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Biomedical subjects

A M Dunn

Publications and source records attributed to A M Dunn.

At least 37 records · Page 2Linked to original sources
PubMed1997

Cellular distribution of a feminizing microsporidian parasite: a strategy for transovarial transmission.

The cellular distribution of a vertically transmitted, feminizing microsporidian was followed in its host Gammarus duebeni. In adult females the parasite was restricted to gonadal tissue, in particular primary and secondary follicle cells. Spores were diplokaryotic with a thin spore wall and a short polar filament, characteristics typical of 'early' spores involved in autoinfection. The diplokaryotic life-cycle, absence of spore groupings and of a pansporoblast membrane typify the genus Nosema. However, the unusual globular polaroplast of the spore and restriction of this stage to host ovarian tissue have not previously been described in Nosema. Sporogony occurred only in follicle cells adjacent to developing oocytes and was in synchrony with the process of vitellogenesis. Oocytes were infected after formation of intracellular connections with follicle cells but harboured only vegetative stages of the parasite. Parasites were associated with the perinuclear cytoplasm and, in developing embryos, segregated to daughter cells along the axis of the spindle. In juvenile animals there was no evidence of pathology linked with feminization and the parasite was found at low density in cells under the cuticle. The parasite is highly adapted to transovarial transmission with an efficient mechanism of oocyte infection and no evidence of pathology.

Animals↗
PubMed1997

The effect of salinity on transovarial transmission of a microsporidian infecting Gammarus duebeni.

This is an investigation of the impact of salinity on transovarial transmission and burden of a microsporidian sex ratio distorter in the inter-tidal crustacean Gammarus duebeni. Exposure of parasitized mothers to increased salinity during the gonotrophic cycle caused an increase in parasite burden in the follicle cells and a decrease in burden in the oocytes. It appears that salinity impedes parasite transmission from the follicle cells to the oocytes during host oogenesis. A lower proportion of the young were infected in broods from elevated salinity and, in infected offspring, parasite burden was lower than in control embryos. Parasite replication occurred during embryogenesis. However, the pattern of parasite growth did not differ between salinities, indicating that differences in parasite burden could be attributed to a reduction in the initial parasite burden transmitted to the gamete, rather than to a reduction in parasite replication during host embryogenesis. We discuss our findings with respect to parasite/host dynamics and the ecology of the host.

Animals↗
PubMed1997

The estradiol-induced luteinizing hormone surge in the ewe is not associated with increased gonadotropin-releasing hormone messenger ribonucleic acid levels.

This experiment was undertaken to determine whether the estrogen-induced LH and GnRH surge in the ewe is associated with activation of a specific subpopulation of neurons in the mid-brain of the ewe as indicated by a change in GnRH mRNA levels. Fifteen ovariectomized ewes were assigned to treatment groups 3-4 wk after ovariectomy. One group of ewes served as controls (n = 2); 50 microg estradiol-17beta (E2) was administered to the remaining ewes. Blood samples were collected from all ewes before treatment (2-h period at 10-min intervals) and continued at 30-min intervals until tissue was collected. At 6, 12, 18, and 24 h after E2 (n = 3 for each time point), brains were collected and processed for localization and measurement of GnRH mRNA by in situ hybridization histochemistry. Serum was analyzed for LH concentrations. Serum LH was pulsatile in controls and decreased at 6 h after E2, and by 12 h the LH surge was initiated. LH levels peaked at 18 h after E2 and returned to basal levels 24 h after E2 treatment. A cRNA probe corresponding to the GnRH-associated peptide region of ovine GnRH prepropeptide mRNA was used to identify GnRH mRNA. Associated with the onset and peak of the LH surge were decreased levels (p < 0.1) of GnRH mRNA in neurons of the preoptic area (POA). Neither the number nor mRNA content of GnRH neurons in the diagonal band of Broca, septal area, or medial basal hypothalamus (MBH) changed during the LH surge. In contrast to E2-induced increases in GnRH secretion during the LH surge, our data indicate that E2 decreases steady-state amounts of GnRH mRNA and that GnRH neurons in the POA are influenced to the greatest extent during the E2-induced GnRH surge.

Animals↗
PubMed1996

Chronic lateral ventricle infusion of a pineal gland-derived decapeptide alters pulsatile secretion of LH in rats.

