injection caused a downregulation of CRF receptors in the amygdala, which could account for the behavioral habituation and the loss of CRF-induced defensive withdrawal. Phenelzine treatment concurrent with mild chronic stress prevented habituation and maintained the anxiogenic effect of CRF in spite of the downregulation of CRF receptors in the amygdala.

Amygdala↗
PubMed1998

A large outbreak of botulism: the hazardous baked potato.

In April 1994, the largest outbreak of botulism in the United States since 1978 occurred in El Paso, Texas. Thirty persons were affected; 4 required mechanical ventilation. All ate food from a Greek restaurant. The attack rate among persons who ate a potato-based dip was 86% (19/22) compared with 6% (11/176) among persons who did not eat the dip (relative risk [RR] = 13.8; 95% confidence interval [CI], 7.6-25.1). The attack rate among persons who ate an eggplant-based dip was 67% (6/9) compared with 13% (241189) among persons who did not (RR = 5.2; 95% CI, 2.9-9.5). Botulism toxin type A was detected from patients and in both dips. Toxin formation resulted from holding aluminum foil-wrapped baked potatoes at room temperature, apparently for several days, before they were used in the dips. Consumers should be informed of the potential hazards caused by holding foil-wrapped potatoes at ambient temperatures after cooking.

Animals↗
PubMed1998

Rat parvovirus type 1: the prototype for a new rodent parvovirus serogroup.

A newly recognized parvovirus of laboratory rats, designated rat parvovirus type 1a (RPV-1a), was found to be antigenically distinct. It was cloned, sequenced, and compared with the University of Massachusetts strain of rat virus (RV-UMass) and other autonomous parvoviruses. RPV-1a VP1 identity with these viruses never exceeded 69%, thus explaining its antigenic divergence. In addition, RPV-1a had reduced amino acid identity in NS coding regions (82%), reflecting phylogenetic divergence from other rodent parvoviruses. RPV-1a infection in rats had a predilection for endothelium and lymphoid tissues as previously reported for RV. Infectious RPV-1a was isolated 3 weeks after inoculation of infant rats, suggesting that it, like RV, may result in persistent infection. In contrast to RV, RPV-1a was enterotropic, a characteristic previously associated with parvovirus infections of mice rather than rats. RPV-1a also differed from RV in that infection was nonpathogenic for infant rats under conditions where RV infection causes high morbidity and mortality. Thus, RPV-1a is the prototype virus of an antigenically, genetically, and biologically distinct rodent parvovirus serogroup.

Animals↗
PubMed1998

Survival of bacterial pathogens in pasteurized process cheese slices stored at 30 degrees C.

Six lots of commercial pasteurized process cheese slices were evaluated for the ability to support the growth of four foodborne pathogens, Listeria monocytogenes, Staphylococcus aureus, Salmonella serotypes, and Escherichia coli O157:H7, during 4 days of storage at 30 degrees C. Individual cheese slices were inoculated separately with each pathogen to yield ca. 10(3) CFU/g. Slices were packaged in sterile plastic sample bags and stored at 30 degrees C for up to 96 h. Population of Salmonella serotypes and Escherichia coli O157:H7 decreased an average of 1.3 and 2.1 log10 CFU/g, respectively, by 36 h and Salmonella serotypes decreased an additional 0.6 log10 CFU/g during the remaining 60 h. Populations of Listeria monocytogenes also decreased, although to a lesser extent, exhibiting approximately a 0.6-log10 CFU/g reduction in 96 h. Staphylococcus aureus levels remained relatively constant during the testing period, and were below levels that support detectable enterotoxin production. The process cheese slices tested allowed survival but did not support rapid growth of S. aureus, whereas populations of L. monocytogenes, E. coli O157:H7, and Salmonella serotypes decreased during the 96-h storage at 30 degrees C.

Bacteria↗
PubMed1997

Ethanol increases carotenoid production in Phaffia rhodozyma.

Addition of ethanol (0.2%) to cultures of the yeast Phaffia rhodozyma increased the specific rate of carotenoid production [(carotenoid)(cell mass)-1(time)-1]. The incremental increase in carotenoid synthesis with ethanol was highest in carotenoid-hyperproducing strains. Ethanol increased carotenoid production when it was added at various points during the lag and active growth phases. Ethanol increased alcohol dehydrogenase and hydroxy-methylglutaryl-CoA (HMG-CoA) reductase activities. Our results indicate that increased carotenoid production by ethanol is associated with induction of HMG-CoA reductase and possibly activation of oxidative metabolism.

Alcohol Dehydrogenase↗
PubMed1997

Children's understanding of epistemic conduct in self-deception and other false belief stories.

