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Biomedical subjects

John Parker

Publications and source records attributed to John Parker.

9 recordsLinked to original sources
PubMed2006

Pesticide mixtures, endocrine disruption, and amphibian declines: are we underestimating the impact?

Amphibian populations are declining globally at an alarming rate. Pesticides are among a number of proposed causes for these declines. Although a sizable database examining effects of pesticides on amphibians exists, the vast majority of these studies focus on toxicological effects (lethality, external malformations, etc.) at relatively high doses (parts per million). Very few studies focus on effects such as endocrine disruption at low concentrations. Further, most studies examine exposures to single chemicals only. The present study examined nine pesticides (four herbicides, two fungicides, and three insecticides) used on cornfields in the midwestern United States. Effects of each pesticide alone (0.1 ppb) or in combination were examined. In addition, we also examined atrazine and S-metolachlor combined (0.1 or 10 ppb each) and the commercial formulation Bicep II Magnum, which contains both of these herbicides. These two pesticides were examined in combination because they are persistent throughout the year in the wild. We examined larval growth and development, sex differentiation, and immune function in leopard frogs (Rana pipiens). In a follow-up study, we also examined the effects of the nine-compound mixture on plasma corticosterone levels in male African clawed frogs (Xenopus laevis). Although some of the pesticides individually inhibited larval growth and development, the pesticide mixtures had much greater effects. Larval growth and development were retarded, but most significantly, pesticide mixtures negated or reversed the typically positive correlation between time to metamorphosis and size at metamorphosis observed in controls: exposed larvae that took longer to metamorphose were smaller than their counterparts that metamorphosed earlier. The nine-pesticide mixture also induced damage to the thymus, resulting in immunosuppression and contraction of flavobacterial meningitis. The study in X. laevis revealed that these adverse effects may be due to an increase in plasma levels of the stress hormone corticosterone. Although it cannot be determined whether all the pesticides in the mixture contribute to these adverse effects or whether some pesticides are effectors, some are enhancers, and some are neutral, the present study revealed that estimating ecological risk and the impact of pesticides on amphibians using studies that examine only single pesticides at high concentrations may lead to gross underestimations of the role of pesticides in amphibian declines.

Amphibians↗
PubMed2005

Intersex inflorescences of Rumex acetosa demonstrate that sex determination is unique to each flower.

* A triploid intersex individual of the normally dioecious species Rumex acetosa showed extreme variability in gynoecium development. Analysis of the development and distribution of these flowers on inflorescences enabled insight to be gained into the mechanism of sex determination. * Floral phenotypes on intersex inflorescences were classified according to gynoecium development. Flower morphology was investigated by scanning electron and light microscopy. Organ identity gene expression in intersex floral primordia was assessed using in situ hybridization. * The distribution of the different floral phenotypes shows that each individual flower is determined separately, and that the phenotype of each flower is not influenced by its position on the inflorescence, or by the phenotype of neighbouring flowers. C-function gene expression persisted in gynoecia that had ceased development. * Gynoecium development in mutant flowers resembled the phenotype of the Arabidopsis mutant ettin and suggests that a hormone gradient may be involved. C-function expression does not appear to control the extent of female development, and indicates that genes which are downstream of the organ-identity genes must control organ suppression.

Chromosomes, Plant↗
PubMed2004

The Canadian Cardiovascular Society and knowledge translation: turning best evidence into best practice.

Care gaps, the discrepancy between processes of care recognized as best practice and care provided in usual clinical practice, exist in cardiovascular disease. Knowledge translation, the process of turning best evidence into best practices, has the potential to reduce care gaps. As the national voice for cardiovascular physicians and scientists, the Canadian Cardiovascular Society is committed to knowledge translation. The present article describes how knowledge translation builds on the constructs of continuing medical education and continuing professional development; what can be done to improve knowledge translation; and what the Canadian Cardiovascular Society is currently doing about this.

Attitude of Health Personnel↗
PubMed2002

Gambling participation in the U.S.--results from a national survey.

Demographic patterns of gambling participation in the U.S. were examined. A national telephone survey was conducted with 2,630 representative U.S. residents aged 18 or older. The sample as weighted for analysis was 48% male, 12% black, and 11% Hispanic. Respondents were questioned on 15 types of gambling: how often they played and how much they won or lost. Eighty-two percent gambled in the past year. Lottery was the most commonly played game, while casino gambling accounted for the largest extent of gambling involvement. Men and women were equally likely to gamble in the past year, but men gambled more frequently and had larger wins and losses, particularly on sports betting and games of skill. Blacks were less likely to have gambled in the past year, but blacks who gambled did so more heavily than other racial groups. Blacks and Hispanics were more likely than average to be pathological gamblers. The rate of past year gambling declined with age, but extent of gambling involvement among gamblers did not vary with age. Rates of participation in most forms of gambling increased with socioeconomic status, but higher socioeconomic status gamblers had lower rates of pathological gambling, and lower extent of gambling involvement, particularly for lottery. New Englanders gambled more heavily than other Americans. Comparison with past studies showed an increase in overall gambling participation in the U.S., and large increases in rates of participation in lottery and casino gambling.

Adolescent↗
PubMed2002

The auditory steady-state response: full-term and premature neonates.

Two studies were aimed at developing the auditory steady-state response (ASSR) for universal newborn hearing screening. First, neonates who had passed auditory brainstem response, transient evoked otoacoustic emission, and distortion-product otoacoustic emission tests were also tested with ASSRs using modulated tones that varied in frequency and level. Pass rates were highest (> 90%) for amplitude-modulated tones presented at levels > or = 69 dB SPL. The effect of modulation frequency on ASSR for 500- and 2000-Hz tones was evaluated in full-term and premature infants in the second study. Full-term infants had higher pass rates for 2000-Hz tones amplitude modulated at 74 to 106 Hz compared with pass rates for a 500-Hz tone modulated at 58 to 90 Hz. Premature infants had lower pass rates than full-term infants for both carrier frequencies. Systematic investigation of ASSR threshold and the effect of modulation frequency in neonates is needed to adapt the technique for screening.

Auditory Perception↗
PubMed2002

The auditory steady-state response: clinical observations and applications in infants and children.

Two studies illustrate the use of the auditory steady-state response (ASSR) in the pediatric clinical audiology setting. A protocol for estimating bone-conduction thresholds from ASSR was developed. Bone-conducted narrow-band noise was used to mask the ASSR for a 1.0-kHz modulated tone. The amount of bone-conducted noise needed to mask the ASSR may distinguish between infants and children with conductive hearing losses and those with sensory losses. The amount of bone-conducted noise may also be used to estimate bone-conduction thresholds; however, the accuracy of this technique needs verification with behavioral methods to determine thresholds for bone-conducted pure tones in infants. When ASSR tests are used as part of the diagnostic evaluation for infants and children at risk for hearing loss, the results yield information about the audiometric contour and residual hearing, which aid in treatment and habilitation decisions.

Acoustic Impedance Tests↗