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Biomedical subjects

C H Johnson

Publications and source records attributed to C H Johnson.

At least 73 records · Page 4Linked to original sources
PubMed1995

The relationship between pregnancy intendedness and physical violence in mothers of newborns. The PRAMS Working Group.

OBJECTIVE: To determine if pregnancy intendedness is associated with physical violence, and to identify factors that modify this association. METHODS: Three to 6 months after delivery, we mailed a questionnaire to a population-based sample of 12,612 mothers of infants born during 1990 and 1991 in four states. We used multiple logistic regression to compute odds ratios. RESULTS: The state-specific prevalences (+/- standard error) of physical violence ranged from 3.8 +/- 0.5 to 6.9 +/- 0.8%; the prevalences of unwanted or mistimed pregnancies ranged from 36.9-46.3%. In each state, higher rates of physical violence were reported by women who had fewer than 12 years of education, lived in crowded conditions, participated in the Special Supplemental Food Program for Women, Infants, and Children, received no or delayed prenatal care, or were of races other than white, under 20 years old, or not married. Regardless of other attributes, women with unwanted or mistimed pregnancies reported higher rates of physical violence than women with intended pregnancies and accounted for 70% of women who reported physical violence. Overall, women with unwanted pregnancies had 4.1 (95% confidence interval 2.7-6.2) times the odds of experiencing physical violence than did women with intended pregnancies. This association was weaker for women with few social advantages than for those with more advantages. CONCLUSION: Physical violence toward women during the periconceptional and antenatal periods occurs in all sociodemographic groups. Women with unwanted or mistimed pregnancies are at an increased risk for violence by their partners compared with women with intended pregnancies.

Confidence Intervals↗
PubMed1995

Is the cell division cycle gated by a circadian clock? The case of Chlamydomonas reinhardtii.

Circadian oscillators are known to regulate the timing of cell division in many organisms. In the case of Chlamydomonas reinhardtii, however, this conclusion has been challenged by several investigators. We have reexamined this issue and find that the division behavior of Chlamydomonas meets all the criteria for circadian rhythmicity: persistence of a cell division rhythm (a) with a period of approximately 24 h under free-running conditions, (b) that is temperature compensated, and (c) which can entrain to light/dark signals. In addition, a mutation that lengthens the circadian period of the phototactic rhythm similarly affects the cell division rhythm. We conclude that a circadian mechanism determines the timing of cell division in Chlamydomonas reinhardtii.

Animals↗
PubMed1995

Occurrence of high-level aminoglycoside resistance in environmental isolates of enterococci.

High-level resistance to aminoglycosides was observed in environmental isolates of enterococci. Various aquatic habitats, including agricultural runoff, creeks, rivers, wastewater, and wells, were analyzed. Strains of Enterococcus faecalis, E. faecium, E. gallinarum, and other Enterococcus spp. demonstrated multiple antibiotic resistance patterns to aminoglycosides.

Aminoglycosides↗
PubMed1995

Bacterial luciferase as a reporter of circadian gene expression in cyanobacteria.

To allow continuous monitoring of the circadian clock in cyanobacteria, we previously created a reporter strain (AMC149) of Synechococcus sp. strain PCC 7942 in which the promoter of the psbAI gene was fused to Vibrio harveyi luciferase structural genes (luxAB) and integrated into the chromosome. Northern (RNA) hybridization and immunoblot analyses were performed to examine changes in abundance of the luxAB mRNA, the native psbAI mRNA, and the luciferase protein to determine whether bioluminescence is an accurate reporter of psbAI promoter activity in AMC149. Under constant light conditions, the mRNA abundances of both luxAB and psbAI oscillated with a period of approximately 24 h for at least 2 days. The expression of these two genes following the same pattern: both mRNAs peaked in the subjective morning, and their troughs occurred near the end of the subjective night. The amount of luciferase protein also oscillated with a period of approximately 24 h, and the protein rhythm is in phase with the bioluminescence rhythm. The rhythm of the luciferase mRNA phase-leads the rhythms of luciferase protein and in vivo bioluminescence by several hours. Comparable results were obtained with a short-period mutant of AMC149. Together, these results indicate that the bioluminescence rhythm in AMC149 is due primarily to circadian oscillation of psbAI promoter activity in this cyanobacterium.

Circadian Rhythm↗
PubMed1994

Circadian clock mutants of cyanobacteria.

A diverse set of circadian clock mutants was isolated in a cyanobacterial strain that carries a bacterial luciferase reporter gene attached to a clock-controlled promoter. Among 150,000 clones of chemically mutagenized bioluminescent cells, 12 mutants were isolated that exhibit a broad spectrum of periods (between 16 and 60 hours), and 5 mutants were found that show a variety of unusual patterns, including arrhythmia. These mutations appear to be clock-specific. Moreover, it was demonstrated that in this cyanobacterium it is possible to clone mutant genes by complementation, which provides a means to genetically dissect the circadian mechanism.

