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Biomedical subjects

D Shelton

Publications and source records attributed to D Shelton.

At least 37 records · Page 2Linked to original sources
PubMed1996

Factors affecting neuronal birth and death in the mammalian olfactory epithelium.

To identify factors regulating neurogenesis and neuronal death in mammals and to determine the mechanisms by which these factors act, we have studied mouse olfactory epithelium using two different experimental paradigms: tissue culture of olfactory epithelium purified from mouse embryos; and ablation of the olfactory bulb in adult mice, a procedure that induces olfactory receptor neuron (ORN) death and neurogenesis in vivo. Studies of olfactory epithelium cultures have allowed us to characterize the cellular stages in olfactory neurogenesis and to identify factors regulating proliferation and differentiation of precursor cells in the ORN lineage. Studies of adult olfactory epithelium have enabled us to determine that all cell types in this lineage-proliferating neuronal precursors, immature ORNs and mature ORNs-undergo cell death following olfactory bulb ablation and that this death has characteristics of programmed cell death or apoptosis. In vitro studies have confirmed that neuronal cells of the olfactory epithelium undergo apoptotic death and have permitted identification of several polypeptide growth factors that promote survival of a fraction of ORNs. Using this information, we have begun to explore whether these factors, as well as genes known to play crucial roles in cell death in other systems, function to regulate apoptosis and neuronal regeneration in the adult olfactory epithelium following lesion-induced ORN death.

Animals↗
PubMed1996

Cigarette smoking and its risk factors among elementary school students in Beijing.

OBJECTIVES: This study investigated patterns of and risk factors for smoking among elementary school children in Beijing, China. METHODS: In 1988, anonymous questionnaires were administered to a multistage stratified cluster sample of 16996 students, aged mostly 10 to 12, in 479 fourth- to sixth-grade classes from 122 Beijing elementary schools. RESULTS: Approximately 28% of boys and 3% of girls had smoked cigarettes. The most frequently cited reasons for smoking initiation were "to imitate others' behavior" and "to see what it was like." Girls were more likely to get cigarettes from home than to purchase their own. Having close friends who smoked and being encouraged by close friends to smoke were strong risk factors for smoking. Smoking was also associated with lower parental socioeconomic status; having parents, siblings, or teachers who smoked; buying cigarettes for parents; performing poorly in school; and not believing that smoking is harmful to health. CONCLUSIONS: Gender differences in smoking prevalence among adolescents in China are larger than those among US teenagers, whereas the proximal risk factors for smoking are similar. Major efforts are needed to monitor and prevent smoking initiation among Chinese adolescents, particularly girls.

Adolescent↗
PubMed1994

Histamine receptors in the human nose.

The aim of this study was to determine the role of histamine receptors in the nose. The effects of intranasal histamine challenge were compared with those of a specific H1-receptor agonist, betahistine and a specific H2-receptor agonist, impromidine, in 11 normal individuals and four with rhinitis. Sneezing, nasal irritation and hypersecretion were induced by histamine and the H1-receptor agonist, betahistine only. Nasal airway resistance (Rna) was measured by passive anterior rhinomanometry. Histamine, betahistine and impromidine all induced rises in Rna in both normal individuals and those with rhinitis but histamine had the most potent effect; the H2-receptor effect on Rna was predominant over that of the H1-receptor. The sensitivity to all three agonists was greater in the individuals with rhinitis.

Adult↗
PubMed1994

Nonlinear approaches for separation of slow and fast phase nystagmus signals.

Central nervous system (CNS) disorders and vestibulo-ocular reflex (VOR) degradation contribute to the loss of orientation and balance, typically causing the illusion of motion. VOR degradation may be caused by illnesses or common prescription medications, and this degradation may have serious repercussions in affecting one's ability to walk, maintain balance, or track moving objects. The two current VOR analysis techniques are applied to nystagmus signals (recordings of eye position during standardized tests) to isolate the two neuronal pathways used. These techniques are only partially successful because the VOR signal is passed through several filtering layers, to isolate the nystagmus signal, leaving it severely altered. In this paper, several alternate approaches are introduced: nonlinear robust ordering procedures, mathematical morphology, and wavelet filtering techniques are demonstrated. All approaches were as successful as the current techniques in isolating data from one neuronal pathway. Techniques for each of the three were also developed which would identify data from the second neuronal pathway as well. The nonlinear approach, which works using raw position data, bypasses layers of filtering. A robust technique is used to identify the points at which the data changes from that due to one neuronal pathway to the other, and the end result is obtained by concatenating the respective segments. The other two approaches work with velocity data obtained by differentiation, and because they are applied to non-original data, their results may be open to the possibility of error. Additionally, the two most recent approaches in the literature (using order statistic filters and fuzzy logic) have been implemented for a comparison of results.

