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C Clements

Publications and source records attributed to C Clements.

At least 19 recordsLinked to original sources
PubMed2000

Glucose-induced pathways for actin tyrosine dephosphorylation during Dictyostelium spore germination.

In the presence of germination signals, dormant spores of Dictyostelium discoideum rapidly germinate to start a new life cycle. Previously we have shown that half of the actin molecules in spores are maintained in a tyrosine-phosphorylated state, and a decline of the actin phosphorylation levels is a prerequisite for spore swelling. In this study, we have established d-glucose as a trigger molecule for the actin dephosphorylation. Present in a nutrient germination medium, d-glucose both may act as a trigger molecule and/or may serve as a substrate within a pathway for actin dephosphorylation depending upon spore age. However, the glucose-induced actin dephosphorylation was insufficient for spores to swell. Other factors in the nutrient medium were required for complete germination of young spores aged 1 to 5 days. In contrast, dispersion in nonnutrient buffer was necessary and sufficient for a decline of actin phosphorylation levels and even the emergence of amoebae in older spores (6 days and beyond). Moreover, the dephosphorylation pathway in the older spores was independent of energy production. We propose that the diversification of the actin dephosphorylation pathway may enable spores to increase their probability of germination upon spore aging.

Actins↗
PubMed1998

High levels of actin tyrosine phosphorylation: correlation with the dormant state of Dictyostelium spores.

Upon removal of nutrients, the amoebae of the cellular slime mold Dictyostelium discoideum differentiate into dormant spores which survive starvation stress. In this study, we demonstrate that half of the actin molecules in the spores are tyrosine-phosphorylated. The phosphorylated actin is distributed around immobile crenate mitochondria and vesicles, as well as in the cytoplasm of the spores. The actin isolated from spore lysates contains phosphorylated and unphosphorylated forms at the same molar ratio as that of the original whole spore lysate. Under actin polymerizing conditions they form actin filaments and then they are completely depolymerized under actin depolymerizing conditions, indicating that tyrosine phosphorylation of actin may not prohibit actin polymerization nor stimulate depolymerization. The phosphorylation levels increase at the end of the culmination stage when spores have matured morphologically and physiologically, and reach maximum levels after an additional 12 hours of development. The levels are stable for 20 days following spore maturation, and decline to undetectable levels within the next 10 days. Spores having high levels of phosphorylation show high viability, and vice versa. Following activation of spores with nutrient medium containing spore germination promoters, the phosphorylation levels quickly decrease with a half-life of about 5 minutes. After 20 minutes spores begin to swell. At this later time, most of the phosphorylated actin already has been dephosphorylated. Also, in heat-activated spores actin dephosphorylation occurs prior to spore swelling. However, addition of phosphatase inhibitors following heat-activation, prevented spore swelling and dephosphorylation of actin. Our data indicate that the high levels of actin tyrosine phosphorylation, specific to the spore stage, may be required for maintaining dormancy to withstand starvation stress. The rapid dephosphorylation of actin leads to a reactivated dynamic actin system which participates in spore swelling, vesicle movement, and mitochondrial shape changes during the spore germination process.

Actins↗
PubMed1997

Genotoxicity of select herbicides in Rana catesbeiana tadpoles using the alkaline single-cell gel DNA electrophoresis (comet) assay.

Pesticides are broadly used for pest control in agriculture despite possible negative impacts they may pose to the environment. Thus, we examined the DNA damage caused by five herbicides commonly used in southern Ontario (Canada). Erythrocytes from Rana catesbeiana (bullfrog) tadpoles were evaluated for DNA damage following exposure to selected herbicides, using the alkaline single-cell gel DNA electrophoresis (SCG) or "comet" assay [Singh et al. (1988): Exp Cell Res 175:184-191; Ralph et al. (1996): Eviron Mol Mutagen 28:112-120]. This approach involves detection, under alkaline conditions, of DNA fragments that upon electrophoresis migrate from the nuclear care, resulting in a comet formation. The herbicides tested, along with their active ingredients, were AAtrex Nine-O (atrazine), Dual-960E (metalochlor), Roundup (glyphosate), Sencor-500F (metribuzin), and Amsol (2,4-D amine). Tadpoles were exposed in the laboratory for a 24-hr period to several concentrations of the herbicides dissolved in dechlorinated water. Methyl methanesulphonate was used as a positive control. The herbicides AAtrex Nine-O-, Dual-960E-, Roundup-, and Sencor-500F-treated tadpoles showed significant DNA damage when compared with unexposed control animals, whereas, Amsol-treated tadpoles did not. Unlike the other responding herbicides, Sencor-500F did not show a relationship between dosage and DNA damage. In summary, the results indicate that at least some of the herbicides currently used in southern Ontario are capable of inducing DNA damage in tadpoles.

Animals↗
PubMed1996

Implicit memory bias for threat in panic disorder: application of the 'white noise' paradigm.

We employed Jacoby's white noise paradigm to investigate implicit memory bias for threat in panic disorder and in normal control subjects. Subjects heard a series of neutral sentences (e.g. "The shiny apple sat on the table") and panic sentences (e.g. "The anxious woman panicked in the supermarket"). Implicit memory for this prior exposure was then tested by having subjects rate the volume of white noise accompanying the presentation of 'old' sentences intermixed with 'new' sentences. Implicit memory for old sentences is revealed when subjects rate the white noise accompanying these sentences as less loud than noise accompanying new sentences. Results revealed that under low noise level, panic patients demonstrated an implicit memory bias for threat information, whereas control subjects did not. This differential priming effect suggests that information about threat may be automatically accessed in these patients.