Circadian Rhythm↗
PubMed1994

Illuminating the clock: circadian photobiology.

Light and circadian (daily) clocks are intimately related. Undoubtedly, the daily light/dark cycle has played a key role in the evolution of these oscillators. Now, light and dark signals synchronize these internal timekeepers to the precisely 24 h environmental cycle. Light also affects the period and amplitude of circadian rhythms. The expression of some 'light-responsive' genes are regulated by an intertwining of clock and light control mechanisms. These genes may help us to understand the evolution of circadian rhythmicity and can be employed as tools to identify and clone other genes which encode components of clock mechanisms or of their entrainment pathways.

Circadian Rhythm↗
PubMed1994

Nitrous oxide anxiolytic effect in mice in the elevated plus maze: mediation by benzodiazepine receptors.

In earlier research, we have hypothesized that exposure to nitrous oxide (N2O) produces an anxiolytic effect that is mediated by benzodiazepine (BZ) receptors. The present research was conducted to characterize pharmacologically the behavioral effects of N2O in comparison with a BZ standard, chlordiazepoxide (CP), in the mouse elevated plus maze. Exposure to increasing levels of N2O produced a concentration-related increase in the percent of total entries into and the percent of total time spent on the open arms, a pattern of response similar to that induced by CP. These effects on N2O and CP were both antagonized by pretreatment with the BZ receptor blocker flumazenil (FLU). In another experiment, mice made tolerant to CP also exhibited a cross-tolerance to N2O. These results support the hypothesis that the anxiolytic effect of N2O is mediated by BZ receptors.

Animals↗
PubMed1994

Cimetidine-induced rise in praziquantel levels in a patient with neurocysticercosis being treated with anticonvulsants.

A patient had neurocysticercosis complicated by a seizure disorder requiring anticonvulsants; previous praziquantel therapy (50 mg/kg/day) had failed to eradicate the disease. In an attempt to inhibit cytochrome P-450 metabolism of praziquantel, cimetidine (1600 mg/day) was coadministered. Before addition of cimetidine, the maximum concentration of praziquantel was 350 ng/mL; concurrent cimetidine administration increased the maximum concentration to 826 ng/mL. The elimination half-life increased from 1.7 h without cimetidine to 3.3 h with cimetidine and the area under the curve for the 12-h sampling period rose from 754 ng.h/mL to 3050 ng.h/mL. Coadministration of cimetidine raises serum praziquantel levels and may be helpful in patients treated concomitantly with praziquantel and anticonvulsants.

Adult↗
PubMed1994

The effects of altering extracellular potassium ion concentration on the membrane potential and circadian clock of Paramecium bursaria.

In some neural models of circadian rhythmicity, membrane potential and transmembrane flux of potassium and calcium ions appear to play important roles in the entrainment and central mechanisms of the biological clock. We wondered whether these cellular variables might be generally involved in circadian clocks, even non-neural clocks. Therefore, we tested the impact of changing extracellular potassium level on the circadian rhythm of photoaccumulation of Paramecium cells, whose membrane potential responds to changes of extracellular potassium in a manner similar to that of neurones. We found that pulse or step changes of extracellular potassium concentration did not phase-shift the circadian clock of P. bursaria cells in a phase-specific manner. Furthermore, modifying the extracellular concentration of calcium did not affect the magnitude of light-induced phase resetting. Therefore, while membrane potential and calcium fluxes may be crucial components of the circadian clock system in some organisms, especially in neural systems that involve intercellular communication, the P. bursaria data indicate that membrane potential changes are not necessarily an intrinsic component of circadian organization at the cellular level.

Animals↗
PubMed1994

Technical note: the measurement of mammographic room protection.

Owing to the inherent design of mammographic X-ray tubes, transmission measurements through the surrounding protective barriers are difficult to obtain using the primary beam. An alternative method has been developed which employs an iodine-125 source. Transmission measurements were obtained through common building materials using both the iodine-125 source and a mammographic X-ray beam generated at 35 kVp. Measurements were converted into an aluminium equivalence, from which correction factors were calculated to convert the aluminium equivalence determined using iodine-125 to the true aluminium equivalence. Average correction factors for samples of glass, chipboard and plasterboard were 1.10, 0.75, and 0.85, respectively.

Construction Materials↗
PubMed1994

Circadian rhythms of gene expression in Chlamydomonas reinhardtii: circadian cycling of mRNA abundances of cab II, and possibly of beta-tubulin and cytochrome c.