Humans↗
PubMed1993

Instantaneous VEP signal frequency analysis.

Various methods have been used in the analysis of visually evoked potential signals. Due to the high noise content of the ssVEP signal, the signal is usually filtered using averaging or an order statistic filter, and then analyzed for frequency content. A frequency analysis technique often employed is the short-time Fourier transform (STFT) which yields information about both the frequency content and the spatial localization simultaneously. In 1946, D. Gabor modified the STFT by using a Gaussian window instead of a Hanning, Hamming, etc. for optimal simultaneous location in time and frequency. The common problem with the windowed DFT/FFT is the ambiguity of the estimate of frequency at a point (frequency localization). This paper will introduce a frequency analysis technique utilizing the WMMR (weighted majority with minimum range) filter, which, while in the time domain, will determine the frequency and spatial properties of a ssVEP signal within one period. This technique has been shown to be robust to impulsive noise of up to 40% and also robust to independent and identically distributed (i.i.d.) noise and DC shifts, for frequency content and spatial localization analysis for sinusoidal signals. The WMMR technique will be compared to the Gabor STFT by application to steady state visual evoked potential data.

Animals↗
PubMed1992

Group caregiver language checklist.

Because young children with language disabilities frequently are placed in group-care settings, there is a need to make judgments concerning the language environment of those settings. The GCLC is offered as one procedure for assessment of the language environment provided by the caregiver(s) in a group setting. The assessment provides information that may assist in matching the environment to a particular child's needs and may provide a basis for assisting caregivers in improving the language environment and addressing a child's needs. The authors welcome comments from the readers.

Caregivers↗
PubMed1992

Race, stage of disease, and survival with cervical cancer.

Significant disparities in survival with cervical cancer were observed according to social and disease characteristics of 3711 patients from Connecticut from 1984 through 1988. Women with advanced disease were 25 times more likely to die during a 4-year follow-up than those diagnosed with carcinoma in situ. Elevated risk of death was also noted for blacks (OR = 1.73; 95% CI = 1.2-2.5) and for women diagnosed after the age of 52 years (OR = 33.4; 95% CI = 16.5-69.9). Persons living in census tracts with large proportions of high school graduates or with high median incomes experienced decreased risk (OR = 0.66; 95% CI = 0.45-0.98 and OR = 0.65; 95% CI = 0.44-0.95, respectively). Multivariate logistic regression analysis found the effects of stage of disease on vital status to be reduced by approximately 50% when adjusted for other factors, reflecting the sizable effect of a woman's background on those variables. Nonwhite and older women were at significantly greater risk of being diagnosed with invasive disease.

Adult↗
PubMed1990

Cephalic blood flow correlates of induced headaches.

The purpose of this study was to examine the cephalic blood flow patterns of subjects with frequent headaches during a headache induction procedure. Thirty-six subjects with muscle-contraction, migraine, or mixed headache symptoms were exposed to a 1-hr stressor designed to induce a headache while multiple cephalic blood volume pulse amplitude (BVPA) was measured. Thirty subjects reported a headache during the procedure, and the procedure was associated with significant changes in several cephalic BVPA measures. Between-group differences were found for several cephalic BVPA sites and there were significant correlations between induced headache activity and cephalic BVPA measures for most subjects. The results support causal roles for psychosocial stressors and cephalic blood flow in muscle-contraction and migraine headache.

Adult↗
PubMed1990

Acculturation, access to care, and use of preventive services by Hispanics: findings from HHANES 1982-84.

Use of preventive health services (physical, dental, and eye examinations, Pap smear and breast examinations) among Mexican American, Cuban American, and Puerto Rican adults (ages 20-74) was investigated with data from the HHANES. Analyses focused on the relative importance of two predictors of recency of screening: access to services (health insurance coverage, having a routine place for care, type of facility used, having a regular provider, travel time) and acculturation (spoken and written language, ethnic identification). Regression analyses controlling for age, education, and income indicated that utilization of the preventive services was predicted more strongly by access to care than by acculturation. For each Hispanic group, having a routine place for health care, health insurance coverage, and a regular provider were each significantly associated with greater recency of screening. Type of facility used and travel time produced less consistent effects. These results replicate past studies that have demonstrated the important link between institutional access and use of health services. Of the acculturation variables, language but not ethnic identification (which was measured only for the Mexican Americans) predicted use. This latter finding, which has been demonstrated in other studies as well, suggests that the effect of language on screening practices should not be interpreted as a cultural factor, but as an access factor, i.e. use of English favors access to services.