Adult↗
PubMed1996

Memory functioning in Lyme borreliosis.

BACKGROUND: To objectively measure memory functioning in patients with Lyme borreliosis and examine the relationship between subjective reports of memory dysfunction and actual impairment. METHOD: A prospective pretreatment study of patients with Lyme borreliosis (N = 21), a patient control group (osteomyelitis, N = 21), and healthy controls (N = 21) was conducted by using tests of verbal memory functioning (California Verbal Learning Test) and self-reported depression (Beck Depression Inventory-Cognitive Index), fatigue (Fatigue Severity Scale), and subjective ratings of memory abilities (Self-Rating Scale of Memory Functions). RESULTS: Patients with Lyme borreliosis performed worse than healthy controls on verbal memory testing, but did not perform significantly differently from patient controls. Lyme borreliosis patients reported increased fatigue, which was correlated with poorer memory performance. Although the Lyme borreliosis patients rated their memory as more impaired, subjective complaints were not correlated with objective memory scores. CONCLUSION: These findings suggest impaired memory performance is not specific to Lyme borreliosis and may be a result of evaluating cognitive functioning in patients with physical illness and somatic complaints. Fatigue is a prominent presenting complaint in patients with Lyme borreliosis and needs to be controlled for since it is known to influence neuropsychological performance. Subjective complaints are not correlated with objective memory assessment, so self-report of memory impairment should not be the criterion for inclusion in studies investigating cognitive manifestations of Lyme borreliosis.

Adult↗
PubMed1994

Photo CD in practice.

Kodak Photo CD is an optical disc-based storage system for recording still photographs. This article explores some of the practical aspects of Photo CD for the medical user. Some potential applications are described, along with hardware and software requirements for the effective use of the medium.

Compact Disks↗
PubMed1987

The insanity defense: asking and answering the ultimate question.

The authors address the main questions in the insanity defense debate: Should it be abolished? Should psychiatrists participate as expert witnesses? Is the profession damaged by such testimony? Is there a logical leap between providing psychiatric findings and providing an opinion to the ultimate question? Because the free will/determinism model underlying the current insanity defense positions can be used to argue either side of the debate, it does not supply any rational answers. The authors reframe the discussion, using a systems approach, and suggest answers to these questions that are in line with the clinical realities and on a firmer philosophic ground.

Expert Testimony↗
PubMed1984

Forensic psychiatry and applied clinical ethics: theory and practice.

The authors briefly describe and then apply a new method--applied clinical ethics--for identifying and working with ethical problems. This method, starting from the clinical context, develops ethical constructs that may be tested in clinical practice and revised if required. The work was done in the context of a combined university-county forensic psychiatric service. The authors discuss three of the identified ethical issues: effects of deinstitutionalization, countertransference with forensic populations, and prediction of dangerousness. They discuss the basis for developing ethical norms from clinical experience and suggest ethical guidelines for medical practice.

Adolescent↗
PubMed1982

Family or individual therapy: the ethics of modality choice.

The authors examine the ethical issues in choosing between individual and social unit (marital and family) therapies. Although usually neglected in the literature, these ethical questions are important and complex. A general systems perspective is used to provide a framework for ethical analysis. The core of the ethical problem is shown to be the interdependence and irreducible conflict inherent between the individual and social unit levels. The authors outline a general systems approach to identification and consideration of these ethical issues in clinical practice.

Choice Behavior↗
PubMed1982

Psychiatry's contribution to medical ethics education.

Two recent trends in medical education, the growth of interest in biomedical ethics and the examination of psychiatry's status in medicine, have important implications for psychiatry. Educators are needed to bring a clinical perspective to bear on ethics instruction, yet psychiatrists risk missing this opportunity. Psychiatrists are uniquely suited to contribute because of their expertise in three areas: an understanding of the affective, nonrational components in ethical thought and behavior, a developmental perspective regarding personal morality, and an appreciation of the rootedness of ethics in the social ethos. Problems with contemporary ethical models of informed consent illustrate the value of psychiatry's contribution.

Affect↗
PubMed1979

Long term follow-up study of a trachoma vaccine trial in villages of Northern India.

A field trial of two high titer bivalent trachoma vaccines was done in a rural area of Northern India in children under the age of 6 years. Three months later 310 of the original 451 children in the study received a booster vaccination of either of the two vaccines or a placebo. Both the sucrose gradient purified and the Genetron purified vaccine protected against trachoma infection for one year. Significant protection for two years was found only with the gradient vaccine. A 12-year follow-up study located and examined 201 subjects that had received booster vaccine. It was found that 31, 27, and 28% of the individuals in each of the three groups (two vaccine and placebo) had evidence of mostly minimally active trachoma. Additionally, from 6 to 10% of the subjects in each group had signs of mild to moderate potentially blinding sequelae. The results showed no protection by either vaccine, and there was no evidence of adverse effects from the vaccines.

Child↗
PubMed1979

Fluorescein angiography in borderline diabetics.

Fluorescein angiography was performed in twenty three men with impaired oral glucose tolerance (borderline diabetics) and sixteen matched, normoglycaemic controls. Retinal abnormalities (microaneurysms and leakage of dye) were observed in 18.7% of the controls, 41.6% of sustained borderline diabetics and 54.4% of initially borderline diabetics who subsequently "worsened to diabetes". Qualitatively the abnormalities were similar in each group. Although the difference in frequency between the sustained borderline diabetics and the controls does not achieve conventional statistical significance, other studies quoted support the conclusion that moderate impairment of glucose tolerance is associated with a raised frequency of minor retinal abnormalities. The significance of these remains to be determined.

Blood Pressure↗