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Biomedical subjects

C A Johnson

Publications and source records attributed to C A Johnson.

At least 19 recordsLinked to original sources
PubMed2006

Cuticular hydrocarbons provide reliable cues of fertility in the ant Gnamptogenys striatula.

In ca. 150 species of queenless ants, a specialized queen caste is rare or absent, and mated workers take over the role of the queen in some or all of the colonies. Previously, it has been shown that reproduction in queenless ants is regulated by a combination of dominance behavior and chemical fertility signaling. It is unknown, however, whether chemical signals alone can sufficiently regulate reproduction. To investigate this possibility, we studied reproductive regulation in the facultatively queenless ant Gnamptogenys striatula, a species where dominance behavior is rare or absent. Active egg layers and infertile workers showed qualitative and quantitative differences in their cuticular hydrocarbon profile. Five long-chain methyl alkanes, 3,13- and 3,15-dimethyl pentriacontane, 3,13- and 3,15-dimethyl heptentriacontane, and 3,11,15-trimethyl heptentriacontane occurred only on the cuticles of virgin and mated egg layers. Pronounced quantitative differences were found in a further 27 alkenes; alkanes; and mono-, di-, and trimethyl alkanes. Workers that had recently stopped laying eggs had profiles similar to infertile workers, and mating status did not affect this chemical pattern. We conclude that the cuticular hydrocarbon profiles of G. striatula workers provide reliable information about their current fertility. In the interest of colony productivity, this allows reproduction to be regulated without the use of aggression.

Animals↗
PubMed2006

Are private school students more likely to smoke than public school students in China?

BACKGROUND: Tobacco use is prevalent among adolescents in China in general, however, little is known about tobacco use among students in private schools with an enrollment of 1.5 million. METHOD: In 2001, cross-sectional survey data from 2725 students in grades seven and eight (1307 sampled from private schools and 1418 sampled from public schools) were included. Smoking measures (risk of susceptibility to smoking, smoking onset, ever smoking, smoking in the past 7 days and past 30 days, established smoking) were compared between private and public school students using chi-square test, logistic regression, and survival analysis. RESULTS: Cigarette smoking was more prevalent among private school students than among public school students (private vs. public: 21.9% vs. 12.3% for susceptibility to smoking, 53.9% vs. 38.2% for ever smoking, 22% vs. 12.0% for 30-day smoking, 15.9% vs. 4.0% for 7-day smoking, 4.5% vs. 1.2% for established smoking). Students in private schools are 3.4 to 3.8 times more likely to smoke than students in public schools after the adjustment of important covariates (gender, grade, peer smoking, parental smoking, and parents' occupation). Risk of smoking onset by age was also greater for private school students than for public school students. CONCLUSIONS: Being in private schools was associated with three to four times increases in the likelihood of current cigarette smoking and heightened risk of smoking onset by age. Findings from this study suggest the urgent need to collect additional data on risk and protective factors as well as the willingness to participate in effective tobacco use intervention prevention among private school students.

Adolescent↗
PubMed2006

K-Train--a computer-based, interactive training program with an incorporated certification system for practicing kinetic perimetry: evaluation of acceptance and success rate.

PURPOSE: To evaluate, in an experimental study, an interactive, computer-based teaching procedure for kinetic perimetry that incorporates an evaluation system for scoring examination technique. METHODS AND SUBJECTS: K-Train was developed and based on the original user interface of the new semi-automated kinetic perimetry (SKP) feature of the OCTOPUS 101 perimeter (HAAG-STREIT, Koeniz, Switzerland). The trainer creates a 3D individual "hill of vision" for a specific pathology and the trainee can individually select target characteristics and independently define origin, end and direction of each kinetic stimulus with the help of vectors. Quality of the perimetric examination can be quantitatively assessed by the ratio of intersection area and union area of the trainee's result and the related trainer-defined original isopter. This ratio and other parameters are used to define a score of "perimetric quality". The general acceptance of K-Train was assessed in 30 participants in two perimetric courses. The success rate was examined by comparing the scores before and after a perimetric training session. RESULTS: The K-Train course was graded by the participants with an average score of 1.35 (range 1-3) in a scoring system ranging from 1=excellent to 6=unsatisfactory. The average perimetric quality score increased from 48 before to 59 (max. 100) after the training (27 trainees) indicating that K-Train was able to achieve and also verify a considerable success rate. CONCLUSION: The acceptance of K-Train, a computer-based, interactive tool that allows for certification, education and quality control of kinetic perimetry, is high. K-Train is capable of improving a trainee's individual performance in kinetic perimetry and of verifying this by an appropriate scoring system.

