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Biomedical subjects

J Snyder

Publications and source records attributed to J Snyder.

At least 19 recordsLinked to original sources
PubMed2005

Reliability of self-reported contraceptive use and sexual behaviors among adolescent girls.

This study examines two issues relevant to adolescents' self-reported sexual and contraceptive use behaviors: reliability of partner-referent reports versus 3 and 6 month reports, and test-retest reliability of reports completed over a 2 week period. Data are from 196 13 to 18 year old girls recruited into this study while they south reproductive care from health clinics in a metropolitan area. All participants reported having had sexual intercourse during the past 6 months. Twice over a 2 week interval, participants completed the same paper and pencil surveys. The survey presented questions about sexual behavior and contraceptive use using 3 sequential frames of reference: within the past 6 months, within the past 3 months, and by specific sexual partners in the past 6 months. Findings demonstrate that adolescent girls can reliably report sexual behavior and contraceptive use over a 6 month interval. Study findings have implications for future research utilizing adolescents' self-reported sexual and contraceptive use behaviors.

Adolescent↗
PubMed2005

6-Hydroxydopamine-induced alterations in blood-brain barrier permeability.

Vascular inflammation is well known for its ability to compromise the function of the blood--brain barrier (BBB). Whether inflammation on the parenchymal side of the barrier, such as that associated with Parkinson's-like dopamine (DA) neuron lesions, similarly disrupts BBB function, is unknown. We assessed BBB integrity by examining the leakage of FITC-labeled albumin or horseradish peroxidase from the vasculature into parenchyma in animals exposed to the DA neurotoxin 6-hydroxydopamine (6OHDA). Unilateral injections of 6OHDA into the striatum or the medial forebrain bundle produced increased leakage in the ipsilateral substantia nigra and striatum 10 and 34 days following 6OHDA. Microglia were markedly activated and DA neurons were reduced by the lesions. The areas of BBB leakage were associated with increased expression of P-glycoprotein and beta 3-integrin expression suggesting, respectively, a compensatory response to inflammation and possible angiogenesis. Behavioural studies revealed that domperidone, a DA antagonist that normally does not cross the BBB, attenuated apomorphine-induced stereotypic behaviour in animals with 6OHDA lesions. This suggests that drugs which normally have no effect in brain can enter following Parkinson-like lesions. These data suggest that the events associated with DA neuron loss compromise BBB function.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed2003

Quantum-classical reentrant relaxation crossover in Dy2Ti2O7 spin ice.

We have studied spin relaxation in the spin ice compound Dy2Ti2O7 through measurements of the ac magnetic susceptibility. While the characteristic spin-relaxation time (tau) is thermally activated at high temperatures, it becomes almost temperature independent below T(cross) approximately 13 K. This behavior, combined with nonmonotonic magnetic field dependence of tau, indicates that quantum tunneling dominates the relaxational process below that temperature. As the low-entropy spin ice state develops below T(ice) approximately 4 K, tau increases sharply with decreasing temperature, suggesting the emergence of a collective degree of freedom for which thermal relaxation processes again become important as the spins become strongly correlated.

Journal Article↗
PubMed2002

In vitro investigation of the interaction between nitric oxide and cyclo-oxygenase activity in equine ventral colon smooth muscle.

The objective of this study was to determine if a correlation exists between the presence of nitric oxide and prostaglandin release in the equine ventral colon smooth muscle, since this relationship may accentuate the inflammatory process during intestinal injury. Tissue was collected from the ventral colon, cut into muscle strips oriented along the circular, longitudinal and taenial layers, and mounted in a tissue bath system. Samples of the bath fluid were collected before, following electrical field stimulation (EFS), and following EFS in the presence of L-NAME, a nitric oxide synthase inhibitor. Muscle strips were also obtained following systemic administration of a cyclo-oxygnease inhibitor and samples were collected using the previously described protocol. Concentrations of prostaglandins were determined in the fluid samples using an ELISA. Electrical field stimulated release of nitric oxide produced a significant increase in prostaglandin production which did not occur in the presence of L-NAME. Systemic administration of flunixin meglumine reduced prostaglandin levels at all sampling periods, although a small increase was present following EFS. The results of this study support the hypothesis that there is a correlation between the release of nitric oxide and the production of prostaglandins in the smooth muscle of the large colon. This association between nitric oxide and prostaglandin may act as an important regulatory mechanism for various physiological mechanisms, such as vascular smooth muscle tone, and may contribute to amplified tissue injury when the induced forms of both enzymes are activated during an inflammatory insult. This suggests that the use and development of COX2 and iNOS inhibitors may help attenuate the inflammatory response following intestinal injury.

Animals↗
PubMed2001

Viruses from extreme thermal environments.