In self-deception persons accept false beliefs through a motivated disregard for countervailing evidence. Such epistemic misconduct renders them responsible for their own deception. It was hypothesized that children's understanding of this responsibility would be associated with an understanding of how evidence informs belief. In the study 4- to 9-year-old children's understanding of the relations between false belief, evidence, and epistemic responsibility was examined using stories involving self-deception, lying, and misleading appearances. Results indicated that younger children who understood false belief understood simpler types of deception, but that understanding self-deceivers' epistemic responsibility was limited to older children who understood the relevance of evidence to belief formation.

Awareness↗
PubMed1997

Acid adaptation sensitizes Salmonella typhimurium to hypochlorous acid.

Acid adaptation of Salmonella typhimurium at a pH of 5.0 to 5.8 for one to two cell doublings resulted in marked sensitization of the pathogen to halogen-based sanitizers including chlorine (hypochlorous acid) and iodine. Acid-adapted S. typhimurium was more resistant to an anionic acid sanitizer than was its nonadapted counterpart. A nonselective plating medium of tryptose phosphate agar plus 1% pyruvate was used throughout the study to help recover chemically stressed cells. Mechanisms of HOCl-mediated inactivation of acid-adapted and nonadapted salmonellae were investigated. Hypochlorous acid oxidized a higher percentage of cell surface sulfhydryl groups in acid-adapted cells than in nonadapted cells, and sulfhydryl oxidation was correlated with cell inactivation. HOCl caused severe metabolic disruptions in acid-adapted and nonadapted S. typhimurium, such as respiratory loss and inability to restore the adenylate energy charge from a nutrient-starved state. Sensitization of S. typhimurium to hypochlorous acid by acid adaptation also involved increased permeability of the cell surface because nonadapted cells treated with EDTA became sensitized. The results of this study establish that acid-adapted S. typhimurium cells are highly sensitized to HOCl oxidation and that inactivation by HOCl involves changes in membrane permeability, inability to maintain or restore energy charge, and probably oxidation of essential cellular components. This study provides a basis for improved practical technologies to inactivate Salmonella and implies that acid pretreatment of food plant environments may increase the efficacy of halogen sanitizers.

Acids↗
PubMed1997

A quantitative description of the Na-K-2Cl cotransporter and its conformity to experimental data.

In epithelia, the Na-K-2Cl cotransporter cooperates with other transport mechanisms to produce transepithelial NaCl transport. The reaction cycle for the Na-K-2Cl cotransporter has been established experimentally, but whether it accounts, quantitatively, for experimental findings has yet to be established. The differential equations that describe the reaction cycle were formulated, and the steady-state solutions were obtained by digital computation. Conformity between this description and the experimental data obtained from the literature was explored by automatic searches for the sets of rate constants that yielded statistical best-fits to the experimental data. Fits were obtained from renal epithelial cell lines, HeLa cells, and duck erythrocytes. Results show that the reaction cycle for the Na-K-2Cl cotransporter conforms well, quantitatively, with the experimental data.

Animals↗
PubMed1997

Co-amplification of the amelogenin and HLA DQ alpha genes: optimization and validation.

An optimized PCR-based system allowing the co-amplification of the HLA DQ alpha and the amelogenin genes has been developed and validated, enabling simultaneous identity testing and sex determination. Sensitivities below 100 pg of human DNA were obtained, using a convenient, high resolution agarose gel system and ethidium bromide staining. Comparison of several co-amplification methods revealed that the best sensitivities and most consistent results were obtained using a hotstart technique employing an inactivating antibody to Taq polymerase. HLA DQ alpha typing results were reliably obtained using the co-amplification process. The sensitivity and ease of this system rendered it directly applicable to forensic analyses. The optimized techniques described here have been validated and successfully applied to forensic cases including People vs. Trujillo, in which the California Superior Court accepted these techniques as scientifically reliable and admissible. Work currently in progress has demonstrated that the described protocol may also be used to co-amplify the amelogenin gene with the AmpliType PM (polymarker) system, allowing identity testing at six loci in addition to sex determination.

Amelogenin↗
PubMed1996

Genetic characterization of Clostridium botulinum type A containing silent type B neurotoxin gene sequences.

A recent study detected genes encoding type B botulinum neurotoxin in some type A strains of Clostridium botulinum that exhibit no type B toxin activity. In this study, we investigated the presence, structure, linkage, and organization of genes encoding botulinum neurotoxin (BoNT) and other components of the progenitor complex. Sequence analysis showed that the silent BoNT/B gene is highly related to that from authentic proteolytic type B C. botulinum. However, a stop signal and deletions were found within the sequence. A non-toxin nonhemagglutinin gene (NTNH) was mapped immediately upstream of both the BoNT/A and silent BoNT/B genes. Significantly the NTNH gene adjacent to the defective BoNT/B gene was "chimeric, " the 5'- and 3'-regions of the gene had high homology with corresponding regions of the type B NTNH gene, while the 471-amino acid sequence in the central region was identical to NTNH of type A. Hemagglutinin genes HA-33 and HA-II were not found adjacent to the NTNH/A gene, but instead there was an unidentified open reading frame previously reported in strains of C. botulinum types E and F. By contrast HA-II, HA-33, and NTNH genes were located immediately upstream of the silent BoNT/B gene. Pulsed-field gel electrophoretic analysis of chromosomal DNA digests indicated the distance between type A and B gene clusters to be less than 40 kilobases.