In Chlamydomonas reinhardtii cells, the amount of mRNA coding for the chlorophyll a/b binding proteins of photosystem II (cab II) oscillates in light/dark cycles and in constant dim light. This rhythmic behavior applies to the overall expression of the entire cab II gene family as well as to a single member of the family. The highest mRNA abundance is found in the middle of the subjective day and the lowest in the middle of the subjective night. In constant darkness the cab II mRNA rhythm damps rapidly. The cab II mRNA rhythm persists in non-growing cells under CO2-starvation conditions indicating that the cab II mRNA rhythm is not merely a consequence of cell division, although cell division may influence the amplitude of the cab II mRNA rhythm. The properties of this mRNA oscillation conform to all the major characteristics of circadian rhythms: the period in constant conditions is about 24 h, the rhythm entrains to 24 h light/dark cycles, and the period is temperature compensated. This report is the first demonstration of a circadian rhythm of cab II gene expression in single cells. beta-Tubulin mRNA also shows an oscillation in its abundance in LD cycles and in constant dim light, although its peak-to-trough amplitude is smaller than that of the cab II mRNA rhythm. The beta-tubulin mRNA rhythm peaks in the early night in LD cycles, but in constant illumination, it peaks at about the same circadian phase (i.e., mid-subjective day) as does the cab II mRNA rhythm. Finally, the amount of mRNA coding for mitochondrial cytochrome c is rhythmic in a light/dark cycle but is constant in constant dim light or constant darkness. Surprisingly, this mRNA exhibits a daily oscillation in constant dim light under the specific condition of CO2-depletion.

Animals↗
PubMed1993

Circadian rhythms in prokaryotes: luciferase as a reporter of circadian gene expression in cyanobacteria.

We have used a luciferase reporter gene and continuous automated monitoring of bioluminescence to demonstrate unequivocally that cyanobacteria exhibit circadian behaviors that are fundamentally the same as circadian rhythms of eukaryotes. We also show that these rhythms can be studied by molecular methods in Synechococcus sp. PCC7942, a strain for which genetic transformation is well established. A promoterless segment of the Vibrio harveyi luciferase structural genes (luxAB) was introduced downstream of the promoter for the Synechococcus psbAI gene, which encodes a photosystem II protein. This reporter construction was recombined into the Synechococcus chromosome, and bioluminescence was monitored under conditions of constant illumination following entrainment to light and dark cycles. The reporter strain, AMC149, expressed a rhythm of bioluminescence which satisfies the criteria of circadian rhythms: persistence in constant conditions, phase resetting by light/dark signals, and temperature compensation of the period. Rhythmic changes in levels of the native psbAI message following light/dark entrainment supported the reporter data. The behavior of this prokaryote disproves the dogma that circadian mechanisms must be based on eukaryotic cellular organization. Moreover, the cyanobacterial strain described here provides an efficient experimental system for molecular analysis of the circadian clock.

Circadian Rhythm↗
PubMed1993

The psbB gene cluster of the Chlamydomonas reinhardtii chloroplast: sequence and transcriptional analyses of psbN and psbH.

We have sequenced and characterized the complete psbB gene cluster of Chlamydomonas reinhardtii chloroplast DNA. Although the petB and petD genes are located elsewhere, the sequential order of psbB, ORF31, psbN and psbH is identical to that of the psbB operon in higher plants. Also, intergenic non-coding regions are much larger in the Chlamydomonas gene cluster. Northern blot analyses indicate the formation of dicistronic transcripts of psbB and ORF31 and monocistronic transcripts of psbN and psbH. It is unclear whether a psbB operon is transcribed to yield a large polycistronic precursor but northern blot analysis with total RNA from cells grown at 15 degrees C does not detect an increased complexity of the transcripts, as has been found in studies of the psbB operon of higher plants. From primer extension and nuclease protection assays, it is apparent that 5' and 3' processing of the primary psbH transcript results in the accumulation of a heterogenous population of mRNAs. Northern blot analyses reveal transcription of Chlamydomonas psbN and show that its mRNA is much larger than that identified in liverwort and pea. The sequence identities of the PSII-H and PSII-N polypeptides as compared to their vascular plant counterparts is 50 to 62%. While the amino acid sequences of PSII-H and PSII-N proteins are significantly conserved, the mass of PSII-H from Chlamydomonas is significantly larger.

Amino Acid Sequence↗
PubMed1993

Rapid glutamate decarboxylase assay for detection of Escherichia coli.

A rapid test procedure for the enzyme glutamate decarboxylase was developed for detection of Escherichia coli. The assay procedure was able to confirm the presence of E. coli in enteric broth cultures with 95% specificity for both pure cultures and environmental samples. The procedure was capable of detecting survivors among chlorine-exposed cells.

Bacteriological Techniques↗
PubMed1992

Circadian rhythms of chemotaxis to ammonium and of methylammonium uptake in chlamydomonas.

Chlamydomonas reinhardtii expresses a well-documented circadian rhythm of phototaxis, which peaks in the subjective daytime. We find that vegetative cells also express circadian rhythms of chemotaxis to ammonium and ammonium uptake (as gauged by uptake of [(14)C]methylammonium). The chemotaxis rhythm peaks in the subjective night. Methylammonium uptake is light dependent, and its rhythm peaks at subjective dawn. Unlike vegetative cells, gametes are not attracted to ammonium. We believe this to be the first report of a circadian rhythm of chemotaxis.

Journal Article↗