Viruses of extreme thermophiles are of great interest because they serve as model systems for understanding the biochemistry and molecular biology required for life at high temperatures. In this work, we report the discovery, isolation, and preliminary characterization of viruses and virus-like particles from extreme thermal acidic environments (70-92 degrees C, pH 1.0-4.5) found in Yellowstone National Park. Six unique particle morphologies were found in Sulfolobus enrichment cultures. Three of the particle morphologies are similar to viruses previously isolated from Sulfolobus species from Iceland and/or Japan. Sequence analysis of their viral genomes suggests that they are related to the Icelandic and Japanese isolates. In addition, three virus particle morphologies that had not been previously observed from thermal environments were found. These viruses appear to be completely novel in nature.

Archaeal Viruses↗
PubMed2001

How 'spin ice' freezes.

The large degeneracy of states resulting from the geometrical frustration of competing interactions is an essential ingredient of important problems in fields as diverse as magnetism, protein folding and neural networks. As first explained by Pauling, geometrical frustration of proton positions is also responsible for the unusual low-temperature thermodynamics of ice and its measured 'ground state' entropy. Recent work has shown that the geometrical frustration of ice is mimicked by Dy2Ti2O7, a site-ordered magnetic material in which the spins reside on a lattice of corner-sharing tetrahedra where they form an unusual magnetic ground state known as 'spin ice'. Here we identify a cooperative spin-freezing transition leading to the spin-ice ground state in Dy2Ti2O7. This transition is associated with a very narrow range of relaxation times, and represents a new form of spin-freezing. The dynamics are analogous to those associated with the freezing of protons in ice, and they provide a means through which to study glass-like behaviour and the consequences of frustration in the limit of low disorder.

Journal Article↗
PubMed2001

A new injectable bulking agent for treatment of stress urinary incontinence: results of a multicenter, randomized, controlled, double-blind study of Durasphere.

OBJECTIVES: To assess the safety and effectiveness of Durasphere compared with bovine collagen in the treatment of stress urinary incontinence (SUI) due to intrinsic sphincter deficiency (ISD). METHODS: This multicenter, randomized, controlled, double-blind trial was composed of 355 women diagnosed with SUI due to ISD and used a standardized pad test and the Stamey continence grade as the primary endpoints. The participants' ages ranged from 26 to 84 years. All patients had an abdominal leak point pressure of less than 90 cm H(2)O (average 51). RESULTS: At 12 months after the first injection, the two materials were equivalent with respect to the improvement in continence grade and pad weight testing. Less Durasphere was injected to obtain comparable clinical results (Durasphere 4.83 mL versus bovine collagen 6.23 mL, P <0.001). When examined 1 year after the date of the last treatment, 49 (80.3%) of the 61 women treated with Durasphere showed improvement of 1 continence grade or more compared with 47 (69.1%) of 68 women treated with bovine collagen (P value for difference = 0.162). Although the adverse events reported for both groups were similar, the Durasphere group had an increased short-term risk of urgency and urinary retention. CONCLUSIONS: The use of Durasphere for the treatment of SUI due to ISD was equally effective as bovine collagen and used less material. The U.S. Food and Drug Administration granted market approval for Durasphere on September 13, 1999. The product design and initial clinical data suggest the potential for greater durability of the clinical benefit, with the possibility of a permanent solution for SUI due to ISD in some patients.

Adult↗
PubMed2000

The contribution of parental discipline, parental monitoring, and school risk to early-onset conduct problems in African American boys and girls.

The association of parental discipline and monitoring with the early conduct problems of 123 boys and girls was assessed in a highly disadvantaged, African American sample. Prospective analyses indicated that, after earlier conduct problems were controlled for, coercive parent discipline and poor parental monitoring at age 4 1/2 were independent, reliable predictors of age 6 conduct problems for both boys and girls. The association of parental monitoring with later child conduct problems was mediated, in part, by parents' choice of higher risk schools for their children's kindergarten education. The association of family income with child conduct problems was mediated by parental discipline and monitoring. These models are consistent with previous research on older, European American, more advantaged, male samples, which supports the generality of the association of family processes with child conduct problems across child gender, age, and ethnicity.

Black or African American↗
PubMed2000

The impact of transplantation on survival with kidney failure.