Adult↗
PubMed2006

Modeling the sensitivity to variability relationship in perimetry.

PURPOSE: Studies in glaucoma patients show that standard automated perimetry results increase in variability as sensitivity decreases. However, the reasons for this change are unclear. This study presents the principle of Divergent Dysfunction as a possible explanation for this change in variability, and incorporates it into a model that can be used to simulate perimetry. METHODS: A computer program was written to simulate visual field test results based on the model, using a Full Threshold testing strategy. The validity of the simulation was tested by comparing it with normal sensitivity values, and with test-retest data from 63 participants evaluated five times each over the course of 1 month. The effect on the simulated data of varying parameters of the model was investigated, such as changing the magnitude of variability and the percentages of false positive and negative responses. RESULTS: The correlation between subject and simulated test-retest data was 0.987. Several factors were found to affect the sensitivity-variability relationship for the simulated data, most notably the rate of sensitivity decline, the percentage of false positives, and the starting luminance of the test procedure. CONCLUSIONS: The principle of Divergent Dysfunction presented here provides a plausible explanation for the sensitivity-variability relationship for standard automated perimetry in glaucomatous eyes. The model and resultant simulation program aim to provide an intuitive demonstration of the principle, which can also be used to examine the effectiveness of different testing strategies. These findings have great implications for future clinical research.

Computer Simulation↗
PubMed2006

Dispersal and genetic structure in the American marten, Martes americana.

Natal dispersal in a vagile carnivore, the American marten (Martes americana), was studied by comparing radio-tracking data and microsatellite genetic structure in two populations occupying contrasting habitats. The genetic differentiation determined among groups of individuals using F(ST) indices appeared to be weak in both landscapes, and showed no increase with geographical distance. Genetic structure investigated using pairwise genetic distances between individuals conversely showed a pattern of isolation by distance (IBD), but only in the population occurring in a homogeneous high-quality habitat, therefore showing the advantage of individual-based analyses in detecting within-population processes and local landscape effects. The telemetry study of juveniles revealed a leptokurtic distribution of dispersal distances in both populations, and estimates of the mean squared parent-offspring axial distance (sigma2) inferred both from the genetic pattern of IBD and from the radio-tracking survey showed that most juveniles make little contribution to gene flow.

Animal Migration↗
PubMed2005

Short-term progestin treatments prevent estrous induction by a GnRH agonist implant in anestrous bitches.

The objective of this study was to test the efficacy and safety of a short-term progestin treatment administered at two different times to prevent estrous induction in response to the administration of an implant releasing the GnRH agonist, deslorelin acetate (DA), in anestrous bitches. Interestrous intervals (IEI) observed prior to and post DA were compared. Forty-two anestrous bitches, with previous IEI history, were randomly allocated to one of the following treatments: PL: placebo sc (n = 12); MA: megestrol acetate 2mg/kg po for 8 days (n = 4); DA: 10mg sc (n = 8); MA&DA-1: MA beginning the day before DA (n = 8); and MA&DA-4: MA beginning 4 days before DA (n = 10). The dose of MA was identical for each treatment. All bitches were examined daily for 1 month and then every 3 months until the next spontaneous post-treatment estrous cycle. Post-GnRH estrous response occurred in 0, 0, 100, 50, and 10% of the PL, MA, DA, MA&DA-1, MA&DA-4, groups, respectively (<0.01). There was an interaction between the treatment and period for the duration of the IEI (< 0.01). Changes in IEI were different among treatments (p<0.01); the three DA-treated groups (147.5% +/- 10.3, 161.3% +/- 14.1, 148.6% +/- 19.2) differed from both the MA (12.9% +/- 17.6) and PL (8.1% +/- 7.8), but not among themselves. It is concluded that an 8 days megestrol protocol and DA on Day 4 was better than DA on Day 1 to prevent estrous response in anestrous bitches and that both protocols significantly increased the IEI.

Anestrus↗
PubMed2005

Obesity, self-complexity, and compartmentalization: on the implications of obesity for self-concept organization.