Acculturation↗
PubMed1989

The mediating effects of psychophysiological reactivity and recovery on the relationship between environmental stress and illness.

The present study investigated the association between psychophysiological reactivity and recovery and physical and psychological symptoms both directly and interactively with environmental stress. Symptoms, environmental stress, and psychophysiological reactivity to and recovery from a laboratory stressor were measured in 50 subjects. As in previous research, the results indicated a significant relationship between environmental stress and symptoms of illness. Although the data did not support a direct relationship between psychophysiological activity and illness, support for a buffering effect was found. Those individuals with greater physiological arousal to or slower recovery from a laboratory stressor exhibited a stronger relationship between environmental stress and symptoms than those who were less reactive or faster to recover. Implications of these results were discussed in the context of theoretical models relating stress and illness.

Arousal↗
PubMed1987

Histamine receptors and pulmonary epithelial permeability.

In seven normal subjects and five asthmatics we have compared the effects of inhaled histamine with that of betahistine (a relatively selective H1-receptor agonist) and that of impromidine (a relatively H2-receptor agonist) on pulmonary epithelial permeability, as measured by the half-time clearance from lung to blood of inhaled 99mTc-DTPA (t1/2LB). Both histamine and betahistine produced statistically significant falls in baseline t1/2LB and peak expiratory flow rate, while impromidine produced no significant effects on either parameter. Similar results were obtained in normal subjects and asthmatics alike. In four of the normal subjects, histamine-induced falls in t1/2LB and peak expiratory flow rate were prevented by oral pretreatment with terfenadine 120 mg but not by cimetidine 400 mg. Histamine-induced increases in lung permeability and bronchoconstriction are both mediated via H1-receptors in normal and asthmatic subjects.

Adult↗
PubMed1987

Growth kinetics of Pseudomonas alcaligenes C-0 relative to inoculation and 3-chlorobenzoate metabolism in soil.

Pseudomonas alcaligenes C-0 was isolated from activated sewage sludge by enrichment with 3-chlorobenzoate (3CB) as the sole carbon source. The carbon balance from [14C]3CB in pure culture could be accounted for in substrate, biomass, and CO2 from all sampling periods and inoculum densities (0.012, 0.092, 0.20, and 0.92 micrograms of dry cells X ml-1), and inorganic chloride was produced stoichiometrically. Monod parameters as determined in culture were compared with the kinetics of 3CB metabolism in soil with decreasing inoculum densities (1.9 X 10(-1), 1.9 X 10(-3), and 1.9 X 10(-5) micrograms of cells X g-1). 3CB was refractile to attack in soil by indigenous microflora, but it was completely metabolized upon inoculation with P. alcaligenes C-0. The saturation constant KS was much higher in soil than in culture, but the yield coefficient Y and the growth rate constant were the same in both systems: mu max = 0.32 h-1; Y = 34 micrograms cells X mumol-1; KS = 0.18 mM in culture and 6.0 mM in soil solution (1.1 mumol X g-1 of soil). The parameter estimates obtained from the highest inoculum density could be used for the lower inoculum densities with reasonable agreement between predicted and observed 3CB concentrations in soil, although the residual sum of squares was progressively higher. Since the growth rate of P. alcaligenes C-0 in soil was comparable to its growth rate in culture, inoculation should be a viable strategy for biodegradation of 3CB in soil if indigenous microflora are unable to exploit this metabolic niche.

Biodegradation, Environmental↗
PubMed1985

Effects of histamine on lung permeability in normal and asthmatic subjects.

The permeability of respiratory mucosa, as measured by clearance of diethylenetriamine penta-acetate (DTPA) labelled with technetium 99m, was similar in seven normal and nine asthmatic subjects. Histamine induced bronchoconstriction was associated with a 50% increase in permeability in both groups of subjects. In normal subjects inhaled salbutamol, given as 1 mg acutely or as 200 micrograms four times daily for two weeks, had no effect on pulmonary permeability. Salbutamol, given before histamine challenge, prevented bronchoconstriction, but did not affect the increase in permeability seen in normal subjects. Low doses of histamine, sufficient to cause bronchoconstriction in the asthmatic subjects, produced little bronchoconstriction in normal subjects but caused increases in lung permeability similar to those seen in asthmatic subjects. These studies suggest that these two effects of inhaled histamine, bronchoconstriction and increased permeability, are independent.

Adult↗