PubMed Health⌕ Search

Biomedical subjects

D Boggs

Publications and source records attributed to D Boggs.

12 recordsLinked to original sources
PubMed1998

Effect of sodium perturbations on rat chemoreceptor spike generation: implications for a Poisson model.

1. The sensitivity of arterial chemoreceptor spike generation to reductions in excitability was examined using rat chemoreceptors in vitro. Axonal excitability was reduced by reducing extracellular sodium concentration ([Na+]o) by 10-40% or by applying low doses of tetrodotoxin (TTX). 2. In normoxia and in hypoxia, an isosmotic reduction in [Na+]o caused a proportional decrease in single-fibre, spiking nerve activity. For a 20% reduction in [Na+]o, nerve activity decreased to 54 +/- 7% of control in normoxia and 41 +/- 5% in hypoxia. 3. Low doses of TTX (25-50 nM) caused a similar decrease in spiking frequency, but this response was variable amongst fibres, with some fibres unaffected by TTX. 4. A reduction in [Na+]o by 20% caused a slowing of conduction velocity, measured using an electrical stimulus delivered to an electrode placed in the carotid body. Threshold current for spike generation was increased by about 2.7 +/- 1.4%. Threshold current increased by 6.5 +/- 3.7% following a 40% reduction in [Na+]o. 5. The spike generation process was modelled as a Poisson process in which depolarizing events summate and give rise to an action potential. The experimental data were best fitted to a high order process characterized by a large number of events and high event threshold. 6. This result is not consistent with depolarization events caused by episodic transmitter release, but suggests that afferent spike generation is an endogenous process in the afferent nerve fibres, perhaps linked to random channel activity or to thermal noise fluctuations.

Animals↗
PubMed1997

The effects of the wingbeat cycle on respiration in black-billed magpies (Pica pica)

Interclavicular and posterior thoracic airsac pressures, tracheal airflows and pectoralis muscle activity were recorded simultaneously to determine the effect of the wingbeat cycle upon the function of the respiratory system. The effects of the wingbeat cycle on the relative positions of thoraco-abdominal skeletal structures were also assessed using high-speed X-ray cinematography of magpies Pica pica flying in a windtunnel. We found that the furcula bends laterally on the downstroke and recoils medially on the upstroke, as previously described for starlings, and that the coraco-sternal joint (the most consistently visible point on the sternum for digitization) is displaced dorsally during the downstroke and ventrally, with respect to the vertebral column, during the upstroke. In magpies, there are generally three wingbeat cycles during a respiratory cycle. When downstroke occurs during inspiration, its compressive effect reduces the inspiratory subatmospheric airsac pressure by an average of 92 % (0.35 kPa), whereas when upstroke occurs during expiration its expansive effect can reduce the expiratory supra-atmospheric airsac pressure by 63 % (0.23 kPa). Corresponding changes occur in tracheal airflow. Changes in respiratory parameters during short flights with respect to resting values include a doubling of tidal volume and a tripling of respiratory frequency. We conclude that the wingbeat cycle can have a substantial impact on respiratory system function in the flying magpie, and that this represents a mechanical basis for breathing patterns and patterns of phasic coordination between wingbeat and respiratory cycles that may result in minimal interference and maximal assistance from the wingbeat upon the respiratory cycle.

Journal Article↗
PubMed1997

Coordination of respiratory cycles with wingbeat cycles in the black-billed magpie (Pica pica)

Magpies fly with a variable pattern of wingstroke, including high-amplitude rapid flaps and low-amplitude slower flaps with interspersed brief glides. This allowed us to test the hypothesis that if phasic coordination between respiratory and wingbeat cycles is important mechanically and energetically, then, as a bird changes its wingbeat cycle, its respiratory cycle should change with it. We also tested the strength of the drive to coordinate respiratory to locomotor cycles by stimulating breathing with 5 % CO2 during flight. We found that magpies (N=5) do shorten their breath cycle time when they shorten their wingbeat cycle time and prolong their breath cycle time when they glide. When the coordination ratio of wingbeat cycles to breaths is 3:1, the pattern of phasic coordination ensures two upstrokes per inspiration and two downstrokes per expiration. Upstroke tends to coincide with the transition into inspiration or with early inspiration and late inspiration. Downstroke tends to coincide with the transition into expiration or with early expiration and late expiration. When magpies switch from a 3:1 ratio to a 2:1 ratio of wingbeat cycles to breaths, they shorten inspiratory time to ensure that upstroke occurs through most of inspiration and downstroke corresponds to the transition into expiration. These phasic coordination patterns ensure that the compression of the airsacs during downstroke can provide a net assistance to expiration and that the expansion of the airsacs with upstroke can provide a net assistance to inspiration. The failure of an atmosphere containing 5 % CO2 to disrupt these phasic coordination patterns between respiratory and locomotory cycles suggests that there may be a potent mechanical and energetic benefit to such coordination.