OBJECTIVE: The relationship between obesity and structural aspects of the self-concept was examined in adult women. Participants were 119 adult women [age range: 18-73, M=26.9; body mass index (BMI) range: 16.2-54.7, M=27.3] who completed measures of self-esteem, self-complexity, and the spontaneous self-concept. BMI was associated with less complex and more compartmentalized self-knowledge and more frequent mention of weight-stereotypic traits as self-descriptive. The findings are discussed in the context of research on obesity- related stigma.

Adolescent↗
PubMed2005

Effects of perceived peer isolation and social support availability on the relationship between body mass index and depressive symptoms.

OBJECTIVE: To examine relationships between body mass index (BMI) and psychological correlates in Chinese school adolescents during the period of economic transition. DESIGN: Baseline data of 1655 Chinese adolescents aged 11-15 y were retrieved from a longitudinal smoking cessation and health promotion program in Wuhan, China. Assessments of body weight and height, depressive symptoms, perceived peer isolation (PPI) and perceived availability of social support (PASS) were collected. RESULTS: Based on the International Obesity Task Force (IOTF) age-and sex-specific BMI cutoffs, 12.5% of boys and 9.2% of girls were overweight. In girls, high BMI was significantly related to higher self-reported depressive symptoms, and was dominantly mediated by PPI. On the contrary, high BMI boys reported significantly lower levels of PPI although high PPI level aggravated depressive symptoms. For both girls and boys, the observed effect of PPI on the relationship between BMI and depressive symptoms was sustained only in low PASS boys and girls. CONCLUSIONS: The present study revealed different effects of PPI on the association of BMI and depressive symptoms between boys and girls, which were buffered by levels of PASS. The findings of this study may contribute to our understanding of the influences of psychological correlates in pediatric overweight in the Eastern cultural environment.

Adolescent↗
PubMed2004

The effect of osmotic stress on the metaphase II spindle of human oocytes, and the relevance to cryopreservation.

BACKGROUND: Knowing osmotic tolerance limits is important in the design of optimal cryopreservation procedures for cells. METHODS: Mature human oocytes were exposed to anisosmotic sucrose solutions at concentrations of 35, 75, 150, 600, 1200, or 2400 (+/-5) milliosmolal (mOsm) at 37 degrees C. A control treatment at 290 mOsm was also utilized. Oocytes were randomly allocated to each experimental treatment. After the treatment, the oocytes were cultured for 1 h, then fixed in cold methanol. Immunocytochemical staining and fluorescence microscopy were used to assess the morphology of the metaphase II (MII) spindle. Logistic regression was used to determine if media osmolality had a significant effect on spindle structure. RESULTS: Osmolality was a significant predictor of spindle morphology. Hyposmotic effects at 35, 75, and 150 mOsm resulted in 100, 67, and 56% of oocytes having abnormal spindles, respectively. Hyperosmotic effects at 600, 1200, and 2400 mOsm resulted in 44, 44, and 100% of the spindles with abnormal structure, respectively. CONCLUSIONS: Anisosmotic conditions lead to disruption of the MII spindle in human oocytes. Applying this fundamental knowledge to human oocyte cryopreservation should result in increased numbers of cells maintaining viability.

Cell Survival↗
PubMed2004

Bone mineral density in Hispanic women: role of aerobic capacity, fat-free mass, and adiposity.

Understanding the etiology of factors influencing bone mineral density (BMD) in Hispanic women for the prevention of osteoporosis was the aim of this investigation. Whole body BMD (WBBMD) of 39 Hispanic, premenopausal women aged 22 - 51 years was measured using dual-energy X-ray absorptiometry (DXA). Maximal aerobic capacity ((.-)VO(2max)) was determined by treadmill ergometry with direct measurement of oxygen consumption. Fat-free mass (FFM) and fat mass were estimated from two independent techniques, DXA and bioelectrical impedance analysis (BIA). A questionnaire was administered to determine weekly physical activity, age of menarche, oral contraceptive (OC) use, parity, and lactation. Factors with significant correlation to WBBMD were weight ( r = 0.74), body mass index ( r = 0.66), fat mass ( r = 0.68 - 0.69), FFM ( r = 0.55 - 0.65), percent fat ( r = 0.43 - 0.55), sagittal diameter ( r = 0.58), waist circumference ( r = 0.53), hip circumference ( r = 0.66) and weekly activity ( r = 0.40). Stepwise multiple linear regression revealed that 73 % of the variance in WBBMD is attributed to fat mass (55 %), FFM (10 %), and (.-)VO(2max) (8 %). When BIA was used instead of DXA in the regression, (.-)VO(2max) was no longer an independent predictor of WBBMD. Fat mass and FFM accounted for 43 % and 20 % of the variance in WBBMD, respectively, explaining a total of 63 % of the variance. The addition of age, age of menarche, weekly physical activity, OC use, parity, and lactation did not make significant contributions to the variance. The findings of this study suggest that fat mass is a stronger predictor of bone mineral density than fat-free mass to BMD; aerobic capacity is another important predictor of BMD in Hispanic premenopausal women.