Although the growth in the incidence and prevalence of ESKD has slowed, there will nevertheless be a substantial increase in the number of patients over the next decade. Indeed, between 1998 and 2010 there will be a doubling in the number of patients in the United States treated with renal replacement therapy. There has also been an increase in the number of new transplants carried out every year. Much of the growth in the number of new transplants has been from the growth in living-unrelated donor transplants. Unfortunately, the rate of increase in the number of new transplants has not been enough to keep pace with the growing number of ESKD patients. As a result, the number of patients on the transplant waiting list continues to increase. The inability to offer more ESKD patients transplantation is unfortunate, since transplantation is associated with improved survival. Indeed, analyses of comparable patients who are placed on the transplant waiting list suggest that transplantation reduces the risk of death by roughly 50%. Thus, it is likely that the overall survival of patients with ESKD will improve if a greater proportion of patients receive transplants in a timely manner. Reducing allograft rejection and the need for repeat transplants may help reduce the demand for donor kidneys. However, this is unlikely to have a major effect on the organ shortage, since the number of repeat transplants has been relatively small (and constant) over the past decade. Thus, only if more cadaveric and living-donor kidneys are made available will more ESKD patients enjoy the improved survival of kidney transplantation.

Adolescent↗
PubMed1999

Approaches to managing carboplatin-induced thrombocytopenia: focus on the role of amifostine.

Thrombocytopenia is a significant problem for patients receiving prolonged or aggressive chemotherapy for malignancy. For carboplatin, it is the predominant dose-limiting toxicity and it is cumulative in nature. A number of agents have been evaluated for efficacy in reducing the problem of thrombocytopenia. Some have proved valueless and have been discarded. Others (eg, recombinant thrombopoietin) are under current study, and one (interleukin-11 or oprelvekin) is now commercially available. In addition, the currently available cytoprotectant, amifostine (Ethyol; Alza Pharmaceuticals, Palo Alto, CA/US Bioscience, West Conshohocken, PA), has been shown to reduce the severity and duration of thrombocytopenia caused by carboplatin. Because of the short half-life of amifostine relative to that of carboplatin, multiple doses of amifostine have been administered in conjunction with carboplatin. The optimal dosing regimen with amifostine and carboplatin needs to be further evaluated in clinical studies. Future trials will also expand these observations to carboplatin-containing combination chemotherapy regimens and will further define the role of amifostine as a multilineage bone marrow protectant. The ability of amifostine to demonstrate multilineage bone marrow protection differentiates it from currently available growth factors and fulfills a medical need, including reducing the need for platelet transfusions and maintaining the desired chemotherapy dose intensity.

Amifostine↗
PubMed1998

Effect of once weekly treatment with 3,4-methylenedioxymethamphetamine on schedule-controlled behavior in rats.

The present study examined the effects of 3,4-methylenedioxymethamphetamine (MDMA), before and after once a week dosing, on the behavior of rats responding under a fixed ratio 20 schedule of reinforcement. Acutely, cumulative doses of MDMA dose-dependently decreased responding when compared to a series of water injections. Rats were then separated into two groups, one of which received only weekly MDMA ('paired') while the other received an additional injection of water each week ('unpaired'). Weekly dosing with MDMA resulted in significantly increased responding at low doses in the paired group but not in the unpaired group. When water injections were readministered there was a significant increase in responding in both groups. During the weekly regimen, locomotor activity also increased significantly over time after both water and MDMA injections. In conclusion, it appears that even weekly dosing with a small amount of MDMA can have long-lasting effects that are manifested in both operant and spontaneous behavior and that may be mediated by a conditioning mechanism.

Animals↗
PubMed1998

Can inexpensive signs encourage the use of stairs? Results from a community intervention.

BACKGROUND: The U.S. Surgeon General advocates the accumulation of moderate-intensity activity throughout the day to improve health. OBJECTIVES: To test the effectiveness of signs to encourage use of stairs instead of escalators. DESIGN: Community intervention. SETTING: Shopping center. PARTICIPANTS: 17901 shoppers. INTERVENTION: Signs promoting the health and weight-control benefits of stair use were placed beside escalators with adjacent stairs. MEASUREMENTS: The sex, age, race, weight classification, and use of stairs were observed. RESULTS: Overall, stair use increased from 4.8% to 6.9% and 7.2% with the health and weight-control signs, respectively. Younger persons increase their stair use from 4.6% to 6.0% with the health sign and 6.1% with the weight-control sign. Older persons almost doubled their stair use from 5.1% to 8.1% with the health sign and increased use to 8.7% with the weight-control sign. Differential use of stairs was observed between ethnic groups. Among white persons, stair use increased from 5.1% to 7.5 and 7.8% with the health sign and weight-control signs. Among black persons, stair use decreased from 4.1% to 3.4% with the health sign and increased to 5.0% with the weight-control sign. At baseline, lean persons used the stairs more often than overweight persons (5.4% and 3.8%, respectively). The health sign increased stair use to 7.2% among normal-weight persons and 6.3% among overweight persons; the weight-control sign prompted stair use to increase to 6.9% among persons of normal weight and to 7.6% among overweight persons. CONCLUSIONS: Simple, inexpensive interventions can increase physical activity. Research is needed to identify effective motivators to promote activity among black persons.

Adult↗