Amino Acid Sequence↗
PubMed1996

Microbial carotenoids.

Carotenoids occur universally in photosynthetic organisms but sporadically in nonphotosynthetic bacteria and eukaryotes. The primordial carotenogenic organisms were cyanobacteria and eubacteria that carried out anoxygenic photosynthesis. The phylogeny of carotenogenic organisms is evaluated to describe groups of organisms which could serve as sources of carotenoids. Terrestrial plants, green algae, and red algae acquired stable endosymbionts (probably cyanobacteria) and have a predictable complement of carotenoids compared to prokaryotes, other algae, and higher fungi which have a more diverse array of pigments. Although carotenoids are not synthesized by animals, they are becoming known for their important role in protecting against damage by singlet oxygen and preventing chronic diseases in humans. The growth of aquaculture during the past decade as well as the biological roles of carotenoids in human disease will increase the demand for carotenoids. Microbial synthesis offers a promising method for production of carotenoids.

Antioxidants↗
PubMed1996

The anxiolytic serotonin 5-HT1A receptor agonists buspirone, ipsapirone and gepirone are inhibitors of tyrosine hydroxylation in rat striatum.

The anxiolytics buspirone (BUS), ipsapirone (IPSAP) and gepirone (GEP) were investigated as 5-HT1A receptor-mediated inhibitors of tyrosine hydroxylation (TH) in a synaptosome-rich preparation of rat striatum. BUS, IPSAP and GEP were moderately potent inhibitors of TH with EC50 values of 48.4 microM, 50 microM and 836 microM, respectively. By comparison, 8-OH-DPAT, a 5-HT1A receptor selective agonist, has been previously shown to be more potent with an EC50 value of 7.0 microM. Each of these agents demonstrated full agonist activity at the striatal 5-HT1A receptors regulating TH. The inhibitory effects of each agent were attenuated by prior exposure to the 5-HT1A antagonist NAN-190, (10 microM) (P < 0.05), but not by the dopamine D2 antagonist (-)-sulpiride (10 microM). The potencies of 8-OH-DPAT, BUS, IPSAP and GEP were correlated with their reported affinities for the 5-HT1A receptor (P < 0.01) but not the dopamine D2 receptor. These results support the hypothesis that BUS, IPSAP and GEP inhibit TH through activation of a striatal 5-HT1A heteroreceptor on dopamine nerve terminals.

Animals↗
PubMed1996

Antimicrobial activity of hop extracts against Listeria monocytogenes in media and in food.

Growth of Listeria monocytogenes was inhibited in culture media and in certain foods by four hop extracts (I-IV) containing varying concentrations of alpha-and beta-acids. Extracts (II and III) containing the highest concentrations of beta-acids were inhibitory at 0.01 mg/l in trypticase soy broth. In food, these hop extracts showed varying magnitudes of inhibition. In coleslaw, hop extract III at 1 mg/g enhanced the rate of inactivation of L. monocytogenes Scott A. Hop extract II was inhibitory at 0.1 and 1 mg/ml in skim and 2% milk, and was inhibitory at 1 mg/ml in whole milk. Hop extract II was listericidal in cottage cheese at 0.1 to 3 g/kg. No inhibition of L. monocytogenes by hop extract III was observed in Camembert cheese. Overall, the antimicrobial activity of hop extracts in food appeared to increase with acidity and lower fat content. Our results indicate that hop extracts could be used to control L. monocytogenes in minimally processed food with low fat content.

Animals↗
PubMed1996

A quasi-one-dimensional theory for anisotropic propagation of excitation in cardiac muscle.

It has been shown that propagation of excitation in cardiac muscle is anisotropic. Compared to propagation at right angles to the long axes of the fibers, propagation along the long axis is faster, the extracellular action potential (AP) is larger in amplitude, and the intracellular AP has a lower maximum rate of depolarization, a larger time constant of the foot, and a lower peak amplitude. These observations are contrary to the predictions of classical one-dimensional (1-D) cable theory and, thus far, no satisfactory theory for them has been reported. As an alternative description of propagation in cardiac muscle, this study provides a quasi-1-D theory that includes a simplified description of the effects of action currents in extracellular space as well as resistive coupling between surface and deeper fibers in cardiac muscle. In terms of classical 1-D theory, this quasi-1-D theory reveals that the anisotropies in the wave form of the AP arise from modifications in the effective membrane ionic current and capacitance. The theory also shows that it is propagation in the longitudinal, not in the transverse direction that deviates from classical 1-D cable theory.

Action Potentials↗