The object of this investigation was to determine whether chronic lateral ventricle infusion of a pineal gland-derived antigonadotropic decapeptide (AGD) would affect pulsatile luteinizing hormone (LH) release in conscious, unrestrained male rats. Adult male Harlan SD rats were bilaterally orchiectomized and maintained under conditions of controlled photoperiods and temperature. After three (Experiment one) or four (Experiment two) weeks each was fitted stereotaxically with a stainless steel cannula for infusion into the right lateral ventricle. Each cannula was attached to a subcutaneous osmotic minipump filled either with artificial cerebrospinal fluid (CSF) or AGD in CSF (0.5 microgram/microliter). CSF (1.0 microliter/hr) or the AGD (0.5 microgram/microliter hr) was infused over a period of four days. Blood samples for determined of LH by radioimmunoassay were obtained at five minute intervals from a Tygon microbore cannula inserted via a femoral artery into the abdominal aorta. LH pulses were defined and identified with a computerized deconvolution algorithm designed to determine spontaneous LH secretory events. Although mean LH levels were not significantly reduced, LH secretory pulse frequency and nadirs were significantly decreased by ADG infusion (p<0.01). Additionally, LH secretory pulse amplitude and LH secretory response to LHRL administration were significantly increased (p<0.01) by AGD treatment. These results confirm initial reports of depressive effects of the AGD on LH secretion and support its hypothesized central site of action.

Activity Cycles↗
PubMed1993

Age-related changes in biogenic amines, opiate, and steroid receptors in the prepubertal bull calf.

Events leading to the increase in pulsatile LH secretion during prepubertal development in the bull calf may include removal of inhibitory or the development of stimulatory mechanisms affecting the hypothalamic release of GnRH. To examine possible contributing systems, serial blood samples were collected from Holstein bull calves at 2, 5, and 10 wk of age one day prior to receiving either no treatment (controls) or two injections of alpha-methyl-p-tyrosine (alpha-MPT), an inhibitor of catecholamine synthesis. Blood was sampled every 10 min for 5 h and serum was analyzed for LH by RIA. Following treatment, animals were killed and hypothalamic and pituitary tissues were removed for analysis of total opiate receptors, mu-opiate receptors, estrogen and androgen receptors and concentrations of monoamines: dopamine, the dopamine metabolite 3,4-dihydroxyphenylacetic acid (DO-PAC), norepinephrine, serotonin, and its metabolite 5-hydroxyindole-3-acetic acid (5-HIAA). Pulses of LH increased from non-detectable at 2 wk to nearly 1.5 pulses per sampling period at 10 wk. Pulse height rose to 0.95 +/- 0.16 ng/ml at 10 wk. Total opiate receptor number as determined by binding to naloxone was unchanged in all tissues between 2 and 10 wk. In contrast, mu-opiate receptors (DAGO binding) increased 2-fold in the preoptic-anterior hypothalamic area between 5 and 10 wk. No age-related changes in estrogen receptor concentrations were observed in any tissue except the anterior pituitary in which binding increased 3.2-fold between 2 and 10 wk. A similar increase was not noted for androgen receptors in the pituitary; however, testosterone binding in the preoptic-anterior hypothalamic area was 4.6-fold higher at 5 wk compared to levels at 2 and 10 wk.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗
PubMed1991

Transovarial transmission.

The success of a parasite depends upon its ability to transmit itself to new hosts. Many parasites are passed on from mother to daughter in a process known as vertical, or linear, transmission. Vertical transmission includes parasites transmitted across the placenta or via milk but in this review Judy Smith and Alison Dunn concentrate specifically on intracellular parasites. Transovarial transmission is widely used by a range of organisms but its importance, particularly in transmission of parasites, has rarely been studied.

Journal Article↗
PubMed1990

Anatomic basis for species differences in peripheral lung strip contraction to PAF.

Platelet-activating factor (PAF) is a very potent contractile agonist in guinea pig peripheral lung strips but is without effect on rabbit peripheral lung strips. Histological examination of guinea pig peripheral lung strips revealed a layer of smooth muscle cells in the visceral pleura that is not present in rabbit peripheral lung strips. Removal of the pleural surface of the guinea pig peripheral lung strips eliminated the ability of these tissues to contract to PAF, and the (removed) thin pleural strip contracted to PAF in a manner similar to that of intact strips. Removal of the pleural surface did not prevent these tissues from contracting to histamine or leukotriene D4 (LTD4), although potency of these agonists was somewhat reduced. The pleural smooth muscle cell layer is present throughout the pleural lining of the guinea pig lung but is thicker in lower than in upper lobes. PAF contractility is also reduced in upper compared with lower lung lobes. Thus we suggest that the pleural smooth muscle is the critical contractile element for PAF contraction of guinea pig peripheral lung strips, whereas other agonists such as histamine and LTD4 contract additional elements in these tissues.

Animals↗
PubMed1990

Community as client: appropriate baccalaureate- and graduate-level preparation.