Journal Article↗
PubMed1996

Bringing reality to the job hunt process. Interview by Barbara J. Linney.

A substantial percentage of the positions that open in medical management are filled through the use of recruitment firms. This is especially true of more senior positions, but it applies across the full spectrum of openings. If the working arrangement between the recruitment firm and the potential candidate is to be effective, certain key ingredients are necessary. The author interviewed a selection of principals of recruitment firms that operate extensively or exclusively in the medical management sector of executive recruitment. What she discovered about their "wish lists" for candidates' characteristics and levels of job hunting sophistication are summarized in the following statements.

Career Choice↗
PubMed1986

Aging and hematopoiesis. VI. Neutrophilia and other leukocyte changes in aged mice.

The concentration of blood leukocytes rose progressively as mice aged. All blood leukocytes increased, although a greater degree of increase was seen in neutrophils and monocytes than in lymphocytes and eosinophils. The total number of nucleated cells per marrow cavity of the humerus was also higher in aged than in young adult mice, the increase primarily reflecting peroxidase-positive cells. Both blood and marrow neutrophils of aged mice responded to perturbations induced by bleeding or by endotoxin injection in a manner qualitatively similar to that seen in young adults. When hematopoietic chimeras were produced by marrow transplantation, blood and marrow neutrophils were characteristic of the age of the recipient, not the cells; i.e., young mice kept a "young" neutrophil pattern and old mice kept an "old" neutrophil pattern when given marrow from either old or young mice. Colonies of granulocytes and/or monocyte-macrophages were grown from young marrow cells placed in plasma clots in Millipore chambers in the peritoneal cavity. The number of colonies was the same in young and in old mice, suggesting that long-range humoral stimulation of cell growth was similar in young and old. Thus, neutrophilia due to increased neutrophil production appears to be a normal part of the aging process in the mouse. The increase in neutrophil production may be due to a changing hematopoietic microenvironment.

Aging↗
PubMed1983

A double-blind, placebo-controlled study of sucrose polyester in hypercholesterolemic outpatients.

Sucrose polyester (SPE) was studied in a double-blind, placebo-controlled trial in 91 outpatients with primary hypercholesterolemia. All patients maintained an isocaloric diet with cholesterol intake of 400 mg/day and a polyunsaturated to saturated fat ratio of 0.8 to 1.2 for the duration of the study. The study sequence consisted of a diet lead-in period, a first 8-wk treatment period, a 4-wk washout period, and a second 8-wk treatment period. Subjects were randomly assigned to six groups that differed by SPE dose (8, 16, and 32 g/day) and by the treatment period in which either SPE or an olive oil placebo was given in a bread spread formulation. Compared to placebo, the 8, 16, and 32 g/day doses of SPE decreased low-density lipoprotein cholesterol by 2%, 4% (p less than 0.05), and 5% (p less than 0.05) respectively, without changing high-density lipoprotein cholesterol. On SPE, 14/91 (15%) of the subjects experienced a decrease in low-density lipoprotein cholesterol greater than or equal to 10%, while only 2/91 (2%) showed this decrease with placebo.

Adult↗
PubMed1980

Nutrient intake: relationships with lipids and lipoproteins in 6--19-year-old children--the Princeton School District study.