Absorptiometry, Photon↗
PubMed2004

Central adiposity, aerobic fitness, and blood pressure in premenopausal Hispanic women.

Hispanics comprise one of the fastest-growing segments of the U.S. population. Mexican-American adults are more likely to be overweight, physically inactive, diabetic, and to have higher levels of hypertension than are white adults. However, studies addressing the relationship between physical fitness and coronary artery disease (CAD) risk factors among Mexican-Americans are much less conclusive. Therefore, understanding the etiology of factors influencing resting systolic (SBP) and diastolic blood pressure (DBP) in Hispanic women was the aim of this investigation. SBP, DBP, peak oxygen uptake (peak VO (2)), weekly physical activity, waist (WC) and hip circumference, blood glucose, and levels of plasma lipids (triglyceride, total cholesterol, low-density lipoprotein-cholesterol, high-density lipoprotein-cholesterol) of 39 Hispanic women age 22 - 51 years were measured. Factors with significant correlation to SBP were age, WC, sagittal diameter, and weight. Similarly, significant correlations were observed between anthropometric indices, age, and DBP. Peak VO (2) ( r = - 0.53, p < 0.01) and heart rate at maximal effort ( r = - 0.34, p </= 0.05) were inversely associated to DBP. There was also a strong inverse correlation ( r = - 0.53, p < 0.01) between peak VO (2) and CAD risk profile (created from one or the combination of: hypertension, obesity, hyperglycemia, dyslipidemia, smoking). Stepwise multiple linear regression revealed that 33 % of the variance in SBP is attributed to age (25 %), and WC (8 %), while DBP is explained by WC alone (26 %). The addition of peak VO (2) did not make significant contributions to the variances in SBP or DBP. The findings of this study suggest that central adiposity is an important predictor of resting blood pressure in Hispanic women. The inverse association between aerobic fitness and diastolic blood pressure as well as CAD risk factors suggests that recommendations regarding prevention of hypertension in this population should be based on the interrelationships between physical fitness and obesity.

Adult↗
PubMed2003

Effects of dexamethasone, glucose infusion, adrenocorticotropin, and propylthiouracil on plasma leptin concentrations in horses.

In experiment 1, nine light horse geldings (three 3 x 3 Latin squares) received dexamethasone (DEX; 125 microg/kg BW, i.m.), glucose (0.2 g/kg BW, i.v.), or nothing (control) once per day for 4 days. DEX increased (P < 0.001) glucose, insulin, and leptin concentrations and resulted in a delayed increase (P < 0.001) in IGF-I concentrations. In experiment 2, mares were similarly treated with DEX (n = 6) or vehicle (n = 6). DEX again increased (P < 0.01) glucose, insulin, and leptin concentrations; the delayed elevation in IGF-I concentrations occurred on day 10, 12, and 19, relative to the first day of treatment. In experiment 3, six light horse geldings received either 200 IU of adrenocorticotropin (ACTH) i.m. or vehicle twice daily for 4 days. ACTH increased (P < 0.001) cortisol concentrations. Further, ACTH resulted in increases (P < 0.01) glucose, insulin, and leptin concentrations. In experiment 4, plasma samples from four light horse stallions that were fed 6-n-propyl-2-thiouracil (PTU) at 6 mg/kg BW for 60 days to induce hypothyroidism were compared to samples from control stallions. On day 52, stallions receiving PTU had lower concentrations of thyroxine (P < 0.05) and triiodothyronine (P < 0.01) and higher (P < 0.01) concentrations of TSH. Leptin concentrations were higher (P < 0.01) in PTU-fed stallions from day 10 through 52. In conclusion, circulating concentrations of leptin in horses was increased by administering DEX. Treatment with ACTH increased cortisol and resulted in lesser increases in leptin, glucose, and insulin. In addition, PTU feeding results in lesser increases in leptin concentrations.

Adrenocorticotropic Hormone↗