This article focuses on the theoretical concept of community as client and its application in community health nursing education and practice. Although the concept of community as client has been widely accepted, it was observed that care to individuals and families within community settings constitutes the bulk of current community health nursing practice. The argument is made that undergraduate nursing students should be prepared as generalists to provide care within community settings. Undergraduate nursing students should be introduced to the concept of community as client, with an emphasis on understanding the relationship between individual or family needs and community needs. It is also argued that graduate nursing students should be prepared at the specialist level, focusing primarily on providing care to the community as client. An example of undergraduate and graduate levels of preparation in one university nursing program is described.

Community Health Nursing↗
PubMed1988

Immunoglobulin E anaphylaxis in rabbits: mechanisms of pulmonary resistance and compliance changes.

Factors causing changes in pulmonary resistance and dynamic compliance with immunoglobulin (Ig) E anaphylaxis in spontaneously breathing rabbits were assessed in ventilated rabbits using tantalum bronchography and wet-to-dry wt ratios. Ventilated rabbits demonstrated changes in resistance and compliance similar to spontaneously breathing rabbits. Chlorpheniramine pretreatment prevented increases in resistance but not decreases in compliance. Anaphylaxis constricted small (less than 1 mm) airways 20.9 +/- 16.0% (mean +/- SD) and intermediate (between 1 and 3 mm) airways 21.8 +/- 19.8%. Chlorpheniramine (10 mg/kg) prevented small airway changes and attenuated those in intermediate airways. Chlorpheniramine prevented histamine-induced constriction of small (23.6 +/- 15.7%) and intermediate (17.6 +/- 15.0%) airways. Lung wet-to-dry wt ratios were unchanged. Changes in resistance and compliance during rabbit IgE anaphylaxis are not due to changes in tidal volume or frequency. Histamine, via H1 receptors, is the principal mediator of pulmonary resistance increases but not dynamic compliance reductions. Chlorpheniramine-sensitive increases in resistance are caused by constrictions of intermediate and small airways, whereas the chlorpheniramine-resistant decrease in compliance is not caused directly by constriction of the smallest measurable airways (0.25 mm) or changes in lung water.

Airway Resistance↗
PubMed1987

The bedfast.

Many geriatric beds are occupied by bedfast patients. Most were immobile from the time of admission and many were admitted from other hospital departments or residential care. More are discharged home than remain in hospital or are transferred to any other institution. Although a small minority of admissions become long-term bedfast inpatients this group require a disproportionate resource commitment. Reduction in the number of bedfast inpatients is more likely to be effected by changes in unit policy than by improvement in clinical practice.

Aged↗
PubMed1986

The responsiveness of rabbit bronchial rings to antigen, AGEPC and histamine.

Rings of intrapulmonary bronchi isolated from rabbits producing anti-horseradish peroxidase IgE antibodies contracted when exposed to antigen. The contractile response had a lag period of about 1 min, reached a peak at 6 min and then subsided. Bronchi from rabbits with detectable levels of specific IgG (in addition to IgE) antibodies did not differ in response from those with undetectable specific IgG levels. Histamine also contracted rabbit intrapulmonary bronchi with an EC50 of 10 micro (SD 1.29). The response to antigen was completely inhibited with chlorpheniramine (30 microM). In contrast to intrapulmonary bronchi, responsiveness of mainstem bronchi to antigen was observed only occasionally, whereas histamine was equipotent on both mainstem and intrapulmonary bronchi. Thus, the amount of antigen-induced mediator release may be less in the mainstem bronchi. Acetyl glyceryl ether phosphorylcholine, in concentrations up to 10 microM, did not contract either mainstem or intrapulmonary bronchi. This study indicates that histamine is the major mediator of (and acetyl glyceryl ether phosphorylcholine does not significantly participate in) antigen-induced contraction of isolated bronchi from IgE-producing rabbits. The results provide a likely mechanism for the increase in pulmonary resistance observed in IgE anaphylaxis in this species.

Animals↗
PubMed1986

Pneumococcus-specific immunoglobulin E in cigarette smokers.

A relationship between elevated serum immunoglobulin E levels and smoking has been demonstrated in epidemiological studies. Allergy skin test data suggest that the excess immunoglobulin E of smokers is not specific for aeroallergens. It is possible that the excess immunoglobulin E is specific for microorganisms that often infect the lower respiratory tract of smokers. To investigate this possibility we utilized a radioallergosorbent test assay for detecting serum immunoglobulin E specific for Streptococcus pneumoniae, an organism commonly isolated from the respiratory tract of smokers with chronic bronchitis. We assayed sera of thirty smokers and thirty nonsmokers for immunoglobulin E specific for Streptococcus pneumoniae. Individual sera were considered positive for pneumococcus-specific immunoglobulin E if the binding was at least twice the non-specific binding at the total immunoglobulin E concentration of the particular serum. Eleven of the thirty sera of smokers and two of the thirty nonsmokers were positive for pneumococcus-specific immunoglobulin E. By chi-square analysis of these data, the prevalence of pneumococcus-specific immunoglobulin E was significantly greater in the smoking group compared with the non-smoking group (P less than 0.02). These results suggest that the excess immunoglobulin E of smokers is, at least in part, specific for microorganisms that infect the airways.