Relationships between nutrient intakes and plasma lipids and lipoproteins were studied in 949 randomly selected children, ages 6--19, in the biracial, suburban, Princeton School District. While nutrient intake increased with age in males, such age-associated increases in nutrient ingestion were much less consistent or were not significant for females. Primarily in the 6--9 and 10--12 yr age groups, white children ingested more total calories, more saturated fat, and a lower ratio of polyunsaturated to saturated (P/S) fat, more total carbohydrates, sucrose, starch, and other carbohydrates, and more protein than black children. After adjusting for age, race, sex, weight, and height, several nutrient-lipid and lipoprotein partial correlation coefficients were significant, but of relatively low magnitude. There were weak but significant inverse correlations between dietary P/S ratios and dietary carbohydrates with both total (r = -.07, -0.7) and low-density lipoprotein cholesterol (C-LDL), (r = -.07, -.08). Plasma high-density lipoprotein cholesterol (C-HDL) was inversely and significantly correlated with dietary sucrose (r = -.07); plasma triglyceride correlated positively with dietary sucrose (r = .08). Potential relationships between nutrients and lipids-lipoproteins were also examined in children at the extremes of, and in the middle of, lipid-lipoprotein distributions. After covariance adjustment for age, sex, race, and Quetelet index, children having the highest levels of C-HDL had the lowest intake of dietary carbohydrate and total calories. After further covariance adjustment for total calories, children at the highest end of the plasma cholesterol distribution had a greater intake of cholesterol and total protein than did children in the lowest end of the distribution. Nutrient intake may play a small but significant role relative to lipids and lipoproteins in children, and as such, may have importance relative to pediatric precursors of atherosclerosis.

Adolescent↗
PubMed1980

Interrelationships between nutrient intake and plasma lipids and lipoproteins in schoolchildren aged 6 to 19: the Princeton School District Study.

Relationships between nutrient intakes and plasma lipids and lipoproteins were studied in 1,669 schoolchildren, aged 6 to 19 years; 948 were selected by random recall and 721 because of elevated plasma cholesterol or triglyceride (hyperlipidemic recall). Nutrient intake data was collected by using a 24-hour dietary recall. Median dietary cholesterol intakes for 6 to 9-year-old boys and girls in the random recall group were 222 and 230 mg/day, with polyunsaturated/saturated fat ratios of 0.34 and 0.33. For boys and girls, aged 10 to 12 years, median dietary cholesterol intakes were 296 and 235 mg/day, for 13 to 15 year olds, 343 and 237, and for 16 to 19 year olds, 418 and 221 mg/day. The dietary polyunsaturated/saturated fat ratios did not change appreciably with age. Partial correlation coefficients describing relationships between lipids, lipoproteins, and nutrients after adjustment for age, sex, race, and Quetelet index (W/H2) were calculated for all children (random and hyperlipidemic recall) after excluding children having plasma cholesterol, triglycerides, and calories less than or equal to the first or greater than or equal to the 99th percentiles for the random recall children. Plasma cholesterol was inversely and triglyceride positively correlated with dietary sucrose. Plasma low density lipoprotein cholesterol was inversely and triglyceride positively correlated with the dietary polyunsaturated/saturated fat ratio, total carbohydrate, and sugar. Potential relationships between nutrients and lipids-lipoproteins were also examined in children having low (first to tenth percentile), intermediate (45th to 55th percentile), and high (90th to 99th percentile) nutrient intake, after covariance adjustment for age, race, sex, and Quetelet index. Total plasma cholesterol fell as sucrose intake increased. Triglyceride rose along with caloric intake, total carbohydrate intake, and sucrose intake, while high density lipoprotein cholesterol levels fell with increasing caloric and sucrose intake. As dietary polyunsaturate ingestion rose from low to intermediate to high, plasma low density lipoprotein cholesterol increased. Nutrient intake may play a small but significant role relative to lipids and lipoproteins in children and, as such, may have importance relative to pediatric precursors of atherosclerosis.

Adolescent↗
PubMedDate not supplied

Lack of evidence for intertypic recombinants in the pathogenesis of recurrent genital infections with herpes simplex virus type 1.

Clinical observations indicate that herpes simplex virus type 1 (HSV-1) is significantly less likely than herpes simplex virus type 2 (HSV-2) to establish latency in (or reactivate from) sacral ganglionic tissue. In an effort to identify viral functions associated with latency, we analyzed HSV-1 isolates from three patients with established recurrent genital herpes and sought evidence of DNA sequences and proteins similar to those found in HSV-2. By restriction endonuclease cleavage patterns and by DNA hybridization analysis using either whole HSV-2 DNA or several cloned segments of HSV-2 DNA as probes, we found that the three HSV-1 isolates from patients with recurrent genital herpes showed no unusual homology to HSV-2 as compared with other HSV-1 isolates. Similarly, the proteins of these isolates could not be distinguished from those of other HSV-1 isolates and were distinct from those of HSV-2. At this level of resolution, there was no evidence to suggest that these recurrent genital HSV-1 isolates were intertypic recombinants, nor did they show any other unusual similarity to HSV-2.

DNA Restriction Enzymes↗