Adult↗
PubMed1985

Participation of platelets in the physiologic alterations of the AGEPC response and of IgE anaphylaxis in the rabbit. Effects of PGI2 inhibition of platelet function.

To further clarify the platelet dependence of acetyl glyceryl ether phosphorylcholine (AGEPC) physiologic activity and of IgE anaphylaxis in the rabbit, PGI2 was employed as an inhibitor of in vivo platelet function. Intravenous infusion of PGI2 (1 to 2 micrograms/kg/min) inhibited the AGEPC-induced decrease in dynamic compliance, increase in total pulmonary resistance, and transient decrease in tidal volume, but the right ventricular hypertension, bradycardia, and apnea were unaffected. Although PGI2 itself produced a marked systemic hypotension, AGEPC still induced a bimodal hypotensive response. Documentation that platelet function was inhibited by PGI2 included partial inhibition of AGEPC-induced thrombocytopenia, abrogation of platelet secretion (as assessed by plasma platelet factor 4 levels), and inhibition of ex vivo platelet aggregation. The AGEPC-induced leukopenia was not affected. In another group of rabbits, chlorpheniramine pretreatment inhibited the lung mechanical changes induced by AGEPC but did not affect the ventilatory or circulatory alterations, indicating that the lung mechanical alterations (but not any of the other alterations) are mediated by platelet-secreted histamine acting via H1 receptors. In IgE-producing rabbits intravenously challenged with antigen, PGI2 had no effect on any of the physiologic alterations, despite substantial inhibition of platelet secretion. From these results, together with previous platelet depletion studies, we conclude that AGEPC may be a significant mediator of the circulatory alterations and apnea of rabbit IgE anaphylaxis by platelet-independent mechanisms, but neither AGEPC nor platelets appear to be important in mediating the anaphylactic lung mechanical alterations.

Anaphylaxis↗
PubMed1985

An evaluation of the foot pump as a driving source for nebulizer solutions.

The foot pump was used to drive a 'Minineb' nebulizer for 10 minutes with 2 ml of solution. It was found that when the operator employed a rate of his own choosing the output varied from 0.9 to 1.9 ml and the oxygen uptake doubled. With a stroke rate of 30/min the output was 1.2 ml and at 60/min 1.4 ml. At 60 strokes/min the average flow rate is 9.1 litres/min which would give a suitable particle size for administration of bronchodilator therapy. It is concluded that the foot pump is useful for occasional use in emergencies as the energy expenditure necessary limits its value in regular therapy and that a fixed stroke rate should be employed.

Adolescent↗
PubMed1985

Effect of specific IgG on IgE-induced systemic anaphylaxis in the rabbit.

Immunization of rabbits as neonates and periodically thereafter has been shown to induce the long-term preferential production of specific IgE antibodies. Specific IgG antibodies are not detected in the majority (greater than 70%) of rabbits when classical immunological detection techniques are used, including heterologous PCA in guinea-pig skin. Nevertheless, in this study we demonstrate that all rabbits neonatally immunized to the antigen horseradish peroxidase (HRP) do produce low levels of specific IgG antibody detectable by an ELISA technique. Serum levels of anti-HRP IgG were found to be log normally distributed, with a geometric mean for the heterologous PCA-negative sera of 31.6 X/divided by 2.69 micrograms/ml. Serum anti-HRP IgE levels (log2 homologous PCA titres) are bimodally distributed. Specific IgG and IgE levels in individual rabbits have a significant direct relationship. Six heterologous PCA-negative and seven heterologous PCA-positive rabbits were challenged intravenously with HRP. All of the respiratory and circulatory alterations typical of IgE anaphylaxis occurred in every challenged rabbit. Regression analysis of percentage changes in the physiological variables vs log specific IgE level indicated that none of the changes was either directly or inversely related to the specific IgG levels. Also the mean changes of the heterologous PCA-positive vs negative rabbits did not differ significantly. Thus, we could find no evidence for either a blocking or enhancing effect of the specific IgG antibodies (range 10-529 micrograms/ml serum) on the IgE-induced anaphylactic reaction.

Anaphylaxis↗